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Buck converter with high amperage?

Lt.Dan

Lt.Dan

Solar Wizard
Joined
Dec 25, 2020
Messages
3,563
Location
Tulare, Ca
Hey guys, with the 48v battery going into my trailer, I obviously need a buck converter to power 12v appliances. Specifically the leveling system, which it alone will draw 70 amps (and it has an 80 amp circuit breaker in the generator compartment). But I haven't heard any talk about high amp converters on here?

I have found this Daygreen converter that seems interesting, but curious what other people think.

www.daygreen.com

36V 48V to 12V 13.8V 80A 1104W DC DC STEP DOWN CONVERTER VOLTAGE REGULATOR

Wide input voltage from 30 to 60V Work for appliances from 0AMP to 80AMP automatically 100% full rated power 100% full stable output current 100% burn-in test High-efficiency up to 95% Waterproof sealed Cooling by free air convection Surface mountable 3-year warranty Over-current, over-voltage...
www.daygreen.com www.daygreen.com
 
Yeah this is the one part of the build i don't look forward to. I step up to 48v for efficiency, but then have to waste efficiency to step back down to 12v. But 12v doesn't really work out for me because of the other equipment I'm purchasing to go with it.

Can I wire 2 or 3 regular buck converters in parallel? Something like these. 96% efficiency and it leaves some redundancy if one goes bad.

 
Yes, the converters can be wired in parallel. I can't speak to any of the converters since I don't use them. Hopefully someone that is using them will speak up. It's unfortunate that Victron doesn't have a 48v model.

An alternative is to implement a 12v battery that powers those high amp loads. Use a DC-DC charger to keep the 12v battery charged up. I still have a 12v lead acid battery in my system to start my generator. But I'm trying to get rid of it as soon as possible.
 
Hmmm. That just gave me an idea.

I already have 2x 100ah Battleborns in the trailer, and a progressive dynamics lithium converter charger. I wonder if I just leave all of that in place, the Battleborns will power the 12v appliances, and the new inverter will power the breaker panel which in turn, will power the converter to charge the Battleborns?

Am I on the right track here?

Edit: Thinking even further here, I don't even need the batteries, so long as i have the Lithium Converter correct? The converter puts out 13.8-14v constant, I can just wire its output to a bus bar, and hook up all my 12v appliances to it, correct?
 
Last edited:
You don't want the inverter on all the time. That's a draw you don't want. If you're in the trailer full time, that's a different story.

A DC-DC charger can be configured to come on only when the observed voltage (as seen on the common bus bars) exceeds X volts, which means the solar panels are providing power. That way the charger isn't pulling (much) power from the main battery bank.
 
I do live in the trailer full time. My entire reason for doing inverter/solar/48v battery is to unplug from the grid, or at the very least, use it when batteries are too dead or there's no sun.
 
I've decided with @snoobler s help, im going to leave my 2x Battleborns in place and just use This buck converter to keep them charged up. My only concern is its only 10a, im thinking I may need 20a.
 
I think something got lost in translation. I think I was talking about that in the context of AGM.

13.8V is too high of a float for LFP.

You also don't want to keep LFP fully charged for extended periods. If they're not going to be cycled, they should be stored at 40-50% SoC. Lastly, LFP don't need to be floated at all. They retain charge for an extremely long period of time.
 
Ohhh now after reading your post again, I understand.

So how should I maintain the 50% state of charge? The regular 48v to 12v converter would keep SOC way too low.

Do I need to get a variable voltage converter? Or an actual charger?
 
A programmable DC-DC charger should allow you to set the voltage thresholds for the target battery.

Problems like these are why I chose to keep my system 12v. I'll take some inefficiency as a trade off for a lot of simplicity.
 
Lt.Dan said:
Ohhh now after reading your post again, I understand.

So how should I maintain the 50% state of charge? The regular 48v to 12v converter would keep SOC way too low.

Do I need to get a variable voltage converter? Or an actual charger?
Click to expand...

Assuming you have a battery monitor that reports actual state of charge by counting current, you'd need to develop a charge/float scheme that would maintain the battery around 50%. I'm guessing 13.2V as a starting point.

Full charge to 100% SoC
Discharge to <40% SoC
Charge/float at 13.2V and see where you land.

Might take a full day of "charging" to fully land on the final SoC as the battery will continue to accept a very slow trickle.

You might find also that you can live with 13.2V, but the SoC creeps up, and every so often, you just run a discharge.
 
I'm trying to find a somewhat affordable 48v to 12v charger with an adjustable output voltage to maintain 13.2v! Its a little harder to find than i thought... lol.

Is keeping it at 50% State of charge that big of a deal? Especially with all the constant 12v draws there are? (Lights, phone chargers, the fridge when set to propane, the wifi system, roof fans etc?) I know I wont be "Cycling" It, but it wont be idle that for sure.

Maybe I'll just have to suck it up and deal with the efficiency losses of the 120v to 12v converter? Seems like a bummer, but it would definitely work.

I also realized I could never just power the 12v side with a buck converter and no battery, because starting the generator would take way more amps than a buck converter could produce!
 
Storage at 100% SoC for a year may cause more degradation than cycling it daily. That's heavily dependent on temperature. High-sh temperatures can be very hard on them.
 
HRTKD said:
If the LiFePO4 batteries are actively in use, why are you trying to keep them at 50% state of charge?
Click to expand...
Thats what I'm wondering. The battery is technically being used. Energy is going in and out of it, the energy is just being replaced, possibly just as fast as its being taken out.

I guess this also leads into the question "what counts as a cycle?"
 
Lt.Dan said:
Thats what I'm wondering. The battery is technically being used. Energy is going in and out of it, the energy is just being replaced, possibly just as fast as its being taken out.

I guess this also leads into the question "what counts as a cycle?"
Click to expand...

This is, in part, a common misconception. If my solar charge controller is dumping 500 watts into the system and there is a 400 watt load, then only 100 watts is going into the battery. Power doesn't go into the battery, just to come right back out to satisfy loads. Power is either going in or out of the battery, not both at the same time.
 
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