emini

When I installed my EVision, I removed my fuel gauge. I'm using a fixed gear ratio, so motor speed isn't particularly interesting. The EVision has an output to drive a fuel gauge, but it needs reprogramming to drive a tachometer. Victor suggested that I bypass the tachometer's circuit and drive the movement directly. This is made especially easy because the tachometer comes out of the instrument cluster on it's own, and the movement is connected to it's circuit board with wires. I simply reconnected the movement to the input of the rev counter circuit and connected the EVision to the existing plug. Unfortunately the EVision's driver wasn't powerful enough to drive the movement beyond 2000 rpm, so I added a small transistor to amplify the signal. Power for the amplifier was already available on the circuit board so this was easy.

One of the great things about an electric car is it can be totally silent when you're not moving. Unfortunately the PWM frequency is about 3kHz and while the tachometer makes a fairly bad speaker, it's quite audible. I'm going to soften the switching with some kind of capacitor, which will hopefully make it silent. I'm also planning to make a circuit to turn off my water pump when the car isn't moving.

If Google Maps is correct in measuring my trip, I'm doing 177109 Wh/km on a return journey with stopping and starting and hills. I was driving like a nanna, and I limited myself to 10 or 11 kW (for 60km/h uphill, >80km/h downhill (56% at this sort of speed, the rest slower)). My record is now >20Ah and 20km without charging.

I still only have only 1/3 of my final battery installed and it's getting quite hot. (this is why I'm limiting my power to 10 or 11kW, about 3C). It's 25℃ at night here and the battery isn't even getting down to ambiant overnight. The trip started at 27℃ in the middle of the battery and ended at 33℃. My record battery temperature is 43℃ (after charging 20Ah at 30A right after discharging about 10Ah at 50-100A right after baking in the sun). This isn't very good for the battery. I need to install more cells so each one doesn't work so hard.

I'm charging without a BMS, I have my charge voltage set very low so it slows down as soon as the first few cells start to come up. Luckily none of the cells have come up by themselves, it's always a group which is enough to slow the charger down and stop it. I last balanced my cells back in September and October. Today I went round with my 3A bench supply and topped up the low ones. Of the low cells, most required only a few minutes of charging at 3A to come up above 3.6V (at 3A). 3 or 4 took about an hour each. I guess these cells have higher self-discharge.

Less than a 10% variance in absolute self-discharge over 4 months or so is really quite good. I've put very few cycles on the battery so I figure self-discharge dominates any other effect that would push them out of balance.

Earlier I reduced the preload in my gearbox by adding a gasket. I didn't have time to properly measure and set the clearance so I did it "by ear". After assembly, I couldn't hear anything slopping about in the box, so I hoped my theory on how it came to be so tight was correct.

Unfortunately it didn't sound so good when driving. I took it apart again and found some bad indications. The oil left in the casing had some sparkly metal in it, and the bearing outer races looked "bruised". I'm not sure if this was caused by running the box too loose or too tight.

I measured the preload using some roofing lead. This is very soft (pure lead is about twice as soft as solder, I could dent the stuff I used with my fingernail) and crushed nicely under the bearings. The basic procedure is to replace the shims under the bearings with small lumps of lead, assemble the gearbox, crushing the lumps as you bolt the casing together. After turning the shafts a few times, you take it all apart and measure the lumps with a micrometer.

I went down to the gearbox factory and was shocked to find that they have a big box of mixed shims, all different diameters and thicknesses. It took half an hour with a micrometer to find shims that set the preload correctly. It would seem that they don't routinely set preloads -- if they did, they would surely have them sorted into some kind of size order.

While I was there, the guy behind me was stripping reconditioned gearboxes, and I recognised my Mirage box. They were making space by getting rid of old boxes that they would never sell, so I rescued one for a spare. This one only cost $150, down from $200 I paid for the first one.

I haven't yet measured the losses with the new preload.