Solar Panel-Battery won't fully charge

Submitted: Friday, Jul 13, 2012 at 14:54

ThreadID: 96847 Views:3766 Replies:5 FollowUps:12

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Jimmy88

I have an 80w solar panel with a built in regulator. It keeps the aux battery topped up fine when running a fridge etc but I tried to use it to recharge the main battery after it had been flattened. It cuts out when the battery reaches around 12v. Can I temporarily rewire it (bypass the regulator) so I can fully charge the battery, even if it means being there with a multimeter and disconnecting the solar panel as soon as it reaches enough voltage to start the engine. The voltage of the panels before it reaches the regulator is around 19-21 volts. Thanks.

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Reply By: Sand Man (SA) - Friday, Jul 13, 2012 at 18:50

Friday, Jul 13, 2012 at 18:50

The "built-in" regulator supplied with the solar panels are not very good and perhaps you should consider upgrading it to a smart solar regulator which is better placed at the battery end of the circuit.

But why is the main battery being flattened? You shouldn't be running any heavy loads off it. That is what auxiliary batteries are designed for.

You should first get the main battery load tested. It may be faulty and either not reaching a full charge, or not maintaining the charge due to a faulty cell.

Bill

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Reply By: Member - Bruce C (NSW) - Friday, Jul 13, 2012 at 19:20

Friday, Jul 13, 2012 at 19:20

Hi Jimmy,
Sounds like it is your solar regulator. As Sandman has indicated
If you are still getting 20 volts or there abouts at the panel before the reg, then it seems the panels are OK. So that points to the reg.

I would get a new reg rather than direct connect.

Cheers, Bruce.

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Reply By: Member - John and Val - Friday, Jul 13, 2012 at 19:53

Friday, Jul 13, 2012 at 19:53

Jimmy,

There is something wrong with your setup. If the panels are delivering any charge, you shouldn't see such a high voltage at the panels. Also, the regulator shouldn't cut out at such a low voltage.

I'd go ahead as you propose and charge the battery directly from the panel, as I think you have a crook controller. (You'll need to disconnect the controller so it doesn't interfere.)

It will be necessary to manually monitor your battery voltage so as to disconnect the panel when that voltage gets up over about 14V. This will take quite a few hours and the battery should be able to start the engine well before it rises that far. (Assuming the battery itself is ok, and nothing is drawing charge while you are charging.)

Cheers

John

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Follow Up By: Member - Bruce C (NSW) - Friday, Jul 13, 2012 at 20:32

Friday, Jul 13, 2012 at 20:32

Hi John,

My 2 nearly new 80 watt panels put out 21 volts also (no load) and have done so since new. Measured before the regulator

The combined folding panels also produce over 10 amps from the regulator when the sun is right and the battery requires it.

They tell you in the specs that the open circuit voltage is 21.5 volts or there abouts.

Hope this helps.
Cheers, Bruce.

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Follow Up By: oldtrack123 - Friday, Jul 13, 2012 at 21:27

Friday, Jul 13, 2012 at 21:27

Hi Bruce
Of course your panels put out around 21v with NO LOAD
That's what they should be WITH NO LOAD connected
However once the battery is connected it should do either of two things depending on regulator type
[a]the input side of the regulator should drop to about 0.5<0.75V higher than the battery voltage
or [b to around 16<17V with some regs

To the OP how long are the leads that you are using to connect the panels to the battery ?
Before you rush out & buy another reg .chech that the REG really is the problem,
With the panel connected to the battery check the voltage at:-
[1] right @ the solar reg output
[2] Right @ the battery terminal POSTS not the lugs
THE ACTUAL BATTERY BATTERY POSTS

If the voltage @ the reg is more than 0.25v higher than the battery voltage you have a lead or connection problem

Peter

FollowupID: 766259

Follow Up By: oldtrack123 - Friday, Jul 13, 2012 at 21:31

Friday, Jul 13, 2012 at 21:31

Hi John
Logic indicates that if it charges the AUx battery OK .there is nothing wrong with the reg or the panels
You need to look@ what is different when you try to charge the crank battery .
Connections , perhaps even the crank battery itself.

Peter

FollowupID: 766260

Follow Up By: Member - John and Val - Saturday, Jul 14, 2012 at 09:52

Saturday, Jul 14, 2012 at 09:52

Bruce -as Peter says, the unloaded voltage of panels should be a bit over 20V. When loaded though this should be about 13 to 17V depending on the type of controller.

Peter, as you say, something has changed in moving from the aux battery to the cranking battery. From what the OP has said, the battery is the obvious change - from a partially charged one to a discharged one. There may also be a connection problem as you suggest. My preference would be to run as I suggested without the controller so as to eliminate one of the variables.

Something worth noting when working with this sort gear involving big batteries - there is a lot of energy stored in a big battery (even a flat battery) and reversing the positive and negative connections can be very expensive. Check and double check before making that last connection.

Cheers

John

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Follow Up By: Nomadic Navara - Saturday, Jul 14, 2012 at 11:20

Saturday, Jul 14, 2012 at 11:20

John, running the panel bare back may increase the charge current but I still don't think it will get up to 1A if the battery is really flat. Even though the panel is capable developing a 21 V output the low impedance of the battery will drag the voltage down to something less than the set voltage of the regulator. See my bit about a really flat battery in further down the thread. I think the problem here is the OP is expecting too much from his system. There is a good reason that the old garage battery chargers were capable of delivering 16 -18 V at high current.

PeterD
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Follow Up By: Member - John and Val - Saturday, Jul 14, 2012 at 12:52

Saturday, Jul 14, 2012 at 12:52

PeterD ,

A panel is pretty close to being a constant current source. Running direct from the panel to the battery without any controller, the panel will deliver close to short circuit current (about 5A in this case) provided the battery can accept it. If the battery is so flat that it's impedance is too high, it won't load the panel sufficiently and the panel voltage will rise towards it's open circuit voltage. This may be what the OP is experiencing, but with the controller involved the situation is very confused. I stand by my suggestion above - to bypass the controller and assume manual control. Thenthere is some chance of charging the battery, and of isolating his problem.

Cheers

John

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Follow Up By: Member - Bruce C (NSW) - Saturday, Jul 14, 2012 at 18:41

Saturday, Jul 14, 2012 at 18:41

Sorry guys, I somehow missed the bit where Jimmy said it was keeping his AUX battery, running a frig, topped up. I must be looking through scooner glasses, or something,

Cheers all,
Bruce.

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Reply By: Nomadic Navara - Saturday, Jul 14, 2012 at 01:28

Saturday, Jul 14, 2012 at 01:28

When you flatten a cranking battery they take a fair bit of power to charge them. They also will not take a lot of current until the charge level rises significantly. The only time I have monitored the charging of a deeply discharged battery I was surprised how much it took to get a charge back into it.

I was using a bench power supply capable of 10 A at OP voltages between 9 & 16 V. In the beginning I had to set the PSU at 16 V to get any sort of current into the battery. At that point the battery would only accept 1.5 A. When the charge level rose slowly until the battery would accept 10 A. I then had to keep reducing the applied voltage to keep the output current at 10 A or below.

When you commence to charge a flat battery like that the solar regulator will not be doing any regulating at all, it will be running flat out (or trying to do so.) Initially the battery terminal voltage will rise to somewhere around 12 V fairly quickly. It will then mark time with a very slow rise in voltage until you start to get some capacity back into the battery . With only 12 V at the terminals you will be only getting a small trickle of current into your battery (see my experience above where it took 16 V to get any significant current into the battery.)

Quote - "It cuts out when the battery reaches around 12v." Did the charger actually cut out or did you not wait around long enough (a few days) to see if the current would keep rising?

PeterD
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Follow Up By: Jimmy88 - Saturday, Jul 14, 2012 at 08:08

Saturday, Jul 14, 2012 at 08:08

From around 11v or so it reached 12.0-12.03v quickly then didn't increase anymore. I left it for over and hour and it didn't go up at all. I just assumed that the regulator cut the power to protect the battery from over charging but had just cut out too early. It made me think that it might be a poor quality regulator.

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Follow Up By: oldtrack123 - Saturday, Jul 14, 2012 at 13:30

Saturday, Jul 14, 2012 at 13:30

Hi Jimmy
what you have found is pretty typical of batteries when well discharged
It can take quite a time for the voltage & charge to move up
The fact that it did rise quickly seems to indicate normal operation

I would suggest you need to leave the panel connected for much much longer It probably need at least 24 hrs of full solar output to FULLY charge depending on battery size
[4DAYS with average sunlight

It is also possible that you will still find the battery is sick & just will not get up to 14+ volts [the point @ which most solar regs start to cut back]
BUT you need to give it a lot more time than an hour or two
.
Why did the battery go flat ,also could be the problem?
What else is connected to the battery?

Has the battery been heavily discharged frequently ?

Peter

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Follow Up By: oldtrack123 - Saturday, Jul 14, 2012 at 13:39

Saturday, Jul 14, 2012 at 13:39

Hi Jimmy
If it was a regulator problem ,it would react the same way with your Aux battery & cut out early

If you can get access to a mains charger that is probably the best way to get it recharged
The sooner it is fully charged the better , you could permanently loose capacity due to sulphation if it is left not fully charged for any length of time

Peter

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Follow Up By: Jimmy88 - Saturday, Jul 14, 2012 at 14:19

Saturday, Jul 14, 2012 at 14:19

I purposely wanted to drain the battery (not too much off course, just to around 11v) to test the panels out after I just bought them. Normally there isn't anything running off the main battery (apart from the car lights etc of course). I didn't want to get stuck somewhere and find out the panels won't actually charge the battery enough to start the engine.
Yeah, I will fully charge it with a mains charger. Good idea. Thanks.
I experimented by putting some charge in the main battery with a mains charger connected to a 300w inverter wired direct to the aux battery...and it seemed to work well. Would that be ok to do/cause any issues?...I'm guessing that would charge a battery just as quick as connecting the panels direct to the battery or quicker.

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Follow Up By: oldtrack123 - Sunday, Jul 15, 2012 at 14:54

Sunday, Jul 15, 2012 at 14:54

Hi Jimmy
RE:"I experimented by putting some charge in the main battery with a mains charger connected to a 300w inverter wired direct to the aux battery...and it seemed to work well. Would that be ok to do/cause any issues?...I'm guessing that would charge a battery just as quick as connecting the panels direct to the battery or quicker. ""

Yes ,there is nothing wrong with doing that in an emergency , but you need to watch how far you pull the auxiliary down
such an arrangement does have energy losses converting from 12v to 240v then back down again to the charger output voltage
these could be 10< 20%

It would need to be well over twice the size of the crank battery & fully charged to get the Crank well charged

What needs to be understood is you have to replace the Amphrs that have been used
A 80W solar panel will only give out about 4Amphrs per HOUR max in good sun

If the battery has an Amphr capacity of around 60Amphrs ,[for a typical crank battery] & is FLAT ,it will require around 80Amprs input to fully charge it

NO MATTER WHAT THE SOURCE

So your Aux battery would need to be over a 100Amp hr capacity
How quickly a mains charger does the job is dependent on IT'S Amps output

Peter

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Reply By: Member - Bucky - Saturday, Jul 14, 2012 at 06:28

Saturday, Jul 14, 2012 at 06:28

Jimmy88
Charge your cranking battery from the mains, for 2 days solid or 2 times overnight if necessary.

If the battery then comes back after you disconnect for 1 hr , with 12.4 volts or lower, then it's probably stuffed.

Pls let us know what you found if you get it sorted.

Look what I did

http://www.exploroz.com/Forum/Topic/89551/Solar_Panels_and_controller.aspx?ky=bucky+&sn=&p=%2fForum%2fDefault.aspx%3fs%3d1%26ky%3dbucky%2b%26pn%3d1

Cheers
Bucky

AnswerID: 490892