BYD 48Volt 150amp/hr ?

[heathnorton]

Hi all
I am based in zimbabwe and am testing some LifePo4 batteries I have managed to source here.
Unfortunately the supplier has no idea technically and I am also just learning .
I am testing a 48volt 150amp hr, it seems the cells are BYD (7.2kwh) presume second life or grade b ?
the battery keeps cutting off at 51.2 volts on the display when i try and run a test load of 300watts
I charge battery to full 54.5 float boost set to 58 volts and set cutt-off @ 48 volts.(not sure if these are correct)
The 300watts load only last 7 hours before the battery cuts off and according to my calculation
that is only about 50amps ? surely is should be getting another 70amps battery life at 80% DOD
As stated i am learning and any help would be appreciated. I am using a PHOCOS 5kva 48 volt inverter
attached are some pics of the battery bank if that helps. many thanks all

 

[thealaskan]

PHOCOS 5kva 48 volt inverter

Never seen that battery before, but what are you charging with, I noticed on the specs that it reads 14.4 v/14.6 v CV. I'm playing with capacitance my self on my grade B set, and am finding low amperage charge of 10 a, is starting to bring them up.

 

[GXMnow]

51.2 volts nominal works out to 3.2 volts per cell (normal for LiFePo4 cells) with 16 cells in series. The Charging voltage showing 14.4 - 14.6 volts seems very odd. I wonder if that is a 4S group rating? If that is for 4S, that would be 3.6 to 3.65 volts, which also looks good for this type of cells. Seems odd they would label it like that, but the numbers seem to work.

Using those numbers, the full 16S pack should have a Bulk charge running constant current up to 57.6 to 58.4 volts on the pack. The 54.5 volts you stated is pretty low for this. I do not know how your charger does a "Boost" charge. Do you see it bringing the cells to 58 volts? The discharge side is rated down to 2.3 volts per cell, so 16S would be all the way down to 36.8 volts. Most 48 volt inverters will not run that low. 40 to 42 volts is more typical. You may not be getting over 80% into the cells, and you might be leaving 20% still in at the end.

What are you using as a test load? Can you measure the individual cell voltages at no load and then at 2 different loads and see how much the voltages drop and how quickly? Are all of the cells dropping evenly together? What is doing the cell balancing? Is it shutting off due to the full pack voltage dropping, or is it a single cell that is dropping out and the BMS is saving it?

If the pack has been heavily cycled and is down to 50% capacity, that would still be over 3 KwH of energy. It should run your 300 watt load for more like 10 hours. 7 hours is not a ton less, and if you are not getting it fully charged and cutting off at 42 volts, it might not be as far off as you think. Also remember that the inverter might be down to 80% efficiency at just 300 watts. Some larger inverters have a fair amount of power just to turn on, and they don't get to rated efficiency until loaded over 50% of their max load. If it needs an amp or so to run the electronics, it may not look bad at 3000 watts, but at 300, it is a fair amount of lost power. You should also check the cell temperatures and make sure you don't have one that is getting hot before the rest. In a series circuit like a battery bank, the whole pack is only as good as the weakest cell.

 

[AussieSim]

There are several vendors of these batteries on Alibaba, but the manufacturer appears to be Blue Carbon Technologies (BCT).

As far as I can tell they've in business for 11+ years, largely as solar street light manufacturer targetting Africa, SE Asia and remote offgrid communities.

Their new line appears to be battery packs with the blue cover, packs with a grey cast aluminium alloy shell, and all in one units with an inverter (these are still under development and not for sale, although listed on Alibaba).

The specifications vary, but universally they appear to be using BYD cells, as shown here.

https://m.made-in-china.com/product/Good-Price-for-LiFePO4-Battery-12-200ah-892218305.html

Their grey cast aluminium series looks much tighter, so I imagine they're using raw cells in these and not BYD plastic packs.

https://m.made-in-china.com/product...ro-Home-Use-as-Storage-Product-902135905.html

The rep has confirmed to me their 12-150 and 24-150 packs are in fact using 130Ah BYD cells, and that they are new Grade A, 0-cycle cells (not second life used cells).

These are photos of the 48-150 blue pack I was sent, with different specifications on the label than OP's.