Solar panels - can they drain/kill batteries?

[Robert Wilson]

House battery kna**ered, starter battery weakened.
For three or four seasons my two 20watt panels have maintained the starter and house battery to a good level.
After a week "down-coast" with bags of sunshine and a lot of motoring, both batteries' "condition" dropped from the green zone, through the yellow and well into the red zone on my monitor.
House battery (110Ahr) wouldn't even turn over the donk-lump.
I disconnected the solar panels because their monitor showed 5%.
I bought a new house battery and over many hours of motoring (for various reasons/conditions) both batteries are into the green zone again.

What does the team think might be the cause; and is there a remedy for the panels?

TIA, as usual
Please try and keep the replies at "numpty level"

 

[ltcom]

What type of batteries? Wet acid? Have you checked electrolyte level? What type of regulator do the solar panels go to? Do the panels give 20Volts when not connected to anything?

 

[sailinglegend420]

Solar panels - can they drain/kill batteries?....

Yes if they are not connected via a solar controller - no matter how small the panels are.

 

[Oletimer]

House battery kna**ered, starter battery weakened.
For three or four seasons my two 20watt panels have maintained the starter and house battery to a good level.
After a week "down-coast" with bags of sunshine and a lot of motoring, both batteries' "condition" dropped from the green zone, through the yellow and well into the red zone on my monitor.
House battery (110Ahr) wouldn't even turn over the donk-lump.
I disconnected the solar panels because their monitor showed 5%.
I bought a new house battery and over many hours of motoring (for various reasons/conditions) both batteries are into the green zone again.

What does the team think might be the cause; and is there a remedy for the panels?

TIA, as usual
Please try and keep the replies at "numpty level"

Am I wrong in thinking that all solar panels have one way diodes to stop just such an experience?

 

[jiris]

Am I wrong in thinking that all solar panels have one way diodes to stop just such an experience?

Yes, you are wrong ;-).

 

[William_H]

I wonder if OP got any useful ideas from the above comments. Firstly I assume OP has a solar panel regulator (controller). He mentions the controller showing 5%. It is unlikely though possible that the controller is discharging the batteries. The solar panels can not discharge the batteries via the controller. Wisdom has it that a panel connected without a diode can discharge a battery at night. I have not been able in tests to show any reverse current. I don't believe my little 5w panel directly connected to the battery has a diode and does not discharge the battery.
My belief is simply that your house battery died of an internal fault and or old age.
However if OP wants to check then use a multimeter on amps range connected between the controller and the battery to check firstly for a charge current from the panel and controller. Make sure battery is not fully charged. Then cover the panels or check when dark for any current flowing form batteries to controller. Move the meter to milliamps range to check. My guess is that the solar system will be fine.
I think Sailinglegend420 is completely wrong in suggesting solar panel without a controller will knacker a battery. It would take a small battery and largish panel to boil a battery with overcharge. Wisdom suggests panels of current capability more than 10% of battery AH rating or more than 10w should have a controller. Ok, but my experience in a very sunny location is that you can have more than that rule of thumb but best to be safe. ol'will

 

[sarabande]

Yes if they are not connected via a solar controller - no matter how small the panels are.

Errm, what is the function of a diode ?

 

[Cactus Sailing]

House battery kna**ered, starter battery weakened.
For three or four seasons my two 20watt panels have maintained the starter and house battery to a good level.
After a week "down-coast" with bags of sunshine and a lot of motoring, both batteries' "condition" dropped from the green zone, through the yellow and well into the red zone on my monitor.
House battery (110Ahr) wouldn't even turn over the donk-lump.
I disconnected the solar panels because their monitor showed 5%.
I bought a new house battery and over many hours of motoring (for various reasons/conditions) both batteries are into the green zone again.

What does the team think might be the cause; and is there a remedy for the panels?

TIA, as usual
Please try and keep the replies at "numpty level"

silly question maybe... but are you consuming more than you're generating during your sailing? our 40W panel only lasts us about 4/5 days of sailing (i.e very little motoring) before the house bank starts to suffer unless we turn the fridge off, or start motoring significant distances .

 

[Graham376]

Wisdom has it that a panel connected without a diode can discharge a battery at night.

It will depend on the regulator being used. Some time ago, I had two regulators of different makes feeding from a common solar cable, to two separate banks. Although no flat battery problem, in the morning both banks would be balanced due to reverse current through one regulator. Problem cured by fitting split charge diode between panel and regs.

 

[Baggywrinkle]

Errm, what is the function of a diode ?

A blocking diode prevents current flowing from the battery to the panels (wired in series with panels), a by-pass diode (wired in parallel with the panel) helps with shading problems on one panel allowing the current from the other panel to by-pass the dead shaded panel and still charge the battery - applicable for panels wired in series.

A blocking diode is not needed if the panels go through a charge controller.

There is a danger if the panels are connected directly to the battery (without a charge controller) - which I would personally never recommend, that they will overcharge the battery and destroy it, or if connected directly to the battery without a blocking diode that they will drain the battery when not charging - and destroy it.

 

[Oletimer]

Yes, you are wrong ;-).

Thank you, I was led to understand that diodes were/are part and parcel of every solar panel.

 

[lw395]

House battery kna**ered, starter battery weakened.
For three or four seasons my two 20watt panels have maintained the starter and house battery to a good level.
After a week "down-coast" with bags of sunshine and a lot of motoring, both batteries' "condition" dropped from the green zone, through the yellow and well into the red zone on my monitor.
House battery (110Ahr) wouldn't even turn over the donk-lump.
I disconnected the solar panels because their monitor showed 5%.
I bought a new house battery and over many hours of motoring (for various reasons/conditions) both batteries are into the green zone again.

What does the team think might be the cause; and is there a remedy for the panels?

TIA, as usual
Please try and keep the replies at "numpty level"

Sounds like you are using more power than you generate.
A voltmeter would be useful, a basic check for very little money.
What is this 'monitor' you have?
2x20W panels is not much power, but we used to go sailing with no solar at all in the old days.
It's a matter of knowing where the power is going.
You need to understand why your engine battery was low.

 

[sailinglegend420]

Thank you, I was led to understand that diodes were/are part and parcel of every solar panel.

Just to clarify Baggywrinkle's post - bypass diodes are now part of every panel, and the more they have the better to combat the loss of current due to shading. Some panels will have two bypass diodes, one across each string of 16 cells in the panel. Better panels will have even more.

Blocking diodes are only added to the output of the panels, usually when two are connected in parallel to the same solar controller, otherwise one in full sun can discharge into the other if it is in total shadow.

Blocking diodes and bypass diodes are the same kind of diode - just wired differently to do a different job.

 

[Robert Wilson]

What type of batteries? Wet acid? Have you checked electrolyte level? What type of regulator do the solar panels go to? Do the panels give 20Volts when not connected to anything?

Yes if they are not connected via a solar controller - no matter how small the panels are.

Sealed batteries, and to be honest I don't know what type. Until this latest episode the inspection "holes" were always showing green. With this failure the 110Ahr battery's inspection point was black. I had it checked in Tobermory and was told it was kaput. It was about five years old and stood, on charge from the solar panels for two years, 2016/17 while ashore.
Last season no problem at all.
They are connected by the supplied controller, which was the item that showed 5%.
I would leave the controller connected to one battery for a while/month, then swap it to the other.

 

[Robert Wilson]

What type of batteries? Wet acid? Have you checked electrolyte level? What type of regulator do the solar panels go to? Do the panels give 20Volts when not connected to anything?

Yes if they are not connected via a solar controller - no matter how small the panels are.

I wonder if OP got any useful ideas from the above comments. Firstly I assume OP has a solar panel regulator (controller). He mentions the controller showing 5%. It is unlikely though possible that the controller is discharging the batteries. The solar panels can not discharge the batteries via the controller. Wisdom has it that a panel connected without a diode can discharge a battery at night. I have not been able in tests to show any reverse current. I don't believe my little 5w panel directly connected to the battery has a diode and does not discharge the battery.
My belief is simply that your house battery died of an internal fault and or old age.
ol'will

Thanks ol'will. I'll do those checks, but I note your comment re internal fault or old age. As said in one of my responses the house battery is about five years old.

 

[Robert Wilson]

What type of batteries? Wet acid? Have you checked electrolyte level? What type of regulator do the solar panels go to? Do the panels give 20Volts when not connected to anything?

Yes if they are not connected via a solar controller - no matter how small the panels are.

silly question maybe... but are you consuming more than you're generating during your sailing? our 40W panel only lasts us about 4/5 days of sailing (i.e very little motoring) before the house bank starts to suffer unless we turn the fridge off, or start motoring significant distances .

Fridge? No such luxury! Anyway, during the last cruise of 11 days the temperature hardly got above 5°C in the cabin
My only "stuff" on while sailing is plotter with AIS, VHF and a "plugged-in" Garmin Handheld device for various motion data.
If I use the Tiller Pilot or anything else I run the engine, or am motoring.

 

[Robert Wilson]

What type of batteries? Wet acid? Have you checked electrolyte level? What type of regulator do the solar panels go to? Do the panels give 20Volts when not connected to anything?

Yes if they are not connected via a solar controller - no matter how small the panels are.

Sounds like you are using more power than you generate.
A voltmeter would be useful, a basic check for very little money.
What is this 'monitor' you have?
2x20W panels is not much power, but we used to go sailing with no solar at all in the old days.
It's a matter of knowing where the power is going.
You need to understand why your engine battery was low.

Engine battery was low because the House battery had drained and I needed instruments and then to start the donk when reaching harbour.
Next effort to start with that battery was an almost failure.

 

[Robert Wilson]

Thank you one and all.
I shall try to get to the boat in the next week or so to carry-out the checks. It is on the mooring with the Solar Panels disconnected.

Sailing has to be curtailed for some weeks as two days ago I collected a six week old labrador puppy; black, naturally...…...………..

When I lost my thirteen year old lad three weeks ago I decided I could never go through the pain again; and I would go sailing.

Hah! Twelve days on the boat then coming back to an empty, silent house changed my mind!!

Canna is asleep in his crate at the moment so I have time to catch up on YBW stuff.

 

[AntarcticPilot]

A blocking diode prevents current flowing from the battery to the panels (wired in series with panels), a by-pass diode (wired in parallel with the panel) helps with shading problems on one panel allowing the current from the other panel to by-pass the dead shaded panel and still charge the battery - applicable for panels wired in series.

A blocking diode is not needed if the panels go through a charge controller.

There is a danger if the panels are connected directly to the battery (without a charge controller) - which I would personally never recommend, that they will overcharge the battery and destroy it, or if connected directly to the battery without a blocking diode that they will drain the battery when not charging - and destroy it.

Depends on the charge controller - my HRDi certainly states it needs solar panels to be fitted with diodes, and without a diode, the system WILL discharge a battery in dull weather! This from practical experience - with a diode I find fully charged batteries; without it I found the level of charge the same as or less than the amount I started with - and this is with a 100W panel.

 

[lw395]

Engine battery was low because the House battery had drained and I needed instruments and then to start the donk when reaching harbour.
Next effort to start with that battery was an almost failure.

Your engine battery should have a reasonable capacity. 40Ah would be on the small side? It should still start your engine if it's 50% discharged. What do your instruments draw? Plotters and AIS can be more hungry than you might expect, but you ought to have several hours of sailing before starting the engine is a problem.

However, personally I would probably be thinking of starting the engine the moment the house battery got low, unless I was racing or there was other good reason not to.
Or at least I'd turn off all the toys. Couple of AAs in the HH GPS and a paper chart and we're good. But unless we're heading for a berth with shorepower, how is the house battery going to get charged?