Bench power supply suitable for balancing LFP cells?

[TheHubbardBus]

Want to pick up a benchtop power supply for the purposes of top balancing our soon-to-be-built LFP bank (using CALB CA100 cells). I know you can go big on amps here but due to cost constraints we're probably looking at 10A continuous.


From my understanding of the process (setting a target voltage & allowing current to decrease as you approach it), the type of power supply required would have CC & CV modes.


My question is: If any given power supply advertises it supports both CC & CV modes, does this mean it will function as I require it to? Are there other things I need to be looking for? I need to be able to both set a target voltage, as well as current limit, at the same time.


Also, if anyone knows of any proven deals on something like this, love to hear about them.

[dzl_]

You should read this article from marinehowto.com if you haven't already. Its long, but well worth the time if you are building and balancing your own LFP bank. In it, he recommends a power supply (mastech I believe)

[TheHubbardBus]

Dzl, I already have. About 10 times lol. I've learned a lot from that for sure!

Thing is, I can buy a 10A no name for less than half the price, and since I've got more time than money, I'm ok with the process going slow.

Just trying to make sure that when one psu says it has cc & cv modes, it means the same in terms of functionality as what that mastech or similar can do.

[dzl_]

Originally Posted by TheHubbardBus

Dzl, I already have. About 10 times lol. I've learned a lot from that for sure!

Haha, yeah, its definitely the type of article that you need to read a few times over, very info dense.

Thing is, I can buy a 10A no name for less than half the price, and since I've got more time than money, I'm ok with the process going slow.

I searched on ebay a while ago, as I recall some of the lower amperage mastech supplies were somewhat affordable (ballpark of $100-125 iirc). They go all the way down to 3A. Looks like you can get a 30V | 6A CC/CV power supply for $120 what is your budget or target price?

Just trying to make sure that when one psu says it has cc & cv modes, it means the same in terms of functionality as what that mastech or similar can do.

This I don't know, I'll be following this thread though, as its something I want to understand better. I'm pretty ignorant in this area so I'm pretty much dependent on the advice and recommendations of others (hence my interest in the mastech).

I believe your understanding of CC/CV is correct, what I don't know is what other factors, features, etc are important.

One thing that I think is important to consider is the precision/granularity. I'm guessing you're are buying this for top or bottom balancing your battery bank or for capacity testing or both. I would guess that you want precision of ideally two decimal places (.01V)--but it seems not even many of the high quality power supplies give that precision.

My concerns with unknown cheaper brands would be (1) are they precise enough for our needs (2) can they handle continuous operation for the period of time required to balance a large battery bank.


Sorry, I've got a lot of questions and half-baked thoughts, but not a lot of useful answers..

[dzl_]

Couple more thoughts:


This is the cheap no-name power supply Will Prowse links to from his website, with the glowing endorsement:

I don't like this one actually. But it's the first one that I have not broken. All the other ones burn out after a few weeks. If you want to spend more, expect to spend $400+. This one works great for manually charging individual lithium cells, and higher voltage batteries.

Looks to be the same cheap psu sold under a bunch of different brand names.

https://www.youtube.com/watch?v=0ZKXYNFwlx0

If you are adventurous you could build your own, it sounds a bit intimidating to me, but it actually looks pretty doable.

https://www.youtube.com/watch?v=wI-KYRdmx-E

[dzl_]

Came across this post, thought you might be interest.

[TheHubbardBus]

Great info, @dzl_! Thank you so much for all of that!


Here's one more source relevant to the topic at hand I found very helpful. I'm guessing you're probably already aware of it, but it's worth adding in to this thread regardless. This is just one page of an ongoing series, and the entire series is gold:


Assembling a Lithium Iron Phosphate Marine House Bank | | Nordkyn Design


Good points on resolution. I had considered building one as well, but with so much to do... if we didn't have a bus to build, it might be a fun project

[john61ct]

The CC/CV thing is really the default for all normal PSUs.

The transition is not controlled by the source regulation but by the battery resistance, SoC, current rate etc.

If you are going to use such a low current source for precise balancing

then so it doesn't take forever

charge to 90-95% SoC in pack mode using your usual charger (0.4C or so?) but watching no cells go too high,

and then put them all in parallel to balance charge

After charging, leave them hooked up that way for a few days to slowly self-balance further.

Then you atomize let them sit another 24 hrs at least

and check each cell.

Any that self-discharged lower than the others may be weak links.

[john61ct]

Super deal here, offer them $140 bet you get it

https://www.ebay.com/itm/264727819688

[TheHubbardBus]

Thanks, John61ct. I was hoping you'd chime in!

[dzl_]

Originally Posted by TheHubbardBus

Here's one more source relevant to the topic at hand I found very helpful. I'm guessing you're probably already aware of it, but it's worth adding in to this thread regardless. This is just one page of an ongoing series, and the entire series is gold:

Assembling a Lithium Iron Phosphate Marine House Bank | | Nordkyn Design

Yes!! Definitely a great resource! And another resource that requires reading at least 3 times before it starts sinking in, and even then.. I still probably retained only like 10% of the information.

1. Solacity: How to Find Happiness with LiFePO4 (lithium-ion) Batteries
2. Marinehowto.com: LiFePO4 Batteries on Boats
3. Nordkyn Design: Introduction to Lithium Battery Systems

I found all three of these articles very very helpful. I consider them required reading if you are going the DIY lithium route, and recommended even if you are just buying drop-in lithium batteries. The Solacity article isn't as in depth as the other two, but its a good technical introduction for the uninitiated, that is less overwhelming for newbies or those with drop-in batteries that just want to learn the basics.

[Doktari]

Good thread. I found a huge power supply on Craigslist. It has “coarse” and “fine” voltage adjustment so hopefully it will get all the cells very close. Dang thing is too heavy though. Must have transformers inside.