# charging without a charge controller



## Sparticle (Nov 1, 2004)

We have a skinny little solar by Solec that we think is around 50 watts. Want to use it to charge a 12 volt Marine/Dual Purpose battery without hooking up a charge controller. How long can we leave it on without damage? Thanks.


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## Jim-mi (May 15, 2002)

Depends on the state of charge of the bat when you hook it up.


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## Qhorseman (Jul 9, 2010)

Should use a charge controller for any panel above 15 watts, Northern Tool has some inexpensive ones for about $15


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## Sparticle (Nov 1, 2004)

Not sure what size charge controller I need. Looked at Northern Tool but didn't see anything for $15. Cheapest there is $30 and its a 7 amp. Will this be sufficient? Thanks folks.


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## wy_white_wolf (Oct 14, 2004)

50 watts divided by 12 volts = ~4.17A

4.17 times 1.5 (allowance for over voltage/high light conditions) = 6.25A

7 amp charge controller works about perfect. You could easily get by with a 6 amp. 

MorningStar makes decient little charge controllers. It's the one area I never suggest to crimp on as it is the heart of a solar system. If it goes bad then either you don't charge the batteries or burn everything up from over charging or over voltage.


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## 12vman (Feb 17, 2004)

Some of those old Solec's didn't go much beyond the desired battery charge voltage. The current would be regulated by the internal battery resistance. It's the voltage that boils batteries.

Can you count the cells? Can you do a voltage test in brigh sun light? (with no load connected) Might not need a controller..


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## Sparticle (Nov 1, 2004)

Hey 12vman! The panel has 33 cells. I don't have the equipment to do a voltage test. I reckon I should. Thanks.


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## mightybooboo (Feb 10, 2004)

Really should get a volt meter,even a cheapy at 10 bucks will find use.


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## barn-apart (Feb 10, 2005)

I read somewhere that a old battery in front of a good battery would act like a controller anyone heard of that?


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## 12vman (Feb 17, 2004)

Sparticle said:


> Hey 12vman! The panel has 33 cells. I don't have the equipment to do a voltage test. I reckon I should. Thanks.


33 cells @ 1/2 volt each.. 16.5 volts open circuit. A good charge voltage is around 13.6-13.8 volts. The internal resistance of the battery will hold the voltage down somewhat as long as you use the battery a little every day. I don't see any need for a charge controller myself..

By math, a 50 watt panel @ 12 volts will produce ~4.2 amps. I'd figure that old Solec will do about 3.5 amps. Get a cheepo volt meter and test the voltage every nite about dark after a few days. If it's around 12.4/12.8 volts, I'd figure it's pretty much charged.

Don't forget a blocking diode between the panel and the battery.


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## SolarGary (Sep 8, 2005)

Hi,
Cheap voltmeter:
http://www.harborfreight.com/7-function-digital-multimeter-90899.html

I'm not a big fan of Harbor Freight, but the reviews are good, and its hard to go wrong for 2 bucks 

Gary


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## Jim-mi (May 15, 2002)

Those old 33 cell panels were suppose to be self regulating . . . .not one of their better ideas.
Carefull if you use a diode. a common diode will have a 1/2 volt drop across it . . . .so you might not have enough to charge a bat enough.

Sorry but my vote is against those cheapy inaccurate meters.
In the long run they will bite you.............


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## Sparticle (Nov 1, 2004)

Well, it turns out I have 2 multi meters but they have so many different settings I don't know where to put the dial. How do use the thing?


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## Qhorseman (Jul 9, 2010)

Sorry about not getting the price right at Northern Tool, haven't looked at their solar equipment in quite awhile


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## Qhorseman (Jul 9, 2010)

SolarGary, I too would be leary of the quality of anything from Harbor Freight, but I know a guy locally that has built a complete solar system for his mobile home from them and is quite happy with it.


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