Solar panel question with two batteries in boat

Submitted: Tuesday, Aug 06, 2013 at 17:18
ThreadID: 103644 Views:2522 Replies:2 FollowUps:6
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G'day all, have a question regarding my setup as follows.

I have a boat with two marine batteries , one is 18months old the other 10months old. They have only had use during the snapper season (VIC) sept to jan. I have a main switch on the boat which can select batt 1,batt2 or batt 1&2 . I also have a voltage sensing relay wired in. I bought a 50watt solar panel with a waterproof regulator. I charged both batteries to full before putting the boat away for the off season (charger is a 7stage projecta intellicharge). I connected up the solar panel to one battery with the hope when it gets to 13.2v the vsr will close the circuit and charge both and maintain. After a couple of months one of the batteries (which had panel directly connected) was down to 11.6v and the other was at 12.56v. I disconnected the panel and batteries (removed all connections) charged both with the projecta to full. I undertook a load test on both and they both came up fine. I then connected the panel back to one of the batteries. After 3 weeks that battery was down to 12.5v.

My questions are, shouldn't the panel disconnect via the regulator when the battery gets down to say 12.6v (give or take) and could the reason be that it is draining because of the lack of sunlight given its winter. So it's naturally discharging and the sunlight isn't enough to bring it back up? The Load testing proved the batteries are in good health, so I am out of ideas.

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Reply By: The Bantam - Tuesday, Aug 06, 2013 at 17:42

Tuesday, Aug 06, 2013 at 17:42
So firstly you have a pannel that would produce 50 watts a shade over 4 amps in Alice Springs in summer, in full sun when correctly oriented....and then for only about 8 hours.

SO you are in Victoria, in winter...does it get full sun all day and is it optimumly aligned...even with everything going for it it will probably produce 2 amp tops an hour each side of midday, an amp for 2 hours either side of that and bugger all in the remaining daylight.

SO you will be averaging less than than half an amp over the 24 hour period.......that would barely keep up with the charging losses on a single large battery.

Now this has to draw power from somewhere to function.....perhaps it is a poor design and draws its functional power from the battery.

Sounds to me like you are trying to push something brown and smelly up a hill with a pointy stick.

That said.
If this rig has any chance of will have to have everything going for you.....I mean every detail right.

First try charging a single battery out of the boat...
make sure you have it all connected with good heavy cables..and as short as possible.
Put the panel in a place where it gets direct sun every hour of the day.
Maximise the angle of the least at midday.

THEN connect a battery that has not been charged and do some voltage readings thru the day, both at the panel before the regulator and at the battery terminals

say here is another thaught.

this isolator...does it isolate both batteries from the rest of the boat electrics.

AnswerID: 516011

Follow Up By: Member - Frank P (NSW) - Tuesday, Aug 06, 2013 at 18:20

Tuesday, Aug 06, 2013 at 18:20
And some isolators draw half an amp to "hold on", so there is a quite significant parasitic load when they're working.

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FollowupID: 795299

Follow Up By: The Bantam - Tuesday, Aug 06, 2013 at 22:11

Tuesday, Aug 06, 2013 at 22:11
OH yess I forgot to mention the hold in current of the have a relay or a solenoid that is designed to switch around 100 amps.....that is going to neeed a good whack of current to hold in...even an efficient modern solenoid.
Step back to one of the types that uses one of the older and more crude starter solenoids and it might take 5 amps to hold in

then ya VSR has to draw some current just to think with

None of this is a problem when you have a 50 pluss amp alternator supplying the charge or even a 15 amp charger.

FollowupID: 795313

Follow Up By: Chris85 - Wednesday, Aug 07, 2013 at 18:21

Wednesday, Aug 07, 2013 at 18:21
Yes the isolator remove all boat electric loads from the batteries. This is the vsr, Bep vsr,
FollowupID: 795341

Reply By: V8 Troopie - Tuesday, Aug 06, 2013 at 23:10

Tuesday, Aug 06, 2013 at 23:10
I have a trailerable yacht that sits for long periods in my back yard. There are two 22W solar panels permanently on board and they have no trouble to keep two 100Ah deep cycle batteries fully charged despite getting full sun only for a few hours when it shines in winter.
The batteries are charged via one of these cheap e-bay MPPT chargers (its actually a fake MPPT but works as an ordinary 3 stage solar regulator very well).
What I do is connect both batteries in parallel and turn off everything else on board. So all that the regulator has to do is to maintain the battery charge. I can read the battery voltage on a digital display and by the end of a sunny day it reads 14V. In the morning it reads 12.6V.
No problems.
I suggest you turn off the voltage sensing stuff while the boat is in storage.
AnswerID: 516029

Follow Up By: V8 Troopie - Tuesday, Aug 06, 2013 at 23:17

Tuesday, Aug 06, 2013 at 23:17
I should also mention that I have a VSR in my 4WD to charge the second battery. Its different by employing a latching relay - a relay that only consumes power during the switching over time which is a tiny fraction of a second. The rest of the time the circuit consumes a milliamp or two, no problem for a car battery. The relay is sold as a kit by Oatley electronics.
FollowupID: 795317

Follow Up By: Chris85 - Wednesday, Aug 07, 2013 at 18:23

Wednesday, Aug 07, 2013 at 18:23
I will try removing all connections to the batteries and connecting them in parallel for the 'off season'. I doubt if the regulator is faulty as the panel used to maintain a 26ah deep cycle battery for me beforehand.
FollowupID: 795342

Follow Up By: The Bantam - Wednesday, Aug 07, 2013 at 22:26

Wednesday, Aug 07, 2013 at 22:26
serioulsy if the batteries are in good condition, charging them once a month should be more than enough.

There is no need to have them constantly on charge.

If they wont hold sufficient charge to start ya boat after 30 days..mate I would not be going far with them.

BTW there is a very big difference between a 26 AH battery and two 50 or 80 AH batteries.

FollowupID: 795359

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