How to charge a 25s lifePo4 battery?

[StinkyGoalieGuy]

I'm building a 25s lifepo4 battery (25s1p, Headway 8Ah cells). Any suggestions on how to charge it? On my current 25s battery, I'm breaking it apart and parallel charging it as 5 banks of 5S batteries using a Chargery 1010B+ RC battery charger.

I would prefer:
- not having to break the battery apart - charge it as a single 25s battery
- add some type of BMS

Ideally, I would only want to charge it to 3.5v per cell, so something configurable would be nice. Charge rate is not so critical.

I see a Cycle Satiator would fit the bill, but that's about $350.

I'm also looking for suggestion for a BMS. I can't find anything that supports beyond 24s. I only need 40 amps, continuous.

Thanks!

 

[999zip999]

Why 25s ? Go 24s 4 groups of 6s and use balance wires or get a BT bms for 24s.
Or charge with three 24v meanwhile in series adjusted to 87v for 25s or 84v for 24s .
Is this just for you? Do you fill OK to run without bms 8ah is small but I do it with 8ah.
But headway has trouble keeping in balance. So find out how your park works. If non bt have balance wires to check real voltage with cellog8 or something. After a dozen charges you should know your battery. What's it for ?

 

[StinkyGoalieGuy]

Why 25s ?

Just trying to maximize my motor RPMs and top speed. The PhaseRunner handles up to 90V - so 25s lifePo4 hits that perfectly fresh off the charger - 3.6v*25 = 90v

Is this just for you? Do you fill OK to run without bms 8ah is small but I do it with 8ah.

Yes, just for me. On my previous battery, I ran without a BMS. Then I would check each 5s group voltage before charging them all in parallel.

But headway has trouble keeping in balance. So find out how your park works.

I wasn't aware of that. Good to know.

What's it for ?

For a BBSHD running off a PhaseRunner.

I will look into the Meanwells and see how to do that as an option.

 

[amberwolf]

But headway has trouble keeping in balance. So find out how your park works.

I wasn't aware of that. Good to know.

Cells not staying in balance is because they aren't well-matched in characteristics.

If you get all new cells top-grade perfect cells that are from the same manufacturing batch (if there is a definite absolute way for you to tell without trusting the seller, who probably has no idea, regardless of what they say), then they should stay in balance fairly well, after you have tested them all and weeded out the outliers with significantly variant internal resistance, capacity, etc.

This typically doesn't happen (sellers don't really know what they have, don't sell matched sets, builders don't typically test their cells, etc), so most packs both DIY and commercial require rebalancing periodically (much more often for some than others), either via automated or manual means.


Another problem that exacerbates the imbalance issue is that most people buy or build packs that can barely handle the loads they put on them, and barely have enough capacity for the range they need, instead of using something with lots of headroom in both capacity and capability (becuase that costs a lot more).

If you use a pack that has much more capability and capacity than you use, you don't push it into areas that stress it and even if the cells aren't perfect or matched it'll still stay pretty well balanced and have a good lifespan.

 

[StinkyGoalieGuy]

As usual, that's great info from Amberwolf.

The cells are used, but from a reputable seller, so I'm not too concerned, but I will do a capacity test on each one before using. I don't plan to use more than 60% of the available capacity between charges and I will be using them well below their current capabilities. I will only be pulling 40amps peak. These are the HEADWAY 38120 HP cells which can supposedly put out 200amps each.

 

[amberwolf]

You might want to look at the discharge curve at that max current level--they probably sag a whole lot trying to do that. Many sellers claim incredible current rates for max performance, but few provide actual discharge testing curves at various rates (because these would show how poorly they can do more than 1C or 2C in most cases, which would gbe 8A-16A for these cells). I don't know what the curve is for your specific model of HW cell (they make several versions of them, and they have changed over the years), but you can find testing curves for at least some of them around the web.

And in used condition, they almost certainly will be poorly matched in characteristics. If you can test their internal resistance you may be able to better predict how they will behave relative to each other. Even a small difference means differing voltage sags on each, and differing power outputs from each, etc.

Differing capacities (or other parameters) means the lowest (worst) one is the capacity of the entire pack, for a 1P pack. If you have more than 1P, you can put the worst and the best cells together in the same groups, doing at least a little evening-out of the performance. Without that, you're stuck with the worst cells' performance.

 

[Chalo]

Electric motor BEMF and inductive/capacitive voltage spikes in your system can exceed battery voltage. I don't think it's a good idea to run any controller at its absolute maximum voltage, because then normal amounts of electrical noise can drive it beyond its rating.

 

[StinkyGoalieGuy]

Electric motor BEMF and inductive/capacitive voltage spikes in your system can exceed battery voltage. I don't think it's a good idea to run any controller at its absolute maximum voltage, because then normal amounts of electrical noise can drive it beyond its rating.

Yeah, that's a good point. Maybe I will just stick with 24s. Then that will also simplify my charging scenario. BMS is easier to find. Or I go with 3x 8s cell log type monitors and charge them as 3 banks of 8s1p batteries in parallel with my Chargery 1010b+ until I find that is too much of a hassle - then maybe go BMS and Cycle Satiator.

 

[999zip999]

I have a small pack of 8ah spaim08 200watt cells no bms and get 7.4ah safely just bulk charge. I do have 4- 5s balance wires if wver needed. Runs good just leave a little in the tank.. I did it that way for 8 years with A123 pack no bms.

 

[999zip999]

There is no reason you can't run a BMS and then run a set of balance wires for 4-6 or 3-8. I would have to know. Plus small battery

 

[Hummina Shadeeba]

Aliexpress has power supplies that get to that high a voltage. Best to get one with headroom and they break when pushed

I use two of these. 24s
Just found this amazing item on AliExpress. Check it out! $91.63 23％ Off | 48V 58.4V 72V 60V 67.2V 84V 87.6V Li-ion LiPo Lifepo4 Lithium Battery Charger Curren Adjust 10A 5A Fast Charge ebike 16S 20S 24S

https://a.aliexpress.com/_mLUKIm4

One I push to 10 amps all the time and the other will only do 6 amps now for unknown reason, but still works.

 

[999zip999]

Wow a cheap Chinese charger that works and doesn't break down in the first week.

 

[calab]

BMS Battery can custom make you a charger for bulk 25s lifepo4.

 

[999zip999]

Why 25s lifepo4 ? Waste of time money and effort
24s lifepo4. Get it.