Solar panels to charge start and house batteries?

davethedog

davethedog

Well-Known Member
Joined
13 Feb 2016
Messages
847
Visit site
Hi all,

Current 12v battery charging set up is twin alternators going to the house and start battery banks.

I am adding solar panels and will be using an mppt controller and I like the victron range as used them before on a previous boat (to just charge the house batteries).

However what I want to do is to charge both the house and the starter battery from the new solar set up but the victron mppt controllers all seem to have just the single battery bank output. So what is the best way to achieve this and ensure the house and start batteries are still seperate?

Thanks
 
One solution is a volt sensing relay which would charge the start battery until full then continue to charge the house one. There's plenty of choice, cheap (relatively) and easy to fit. I've fitted two which worked well but I just had a single alternater.
 
Two solar controllers is a fairly simple solution. It leave you with some redundancy and can be used to ease shading problems.

Why bother with your start battery though?

Mike
 
Agree with ibbo on the 'why' question. it is only the domestic bank that needs charging via solar as the enging bank is only used to start the engine and is then recharged by the engine itself.

If the enging battery dies, a simple switch over to start from the domestic supply would be sufficient to get you home before getting a new battery.
 
davethedog said:
Hi all,

Current 12v battery charging set up is twin alternators going to the house and start battery banks.

I am adding solar panels and will be using an mppt controller and I like the victron range as used them before on a previous boat (to just charge the house batteries).

However what I want to do is to charge both the house and the starter battery from the new solar set up but the victron mppt controllers all seem to have just the single battery bank output. So what is the best way to achieve this and ensure the house and start batteries are still seperate?

Thanks
Click to expand...
We had the same dilemma. What I did was make a small folding solar panel from two rigid 20w panels. I think in hindsight, I could have used a pair of 10w panels. I simply plug in the panel via a dedicated solar reg to charge the engine battery once I arrive somewhere. It's super simple. The engine battery gets a nice gentle charge. The panel is stored down below when on passage. The long charging wire I fitted plugs in in one of the cubby hole lockers in the cockpit. The wire is long enough that I can park the panel in various locations on deck. The cable coils up and stores inside the folded panel. I made a simple catch to keep the panel closed in its stored position. The whole thing cost very little. A 10w panel on eBay is about £18.
I like the fact that the engine battery isn't being aggressively charged by a battery combiner.
 
ctva said:
Agree with ibbo on the 'why' question. it is only the domestic bank that needs charging via solar as the enging bank is only used to start the engine and is then recharged by the engine itself.

If the enging battery dies, a simple switch over to start from the domestic supply would be sufficient to get you home before getting a new battery.
Click to expand...
+1. If you have a dedicated engine start, preferably an AGM then it is always fully charged as soon as you run the engine and slow to self discharge. Can see geems point if you do leave the battery unused for long periods and don't have access to shorepower than a small dedicated solar may be useful. In the highly unlikely event of the start battery going flat if you can switch to using your house bank to start the engine then it will quickly charge the start battery. In the 25 years or so of having separate battery banks and a parallel switch I have never once had to use it. The AGM battery in my Morgan has a similar usage cycle to many boat engine batteries - long periods of idleness followed by a short burst of use. It is now 19 years old and all I do is plug in the trickle charger if I don't use the car for a couple of months or so.
 
small second panel and cheap basic controller for the engine start - it will only need to keep up with self discharge if the boat just sits unused for a while away from shore power / trickle charger. 5 W would do. Dual output MPPT controllers just add something else to go wrong.
 
jac said:
small second panel and cheap basic controller for the engine start - it will only need to keep up with self discharge if the boat just sits unused for a while away from shore power / trickle charger. 5 W would do. Dual output MPPT controllers just add something else to go wrong.
Click to expand...
We actually use a Victron MPPT as I had a spare. Batteries take about 50 to 60w per day keeping them topped up. They never need water as they only get a gentle charge with 40w of solar. We are a 24v boat so we have two 12v batteries in series. The batteries do go through a bulk, absorption and float phase each day
 
OP does not say what sized solar panels he will fit. This decision depends on location of panels. So if he can accommodate and wants large panels like 50w or more and if he wants to charge engine battery as well as domestic battery then yes a dual output controller might be best. Now if OP has small panels then VSR might well soak up more power than the panels provide. Check but I imagine a third of an amp or so for current wastage in the coil of the VSR. Significant if you are only generating half an amp from solar.
So for small panels (less than 10w) simplest is 2 separate panels one for each battery. With or without controller. Or as argued above don't worry about engine start battery. Or simplest is a small panel with 2 diodes one to each battery.
ol'will
 
Hola !
I have been successfuly using EPEVER solar MPPT controller for years and recently acquired their DUO model which has 2 batteries outlets ; 1 for your main house
battery and the second with a 1A trickle charge for your starter batterry .
 
I think you're possibly overthinking this. With a VSR connected to alternator and solar, the start battery is recharged within a few minutes of starting, then the house battery is topped up. When the boat is unoccupied, the solar panel trickle charges the house battery but if the starter battery voltage drops for any reason it will top that up as well. Mind you if the start battery drops with no use, you probably need a new one.
I installed a VSR and never had any problems on my drying mooring.
 
You must log in or register to reply here.

Other threads that may be of interest

W
Battery suicide
Replies
17
Views
537
Refueler
Refueler

Share this page

Top