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Discussion Starter · #1 ·
I took a chance on this and bought it used for $80. It is a 2008 vintage that was in storage. It was in the box and seems to have little or no use. The guy said he never used it.

I hooked it up to my car battery tester and it shows 16v + output. The needle is max to the right on the scale, so can't really tell what it is. The instructions say it is 13 watts and 17.50 volts.

Is this a good solar setup to charge a car battery for emergency solar power?

When I hit the load switch on the battery tester it brings the volts to zero. If I find out it is 17.50 volts does that mean it is producing 13 amps? What type of electric tester should I use for checking out solar panels?


Light Building Solar power Window Solar panel


If this 14 year old panel does in fact put out the proper power, it looks like storing solar panels in the dark does not hurt them.
 

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17.50 volts doesn't mean too much.
That reading will change depending on the sun.
I Have a 1.5 watt panel that reads as much as 22+ volts.
I'd take a multi meter and measure the amps , at peak sun ideally ..... then you will know.
Harbor freight carries cheap multi meters .. at least they used to be cheap even free at times.

Amps is what you want to know which of course can then give you watts.
It will vary during the day/sun of course.
13 amps will given time depending on your sun, charge a car battery.
 

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You paid $6 per watt for that 13 watt panel. You can buy a 100 watt Renogy panel on Amazon for $100. That's $1 per watt.

On a good day you might get 1 amp at 13 volts. You can't measure amps directly across the power leads coming off the panel or you will blow the fuse in your meter. You need to measure amps through a load such as a 12 volt car headlight. At 55 watts it would pull 4.58 amps from a car battery so connected to a 13 watt solar panel it would be very dim.
 

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a battery load tester shown in the photo is not the correct meter to check output.
The tester is a battery load tester.

some handheld meters(not many) will measure up to 10 amps DC, but Lagner is correct, you will blow the meter fuse on most meters.
 

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I wouldnt trust that thing to not over charge a battery. In reality if you need one of these for seasonal storage your battery or machine isnt working properly. If your useing this to just keep a battery on a shelf topped off they make better devices for alot cheaper.
 

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Discussion Starter · #9 ·
17.50 volts doesn't mean too much.
That reading will change depending on the sun.
I Have a 1.5 watt panel that reads as much as 22+ volts.
I'd take a multi meter and measure the amps , at peak sun ideally ..... then you will know.
Harbor freight carries cheap multi meters .. at least they used to be cheap even free at times.

Amps is what you want to know which of course can then give you watts.
It will vary during the day/sun of course.
13 amps will given time depending on your sun, charge a car battery.
OK, I will look for an amp meter.
 

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Discussion Starter · #10 ·
You paid $6 per watt for that 13 watt panel. You can buy a 100 watt Renogy panel on Amazon for $100. That's $1 per watt.

On a good day you might get 1 amp at 13 volts. You can't measure amps directly across the power leads coming off the panel or you will blow the fuse in your meter. You need to measure amps through a load such as a 12 volt car headlight. At 55 watts it would pull 4.58 amps from a car battery so connected to a 13 watt solar panel it would be very dim.
Wow, I didn't do too good. The guy said he paid $200 for it. Thought it was a OK deal. Well, at least it was not too big a loss. I just looked at the size and thought it was big enough for $80. I didn't know there was such a difference in power in the panels. Well, gotta learn somewhere.
 

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Discussion Starter · #11 ·
You paid $6 per watt for that 13 watt panel. You can buy a 100 watt Renogy panel on Amazon for $100. That's $1 per watt.

On a good day you might get 1 amp at 13 volts. You can't measure amps directly across the power leads coming off the panel or you will blow the fuse in your meter. You need to measure amps through a load such as a 12 volt car headlight. At 55 watts it would pull 4.58 amps from a car battery so connected to a 13 watt solar panel it would be very dim.
That is complex stuff...for me. Know next to nothing about electronics. Will have to study it up. It said it has a diode in it for only putting out power one way if that is any benefit.
 

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Discussion Starter · #12 ·
I wouldnt trust that thing to not over charge a battery. In reality if you need one of these for seasonal storage your battery or machine isnt working properly. If your useing this to just keep a battery on a shelf topped off they make better devices for alot cheaper.
No, I was looking for a shtf device. I would run things off my acid battery and charge the battery with this.
 

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you don't need a fancy pants meter. Walmart has a clamp on ammeter for $25.


you need a charge controller. a cheap PWM controller will work fine. an MPPT controller would be better

Skeet:

reputed to be good:


the lowest price real MPPT I can find:


PWM cuts voltage off in excess of charge voltage and wastes it. MPPT maximizes power in to battery out and charges the battery in less time.
 

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It said it has a diode in it for only putting out power one way if that is any benefit.
The diode is so the battery won't back-feed the solar panel and ruin it.
You need a meter like this fitted in line to see what it is putting out where it shows watts amps and volts as well as Amps Peak and Watts Peak,
I have two of those. They have a built-in shunt which gives them the high current rating. You still need to wire it in series with a load.
you don't need a fancy pants meter. Walmart has a clamp on ammeter for $25.
Clamp-on meters only work with AC current such as your home wiring. You measure DC current by connecting your meter in series between the power source and the load. Observe polarity.

The purpose of the charge controller is so the higher (15vdc or more) voltage the panel puts out is regulated down to 13.8vdc and then when the battery is charged it goes into trickle charge or float mode. This is so the higher voltage doesn't boil the electrolyte when the battery is fully charged. Even so, you need to check the water level in the lead-acid batteries regularly.
 

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you don't need a fancy pants meter. Walmart has a clamp on ammeter for $25.


you need a charge controller. a cheap PWM controller will work fine. an MPPT controller would be better

Skeet:

reputed to be good:


the lowest price real MPPT I can find:


PWM cuts voltage off in excess of charge voltage and wastes it. MPPT maximizes power in to battery out and charges the battery in less time.
That clamp on the meter only does AC on the clamp side, it says that in the specs. You need to spend a bit more money to get a DC clamp meter.
Also I have used the blue charge controllers in the Ebay link. There listed as MPPT but really PWM and suck. Your really better off buying a used name brand MPPT..but with only 13w it's really a waste to bother with MPPT because the system.
 
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