PCB Meter Shunts - Page 1
Forum section: electronics / testgear

author: German_EE
author_rank: Super Contributor
timestamp: March 27, 2015, 07:32:30 pm
content: 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.

author: dom0
author_rank: Super Contributor
timestamp: March 27, 2015, 07:38:24 pm
content: 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 µm cooper thickness has quite some of it according to people who measured that.

author: SeanB
author_rank: Super Contributor
timestamp: March 27, 2015, 07:50:01 pm
content: 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.

author: German_EE
author_rank: Super Contributor
timestamp: March 27, 2015, 07:54:58 pm
content: 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.

author: dom0
author_rank: Super Contributor
timestamp: March 27, 2015, 08:02:58 pm
content: 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.

author: daqq
author_rank: Super Contributor
timestamp: March 27, 2015, 09:48:05 pm
content: See:http://electronicdesign.com/power/battery-board-measures-current-without-shunt-resistorhttp://www.embedded.com/design/automotive-design/4010022/Hall-effect-sensor-ASIC-integration-shrinks-current-transducers-Part-1-of-2-

author: tautech
author_rank: Super Contributor
timestamp: March 28, 2015, 07:04:03 am
content: 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

author: German_EE
author_rank: Super Contributor
timestamp: March 28, 2015, 12:21:56 pm
content: 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.

author: TimFox
author_rank: Super Contributor
timestamp: March 28, 2015, 04:41:32 pm
content: Do they get hot enough to light a cigarette?

author: German_EE
author_rank: Super Contributor
timestamp: March 28, 2015, 06:15:08 pm
content: 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.

author: mzzj
author_rank: Super Contributor
timestamp: March 29, 2015, 09:37:39 am
content: Quote from: German_EE on March 28, 2015, 12:21:56 pmAnd you think that this will be more reliable than wirewound resistor?I would use* something like this if I want to be cheaphttp://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