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Short circuit testing of batteries

alanapar

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Joined
Dec 1, 2021
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17
In the light of various recent posts regarding short circuit currents of batteries, and choosing protection devices, etc., and with a general lack of data from manufacturers on Lithium Ion (in particular, LFP) battery short circuit capability, and the wide spread in possible short circuit currents being mentioned, I'm thinking of doing some actual tests to satisfy my curiosity.

For simplicity and cost reasons, I would do these tests on single cells, rather than assembled batteries. The tests may well be damaging to the cells, especially if the current is not of very limited duration.

To achieve a true bolted fault with the low open circuit voltage of a single cell, and the potential very high currents involved, I don't think semiconductor switches will be practical for me. If the short circuit current is say 10kA for a typical cell of the sort this forum would be using, then to achieve a "shorted battery terminal voltage" of less than say 0.3V (ideally less than 0.1V) would require less than 30uOhm (ideally less than 10uOhm) resistance in the switch. That's a lot of FETS in parallel. The setup should also have minimal inductance.

Instead, I'm thinking of a mechanical switch of some sort. It's a bit hard to know how well this can be made to work until you try it, but the low standoff voltage required will no doubt help, and it should not be difficult to interrupt the current involved mechanically with the low recovery voltage required.

So here's my question - I'm thinking of buying a couple of cells to get started. I've done little work with individual cells before, preferring to buy assembled battery units from vendors. Can people suggest a type of cell to get, and a source for it? These cells should be typical of those used in larger packaged batteries, or employed by DIY'ers to build large systems.

In particular, I'm currently interested in the newer Victron LFP batteries which have much higher energy density than their previous offerings - for example, the Victron LFP-Smart 12.8/330 or LFP-Smart 25.6/200-a. Does anyone know what cell they employ? Just pop the top off your battery and have a look please ;-)

After throughly testing a given cell, I'm also thinking of cutting at least some open to look at internal construction, and obvious damage from testing etc. Also, to separate electrode and tab, etc. resistance from electrochemical effects, it might be interesting to somehow short the battery electrodes together within the cell body, and to measure the resistance at the terminals, since this resistance acts as a minimum for the overall effective impedance of the operating cell. Does anyone have experience with dismembering cells?

I don't expect to accomplish this work very quickly. Apart from other commitments, I am fairly recently retired and moved to a new state, and no longer have ready access to the vast amount of electrical test gear I used to have available. So this will finally prompt me to buy a decent oscilloscope, etc. But I do want to mull over the options before pulling the money trigger. I need to do this anyway in support of my large Li-Ion boat project for next year and beyond.

One other thought: once I get started, if anyone has a spare cell they could send me, I'd perhaps be able to do some tests. Such a cell could be say an outlier you didn't want to mix into your packs, but should not be damaged or faulty to the extent it would not yield representative results.

I'm putting this out in part to get me off my backside and into action. I've found that COVID has not helped my motivation level over the last year or two, and I need some interesting project (other than fixing my new house, which I'm tired of) to get me moving.
 
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If you do this stupid thing please do it outside on keep yourself clear by many yards.
 
Look guys, I'm a physicist with a great deal of power electrical engineering experience, having worked on high voltage AC and DC systems up to the 1000MVA level. I know how to do this and do it safely.

Instead of nonsense comments, how about some help with the questions I asked, in particular, suggestions for a representative type of cell or two to buy and test, and a good source for them.
 
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Look guys, I'm a physicist with a great deal of power electrical engineering experience, having worked on high voltage AC and DC systems up to the 1000MVA level. I know how to do this and do it safely.
It sounds like you've got it all under control then. I imagine as a physicist you probably have access to material that's behind a paywall, and you could probably get much more technical information from there, as opposed to a DIY forum on the internet.
 
If you read my post, you will see I'm retired. I no longer have ready access to the "behind paywall" research literature and the tools for making extensive searches of that literature. As working professionals, we depend on the paid access provided by our institutions. In any event, that literature may not directly answer my questions: In particular, what is the actual short circuit current (vs. time) of a specific brand/model LFP cell. That's more in the nature of what would be a manufacturer's specification or typical test result, if they were to provide it.

I've also moved far away from my old haunts, so popping in to the library, etc. is not practical, even if I could finagle access (secure facility). I can ask a friend for specific things, but extensive searches strain that friendship. It's a pain. Likewise, I no longer have ready access to test equipment, but I am acquiring some for myself.

In any event, the help I asked for is right up this DIY forum's alley: what batteries to get, to be representative of what you guys use (that way, anything I discover and post here will be useful to others), and a good source to purchase those cells from.
 
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I wish I could could help you! Please do record your tests and publish on YouTube for curious minds to see.
 
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