Foxglove
New member
Hi all - I’d like to get a solar trickle charger to keep my 12v battery topped up between trips.
Any advice on what wattage I should aim for? Is 20W overkill?
Any advice on what wattage I should aim for? Is 20W overkill?
Solar Trickle Charger - is 10W enough?
- Thread starter Foxglove
- Start date
mikegunn
Well-known member
It all depends on how discharged your batteries are when you start to use the solar charger. 20W is less than 2 Amps so will not harm the batteries but may not be enough to recharge batteries after a weekend of use. Can you please tell us a bit more about your installation and your pattern and rate of usage?
Mike
VicS
Well-known member
My 5 watt panel has kept my70Ah battery topped up between week end trips. Being only 5watts a controller has not been necessary.
If I wanted to provide enough power for longer trips a larger panel would be needed (I'd probably choose a folding type that could be deployed when necessary)
The rule of thumb about the need or otherwise for a controller is:-
If the panel power, in watts, exceeds 10% of the battery capacity, in Ah, a controller is needed,
but panels over 10 watts should have a controller regardless
If I wanted to provide enough power for longer trips a larger panel would be needed (I'd probably choose a folding type that could be deployed when necessary)
The rule of thumb about the need or otherwise for a controller is:-
If the panel power, in watts, exceeds 10% of the battery capacity, in Ah, a controller is needed,
but panels over 10 watts should have a controller regardless
sarabande
Well-known member
Don't forget to wire in a fuse on the positive as near to the battery as you can .
I use these with blade fuses.
5Pcs In Line Standard Blade Fuse Holder Waterproof Splash Proof Car Boat 16 AWG | eBay
I use these with blade fuses.
5Pcs In Line Standard Blade Fuse Holder Waterproof Splash Proof Car Boat 16 AWG | eBay
Refueler
Well-known member
I use a 10W on a 7A/hr SLA without regulator ... its fine on my speedboat.
My main boat has two ~90A/hr Lead Acids .... with each maintained by 1.5A mains powered trickle chargers. Given that my boat is a Motor Sailer ... so about 40% of time is with motor running ... it serves well.
If I was to change to solar .... then I would look to have about 5A steady to a solid state splitter I also have ... which divides without loss - charge to two batts ... once any batt is full - it then shuts off to that battery waiting for it to be drained and need topping up again.
5A at 12V nominal means 60W ..... but given the output will not reach full spec of a panel ... I would be looking for a 100W panel ....
That's my take anyway.
My main boat has two ~90A/hr Lead Acids .... with each maintained by 1.5A mains powered trickle chargers. Given that my boat is a Motor Sailer ... so about 40% of time is with motor running ... it serves well.
If I was to change to solar .... then I would look to have about 5A steady to a solid state splitter I also have ... which divides without loss - charge to two batts ... once any batt is full - it then shuts off to that battery waiting for it to be drained and need topping up again.
5A at 12V nominal means 60W ..... but given the output will not reach full spec of a panel ... I would be looking for a 100W panel ....
That's my take anyway.
Foxglove
New member
Hi Mike - I’ve got two Numax Leisure LV22MF batteries, both 75Ah. I think one is purely for backup (have only had the boat a few weeks so am getting to know her!). I tend to go for half-day/evening trips once or twice a week. Less frequently in winter, no doubt.
I can connect a trickle charger to shore power but worry slightly about leaving it connected for days/weeks on end…
VicS
Well-known member
Do you have any other charging ?
Engine driven alternator? Battery charging from outboard? Or are you relying on the solar panel with a bit of back up, if necessary, from the shore power charger.
What electrical equipment do you have? I suspect we are talking about a relatively small boat with only the basics ?
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Foxglove
New member
hi Vic - I believe the outboard (Evinrude e-tec 50HP) has an alternator, although when I plugged a battery monitor into the 12v cigar lighter it said that the alternator was ‘dead’. No idea if that’s true, or whether it’s just not able to get a health reading on the alternator from the cigar lighter socket.
The boat (a Hardy Pilot 20) came with a charger, but I think it’s pretty basic. Certainly not a smart charger with all the associated battery protections against over/under-charging.
I suppose an alternative to solar trickle charging would be to buy a decent plug-in smart trickle charger which I can confidently leave it hooked up to for weeks on end if need be.
if I went that route, what wattage should I aim for? 2W?
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Foxglove
New member
Thanks for this - v helpful and clear.
Slowboat35
Well-known member
10W panel should be more than enough to keep a bank of 150Ah alive. long term, as long as they are isolated.
Refueler
Well-known member
I have this ... one for each battery permanently connected .......
Smart Car Battery Chargers Maintainer Auto 12V Trickle For Truck Van Motorcycle | eBay
In fact I have 4 of them ...... as I also have one for each of my Lawn Tractors to make sure their batterys are always 100%.
Cheap - but they really do work.
jac
Well-known member
It would be worth understanding how this works.
Traditionally ( and now considered old hat) is to have two basically identical batteries ( or banks of batteries) with use determined by a switch that selects, battery 1, battery 2, Both or Off. If 1 or 2 are selected, convention set up ensures that everything going in or out of the battery goes top the selected battery. the basic principle of that is that if the engine is running for a while you switch to both to ensure both are fully charged before then switching to one of the batteries when the engine / charger is off to run whatever is left. That way if you run battery 1 down so low that you can't start the engine, you can switch to 2 and start.
More modern set ups will have one battery purely for engine start and a totally separate one ( Often much larger) for all the domestic stuff. These each have their own switch to isolate them, and then some arrangments to " jump start" if the engine battery is dead. this may be jump leads or a preinstalled link and suitable switch. In this second more modern set up you might already have a way to ensure that both batteries are kept charge d either by something simple like a VSR or something like one of the smart chargers.
If it's the first, you really need a panel big enough to cope with the two batteries together with a controller that can monitor both and switch charge as appropriate. ANy such controller also needs to make sure that the batteries stay isolated rather than always being "both."
If it is the second, the dedicated engine start battery probably only needs a very small panel indeed, just enough to deal with self discharge, Most boats don't even do that. Starting the engine every month or two should do it or you could always switch on the charger if the boat was ashore for a while over the winter when you were there. In contrast, the domestic may need a larger panel if your pattern of use means you come back with it discharged.
VicS
Well-known member
Your 50 hp e-tec does, in theory, have a fully regulated 25amp battery charging system. If you cannot detect any output it is likely to be because the rectifier/regulator has blown Possibly as a result of reversed battery polarity connection or opening the battery isolation switch(es) while the engine is running.
As far as I can see the rectifier and regulator is part of the engine management module (EMM) and not separately replaceable parts. . . . A new EMM is more than $1300 but check the wiring for bad connections. The battery charging output from the EMM will probably be a red wire connected to the main battery cable at the starter solenoid
You are probably right about the second battery being a reserve or back up battery but it could be to provide power for accessories The standard method of connecting a back up battery is with a 1,2,both selector switch
Unless you are prepared to fork out for a new EMM your solar panel will be your primary charging system To properly size the panel you will first need to estimate the power consumption of the starting, power T&T and other engine systems and other onboard electrical equipment.
A fuly automatic multistage battery charger which be left on when necessary would be a good investment especially for winter use when solar charging will be at its lowest
In the absence charging from the engine you also need to consider how you will charge the secondary battery.
Fantasie 19
Well-known member
Exactly the same here..
Helidan
Active member
My Nasa Marine 20w panel kept my start and house batteries good over the winter months.
2hullsonemarinaberth
Member
So for those that know what the numbers mean, would someone suggest a suitable battery (budget preferably) and solar charging requirement to run my caravan mover for lugging my dinghy up the ramps either side of the sea wall (max 7 minutes each way) please? Motor is as shown. I will keep this at the dinghy club and rely on solar to keep it charged. The mover will not enter the water.
All thoughts welcomed (except those suggesting a lighter dinghy).
All thoughts welcomed (except those suggesting a lighter dinghy).
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ghostlymoron
Well-known member
When I first bought a solar panel it was considered cutting edge and a ten watt was expensive. However costs have dropped rapidly and a controller can be had for under £15 so I'd always install one as it shows state of charge and if it's being charged.
Poey50
Well-known member
I always thought the 10% rule was completely bomb-proof until someone brought this video to my attention from the estimable Rod Collins. Spoiler alert - you might need to think again. I think the rule flourished during the golden age of flooded lead acid which are a lot more tolerant of some over-charging than e.g. AGMs.
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Stemar
Well-known member
Do the sums as Vic suggests, but remember that panels don't give you much on a dull cloudy day. I'd fit as much solar as convenient, along with a controller. If you need to charge both batteries separately, I used on of these on my last boat and, while less efficient than more expensive controllers, it worked well
EP Solar Duo-Battery Solar Charge Controller 12/24v 10A. £33.30
This will handle up to 100w of solar, IIRC, there's another model that's good up to 200w, but I think that's likely to be overkill.