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  #1  
Old 01-31-2014
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Solar battery charger showing 19 volts?

I know nothing about this charger, it came with my boat. It's old and small and raggedy looking and falling apart at the seams (literally). I didn't expect it to work, and hesitated to hook it up to my battery for fear it might short it out and kill it.

Well. Was I surprised. I hooked it up to a multimeter and got almost 20 volts from it - and today is overcast!

So my question is, is it even safe to use? I'm an electrical dufus. Am I even testing it properly?





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Old 01-31-2014
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Re: Solar battery charger showing 19 volts?

it works, but not in a way that I would count on for my boat....it is not regulated for the use you want.

You can search the web for a DC to DC converter/regulator circuit to augment the panel...

that being said, it would not be on my boat as a battery charger..as is.
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Old 01-31-2014
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Re: Solar battery charger showing 19 volts?

You are testing it with no load apart from the meter, i.e. effectively open circuit. The specs (second photo) indicate it might produce uo top 23,8v in this condition. You're getting just uner 20v on an an overcast day. Seems OK.

In UK these small panels are often used with no regulator, just connected direct to a 12v battery. They work fine. Check this forum if you want to be convinced 5w solar panel

Hope this helps. It has reminded me that my 60W panel and regulator need to be removed from under the bunk and connected up, so thanks for that!

Andrew
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Old 01-31-2014
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Re: Solar battery charger showing 19 volts?

It's working good! Re sew/seal the edges and use it. I have 4 Uni-Solar 32 W panels and love them. Easy to store and use and bullet proof.

The only thing you need to consider is battery bank size. If you have a large(ish) bank, connect it direct. If only one small battery, get a small controller.

I can't remember the panel size to battery equation just now, but I am sure some one will jump in. AND, like was said, do a search.

Greg
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Old 01-31-2014
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Re: Solar battery charger showing 19 volts?

Quote:
Originally Posted by Andrew Thompson View Post
You are testing it with no load apart from the meter, i.e. effectively open circuit. The specs (second photo) indicate it might produce uo top 23,8v in this condition. You're getting just uner 20v on an an overcast day. Seems OK.

In UK these small panels are often used with no regulator, just connected direct to a 12v battery. They work fine. Check this forum if you want to be convinced 5w solar panel

Hope this helps. It has reminded me that my 60W panel and regulator need to be removed from under the bunk and connected up, so thanks for that!

Andrew
Good reply. Yep, that's open-circuit (unloaded) voltage; the PV panels on our house, nominally 24VDC, run upwards of 39.5V open circuit. Attach them to some thirsty batteries, PV voltage at the charge controller drops to around 32VDC.

5W is near the upper limit I'd want for an unregulated charger; it prolly won't overcharge the battery, but it can cause excessive water loss, which will kill it just as dead.
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Old 02-01-2014
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Re: Solar battery charger showing 19 volts?

I would be very careful connecting any solar panel to a battery or batteries without a controller. This link - first post - by Mainesail explains in detail the damage that is possible.
Do I Need A Solar Charge Controller ?? - SailboatOwners.com
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Old 02-02-2014
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Re: Solar battery charger showing 19 volts?

Notice that on the spec sheet it says "23.8 open circuit voltage" The panel is probably working as designed, your voltage reading is low but it doesn't seem to be in bright sunlight.
This small panel can be connected directly to a battery of 100 amp hours or more but a charge controller would still be desireable.
(Check battery voltage without the panel connected and then with it connected in bright sunlight. The voltage should be higher when connected but with that size on panel it may be so slight as to be hard to detect.)
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Last edited by norahs arc; 02-02-2014 at 09:55 AM.
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Old 02-02-2014
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Re: Solar battery charger showing 19 volts?

if your solar panel is permanetnly attached to the battery there is a slim risk the battery will boil. Not fun.

Most likely when you attach the panel to the battery, the voltage will go down to something close to the battery voltage (.. as it was before you attached). this is hopefully ~12.5 V. Slowly, as the panel is a small one, voltage will increase.
Maintenance charge voltage is in the range 13.5 - 13.8 V (about, let's not go to deep here). It is OK as long is you are not exceeding this.

Fast charge voltage is ~14.5 V. Above that is certainly not good at all. Here ae are talking boiling.

With your small panel, and a battery of ? 100 Ah? 75 Ah? there should not be any risk to have a semi-permanent attachent, but then I am speaking from experience of a very dark country (but not in the summers ). In any case, I would not leave the panel attached for moths without monitoring now and then.

Using a regulator (which I do, but then I have close to 100 W of panels) consumes some of the energy. Unavoildable. Small and cheap ones are close to worthless; I had one such, wasted $150 ...
So either you get a good one, which is likely to cost, or you live happily with what you have and keep an eye on things.

Another view: PO seems to have used it intensively.

/J
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Old 02-02-2014
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Re: Solar battery charger showing 19 volts?

Isn't the meter showing: negative 19 volts?
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Old 02-02-2014
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Re: Solar battery charger showing 19 volts?

Quote:
Originally Posted by Froggy View Post
Isn't the meter showing: negative 19 volts?
If the leads of a digital meter are the wrong way around the reading is negative. With an analog meter you don't get a reading.
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