54.6V charger on a 58.4V lifepo4 pack

[redwing0001]

Can anyone clear this up for me? The Lifepo4 pack I bought from a store here in the Philippines is 48V 20Ah but came with a 54.6V charger.... It does work but I know it does not charge to full charge at 54.6V (@3.4V per cell) when full charge voltage for each cell is 3.6V, or 58.4V. The seller said the BMS they use are 16S as well but I know 16S batts have a full charge voltage of 58.4V, 15S batts have 54.6V full charge.

The seller then told me I should leave the 54.6V charger on the battery overnight so charging voltage goes to 58.4V where it does, BUT it does not stay even close to 58V when I use it, it almost immediately goes down to 54.6V and lower when I use it.

The reason I am asking about batteries here is that the seller does not know more than me about lifepo4 batts. When I told him that 16S batts have a full charge voltage of 58.4V, he told me that's "fake voltage" and that you only need a 54.6V charge for 16S because 3.2x16= 51.2V.... I know that is not the full story but when he told me that was "fake voltage" I did not reply back, knowing what I know about nominal and full charge voltage on lifepo4 cells.

I have found an online seller for a 58.4V 4A charger that ships locally but I have a question on whether is it ok to use it on a 16S lifepo (alum can prismatic) 20ah battery or not? I know you have to use a charger that is the same with the total full charge voltage of the battery but undercharging it a bit extends life (from 3.6 to 3.4)...

the online store lists the model as UY240 and its 58.4V 4A lifepo4 charger. If you need to look at the specs:

https://www.lazada.com.ph/products/...T9nNKT5QIVA3ZgCh2dwgDNEAQYASABEgLrt_D_BwE:G:s

Anyone with knowledge on lifepo4 batteries, BMS and lifepo4 battery chargers can chime in to this one... I dont have much knowledge on lifepo4 batts and chargers but I have enough DIY knowledge on 18650s but I need more inputs before I buy that 58.4V charger.

 

[dustNbone]

As long as you can verify that it's indeed a 16S LiFePo4 pack, then yes the 58.4V charger is the correct one.

 

[john61ct]

If the cells are genuine LFP, then the **resting** voltage for 16S at 100% SoC should be 53.4 - 53.60V. If a little higher, just "surface charge", remove 0.5% capacity and it will drop to that.

The **maximum rated** very stressful top charging voltage should be 57.60V

Personally at healthy low charging C-rates like 0.3-4C, I would not go higher than 55V.

The actual useful capacity Ah between the two SoC levels will only be a few percent, not worth the longevity hit.

That 54.6V charger is **perfect**, so long as it charges at a low C-rate, or holds that Absorb voltage for some time (CV stage), until current starts to drop, say down to 1-2A.

If it stops immediately when hitting 54.6V (CC-only) the only issue is a few more percent lower capacity not utilized, maybe a few minutes range, hardly significant.

All the above is wrt LFP cell health, the requirements of your cell balancing gear is an entirely different topic.

I know 16S batts have a full charge voltage of 58.4V

That would be 3.65Vpc, absolutely stressful if used in normal daily cycling.

I would only go that high a few times a year, if necessary for manual re-balancing, or doing capacity benchmarking via CC load testing from there down to 3.0Vpc as 0%.

Going that high every cycle would drop a large percentage of cycle lifespan.

> 3.2x16= 51.2V

That is "nominal" voltage, practically 0% SoC if at rest, a good LVC for high C-rate discharge to protect pack lifespan.

 

[redwing0001]

so, that "leaving the charger plugged in" routine is really useless and the voltage will eventually go down to 53-54V when the batts are in use.... hmm.... I might not want to buy that 58.4V anymore noting that charging to 58.4V will reduce the lifespan of my batts.

I think this is also why the ryobi 18V lithium packs charge only up to 4.0-4.1V..... the ones I use here still charges good even after 4 years... yeah, 4 years of use and still holds good charge.

 

[john61ct]

so, that "leaving the charger plugged in" routine is really useless

Not sure what you mean.

A proper charger turns itself off once its algorithm determines the charge cycle is complete. No current should be flowing in either direction.

Ideally you only charge just before using, very harmful to let a LI battery sit at high SoC, so of course should never be floated.


> voltage will eventually go down to 53-54V when the batts are in use

~53.6V is the resting voltage **when sitting isolated** after a full charge.

As soon as a load is serviced, voltage will go much lower, depending on the C-rate.

If only for a few seconds then isolated, as the pack rests, voltage will slowly bounce back, maybe to 52V or higher.

Resting at 51V will be somewhere between 20 and 80% SoC.

Resting anywhere near 50V should be considered empty, and regularly going that low is not great for longevity.

Going below 48V is dangerous, borderline risks rendering the whole pack instant scrap.

 

[redwing0001]

so you really do need to charge it when it nears 48V.... huh, never thought that was real on lifepo4... on 18650s, I routinely get to cutoff voltage before I charge... and the cells I use still good up to now... some of them are 4 years old and still good (even if they are just 60% of their capacity...)

 

[john61ct]

Let's say under "normal" care a given cell reaches 80% capacity after 150 cycles.

But by coddling it can go 250.

Up to you if that's worth it.

I would not continue to use cells at 60% myself.

 

[john61ct]

That was LI and LiPo range.

I've seen dozens of LFP banks go 2000 cycles with zero or very little capacity loss.

That's top-notch cells though like A123. well coddled, and low C-rate usage, not propulsion.

I reckon 10,000 cycles is possible, and that's what I strive for in designing the infrastructure whenever possible.

 

[redwing0001]

even 1000 cycles on LFP is still better than 500 cycles max for lead acid, gel cel or VRLA with twice the weight and half the capacity for the same size.