Possible to use MPPT to charge a 12v house battery off a 48v battery in my RV?

[Dave_11]

In planning phase for a power system for my 5th wheel. Thinking I’d like to go 48v, but still have lots of 12v needs, including high draw leveling jacks. Rather than get some sort of high amp dc-dc converter, I’m thinking of just keeping the cheap 12v lithium battery in place and just running a charger to keep it topped off. Would it work to just use an MPPT scc for this? Input from the 48v, output to the 12v system.

 

[Rednecktek]

Yup, works fine.

 

[chrisski]

I don’t think a company would say “yes our solar charge controller works fine with batteries instead of solar panels” if that’s what you mean with the 48 volt battery as an input.

When I read the owners manuals, the SCCs I have looked at always stayed input is for solar panels only.

When I upgraded from 12 volts, had trouble finding a 48 volt to 12 volt converter from a reputable company capable of handling a 12 volt 15 amp leveling jack, and I could not find a reputable company with a 48 volt to 12 volt battery charger. I upgraded to 24 volts for this among other reasons.

 

[fratermus]

Would it work to just use an MPPT scc for this?

I think so. I've done it from 24v -> 12v for a DIY converter.

I don’t think a company would say “yes our solar charge controller works fine with batteries instead of solar panels” if that’s what you mean

Something like that happened here on the forum. The next few comments after that post provide context.

 

[Warpspeed]

It will possibly work, or it might also self destruct.

A Maximum Peak Power Tracker that works properly will try to pull the maximum peak power the power source can supply, unless the circuit has some kind of inbuilt over current limiting protection.

Over current protection is not needed for solar panels, because its not possible to draw more current than the rated short circuit current the panel can produce.

So a cheapy MPPT controller might not have a built in maximum current limit feature.
If you connect something like that to a big battery, its going to keep trying to draw more and more current to maximise the power transfer.
That is exactly what its designed to do !!

If it does have inbuilt protection it should work fine.

Many people just connect up their MPPT solar controller to a big battery and it works perfectly well.
But no guarantee.
If the user manual says definitely solar panels only, I wish you luck.

 

[HarryN]

Some motors have a locked rotor amps / start up amp pull that is pretty high.

I guess most 12 volt Li batteries can supply 100 amps now days without tripping the BMS ?

If in doubt - of course an AGM is not bothered by this problem.

If the inverter will be on anyway, then using a 120 vac charger can also work.

 

[DIYrich]

Victron Orion-TR 48/12

 

[Dave_11]

Victron Orion-TR 48/12

Will that safely charge a 12v LiFePO4 battery?

 

[Dave_11]

When I upgraded from 12 volts, had trouble finding a 48 volt to 12 volt converter from a reputable company capable of handling a 12 volt 15 amp leveling jack, and I could not find a reputable company with a 48 volt to 12 volt battery charger. I upgraded to 24 volts for this among other reasons.

Are you saying you upgraded your 12v devices to 24v?

Side note: looking at going with there victron 100/20 scc

 

[DIYrich]

Will that safely charge a 12v LiFePO4 battery?

Yes. That is what it is designed to do. The regular version is constant voltage, so set it to a float voltage. The "smart" is a charge controller and has more settings, but may not come in a 48/12 version.

 

[SamDeleted]

I've done it, it worked fine

 

[timselectric]

Yup

 

[chrisski]

Are you saying you upgraded your 12v devices to 24v?

Side note: looking at going with there victron 100/20 scc

I upgraded the battery to 24 volts and kept all the 12 volt items in place. For the 12 volt items including the 50 amp leveling jacks, I used a Victron Orion 35 amp 24 volt to 70 amp 12 volt converter.

 

[timselectric]

I've used a couple of the Orions, on Tow Boats.
They are very nice, and just do what they are supposed to. 24/7 , year after year.