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simon22 avatar image
simon22 asked

Multiplus-II 48V - reusing AGM batteries

Hi!

I have a 7.5kWp PV setup and want to install an ESS (not for profit, just for technical interest and fun). My end goal is to have a Multiplus and some pylontec batteries to supply my house over the night.

I have four deep cycle 12V 40Ah AGM batteries that are more or less new from an unrelated project. They are rated at 4-500 cycles at 75% discharge.
I was thinking to buy the Multiplus and use my spare batteries until they die (and switch to pylontec then).

Is it possible to use four of those batteries in series as an 48V pack with that low 40 Ah rating?


Multiplus-IIESSAGM Battery
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4 Answers
nickdb avatar image
nickdb answered ·

What multi do you want to use? With that small rating, you're not going to get much use out of them.

They are unlikely to take kindly to any form of significant load, though you can limit the inverter.

Just toss/sell them and get yourself the pylons, you are likely just to be irritated by them when you try use the system and the inevitable battery warnings start to appear.

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Rob Duthie avatar image
Rob Duthie answered ·

Hi

Yes they will be Ok to use.

Regards

Rob D

NZ

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marekp avatar image
marekp answered ·

@Simon22

Yes they can be connected in series to get 48V.

They will last longer if you install 3 balancers.

https://www.victronenergy.com/batteries/battery-balancer

If you want to just play and learn the Victron system, those AGM batteries are up to that task.

They will provide up to 1kW of power when grid fails for around 1 hour.

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simon22 avatar image
simon22 answered ·

I was planning on getting the Multiplus-II 48/3000/35-32.

Limiting would be no problem, I want to use the system basically to get rid of the over night stand-by consumption (~80-150W). So if i could limit the system (for now) to 200W or something similar it would be fine for me.

It's more of a fun project to start and get some experience :)

My PV setup started the same way, I had 2.5kWp on a small roof and got 7.5kWp now (mostly DIY at a bargain price).

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nickdb avatar image nickdb ♦♦ commented ·
With the ESS assistant loaded you can set the inverter limit (also limits AC loads from pv) and set scheduled charging, where you can control the times when the battery can discharge.

It’s quite flexible.

At 0.2kWph your batteries are still a bit small.

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marekp avatar image marekp commented ·
@Simon22

I had the similar idea when started with Victron. But also wanted to eliminate a frequent short blackouts from my crappy grid system.

I needed 3 phase system so my first setup consisted of 3 MP-II/48/3000/35-32.

I did not have AGM batteries lying around so I decided to buy 10kWh Winston LFP battery with DIY BMS.

I am still learning but now I have 6 MP-II/48/3000 units and 20kWh battery.

If your night load stays at 200W this AGM battery should last for 5 hours since you cannot discharge them lower than 50% SOC.

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simon22 avatar image simon22 marekp commented ·

The datasheet says my AGMs are deep discharge optimized and last 4-500 cycles at 75% discharge. So I might get 7.5 hours.

If I remember correctly the standy-by consumption drops to around 80W when the heating system is off.
So my cheap setup could survive the night :)

I think I will give it a go, All I have to spend is some money for some decent cabling and a fuse. I will skip the balancer for now and monitor the cells every now and then.


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