Solar panel without charge controller?

[john_morris_uk]

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

Six or seven months.

 

[john_morris_uk]

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

That’s one of the options I’m considering.

 

[jamie N]

A solar controller isn't used because it's a fashion accessory, it serves a purpose.

 

[vyv_cox]

Six or seven months.

Same for us. Disconnect everything, batteries from boat and each other. Our experience is they will easily do that time with minimal loss of voltage. Ours are Winner Solar, designed for many discharge cycles.

 

[B27]

A solar controller isn't used because it's a fashion accessory, it serves a purpose.

Unfortunately, the vast majority of solar charge controllers are designed for the purpose of applications like lights on a daily cycle.
Even the expensive ones don't really seem to be optimised for maintaining batteries in long-term storage.

 

[B27]

Same for us. Disconnect everything, batteries from boat and each other. Our experience is they will easily do that time with minimal loss of voltage. Ours are Winner Solar, designed for many discharge cycles.

Lots of people however leave their batteries idle and disconnected over the winter and find they are flat in the Spring.

Once your batteries are older, the more likely you will see self discharge.
Back when solar panels first became affordable, a 5W panel made a huge improvement

 

[noelex]

Flooded lead acid batteries are reasonably tolerant of overcharging, especially if you can add water. Nevertheless, charging them with the correct voltage set points (don’t forget to adjust for temperature) will ensure the longest life.

Given your results, a cheap charge controller will pay for itself in extended battery life. Buy one with user adjustable (or at least suitable) charge parameters. Some charge controllers are very conservative. They can undercharge the battery, which is worse. Lead acid batteries are not very happy if consistently undercharged.

 

[PaulRainbow]

Unfortunately, the vast majority of solar charge controllers are designed for the purpose of applications like lights on a daily cycle.
Even the expensive ones don't really seem to be optimised for maintaining batteries in long-term storage.

The level of electrical misinformation on these forums reaches new levels on an almost daily basis.

 

[B27]

Flooded lead acid batteries are reasonably tolerant of overcharging, especially if you can add water. Nevertheless, charging them with the correct voltage set points (don’t forget to adjust for temperature) will ensure the longest life.

Given your results, a cheap charge controller will pay for itself in extended battery life. Buy one with user adjustable (or at least suitable) charge parameters. Some charge controllers are very conservative. They can undercharge the battery, which is worse. Lead acid batteries are not very happy if consistently undercharged.

Being on hand regularly and frequently to monitor the situation and maybe add water is a great help, but a lot of people seem to want to leave their boat on the hard for months at a time while they are in another country. That's actually quite a big ask.

 

[Zing]

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

What makes you think the battery will reach a float voltage of 15v? It won't if the power is low enough as I suggested. I don't think you have taken account of internal resistance.

 

[B27]

What makes you think the battery will reach a float voltage of 15v? It won't if the power is low enough as I suggested. I don't think you have taken account of internal resistance.

Could it be the big '15' in the picture of the multimeter in the OP?

 

[vyv_cox]

Being on hand regularly and frequently to monitor the situation and maybe add water is a great help, but a lot of people seem to want to leave their boat on the hard for months at a time while they are in another country. That's actually quite a big ask.

And that is why charging them in your absence is such a bad idea. If a cell goes down with a short when the lead sulphate falls off a plate the charger keeps increasing the charge rate. I know of at least half a dozen cases in which batteries have been found to have burst due to overheating and a couple of serious fires for the same reason.

 

[noelex]

Some good battery manufacturers publish both the ideal "cyclic" (the battery is being charged and discharged) and "storage" voltage set points. If leaving the battery with no loads for long periods it is worthwhile adjusting the parameters to the storage voltage set points. This is one reason why a user adjustable controller is worthwhile.

If you cannot find any data from your battery manufacturer, reducing the voltage set points by around 0.4v is a good start. So, for example, the bulk charge voltage of 14.6v is reduced to 14.2v and the float voltage is reduced from 13.7v to 13.3v. The absorption time should also be reduced to the minimum level, especially for solar controllers.

 

[Zing]

Could it be the big '15' in the picture of the multimeter in the OP?

That's a different situation because my suggestion was in response to the later discussion about the engine battery, where I proposed a 2w low volt panel, instead of using the 20w high volt panel.

 

[Refueler]

Simple Charge Controllers are plenty on eBay ... for a 20W panel - I wouldn't be too worried about having MPPT etc.

I have a 20W on one boat via such PWM ... works a treat.

My latest MoBo - has twin 20W panels going into a cheapo PWM ... works a treat ... charges up two 90A/hr batterys.

 

[PaulRainbow]

That's a different situation because my suggestion was in response to the later discussion about the engine battery, where I proposed a 2w low volt panel, instead of using the 20w high volt panel.

Silly us, we should have guessed you were suggesting something that didn't relate to the OP.

 

[Zing]

Silly us, we should have guessed you were suggesting something that didn't relate to the OP.

It does though. Actually the whole thread is about the generator engine battery. It's not hard to understand if you follow the context and order of the posts. Try it next time.

 

[B27]

And that is why charging them in your absence is such a bad idea. If a cell goes down with a short when the lead sulphate falls off a plate the charger keeps increasing the charge rate. I know of at least half a dozen cases in which batteries have been found to have burst due to overheating and a couple of serious fires for the same reason.

I don't disagree with that, but it comes down to being away from your boat for a long time with no supervision has a cost in battery life.

If you want your batteries to last as long as possible, all the manufacturers will tell you to float charge them every month or something.
I don't fully trust any solar controller to be completely risk free when unsupervised.
Maybe the very best of smart maintenance chargers will detect the difference between a battery which needs charging because it's showing 10.5V and a battery which has a cell shorted in series with 5 fully charged cells? There are certainly 'battery analysers' which do that.

Two people in my club were moaning about needing new batteries for their RIBs this month, my mate pointed out their batteries cost a lot more than a little solar panel.

OTOH, they quite likely had batteries not 100% charged at the end of last season.

If you've got one shorted cell and a 5W solar panel, I doubt anything dramatic will happen, the trickle charge will simply slowly dry out the other cells.
If you've got a shorted cell and a high power regulator or another 12V battery in a bank, that's a different matter, serious current can flow and heat can build up.

Personally, I've had too many motorbike batteries go flat in a couple of months with no current drain (we're talking old bikes here, not your 'modern' ECU continuous drain problems!), so I am resistant to the 'disconnect everything and expect it to be OK' approach. I'm sure motorbike 12V batteries tend to be subtly different from deep cycle batteries of course.

 

[john_morris_uk]

I’m in the fortunate position of having someone local who is keeping an eye on things. He says he’ll go down every month or so and connect the panel for a few hours. If I ask him he might monitor the battery voltage before he connects the solar panel.

I’m exploring getting a simple regulator.

We leave our house bank connected via a Victron MPPT controller but the panels are lashed down vertically so don’t produce full output. When we returned to the boat last time after six months unsupervised in Caribbean sunshine, the batteries were merrily floating at 13.5 volts and as far as I can tell are in perfect condition.

 

[William_H]

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

20w is too big without a controller.

Not like me disagree with Paul however the voltage he is measuring must be battery voltage which is also panel voltage as he is connecting panel direct to the battery. Much as would be expected in bright sun. Actually panel voltage not connected would be closer to 20 volts.
However yes 20 w is too big assuming it is connected to a around 50 AH battery. Yes 15v battery voltage sustained would indicate battery is being over charged. The panel will be pushing in 1 amp regardless of battery charge state.
It may be practical to cover part of the panel. Assuming panel has stripes of cells then cover must be over part of each cell ie leaving part of every cell exposed.
A simpler option might be to add a ressitor to panel lead of around 20 ohms to halve the panel capability. Which may help to avert overcharge. But as said fit a regulator. ol'will