LFP Ext. Regulators: Why do Volts and Amps need to be sampled?

[Baronkrak]

Originally Posted by wholybee

...Show me the ABYC recommendation or any statement from the ABYC that batteries should not be paralleled.

According to Statistical.

Originally Posted by Statistical

... Yeah ABYC agrees with you on that....

[tanglewood]

Let's just state this clearly.


There is nothing wrong with paralleling batteries of the same chemistry. It is done everywhere, and has been done for 100+ years. Saying it's bad engineering or whatever is just ridiculous. Yes, there might be fusing requirements and good vs bad cabling practices, but that's true for most everything.



The ABYC "prohibition", and it's actually just a recommendation at this point, is to NOT parallel batteries of different chemistries. This is in E-13 which is the Lithium Battery standard, and is targeted at the practice of paralleling a lithium ion battery bank with a lead acid battery to address some of the side effects of a BMS disconnect. It has never occurred to me that someone would try to parallel different Lithium Ion chemistry cells into a bank. That seems obviously a bad idea.


So whatever confusion exists, it's either because different people are talking about different things, or because we have descended into Alice and Wonderland.

[s/v Jedi]

Completely agree with Tanglewood.

But about cells in parallel: for factory rejects or used cells connecting them in parallel does cause problems. If you, for example, don’t want to buy 4 quality 400Ah cells because they cost more than 8 used 205Ah cells then you can still get a decent system by building two 205Ah batteries each with 4 cells in series so that you do not have parallel cells.

Of course now you have to buy an additional BMS, fuse, switch, battery monitor etc. but that’s the consequence of the decision to buy small used cells.

[Baronkrak]

It remain that

Originally Posted by tanglewood

It only takes one shorted cell. Doesn't require all of them.

Originally Posted by tanglewood

there can suddenly be a whole lot of energy available to dump into that lead battery…

The above is incorrect and unnecessary scare mongering.

Originally Posted by tanglewood

Let's just state this clearly.

There is nothing wrong with paralleling batteries of the same chemistry. It is done everywhere, and has been done for 100+ years. Saying it's bad engineering or whatever is just ridiculous. Yes, there might be fusing requirements and good vs bad cabling practices, but that's true for most everything.

There is everything wrong with paralleling batteries of the same chemistry that are not protected by a Battery Management System. Paralleling batteries of the same chemistry is not done everywhere and has been recognised as bad engineering for at leats 70 years.

It would be good if the ABYC could keep up with progress.

[Baronkrak]

Originally Posted by s/v Jedi

Completely agree with Tanglewood.

Originally Posted by s/v Jedi

For AC, the arc has to be started 50 or 60 times a second as the voltage crosses through zero, while dc is continuous.

By the way there is two zero.

[tanglewood]

Originally Posted by Baronkrak

It remain that





The above is incorrect and unnecessary scare mongering.



There is everything wrong with paralleling batteries of the same chemistry that are not protected by a Battery Management System. Paralleling batteries of the same chemistry is not done everywhere and has been recognised as bad engineering for at leats 70 years.

It would be good if the ABYC could keep up with progress.

Well, I guess you have better engineering knowledge and skills than the rest of us. That said, one hallmark of an exceptional engineer is their ability to explain and convince others. On that, you get an "F".

[capn_billl]

Originally Posted by Statistical

No they don't. Do you seriously think massive 2000 MWh grid storage batteries are one giant battery. Parallel batteries are used all over the world all the time under all kinds of applications.

This "never put batteries in parallel" rule is something you made up in your head.

The sheer irony is that all batteries already have cells in parallel. There is no primary cell of any kind with a voltage above 4V. So if you have a battery with a voltage 4+ volts of any kind for any application using any chemistry it has multiple cells in parallel.

That is SERIES Captain.

You need to know the difference before designing any sort of battery system.

[s/v Jedi]

Originally Posted by capn_billl

That is SERIES Captain.

You need to know the difference before designing any sort of battery system.

Lol, this is like a psychological study

I don’t know of any LA battery with parallel cells. I do know of lithium based batteries with parallel cells. The question is why…

[rgleason]

Since we've been discussing off-topic... but very relevant issues?

What about this proposed BMS regimen? Is it legitimate?

https://www.bos-ag.com/products/le30...gement-system/

[hjohnson]

Originally Posted by rgleason

Since we've been discussing off-topic... but very relevant issues?

What about this proposed BMS regimen? Is it legitimate?

https://www.bos-ag.com/products/le30...gement-system/

I'm not sure what problem they're trying to solve. But also, their last point is pretty laughable:

For extended power usage, or on cloudy days when no solar energy is generated, the lead-acid battery with its cheap large storage capacity remains as a backup. This way, both batteries can do what they are designed for: A downsized lithium battery runs the daily cycles, and a lead acid remains as a backup, ready to jump in when larger amounts of energy are needed

Unless we're talking a left over site from a telecom installation or something, lead acids always have comparatively small storage, and in the modern era are more expensive on a $/Ah basis.

also, they seem to be assuming small drop-ins with dumb BMSs with low c-rates. Lithium systems that use a contactor based BMS wouldn't face the drop-out issues.

[tanglewood]

I agree with hJohnson. Not clear what problem they are trying to solve.

[rgleason]

Yes, they are small litium batteries. It looks like they are paralleling lfp and fla, so I thought it to be relevant to the discussion.