Batteries - Solar Chargers

[Spartan]

OK guys, bear with me. I'm new to the Forum and have quickly looked for the answer but can't find it. No doubt this subject has been done before, but here goes anyway.

I currently have 2 batteries on board linked together (in tandem ?) and while she was moored last year I sometimes attached a solar trickle charger to one of the batteries.

Near the end of the season both batteries went flat and it was only then that I realised that I had hardly ever ran the engines for any time to charge them up. I know that was a rediculous thing to do, being a newby, I never thought about that part of sailing. As soon as I could I got the sails up I did as I just wanted as much practice as I could using the wind to get me where I wanted to go. I never really gave the batteries a thought

Anyway, this season, I plan to motor more to at least recharge the batteries.

However, the main reason for my post is: while I'm at work, if I put a small solar trickle charger to one of the batteries, will that help keep one or both batteries charged, or do I need 2 solar chargers - one attached to each battery ?

I appreciate that all you hardened, more technical minded sailors will wonder what planet I'm from asking such a daft question. The problem is, although the answer will no doubt be obvious to you, it isn't to me.

Any views or thoughts will be welcomed. I'm sorry if this has been covered a multitude of times before - but like I said before, I'm new here and am just learning.

 

[saltwater_gypsy]

Firstly...welome to the Forum
Couple of points.
It is essential that your charger has a diode in the circuit so that the batteries don't discharge through the solar panel during the night.
You can charge both batteries from the same 12v solar charger BUT this time you would need a blocking diode to prevent one battery discharging into the other.
I am presuming that your electrical system is 12V , in which case the batteries will be connected in parallell possibly with a selector switch.

 

[whipper_snapper]

Anyway, this season, I plan to motor more to at least recharge the batteries.

Congratulations on the 1st novel concept posted here for a long time! Most of us swear that this season we will motor less and sail more!

In answer to your question. If your batteries are linked permanently (ie without a switch to separate them) then they are to all intents and purposes one battery and can be charged as a single unit by a single solar panel without a diode between the batteries.

There should be a diode in the circuit to the solar panel. Virtually all panels include a built-in diode to prevent discharge over night. But it is important to check this.

 

[VicS]

I dont know what you mean by small but i suggest you should be looking at 5 or 10 watts at least.
I have a 5 watt panel, that keeps my 60Ah battery charged. Its the only battery but I do not use it for engine starting.

Talking to someone yesterday who has 10watt panel and is well pleased with that (charging a 110 Ah battery)

Regard the very small panels ... anything below 5 watts ... as merely a means of maintaining a charged battery in a fully charged state while not in use.

You can use up to a 1 watt per 10Ah without needing a regulator but you should fit one above that ratio or if you fit a panel in excess of 10 watts anyway.

Really you should make a reasonable estimate of your electrical consumption and they fit a panel which will provided enough power to replace it reasonably quickly as you do not want to leave your batteries in a partly discharged state for too long.

You might consider relying on the engine to recharge the engine start battery and use the solar panel to recharge the one you use for all other purposes, if that is how you use your batteries.

 

[nct1]

Assuming they are the big leisure batteries, you will need two independent 15w panels and two regulators.

You can buy panels that accept the curve of most coach roofs, and are not glass covered, which could be convenient (try BP).

If your batteries are permanently wired together that may be a problem, because if you have one duff battery, it will bring the other one down. Best get them on one of those 1,2 or both switches.

 

[whipper_snapper]

Assuming they are the big leisure batteries, you will need two independent 15w panels and two regulators.

You can buy panels that accept the curve of most coach roofs, and are not glass covered, which could be convenient (try BP).

If your batteries are permanently wired together that may be a problem, because if you have one duff battery, it will bring the other one down. Best get them on one of those 1,2 or both switches.

Cool!

Between us we have now completely baffled this poor guy!

I think that pretty much everyone said something more-or-less true, but somehow managed to convey complety contradictory information! The perfect introduction to the ybw group!!!

 

[jeremyshaw]

Between us we have now completely baffled this poor guy!

Indeed. Of course the truth is that no one is quite sure of the setup and for once was being nice to the OP.

OP:
First, people are assuming you have lead acid batteries. These do self-discharge at the rate of 2% to 10% (unlikely) per week. This is why you can't leave them all season. If you are planning to replace them you could consider something like AGMs which have a very low self discharge rate.

Second, although it is true that one battery may 'bring down' another when they are charged/connected together, that's what the great majority of people do. It's considered good practice to separate service batteries from engine batteries, but a bank of more than one batteries is usually charged collectively whether by solar, wind, whatever.

Third, it's a good idea to take your charge to either end of the bank. I.e. don't connect the pos and neg from the solar panels to the nearest battery. Go to one pole of the nearest and the opposite pole of the furthest.

Fourth, lead acid batteries don't like to fall below 12v. Most people like to keep them above 12.2v. If you let them get really low say to 11v they never really recover. Try www.batteryuniversity.com for good simple explanations about different kinds of battery and their attributes and maintenance. You can also find graphs showing how lowering the 'at rest' voltage shortens the life.

 

[nct1]

Cool!

Between us we have now completely baffled this poor guy!

I think that pretty much everyone said something more-or-less true, but somehow managed to convey complety contradictory information! The perfect introduction to the ybw group!!!

Well the advice I dispensed, was the very advice I got off this forum, and has served me well for 8 years.

I have two batteries that are independently charged, and normally run off one, leaving the other in reserve by use of the 1,2 both switch.

WS you are quite correct, there is always more than one way to do something, the point of this forum is for people to provide their practical experience, and allow others to make their own mind up.

Yes you can do it on the cheap by having one panel charging both, and for economic reasons some do this, but if you have the choice, it is far safer to have independent charging. I have had one battery go whilst underway, it was quite a shock seeing all the instruments switch off, but I had the luxury of switching to the other battery. Had the one battery brought the other one down I would have been changing my underpants.

All IMHO

 

[mcframe]

As others say, it depends what you've got and what you want.

What size is your solar charger?
The little 2W ones will only prevent self-discharge.

Are your batteries really in parallel? Unless you've got a separate start battery, then the only way you'll normally get that is if the off-1-2-both switch is on both - not a terribly good idea.

(usual stuff about alternator regulators, monitors, VSRs, etc)

*My* requirements, ~40-60 AH over the week (from a 20W panel into 180AH bank*) on a swinging mooring to allow instruments+fridge+heater at the /next/ weekend are vastly different from my friend who is aiming for 7-10 days of instruments+fridge+freezer+heater before motoring/shore power to charge his 350AH domestic bank.

Maybe you could suss out your wiring, then we can suggest fitting a monitor and more ideas ;-)

* I felt /slightly/ swindled last w/e when I got back to the mooring - after more motoring than usual - and the battery monitor claimed 105%, 12.9V...

 

[fireball]

Welcome to the forum ...

I can only offer our experiences ...

We have 2 battery banks - 1 small engine start battery - completely dedicated to the engine and 1 house battery bank (2 x 140Ah) - all the batteries are starting to come of age ...

The boat has a split diode charger block on the output of the alternator - so when the engine is running it charges both banks up at the same time. It also has a shorepower charger - but we're on a swinging mooring most of the time - so no shorepower!

The engine one has been absolutely fine - no issue with charge - it gets sufficient charge from the engine.
The house batteries are not so good - and this is what we wanted to resolve with a reasonable method of unattended charging.
We purchased a 30w solar panel - semiflexible - and connected it to the housebank (2 batteries connected in parrallel) via a fuse. The panel has a blocking diode built in. This tops up and keeps the house batteries fully charged through the summer when at idle - it isn't enough to replenish the charge whilst we're on board though, but as we mostly sail at weekends it has a week to recover.

Theoretically we should have a regulator fitted, but didn't bother as I don't believe the batteries are being cooked.

 

[Spartan]

Wow, thanks for that guys. And here was me thinking that I would get a simple answer.

Anyway now I think I have a better idea what I've to do - even though, as Whipper_Snapper said, at times it looked as though everyone was trying to completely baffle me. An easy task

Anyway, I'll put on my thinking hat next weekend and see how it's all looking down below and, depending on the set up, take it from there.

On reading other posts, I should have realised the suggestions/advice received would almost certainly be differing.

Again, thanks for taking the time to offer advice and suggestions. Much appreciated.