Can I connect a second solar panel to the solar controller?

[41 plus]

Hello there,

My motorhome batteries are not maintaining their charge very well this winter. There seems to be a small, but constant, drain somewhere. Its probably been there all the time, but normally I would be away in the van for most of winter and hence not a problem - not this year.

I have a 100W panel on the roof, which feeds to "Technology International" Solar Charge Controller, and onto the Sargeant van electrical system.

Like most, the 100W panel is flush on the roof, so too low for the sun at this time of year. I am thinking of getting a small (25W?) panel, propping it in the windscreen, which would be ideal for the low sun, and just stringing wires across the cab and then connect them it to the input terminals of the Solar Controller - ie on top of the existing panel's wires.

The question is: would this work!

bob m

 

[flatpackchicken]

With such a small sp yes this would be ok as most controllers start with a 10a fuse and your no where near that even with a small extra panel

 

[Jake Royd]

As far as I know, yes it would, two panels in parallel.
But a 25w panel isn't going to add that much during winter.

 

[Phill D]

HI and welcome

the only watch out from me would be to suggest that you cover the 25w panel while you connect up. although the current is likely to be small and not be an issue, you would kick yourself if it did some damage to the controller because of poor connection or shaky hands!!!

 

[Lenny HB]

I think your controller is 10amp so it will be fine but 25 Watts will do naff all in the winter.

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[XxAnthxX]

Why not stick one of these in or on your windscreen and temporarily connect it to whichever battery needs help.

ECO-WORTHY 120W Foldable Solar Panel Charger for Portable Power Station and RV Battery, DC Output for Solar Generator, with 20A Controller for SLA/AGM/Lithium Deep Cycle Battery RV Camping Amazon product ASIN B07RVG179M

The folded size and weight also makes it easy to take on the road with you too, or use on anything else.

 

[autorouter]

Two panels in parallel wired to the same controller need to have the same 'Open Circuit Voltage', Voc. Two identical panels would be OK, but for two very different panels you need to check the Voc, it's unlikely they would be compatible.

One option for the second panel is to upgrade the STI solar controller (which is a PWM type) to an MPPT type, which would be a bit more efficient in low-light conditions. You could choose to use the new controller for the second panel, or swap the controllers and use the old one for the second panel.

Two controller connected to the same batteries would work together quite well. Alternatively the setup suggested by XxAnthxX is worth considering.

 

[Compactliner]

You've answered your own question....the Sargent ECxxx PSU takes an almighty load to run itself and in winter this will be more than the panel produces...see the Auto Sleepers owners forum, it's riddles with the same complaints even in new vans.
If you can run the (suitably fused) controller output cables directly to your batteries (bypassing the PSU) you'll be amps in!
In the interim you could power off the ECxxx but then the solar is only sent to one battery (which one it is depends on the particular PSU model).

 

[41 plus]

Thank you for the responses - it sounds as though the answer is "yes but" - maybe. I think I will carry on with what I'm doing at the moment: cycling over to the storage site and firing it up for a while. I know that takes a chunk out of the van battery, but it seems to be a working solution. If necessary I bring it back to the house and plug it into the mains for a few hours. That gives the tyres a turn too.

Just think, it was only this time last year I was most of the way down the foot of Italy....

 

[41 plus]

Having re-read the responses I think I will go for Compactliner's suggestion: switch off the ECxxx. I should be able to detect which battery is being charged, and perhaps it depends on which was selected before it is switched off.

It gives me an excuse to replace my 30 year old multimeter - that I lost the instructions for 29 years ago.

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[Lenny HB]

Thank you for the responses - it sounds as though the answer is "yes but" - maybe. I think I will carry on with what I'm doing at the moment: cycling over to the storage site and firing it up for a while. I know that takes a chunk out of the van battery, but it seems to be a working solution. If necessary I bring it back to the house and plug it into the mains for a few hours. That gives the tyres a turn too.

Just think, it was only this time last year I was most of the way down the foot of Italy....

Take it for a drive, with modern diesels you should always drive of immediately after starting, can cause a lot of damage running stationary from cold.

 

[Compactliner]

Having re-read the responses I think I will go for Compactliner's suggestion: switch off the ECxxx. I should be able to detect which battery is being charged, and perhaps it depends on which was selected before it is switched off.

It gives me an excuse to replace my 30 year old multimeter - that I lost the instructions for 29 years ago.

Where it sends the charge will be apparent with a multimeter, as you say, but it will be dependent on the model of PSU. The Sargent PDF for the EC500 says it charges the leisure battery only.
I can't find the detail the EC700 another. This can only be changed with the unit switched on, which defeats the object.

 

[Jimbohorlicks]

Some small solar panels are designed such that you can connect them directly to your battery or via a cigtype lighter connection provided it's a live connection when the ignition is off.

 

[Borsuk]

Can you disconnect and take home the leisure battery (ies) leaving the solar panel connected to the engine battery only. Then put leisure battery on charge at home.

 

[XxAnthxX]

Can you disconnect and take home the leisure battery (ies) leaving the solar panel connected to the engine battery only. Then put leisure battery on charge at home.

You’ll probably find it’s the leisure battery that is powering the controller.

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[Billy192]

I use a "Sunshine 15W Solar Car Battery Saver/Maintainer" keeps my starter batt ok.

 

[Borsuk]

If the van is laid up, do you really need the leisure batteries available. I'd run the solar direct to the engine battery, that's the one you are going to need to bring it back from storage.
The solar controller gets its power off the panel, at least my last 3 have. My current van might go through the solar connection on the control board for distribution but the only power in is from the panel itself. Take the leisures home and stick them on a maintenance charger. It's a faff but probably less of a faff than changing out a flat starter battery.