DIY Lifepo4 Daly BMS cell voltage drop issue under load

[Volt_Ampere]

You could experiment by moving your doubled up bus bars to different batteries and see if the low readings under load change.

[DaveTM]

If your going to make contact between copper connections and aluminum I would strongly suggest using this compound at that connection. Just "slather" it on and the two different metals will work together much better. You can buy this at Home Depot or Lowes and likely on line somewhere.

I used this on FLA's and NEVER had the large (or small) puffs of green stuff from the gassing that occurs during charging.

[expoman55]

Hello, Newbee Club cart owner here. I have just purchased a 2006 CC Precedent from my favorite builder.. It has a full Madjax 6" lift, Alpha body kit, new seats( newer gators seats on way) et al. DONE.. It has NEW Trojan(4) Motive T-1275 Plus batteries. My builder said he'd buy back the trojans as I want to put Lithiums in the buggy as i hate acid etc.

Here is my question for you experts: WHY is it unadvised to buy 4 - 12v/100 ah batteries and replace these one for one with individual lith bats with BMS on each one? I am being told NO NO NO you MUST go to something like ROYPOW or ECO Battery and get a Package all in one for your buggy.... PLEASE help me understand it..
This whole lithium and electric buggy is new for me ... OH my buggy will be garage kept, will do some off roading but mild NOT mudding.. and pull my yard cart around etc.. primarily for the wife and I along with pups to go for rides around the community we live in.

I know the benefits of Lithium but am trying to understand why not 4 battteries vs one package.

[Pat911]

That subject has been beaten to death on here and you should really start a new thread for that question so as not to hijack and derail this one. But here goes anyhow...

You should never connect lithium batteries in series if you want a reliable solution. I know 4 x 12v batteries in series equals 48v, that’s not the issue. There are 4 BMS’s all doing their own thing. The issue is no two batteries are ever equal, there are tolerances.

With Lead Acid batteries in series, when one battery becomes fully charged, the charger keeps charging. The fully charged battery is overcharged while the other batteries catch up. With Lead Acid, it’s no problem. Lithium batteries on the other hand absolutely cannot be overcharged so when the first battery in the string gets to full charge, its BMS disconnects to prevent overcharging. Since the batteries are in series, the first BMS that disconnects will stop charging all 4 batteries together, therefore, the other 3 batteries will never reach full charge.

When one cell in a battery starts getting close to full charge, the BMS begins bleeding off charge on that cell so that the others can catch up. This is best done whilst monitoring all 16 cells together, and not 4 banks of 4 cells.

The energy stored in a series connected lithium battery is only ever as good as the least charged battery. In the above example, assume you have 100Ah batteries, but when the first battery cuts off at full capacity, the least charged battery only has 80Ah in it. Well, your 100Ah is now only 80Ah as its BMS will disconnect once this battery is discharged to 0% prevent damage. As you go through more and more charge/discharge cycles, this capacity difference will increase, reducing the pack capacity further.

This can be fixed from time to time by fully charging each battery individually using a 12v lithium charger, but they will drift out again, sometimes in as little as months. Lithium is touted as being maintenance free, having to top balance manually every few months certainly isn’t maintenance free! A single 48v battery with a single BMS will keep the internal cells in balance.

48v Parallel connected batteries on the other hand are less troublesome but still not advised if possible. The issue here is that if one pack’s BMS disconnects while the other keeps going you will never know. You may also damage the pack that is still in use because it may be undersized for the particular application. Also, if the two pack are connected together when they are not at a similar SOC, very large currents will flow between them, possibly tripping off the BMS and preventing a parallel connection.

Parallel connected batteries are ok if you understand how they interact, but series connected batteries are definitely a no no.

Cheers
Pat.

[Volt_Ampere]

What Pat911 said!!!!! Do not go with individual 12V Lithium batteries.

[WalterM6]

Just now noticed in your setting screen shot that your batteries are 90Ah. These wouldn't be the 90Ah batteries with 3 or 4mm screws to connect the bus bars. If it is that's your problem not your bus bars. DAMHIKT