The Porsche 914 ended up about 150lbs over the estimated weight, but that’s likely due to not considering the weight of the coolant and the use of steel battery racks instead of the planned aluminium ones. The (almost) final weight is 1230kg or just over 2700lbs, although it’s a bit higher than your average 914 it also has quite a bit of power and the battery capacity to provide a lot of range.
On the plus side the front/rear weight distribution came out perfectly which is probably why the car feels so good. The front came out to 49.6% with the rear at 50.4%
The car is an absolute joy to drive, it handles well, has plenty of power and cruises very nicely. The 12kw EMW charger is finally up and running, it’s been tested at 5kw which is about the limit of my power source at the moment, I’ll do further testing on a 40 and 50A breaker when the charger is complete and mounted in the car. A quick test drive to and from the scales yielded decent energy use results, however due to a cable issue regen wasn’t working. A 92km round trip used 41.6Ah out of the 90Ah total capacity at speeds ranging from 80-125km/h. That works out to about 250wh/mile which is pretty good for mostly higher speed driving and no regen. If average energy use with regen comes in around 220-225wh/mile the car will meet it’s range target. With some hypermiling and getting use to the car it shouldn’t be difficult to get the energy use down below 200wh/mile for 60-80km/h drives.
Again it’s been so long I’m not sure where to start. First the car is not complete, but it is nicely drive able (and a joy to drive at that). Parts, ideas and plans come and go, today, and for the past year or two really there is one goal. I want a reliable daily driver. I’m pretty close to being there, I will get to the point that the car just isn’t going to need me anymore, it will just work. I both can’t wait and dread that day. It would be nice to just get in and drive, without thinking about the Ah counter, is everything working, how do the temps look today, I wonder if the battery is warm. The flip side is that when I get there the car is “done”, and I think I’m ready for that.
The parts have been ever changing, here’s what’s in the Porsche 944 today, and what’s planned for the near future.
-Siemens 1PV5135 – Great motor, liquid cooled.
-DMOC645 Inverter – Also great, but needs a “GEVCU”
-GEVCU – Seems to work great, not quite as feature rich on the traditional IO side as the Wolftronix, but more capability on the CAN side
-CALB CA60FI x83 (the volt pack and range extender, are no longer viable options I may look at more CALB’s)
-Azure Transit Connect DC/DC converter, sorry the name has failed me, I’ll update the part number – Liquid cooled, works great
-Mes Dea vacuum pump – A bit noisy, to be replaced by the Transit Connect pump-Cheap Chinese temp meter to turn on/off the battery heating
-Cheap Chinese temp sensor to turn on/off the battery heating system automatically
-JLD style volt meter, measures the charging voltage (120/240v) and selects series or parallel for the battery heating so regardless of what I plug in to I get full power to the heaters
-Heated seat pads (drivers seat only for the moment, wonderful on chilly days when you don’t necessarily need to turn on the main heater)
-Brusa NLG513 Charger – Bought two, installed one, one is enough for the small pack.
-JLD404 – Not much to say, it works and hides in the glove box, to be replaced/augmented by the EV Display
Items to be installed:
-The Vacuum pump mentioned above
-EV Display main display to be installed where the factory clock was located
-Joying Android car stereo
-Various suspension and normal car tweaks.
The Joying Quad core Android car stereo has a radio, bluetooth, GPS and 7″ screen and some physical buttons so it should give a better car experience than the Samsung tablet. I could never keep the tablet charged (android battery life sucks even when it’s sleeping) and in it’s happy temperature range, the Joying is controlled by the ignition and operates like a traditional car stereo (with the extended Android boot up time of course). It comes with the Torque Pro app installed and was designed to work with it, apparently there are two bluetooth radio’s, one for connecting to the Torque device and the other to connect your phone. It has all sorts of functionality related to phone display and screen mirroring that should provide a nice experience and lots of features when desired. It has a volume KNOB, I’m a fan of controlling the volume on devices with a knob. It has built in functionality for a backup camera and/or dash cam. The backup camera add on was $20 so why not, I got use to it in the Infiniti and although the Porsche is much smaller the visibility is also much worse. And I find pedestrians don’t tend to notice I’m backing up because of the silence, so if I can keep a better lookout for them there’s less chance of an accident.
I’ll give a full review and comparison of the Joying stereo vs the Samsung tablet as well as the Nexus tablet that’s in the Porsche 914.
This update was supposed to come out before the posts about the 914, but I never got it finished so this is much less of a surprise. The price of oil has dropped significantly, the company I worked for (note the past tense) made control and automation systems for the oil industry. When I first started we made SOFC test stands (Hydrogen fuel cell test stands), that was interesting stuff, oil rig stuff, not so much but the job was stable with good benefits. I and a large portion of the company were recently let go, we got a decent severance to make us just go away. A friend and fellow EV conversion owner (he actually has 3) has been trying to get me to start something with him in the EV conversion space to augment his existing automotive repair business. What is a freshly unemployed EV fanatic supposed to do? Take that offer and run with it. I am now a full time EV Converter at Cardinal Automotive, (Go check it out, follow us on Facebook) this is what I’ve wanted to do for many years, but it’s still a bit scary to think this IS what I’m doing. It’s an iffy time for EV conversions, on one hand there are OEM EV’s to get people familiar with EV’s and what they can do. On the other hand there are OEM EV’s for a customer to run out and buy TODAY.
ElectraFest 2015 was a great show, lots of interesting people and nice cars. The majority of vehicles were OEM’s but there was a handful of conversions at the show. The single most attractive feature that most people found with the 914 was the 200+km range. This seems to be a mental threshold where all but a few people said “That would work for me.” My 944 with 100+km range doesn’t get the same response with probably 50% of people saying that’s not quite enough.
The lead up to the show was hectic and we actually left at the last minute not giving us much extra time. The 914 is an old car and as I found out not all of the grounds are good. I had reused a factory ground point for the inverter wiring and this turned out to be an issue. I wasn’t getting a good enough ground for the inverter to call it “ground”, it was close but not close enough. This caused the inverter to boot up, but the signal inputs (mostly grounded/floating) weren’t registering correctly meaning the inverter wouldn’t fully turn on. This took hours of troubleshooting and wondering if something in the inverter itself had failed. In the end I ran dedicated ground wires and all the problems went away. The car runs great and after some software tuning the regen/shifting and throttle feel pretty good. The potentiometer on the brake pedal gives a nice feeling of power brakes with the adjustable regen on the completely mechanical brake system of the 914. The regen disable signal runs through both the clutch pedal microswitch and the center console regen disable switch. There is a small amount of regen dialed into the throttle pedal when fully released to mimic engine braking. When the clutch pedal is pressed it disables regen from the off throttle position and/or regen based on the brake pedal. This makes shifting easy and the car is quite fun to run through the gears. Starting in 2nd it feels really good with plenty of torque and is easy to shift to 3rd and beyond. 1st and reverse aren’t really needed, which is okay as they are somewhat segregated in the transmission requiring a firm push to the left against a spring plate to engage them. 2nd gear is good for forward or reverse using the electric forward/reverse switch in the center console.
The cooling system is installed and being evaluated for both size and effectiveness, the Siemens Inverter seems to produce more heat than my DMOC645, but it does have a built in DC/DC converter as well. The overkill cooling system in my 944 has a temperature rise of 3 degrees C over a 30-40 minute drive, depending on ambient temperature 10-20C is perfectly acceptable in the 914, however driving at highway speeds for more than an hour will have to stay within the thermal limits of the Inverter. The pump and a single low speed fan run all the time, there are two higher speed and higher power fans that will be controlled by the Inverters fan output to assist in cooling when required.
The stereo has been updated with a Bluetooth capable media player that can connect either to the tablet in the center console or a smart phone to easily accept phone calls and stream music. The front factory speakers are in the kick panels which is close to the ideal location in most vehicles as far as imaging goes. The aiming isn’t perfect but it’s not bad and works better than most door locations. The problems came in the speaker mounting, the aftermarket coaxial speakers have a protruding tweeter that doesn’t allow the speaker to sit flush with the housing and mount the way the factory speaker would have. Because of this the front and rear wave weren’t isolated so there was ZERO bass. The solution to this was to design and 3D print speaker spacers that allowed the speaker to be sealed to the front of the enclosure as they were meant to be. The sound is much better, but only as good as a 4×6″ speaker can be, I’ll do some testing with a small and lightweight subwoofer to augment the low end.
The 3D printed spacer is visible through the grill and surrounding the speaker, printing in black ABS blends the part with the existing plastic housing.
The Tachometer is connected and working properly, the existing set up was for the Porsche 928 which had a V8, the 914 was a 4 cylinder car so the output pulse count had to be adjusted. This wasn’t too difficult to find in the software, F_out_Factor lets you change the pulses per revolution which was set to 4 for the V8 and needed to be changed to 2 for the 4 cylinder (2 pulses per revolution). Although not completely intuitive the Siemens software is quite flexible and allows most important parameters to be adjusted easily.
The dash and door panels had a few cracks from age (what car from the 70’s or 80’s doesn’t have a cracked dash?) This is now a thing of the past and now looks quite exceptional thanks to a vinyl repair shop, they did some amazing work, recovering the tops of the door panels and fixing up the dash. The car looks so good now I’m probably going to get a quote from them to fix my 944 dash, it has a couple of similar small cracks. Between that and a new windshield my 944 can have a similar facelift.
We’ve had the car out to a few shows now and the response is overwhelmingly positive, and the more I drive the car the more I love it. It’s still a bit quirky, it is of course still a 1972 Porsche 914, but the driving experience is tough to beat! Remove the top and cruise around on a sunny day and the EV grin multiplies. The Siemens power system is perfect for a car this size and weight, there is plenty of torque and it accelerates very nicely, it cruises smooth and quiet and is simply a joy to drive once you get the hang of that 1972 gear box. Yes it does take a little bit to get use to, it’s not quite the same as a modern manual transmission however it does work very well and shifts smoothly when you get the hang of it and where the gears are located.
The Porsche 914 next to it’s modern equivalent the 2010 Tesla Roadster!
The to do list is getting shorter and shorter and the car is driving better and better every day. It won’t be long till it’s ready for someone else to enjoy this beauty every day.
For those of you in the Vancouver area you may have already heard about ElectraFest 2015.
We will be bringing the 914 to the show, come down, say hello and check out the car.
The Porsche 914 trunk area had been abused for decades, a hole for this, a new hole for that. All of those holes are filled and finally painted. The remaining holes are for the Siemens Inverter, the main power input, motor output, cooling hoses and DC/DC output all required routing outside the trunk area. The repair process went fairly smoothly however it was much more time consuming than I would have expected.
Repaired and painted:
The trunk carpet from 914 Rubber fits nicely (sorry for the varying white balance, the car didn’t change colors!)
Although the inverter barely has any miles in it, the conversion that this piece came out of is a number of years old now and it’s showing it’s age. The casing was stripped down and repainted as well to match the the fresh install, can’t have the center piece of the trunk looking old and ratty.
The trunk with new gasket, new light, new roof holders all installed and the cooling lines connected to the inverter.
There is still enough trunk space for a few bags or other small cargo including the hard top that can be removed and stored in the trunk above the inverter.
New LED headlights, new LED turn signals, new gaskets, new boots. The 914 Rubber kit included boots and gaskets for all of the turn signal related requirements, everything fits nicely. The new front trunk gasket is also in and fits very well compared to the old multi piece version that was falling apart.
New gasket for the tail light housing to car, and more LED bulbs. Although the inverter has a very good built in DC/DC converter there’s no need to waste power, this should help keep the load on the 12v system to a minimum as well as brighten up what were otherwise dim lights all around. The new tail light and front turn signal lenses are in transit and should complete the transformation nicely.
With the re-arranged Volt modules in the front of the car, the stock plastic covers didn’t fit properly. Now modified slightly they fit nicely and continue the clean appearance through the front of the car. I have some terminal covers designed that will go over the positive and negative terminals to make the front area touch safe. These will be 3D printed and tweaked as required to fit the various requirements and cable terminals used. A fuse cover is also in the works that will be 3D printed and will complete the process of making the front trunk area touch safe. There isn’t a lot of space left, but some small items or a tool kit could easily be stored up front.
The Porsche 914 has one major thing that my Porsche 944 didn’t have, RUST!!
This provides a time consuming challenge that I simply didn’t have to deal with before, but it will all be properly repaired and give the car many more decades of service. Another problem is along with being 43 years old, the car was a previous EV conversion, so instead of dealing with stock parts and pieces there was already one level of modification, odd wiring and changes that made it difficult to figure out what parts are stock, what parts are missing and what parts I don’t even know are missing. The car will be put back as close to stock operation as is practical in an EV conversion, and be a great example of a 914 regardless of the drive system. Any pieces reused from the original EV system have been cleaned up and restored/repainted where required to make the car look as good as it performs.
The front trunk area is complete, this area holds two liquid heated/cooled Chevy Volt modules in parallel reconfigured for 133v nominal and 90Ah. Two of the temperature controllers are mounted to the front of the Volt module on a 3D printed bracket. One controller monitors the center front battery, the other monitors the lower rear battery in the back of the car, either one will trigger the Volt heater to turn on if the temperature is below the preset threshold. Gone are the plans of incorporating the gas heater, mainly because there is a nice included Chevy Volt electric heater that came with the battery pack, and with the doubling of the battery pack space is at a premium. This car also likely won’t be driven in extremely cold weather, so a heater that works down to -5° or -10° should be plenty.
With the gas heater out of the equation it became necessary to incorporate a heat exchanger into the stock fan box that will transfer heat from the coolant heated by the Volt battery heater into the cabin. This makes for a smaller and fully electric solution that will have a small impact on range but keep both the batteries and passengers warm on those cold days.
The area formerly occupied by the fuel tank is now home to another Volt module in a stock configuration of 111v nominal 45Ah, it’s parallel partner is located in the rear of the car beside the motor & transmission. The pump and stock Chevy Volt heater are located below the Volt module, a repurposed Subaru overflow tank serves as a reservoir and fill tank for the coolant. It fits nicely with the contour of the space and almost looks like it belongs there.
The instrumentation for the car has all arrived and been configured, this consists of an EV Display 450v version with bluetooth dongle that allows it to talk to the Torque Pro app installed on a Nexus 7 tablet that will reside in the center console in a 3D printed mount. I finally installed this same system in my 944 as well, and for daily instrumentation it’s simply amazing not to mention so much more intuitive to read than the JLD404. It may seem like such a simple thing, but with the JLD404 you must know the pack capacity since it starts at zero and counts up. It wouldn’t be difficult for anyone unfamiliar with the car to just drive it till it stops because there is no indication of when the battery is “empty”. The EV Display and Torque app let you program in the battery capacity as well as provides a fuel gauge that can have a programed empty buffer. IE when the fuel gauge reads zero the State of Charge may be 10% which would allow the car to limp to a charging station. The Ah counter itself starts at the battery capacity and counts down, IE the 90Ah pack in the 914 will start with a 90Ah reading and decrease towards zero as energy is used. The Torque app also allows programmable warnings for each gauge. Once the pack drops to 10Ah for example the that gauge will start flashing to alert the driver that it’s time to recharge. The same can be done with temperatures, voltages, or any of the other parameters incorporated into the display.
Above you can see the 3D printed Nexus mount, the 3D printed temperature controller mount and the machined bracket for the Bosch throttle.
The new rubber parts have arrived from 914rubber.com, they have an excellent selection of just about every rubber piece that was originally on the car. These parts aren’t exactly cheap, mainly because you need to replace every rubber part on the car because after 43 years very few of them have survived. The rubber kit that they provide is excellent, and included parts that I didn’t even know I needed as they were missing from this car.
Due to recent changes in situation, this car will be for sale at the end of the conversion and restoration. Not only is this going to be a 200km+ electric car, it will be a restored 1972 Porsche 914. The interest and attention that these cars gather at car shows is amazing, my 944 drew a lot of attention, interest and questions at last weeks local car show. Not only will you have the coolest (and greenest) car on the block it will gather a bigger crowd and get more attention than a $120,000 Tesla and you don’t have to spend anywhere near $120,000 to get it.
The car has been outfitted with the 4 piston big brake kit on the front along with the 911 suspension upgrades and 5 bolt conversion from Renegade Hybrids. The rear retains the stock suspension and calipers, however has the same 5 bolt conversion as the front that allows the use of more modern Porsche wheels. This car stops just as well as it goes!
The car is currently outfitted with lightweight 16″ Fuch wheels and Falken 205/45-16 tires which have a good balance of performance and efficiency. The wheels will be cleaned up and the centers will be refinished to return them to the period correct black center.
The headlights have been converted to LED’s, using the same exceptional 7″ round Trucklight headlights that I installed in my 944, they give HID type performance with even lower energy use. They are one of the few DOT approved LED headlights available at the moment and well worth the high price tag.
The front and rear of the car gets similar treatment with LED’s all round, parking lights, turn signals, brake lights, backup lights all LED!
The licence plate lights, trunk light and dome light also get LED treatment, this is more important than it sounds, these older VW style interior lights don’t provide much light with the stock bulbs, switching over to LED provides a much brighter and more usable light inside the cabin and trunk.
The dashboard gauges are also being outfitted with LED’s to improve visibility of what are otherwise dim and tired looking gauges. A replacement multi gauge is on route that will complete the stock trio of instruments and connect to the EV Display to drive the fuel gauge portion along with the low fuel indicator. Other indicators including a green light to show ECO mode is on and other functions/warnings as appropriate.
The front and rear bumpers are out for repair and rechroming. The mounting brackets were, you guessed it, RUSTY. This will all be taken care of and clean, solid and beautiful bumpers will go back on the car. The remainder of the trim is polished aluminium, it appears Porsche saved weight wherever possible and instead of using chromed steel parts they used polished aluminium. These parts will be cleaned and buffed to restore their appearance as well.
In the world of DIY EV’s there are many choices to be made, type of donor vehicle, automatic or standard, clutch or clutchless, battery size, high voltage or low voltage, but one of the biggest ones is AC or DC motor & controller/inverter. I have the benefit of having used both in my 944, same car, same battery, same transmission set up.
I’ll list the main points first and go over them in more detail individually.
Almost all EV Conversions have a budget. Paying retail the DC system is almost always cheaper. On paper this gets even more one sided if you consider a used forklift motor and performing some modifications to make it “more” suitable for EV use. On the other hand with more OEM EV’s on the market and the availability of surplus and salvage pieces the prices can drop significantly below “retail”. On the other hand if one of the HPEVS systems fits your performance needs they are priced quite fair. My DC system was purchased new and used some of the higher end pieces available. The Warp 11HV was not a cheap motor, the Soliton1 was also a fairly pricey piece. Due to the demise of Azure Dynamics my AC system was less than half the cost of my DC system.
If you simply look at 0-60 times and HP/Torque numbers the DC system was in a different league, with almost 300ft-lbs of torque and 270HP the car was fast and powerful, 0-60 in 4.8 seconds with traction problems, with the right suspension set up I’m sure the car would have gotten into the mid to low 4’s. The AC system while still fun, simply doesn’t come close, 220ft-lbs but less than 150hp. It’s more than enough for a daily driver in a vehicle of this size, but it’s no longer faster off the line than almost anything I could pull up against.
On the surface it’s no question, the AC system has no brushes or wear items with the exception of bearings. Many of the AC motors are sealed including the Siemens motor I purchased. This virtually removes the possibility of contamination, either dust/dirt/rocks/snow/rain/fluids from damaging the motor. The electronics are actually more complicated than the DC system, so long term reliability of the electronics will depend on the design and ruggedness.
A very minor pet peeve of the DC system was how well the car coasted, normally that would be a good thing, however if the traffic in front of me let off the gas the engine would slow them down slightly, when I let off the throttle the car coasted really really well, so I had to use the brakes a lot to avoid getting too close to the vehicles in front of me. Same with going down a hill, the car just coasted too well and I was always catching the vehicles in front of me. I was always on the brakes with the DC motor, being on the brakes means wasted energy and momentum. The AC system is about as opposite as a vehicle can get. I almost never have to touch the brakes now, regen is set up on the throttle pedal and I can drive the car 90% of the time without removing my foot from the throttle. I capture quite a bit of energy that would otherwise be wasted as heat and traffic jams are really not that bad anymore. I can speed up and slow down using the throttle pedal and cruise at any speed, there is no minimum speed like a manual and I’m not riding the brakes like an automatic. I couldn’t be happier with the driveability of the car.
For the first time in my EV I’m working on new things and tidying up loose ends that I never got to before. The car just works, I’m not worried about brushes or heat, I look at the pack temperature if it’s chilly to make sure I’m ok to use regen (charging batteries below zero is bad, that includes regen charging) and just drive.
With a liquid cooled motor and controller and the fact I went back to the stock radiator and two loops there is no worry about heat. The inverter typically reaches 5 degrees above ambient temperature at the end of a drive, the motor fluctuates based on load but comes down quickly with the cooling system. Again I no longer have to worry about heat and how long my motor is going to last. The stock radiator is overkill but keeps things nice and cool even without the use of a fan.
This is where things start to get interesting. In theory there isn’t much difference between an AC system and a DC system, perhaps a few percent which could easily be overcome by driving style. In reality there are a large number of factors that together have significantly increased the efficiency of the car. First there is power, sure it’s not an apples to apples comparison, the DC system had almost double the power, but with double the power it makes it easier to “waste” energy, accelerating a bit faster than you should, passing or driving a bit faster than ideal. Many people would choose the DC system over an AC system to get higher peak power, so I’d say this is a fair comparison to leave in. Next is regen, now this depends on where you live, how you drive and how regen is set up in your vehicle. For me with regen on the throttle I use it all the time before mechanical brakes. When I first set up the GEVCU I didn’t have the brake lights connected so I have a very small amount of regen configured, it basically mimicked engine braking and let me slow down when traffic slowed down without riding the brakes. To come to a complete stop I had to use mechanical brakes almost all the time. Energy use was already down significantly compared to the DC system. A conservative drive in the 944 with DC was 300wh/mile, right where the rule of thumb says I should be for a roughly 3000lb car. I was able to get it down to 275wh/mile with ultra conservative driving, but this took a lot of work and just wasn’t much fun. On the other hand a few heavy accelerations put energy use up around 350wh/mile and spirited driving resulted in almost 400wh/mile. From day one and very limited regen the AC system was around 250-275wh/mile with average driving, no attempt to drive conservatively. With more aggressive regen enabled that average energy use dropped below 225wh/mile, and conservative driving resulted in 200wh/mile. This is all mixed driving with some 60km/h, some 80km/h and 100km/h zones. The comparable numbers are, between 300-350wh/mile for the DC system is around 225wh/mile with the AC system in average driving, and 275wh/mile for the DC system vs 200wh/mile for the AC system with ultra conservative driving.
The range of an EV is just an extrapolation of it’s efficiency but I wanted to point out how significant the difference is with the same car and battery. The pack is 16kwh, but ideally shouldn’t be discharged past 80% very often, this gives us 12.8kwh of energy to use on an everyday basis (I don’t use that much but we’re comparing numbers here). We’ll use 325wh/mile as an average of the normal driving with the DC system, this results in 63km or just shy of 40 miles of range, and conservative driving bring that up to almost 75km or 46miles. Due to the efficiency increase the AC system is 91km or almost 57 miles with average driving and 102km or 64 miles of range with conservative driving. Now of course your results will be different, but this is the difference between a 1986 Porsche 944 with a Warp11HV and Soliton1 vs Siemens 1PV5135 and DMOC645.
I’ll start by saying I wish the car had a bit more peak HP, it’s not bad, but I think that a 150-200kw AC system would be amazing in this car, sure it would decrease the range without very careful driving but it would be worth it for day to day use. Second I’m amazed at the difference in energy use switching from DC to AC* (*in this specific situation/car/components). I love this car, no question about it, if I were to do it over again I would have kept the clutch in the AC system, first gear is amazing, but like an ICE you need to shift fairly quickly and without a clutch that’s a 2 second event which kind of kills your speedy acceleration. I have yet to test it but I’m pretty sure my 0-60mph time would be faster in 2nd gear only instead of being quicker off the line but a slow 1-2 shift. I would probably be happier with the power level of the car if I had kept the clutch. This issue didn’t exist with the DC system, it had unbelievable power from 0-5500rpm with no obvious decrease in power within that range. 1st gear was unusable and traction was even an issue in 2nd gear at times. In short I would never build another daily driver with a DC motor, but I would use a DC motor for a toy, or something that might make it to the track or autocross event if an AC system at the desired power level didn’t exist or was simply too expensive. (I still have the 11HV, and one day I might repair it and use it in something else with a Zilla 2k, unless of course Tesla drive systems become available and usable with 300kw+)
In previous posts I’ve mentioned accumulating and testing used laptop batteries and other sources of 18650 size cells. A project came up that makes good use of 91 of these cells (the range extender for the car may or may not still happen). Many people have already done this, but the following is my method of assembling a 24v 26Ah bicycle battery specifically designed to fit in the existing case and charge using the existing charger. The bike originally used a pair of 12v 12Ah lead acid batteries.
The first step was to layout the connection scheme for the 91 cells and create a drawing and then tool paths to drill and engrave the copper clad board which will be used for the bulk of the cell connections.
Then drill and engrave the PCB material.
The layout of the PCB combined with the layout and orientation of the cells gives the desired series/parallel arrangement.
Tin the tops of the cells, take care not to heat the cells too much, others have said this can damage the cells.
I used resistor leads for the connections from cell to PCB, bend the lead as shown to make a good electrical and mechanical connection to the top of the cells.
Solder the lead in the very center of the cell.
Trim the lead, leaving roughly 1/2″ sticking up. I found that each resistor would make 4 connections. After all the cells are done, the PCB is placed overtop of the protruding leads, this takes careful alignment to make sure they all stick through, careful soldering in the previous step helps out a lot here.
Bend and solder the leads to the PCB making sure not to get too close to the engraved dividing lines.
Repeat on the other side with the appropriate PCB and as many modules are being assembled. Due to the shape/size required I had to make 4 stacks of 5 cells to the side of the main blocks, these were simply soldered together with wire.
Complete the electrical connections (don’t forget to include a fuse!)
Connect the cell log 8 for monitoring and plug in the charger.
Once the pack passes basic tests use electrical tape or other insulating material to cover the exposed electrical connections.
For this application the pack will be balanced on the first charge and simply monitored and rebalanced as required. If the pack won’t stay balanced using this method either a top balancing BMS or RC charger with balancing leads may be adapted for long term use. The existing lead acid charger charges at 3A CC-CV to 28.82v which is 4.117v per cell on a 7S13P pack, this is low enough that minor cell imbalance over time shouldn’t be an issue.
The whole system is a compact box with built in charger. The original battery was a series pair of 12v 12Ah SLA UPS style batteries, at 50% discharge that’s about 6Ah if Peukert doesn’t decrease it even more. The new battery is 25.9v nominal, giving a slightly higher average voltage during discharge and a capacity of 26Ah, though it shouldn’t be discharged 100% it can be done with slightly accelerated aging. This gives 4.3x the Ah’s but with the higher voltage during discharge it’s about 5x the usable energy in a package that weights about 2/3 as much as the original lead.
The Porsche 914 is an iconic car from the 70’s that has stood up against the test of time. It has great looks, great performance (not exactly powerful, but great handling). Parts are available, but not always easy to find. There have been countless engine transplants, and an abundance of EV conversions. The car simply makes a great platform for customization.
This particular car was initially converted to electric drive using a Series DC motor, and lead acid batteries by the previous owner. The car worked, but it never had very good range and was significantly overweight. Later in life the car was then converted to LiFePO4 with the same motor/controller combo. This made a significant difference, but range was still limited, and the DC motor less than ideal.
The next chapter in the 914’s life is a switch to a 3 phase AC induction motor and inverter combo made by Siemens along with the Lithium battery out of a Chevy Volt, two of them in fact totalling 30kwh. With regenerative braking and a 30kwh battery, the cars range will be up around 200km on a charge.
Along with the EV reconversion, the car is getting a facelift. Most of the rubber on the car has deteriorated, the tail lights and marker lights are faded/cracked, these will all be replaced with new parts. The headlights will be upgraded to LED, this not only reduces power consumption but drastically increases the quality and quantity of light produced. All side marker/brake/turn signal bulbs will also be upgraded to LED’s. The brakes have already been upgraded, and the wheels are the lighter and more modern Porsche 911 style.
Some of the more mundane but important upgrades include a washer fluid pump, the original Porsche 914 used air from the spare tire to pressurize the washer fluid bottle and using a fluid valve in the steering column allowed the driver to spray washer fluid on the windscreen. There are compatible parts from newer Porsches that allow the control of an electric pump which will simplify and modernize this oddly implemented feature.
The mis matched, broken and worn parts throughout the car will be replaced with original or better parts that will make this car equally at home as a daily driver and at a car show. The original (and correct) door hardware shown on the left vs the compatible but incorrect parts on the right (passenger and drivers door respectively).
The functional but incorrect Amps gauge in the instrument cluster will also be replaced with the correct “fuel” gauge found in the car originally. The stock fuel gauge will be interfaced with the Ah counter to give the driver an indication of the remaining “fuel”.
To incorporate the necessary EV instrumentation into the 914, a 2″ round gauge made by EV Display will be located in the center console replacing the clock or volt meter commonly found there. This can display Voltage/Current/Battery Temp/Amp Hours/State of Charge/Fuel Gage/Wattage/Watt Hours, well any two of these items at a given time.
To give modern functionality and a more informative display an Android tablet will be incorporated into the center console which in conjunction of the EV Display and Torque app will allow a customizable gauge cluster to be created in software. Real time availability of motor power will allow the driver to choose the most efficient gear for cruising, unlike gas vehicles 5th gear may not be the most energy efficient highway gear.
Having an Android tablet integrated into the car will also allow the use of GPS Navigation, Audio apps, and while parked even let you watch movies or play games. The audio output will be routed through the indash stereo.
The Porsche 914 and it’s VW cousins of the era were never known for good heat. The air cooled engines simply didn’t have an efficient method of collecting the waste heat and getting it into the cabin. Many people augmented the stock heater with a VW gas heater which was a factory option in some countries. Now it may seem counterintuitive to put a gas heater into an electric car, however there is one thing that gas is good at; making heat. The propulsion of an automobile has a total efficiency in the teens for an average vehicle up into the 20’s for a very fuel efficient vehicle. On the other hand home furnaces can reach into the upper 90% efficiency range burning natural gas or similar fuels, we typically don’t heat our homes with electricity for a reason. The range impact on an electric vehicle from the heater can easily be 25% or even more in very cold weather. The other problem with cold weather is most batteries don’t perform as well in the cold to begin with. If the car is limited to 75% of it’s range just because it’s cold, then we take another 25% in order to heat the cabin we’ve significantly reduced the usable range of the vehicle. The VW gas heaters are VERY fuel efficient, one of the most common is rated at 0.32 – 0.38 litres per hour with constant usage and in most cases the car is going to get too hot with constant use, so running the heater intermittently for 1/2 – 2/3 of the drive will be more comfortable and efficient. Assuming a speed of 100km/h (typical of Deerfoot or Stony Trail here in Calgary) the car would burn 0.16 – 0.25 Litres of regular gasoline for a 100km drive with intermittent use (16 to 25 cents at today’s prices) the electricity cost to drive that 100km would be roughly $1.20.
Above you can see the vintage heater almost ready for testing before it gets torn down for cleanup and repainting.
The 914 is a very popular car for conversions partially because of the large amount of space that can be used for batteries. The front trunk, rear trunk, engine bay and fuel tank location are all suitable spaces for mounting EV components. In this case, part of the front trunk will be used for batteries, holding just over 1/3 of the pack. The Chevy Volt battery is liquid heated and cooled, this is a very efficient way to control temperature and something that will be maintained in the 914. The liquid heater from the Volt will be reused and capable of bringing the battery pack up to safe charging temperature or simply warming the battery on a cold morning using wall power instead of battery power for better range and power. The cars cabin may be included in this loop to preheat both the car and the battery to further reduce the need for gas or electric heat while driving.
Above the test fit and temperature monitoring of a small portion of the Chevy Volt battery pack. The Volt battery comes as a complete unit configured for a very specific purpose as far as electrical and cooling connections are concerned. Due to the size and shape of the 914, not all of the stock modules will fit the car as is. In order to reconfigure the modules some extra parts are required, it’s not going to be as easy as dropping by the local Chevy dealership and requesting a very specific battery cooling part, the battery is likely not meant to be serviced outside the factory, only replaced. While very specific the parts aren’t very complicated, simple plastic pieces needed to plug unnecessary cooling ports to start. These parts were 3d printed using ABS material which has a suitable temperature range and chemical stability to work in the heating/cooling system.
The stock black gasket is on the left, with a 3d printed flexible version in white at the top, this white version won’t be used unless a replacement is required. The center and right show the two types of blanking plates required to block off the cooling ports on one end of a battery module, one holds a gasket, the other seals up against the gasket in the last battery plate. The 3d printed parts have studs incorporated into them similar to the stock pieces and are meant to be melted once installed to hold them in place. The existing cooling ports and end plates are all interchangeable and can be configured as desired, I simply found I didn’t have enough blanking plates to seal off the ends of a few of the module groups in my planned configuration. Unlike the Volt where the first two battery assemblies are in a row then feeding the final module through the “side” ports I found the need to have some of the assemblies side by side with cooling ports on one end only.
The Chevy Volt battery can be easily broken down into its 1kwh and 2kwh building blocks, 6 and 12 cell respectively then rearranged and bolted back together in the shape/size you desire just like Lego. Changing the total length of a module does require different bolts to put it back together, but M6 x 1 threaded rod works perfectly for this. Making a module shorter can be done two ways, either replacing the existing bolts with M6 threaded rod or cutting the existing bolts and threading the end with an M6 x 1 die (The stock bolts are only threaded about 1 inch on the end). Remember you need four threaded rods per module. M6 x 1 is commonly available in 1m lengths which is slightly longer than what is required to make a 4x 2kwh block using the “side” cooling ports.
Reassembly (compression) using a ratchet strap makes it easy to get the bolts started and using the built in wire guides and a 1″ strap keeps everything in place with minimal chance of the strap sliding off or out of place. For longer modules like the one shown, using two ratchet straps, with a ratchet on each side make it easier to evenly compress the modules and get the nuts on the threaded rods started.
Steel or Nylon straping used for banding skids for shipping should work well to replace the stock steel(?) band around the top of the battery assembly. Nylon is probably cheaper/easier/safer for use around a battery and doesn’t require fancy tools to install.
In the name of recycling even parts of the battery assembly base can be reused to make new battery mounts and reuse the existing hardware and mounting method. First find all of the somewhat camouflaged spot welds and drill them out with a 15/64th’s drill bit (or similar) being careful to get as close to center as possible. Then enlarge the holes with an 11/32nd’s (or similar) drill bit to completely remove the spot weld. This is slightly larger than the spot weld itself allowing for being slightly off center.
After all of the spot welds in a given section are drilled out the clamping portion of the base can be pried off. There was some sort of adhesive in the bonding of these two pieces but tapping flat screwdrivers or other long wedges between the two pieces will separate them nicely.
The liberated plate now has the required mounting lip and studs to reuse the original clamping bars. This plate can be welded to the bottom of a battery box or directly to the vehicle, I would recommend welding all of the previously drilled out spot weld holes to make a nice solid mount, an adhesive like liquid nails probably wouldn’t hurt, but might make removing it even more difficult than from the Chevy plate.
The finished product will be a smooth and quiet easy to drive 100kw, 200km convertible ready for the daily commute or the open road. The combination of small lightweight car and a fairly large battery pack (30kwh) will give this Porsche 914 more range than almost all of the OEM EV’s available today (with the exception of Tesla). Charging has not been decided yet, however a 10-12kw solution would extend the total daily usable distance by a significant margin allowing the car to charge from 20% to 80% in about an hour and a half.
For daily use my pack provides more than enough range for what I need and want the car to do. However there are situations where it would be nice if the car had 2 or 3 times the current range. The Tesla Roadster and Model S have the highest range in the EV industry for production cars and they use massive packs of 18650 cells. They benefit from the economy of scale of the laptop and power tool industry as these are the most common cells used. In the coming years this may reverse and the laptop and power tool industries may benefit from high quality cells developed for the EV industry.
Jehu Garcia is currently working towards an 18650 based pack for his VW Samba Bus using recycled laptop batteries. I already have a few hundred 18650 cells on hand so I thought it just might be a worthwhile project to build a removable high capacity battery. Although I have a few hundred cells, what I need to make this work is a few thousand cells. If any of you guys have a stash of “dead” or unused laptop batteries and just want to get rid of them please feel free to send them my way to speed up this project.
The IT department at my day job was happy to give me the dead laptop packs since there wasn’t an established recycling process in place yet, I’m willing to bet the same exists in many companies large and small.
To put all of these cells together there are some inexpensive plastic holders available from Fasttech.com.
The initial plan is to use small fuse wires just like Jehu, and I may use a copper clad board as the current collector, it provides stability and is easy to solder to. The currents won’t be that high and with a massive width of copper sheet on the PCB it actually has a fairly high current carrying capacity.
The main purpose of this pack is not to drive the car on it’s own, but to supplement the existing pack in the car for longer range so the maximum current output doesn’t have to be as high. I would like to build a pack with between 60 and 100Ah at ~86 cells which is a voltage that would match quite closely the nominal and charged voltage of the LiFePO4 main pack in the car. Assuming roughly 2Ah per cell on average from used packs I will need 30-50 cells per module and 86 of those in series, totalling 2580 to 4300 cells for the desired capacity. This pack would weight around 275 to 450lbs which although significant is worthwhile for 2 – 2.7x the range.