Monday, July 21, 2008

Charging update

Last Saturday, my son Paul and I spent half a day working on the twike batteries. After several hours of charging, the Battery2 was at 320 volts and slowly climbing (a good sign) but Battery1 was only at 110 volts. A closer inspection revealed numerous cell venting events and the black areas indicated some fires. I assume these happened over the years when the previous owner tried to revive the batteries. I did get one cell to vent myself when I let a group of 20 cells draw 5A for 100 seconds while trying a technique to revive it. Ok, give up on that battery. We pulled it and decided to replace it with one of the spares that has good looking cells (clean ends, no discoloration) but is lacking a BMS card. I proceeded to drain all the cells to zero in the old pack before beginning the process of unsoldering the BMS to move it to the new batteries. A couple of hours later we had the old board out and soldered into the new battery. I put it back in the Twike and powered up and monitored the voltage. The charger/controller is very smart and will only apply a small current until the voltage comes up to about 340 volts. I'll need to get both packs to that voltage to get the built-in charger to give the batteries a full charge (410 to 420 volts). I'll either have to jump start the cells again (will less current this time) or be patient to see if the cells will get to 340 on their own with the charger. Peter Zeller from Switzerland has been very helpful in answering some questions about the batteries and such. At this point, I have no hope to make the battery pack have a useful range, but I just want it to get to the point I can check out all the operations of the Twike. I need to fix anything that is broken before proceeding. I might have a problem with one of the relays since I notice the DC/DC led stays on even after I push down the red button. The docs I have say this is supposed to remove all power except for the batteries themselves. If so, then why is the LED on? Oh well, more to learn.

1 comment:

getsweekendsoff said...


Wish you best of luck with your project. A german TWIKE pilot has launched a similar project using LIFePo4 cells. His project website is hosted here:
Its in german but you might find the contained links useful for your projects.
An online translation tool might also help.

English TWIKE Forum