Solar panel - overcharging question

Submitted: Tuesday, Jun 14, 2005 at 12:34
ThreadID: 23849 Views:3186 Replies:10 FollowUps:7
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Hi all :)

Just wondering what a couple of knowledgeable people here might be able to advise me on in regards to a solar panel setup.

We want to setup a simple panel (say 50 or 60 watts) to keep a 250 AHr battery charged for weekend use - about twice a month. We'd be using the battery to power a 500watt PSW inverter to run a couple of 40watt lights and a couple of chargers - one for phone, one for laptop. On occaision we'd be running a 400watt drill for maybe 1/2 hour per day - 2 days at a time. We figure that our total consumption in kilowatt-hours won't exceed what the 250 AHr battery will give us.

My question: If we leave this set up permanently down there on our property, and don't use it at all for several weeks on end, is the solar panel/regulator going to "overcharge" the battery? We aren't there to use the accumulated power all the time, so is this going to harm the battery if just left alone for weeks or months on end without being discharged at all?

Cheers and TIA :)
Chris
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Reply By: Shaker - Tuesday, Jun 14, 2005 at 12:42

Tuesday, Jun 14, 2005 at 12:42
Simple answer is yes!
You will need to fit a relatively cheap diode or regulator.
AnswerID: 115693

Follow Up By: Member - Chrispy (NSW) - Tuesday, Jun 14, 2005 at 12:57

Tuesday, Jun 14, 2005 at 12:57
Thanks Shaker

I mentioned that the panel has a "regulator" as part of it, so do some "regulators" allow for my scenario and others not?

Are there any circuit diagrams that you know of in regards to the diode installation? I can't imagine that it would be anything more than inline (the correct way around of course) with the output of the regulator...

Cheers
Chris
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Reply By: techie - Tuesday, Jun 14, 2005 at 13:13

Tuesday, Jun 14, 2005 at 13:13
Think of your battery as a rainwater tank and the solar panel as the rain.
(The brighter the sun the greater the outpou from the solar panel.)
The more rain the more the tank fills.
You don't want the tank to overflow - overcharge the battery.
By fitting a regulator you turn the water (electricity) off to the tank (battery) when it is full (charged).
If the battery is overcharged it evaporates the acid.
Regards
AnswerID: 115704

Follow Up By: Member - Chrispy (NSW) - Tuesday, Jun 14, 2005 at 13:33

Tuesday, Jun 14, 2005 at 13:33
Thanks for the entertaining reply :)

I understand the concept, but I guess what I was asking was do some regulators simply regulate line voltage (to compensate when very bright sunny conditions exist) so as not to apply an over-voltage to the battery and others actually "know" when a full charge condition exists and then kill the supply from the panel until the battery requires to be charged again?
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Reply By: techie - Tuesday, Jun 14, 2005 at 13:57

Tuesday, Jun 14, 2005 at 13:57
Think of it as a switch - as long as the voltage on the output is below a certain level, the regulator will let electricity through.
Once the voltage indicates a charged battery, the regulator either turns off until the charge reduces or will regulate the current tomaintain the charge.

The absolute basic you need is a 7812K regulator for 12V
or LM388K (with a couple of resistors) for a variable regulator. both probably avail from dick smith.
Regards
AnswerID: 115710

Follow Up By: Member - Chrispy (NSW) - Tuesday, Jun 14, 2005 at 14:01

Tuesday, Jun 14, 2005 at 14:01
Cheers and thanks mate. Will look these up.

Ta
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Follow Up By: V8troopie - Tuesday, Jun 14, 2005 at 17:08

Tuesday, Jun 14, 2005 at 17:08
A simple 12V regulator (7812K) will never charge the battery, you need at least 13.6V coming out of the regulator.
Much better to spend a little extra and get a "proper" 3 stage regulator, designed for solar panels. The 10amp version would do for a 60w panel and it would charge the battery at the optimum rate for long battery life. once it senses the battry is full it provides a small trickle charge to make up for battery losses.

I had tinkered with home made solar regulators years ago when commercial ones were rare and expensive, I would not think of building one nowadays.

Klaus
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Follow Up By: Mainey (WA) - Tuesday, Jun 14, 2005 at 22:55

Tuesday, Jun 14, 2005 at 22:55
Yes
V8troopie, has said it right.
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Reply By: Member - Jeff M (WA) - Tuesday, Jun 14, 2005 at 14:07

Tuesday, Jun 14, 2005 at 14:07
A 60 watt pannel probally would overcharge a 250amp hour battery in summer. A simple 3 stage Regulator would do the trick. The regulator you've got now might even be that so you probally don't have to worry.
AnswerID: 115712

Reply By: Member - Jimbo (VIC) - Tuesday, Jun 14, 2005 at 18:07

Tuesday, Jun 14, 2005 at 18:07
Beware of cheapie regulators. I tried one and found it was leaking charge back into the panel at night. I now use a Morningstar 10 amp, cost around $110.

Cheers,

Jim.
AnswerID: 115745

Reply By: Mainey (WA) - Tuesday, Jun 14, 2005 at 18:12

Tuesday, Jun 14, 2005 at 18:12
Do you presently have a a regulator?
does it have any specifications written on it?
AnswerID: 115748

Follow Up By: Member - Chrispy (NSW) - Tuesday, Jun 14, 2005 at 18:19

Tuesday, Jun 14, 2005 at 18:19
No Mainey - I don't yet have one. I suppose I was posing the questions here before jumpin in....

Any recommendations?
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FollowupID: 371349

Follow Up By: Mainey (WA) - Tuesday, Jun 14, 2005 at 22:46

Tuesday, Jun 14, 2005 at 22:46
Any recommendations ???
yes,
for what it's worth I use a German made Steca three stage regulator with pwm.
The Steca model shown by 'porlsprado' is different to my own, however it may have similar mechanical specifications, I opted to get one with the visual display window, so I could actually see what was happening with the solar system.... $225.
I can see;
amps produced at the solar panel
amps sent to the battery system, most often different numbers
voltage of the batteries
% of charge of the batteries
amps going to the Fridge
amps total that have gone to the fridge during the day/week
deep discharge voltage warnings

But you don’t need to see all of those numbers if you are not interested in the overall performance of the solar system, it was my choice, and does not mean it is best.
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FollowupID: 371386

Reply By: angler - Tuesday, Jun 14, 2005 at 21:08

Tuesday, Jun 14, 2005 at 21:08
I use one that I purchased fromJaycar. It's a 20 amp version however they do have a lower rated one. They work really well and actually switch off when a preset voltage is reached. Mine was set to 14.1 Volts and thats about right for most applications.
It checks every 20 minutes or so if more charging is needed.After hours it turns off completely to Prevent any discharge. I am very happy with the regulator.

AnswerID: 115777

Reply By: porlsprado - Tuesday, Jun 14, 2005 at 21:12

Tuesday, Jun 14, 2005 at 21:12
I use this for my 2 x 40w panels. Hasn't failed and seems cheap but approved by the World Bank for development projects so i believe reasonably robust.

http://www.solazone.com.au/Regulators.htm#Stecca

Other places do sell them this was just the first one i found as a link.

Porl
AnswerID: 115780

Reply By: 4X4Treker - Tuesday, Jun 14, 2005 at 21:23

Tuesday, Jun 14, 2005 at 21:23
I am using both the 20amp and 5amp regulators from Jaycar Electronics on two different applications and they both work great, the 5amp is OK for a 60 watt panel and does all the right things (shuts off when battery charged and stops loss of charge at night into panel) One Installation that I am using is in the Flinders Ranges Sth Aus and we only go there once or twice a month and all has been working OK now for twelve months, one other advantage with the Jaycar regulators is that they have LED indications to show what is happening.
5amp is about $26.00 and 20amp is about $65.00

Cheers
Treker
AnswerID: 115782

Reply By: Member - Collyn R (WA) - Wednesday, Jun 15, 2005 at 08:56

Wednesday, Jun 15, 2005 at 08:56
Most solar modules have 36 cells and produce 17-20 volts. These must have an external solar regulator to ensure the battery is adequately charged but not overcharged. The most commonly used in Oz are probably the Plasmatronic range and these cost from $75 - $600.

For the purposes of the system in this thread the basic regulator unit will do. As long as that regulator is fitted the system may be left on permanent charge - subject only to regulator topping up the battery with distilled water. The more costly units have monitoring facilities but may be overkill for this use.

There are also so-called 'self-regulating' solar modules. But their name is misleading. The modules have 33 cells and produce a lower voltage output. They are more or less OK in temperate climates (or where a very small module is used to charge a very large battery) but in Oz they have a tendency to either undercharge or overcharge. Not recommended!

As a matter of hopeful interest (if I may be forgiven thbis small plug) all this is covered in depth in my new 'The Camper Trailer Book' - available around September.
Trust this helps.
Collyn Rivers
AnswerID: 115830

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