# Question on solar battery charging, please help



## sideKahr (Oct 15, 2014)

My tiny 2-battery backup system is working fine. Charging off the mains shows 14.6 V at the battery terminals, and results in a good 13.0 V charge on my AGMs. I can actually wash clothes with it.

But charging with my new solar panel shows only 13.3 V at the battery terminals, even on a cloudless day at noon. The panel seems to be okay, reading 6.1 amps at the charge controller, okay for a 100 watt panel I guess. The 30 foot cable run into the house seems to be causing some serious voltage drop, even though I'm running #8 AWG wire.

My question is: do you think I can fool the charge controller into supplying more voltage by cooling the battery temperature compensation probe? Maybe burying the probe in shaded earth, or immersing it in cold water?

This may be a crazy idea, I'm new at this.


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## dwight55 (Nov 9, 2012)

1st question, sideKahr, . . . that there #8 awg you used, . . . is it solid wire or stranded????

If it is solid, . . . it is "possibly" your problem, as solid wire has a greater resistance than stranded, . . . and even though you are only going 30 feet, . . . you've only got 13 volts pushing that, . . . if you had one hundred and 13, . . . it would not matter.

Whatever you do, . . . don't go trying to fool the electronics. They are there for a purpose, . . . remember the old saying: "It's not nice to fool mother nature"??, . . . same goes for electricity and especially electronics.

May God bless,
Dwight


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## Back Pack Hack (Sep 15, 2016)

dwight55 said:


> .......... as solid wire has a greater resistance than stranded, . . . ...........


Since when?


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## inceptor (Nov 19, 2012)

Here's what I found.

Solid vs Stranded Wires


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## Back Pack Hack (Sep 15, 2016)

inceptor said:


> Here's what I found.
> 
> Solid vs Stranded Wires





> A stranded wire will have higher resistance than a solid wire of the same diameter since the cross-section of the stranded wire is not the same size.


So which is it? Stranded or solid has more resistance?



> than a solid wire *of the same diameter *since the cross-section of the *stranded wire is not the same size*.


So let's compare apples to apples, shall we?

10ga solid has the same CSA as 10ga stranded, and the latter is merely larger in diameter to make up for the gaps between the conductors.


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## paraquack (Mar 1, 2013)

Quoting Solid vs Stranded wires "At *high frequencies*, current travels near the surface of the wire because of the skin effect, resulting in power loss over the conductive wire. Stranded wire might seem to reduce this effect, since the total surface area of the strands is greater than the surface area of the equivalent solid wire."
Since the term DC is used to refer to power systems that use only one polarity of voltage or current, and refer to the constant, zero-frequency.

So I don't understand their thought about Sold vs Stranded wire.
Need an explanation please.


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## dwight55 (Nov 9, 2012)

Back Pack Hack said:


> Since when?


Well, . . . since 1964, best I recollect, . . . that was the official training I and all the others received in Electrician's Mate instruction in Class A school at Great Lakes, Illinois.

To bolster the teaching, . . . ALL, . . . each and every one of the battery cables I worked with for 4 1/2 years in the Navy and 8 more years in the USNR, . . . they were ALL very finely stranded.

The rationale I was told was simply that the current tended to flow closer to the skin of the wire, . . . and since finely stranded wire had a much greater surface skin area, it tended to have lesser resistance to the current flow than did a solid wire that had the same overall cross sectional area.

We also tested it with multi-meters as part of our lab, . . . and at least the pieces we used in the lab, . . . proved the theory correct.

Anyone wants to call the Navy wrong, . . . it's your ball game, . . . jump on it. But go out and see for yourself on the battery cables of your car, boat, truck, plane, generator, 4 wheeler, motorcycle, . . . doubt seriously if any of you will find a solid wire there.

May God bless,
Dwight


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## csi-tech (Apr 13, 2013)

I am using Copper clad aluminum 8 gauge wire to go between my controller and my battery bank. It's only 3'. There was less resistance and higher efficiency from the lower strand count wires that I replaced because of corrosion. Going back to battery cables.


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## inceptor (Nov 19, 2012)

Back Pack Hack said:


> So which is it? Stranded or solid has more resistance?
> 
> So let's compare apples to apples, shall we?
> 
> 10ga solid has the same CSA as 10ga stranded, and the latter is merely larger in diameter to make up for the gaps between the conductors.


When I need information I try to go to a valid source, in this case a manufacturer. I'm sure you are smarter than them though. I would continue this debate with them.


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## Back Pack Hack (Sep 15, 2016)

dwight55 said:


> ............ But go out and see for yourself on the battery cables of your car, boat, truck, plane, generator, 4 wheeler, motorcycle, . . . doubt seriously if any of you will find a solid wire there.
> 
> May God bless,
> Dwight


Uh.... because of *VIBRATION.*........... stranded wire is used.

You might want to go back to school and learn about skin effect and frequency........ the latter of which does not exist in DC circuits.

I'm sure 99.99999% of Americans also believe George Washington was the first president of the US.


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## inceptor (Nov 19, 2012)

Back Pack Hack said:


> I'm sure 99.99999% of Americans also believe George Washington was the first president of the US.


I thought you were. Am I wrong?

I also figure you led George Soros, Bill Gates and Warren Buffet to their riches. I hope you at least got a cut from the action.


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## dwight55 (Nov 9, 2012)

Back Pack Hack said:


> Uh.... because of *VIBRATION.*........... stranded wire is used.
> 
> You might want to go back to school and learn about skin effect and frequency........ the latter of which does not exist in DC circuits.
> 
> I'm sure 99.99999% of Americans also believe George Washington was the first president of the US.


You had your teaching, . . . I had mine.

And mine is fully documented by the library of congress among others.

Yours??? Sounds like something from Wikipedia.

Mine has served me well for 50+ years, . . . maybe the "new" instruction you received will do you well for 50 years, . . . maybe not.

At least it served me well enough to be able to make a comfortable living for myself and my wife and family.

May God bless,
Dwight


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## Back Pack Hack (Sep 15, 2016)

inceptor said:


> I thought you were. Am I wrong?
> 
> I also figure you led George Soros, Bill Gates and Warren Buffet to their riches. I hope you at least got a cut from the action.


Ah, yes. The classical "I don't have a leg to stand on, so I'll resort to personal attacks" ploy. Works wonders on the elementary school playground and PeeWee Herman movies.


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## Back Pack Hack (Sep 15, 2016)

dwight55 said:


> You had your teaching, . . . I had mine.
> 
> And mine is fully documented by the library of congress among others.
> 
> ...


Believe what you wish.

I guess the National Electrical Code is incorrect as well.


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## inceptor (Nov 19, 2012)

Back Pack Hack said:


> Ah, yes. The classical "I don't have a leg to stand on, so I'll resort to personal attacks" ploy. Works wonders on the elementary school playground and PeeWee Herman movies.


No, I'm just awed by your superior intellect as I should be.


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## Back Pack Hack (Sep 15, 2016)

inceptor said:


> No, I'm just awed by your superior intellect as I should be.


Keep doubling down. Some day, it'll pay.


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## inceptor (Nov 19, 2012)

@Back Pack Hack It figures you would be a fan of Pee-wee Herman.


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## Back Pack Hack (Sep 15, 2016)

inceptor said:


> @*Back Pack Hack* It figures you would be a fan of Pee-wee Herman.


Another double down! You're on a run!


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## Mad Trapper (Feb 12, 2014)

sideKahr said:


> My tiny 2-battery backup system is working fine. Charging off the mains shows 14.6 V at the battery terminals, and results in a good 13.0 V charge on my AGMs. I can actually wash clothes with it.
> 
> But charging with my new solar panel shows only 13.3 V at the battery terminals, even on a cloudless day at noon. The panel seems to be okay, reading 6.1 amps at the charge controller, okay for a 100 watt panel I guess. The 30 foot cable run into the house seems to be causing some serious voltage drop, even though I'm running #8 AWG wire.
> 
> ...


See if you can find some used cables from an arc welder.


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## MaterielGeneral (Jan 27, 2015)

Back Pack Hack said:


> You might want to go back to school
> I'm sure 99.99999% of Americans also believe George Washington was the first president of the US.


I haven't been on much lately because I have been busy and I might be reading this wrong but it really sounds like your a dick. I noticed other threads your kind of a dick and it suprises me because your an older guy and so...apparently your one of those old guys that are just a dick.


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## Chiefster23 (Feb 5, 2016)

SideKahr. With the system in operation, measure the voltage at the output of the solar panels. Then measure the voltage at the input to the charge controller. That will tell you the actual voltage drop across your wires. Try to do this on a cloudless day so your results aren't screwed up by a passing cloud.


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## 8301 (Nov 29, 2014)

dwight55 said:


> 1st question, sideKahr, . . . that there #8 awg you used, . . . is it solid wire or stranded????
> 
> If it is solid, . . . it is "possibly" your problem, as solid wire has a greater resistance than stranded, . . . and even though you are only going 30 feet, . . . you've only got 13 volts pushing that, . . . if you had one hundred and 13, . . . it would not matter.
> 
> ...


Since electricity mostly runs on the outer part of a wire strand Dwight is correct in saying that stranded wire will have less resistance to current flow but in this case using #8 wire with such low amperages I doubt you'd get much benefit by using stranded wire.


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## 8301 (Nov 29, 2014)

sideKahr said:


> My tiny 2-battery backup system is working fine. Charging off the mains shows 14.6 V at the battery terminals, and results in a good 13.0 V charge on my AGMs. I can actually wash clothes with it.
> 
> But charging with my new solar panel shows only 13.3 V at the battery terminals, even on a cloudless day at noon. The panel seems to be okay, reading 6.1 amps at the charge controller, okay for a 100 watt panel I guess. The 30 foot cable run into the house seems to be causing some serious voltage drop, even though I'm running #8 AWG wire.


When a battery isn't fully charged the charge controller gives it all the power it can and the volts are below the desired "charging voltage" as the drained batteries suck the voltage down. (bulk stage of charging). The deeper the battery is discharged and the amount of solar power you are feeding the batteries will determine how long this "Bulk" charging will go on. If you tell me your total solar panel rated wattage is and your battery amp hour rating I can tell you your C rate. It sounds like your C rate is a little low while your mains provided plenty of power for faster battery charging, or you batteries are simply more discharged this time..

As the battery becomes more charged the volts slowly rise until the battery is about 85-90% charged and the voltage gets to the desired absorb voltage (around 14.7v). At that point the controller will reduce the amperage it passes through to the battery to maintain the desired Absorb voltage for the set time (roughly 3 hrs). After that the battery will be full or nearly full and the controller will then go into the 3rd stage of charging called Float. In Float the controller will do it's best to maintain your battery at about 13.6v keeping them topped off and allowing a slight current to assist in balancing the cells. Keep in mind that during the hard charging portion the cells may have charged slightly unevenly and Float will help them balance out a bit for a few hours until the sun goes down.

If you have lead acid batteries using a hydrometer occasionally to get a accurate measurement of the SOC (state of charge) of each cell allowing you to fine tune your controller settings to maximize battery life (this assumes you controller can be adjusted) but with those AGM batteries you've that isn't an option.


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## 8301 (Nov 29, 2014)

sideKahr said:


> My question is: do you think I can fool the charge controller into supplying more voltage by cooling the battery temperature compensation probe? Maybe burying the probe in shaded earth, or immersing it in cold water?
> 
> This may be a crazy idea, I'm new at this.


The proper charging voltage is related to temperature with a battery temperature of 80 being the standard temperature charge controllers use. Let me give you an example using my 48v battery bank.

When the battery is 80 degrees I want my absorb voltage to be 59.2v. Trial and error with SG testing and the battery manufactures suggestions helped me arrive at this as being the correct absorb voltage with a 3 1/2 hr absorb for my batteries and I make tiny adjustments to these numbers occasionally.

When the batteries have warmed up to 90 degrees the temperature compensated controller will drop the desired absorb voltage down to 58.5v.
In the winter and the batteries are 60 degrees the temperature compensated controller will raise the desired absorb voltage to 60.6v.

Do not try to "fake out" the temperature probe. As I suggested in the previous post I think your charging battery voltage is low because your batteries are still in the "Bulk" phase of charging.


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## sideKahr (Oct 15, 2014)

Thanks everyone for your explanations and suggestions. I'll have some time tomorrow to do some experimentation; I hope we have some sun.

This is fun!


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