Recommend a physically small 12v lifepo4 charger for a tight space?

[SlimyLemur56]

I have built a battery into a portable pelican (clone) case for a certain application. In this application there are a great many random parts involved and I have made painstaking effort to combine objects where possible to make packing and traveling and setup as easy as possible. I have a Lifepo4 charger I bought a while back which works fine, but I would really like to embed a charger into the case so that if I take it with me somewhere, I don't have to deal with an extra object (the charger) to keep track of. The hard case the battery is in is a very close fit, which is exactly what I want since portability is key, but it only leaves 1.5 inches (max) over the cells for circuitry like the BMS or anything else. The BMS fits nicely in this small space as does everything else except my charger is way too big.

Can anyone recommend a safe (preferably smart) charger that could fit in this small amount of space? If I need to have something with lower amps that is better than nothing, since I can always use my other charger if I need speed. 4amps or more would be nice since I could charge at roughly the same rate I drain it, replacing during the night what I use during the day. But even if 4 amps is not possible, it would be nice to have something in there so I can do some basic charging if I am traveling.

 

[Mattb4]

You did not mention voltage. However there are several small style chargers designed for electric bikes over on Aliexpress for LiFePO4 batteries. you might have to request actual dimensions to see if they would fit your application.

 

[SlimyLemur56]

Whoops thanks for pointing that out. It's a simple 12v 4s battery, and I added that to the title. I'll hunt around on AliExpress. The problem was that things turned out to be bigger than they appeared as I was shopping for them. But I could try requesting dimensions, I think ali express ironically has a better seller-communication system than amazon.

Still if anyone has a specific item they think would fit and vouch for, and can point me at it, I'd be appreciative.

 

[JoeHam]

I use this one when I’m patient enough for 2 Amps to get the job done :

https://www.amazon.com/gp/product/B085RXS63Q/

You could take the guts out of the plastic, hardwire to AC, and it may fit.

Not too expensive to experiment with.

And it’s “intelligent” also.

 

[Luthj]

Since LFP doesn't need fancy charge profiles, you can build a basic and effective charger this way.

Dumb single voltage power supply (with integral current limit). Set it to whatever you want your final termination voltage to be.
Programmable voltage sensitive relay. Set the rely to open when the target voltage is met. You can wire the relay so that it powers itself, so the charger and relay won't reconnect or use power once the termination voltage is met.

There is a large range of DC power supplies available, many with adjustable outputs. See Digikey/mouser/ebay. Voltage sensitive relays with adjustable trigger are common in industrial applications, and there are dozens of DIN mount styles.

Alternatively, if you don't mind a bit of absorb time (not a big deal if you are using voltages at the lower end), then you can just use a simple timer relay. Push a button to latch the relay on, and when the relay timer ends, the charger disconnects. Just set the timer to allow for a full charge from your typical depth of discharge.

 

[SlimyLemur56]

Thank you for the comments.
What Luthj suggests is probably the really best solution, however although I've worked up a decent understanding of these batteries and the nature of charging, I don't have the experienced confidence in that understanding to feel safe using something I've built up from scratch.

I've currently got two in mind
https://www.amazon.com/gp/product/B08MPX414R/ which is 4A and it says 1.46" tall.
https://www.amazon.com/gp/product/B082LV7RKL/ which is 5A and it says 1.8" tall.

I'm going to keep those in my pocket and make a decision after I have finalized the foam padding in my case and then taken a proper measurement of the actual space available (since me saying 1.5" is a very loose estimate) for adding a charger the way I am thinking. The idea of taking guts out of the plastic shell might also come in handy.