105ah lifepo4 pack combining

[georgia088]

In that thread I was also told:

Originally Posted by Pat911

1C/3C 30 second cells will suffice if you’re looking at 105Ah.

Cheers
Pat.

This was a 2wd cart. I know. But here is what I see:

With this cart IN 4wd if I am on flat ground and run CONTINUOUSLY I see around 100 amp draw CONTINUOUSLY at WOT (less in 2wd) now that the connections are good. I do see spikes on hills or on take off of 300-400 amps. NEVER for more than 5-10 seconds. The cells are rated for 315 for 30 seconds. It’s stated clearly in the data sheets that are there for a reason. I’ve never, even with bad connections going up a hill with pedal to the medal, seen close to 30 consecutive seconds of any where near 300 amps.

Is this the best pack?… no. Is it capable? YES! How long will it last? Only time will tell. Is it a hazard? I can’t see it as one. There is a bms in place to prevent the cells from going above or below their spec voltages and temperatures to prevent bad things from happening. I am not exceeding the 1c CONTINUOUS rating or the 3c surge rating. What am I exceeding? The pack delivered all 105 ah of capacity on a 20 mile ride. No hiccups. Would two packs or more be better… Well, hell yea it would. I’m not trying to mislead anyone. I’m providing the data as I see it. Am I exceeding the cells capability with the 400 amps of surge for 3-5 seconds. Maybe, but that data is not in the specs that I see.

According to the bms I pulled 105 ah on the 20 mile ride. The drive took me well over 3 hours with stops and typical (less than WOT) driving. This seems to make the continuous draw of the pack less than 100 (around 33 amps per hour or .33C if my math is right). 40 degrees Celsius was the highest temp I saw on the bms temp probe that is placed near the cell terminals/bus bars. I know this isn’t true controlled data, but it is what this cart MAY see on a HARD day.

I will keep an eye on the pack and see if things change… I hope not.

Thanks!

[Pat911]

Once again for clarification, the ratings are maximum ratings. What the 1C/3C 30 seconds means that it can supply up to 105A continuously, 106A-315A for up to 30 seconds and should never be allowed to supply 316A or more. So, if your cart is drawing 106A for more than 30 seconds, you’re exceeding the cell limits. You don’t need to be anywhere near 315A to exceed the limits of the battery.

Having said that, I’m glad your pack is finally performing to your expectations……..and I hate having myself quoted back to me…

[georgia088]

Originally Posted by Pat911

Once again for clarification, the ratings are maximum ratings. What the 1C/3C 30 seconds means that it can supply up to 105A continuously, 106A-315A for up to 30 seconds and should never be allowed to supply 316A or more. So, if your cart is drawing 106A for more than 30 seconds, you’re exceeding the cell limits. You don’t need to be anywhere near 315A to exceed the limits of the battery.

Having said that, I’m glad your pack is finally performing to your expectations……..and I hate having myself quoted back to me…

Thanks. I would have never gotten it to work as well as it does without your help.

[Volt_Ampere]

As long as your BMS is set correctly to protect those cells, then it's safe to use.