Sizing LFP Batteries

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bulraydin asked Jun 1, '19

Sizing LFP Batteries

Hello, we have an application where the system will be used as backup for only 10 minutes.

According to request, 100kW should be supplied directly from the batteries during 10 minutes.

How can I best choose the optimal battery size for this ?

When I look at the spec of LFP batteries of Victron Energy, I see that for example for LFPSmart 12,8/200, a max continuous discharge current of 400A is allowed.

So in order to provide 100kW, I need 2000A from the batteries, does that mean for such a system I need at least 5 x 4 x LFP 12,8/300 ?

Lithium Battery

2 |3000

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Answer 1 · 2019-06-01T09:56:07Z

kai answered · Jun 01, 2019 at 09:56 AM

You might benefit from contacting a Victron system designer direct.

Theoretically, you're right. a 5P4S pack would allow for 2kA to be drawn at 48v nominal without going over the continuous discharge limit. But its an expensive pack for the requirement of 10 minutes. The pack at say 30% DOD would give 1000AH * 0.7 = 700AH which is double your 333AH requirement.

A system designer would be able to look at the rest of your application and possibly propose more suitable solutions.

edit: I just noticed you changed from the 200AH unit to the 300AH unit at end of your post. My post above references the 200AH unit.

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bulraydin commented · Jun 01, 2019 at 01:12 PM

Thanks alot for your comment, indeed it was a typo, I meant 200Ah.

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Answer 2 · 2019-06-01T10:06:25Z

Paul B answered · Jun 01, 2019 at 10:06 AM

Also keep in mind when you ask the system designer

that some batteries can supply over there limits but this reduces there cycle life, now depending on how often this may happen a reduced life span maybe acceptable.

I mention its as its worth the discussion as a point at that time

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