charging the battery off the car?

[jimmyq]

hi guys ive had a few cars in with voltages below 4volts odis will not allow to charge and no option to close contractor on this car to charge or restart high voltage system as it says battery regulation J840 must be higher than 20volts

there is someone who charges these off the car but miles away

what do i need to charge is there a charger i can buy or some setup to charge

please be gentle im new to all this i have a few spare batteries which i can open if i need to use anything from inside

[uhi22]

Which kind of battery? Which chemistry? How many cells in series? BMS?

[jimmyq]

Golf Gte
Audi etron

[jimmyq]

https://openinverter.org/wiki/File:A09A7628.jpg

Same as this

[jimmyq]

Anyone??

[uhi22]

First recommended action is to check the voltage of each cell. If below 2.5V, I would not charge anymore. There is the topic with the dentrids which lead to internal shortcuts and thermal runaways. If all cells above 2.5V you should be safe to charge maybe block-wise with an adjustable bench supply. E.g. if you have a 30V supply, charge 8 cells to nearly 8*4V, and then the next 8 and so on. Takes a while.

[jimmyq]

Thanks on diagnostics showing 4.5volts i need to disconnect the power connector on the battery from the car and charge it direct thats what i need saves me taking battery off? If i isolate it all and get a connector + - attatch power supply or some sort of charger direct is what ime after?

Thanks for the reply

[jimmyq]

Can you recommend a charger/supply to do it in series from just the positive and negative side

[jimmyq]

https://www.te.com/en/product-2141227-2.html

I want ti try charge from this connector

[Aragorn]

4.5volts doesnt make any sense. It cant be cell voltages as those dont go above 4.2 or so. If thats module/pack voltage then the module is scrap, or its a false reading.

To charge using the main battery connection you would need an actual charger, cheapest option is probably something salvaged from another EV.

But the bigger issue is the battery wont close its contactors without you being able to talk the appropriate canbus messages to the internal BMS control unit. And if the problem is that the BMS has decided the battery is broken, your not going to get it to close the contactors.

Before trying to charge it, you need to measure all cell voltages and ensure none have gone dangerously low. If they have its not safe to charge and the bad modules need to be replaced. Its somewhat likely, if the BMS has decided that the battery is broken, that there is actually something wrong with it.

[jimmyq]

Thank you