Battery charging questions - Page 7 - Fiberglass RV


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Old 11-14-2013, 05:01 PM   #85
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Raz, When I looked at the cable it appears like it 4 wires. If so it's Kelvin which should negate noise in the measurement lines. Also according the web site the monitor is supposed to measure down to .5 amps. I agree with DVM not reading the voltage drop at any distance from the shunt. Short leads and right at the shunt, I think it would depend on the DVM.
I'm not familiar with "Kelvin" other than a temperature scale. The wire they are using looks like twisted pair to me?? Is Kelvin a brand? Edit: Looked it up. 4 point probe. Got it.

When I read the Trimetric installation manual it appears that these instruments are intended for the solar industry with kilowatt arrays supplying banks of batteries. It recommends if you have a current as low as 70 amps to use the 100 amp, 100 mV shunt. Much higher than RV applications in most cases. .





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First off make up your mind is it 200' or 100' .

Second AWG 14 is .2525 ohms per 100' At 10 amps that 2.525 volts drop.

In your second post you said 200' that would about 5 volts. 200' is also long ways about 2/3 of a foot ball field.
perhaps 100 ft of cord, two conductors, 200 feet?? Raz
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Old 11-14-2013, 05:12 PM   #86
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Originally Posted by P. Raz View Post
I'm not familiar with "Kelvin" other than a temperature scale. The wire they are using looks like twisted pair to me?? Is Kelvin a brand? Edit: Looked it up. 4 probe. Got it.

When I read the Trimetric installation manual it appears that these instruments are intended for the solar industry with kilowatt arrays supplying banks of batteries. It recommends if you have a current as low as 70 amps to use the 100 amp, 100 mV shunt. Much higher than RV applications in most cases. .







perhaps 100 ft of cord, two conductors, 200 feet?? Raz
Kelvin is using 4 wires for measurement. Two wires are sense wires and the other two are measurement wires. You eliminate the wire resistance and common mode noise.

I found a bit information, but I don't think it's complete. Also I would have to see the schematic for the trimetric measurement system. Here's a bit, I had to search on "Kelvin Clip".

I can't remember when the last time I used a Kelvin Clip or Kelvin measuring system, it's been a while.
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Old 11-14-2013, 05:22 PM   #87
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Trimetric's Manual

"Which shunt should
you use?
Most systems with medium and large inverters should use a 500A
-
50 mV shunt, which will
work for systems to 400 amps maximum (4000 watts with 12 V systems and 8000 watts for 24V systems.) With this
shunt you can measure current as low as 1/10 amps. You can use a 100 A/100mV shunt with smaller systems which don't
use or charge with over 75 amps, (800 watts for 12 system, or 1600 watts for 24 volt system) or if the shunt is used only
for measuring solar or wind input with currents less than 75 amps
. This shunt has the advantage that it will show an extra
digit to the right of the decimal point, and resolve currents as low as 1/100 amp"

This is of course ± the lest 1 of least significant digit. Other than that I have no idea how accurate it would be.
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Old 11-14-2013, 05:51 PM   #88
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500amp, 50mV shunt R = 0.1 milliohms

At 1/10 amp (100 milliamps) there would be a voltage drop of 100 milliamps x 0.1 milliohms = 10 microvolts. Neat trick Raz
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Old 11-14-2013, 06:14 PM   #89
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Originally Posted by P. Raz View Post
500amp, 50mV shunt R = 0.1 milliohms

At 1/10 amp (100 milliamps) there would be a voltage drop of 100 milliamps x 0.1 milliohms = 10 microvolts. Neat trick Raz
You can measure pretty low voltages with a 4 wires and resistive bridge. (my memory is coming back). Then through an amplifier to get the voltage high enough for an A to D converter. Not that impossible.
The specs on my Fluke 87 say it's resolution is .1 mv and and .1 microamp, that's for a hand held 2 wire measurement.
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Old 11-14-2013, 11:46 PM   #90
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I just went out to the Scamp and read the Trimetric. 12.5v, 86% batt life, -.1A. I then turned on LED lights one by one. Each consumed .2A and read 1A with 5 lights on. I don't know if the -.1A is due to a phantom load, or just a calibration issue with the Trimetric or shunt contamination. When I get a chance I'll put the Fluke in series and see what it says. Just for grins I plugged in one of those cigarette lighter battery condition meters. It read 12.4v, one tenth volt lower than the Tri. I'll plug in the CTEK and let it run over night to get the battery back up.
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Old 11-14-2013, 11:55 PM   #91
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Don't forget your trimetric consumes power. It will show a negative amp reading if all of your appliances are off. If I recall correctly mine draws .03 to .04 amps. I get the extra digit on my meter with the 100 amp shunt.
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Old 11-15-2013, 12:07 AM   #92
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I plugged in the CTEK about 10 minutes ago. It has already ramped through 3 steps. First step 14.2v Tri reading -.1A Second and third step 14.3v Tri reading -.1A. The charger is obviously putting current into the battery, but the Trimetric shows the opposite. ??? I will remove the shunt and clean it when I get some time. I may just send it back to Deltec for a calibration. Then I will remount it properly protected.
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Old 11-15-2013, 12:08 AM   #93
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Don't forget your trimetric consumes power. It will show a negative amp reading if all of your appliances are off. If I recall correctly mine draws .03 to .04 amps. I get the extra digit on my meter with the 100 amp shunt.
Drew,
Is that with the meter LED turned off?
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Old 11-15-2013, 12:44 AM   #94
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That's when it's on and displaying the numbers. I'm winterized (batteries pulled out) or I'd just go and look to be sure.

I've used a few different chargers and they've always shown positive amps going in with the green charging light illuminated.
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Old 11-15-2013, 02:01 AM   #95
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Drew,
I just went out to check charging progress. After 1.5 hours it picked up just 1% to 87%. Charge voltage read 14.2 and amps still negative .1. The green charge light is not lit. I put my Fluke 337 true RMS clamp meter on the CTEK charge line and got 1.9A, So the Trimetric is probably being fooled by the shunt about 2 amps worth. I had forgotten the Fluke could read DC, so didn't think to use it previously.
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Old 11-15-2013, 05:51 AM   #96
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You can measure pretty low voltages with a 4 wires and resistive bridge. (my memory is coming back). Then through an amplifier to get the voltage high enough for an A to D converter. Not that impossible.
The specs on my Fluke 87 say it's resolution is .1 mv and and .1 microamp, that's for a hand held 2 wire measurement.
I took a second look and I'm not sure they are doing a 4 point probe measurement as suggested in the link you provided. That appears to be for impedance measurements. I think they are using two wires for shunt voltage and two wires for battery voltage and keeping them separate at the meter because the two are orders of magnitude apart. When you get yours check it out and let me know if I'm wrong . Raz
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Old 11-15-2013, 10:43 AM   #97
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Originally Posted by P. Raz View Post
I took a second look and I'm not sure they are doing a 4 point probe measurement as suggested in the link you provided. That appears to be for impedance measurements. I think they are using two wires for shunt voltage and two wires for battery voltage and keeping them separate at the meter because the two are orders of magnitude apart. When you get yours check it out and let me know if I'm wrong . Raz
You could be right. I counted 4 wires in the picture of the cable.
I'm not about to buy one. It's too easy to buy all this stuff and get into an information overload rather than enjoying the great outdoors.
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Old 11-15-2013, 11:14 AM   #98
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Drew,
I just went out to check charging progress. After 1.5 hours it picked up just 1% to 87%. Charge voltage read 14.2 and amps still negative .1. The green charge light is not lit. I put my Fluke 337 true RMS clamp meter on the CTEK charge line and got 1.9A, So the Trimetric is probably being fooled by the shunt about 2 amps worth. I had forgotten the Fluke could read DC, so didn't think to use it previously.
Russ
Just to make sure you've set it up right, did you connect your chargers negative wire to the shunt? I've seen this type of behavior if the charger was directly connected to the battery bypassing the shunt. I'd also make sure all of the smaller wires connected to the shunt are in good condition. If those are corroded or broken (they are pretty thin) it might cause an issue.

It does sound like your charger is working or you wouldn't have such a high voltage. The battery % likely won't be accurate if the meter isn't recording amps going in.

If you're sure the meter is programmed correctly and the shunt is wired according to the diagram in the manual I'd likely replace the shunt as a next step. Sounds like it might have gone bad or perhaps was a lemon to start with. With some luck it's just the shunt and not a bad meter.
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