DIY Lifepo4 dc2dc charger?

[crystalclear]

I had some extra lifepo4 batteries lying around so instead of buying a ecoflow/jackery/etc type unit, just used a battery box with some 12v/usb sockets installed into it. Charging from ac I have - but wanted to know if anyone has a diy parts list/schematic to make a simple lifepo4 compatible dc2dc charger

ive seen the cheap voltage converters as well as bare bones cheap controllers - but wanted to see what people have come up with instead of purchasing $100-200+ units

 

[john61ct]

Buck or boost?

From what voltage to what voltage?

At what max current rate?

 

[OllieChristopher]

How many total mV are the batteries and the mAh? What brand and specific heat range specs? Give us those numbers and I'm willing to bet some of the members here can help you safely configure your system. I will caution you that I doubt you will to do it cheaper than one of the already manufactured units and come in at the capacity with small size and light weight.

If you want a really accurate measurement that is much easier to understand then do your amperage calculations in coulombs. When building out your battery box you will find that by using coulomb as your base unit of measurement it will be much easier to calculate and size your other components accordingly.

For some reason a lot of people get confused when configuring a system and use amperage as a measurement when figuring out battery capacity. When building your own system it is very important to know the not only the speed of the current (amps) but amount of charge (coulomb) that can go through the battery pack so as not to overheat them.

Just knowing the math to convert a coulomb into amp hours (1C = 2.7778⋅10-4Ah) is not enough. The average DIY battery box has to be carefully configured when using Lifpo batteries so as to prevent overheating and a fire.

AGM batteries are a lot more forgiving in this regard. This is one of the reasons the already made Lifpo solar generators and power packs are so popular.

 

[crystalclear]

appreciate the input - realized i definitely should have been more specific

the extra lifepo4 batts i have are renogy 100ah units

 

[RDinNHand AZ]

I built a 50ah box and all the components came from Amazon as it was returnable as I figured it all out. So far I haven’t bought a B to B charger but I plan to. See: diy-power-pack-lifepo4-wattbox.221586
B to B charger I am thinking about because I could charge form my car lighter socket=15 amps: Amazon product ASIN B01LYZZRBQ

 

[jonyjoe101]

for dc to dc charging you need both a boost and buck converter. The boost is to take the input voltage up to 18 volts, and the buck to take it back down to 14.6 volts without losing any amps during the process.
You can find the boost/buck converters on ebay, they have different wattages for how many amps you want to charge at. I charge at 6 amps with my boost/buck charger, I'm never in no hurry. The converters you can find for around 10 dollars each for the low wattage ones. The converters that can handle more amps are in the 30/40 dollar range and are much larger. Since the output voltage amps are adjustable, you can use it to charge any battery li-ion,lead acid, anything that requires cc/cv charging. These chargers work great, I charge all my batteries with these, with the LED meter there is never any guess if your battery is almost charge, the amps drop to about 100ma when it reaches full charge.
Also get a volt/amp led meter (about 6 dollars) so you can see how the charge is progressing. Put a fan on the converters they get hot while running. If the boost converter doesnt have a fuse, add one at the input. I never had a buck converter fail but lost 2 boost converters if they get too hot, thats why I use large fans and keep charging at 6 amps.

6 amp boost buck converter (400 watt boost/ 280 watt buck)


This is the LED meter, note the large fan.

 

[OllieChristopher]

Another alternative to the "boost-buck converter" is to go with a flyback converter as a charging solution. It has the advantage of using either AC or DC input to regulate DC output. As far as cost I have no clue as I have not considered either as an application for step down charging.

jonyjoe101, That is a very clever use of components and the price is amazing. Outstanding and very functional fabrication for sure!! Thank you for sharing Sir!!

 

[Afford9217]

These chargers work great, I charge all my batteries with these

That's exactly what I was looking for - a power module with a constant current output. Thanks.
(I have various car chargers that can boost, but was looking for a thing to do the buck.)

Would you happen to have done any efficiency measurements? Assuming not, the simpler version: does it get very hot?