AMPMETERS AND SHUNTS?

[EDMO 1078]

Do most all auto type analog Amp meters contain an internal shunt?     How do you test one to see if it needs an external shunt? 

EdMO

Edited 9 Nov 2015 by EDMO

[Av8r_Sed 82]

You can measure the resistance across the terminals of the amp meter.  If it's really low, say 0.1 or 0.2 ohms, the meter has an internal shunt.

[EDMO 1078]

You can measure the resistance across the terminals of the amp meter.  If it's really low, say 0.1 or 0.2 ohms, the meter has an internal shunt.

What would it be if it didn't have a shunt?

Thanks,  EdMO

[nlappos 413]

An ammeter is really just a voltmeter that reads the voltage drop across a known resistance (the shunt), following OHM's Law (V=IR). The shunt is generally inside any analog meter case, but external to any digital device. If you have an analog gauge, the resistance across the poles if there is no shunt would be a few hundred ohms for the windings of the galvanometer.

[EDMO 1078]

Thanks Nick - Just got to start testing and decide which I want in my panel - I have a few.  I didn't want to smoke one and have to rewire when the IP is in the plane.  Feel better about it now.

EDMO

 

[nlappos 413]

I bought a small digital one to install this winter. It has a shunt that can mount on the firewall (inside a plastic box to prevent shorts!)  I checked it out and it worked quite well, darned accurate. 

Here is the Amazon listing: http://www.amazon.com/gp/product/B00GJKNN40?psc=1&redirect=true&ref_=oh_aui_search_detailpage

[EDMO 1078]

I looked at several of those on ebay - bought voltmeter that plugs in the lighter socket to check the battery drain on my truck - seems to work good.

I have a Dayton (?) Whatever, 1" round aircraft type digital voltmeter for the plane, and already have the 2" round hole for the ammeter - but maybe could use that hole for something else.

Thanks again,  EdMO

[Knuckledragger 135]

An ammeter is really just a voltmeter that reads the voltage drop across a known resistance (the shunt), following OHM's Law (V=IR). The shunt is generally inside any analog meter case, but external to any digital device. If you have an analog gauge, the resistance across the poles if there is no shunt would be a few hundred ohms for the windings of the galvanometer.

takes me back to B Dub'l E :)

[RobS 52]

Nick,

Looks like a good unit and at that price it wouldn't hurt too bad if it did go up in smoke.  How do plan on wiring it up to measure the total load of your plane?

[nlappos 413]

Rob, That is a good question. I haven't installed it yet, but I intend to have all my extra my avionics loads on it. I have already installed a small fuse box on the firewall, and brought a clean power and ground to it, picked off after the starter and battery charge line. I then ran this master power thru a new panel switch so I can turn it off during starting so no starter voltage spikes go through my extra things. I intend to have the shunt as part of the input to that fuse box so the ammeter will read most of the loads on the aircraft, except the starter.

[RobS 52]

Sounds like a good plan. Thanks.