DIY 48V Battery - Form Factor Pros and Cons - Building Two 24V Battery Boxes or One Single 48V Battery Box

[再生可能 エネルギー]

Hi, just doing some brainstorming... I am in the design to build a 16 Cells 48V battery
and I am evaluating various layouts for putting together all the cells.

My first idea was to make a box with two rows of eight cells. So the box will be about 30" x 18" x 12".
But my concern is about the total weight, which will be about (16 x 12 lbs) = 192 lbs or 87 kg.

A second design would build two 24V batteries boxes, so the weight would be only 96 lbs or 44 kg each.
So each battery would be easy to carry and the 9" width would make it easy to put against a wall.

I am considering to install the batteries outside, so having two batteries would looks more like a powerwall,
and it would be easy to add a second 48V battery set in contiguity along the outside wall.

Questions:
In the case of making two boxes, would it be better to have two separate 24V BMS,
or to use one single 48V BMS in one box and having eight of the wires connected to the second box?
Also I am considering adding a second 48V battery in parallel, would it be better to have two 48V BMS or four 24V BMS?

Note: I would prefer having one single 48V BMS, but I wonder if at some point, when transporting the batteries,
would having eight of the cells of one box connected to the BMS and the other eight wires not connected could damage the BMS?

 

[gotbeans]

I wouldn't do the 24v just because of dealing with the 2 BMS
also in series 1 of the 24v batteries could be a weak link so make sure that the cells in each are pretty equal to each other.
When charging you'd maybe have to do them separate or else 1 of the batteries would forever be lower / higher than the other

 

[Brucey]

If you are going external power wall design, have you considered heating requirements if needed?

 

[再生可能 エネルギー]

I wouldn't do the 24v just because of dealing with the 2 BMS
also in series 1 of the 24v batteries could be a weak link so make sure that the cells in each are pretty equal to each other.
When charging you'd maybe have to do them separate or else 1 of the batteries would forever be lower / higher than the other

Thank you for the reply. I would certainly prefer a 48V BMS approach, but I was just watching this vise from DavidPoz,
where he stacked several batteries in series and parallel, so having separate 24V batteries seems cleaner.

About charging separately the batteries, it seems difficult to have two 24V Solar Charger Controller (SCC) in series.

 

[再生可能 エネルギー]

If you are going external power wall design, have you considered heating requirements if needed?

In my area, winter temperature is between 40F and 50F.
I haven't been using a heater for many years, however I replaced the windows with double-pane windows.
Looking at the weather history the record was 26F about 50 years ago.

 

[Brucey]

Thank you for the reply. I would certainly prefer a 48V BMS approach, but I was just watching this vise from DavidPoz,
where he stacked several batteries in series and parallel, so having separate 24V batteries seems cleaner.

About charging separately the batteries, it seems difficult to have two 24V Solar Charger Controller (SCC) in series.

Looks like has a centralized BMS system so just disconnects the BMS leads via plug on the front of each module. With a traditional BMS (seplos/jk/jbd) I think you'll need a BMS for each 24V module and so potentially double your BMS costs versus a 48V design.

 

[Brucey]

In my area, winter temperature is between 40F and 50F.
I haven't been using a heater for many years, however I replaced the windows with double-pane windows.
Looking at the weather history the record was 26F about 50 years ago.

So you'll need protection against charging at freezing, if you aren't going to heat. Here is a chart seagal posted the other day. Be aware of your charge rate (C rate) when temps are cooler (but still above freezing)

 

[再生可能 エネルギー]

So you'll need protection against charging at freezing, if you aren't going to heat.
Here is a chart seagal posted the other day. Be aware of your charge rate (C rate) when temps are cooler (but still above freezing)

Would the C rate be controlled by the BMS, like 0.2 for 5 degree C or 41 F?
I was thinking that the BMS was only able to shutdown the charging or discharging
when the temperature was below the value set.

 

[Brucey]

Would the C rate be controlled by the BMS, like 0.2 for 5 degree C or 41 F?
I was thinking that the BMS was only able to shutdown the charging or discharging
when the temperature was below the value set.

@SeaGal

 

[SeaGal]

I was called

In a closed-loop system where the BMS feeds back data to the inverter, it is the BMS that tells the inverter what rate to charge at.

If there is no comms between battery and BMS, the BMS is just there to protect the batteries from under / over current and voltages.

Personally, if the design is up to you, I'd go for 16 cells in one battery pack - there will be no issues with putting system in series and or having extra bus-bar / wiring complications.

You don't mention what capacity, but with the figure of 87kg you quote, I am guessing around 300Ah cells.

Is moving / transporting the system going to happen often? If 87kg is too heavy for whatever reason, you could consider having more parallel packs of smaller capacity - e.g. use 100Ah or 130Ah cells to build smaller 48V, self contained units.

 

[Brucey]

I was called

In a closed-loop system where the BMS feeds back data to the inverter, it is the BMS that tells the inverter what rate to charge at.

If there is no comms between battery and BMS, the BMS is just there to protect the batteries from under / over current and voltages.

Personally, if the design is up to you, I'd go for 16 cells in one battery pack - there will be no issues with putting system in series and or having extra bus-bar / wiring complications.

You don't mention what capacity, but with the figure of 87kg you quote, I am guessing around 300Ah cells.

Is moving / transporting the system going to happen often? If 87kg is too heavy for whatever reason, you could consider having more parallel packs of smaller capacity - e.g. use 100Ah or 130Ah cells to build smaller 48V, self contained units.

So do all BMS have charge rate slope based on temp sensors assuming there is comms enabled? Or is that something you came up with yourself?

 

[SeaGal]

So do all BMS have charge rate slope based on temp sensors assuming there is comms enabled? Or is that something you came up with yourself?

I'm sure none are as sophisticated as mine

Seriously though... IMHO they should do! Obviously they're all proprietary, so we don't know for sure, but I've read somewhere on here that PylonTech reduce charge rate below +5degrees C.

Fox ESS also do something similar - different rates vs. temp as detailed in this posting and commented on in my reply..

Solis RAI not charging Fox-ESS LV5200 correctly

Hi all, hoping someone can shed some light on this. My Solis RAI charger is programmed to charge the battery from the grid for 4 hours every night on cheap-rate electricity, but it is not getting much of a charge. Software I have on the computer shows 640W going out to the workshop, where the...

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Also see this posting and thread if you suffer from insomnia!

Solis RHI 6K 48ES 5G Inverter Fox ESS LV5200 Battery - Charging limit ? and export to grid ...

I'm thinking - based on the seeming randomness - that it is temperature related and the FOX ESS has got a faulty temp measurement. - i.e. it thinks it's colder than it is. Is it warmer and sunnier where you are today? Call FOX again if they haven't got back yet.

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