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Rasmus Mikkelsen avatar image
Rasmus Mikkelsen asked

Wire size when doubling battery capacity

Hi all


I have a question I'm thinking about.

Currently I have a 14s200p 18650 li-ion 20kwh of storage working really good. With multiplus 2 48/5000, 6.2kwp solar panels with 250/100mppt.

I'm in the process of doubling my battery capacity so I will have 2 banks of 14s200p.

I'm currently using 70mm2 cable from battery to main breaker to victron distributor, and from there to MP2 aswell.

Please see the drawing I made.

I know the manual states 70mm2, but wondering since the current draw from each bank will be half, if I can double down on wire size to 35mm2?

#1 On the picture is current setup

#2 Is what I'm thinking about doing.

I have never experienced dc ripples, but I'd like to avoid that, thats why im asking :-)

Thank you

Regards Rasmus

screenshot-20230928-091045-gallery.jpg


Multiplus-IIESSLithium Batterybattery connection
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4 Answers
jetlag avatar image
jetlag answered ·

A 35mm² cable is absolutly fine for ~42A per bank. In theory you could even go down to 10mm² for each bank.

The 70mm² between the distributor and breaker and Multiplus2 is also way oversized. It may depend on the cable length, but I quess it is not more then 2m.... So with that proposed sizes you are absolutly fine.

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Rasmus Mikkelsen avatar image Rasmus Mikkelsen commented ·
Thank you, yea I just worry about dc ripple I have heard so much about, that's why I used 70mm2. I think I have more than 2m, probably 3-4m iirc :-)
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kevgermany avatar image
kevgermany answered ·

Try to keep the cable lengths the same to each bank. Although your cables may be larger than needed, better to do this and avoid a rewire when you install a larger consumer.

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Michelle Konzack avatar image
Michelle Konzack answered ·

Because i am courious:

Is the 14s200p a DIY project?

If yes, how long did it take you to solder 2800 cells together?

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Rasmus Mikkelsen avatar image Rasmus Mikkelsen commented ·

Hi yes from dead e-bikes. Well it takes a bit of time, I'm not soldering I'm spot welding with fuse wire.

Generally a big project testing all those cells, and im only using cells that test within 15% degradation. Meaning I have to type in every cell in a spread sheet and compare capacity to when they were new.20230924-130728.jpg

Also when you have some sort of OCD it takes even longer :-)

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Michelle Konzack avatar image Michelle Konzack Rasmus Mikkelsen commented ·
Wow, you are realy crazzy, but not alone. On Youtube I found many others too...


Have fun and nice day


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giorgos avatar image
giorgos answered ·

it is important for the cables to the batteries to have the same resistance whatsapp-image-2023-09-28-at-223619.jpg


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Rasmus Mikkelsen avatar image Rasmus Mikkelsen commented ·
Thanks, yes from each battery pole to victron dist. I will make sure will be exactly equal lenghts.
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