Solar panel without charge controller?

[john_morris_uk]

When I leave the boat for an extended period the generator battery (like all wet lead acid batteries) will slowly self discharge. The main house batteries have a bank of solar wired to them via a Victron MPPT controller so they’re maintained perfectly. My solution for maintaining the generator battery was to buy a small solar panel without controller and just leave it connected. I thought I’d done my research well enough and bought a 20 Watt panel but even when the conditions are a bit overcast the float voltage is up at 15 volts or so. (The boat’s ashore in St Kitts in the Caribbean so gets plenty of strong sun!)

Here’s the float voltage with panel connected:



Should I be worried about the nigh float voltage? Should I fit a cheap controller? Am I worrying about nothing? Any suggestions?

 

[Sea Change]

I've killed a battery before by not fitting a charger control. A cheap PWM one will do the job.
If you can't get one, could you remove the generator battery and place it in parallel with the house ones?

 

[shanemax]

I have a 5 watt panel charging my spare battery 24/7/52. Keeps it topped up in the event I may need it. I use a controller on my other two batteries but not on the spare and it has never done it any harm. I am not to sure about a 20 watt as that is approx one amp per hour so on a sunny day thats 12 amps where you are.

 

[Stemar]

I'd be concerned about that voltage too. How hard would it be to rig up something like Sea Change's idea? It could be as basic as a bit of twin flex and a few clamps, or it could be a permanent setup in parallel with the engine battery. Just add a VSR or diode so it isn't trying to start the engine

 

[harvey38]

My limited understanding is you could quite easily over charge your battery without a controller. Given your location, I thinks it's more a case of when, rather than if..........

I'd disconnect it rather than have a puddle of sulphuric acid sloshing around somewhere it shouldn't be.

 

[john_morris_uk]

My limited understanding is you could quite easily over charge your battery without a controller. Given your location, I thinks it's more a case of when, rather than if..........

I'd disconnect it rather than have a puddle of sulphuric acid sloshing around somewhere it shouldn't be.

It’s disconnected atm. I’m inclined to get a cheap charge regulator.

 

[john_morris_uk]

I'd be concerned about that voltage too. How hard would it be to rig up something like Sea Change's idea? It could be as basic as a bit of twin flex and a few clamps, or it could be a permanent setup in parallel with the engine battery. Just add a VSR or diode so it isn't trying to start the engine

My issue with paralleling it up with the house batteries is that they’re very different batteries. Three deep discharge 125 aH lead acid batteries vs a small starter battery.

 

[rogerthebodger]

In the past it was considered that the max solar wattage to use to charge a battery without a regulator was 10% i.e if you have a 100 Ah battery the max solar panel would be 10 watt

I have a 50 watt solar keeping my 120 Ah engine start battery topped up with a simple on /off regulator that has a float voltage of about 13.5 V and has worked for over 10 years without a problem.

I have a mains battery charger that over charged my engine battery in to just over 15 Volts and it cooked the battery and blur the charge indicator and distorted the battery case . I have just replaced the engine start battery and I will have to check my Domestic batteries to see it they have been damaged also

 

[vyv_cox]

How long is an 'extended period'? My batteries were left for three years due to covid. All disconnected from each other and the boat. Voltage was 12.4 when I returned, started the engine and have been fine ever since

 

[ghostlymoron2]

For the sake of a tenner I'd fit an ebay controller.

 

[B27]

I suspect it depends on the battery.
Many modern 'engine' batteries are not just plain lead-acid, the chemistry is a little more subtle giving some resistance to losing electrolyte through over charging. Some batteries re-combine the gassing of H2 and O2 back to water.
A lot of old-skool batteries would gas like made at 15V and draw a lot of current, which a 20W panel isn't going to be providing.

But typically a 5W solar panel is OK for a 100Ah battery in a UK Winter.

Also a lot of solar 'regulators' are not reliable long term, they often seem to have dubious 'bulk' and 'float' modes and strange logic for when they are in which mode. I think one of the cheap ones I have enters a new hour of absorption charge voltage every time the sun comes out.
So I'm not convinced that those £10 ebay controllers are a good answer for long term float charging.
Over the winter, I resorted to using a simple voltage regulator set to 13.5V.

My engine battery is pretty old, so it owes me nothing, but if I have to replace it, I'll need to look after the new one a bit better.

 

[PaulRainbow]

When I leave the boat for an extended period the generator battery (like all wet lead acid batteries) will slowly self discharge. The main house batteries have a bank of solar wired to them via a Victron MPPT controller so they’re maintained perfectly. My solution for maintaining the generator battery was to buy a small solar panel without controller and just leave it connected. I thought I’d done my research well enough and bought a 20 Watt panel but even when the conditions are a bit overcast the float voltage is up at 15 volts or so. (The boat’s ashore in St Kitts in the Caribbean so gets plenty of strong sun!)

Here’s the float voltage with panel connected:

View attachment 177521

Should I be worried about the nigh float voltage? Should I fit a cheap controller? Am I worrying about nothing? Any suggestions?

15v isn't float voltage, it's just the voltage from the panel.

20w is too big without a controller.

 

[Graham376]

Most of the solar car battery chargers are trickle, rated at 10W or less. Although my domestic bank stays on regulated charge whilst we're away, engine battery (sealed la car battery) isn't and will start the engine after several months.

 

[Boater Sam]

You could cover part of the panel to reduce its output to around 5w. Free fix!

 

[bedouin]

I was happy using 5W to top up 200Ah of batteries on a swinging mooring in UK.

20W for a small engine starter battery in the sunny Caribbean sounds far too much for me

You can buy small 2W or so panels designed to top up car batteries that would do the job you need - or a controller

I am a bit surprised you need any topping up - a battery in good condition should go a year without needing anything in the way of top up

 

[NormanS]

After leaving my car for five weeks, I came home to a flat battery. The car is a hybrid, and according to the very helpful AA man, that's what happens. Apparently there are many security and diagnostic things going on to drain the battery. I was the third that he had helped that day with the same problem. He advised a two or four watt panel, with no regulator. I have fitted one, and leave the car parked facing south. All fine.

 

[B27]

.....

I am a bit surprised you need any topping up - a battery in good condition should go a year without needing anything in the way of top up

Lead acid batteries generally have a self-discharge issue over time.
This can get worse with older batteries.
I've noticed that some of the 'best' motorbike batteries, packing more current and generally lasting longer in normal use, have a higher self discharge.
With more modern vehicles, there are usually things draining the battery all the time as well as the battery itself discharging.

I don't think I've ever seen a battery manufacturer claim their lead-acid battery doesn't benefit from being charged every month or 6 weeks or similar, even when disconnected..

 

[Zing]

It's good for your battery to keep your lead acid battery topped up on a float voltage and will extend life, so I wouldn't leave it.

I used to top up a 30Ah battery with a 4W panel and no controller with no voltage excursions. It's all about resistance at full charge. You probably only need a couple of watts if that. Costs just a few quid. Make sure it has a reverse current diode or fit one.

 

[NBs]

Hi,
Wrong place to save about 20€ and a bit of work to install the charge controller and fuse.

NBs

 

[PaulRainbow]

It's good for your battery to keep your lead acid battery topped up on a float voltage and will extend life, so I wouldn't leave it.

I used to top up a 30Ah battery with a 4W panel and no controller with no voltage excursions. It's all about resistance at full charge. You probably only need a couple of watts if that. Costs just a few quid. Make sure it has a reverse current diode or fit one.

When did 15v become float voltage for lead acid batteries ?