Author Topic: Voltage difference from charge source to batt terminals  (Read 1528 times)

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josephbird1

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Voltage difference from charge source to batt terminals
« on: April 11, 2009, 06:45:28 PM »
I was wondering if someone could help me solve a small problem with my wind charging arrangement.

I'm using a danb 10ft clone connected to 2 6volt 220ah batteries that are in series for 12v.


I have 2 identical digital meters that are exact in their measurements, well within the 0.1v range that i need anyway.


One is connected to the + and - of my rectifiers

and the other is connected directly to the battery terminals.


The wires coming from the + and - of the rectifiers to the batteries are 14 inches of #10 awg wire.


My question is, I monitored the mill over several hours by using a camcorder pointed at the 2 meters. The current for most of the day was 17 amps + or - an amp or 2 shown on another meter.


Now while the mill was putting out the 17amps the meter at the rectifiers showed 13.1 volts and the meter connected directly to the battery terminals showed 12.5 volts.


I'm not understanding how during charge that I would get a voltage differential of 0.6 volts through 2 #10 awg wires 14 inches in length.....

When there is no charging going on the voltages on both meters is the same.


could someone please give me an idea about why I would have a discrepency?

Is this normal and if so should I only monitor the voltage directly at the battery terminals?


Thank you.

« Last Edit: April 11, 2009, 06:45:28 PM by (unknown) »

Simen

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Re: Voltage difference from charge source to batt
« Reply #1 on: April 11, 2009, 01:10:10 PM »
With your data, you should have a drop of 0.08V.


My guess would be some not-so-good connections at the battery...

« Last Edit: April 11, 2009, 01:10:10 PM by (unknown) »
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scottsAI

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Re: Volt drop from charge source to batt terminals
« Reply #2 on: April 11, 2009, 02:14:00 PM »
josephbird1,


Where in your circuit is the amp meter?

Could be voltage drop due to amp meter.

If not, do you have a no contacting temp meter?

Run it along the wires, 17 * 0.6 = 10.2 watts, should be a noticeable temperature rise.


Have fun,

Scott Beversdorf.

« Last Edit: April 11, 2009, 02:14:00 PM by (unknown) »

josephbird1

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Re: Volt drop from charge source to batt terminals
« Reply #3 on: April 12, 2009, 10:08:20 AM »
Hi, Thanks for the replies. The amp meter is a non contact amp meter.

and all the wires were the same temperature + or - 0.5 degrees C


I cleaned the battery terminals nice and shiny and that helped a small bit. instead of the 0.6 volts difference it's now 0.4 volts difference.


What my biggest concern is that my dumpload controller that takes it's reading directly from the battery terminals will trigger at the wrong voltages since I'm off by 0.4 volts which is huge for the state of charge on the battery.

shows 13.0 volts going in on the rectifier side and only 12.6 volts at the terminals.


Which one do I believe? less than 20 amps through a #10 guage wire should certainly not drop .4v should it?


SHould I be using thicker wire?

It almost seems like the battery doesn't want the power.. 13.0 at the regulator and in 12 inches of wire I'm loosing 0.4 volts. The resistance of that wire should be around 0.0009 ohms for 12 inches.


Any ideas?


Thank you again.

« Last Edit: April 12, 2009, 10:08:20 AM by (unknown) »

scottsAI

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Re: Volt drop from charge source to batt terminals
« Reply #4 on: April 12, 2009, 10:37:37 AM »
josephbird1,


I would be concerned about 0.6v. Regardless of load dump, 5% power loss.


The gage of the wire is OK, as Simen calculated 0.08v drop... fine.


Look for another bad connection problem like you already discovered.

Measure the voltage along each wire, possibly a crimped on spade lug is in need of soldering.

Measure using one meter from one side of the wire to the other, 0.08v is measurable. Do for both wires.

Test from actual battery terminal to get all the voltages being dropped. May fine more cleaning is needed.


Have fun,

Scott Beversdorf.

« Last Edit: April 12, 2009, 10:37:37 AM by (unknown) »

Nothing40

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Re: Voltage difference from charge source to batt.
« Reply #5 on: April 14, 2009, 11:09:34 AM »
"shows 13.0 volts going in on the rectifier side and only 12.6 volts at the terminals."


Are these measurements on either side of the rectifier? 0.6-0.7V is the 'typical' voltage drop of a silicon diode.

« Last Edit: April 14, 2009, 11:09:34 AM by (unknown) »

josephbird1

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Re: Volt drop from charge source to batt terminals
« Reply #6 on: April 22, 2009, 02:11:30 PM »
Thanks for the suggestions, I did as you suggest and found no appreciable voltage drops. So I re cleaned all joints, soldered all connections ect..


When there is 0 power coming from the turbine, the voltage at the battery terminals is exactly the same... BUT when the generator is pumping power into the batteries the voltage at the rectifiers + and - terminals is always higher than the voltage directly at the battery terminals.. the higher the current going in the larger the voltage difference is.... how do charge controllers deal with this issue? I've seen as high as 0.6 volts difference no matter what I do. I've even shortened the wire going from the rectifiers to the batter bank..


Here is an exact pic of how its connected. with 0 charge current meters are identical, but during charging meter1 is always higher than meter2




If I connect a charge controller where meter1 sits then it's going to be off by up to 0.6 volts or more. as I said this effect only shows up during charging.


Any ideas?


Thanks

« Last Edit: April 22, 2009, 02:11:30 PM by (unknown) »

commanda

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Re: Volt drop from charge source to batt terminals
« Reply #7 on: April 22, 2009, 08:15:24 PM »
Are the 2 meters identical?  I'm wondering if one of them isn't reacting more to the AC ripple. What happens if you swap the 2 meters?


Amanda

« Last Edit: April 22, 2009, 08:15:24 PM by (unknown) »

josephbird1

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Re: Volt drop from charge source to batt terminals
« Reply #8 on: April 23, 2009, 08:12:17 AM »
Hi Amanda, the meters are identical and I tried swapping the meters as you suggested with the same result. The meter closest to the charge source always reads higher during charge only... I added 4 20,000uF capacitors in parallel at the rectifiers + and - (before meter1) and still no joy... I kinda figured this was an oddball since all charge controllers everywhere would experiance problems unless they referenced the battery with seperate wires tied directly to the batteries..


I know thats one solution for me but this discrepency I driving me crazy lol since I know it shouldnt be there..


Thank you for any suggetions..


Joe

« Last Edit: April 23, 2009, 08:12:17 AM by (unknown) »

ghurd

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Re: Volt drop from charge source to batt terminals
« Reply #9 on: April 23, 2009, 08:57:05 AM »
When it is pumping power, and there is a 0.6V drop, measure the voltage drop in the pos wire and neg wire.

The voltage drop has to be there somewhere.


Is the wire used?

Could be the wire is corroded inside the insulation, broken strands from too much flexing and stretching in a previous life, bend kinked stretched solid wire, etc.


I have seen corroded wire in the middle of a 250' spool.  Not all wire is completely water proof.  Moisture gets in through the insulation.


If it is not the meters or connections, the only thing left is the wire.

It is 2 x 14" of #10, cheap to change them and see what happens.


G-

« Last Edit: April 23, 2009, 08:57:05 AM by (unknown) »
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