tiistai 7. elokuuta 2012

Street legal

So I had the bike inspected yesterday. The inspector was mainly interested in the motor and battery mounts and the weight of the bike which we measured on site. The scale tipped at a light 170 kg. 60 kg less than previous curb weight. Not a bad weight loss plan I'd say. The brakes or suspension were not inspected at all which is reasonable since they were stock and weight hadn't increased either.

Parts of the registration form for the Finnish readers. The papers cost 100€.

I also took the bike for a ride. A tankful so to speak. Spent almost everything on a 40 km trip. This did include quite a bit of top speed testing which resulted in 110 km/h. Slightly less than the 130 km/h I had calculated, but it did reach it very nicely so if more was required I think I could get it by changing sprockets. Driving at top speed isn't what the bike is for so I think I'll stick with the quite nice acceleration it now has instead. Driving slower should improve range as well. I'll let you know how many kilometres I get once I drive a tankful that way.

A friend of mine giving the bike a short test ride and the EV impression.
Don't get confused by the ICE bike starting nearby.

Charging the bike in the evening took less than 7 hours. The cells we're within 1% of 3.0 when near empty. Shortly after the charge most cells were around 3.3 volts with a couple nearer to 4 V. This is to be expected and quite normal when using bottom balancing. As you may or may not remember all cells were drained to about 2.75 volts before use which means they are equalized when empty. All cells are not created equal however and when charged the weakest ones will reach the highest voltages while the best cells don't go above 3.4. The charger then simply cuts off the current when 87.6 V total is reached. Even the weakest cells will then come down in voltage reducing the total by a couple of volts.

In other words no fire hazard also known as a BMS is needed. You just have to keep your eye on the amp hour counter and not kill the cells by draining them dead. Just like you wouldn't want to drive your gas tank to empty in the middle of nowhere. As an additional precaution the controller is set not to work below a certain voltage which will also prevent you from killing the cells. 

A slight over voltage when charging at slow speed is not that dangerous. Not at least compared to discharging them below rated voltage at 400 amps. This is why bottom balancing works and BMS does not. If you're using a top balancing BMS you charge all cells to same voltage, but when the pack is near empty you can have most cells above 3 volts while the weakest go way below that near to 2 volts which will cause them to die and you won't notice anything until it's too late. Especially because of how fast things happen at 400 amps.

3 kommenttia:

  1. Where did you buy that mysterious "cheap external 6A" charger? I didn't find any on the website of the EV-power

  2. It's not from ev-power.eu, but EV Assemble:


    I have to note that the fan was broken on arrival, but otherwise the charger works well. I installed a new fan (10€) and reversed the direction. I'm quite sure the original fan had failed because it was mounted so that it couldn't rotate freely due to touching the case (sucking air in - now it blows instead).

    I really should have gotten a 12 A model or better, but at that point I didn't even know what batteries I'd be using.

    1. Also the 6 A model was the only one ready to ship immediately and I couldn't wait several weeks for it to arrive. Now I'd have more time and am looking into upgrading. Hmm. I could sell you mine if I get a bigger one for myself? I'd have to receive it first though.