diy solar

diy solar

New here.. looking to fit my first system.

Tomm5235

New Member
Joined
Sep 13, 2021
Messages
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Hi All im looking for some advice. i have a little experience with 12V systems but not a huge amount. im based in the UK and a new boat owner looking to add solar to it.

i will list my scenario and then put forward the questions!

boat is a 23 foot sail boat, she has a Yanmar diesel engine running a 35 amp alternator.
it has 2 35ah (038) batteries on a split charge isolator switch.
off.
batt1
batt2
both batteries (not sure if this is 12v at 70ah or 24v at 35ah)

the engine is used sporadically the boat is river and lake based so there are times where the engine might be needed for 10 minutes but thats all.

im looking to upgrade my batteries and fit solar.
physical battery size is a limiting factor, i cant fit physically bigger batteries

space for mounting a panel is limited (750mm x 650mm) running a PWM controller (cant afford an MTTP)

im looking at an 80w panel:
https://www.photonicuniverse.com/en...-controller-mounting-brackets-and-cables.html


so onto my questions:
will 80w be enough to charge these batteries
if i upgrade to say 42ah batteries will my alternator be able to handle the difference? (i assume it will charge them slower?)

does anyone have any thoughts or suggestions on the whole sporadic use of the engine? i dont want to have to leave it idling just to keep putting charge into the starter battery...

essentially if anyone has any thoughts about what im trying to achieve or any suggestions it would be greatly appreciated!

Thanks
Tom
 
The battery switch indicates to me that it is a 12V system.

Usually, you have one battery you keep ‘holy’ and use for starting purposes only, and use the other independently while under sail or on the hook, and select 1&2 while “charging.”
So at anchor or underway by sail you select the second battery for onboard systems, lighting, etc. While under power ‘typically’ you would select the 1&2 position for alternator charging. However, in your case, I would select only the primary starting battery while under power (because your run time is short) and let solar handle the accessories.
This departs from open-water conventions slightly but you say you’re inland so not so much of a safety concern. In an urgent situation you can use the diesel to recharge of course.

One thing about the batteries: if those are 35Ah starting batteries they won’t last well if you are using them for accessories. Starting batteries want to take a big amp hit (starting) and immediately get to being fully recharged. Unless it’s a “big” motor, I usually install deep cycle marine batteries with excess capacity- that way they will still start the motor but not be as concerned with extending the time to recharge. There’s like a dozen other things that you can do but this is just information to consider.

The other advantage to non-starting battery isolation is that you can turn the switch ‘off’ while leaving the pwm to charge the accessory battery. Alternatively, if you can install a load disconnect you can use the pwm to keep the batteries fully in float.

I hope I interpreted your needs well so this is useful to you.
 
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