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Hooking up a 24 volt battery to a mppt charge controller input and it works !! It’s charging a 12 volt battery. What’s the long term affect?

sirslayer

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I had an extra solar charge controller and a 12 volt battery and got curious if the mppt controller can charge the 12 volt battery by using 24 volt battery instead of using solar panels on the mppt input. It works!! Do anyone know what’s the long term affect by using this combination?? The 24 volt solar system is still charging the 24 volt battery and supplying the 12 volt mppt charger! Let’s here your opinions!!
 
This is generally not recommended as the battery can provide a massive amount of current, and it prevents the MPPT from functioning as an MPPT and forcing it to work at battery voltage. Of the two, the former is a much greater concern.

At a minimum, fuse the battery (+) to MPPT with a class T fuse rated for the lesser of 1.25X the wire rating or 1.25X the maximum draw from the battery.
 
Right on, it’s a 100a mppt and on the panel it stats the solar charging is at 70 amps plus.. the T fuse is a great ideal, thanks for the advice .. my setup have been on all day so I’ll have to see what happens at night !!
 
Right on, it’s a 100a mppt and on the panel it stats the solar charging is at 70 amps plus.. the T fuse is a great ideal, thanks for the advice .. my setup have been on all day so I’ll have to see what happens at night !!

How does night have anything to do with it? It will work until your 24V battery runs out of juice or it meets the charger termination specifications.
 
I was just thinking out loud!! I have searched the forum but no mention of using a battery to a mppt input
 
Thank you , so victron doesn’t recommend it but as long your within specs , why not?!! The only odd part on the 24 volt solar charger on the panel display , it shows 0 volts to battery.. but the battery charging icon show it’s charging
 
Thank you , so victron doesn’t recommend it but as long your within specs , why not?!!

Because it's not designed for that. There are other ways for DC-DC charging that don't require MPPT operation. Again, doing it unfused is asking for trouble.

The only odd part on the 24 volt solar charger on the panel display , it shows 0 volts to battery.. but the battery charging icon show it’s charging

Sounds like it's not working.
 
I just found a 100 amp breaker , quick disconnect would be nice but the 24 volt charger is showing 26 volts when I just disconnected. The 24 volt battery is almost fully charged.. wish me luck and I’ll do a observation every few hours
 
Have fun.
If I ever get my Ford lighting, I'll be trying out a couple of SCC's on the 300+ battery.
And yes, everything will have OCP.
 
Have fun.
If I ever get my Ford lighting, I'll be trying out a couple of SCC's on the 300+ battery.
And yes, everything will have OCP.
I've wanted to use a 250v MPPT on my Prius traction battery which runs around 200v, but everybody says using an MPPT on it is a bad idea. I would be more concerned about blowing out the Prius electrical system than the MPPT though.. cost and repair difficulty wise.
 
I've wanted to use a 250v MPPT on my Prius traction battery which runs around 200v, but everybody says using an MPPT on it is a bad idea. I would be more concerned about blowing out the Prius electrical system than the MPPT though.. cost and repair difficulty wise.

Use of a battery on the MPPT defeats the MPPT's primary function.

NiMH nominal is 202V and you'll almost never see it that low. Can be a touch over 280 under heavy braking. Worth noting that the usable capacity in the hybrid battery is less than the total capacity in the 12V, so unless you're using it as a generator with the engine idling (a 1.5L engine running to produce about 4500W - not particularly fuel efficient).

Numbers:
Traction: 6.5Ah * 1.2V * 168 * 40% = 524Wh
12V: 45Ah * 12V = 540Wh
 
Just curious, do you have the - of the 24V battery common with - of the 12V battery?
 
Use of a battery on the MPPT defeats the MPPT's primary function.

NiMH nominal is 202V and you'll almost never see it that low. Can be a touch over 280 under heavy braking. Worth noting that the usable capacity in the hybrid battery is less than the total capacity in the 12V, so unless you're using it as a generator with the engine idling (a 1.5L engine running to produce about 4500W - not particularly fuel efficient).

Using it as a stop / start generator is the plan. It's Atkinson engine coupled with a hybrid system makes it a pretty nice option for a gasoline inverter generator that is always ready to go, with a fairly large fuel tank and simple controls. I already have another propane generator I use for propane, but gasoline is never going to touch it. Supposedly the Prius is a far more efficient gasoline generator than any off the shelf commodity inverter generator available, and the gasoline kept in it is less likely to go bad than gasoline I store in canisters sitting off to the side somewhere.

I wouldn't suggest buying a brand new Prius for something like this, but if you already have one, and don't depend on it for anything else anyway..

Being as it's hard to find DC to DC converter chargers that support the Prius hybrid voltage range I was hoping an MPPT might work to drop it to a stable 48v range to use with existing batteries/inverters.

I just wanted to use something cheaper and less ugly than this pricey option.

Plug-out power
 
No the 24 volt system is separate system that’s is connected to the solar panels and the plus and minus of the 24 volt battery goes straight to the plus and minus of the mppt input of the 12 volt system . This type of arrangement does make since because it’s still powered from the solar panel from the 24 volt scc system to the 24v battery to the 12v scc to the 12 v system .. the only issue I had was I had 24 v 100 ah battery that was almost at 5 % of state of charge in the morning( AGM) batteries.. from being connected over night and the 24 volt system didn’t charge the battery at night or cut off the battery ( it can’t!! the connection to mppt is not seen by the 24 volt scc..) ( using utility mode will fix it) but I went ahead and installed a 24 volt 280ah battery and that helped for the over night usage. And the 12 volt 280ah battery is connected only to a 2000 wattt inverter and the 24 battery is to a 3000watt inverter ( all in one unit). Hey it’s not as efficient as a single 5000 watt inverter 24 volt system but for having extra parts laying around ., why not and it’s as good of a dc/dc converter
 
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As the MPPT draws more amps, the voltage is pulled down. The MPPT backs off, when the voltage gets too low to get the most wattage. Constantly increasing and decreasing the amps drawn, to keep the wattage at its highest. I believe that when connected to a battery, it will pull full amperage limit. Because the voltage won't drop from the load. Until the battery reaches the lower knee. I wouldn't let it get anywhere near 50%. It would just be used for emergency battery charging.
 
Most AIO's are adjustable. But, i want full power for the shortest time. I'll have two connected for 200a of charging.
 
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