Lifepo4 battery

Hello everyone.

I have a question here.

I have 2 banks of lifepo4 batteries. They are 280ah. It's a 16 cell. I have a 48v system. I have JK BMS. I want to order 16 cell more. If I order 304ah this time. How would it work? Can it work? Since the controllers are set to stop charging at a certain voltage. So of the 2 banks that are 280 ah are at the top level it will indicate the controllers to stop the charge. So what happens to the 304 ah battery bank?

It will work but you're wasting money IMO. Depends on how you have them setup and resistance between each pack and inverter - wire gauge, connections, wire lengths, crimp resistance etc. I assume these are in parallel. If all other variables equal, inverter will draw from each pack equally. You basically will not see the extra theoretical 24 ah in the higher grade cells unless you're past the low voltage cut off on the other two packs - eg they stop discharging and only the 304ah pack is above the low voltage cutoff. Its not recommended to get to your last fail safe for a few ah. I think sometimes the 304ah actually have more capacity - check the test results on data sheet if you get them but I would stick to the same cell size at 280ah if it were me.

You could make the other two packs slightly higher resistance via longer wire, but your ohms change with DOD, voltage, cell aging etc. Small differences in ohms can lead to a big difference in amount discharged in each pack. You reallllly have to know what you're doing from what i understand

RogerW said:

Hello everyone.

I have a question here.

I have 2 banks of lifepo4 batteries. They are 280ah. It's a 16 cell. I have a 48v system. I have JK BMS. I want to order 16 cell more. If I order 304ah this time. How would it work? Can it work? Since the controllers are set to stop charging at a certain voltage. So of the 2 banks that are 280 ah are at the top level it will indicate the controllers to stop the charge. So what happens to the 304 ah battery bank?

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You can search andysgarage on youtube, he has done this

RogerW said:

Hello everyone.

I have a question here.

I have 2 banks of lifepo4 batteries. They are 280ah. It's a 16 cell. I have a 48v system. I have JK BMS. I want to order 16 cell more. If I order 304ah this time. How would it work?

Click to expand...

Yes

RogerW said:

Can it work?

Click to expand...

Yes

RogerW said:

Since the controllers are set to stop charging at a certain voltage.

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Then all batteries, if properly wired in parallel, will charge to this voltage and achieve a 100% or near 100% state of charge if charging to 55.2V and higher

Refer to the resource in line #6 of my signature for best practices on paralleling batteries.

RogerW said:

Hello everyone.

I have a question here.

I have 2 banks of lifepo4 batteries. They are 280ah. It's a 16 cell. I have a 48v system. I have JK BMS. I want to order 16 cell more. If I order 304ah this time. How would it work? Can it work? Since the controllers are set to stop charging at a certain voltage. So of the 2 banks that are 280 ah are at the top level it will indicate the controllers to stop the charge. So what happens to the 304 ah battery bank?

Click to expand...

The batteries will charge and discharge proportionally to their capacity. Ideally all battery cable lengths are the same.

utkvols said:

It will work but you're wasting money IMO. Depends on how you have them setup and resistance between each pack and inverter - wire gauge, connections, wire lengths, crimp resistance etc. I assume these are in parallel. If all other variables equal, inverter will draw from each pack equally. You basically will not see the extra theoretical 24 ah in the higher grade cells unless you're past the low voltage cut off on the other two packs - eg they stop discharging and only the 304ah pack is above the low voltage cutoff. Its not recommended to get to your last fail safe for a few ah. I think sometimes the 304ah actually have more capacity - check the test results on data sheet if you get them but I would stick to the same cell size at 280ah if it were me.

You could make the other two packs slightly higher resistance via longer wire, but your ohms change with DOD, voltage, cell aging etc. Small differences in ohms can lead to a big difference in amount discharged in each pack. You reallllly have to know what you're doing from what i understand

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That is not correct. I run a 280Ah and a 105Ah 24v batteries in parallel. They used their capacity proportionally. It works perfectly

TimE said:

That is not correct. I run a 280Ah and a 105Ah 24v batteries in parallel. They used their capacity proportionally. It works perfectly

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But does the charging work. If one is charged before. Doesn't it trigger the charge controllers to stop charging?

RogerW said:

But does the charging work. If one is charged before. Doesn't it trigger the charge controllers to stop charging?

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It's a two way street.

sunshine_eggo said:

Then all batteries, if properly wired in parallel, will charge to this voltage and achieve a 100% or near 100% state of charge if charging to 55.2V and higher

Refer to the resource in line #6 of my signature for best practices on paralleling batteries.

Click to expand...

RogerW said:

Hello everyone.

I have a question here.

I have 2 banks of lifepo4 batteries. They are 280ah. It's a 16 cell. I have a 48v system. I have JK BMS. I want to order 16 cell more. If I order 304ah this time. How would it work? Can it work? Since the controllers are set to stop charging at a certain voltage. So of the 2 banks that are 280 ah are at the top level it will indicate the controllers to stop the charge. So what happens to the 304 ah battery bank?

Click to expand...

Did you test any of your 280s? I have 64 of them and every single one tested above 300 so I have them all set at 300 in my BMS. I just got 32 more 304's that I need to do some testing with. I'm going to do the same thing you are, add those in with my existing JK BMS and hook them parallel and enable parallel com's between them.

No problem.

(Mike drop)

TechRider said:

and enable parallel com's between them.

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Could you please explain what that means?

Thanks!

I've got the inverter based JK BMS so it has the ability to parallel the communication between the BMS's then connect the primary to the Inverter. As a result, I've got closed loop communication between the BMS and inverter. It allows them to communicate to, hopefully, more efficiently charge the batteries. Plus I get something like the image below with one cable to solar assistant.



When I add the other 2 batteries, they'll have the same BMS so they'll show up as Pack #5 and Pack #6.

RogerW said:

But does the charging work. If one is charged before. Doesn't it trigger the charge controllers to stop charging?

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Because the batteries are in parallel, their voltages are the same. The smaller battery tends to lead when being charged but all that happens is the rate of charge acceptance on the smaller battery reduces until it takes no charge. This only happens for a short while as the larger battery catches up. I don't charge above 28.7v (3.475v/cell) as there is no need. We rarely charge to this 100% voltage anyway as we would just be wasting solar output. We use a JK bms with 2A active balancing so when we do get to absorbtion occationally, we can do balancing in a very short period of time. The OP is propsijg to use batteries with a similar capacity. He will have no issues at all. My batteries are hugely different in capacity and it works fine

Simply Put - a different way to look at it.
All LFP Battery Packs have the same Voltage Curves and the Working Range is 3.000-3.400 which is what actually delivers the actual amp hours.
My "BANK" of batteries was 2x175AH, 1x 105AH, 3x280AH and ran without issues or incidents and provided all the AH as expected.

All Battery Packs will Charge/Discharge PROPORTIONATELY relative to their size (AH Capacity).
EXAMPLE: a 100AH, 200AH & 300AH in Parallel. If pulling 60A off battery would look something like this: 10A, 20A, 30A when monitoring it and that will float around slightly while ongoing (normal).

The REALLY Critical thing for a Bank is to have EXACT the same Gauge & Length of Wire for ALL the Battery Packs. The lines must be close & tight together otherwise this will deviate and result in numerous quirks leading to a lot of tail chasing.
Every Battery Pack must be Fused or have a Breaker.
(+) & (-) Wires should be kept together to prevent EMI/RFI noise (DC is noisy with magnetic fields)

Terminology Correction.
A Battery = a Collection of Cells + BMS which make up a completely functional Battery Pack.
A Bank = a Collection of Completed Battery Packs placed in Parallel/Series to act as one common battery bank.

Below is an image with 3x AIO Systems in Parallel and Battery Packs within a Parallel Bank.

I’d love to see some tests of different battery connection lengths to see how much a difference it makes.

Like if one lead from the battery to bus bars is 2’ if the other is 4’ how much does that throw off? 4’ and 6’?

Is it like 5% imbalance between banks each 10 cycles or.

For DIY batteries there’s internal connections that have various lengths that gets overlooked.

For inverter connections of units in parallel I can see that plays a much bigger role, but I’m more curious of battery to bus bar.

740GLE said:

I’d love to see some tests of different battery connection lengths to see how much a difference it makes.

Like if one lead from the battery to bus bars is 2’ if the other is 4’ how much does that throw off? 4’ and 6’.

For DIY batteries there’s internal connections that have various lengths

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For my DIY batteries, I made sure all my internal connections were the same length. I cut all the connecting cables at the same time to make sure they were that way. I also oversized my cables to reduce loss from resistance.

There are several vids on YT showing issues, quirks & voltage differences, I believe even Will did a couple a while back. I think Ray builds cool stuff did a long bit on it 2 or so yrs ago.

My own Exp with Parallel, YEAH it makes a difference regardless of wire gauge.

It does make a difference. I've seen it in my temporary setup. I just hooked things up without regard to balancing.
Voltage drop is the issue. Different points in the system will always have different voltages. The goal is to try to keep similar parallel points at the same Voltage.
like batteries and inverters.
If you want two things to function the same, they need to be at the same Voltage, or as close as possible.

timselectric said:

It does make a difference. I've seen it in my temporary setup. I just hooked things up without regard to balancing.
Voltage drop is the issue. Different points in the system will always have different voltages. The goal is to try to keep similar parallel points at the same Voltage.
like batteries and inverters.
If you want two things to function the same, they need to be at the same Voltage, or as close as possible.

Click to expand...

I don't think it makes enough difference to be a concern. My 105Ah 24v battery and my 280Ah 24v play nicely together. They both have the same size cable but the 105Ah battery is pulling less load so its wire resistance is effectively lower, even though the cables are slightly longer between the battery and busbar. This 105Ah battery therefore leads when being charged as its path has the least resistance. Voltages in parallel connected batteries can only be very slight different since the positive wires are common and ditto the negative wires. At high loads the potential difference in battery voltage could create a slight difference in battery voltage but as the battery approaches full charge, the current drops in the lead battery and the resistance of the cables becomes negligible simple because so little current is flowing. At this point the battery voltage will be the same

TimE said:

I don't think it makes enough difference to be a concern. My 105Ah 24v battery and my 280Ah 24v play nicely together. They both have the same size cable but the 105Ah battery is pulling less load so its wire resistance is effectively lower, even though the cables are slightly longer between the battery and busbar. This 105Ah battery therefore leads when being charged as its path has the least resistance. Voltages in parallel connected batteries can only be very slight different since the positive wires are common and ditto the negative wires. At high loads the potential difference in battery voltage could create a slight difference in battery voltage but as the battery approaches full charge, the current drops in the lead battery and the resistance of the cables becomes negligible simple because so little current is flowing. At this point the battery voltage will be the same

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I have 5 diy 280ah batteries and 1 server rack 100ah battery.
All In parallel with no issues. Voltage is the great equalizer.
I have balanced my connections to keep Voltage drop at a minimum.
It's not super important for the batteries. But very important for stacked inverters.

timselectric said:

I have 5 diy 280ah batteries and 1 server rack 100ah battery.
All In parallel with no issues. Voltage is the great equalizer.
I have balanced my connections to keep Voltage drop at a minimum.
It's not super important for the batteries. But very important for stacked inverters.

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We have a relatively simple system installed on a yacht. A single 3kw 24v inverter deals with 220v AC loads. We have plenty of battery capacity. The second 105Ah battery was only installed to provide some resilience should the 280Ah battery fail in some way. We do carry a spare JK bms but the small battery will see us through until I can swap a bms. It's only a 10 minute job but down time on Autopilot, navigation lights, chart plotter, etc would not be good.