Single solar panel to two MPPT solar chargers

geem

geem

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I am told this wont work but thought I would share the idea and see what the forum think.

I have a 40w panel dedicated to my engine battery. The panel is actually two framed 20w panels made into a folding 40w panel, wired in series to give 40v open circuit. I use it to charge my engine batteries that are a pair of 12v batteries wired in series to start my 24v engine. The solar panel charges through a Victron smart solar 75/15.

My generator battery has a 12v AGM battery. My thought was to wire my generator battery via a spare Victron smart solar 75/10 that I have so it also takes a parallel feed from the same 40w panel.

The panel doesnt have much to do as the engine batteries spends most of their time fully charged. There will be ample juice from the 40w panel to keep both the engine batteries and generator battery charged. I cant see any reason why this wont work. Any thought?
 
I’d be more inclined to add a vsr to the system. Or to split the panels and have 20w going to each battery through its own controller.
 
I really don't think it will work. An MPPT tracker constantly tweaks the current it draws from the panel to maximise the power, and it can't do that if another one is sucking power out at the same time.

Why not buy a dual-output controller? Readily available from (eg) Photonic Universe in PWM (£33.99) and MPPT (£119.99) versions.
 
B
JumbleDuck said:
I really don't think it will work. An MPPT tracker constantly tweaks the current it draws from the panel to maximise the power, and it can't do that if another one is sucking power out at the same time.

Why not buy a dual-output controller? Readily available from (eg) Photonic Universe in PWM (£33.99) and MPPT (£119.99) versions.
Click to expand...
one battery is at 24v the other is at 12v. I already have the Victron MPPT in stock.
I understand about the power point tracking but does it matter if the batteries get charged? I dont need perfect efficiency. The 40w panel will simply be trickle charging two batteries
 
interesting! Give it a go! Hard to know but guessing they'll both try to not let the panel voltage go too low so might work. Victrons will turn on when the panel gets 5v above battery voltage which takes next to no light so they might play nice together both sipping power to keep the panel voltage up, then if 1 set of batts gets full the other regulator should be able to pull so more power while keeping the panel voltage high.
Worth a try and see how they behave, hard to imagine how they could do any damage.
 
geem said:
I understand about the power point tracking but does it matter if the batteries get charged? I dont need perfect efficiency. The 40w panel will simply be trickle charging two batteries
Click to expand...
I doubt it will charge either. You'll just have two hopelessly confused controllers. 24v to 12v battery charger?
 
JumbleDuck said:
I really don't think it will work. An MPPT tracker constantly tweaks the current it draws from the panel to maximise the power, and it can't do that if another one is sucking power out at the same time.

Why not buy a dual-output controller? Readily available from (eg) Photonic Universe in PWM (£33.99) and MPPT (£119.99) versions.
Click to expand...

It's worth noting, the dual MPPT controller isn't exactly what it says on the tin. It is a MPPT controller for one bank and a trickle charger for the other bank (max 1A).
 
geem said:
Batteries are at two different voltages. 24v and 12v
Click to expand...

Sorry, missed that in your OP.

As you already have the controller, i'd connect it and see what happens. Both controllers are "Smart", so you can easily monitor what's going on. I certainly cannot see anything that'll cause a problem, other than if they won't play together they won't charge the batteries. I'd be interested to hear your results.
 
geem said:
I am told this wont work but thought I would share the idea and see what the forum think.

I have a 40w panel dedicated to my engine battery. The panel is actually two framed 20w panels made into a folding 40w panel, wired in series to give 40v open circuit. I use it to charge my engine batteries that are a pair of 12v batteries wired in series to start my 24v engine. The solar panel charges through a Victron smart solar 75/15.

My generator battery has a 12v AGM battery. My thought was to wire my generator battery via a spare Victron smart solar 75/10 that I have so it also takes a parallel feed from the same 40w panel.

The panel doesnt have much to do as the engine batteries spends most of their time fully charged. There will be ample juice from the 40w panel to keep both the engine batteries and generator battery charged. I cant see any reason why this wont work. Any thought?
Click to expand...
Worth giving it a try if you have the controllers otherwise a better system might be to charge the 24 volt battery via an mppt controller and the 12 volt battery via a 24 volt dc to 12 volt dc battery to battery charger
 
How are you going to wire the two panels in both series and parallel at the same time?
You could tap 12v from one panel but you can't wire the panels in series if they are paralleled. You would just be shorting them out.
 
Buck Turgidson said:
How are you going to wire the two panels in both series and parallel at the same time?
You could tap 12v from one panel but you can't wire the panels in series if they are paralleled. You would just be shorting them out.
Click to expand...
The suggestion is to use the two panels in series to feed two controllers in parallel. I don't suppose it will actually blow anything up, so there is that.
 
Buck Turgidson said:
How are you going to wire the two panels in both series and parallel at the same time?
You could tap 12v from one panel but you can't wire the panels in series if they are paralleled. You would just be shorting them out.
Click to expand...

You obviously can't, nor do you need to. The two panels in series will produce circa 40V, a single controller will "convert" this to whatever the battery/bank will need, whether that be for 12V or 24V batteries/bank. So one controller will convert for the 24 bank whilst the other controller will convert for the 12V battery.
 
IO think OP will find it works fine as envisaged. If one controller is sucking too much current from panels the other will especially if not much charge current is needed back off drain from panels. No problem just limited charge current due to limited panel size. More panels might be a better solution if you need more charge. ol'will
 
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