Good LifePO4 these days?

[createthis]

Howdy,

What's a good LifePO4 battery + BMS solution these days? The GBS stuff seems the most visible. Is it any good? I'm looking for something in 100ah 12v range.

Thanks

 

[Occam's Laser]

You looking for individual cells that you plan to assemble yourself?

 

[999zip999]

What for ?

 

[createthis]

I don't really care how it comes. Assemble myself, already assembled, no big deal. I'm handy. I just want good quality, even if it costs more.

It's for a portable solar generator, but since it's designed to be lightweight, I figure it should probably be designed to EV LFP rules rather than usual renewable energy solar LFP rules. It's going in here: https://youtu.be/zIMFqdpq3Ew <--- youtube tag doesn't work?

 

[Hillhater]

Quality , proven LifePo4, cells can be purchased as 12 volt packs from A123 ...looks like a conventional car battery.
Several other vendors also claim to use the A123 cells , but the original manufacturer is best.
They won't be cheap, but they will be reliable.

 

[createthis]

So that's an internal bms right? Can you top balance something like that? How does that work?

 

[Occam's Laser]

I second A123, you can get them here: http://www.a123batteries.com

As to whether they can be balanced, yes of course they can; but you're either going to have to pay for a module with built in BMS, add the BMS yourself, or do manual balancing.

 

[Hillhater]

So that's an internal bms right? Can you top balance something like that? How does that work?

Check the A123 site for details.
..but it is a complete 12volt battery, BMS, etc included, designed to be a drop in replacement for a lead battery (and even looks like one !)..right down to the terminal posts.
Look for "12 volt starter battery" .

 

[createthis]

I second A123, you can get them here: http://www.a123batteries.com

As to whether they can be balanced, yes of course they can; but you're either going to have to pay for a module with built in BMS, add the BMS yourself, or do manual balancing.

I only see cylinder cells and pouch cells in their store. Are these special order things?

 

[createthis]

I called a123 batteries and they're working on a quote. These batteries are fancy, but they've only got them in 60ah. 80ah is coming q4 2016. They're really large, physically, too. Probably not going to work for my purposes. What's the next best?

 

[Occam's Laser]

There are a number of LFP automotive battery replacement packs that are essentially 12V LFP packs.

These guys have a solid BMS though the 100ah is $1300... I doubt you'll get cheaper: http://www.lithiumion-batteries.com

 

[createthis]

I could get a gbs system with a bms that has outputs for about the same price. Maybe a little less. Is there an advantage to using a round cell system vs prismatic?

 

[Occam's Laser]

Round cells handle internal pressures better which is fairly negligible as factor.

 

[createthis]

Round cells handle internal pressures better which is fairly negligible as factor.

Do people still use prismatic cells in projects? I guess that's what I'm asking. I'm not trying to make a super car. I just want something fairly reliable and light weight. I'd hate to spend 1.2k just for someone to tell me, "dude, no one uses those anymore because of X" and then feel like a dumbass.

 

[createthis]

My charge controller wants to know when to stop charging via a signal from the BMS. That's the only reason I'm not keen on internal BMS without any outputs.

 

[999zip999]

Link or pic of your charger hookups.

 

[createthis]

Link or pic of your charger hookups.

See the youtube link above.

 

[Occam's Laser]

Cylindrical and prismatic cells are both still used, you won't get laughed at for form factor choice (not for any good reason anyway.)

 

[999zip999]

What charge and discharge rate ?

 

[createthis]

What charge and discharge rate ?

For a 1200wh battery, I'd want 1.5C discharge and 1C charge. The 100ah GBS prismatic battery I keep coming back to meets those criteria.

 

[Occam's Laser]

What charge and discharge rate ?

For a 1200wh battery, I'd want 1.5C discharge and 1C charge. The 100ah GBS prismatic battery I keep coming back to meets those criteria.

That GBS system will work fine I think, but I'm not sufficiently familiar with the cycle life and safety specs on it to give a good comparison with the LFP options.

 

[createthis]

The problem I have is this charge controller. It doesn't really have a LifePO4 charging profile. It only allows you to adjust the Bulk MPPT, Absorb, and Float voltages. There's no way to turn off float at a certain voltage in software. So I have to use the AUX2 12V logic input to tell the charge controller "it's time to stop charging, dude."

That's problematic because it seems like most of the BMS systems made these days don't have an over voltage alarm output. This is the only one I've found so far that has the over voltage output: http://jumpycalm.com/file/User%20Manual%20for%20EMS%20System.pdf It doesn't look particularly high quality to me, which makes me nervous. It's fairly expensive, and it duplicates a lot of the functionality my Victron BMV-700 provides, so I don't think the value proposition is good.

I'm not an electrical engineer, so maybe I'm just avoiding the most straight forward solution because I lack experience. Would most people in this situation just wire up their own circuit that signals the logic input on AUX2 at a certain voltage? Alternatively, are there inexpensive over voltage alarm units I can purchase that will work well with LifePO4 batteries with an internal BMS? I just need to drive a 12V input to ground when the battery is fully charged.