Couple lithium questions.

[panteramatt]

Just picked up a 01 Club Car DS with dead batteries. It has an upgraded motor and alltrax 500a controller. I wanna do a lithium swap asap but with this corona virus my wife and my jobs are slowing down. I would love to do a 14s leaf pack but would a 7 pack be fine for a weekend campground? Hows is this setup?
https://www.ebay.com/itm/48v-Nissan-...53.m1438.l2649

Is the charger and bms good in these kits and is the G2 batteries worth the extra $?

[bronsonj]

The pre-built lithium packs all seem to have a weak spot in the BMS unit that limits current draw. From the link it says in the BMS section:
60 Amp continuous discharging, 120 Amp peak discharge

Your upgraded motor isn't going to do very well if you limit the current draw from the batts to 120 amps.

The other thing that is concerning is the condition that is listed... "Frame, BMS, Display Meter are brand new, and the batteries 65% capacity".

There's another thread in the lithium section to a place where you can buy the Leaf cells for $50 each. Here's the link to that thread:
http://www.buggiesgonewild.com/showthread.php?t=161633
and a link to the cells:
https://batteryhookup.com/collection...y-module-gen-1
They are untested G1 at $50 each... Pretty incredible price...

[panteramatt]

Yea I saw those cells BUT they are gen1 and untested so wouldnt they be worse and older?Also, can you tell me how the bms would hold my motor back, not sure how it works. Im in need of getting this stuff ordered asap but its been overwhelming.

[bronsonj]

The cells in the pack can handle gobs of current. The current will slowly drain the cells. The BMS stands between your cells and the output cables from the battery pack to your controller. So all the current flows through the BMS.

If you create your own DIY pack there are a dozen ways to wire your own BMS and you can bypass the LV cutoff or use a different solenoid to do the LV cutoff. In these pre-built packs though, the BMS itself does the cutoff. But the BMS has nowhere near power handling capability of the leaf cells. So if your controller will pull 350 amps and the nissan leaf cells can certainly give you 350 amps, the weak point in between is the BMS and it is listed according to the seller as capable of 120 amps in short bursts and 60 amps continuous.

Yes, G2 are better than G1 cells. But the BMS is the weakest point with a pre-built pack.

[panteramatt]

Thanx alot for the explanation, clears it up. So I ordered the cells and charger. I plan on setting to charger to turn off at 90% charge and adjust my controller to shut down at 20%. Any reason this wouldnt work without a bms?

[bronsonj]

Most people run a BMS. The issue is "Catastrophic failure doesn't happen slowly". (I think that was a quote from Sergio)

So today you charge the cells and when the charger cuts off all cells are 4.12vpc (57.68v for the pack). If you have on cell go bad you can still charge the pack to the same V but you may end up with 13 cells at 4.05v and one cell at 5v.

Similarly on discharge, if you have your controller set to shut off at 47.6V and today all cells are in balance at 3.4vpc. In the future you may have 13 cells just fine with one cell at 2V.

And you won't know this... So the weak cell is now being worked far beyond the V it is designed for so it gets weaker and weaker. Then very soon you get 13 cells charged to 3.95vpc and one cell at 6.33v and on fire.

Also, even if all your cells are healthy, the further you discharge the cells the more variation you will see in individual voltages because of the lithium discharge "knee". You may be within 0.01vpc when charged to 4.1v but could well have 0.5v difference when discharged.

Also, fuses are good, but they will not help you protect against overcharge. So do use fuses, but that's not the only thing you need. That's my nickel's worth.

[DaveTM]

Originally Posted by panteramatt

Any reason this wouldnt work without a bms?

Yes, as Bronsonj stated that kind of setup only controls "Pack" voltage. Not individual cell voltage.

So...unless your going to manually check the cells charged voltage on a regular.....very regular basis you could run into big trouble.

A good BMS will "take from the rich and give to the poor" in terms of battery charge. So....if you set an upper limit of say 4.1 for each cell....and one or two cells are at 4.2 and you have a few at say 4.05, the BMS will reduce the higher cells and give that power to the lower cells.

The big reason for that is when your dealing with Lithium....if you overcharge or undercharge ONE cell, that cell is now damaged forever and if you continue to charge a damaged cell.....you will likely experience "Thermal Runaway" or essentially....that battery will start a very hot.....very fast fire.

See the sticky post on the fellow (teenager) who did just that and he may still have the photos still there. His cart ended up a small pile of melted plastic....and melted metal.

Hence the "insurance factor" of a BMS.

FWIW

[bronsonj]

Originally Posted by DaveTM

See the sticky post on the fellow (teenager) who did just that and he may still have the photos still there. His cart ended up a small pile of melted plastic....and melted metal.

I found the link Dave mentioned, it was in the Club Car Lithium section.
http://www.buggiesgonewild.com/showthread.php?t=150460