Roll the dice, battery gamble.
- Thread starter Mattb4
- Start date
Just imagine putting two batteries of identical capacity in parallel and charging them (something you did) each pulled the same current meaning each battery pulled the equivalent of 1/2 of what the two together pull.
Unless there is some difference
- in cable resistance/internal resistance (for example you put an AGM and Lithium in parallel charge rates are not going to divide in proportion to capacity)
- or cell imbalance,
- or State of Charge
The cell imbalance only comes into play near the ends of the charging range. If one cell is so far ahead of the rest that it charges substantially differently from the rest, that can affect the current split. Of course, if the cell hits a voltage limit and the BMS shuts off the whole battery, there will be no split and the current will likely drop by about 1/2 for the single remaining battery.
So I would say the first order model is that charging currents for parallel configurations of similar batteries are going to be divided based on capacity assuming both batteries are nominally at the same state of charge.
Second order effects that would cause deviation from the first order model are listed above.
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Hard to do real world testing thanks to the perpetual darkened skies. I know mankind had to try that to prevent the take over of the machines but it wrecks havoc on solar production. Here's my thoughts after a few days.
Since likely similar 100ah 48vDC batteries will be marketed in the States things a person should look out for. Battery size and weight. Most 100ah LiFePO4 cells seem to be at least +2kg (4.4lbs) in weight. 16 of them for 48vDC will mean any 100ah rated battery that comes in under 34kg or 75lbs should be suspect of not having 100ah cells in it. Based on weight and size I figure these batteries I have are in the 75 to 80ah level. This also seems borne out by the charge/discharge amperage results I am observing.
The batteries have held full charge for 2 days now and I am seeing almost no resting self discharge. (54.6v down to 54.2vDC). That is good.
I expect going forward I will consider these having 70ah of capacity and the battery charger is a 4A unit. If someone buys these you can reasonably expect it will take a full day of charging with the supplied charger if you have no other charging means.
Since likely similar 100ah 48vDC batteries will be marketed in the States things a person should look out for. Battery size and weight. Most 100ah LiFePO4 cells seem to be at least +2kg (4.4lbs) in weight. 16 of them for 48vDC will mean any 100ah rated battery that comes in under 34kg or 75lbs should be suspect of not having 100ah cells in it. Based on weight and size I figure these batteries I have are in the 75 to 80ah level. This also seems borne out by the charge/discharge amperage results I am observing.
The batteries have held full charge for 2 days now and I am seeing almost no resting self discharge. (54.6v down to 54.2vDC). That is good.
I expect going forward I will consider these having 70ah of capacity and the battery charger is a 4A unit. If someone buys these you can reasonably expect it will take a full day of charging with the supplied charger if you have no other charging means.
yabert
Solar Addict
Matt, thanks, I like all this, but... where are the pictures of the inside 
Awaiting a trip to town to stop by the Fotomat.Matt, thanks, I like all this, but... where are the pictures of the inside
Ask them if they considering to add Express-service. Some thing like "For +30% fee, we will process within 1 hour".
Happened to spot a LiTime 60ah Golf cart 48vDC battery on Ebay and the look plus specs for case size and weight (aprox 26kg) is identical to my 100ah (claimed). There is an image of the prismatic cells inside and I would bet that is how mine is made only perhaps a different rated BMS. Mine does have the inset LCD voltage and capacity display which was not shown/mentioned that mine would come with. LiTime has a 5 year Warranty mine none.
I would not be at all surprised that the ones I bought are really 60ah. Still not a bad price I paid compared to buying in the USA, LiTime wants $630 for theirs.
I would not be at all surprised that the ones I bought are really 60ah. Still not a bad price I paid compared to buying in the USA, LiTime wants $630 for theirs.
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wpns
Solar Joules are catch and release
Looks like cylindrical cells, not prismatic...
yabert
Solar Addict
Prismatic? Those look like cylindrical.
yabert
Solar Addict
Yeah! I bet the 3D designer who work for the sale don't speak often with the battery designer team
If really you have 60Ah cells, that start to be relatively high price at 140$/kWh.
Price equivalent for a 100 amp-hr battery is $630*100/60=$1050
In December, I ordered one of the expert-power 48V 100 amp-hr batteries. It was $899 shipped (no tax and arrived in 3-4 days from US warehouse)
They are $999 now but still cheaper cheaper than the 60 amp-hr battey. Not sure if the free shipping and no tax still apply. You can get something cheaper from Aliexpress but I don't know what the import tariffs will affect the cost due to delays of container ship shipment. I have 3x16 EVE 310 Amp-hr cells in transit. They are currently 1/2 price. so an added 10% tariff is still acceptable.
48V 100Ah LiFePO4 - EP48100Default Title
Nominal Voltage: 51.2v Charging Voltage: 57±0.2v Rated Capacity : 100Ah (0.2C, 25°C) Dimensions (L x W x H): 19 x 18.9 x 7 Inch Weight: 104lbs
www.expertpower.us
The ones I got off Aliexpress were $430ea. with tax shipped. That is partly why I called them a gamble since $430 for a 100ah 48vDC battery is quite a bit less than any offered shipped from the US. So using your math $430*100/60=$716
As an update. So far these 2 batteries seem to be doing the job. They continue to charge and discharge equally and in the proportion compared to the 105ah battery. Bit of a shame that the seller felt the need to falsify actual capacity but that is the Chinese for you.