Author Topic: PCB Meter Shunts  (Read 3791 times)

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Offline German_EE

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PCB Meter Shunts
« on: March 27, 2015, 07:32:30 pm »
Does anybody have experience or data regarding high current shunts made using FR4 PCB material? I need to make a 50A and a 100A shunt and I'm looking for alternatives to wirewound devices.
Should you find yourself in a chronically leaking boat, energy devoted to changing vessels is likely to be more productive than energy devoted to patching leaks.

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Offline dom0

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Re: PCB Meter Shunts
« Reply #1 on: March 27, 2015, 07:38:24 pm »
You probably know that, but cooper has a terrible tempco... like, 2000 times higher than good precision resistors, if I remember correctly. Another question would be PCB variance, the 35 ┬Ám cooper thickness has quite some of it according to people who measured that.
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Online SeanB

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Re: PCB Meter Shunts
« Reply #2 on: March 27, 2015, 07:50:01 pm »
You are stuck with either wirewound devices or with cutting a shunt out of some stainless steel plate. Copper board and a local temperature sensor then apply compensation scaling will work, but will lose accuracy at the high end and add an extra time constant.
 

Offline German_EE

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Re: PCB Meter Shunts
« Reply #3 on: March 27, 2015, 07:54:58 pm »
Stainless steel plate is an idea I had not thought of, thank you for that.

This is not a precision application, the meter will probably be calibrated in 5A increments so variation over temperature will not be a problem. I'm just worried about wirewound devices going open circuit and blowing up the meter movement.
Should you find yourself in a chronically leaking boat, energy devoted to changing vessels is likely to be more productive than energy devoted to patching leaks.

Warren Buffett
 

Offline dom0

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Re: PCB Meter Shunts
« Reply #4 on: March 27, 2015, 08:02:58 pm »
Oh we're talking about electromechanical meters? I've seen many shunts for those apparently made of simple copper bus bar. I guess thermal drift isn't much of an issue with +-2.5 % or higher tolerance meters anyways.
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Offline daqq

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Offline tautech

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Re: PCB Meter Shunts
« Reply #6 on: March 28, 2015, 07:04:03 am »
I have made small current shunts using several strands of Constantan and ceramic bodied screw terminal blocks. Final "trimming" can be done with a crease from sidecutters and/or a dividing trimmer across your meter.

Googleing shows there is a better alloy for shunts: Manganin.
http://en.wikipedia.org/wiki/Manganin
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Offline German_EE

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Re: PCB Meter Shunts
« Reply #7 on: March 28, 2015, 12:21:56 pm »
Success!!  Three pieces of 15mm wide clock spring each 31mm from clamp to clamp. One piece can be used to make a 50A shunt and two pieces can be used for a 100A device, adjust distance between clamps for calibration. They glow cherry red under full load but this is not a problem.

A fun way to spend a Saturday morning.
Should you find yourself in a chronically leaking boat, energy devoted to changing vessels is likely to be more productive than energy devoted to patching leaks.

Warren Buffett
 

Offline TimFox

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Re: PCB Meter Shunts
« Reply #8 on: March 28, 2015, 04:41:32 pm »
Do they get hot enough to light a cigarette?
 

Offline German_EE

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Re: PCB Meter Shunts
« Reply #9 on: March 28, 2015, 06:15:08 pm »
Probably, I have not smoked for over thirty years. As I said the portions of spring glow cherry red under full load so they are probably operating at the limit.
Should you find yourself in a chronically leaking boat, energy devoted to changing vessels is likely to be more productive than energy devoted to patching leaks.

Warren Buffett
 

Online mzzj

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Re: PCB Meter Shunts
« Reply #10 on: March 29, 2015, 09:37:39 am »
Success!!  Three pieces of 15mm wide clock spring each 31mm from clamp to clamp. One piece can be used to make a 50A shunt and two pieces can be used for a 100A device, adjust distance between clamps for calibration. They glow cherry red under full load but this is not a problem.

A fun way to spend a Saturday morning.
And you think that this will be more reliable than wirewound resistor?  ;D

I would use* something like this if I want to be cheap http://www.ebay.com/itm/Analog-Current-Meter-Divider-DC-100A-75mV-Shunt-Resistor-for-Amp-Meter-Ammeter-/161366204100?pt=LH_DefaultDomain_3&hash=item25922cdec4

* I have bunch of 50 to 600 amp shunts like this that I have kept from junkyard equipment:
http://www.thermovolt.se/index.php/products/standard-60-mv-shunts/without-socket/20-150-a-60-mv-0-5
 


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