From 12v to 24v

[Ronwattson]

Greetings all. I have a question in regards to changing from 12v to 24v. I have 10*12v100ah batteries and am looking at going to 24v so I can obviously add more solar per scc's I am currently running. I don't want to series them as they are. I'm thinking the better way is to remove the cells and BMS and build 24v packs out of the batteries.
My question is do I need to change out the BMS? Or will the 12v that's currently in the batteries operate on 24v? Also is this the better option than balancers and series as they are?
Many thanks in advance!

 

[wpns]

In general 12V BMS are for 4S and won't have enough leads to work with 8 cells in series, so you will need new BMS. Unless you built them yourself using one of the universal 3S-24S BMS, in which case you already have all the leads you need.

Only you can tell if this is a better solution than using the existing batteries with interbattery equalizer/balancers, as you'll need new boxes and wiring and such, but there are kits for that.

Open one of them first and make sure what kinds of cells they are and if you can work on the terminals, etc.

 

[Ronwattson]

In general 12V BMS are for 4S and won't have enough leads to work with 8 cells in series, so you will need new BMS. Unless you built them yourself using one of the universal 3S-24S BMS, in which case you already have all the leads you need.

Only you can tell if this is a better solution than using the existing batteries with interbattery equalizer/balancers, as you'll need new boxes and wiring and such, but there are kits for that.

Open one of them first and make sure what kinds of cells they are and if you can work on the terminals, etc.

Thanks! They are prismatic cell. I see people use them without boxes in stationary systems. Is box optional in that case?

 

[wpns]

Thanks! They are prismatic cell. I see people use them without boxes in stationary systems. Is box optional in that case?

Well, sorta. I mean you have to keep them from falling off the shelf or the shelf collapsing (see the 'burned my house down' thread) but people build boxes out of wood or repurposed containers of all kinds. I'd probably strap two batteries together and run wires between them, as you already have the batteries, and they already have cases...

Make sure you create a build thread!

 

[RV8R]

Hi @Ronwattson

I would have to know more about your system & application, but instead of altering the battery bank, why not just add a Solar Charger & panels ?

 

[wpns]

Hi @Ronwattson

I would have to know more about your system & application, but instead of altering the battery bank, why not just add a Solar Charger & panels ?

Because:

add more solar per scc's I am currently running

 

[Ronwattson]

Well, sorta. I mean you have to keep them from falling off the shelf or the shelf collapsing (see the 'burned my house down' thread) but people build boxes out of wood or repurposed containers of all kinds. I'd probably strap two batteries together and run wires between them, as you already have the batteries, and they already have cases...

Make sure you create a build thread!

Great idea! Thanks a million for your help and clarity. It will be my first diy so wish me luck

 

[wpns]

Great idea! Thanks a million for your help and clarity. It will be my first diy so wish me luck

Put a pointer to it here so we don’t miss it.

 

[Ronwattson]

Hi @Ronwattson

I would have to know more about your system & application, but instead of altering the battery bank, why not just add a Solar Charger & panels ?

I have two 100/50 and two 100/30 victrons already and 4000w of PV in 4 different sizes and quantities that would pair perfect at 24v with what I already have. More scc's, wire, cable, breakers etc don't seem very cost effective at this point vs going 24v.

 

[Ronwattson]

Put a pointer to it here so we don’t miss it.

Will do!

 

[RV8R]

I have two 100/50 and two 100/30 victrons already and 4000w of PV in 4 different sizes and quantities that would pair perfect at 24v with what I already have. More scc's, wire, cable, breakers etc don't seem very cost effective at this point vs going 24v.

Thanks for the clarification - that helps me understand what you are up against & why you are considering 24vdc ,,, IIRC those Victron solar chargers are 12vdc or 24vdc (so in the case of the 100|50 you go from 700W to 1400W in 24vdc)

Of course then there is the load side of the equation.

 

[Ronwattson]

Thanks for the clarification - that helps me understand what you are up against & why you are considering 24vdc ,,, IIRC those Victron solar chargers are 12vdc or 24vdc (so in the case of the 100|50 you go from 700W to 1400W in 24vdc)

Of course then there is the load side of the equation.

I would imagine my situation is why anyone would go 24v if they desire more power with existing equipment.

 

[740GLE]

I would imagine my situation is why anyone would go 24v if they desire more power with existing equipment.

And they have 4000w of PV, that’s ~140a of charging current.

 

[740GLE]

Greetings all. I have a question in regards to changing from 12v to 24v. I have 10*12v100ah batteries and am looking at going to 24v so I can obviously add more solar per scc's I am currently running. I don't want to series them as they are. I'm thinking the better way is to remove the cells and BMS and build 24v packs out of the batteries.
My question is do I need to change out the BMS? Or will the 12v that's currently in the batteries operate on 24v? Also is this the better option than balancers and series as they are?
Many thanks in advance!

What brand batteries? These are LiFePo right?

I would only break down the 12v batteries if they have bolted connections. Most OTS units have welded cell connections.

They have battery balancers to allow 2s 12v units to run in 24v. You could do 5p2s but it might be better to do to do 2s5p with 5 balancers.

 

[Vigo]

More scc's, wire, cable, breakers etc don't seem very cost effective at this point vs going 24v.

In my personal opinion you are likely to find welded cell interconnects making this project a huge time sink and introducing a lot of risk of mishap during the process. I think the time+frustration involved means the 'opportunity cost' of the project is more, if equated to dollars, than simply buying some new pieces of equipment to suit your goals.

I love me some 12v LFP because of the simplicity and relatively forgiving nature of the all-parallel connection, but i could see 'managing charge current' being a valid reason to abandon 12v with 4kw of solar. If you're just trying to run higher string voltages though, there are some 12v AIOs with 450-500v mppts available for ~$250 which could be used purely as an SCC and will take about 2kw of solar each.

 

[Ronwattson]

What brand batteries? These are LiFePo right?

I would only break down the 12v batteries if they have bolted connections. Most OTS units have welded cell connections.

They have battery balancers to allow 2s 12v units to run in 24v. You could do 5p2s but it might be better to do to do 2s5p with 5 balancers.

I plan to open one up this morning. They are supposed to be serviceable. Hysincere and Sjy are the brands. I see so many have balance issues over time even with balancers so I'm leary of doing that though it's the easiest way. If I did it would be 2s5p for sure. I don't know but I would think 2s2p in a string would likely increase the chances of balance problems. 2s5p would equate to 24v500ah correct?

 

[Ronwattson]

In my personal opinion you are likely to find welded cell interconnects making this project a huge time sink and introducing a lot of risk of mishap during the process. I think the time+frustration involved means the 'opportunity cost' of the project is more, if equated to dollars, than simply buying some new pieces of equipment to suit your goals.

I love me some 12v LFP because of the simplicity and relatively forgiving nature of the all-parallel connection, but i could see 'managing charge current' being a valid reason to abandon 12v with 4kw of solar. If you're just trying to run higher string voltages though, there are some 12v AIOs with 450-500v mppts available for ~$250 which could be used purely as an SCC and will take about 2kw of solar each.

I can feed it by my calculations 200a as it is with 1,000ah and still be at a 2c charge rate. Problem with all in one at 12v is I can't seem to find one with any decent amount of power output. I'm currently running a 5,000w that runs all my house 120v loads. A 3,500 that runs my freezers, washer and one 120v circuit in my shop. I haven't found anything AIO to get close to either of my current inverters. My batteries are rated at 50a max continuous CC so I might be better off just throwing another controller at it.

 

[Rednecktek]

You know you'll have to buy new 24v inverters if you change over, right?

A 5000w 12v inverter is some Honkin Huge cables!

 

[Ronwattson]

You know you'll have to buy new 24v inverters if you change over, right?

A 5000w 12v inverter is some Honkin Huge cables!

Yes I know a 24v inverter is needed in that case. And yep I got 20" long 4/0 cables going to the 5,000w currently but it's fused to 300a.

 

[740GLE]

I plan to open one up this morning. They are supposed to be serviceable. Hysincere and Sjy are the brands. I see so many have balance issues over time even with balancers so I'm leary of doing that though it's the easiest way. If I did it would be 2s5p for sure. I don't know but I would think 2s2p in a string would likely increase the chances of balance problems. 2s5p would equate to 24v500ah correct?

2s5p or 5p2s will still equal 500ah. It’s just which way it better to deal if a single 12v battery that goes peer shaped. 2s5p with OCP and balancer per string is the best.

IMO I don’t like Ah for units, KWhr takes away any sort of confusion be it 12 24 or 48.

It might be better to think of it as a 13kwhr battery configured for 24v.

Sounds like you are tapping out a 5kw +3.5kw inverter and looking for a single 8-10kw inverter? Do your peak loads really demand such high wattage?

If so don’t bother with 24v, if you’re buying a new inverter go straight to 10k 48v.

 

[wpns]

Yes I know a 24v inverter is needed in that case. And yep I got 20" long 4/0 cables going to the 5,000w currently but it's fused to 300a.

But 5KW at 12V is over 400A...

 

[HarryN]

There is "ideal" and there is "what can work".

There are many 24 volt systems that are built up from 12 volt batteries.

What you could do is just charge them all to be "full" and this makes them essentially all ~ identical.

Wire them up in 24 volt without taking them apart and use them as is.

Every 90 - 180 days, check the voltage of each one and see if action is actually needed.

Switching from 12 to 24 volt makes perfect sense, and is easy.

 

[Ronwattson]

2s5p or 5p2s will still equal 500ah. It’s just which way it better to deal if a single 12v battery that goes peer shaped. 2s5p with OCP and balancer per string is the best.

IMO I don’t like Ah for units, KWhr takes away any sort of confusion be it 12 24 or 48.

It might be better to think of it as a 13kwhr battery configured for 24v.

Sounds like you are tapping out a 5kw +3.5kw inverter and looking for a single 8-10kw inverter? Do your peak loads really demand such high wattage?

If so don’t bother with 24v, if you’re buying a new inverter go straight to 10k 48v.

I have no idea what OCP is. Mainly just trying to get more out of each SCC and not have to add more. The amount of usable power I have on the system is plenty coming out of the inverters to do what I need to do really. I guess it's buy balancers and series, buy new BMS and build my own 24v or buy more scc's and PV wire so I can run all that I have on hand as far as PV goes. Hard decision to say the least. I don't know what's my better option
Edit to say over the last year you have been a great help getting me this far as you always give input and I really appreciate it.

 

[Ronwattson]

There is "ideal" and there is "what can work".

There are many 24 volt systems that are built up from 12 volt batteries.

What you could do is just charge them all to be "full" and this makes them essentially all ~ identical.

Wire them up in 24 volt without taking them apart and use them as is.

Every 90 - 180 days, check the voltage of each one and see if action is actually needed.

Switching from 12 to 24 volt makes perfect sense, and is easy.

It's looking a lot like that's what I need to do. Thank you sir

 

[wpns]

I have no idea what OCP is.

Over Current Protection

Mainly just trying to get more out of each SCC and not have to add more. The amount of usable power I have on the system is plenty coming out of the inverters to do what I need to do really. I guess it's buy balancers and series, buy new BMS and build my own 24v or buy more scc's and PV wire so I can run all that I have on hand as far as PV goes. Hard decision to say the least. I don't know what's my better option
Edit to say over the last year you have been a great help getting me this far as you always give input and I really appreciate it.

There's no 'best' option other than than maybe buying new batteries at the intrinsic voltage you want with BMS with some kind of comms, plus new inverter and <throw everything away and start over>, so it looks like you've identified the three least-worst options:

1) Reconfigure your existing batteries as individual 24V strings of 12V batteries, each with a balancer. Expensive, but a known solution.

2) Tear apart your existing batteries and build new ones using an external BMS. Unknown complexity, cost, results.

3) Add more SCC, wiring, etc. Probably the most straightforward but feels wasteful/inefficient.

Honestly, 1) is my current favorite by a slight margin, at least until you cut one of them open and discover how much work it's really going to be to build 24V batteries.