Solar Panel Discharging Battery When Dark

P

Pkewish

Well-Known Member
Joined
14 Mar 2012
Messages
78
Location
Dorset
Visit site
I have a 110mah leisure battery which charges up OK from the mains charger and holds it's charge for months when not connected, or provides a good supply of power for Nav aids and VHF etc for a few days whilst on board. I also have a 120watt solar panel connected via a regulator. If I put a multimeter over the solar panel connection in daylight, it's putting out over 13V. Great! When it's connected up via the regulator in daylight, all seems to charge up OK. However, if I leave it over night (dark), the battery if flat by morning. The regulator is a 12v PWM 10A, all fitted via a fuse.

Is it possible that the panel could be pulling the charge back out of the battery?
Could the Reg be faulty?

Your ideas would be appreciated.
 
Is there a diode in the circuit anywhere? If not why not?

If there is no diode, or if it is not working, the battery will discharge through the panel.

Perhaps I'm wrong but I would have expected a higher voltage from the solar panel.
 
No. Whilst there is a small drain in a PV panel without a blocking diode, it certainly wouldn't be sufficient to flatten a battery overnight.
When you say "flat" what is the precise voltage shown by the battery after a night?
I'd bypass the regulator, as a check, and see if the same thing is happening.
From what you describe the battery is the most suspect item.
 
Why not check the current from regulator ...... during daylight hours just to see what you get, it'll depend on the state of charge of the battery, and again after dark. If there is then a current flowing in the opposite direction you have a problem with the panel or more likely with the regulator.
 
SAMYL said:
Is there a diode in the circuit anywhere? If not why not?

If there is no diode, or if it is not working, the battery will discharge through the panel.

Perhaps I'm wrong but I would have expected a higher voltage from the solar panel.
Click to expand...

There is no separate diode, I assumed there was one in the regulator. As for voltage, in direct sunlight, it increases quite significantly (about 16-18v)
 
Pkewish said:
There is no separate diode, I assumed there was one in the regulator. As for voltage, in direct sunlight, it increases quite significantly (about 16-18v)
Click to expand...

The regulator should stop any drain at night even if there is no diode in the panel

Check the current as I suggest above.... Then you know what is going on.
 
VicS said:
The regulator should stop any drain at night even if there is no diode in the panel

Check the current as I suggest above.... Then you know what is going on.
Click to expand...

Thanks Vics, I'm down at the yard on Thursday so will check the voltages both ways. I have checked the detail of the Reg, it is supposed to stop discharging according to the blurb, maybe time to replace it then! P
 
I can't add to what has already been said other than to suggest that, if you do have to renew the regulator, it may be worth thinking about getting a 15 or 20 amp one. Whilst your 10 amp one is theoretically right for a 120 watt panel it's probably worth having a bit more leeway.
 
You have to have a one way valve on the wire a diode to stop the battery making the pannel into a radiator at night you can get these at Maplin's for a cheep price

Cliff
 
cliff@jansun.co.uk said:
You have to have a one way valve on the wire a diode to stop the battery making the pannel into a radiator at night you can get these at Maplin's for a cheep price

Cliff
Click to expand...

The regulator usually prevents this...... The Op has already said that this is so for his .

It has also been suggested in the past on these forums that the small loss through a solar panel at night is in fact less than the loss in charging during the day due to volts drop across a diode.
Presumably your user name indicates that you are in the solar energy business. What then is the expert view on this?
 
I always used a blocking diode until I read this in Nigel Calders book;

The reason for installing blocking diodes is that while a solar panel puts out in sunlight, it takes back after dark (although the reverse current flow is much less). But the voltage drop through the diode will often reduce the output of a panel by more than the nightime drain back into the panel). So although such diodes are fitted routinely, they would often be better left out.
Click to expand...

He then goes on to say that a diode makes little or no difference with 36 cell panel, that a 33 cell panel will be a little worse off with a diode, and that a 30 cell panel will almost always be worse off with a diode.

When I checked the readings on my setup it seemed to confirm Calders comments. I would add to his comments by pointing out that in summer our long days and short nights make even more difference.

I now remove the diode in the summer and put it back in late autumn. When the boat goes under cover I disconnect the panel altogether.
 
VicS said:
The regulator should stop any drain at night even if there is no diode in the panel

Check the current as I suggest above.... Then you know what is going on.
Click to expand...

Unfortunately, some regulators don't stop backfeed as I found out with one of mine. I suggest a diode between the panel and the regulator.
 
Norman_E said:
Most panels have a diode fitted. If the panel does not have one I suggest fitting one
Click to expand...

If you mean a blocking diode, NONE of the Kyocera panels have ever fitted one. The minute loss overnight is outweighed by the loss of power during the daylight hours, according to their calculations.
I suspect that the OPs regulator is either faulty or has an error in wiring.
Whilst he's finding out and (probably) replacing his regulator, I'd suggest considering an MPPT controller rather than an on/off regulator.
 
charles_reed said:
If you mean a blocking diode, NONE of the Kyocera panels have ever fitted one. The minute loss overnight is outweighed by the loss of power during the daylight hours, according to their calculations.
I suspect that the OPs regulator is either faulty or has an error in wiring.
Whilst he's finding out and (probably) replacing his regulator, I'd suggest considering an MPPT controller rather than an on/off regulator.
Click to expand...

He says its a PWM regulator.
 
The original message inferred the battery might be a 110 mAH battery, about 10% of the capacity of that of a mobile phone - i'm assuming this is an error and it's really 110 ah.

Re Pulse Width Modulation vs a Maximum Power Point Tracker. PWM Prevents the input charge falling below that of the battery - it however does not ensure the battery is getting charged - 13.0v will prevent farther battery discharge but is unlikely to put much into a discharged battery. An MMPT controller will usually ensure input voltage is at least 1v above current battery potential.
I'd suggest that at least 13.5 v is required to charge the battery - my MPPT unit is at least 1volt above system volts up to 14.4 when it goes into float.
though this doesn't entirely answer the OP's question it raises the following points:
1. Is the PV panel putting out any appreciable current (ie amps) - it may be partially shaded or just have some duff cells - to check just see what volts it goes to under no load - should be c 18.6v.
2. Is the regulator at fault - which is my suspicion - wiring it out of the circuit would be one way to find out.

However his original question, would a PV panel backfeeding flatten a 110ah battery deserves a resounding no.
 
You must log in or register to reply here.

Other threads that may be of interest

D
Solar Panel wiring question
Replies
3
Views
222
William_H
W
W
Battery suicide
Replies
17
Views
601
Refueler
Refueler

Share this page

Top