Solar panel issue?

[Buckman]

At the end of Sept we put the caravan into storage. On 12th Oct we were notified that the battery was low. On checking we found that we had left the 12v switch on even though everything else was switched off including the fridge. The battery was down to about 10.5v. We switched off the 12v switch.
On Saturday we went to the caravan again and found that the battery was completely flat. On checking the graph we could see that since the 10th Oct the battery had starting discharging until it was flat.
The solar panel and controller are both Truma and checking no green light was being displayed indicating that the battery was being charge. Between the end of Sept and about the 10th Oct the graph showed that the the voltage was going up and down indicating that the controller and panel were working okay.
We now suspect that the controller has gone faulty unless the controller shuts down completely if the voltage drops below 11v? I have a spare 110ah battery but do not want to install it in case the same happens to it.

 

[Guzzilazz]

As always I preamble with I'm not experienced in caravans, but have loads of experience on boats. Current boat has had 2x45W panels charging 3x110 AH AGM batteries through a 10A PWM controller to run the domestics. Also the boat is kept on a swinging mooring so no mains hookup. I upgraded to 2x100W panels through a 20A MPPT controller last October.

Your symptoms (battery down to 10.5V, then flattened) indicate that the controller can't be preventing the panels DRAWING power when they're not charging. On small installations without a controller you absolutely have to have a blocking diode to stop this. You need to "assure" this is correct, and will need at least a multimeter, and for preference a DC clamp on meter. The latter will allow you to see if there is current drain without disconnecting anything.

Unfortunately you will need to use your replacement battery to test, but as your original battery is toast anyway (any discharge below 10V will screw a standard lead acid battery), but if you can isolate the fault to the controller, you can just leave the new battery disconnected till you replace it.

 

[Buckman]

Thanks for the info. The solar panel is a 100w panel linked to the Truma controller and came standard with the caravan so would assume that it as installed correctly with a diode. As said it worked okay until 12th Oct or 2 weeks and then the battery started draining and never recovered which is why I suspected that the controller had gone faulty. Battery voltage is at present 5.6v. Collecting it today to put on charge.
Both the controller and the battery are less than a year old so I am hoping that if the controller is faulty that the battery will be replaced by the dealership.

 

[Guzzilazz]

The controller should do all the blocking internally, so yes deffo defective. At 5.6V if the battery is a straight or sealed lead acid it's done for. I did recover a set of 3x AGM 110AH about 12 years ago, when they had dropped to 4V... Hence I have a personal love for AGM's which now aren't so much more expensive than sealed.

 

[Buckman]

The controller should do all the blocking internally, so yes deffo defective. At 5.6V if the battery is a straight or sealed lead acid it's done for. I did recover a set of 3x AGM 110AH about 12 years ago, when they had dropped to 4V... Hence I have a personal love for AGM's which now aren't so much more expensive than sealed.

The last time I checked AGM batteries were in the vicinity of about £250, but you are correct and they can now be bought for well under £100. cheapest I have seen is £79!

 

[Buckman]

I have taken the battery out of the caravan and was surprised to find it came standard with a Yuasa 95ah 800 amp AGM battery. I have put it on charge with my Ring battery charger and initially the light was orange to indicate it was charging, but within 10 minutes changed to green which normally shows it as fully charged. Weird?

 

[Guzzilazz]

AGM's need a slightly different charge profile, so if the Ring is a standard trickle charger it probably won't work. I use a Halford's charger I bought years ago which as a profile for VRLA (Vapour Regulated Lead Acid) as well as flooded LA.

I have a CTEK charger permanently connected on the boat, they are absolutely brilliant...

 

[Buckman]

To get around it I connected up a lead acid battery in parallel to the AGM and then connected the charger to the lead acid battery. This fools the charger into thinking that the lead acid battery requires charging. After an hour the voltage was up to 11.5v from 5.8v.