Single solar panel to two MPPT solar chargers

[Jamie Dundee]

I cant charge a 24v battery bank with a 20w panel that is 20v open circuit

Missed the 24v bit…..?

 

[JumbleDuck]

So then, how do you know? describe just what happens between the 2.

I suggest that you investigate how MPPT controllers work, or at least find out what they do.

 

[GHA]

I suggest that you investigate how MPPT controllers work, or at least find out what they do.

I do know how they work. And logged the panel voltage as they wander around looking for max power. Can you answer the question - or a least provide a little hint of the mechanism you are so sure of?

 

[andsarkit]

Nobody here knows what will happen so just try it and let us know how it goes. It can't damage anything and it will either work fine or depending on the time constants of the controllers it might oscillate between them. Monitor the voltages or better still the current to each battery with a meter that updates fairly fast.

 

[Graham376]

Before I paralleled two banks and used 100/30, I had two MPPTs one feeding each bank off the same panels, they were of course both 12v but no problems except had to use diodes to stop reverse flow at night between the unequal voltage banks - cheap Chinese controllers. Can't think why OP shouldn't try it.

EDIT - I used to use the two banks alternatively so charge to each bank was different when panels working, each controller/bank drawing what was needed so guess one charging at 12v and the other 24v will be much the same.

 

[Zing]

It will work. Panel voltage will always be above the minimum at both controllers, so both will have a supply within spec and that’s all that is required.

I‘d be more interested to top up my house batteries though.

 

[geem]

It will work. Panel voltage will always be above the minimum at both controllers, so both will have a supply within spec and that’s all that is required.

I‘d be more interested to top up my house batteries though.

House batteries have their own mppt and 720w of solar. They are doing fine?

 

[Zing]

House batteries have their own mppt and 720w of solar. They are doing fine?

You could feed the engine panels into them and charge the engine/genset with dc-dc supplies or parallel your solar chargers from them or some of the panels, depending on voltages and specs. That way you would not lose their unexploited capacity.

 

[TernVI]

If both chargers are actively trying to track maximum power point at the same time, all sorts of things could happen.
As each modulates the current drawn to seek maximum power, it will affect the other.

However, both are being used to charge batteries with low demands, basically a float charge to replenish from infrequent engine starting.
So, most of the time there will be ample solar input and no MPPT action will be taking place.
But it could be chaotic at sunrise for instance, as the two controller compete for the available power.
I doubt the controllers are designed with this in mind, so if it causes them to have some kind of firmware tantrum, you're on your own.
It's the kind of technically ugly thing that rarely goes wrong, but when it does catch someone out it keeps a troubleshooter busy for a week at a good hourly rate.

 

[geem]

You could feed the engine panels into them and charge the engine/genset with dc-dc supplies or parallel your solar chargers from them or some of the panels, depending on voltages and specs. That way you would not lose their unexploited capacity.

Engine and domestic batteries are 24v. Generator is 12v. Usage patterns and battery types for domestic and engine banks are vastly different so quite happy to have separate solar set up for each. We use spare solar power to heat domestic hot water when we want to