Lithium Conversion 48 volt system

[gman@engineer.com]

I have a citicar golf cart I am converting from 8 6 volt Trojan T-105 225 amp lead acid batteries to Lithium. I decided to try the G2 leaf battery kit from TechDirect. They provide two 58 volt boxes with leaf G2 batteries that I hook in parallel to give the needed amps. I installed these and found that they cut off when I go up a hill or put too much of a load on them. I have a power meter hooked to the system now, it appears when you get near 200 amps the system cuts off. Can I hook a regulator in line to the system to reduce the power pull from the motor?

[Sergio]

Did You get the kit with the PC board for buss-bar?

If so there is not much You can do since if you remove the BMS FET current path limit from the system those boards would likely fry.

If You are using solid copper for buss-bars, You can re-engineer the system to provide all the monitoring, balance, LV and HV disconnect but connect the pack discharge directly to the Controller.

Personally I would not have the packs permanently in parallel unless the system is charging and/or discharging, at the very least a fuse between the connection between packs is advisable in case of a cell failure in one pack creating thermal runaway condition between packs.

This is one way to use your BMS without passing current through it:

http://www.buggiesgonewild.com/lithium-club-car/160302-basic-nissan-leaf-7-module-lithium-setup-generic-chinese-bms.html

If You can program your controller you could also limit the current.

[gman@engineer.com]

The system I got did not have a bus bar or PC. The system was sold by Techdirect to be hooked in parallel with a separate BMS with each system and Anderson cable designed to hook the two together. https://www.techdirectclub.com/48-vo...rger-lot-of-2/

[gman@engineer.com]

I had to read your post twice. There is a cut off for each 48 volt unit and a 80 amp fuse with an extra included with the system. There is a board included, but I was assuming this is the BMS, not sure if that is the same as a PC board. The 80 amp fuse must be to prevent the thermal runaway when hooked in parallel.

[gman@engineer.com]

I did hook up a bus bar. Can you explain.

If You are using solid copper for buss-bars, You can re-engineer the system to provide all the monitoring, balance, LV and HV disconnect but connect the pack discharge directly to the Controller.

[Sergio]

Scroll through the pictures from that pack in a kit form and You will see how the modules are connected in Series using a large PC board instead of the flat copper buss-bars.

https://www.techdirectclub.com/48-vo...mbly-required/

You can see the copper buss-bars in this item:

https://www.techdirectclub.com/for-n...series-no-bms/

[bronsonj]

If you look at the description it says 60 amp max discharge. I assume that's per unit, so 120amp max. It says it uses circuit breakers, again 60 amps (I assume two of them in parallel). So the battery they sell is intended for up to 120 amp current draw, pretty low for a cart.

You get up to nearly 200 amps and it cuts off, sounds about right for the breakers they said they use.

The cells will handle loads more, but the rest of the system they sold you is your limiting factor. You can set your controller to limit your battery amp draw to 140 or so and see if that helps, but the performance will suffer. You can rebuild the BMS and whatnot to allow for higher amps. Or you can see if you can get the manufacturer to help or refund you. They state it is for a golf cart specifically in their description, but 120 amps of design capacity is not enough for a stock golf cart.

[gman@engineer.com]

After a few emails to Techdirect, they directed me to a call Fred. Fred (techdirect service guy) indicated that I had 3 options 1) remove the BMS 2) replace the BMS with a 100 amp limiting system, and 3) buy a third battery. He is suggesting option 3. The reason is because going at 100 amps for a given box will heat up the batteries and reduce the life. He stated I could get more power but I would reduce the number of cycles. Techdirect does not sale a replacement 100 amp BMS, he indicated it would be around $100, and require a good bit of rewiring.
Thanks for the answers.

[Sergio]

Do a little research and you will find out the comment about the 100 amp limit is their opinion and likely because they don't want to get involved in re-wiring or admitting the shortcomings of their design.

Good luck whatever route you take, but any BMS that passes the current through itself is not really designed for a golf cart, they are usually for electric bikes or power walls.

[WalterM6]

Not saying this will solve your problem but you might want to consider wiring your modules like the person in this post did.

http://www.buggiesgonewild.com/lithi...onversion.html