Shunt heating up

tazmann

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Sep 1, 2020
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Hello All
I installed a couple gauges one for input and one for output using the same shunt and it works ok but today I fired up the roof air, it pulls normally 1700 watts after the compressor kicks in and runs a bit but instead it was 1200 and the dc voltage was dropping fast as reported on the digital readout on the inverter, the watts did build to about 1400 then the inverter shut down with OL light flashing. The discharge gauge showed the voltage still up around 24.5 but amps at 45 . Started checking things out and found that the flat strap part of the shunt was heating up not where the 2/0 cable ends hook up but the strap part itself and it had warmed up in just a few minutes.
Tells me the shunts are not up to par, supposed to be 100 amp rated, at most I should have been pulling 85 amps at 24 volts.
bayite DC 6.5-100V 0-100A LCD Display is the gauge and shunt I installed. Anyone else had any problems with these?
 

RCinFLA

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Jun 21, 2020
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Shunts get hot when running high current. 100 amp,100 mV output shunt at 85 amps would be 85A^2 x 0.001 ohm = 7.2 watts

If running sinewave inverter at 85 amp average DC current, is 133.45 amp peak, or 94 amps r.m.s. , so heating will actually be 94A^2 x 0.001 ohms = 8.9 watts.
 
Last edited:

gnubie

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Sep 20, 2019
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If you suspect the shunt is responsible for voltage drop put a multimeter in voltage range across it's terminals and check. If it's millivolts thats good. If it's > 1 volt that's not good. You can also do a 2nd test by putting the meter onto the lugs on your cables. That will tell you if you have an issue with the connection between the shunt and the wire lugs. You can take that further in tracing the problem by metering on the wires themselves to see if you have an issue with the way the lugs are attached to the wires.

Basically if you are seeing unexpected voltage drop at your inverter you either have an undersized battery or you should be able to find that voltage drop across some part of your overall system.
 

tazmann

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Sep 1, 2020
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109
Thanks for the replies. will do the voltage check on the shunt, I was just going to by pass it but my cable is just a smidge to short and I am out of ends to make a longer one. The system worked fine before installing shunt
 

tazmann

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Sep 1, 2020
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109
Well I just checked the voltage across the shunt no difference, Only place I am getting any difference is at the inverter at the battery connection 2/10 of a volt less with 550 watt load. Ran the ac again and this time the watts registered about right but it still shutdown after about 5 minutes from OL. I guess it could be something with the inverter but it has been working flawless for over a month now 24/7 running fridge with occasional microwave use and it's been hot weather to boot. Only other thing that has been changed was I moved the inverter out of cabinet and mounted on wall so the cables are about 30" longer than before, inverter was getting pretty hot to the touch in the cabinet when the temps were 108 outside
 

Bob B

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Sep 21, 2019
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Seems like the cables from the battery to the inverter are fine with only .2V drop ...... but, my first rule of troubleshooting is .... what has changed .... So, I would unchange (probably not a real word) it just for troubleshooting.
 

gnubie

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Well I just checked the voltage across the shunt no difference, Only place I am getting any difference is at the inverter at the battery connection 2/10 of a volt less with 550 watt load. Ran the ac again and this time the watts registered about right but it still shutdown after about 5 minutes from OL. I guess it could be something with the inverter but it has been working flawless for over a month now 24/7 running fridge with occasional microwave use and it's been hot weather to boot. Only other thing that has been changed was I moved the inverter out of cabinet and mounted on wall so the cables are about 30" longer than before, inverter was getting pretty hot to the touch in the cabinet when the temps were 108 outside

Weren't you getting an unexpected voltage drop though which is what led you to suspect the shunt? I guess there could be a connection problem within the inverter where you can't check.
 

tazmann

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Sep 1, 2020
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109
Weren't you getting an unexpected voltage drop though which is what led you to suspect the shunt? I guess there could be a connection problem within the inverter where you can't check.
Yes the DC voltage and AC watt output on the digital screen of the inverter with the shunt getting pretty warm.
 

tazmann

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Sep 1, 2020
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109
At this point it could be a lot of possibilities. Just checking battery voltage before sun comes up bayite gauge showing 22 watt discharge that is the inverter on, step down converter on and charge controller with no loads or inputs. Depends on which volt gauge you want to go by, my newish volt tester shows 24.6 at terminal strip, inverter readout shows 24.5 and the epever charge controller shows 24.8, both bayite gauges are within .05 volts of the Epever so I am assuming about 80% capacity left so I don't think it is a battery problem but I can't rule that out ether because of the volt variance, it could be I'm not getting full capacity charge
 

tazmann

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Well it was user error Yesterday when I turned on the AC I had glanced at the meter just looking at battery state bars and the smiley face thinking it was almost at full charge, not even close and I only had 400 watts of panels hooked up with an overcast day. I hooked up another 400 watts this morning and waited till it hit 29.2 volts with the amps starting to taper off then tried it again and it worked great, still have smoky overcast skies but was getting around 18 amps input. ran the AC till the volt reading on inverter was down to 23.8 and shut it down took about 20-30 minutes . Then I found out the fridge had come on when ac was running pulling another 90 watts. Shunt didn't even warm up
 

ianganderton

Auckland, NZ
Joined
Nov 8, 2019
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Location
Auckland, New Zealand
Well it was user error Yesterday when I turned on the AC I had glanced at the meter just looking at battery state bars and the smiley face thinking it was almost at full charge, not even close and I only had 400 watts of panels hooked up with an overcast day. I hooked up another 400 watts this morning and waited till it hit 29.2 volts with the amps starting to taper off then tried it again and it worked great, still have smoky overcast skies but was getting around 18 amps input. ran the AC till the volt reading on inverter was down to 23.8 and shut it down took about 20-30 minutes . Then I found out the fridge had come on when ac was running pulling another 90 watts. Shunt didn't even warm up
Well done on finding the problem
 

Thomas Barlow

New Member
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Nov 22, 2020
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6
I was going suggest a bad wire crimp or bad connection.

Wise electrician once said "loose wires start fires!"
 
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