Really basic solar panel questions

[sgr143]

[I did search through the "back numbers" but couldn't find anything obvious about numpty questions like I'm going to ask.]

I'm thinking of putting a small top-up panel (20-30W) on the hatch garage - or "turtle" as I find it's referred to in foreign parts. The boat (Westerly Merlin) has very basic electrical demands: lighting, gps, radio, phone charging sockets (no pumps, fridge etc.) run from a single 110Ah battery. This domestic battery and the start battery are each independently isolated via 1/4 -turn keyswitches (with a cross-over keyswitch in case of emergency). On the charging side, the engine's alternator connects to the batteries via a voltage-controlled relay; if voltage is below 12.4V, it charges the start battery only; when voltage rises above 12.4V it charges both batteries. Oddly, this VCR lives behind the electrical panel by the chart table.

Questions:
1) The charge controllers I've looked at on amazon etc. have three sets of connections - panel, battery and load. Would it upset the controller not to use the "load" connection, and have the lighting etc. circuitry just left straight from the battery as it is now? Is that a sensible thing to do?
2) How best to wire the controller with the VCR?

Thanks -

Steve

 

[RichardS]

You can ignore the Load connection. I'm not sure that anyone uses it on boat applications .... I certainly don't.

The VCR experts will be better to advise you about the second part.

Richard

 

[sgr143]

You can ignore the Load connection. I'm not sure that anyone uses it on boat applications .... I certainly don't.

The VSR experts will be better to advise you about the second part.

Richard

Thanks Richard - that's good to know.
Steve

 

[PaulRainbow]

Ignore the load connection, as Richard said.

You don't wire the controller to the VSR, you wire it to one of the batteries, the VSR then works the same as it does with the alternator. If it's a single sensing VSR, you connect it to the same battery as the alternator, if it's dual sensing, connect to whichever you want, makes little difference, but i tend to connect to the domestic bank.

 

[sgr143]

Ignore the load connection, as Richard said.

You don't wire the controller to the VSR, you wire it to one of the batteries, the VSR then works the same as it does with the alternator. If it's a single sensing VSR, you connect it to the same battery as the alternator, if it's dual sensing, connect to whichever you want, makes little difference, but i tend to connect to the domestic bank.

Thank you Paul - helpful as always!

I think my VCR is dual sensing (since AFAIR if I connect a battery charger to either of the start or domestic batteries it trips at 12.4V), but I'll check again.

Steve

 

[PaulRainbow]

Thank you Paul - helpful as always!

I think my VCR is dual sensing (since AFAIR if I connect a battery charger to either of the start or domestic batteries it trips at 12.4V), but I'll check again.

Steve

You're welcome, do you recall the make/model of VSR ?

It might also be more convenient to connect the controller to a battery connection at the relevant isolator switch, which is perfectly acceptable. Don't forget to fit a fuse wherever you connect the controller to..

 

[William_H]

I would suggest you may find with a small panel and 110AH battery that the charge may never or not often reach the voltage that the VSR is set to operate at. ie 13.7v or so. Further a vSR will draw some current continuously and even more when operated. Not a lot of current but then (24/7) and you won't get a lot of current from small panel. I think you would be better off getting a charge controller that has output for 2 batteries. So all electrics isolated except the charger when you are away. Or not use a controller but feed each battery positive via a schotky diode from the panel pos.
This on the assumption that the panel will never overcharge the 2 batteries being not at an ideal angle and being in UK. The wisdom is max 10w or 10% of battery AH but I think this could be stretched a bit. ol'will

 

[alahol2]

I've got the same basic system you are proposing (30W). The controller is only wired to the house battery because the start battery is never run down. I use the 'load' terminals on the controller to run the 'burglar alarm' flashing LED in the cockpit.
Well worth the expense and time to fit, the battery is invariably fully charged when we get back to the boat each week. It also helps keep the battery up when we are on board for a week or more.

 

[sarabande]

I am with William H on this. Does the OP really need a controller ? Given that the panel will be almost horizontal, the input from the panel even at 1300 on Midsummer's Day will be limited by the altitude of the sun (about 62 ^o) to approx 2/3 of nominal max.

In supplication to the KISS and economic principles of boating, are there any compelling reasons against making a direct (fused ) connection to a battery bank ?

 

[ghostlymoron]

I had a similar setup on my Mirage 28 - 20w panel, on/off charger, two batteries, VSR. It worked well, the solar only charged the domestic battery, the start was prioritised by the VSR. Nowadays I'd fit a larger panel and a PWM controller as prices have fallen.
On my smaller boats with no inboard engine I had 20w panels with PWM controllers (seven quid off eBay).

 

[sgr143]

Thanks everyone.

Paul - the VCR/VSR is by KDD, as originally fitted to the boat.

Seems like the best way forward will be to use a basic PWM controller (point taken, Sarabande and William H, but given the controllers aren't a whole heap of money, I may as well play it safe) and to wire it to the domestic battery, on the battery side of the isolation switch, with a suitable fuse. If I'm off the boat (all isolators off and keys removed), it will charge the domestic battery. If I'm on the boat with the isolators on, should the volts rise high enough (seems to be about 12.4V) it will charge the start battery as well via the VCR. If I've got a well -topped up domestic battery but a flat start battery there's always the get-out-of-jail-free crossover switch (only needed it once so far, but, my word, the relief when it worked!).

Sounds like a project!

Steve