EMW EV Dashboard, and turning up the Heat

The EMW Deluxe EV Dashboard hardware has arrived, mine is apparently the first copy outside of EMW’s test cars so documentation and instructions were a bit lacking.  Valery did provide me with a copy of the PCB layout which has some pin markings on it which points to some basics like HV Gnd, mV, bV, mC, bC, bCC, t_mC, t_bC +5v.  With these markings and a growing understanding of how Valery designs his products I got the basics sorted out and wired up, some quick tests on the bench had it talking to the tablet and displaying battery voltage, discharge current, power and wh/mile.  It looks like Valery took note of Jacks criticism on the floppy hall sensor that was attached to the basic version and has now created a very simple but solid mounting for the new shunt like hall sensor blocks.  There are two different sensor blocks, one for the motor loop and one for the battery loop.  The app of course doesn’t yet do anything with motor voltage or current so I haven’t hooked that up yet.  The set up is the same as the basic version, there are two buttons that guide you through the set up and enter configuration values.  The core of the Deluxe hardware is an arduino like microcontroller with a breakout board on top with a group of eight db9 connectors, two of which are used for voltage/current/temperature for both motor and battery.  This leaves six more db9 connectors that are wired to various digital/analog inputs and outputs along with other functions that appear to be preconfigured on the board.  There is a trim pot for tweaking the displayed battery voltage when compared to a trusted volt meter.  A bluetooth module plugs into this board which does the micro to tablet communication.  The high voltage monitoring for battery and motor voltage are isolated using a very similar design as used in the 10kW charger.  The system looks like it will have an incredible potential for expansion and customizability when the right people get their hands on this hardware.  The controller code will apparently be released for end user tweaking which will make this a powerful starting point for EV instrumentation and control.

The board is lacking mounting holes and is likely still a work in progress, I will be machining an aluminium top plate with some engraved wording that will mount and protect the PCB’s.

Since the hardware requires constant power I’ll have to revisit my 12v system to handle the constant draw without causing problems or draining the 12v system.  Since the car itself has virtually no draw on the 12v system when the car is off I hadn’t planned for an always on dc/dc converter or anything like that.  I may use a battery charger/maintainer or other small power supply on the 12v system that’s on whenever the car is plugged in.  I’m also thinking about an automatic cut off system that turns off the 12v battery if the voltage drops too low.  I would lose my state of charge indication but easily be able to restart the car and SOC would reset on the next charge cycle.  Better than being stranded because my electric car has a dead 12v battery!

 

I had some issues with the heater, in the end it turned out to be caused by too much heat.  I’m using the very inexpensive Kats tank fluid heaters meant for 1500W at 120v, it’s just a resistor so it doesn’t care if it’s AC or DC power.  I had tested one at about 140v DC and it worked beautifully, I didn’t have the final reservoir so I tested it in a closed loop sealed system.  The final plan is an open system so that pressure can’t build up and burst.  As it turns out at 150V the Kats heater can produce an incredible amount of heat, as measured around 2300 watts.  The problem is in an open system the fluid will boil at a lower temperature than in a pressurized system.  The 140v test likely worked because it was sealed, the fluid didn’t boil and the pump was able to keep the fluid flowing.  Once I had it all hooked up in the car with the proper reservoir the first test failed, I burnt up the first heater in a matter of minutes.  The heater was boiling the fluid causing the pump to choke on the steam and stop moving fluid, once the fluid stops the heater element heats up, trips the overtemp switch however this switch doesn’t work well on DC, I don’t think it actually opened the way it is supposed to.  The element itself then burned up going open circuit.

The solution is a lower power version of the same heater, instead of the 1500W heater I installed an 850W heater, it’s the same size/shape but the element has a different resistance.  On 150V it produces about 1350W which doesn’t boil the coolant and things heat up and circulate as expected.  I’m now using a pair of these 850W heaters wired in parallel, with the fluid flowing in “series” which gives me about 2700W of heating power.  The system seems to be working well, but only a cold day will truly tell.  I have also revised how the temperature switch is wired in, it interrupts the 12v signal that turns on the contactor which it handles with ease.  I could probably use a pair of the 1000w version for a bit more heating power and still not boil the coolant, but I’ll see how these 850W units work when we get some cold weather.

As with all things in the car I strive for a stock appearance and function, at the moment the heater switch is simply a pair of wires and switch laying on the passenger side floor, however initially I will wire it up in place of the stock rear defrost switch.  This sits to the immediate left of the rest of the heater controls and is the most appropriate.  When I have more time I’ll test the behavior of the vacuum operated fluid valve that is part of the factory heating system, I may be able to install a microswitch on the vacuum valve that would turn on the heater system when the temperature dial is turned up above the cars ambient temperature and to a certain degree turn itself on and off as required based on the heat setting.  This would eliminate the need for a dedicated “heater” switch that isn’t part of the normal and intuitive operation of the car.  If I go that route I will have a hidden manual override switch that turns off the heater if there is ever such a need.  The other option is to put the EMW Dashboard in control of the heating system, Valery has already coded and assigned heating and cooling inputs/outputs designed to monitor temperature sensors in the battery boxes and cabin and turn on heating and cooling as required.  This would be a more complex but easily programmable system that would provide more flexibility and control to the frequency that the heating element turns on and off.  It would require some sort of control input to “set” the desired temperature however that might be able to be hijacked from the existing temperature control knob and be made to operate in a very intuitive way.

Well I haven’t even posted this update yet and plans have changed again.  Early on I looked at the RM3 and RM4 heaters sold by Metricmind, since that’s where I bought my vacuum pump.  At regular price they are very expensive so I ruled that out at the time.  As it turns out a batch of RM3 200-450V 4kw heaters with attached pump just came up on the surplus market, for a very reasonable $120US, buy a pair and that comes down to $100 each + shipping.  It should look like the one below except the orange connector and wire has been cut off. New the heater was over $400 and the pump was another couple hundred.

RM3Bosch

I will keep one of the Kats heaters in the loop for preheating the car off of 120v but the RM3 should nicely take care of heating the cabin while driving.

 

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