180 kWh gel batteries

[Kwatt]

Hi this is my first post here

We got our hands on 72 cells Sonnenschein a602/1250 gel batteries with a total capacity of 180 kWh. The cells are 2v each and the plan is to make 3 separate 48v 24s packs that are then connected to the same inverter (haven’t found one yet). My biggest concern having only worked with LFP and li-ion batteries before is what, if any bms is required. Our goal is to be able to pull 100kW of continuous power from the pack. Anyone done a project like this before? The plan is to start by parallel connect them all to make sure the soc is well balanced before we do any series connection. Any ideas on what equipment we should use to test the capacity of the cells?

 

[SamDeleted]

That is one big project!


3 packs connected to the same inverter (parallel) is essentially one pack .... Unless you're going to fit transfer switch and use one pack at a time ?

What inverter(s) are you planning on to be able to pull 100kw ?

You're going to need some crazy thick cables , for 100kw from a 48v system. (42v minimum)

100,000w ÷ 42v = 2,400amps

Over 3 packs that would be 800amps draw per pack , 340mm² cable per pack!! Or lots of smaller cables in parallel eg. 10x 35mm² cables in parallel



This kind of system is well above my pay grade lol so don't take my napkin maths as gospel

 

[SamDeleted]

Very ambitious for a DIY system , really it's a job for an electrical engineer

 

[Kwatt]

That is one big project!


3 packs connected to the same inverter (parallel) is essentially one pack .... Unless you're going to fit transfer switch and use one pack at a time ?

What inverter(s) are you planning on to be able to pull 100kw ?

You're going to need some crazy thick cables , for 100kw from a 48v system. (42v minimum)

100,000w ÷ 42v = 2,400amps

Over 3 packs that would be 800amps draw per pack , 340mm² cable per pack!! Or lots of smaller cables in parallel eg. 10x 35mm² cables in parallel



This kind of system is well above my pay grade lol so don't take my napkin maths as gospel

Yeah we’ll see how things go, a more realistic goal would be to go with “only” 50kW so we can drop the cable sizes, put less stress on the system and get costs down. Plan is to use it as a pilot project to sell reserve energy to the grid for frequency containment needs. We’ve installed almost a dozen 180kW superchargers for EVs so we got a little meat on our legs. but I’ve done nothing with gel batteries before but the cost for these were $2k so I couldn’t really turn it down since that makes it $11 per kWh?

 

[Vigo]

Damn, for 2k i would have bought that too.. and then built a small building to house it in.

My first concern would be to systematically charge and test capacity because a system that size is going to require a bunch of $$$ hardware which would turn out to be a silly mistake if the pack turns out not to even be capable of 50-100kw for any meaningful length of time. I would establish that first before deciding what hardware these will hook to.

 

[Kwatt]

Damn, for 2k i would have bought that too.. and then built a small building to house it in.

My first concern would be to systematically charge and test capacity because a system that size is going to require a bunch of $$$ hardware which would turn out to be a silly mistake if the pack turns out not to even be capable of 50-100kw for any meaningful length of time. I would establish that first before deciding what hardware these will hook to.couldn’t turn it down

Damn, for 2k i would have bought that too.. and then built a small building to house it in.

My first concern would be to systematically charge and test capacity because a system that size is going to require a bunch of $$$ hardware which would turn out to be a silly mistake if the pack turns out not to even be capable of 50-100kw for any meaningful length of time. I would establish that first before deciding what hardware these will hook to.

I couldn’t turn it down lol, either it’s the best deal in history or we have to sell them for the same $$ for recycling so the upside is huge. Yep definitely gonna need a lot of capacity testing under load, the batteries are 8 years old but according to the manufacturer they have a 20 year lifespan and haven’t been cycled that much. We’ve got a couple 10kW inverters to parallel connect and try and pull 20-30kW just to see if they still have some juice left. Probably best to start doing capacity test on individual cells to see how many have gone bad