Input/output specs on charge controller????

[(unknown)]

Hello folks-

I've been reading & searching this & other forums to find my answers, to no avail.

So, here goes.

I've started setting up a small solar backup battery charging system for use in power outages & the like.  I have purchased a Northern 15w panel for initial testing & set up of the system.  The charge controller is also from Northern, a Sunforce 7a unit.  Voltages & amperage are making me crazy.

I have metered the panel @ 24.8v max @ 830 ma.  The unit is supposed to be 15w 1a output, but 24.8v @ 830 ma comes out to be 20.6 watts.  ANYway, when I connect the charge controller & measure the output at the battery side, I'm getting 23.5v @ 8.12ma!

I called Northern, & they referred me to Sunforce.  The fellow there wasn't sure of the output amperage specification, but thought I should return the unit for replacement.

Here are my concerns:  

1. The 23.5v output to the battery seems extreme to me, even though the instructions indicate the controller should reduce the panel voltage by 5-10% (my reduction was 5%).  23.5v is well over the "gassing" voltage of the cells.  Is the high voltage the problem I think it is?
   
2. What should I expect on the battery side of the controller given the 830ma going in?  I've read specs on other controllers that indicate a +/-4ma internal power usage.  That's not so bad, but losing 99% of the power produced is unacceptable!
   
   

Any help to answer my questions (or additional comments/suggestions) would be greatly appreciated!

Regards to all,

Jack

[electronbaby]

Is this for a 12v nominal system? If so, hook it up to the battery (make sure to get the right polarity) and then measure the current. Dont count on the output current and the nameplate rating of the panel to add up unless you have STC conditions. It sounds like you were measuring the controller output voltage with no battery (no load). Im assuming its not a fancy controller (no PWM). Probably just open/close circuit. Not sure though.

Maybe this helps.

[Hank]

Jack,

I'm not all that sure about your panel.

What I suspect you are measuring is open voltage (panel is not connected to anything)and I'm not sure how you are measuring the current.

The best way to measure your panel output is to connect it to a battery and measure the charging current, I think you will find that all will be okay.

Open voltage on solar panels is always higher then the intended battery voltage and will drop to battery voltage once connected to a battery.

Also, unless you are charging a small amp-hr battery you probably don't need a charge controller with such a small panel.

Hank

[(unknown)]

You gents are correct in that I'm measuring the output w/no load, i.e. not connected to the battery. When the battery (12v) is connected, I read battery voltage, IOW, charger disconnected yields the same reading.

How can I read the amperage when connected to the battery?  Last time I tried that I toasted my meter (the new one is a Sperry digital unit, & appears to be accurate).  

Is the unloaded 8+ma output of the controller NOT an issue?

Sorry for my angst guys, but my mediocre understanding of this stuff is not balancing well with my intuitive understanding and/or expectations.

I appreciate your patience...

Jack

[Volvo farmer]

Break a wire between the charge controller and the battery (either positive or negative) and put the ammeter between them. Even $3 Harbor freight digital meters have a 10A function.

Battery is like your water tank, solar panel is like your hose filling the tank. Voltage is an indication of how full your tank is, amperage is how fast the water is flowing in the hose.

Voltage (pressure)at your panel must be higher than at the battery (water tank) or the amps (water) won't flow in the right direction. That's why you're reading such high open circuit voltages. It's normal. You are also measuring short circuit amps, which is OK straight across the terminals of a puny solar panel but when you try it with a battery straight across the terminals on amps, you blow the fuse in the meter because a battery can deliver hundreds of short circuit amps and a meter can only measure ten or so.

 

[Flux]

This can all be very confusing to newcomers.

Current must be measured in a series circuit, as Volvo said you must break one of the leads and insert the ammeter in series. Voltage is simpler as you measure it across the terminals.

The power produced by the panel will be the current that flows into the battery multiplied by the battery voltage. Unfortunately it will be considerably less than the nominal panel rating. Unless you have a clever controller that matches the panel voltage to its optimum point ( depends on light and temperature) you can't hope to see the nominal rating. For small installations the losses in the clever controller would still prevent you seeing much improvement.

To make matters worse the panels are specified at a light level that you may not often see and it is also specified at a lowish temperature ( 25 deg C?). On most days when you see the specified light level it will raise the panel temperature much above this.

In real life you are going to have to live with about 13v at 800mA or about 10 W out.

Your controller will also cause a small loss and there's not much you can do about it, nothing is perfect.

I don't think the way panels are rated is unfair, but it is certainly confusing.

Flux

[(unknown)]

::sigh::

Please use the chant I've come to love:

"Owa' tobo' Biyam"  (repeat 3x)

THANK YOU for your help.  I've been doing the functional testing all wrong, getting myself all worked up over it, & even had Northern send me a new charge control unit (at no cost, I might add) because the initial one was "defective" (I'll be sending it back, w/my thanks, when it arrives).

We're in the middle of some lousy weather here (read "cloudy/stormy skies"), so I can't tell much, except when I utilized the methods you guys suggested, the readings were entirely different, & more positive.

I just wish someone in the "technical" department at the manufacturer and/or distributor had given me this insight & avoided the entire nuisance.

Kudos to you gents, & thanks for actually ANSWERING my questions.

I'll try to be a little smarter next time, really.

"Owa' tobo' Biyam"

[Hank]

Jack,

We are all learning here. Good luck with your projects.

By the way are you in New Hampshire if so where abouts. I live in MA just south of NH.

Hank

[(unknown)]

Hank-

Yeah, my southern property line is the NH/MA border; I'm due north of Fitchburg, MA.

You?

[Hank]

Jack,

I live in Haverhill a few miles east of you.

All my RE projects are located in the Berkshires at my daughters land.

Currently I have one windmill up and running sometimes (will need a repair). One old one on the the ground (single rotor iron core axial).

Several solar panels charge controllers, backup generator, etc. It's totally off grid (power lines are about 1.5 miles away).

Best not to use up to much space here Tom will kick us off.

e-mail hl_chylinski at hotmail dot com

Have a good one,

Hank