Thursday, February 9, 2017

Karmann Ghia EV Conversion - Voltmeter for main batteries

I decided not to use the Xantrex linkLITE which I originally purchased. The problem was with the voltage prescaler and the voltmeter. I ended up shorting it out a couple of times before I figured out how to properly isolate the 12 volt system. Also, the linkLITE cannot be calibrated and it is pretty expensive. The linkLITE only measures voltages up to 35 VDC so it cannot measure a high voltage battery directly. I also don't like the look of the Xantrex digital gauge in the dash. It does not match the other gauges. Instead, I decided to go with a voltmeter that can measure the full voltage of the batteries without a prescaler and that could also measure amperage off my existing shunt. The Xantrex came with a 500 amp 50 mV shunt which I already installed.

Here is a circuit diagram showing the isolated power supply, the voltmeter, current meter, low voltage, and high voltage systems:

I found a digital panel meter on eBay which measured high voltage and amperage simultaneously. The seller agreed to program it to work with my existing shunt. I mounted it under my dash with a bracket. It is not in the driver's line of sight, I have to look down to see it. This is fine for my purposes.

here is the eBay Item:
DC +/- 500A 200V Amp Volt Combo Meter Battery Monitor Charge Discharge Shunt DS

I hooked it up using a fuse on the high voltage side and with an isolating DC/DC converter to make sure that the high voltage and low voltage circuits remain isolated. VERY IMPORTANT!

Picture of back of panel meter

Isolated power supply: DC-DC Converter Isolated Power Module In 10-16V Out 12V DIY Favor
1/2 amp fuse: GOULD SHAWMUT ATM1/2 FUSE ATM 1/2 FUSE 600 VOLT 1/2 AMP

Karmann Ghia EV Conversion - Speed sensor problem / New gauges

I have come to the conclusion that I will not be able to get the WarP motor speed sensor kit to be compatible with the Synkromotive controller. There is a glitch that arbitrarily limits motor RPM to approximately 3600. The sensor seems to display RPM accurately.
Since I could not fix this problem, I decided to by a 52mm tachometer which will fit in the dashboard in place of the original clock. This will not prevent over-revving the motor but should give satisfactory feedback to the driver to avoid damage.

Tach from amazon

I installed it in the hole for the clock on the dash and it works nicely.

I ended up not liking the appearance of the amazon tach. Instead I bought matching gauges for RPM and Voltage from VDO. I like that the gauges match and they look similar to the original equipment. VDO makes the original gauges for the car. The other nice thing is the gauge light comes on with the headlights, not all the time, and it is attached to the main dimmer. It all works together nicely.