ammeter shunts

[xmarkox]

Hello.

 I want to iuse an ammeter for with 100a capabilty.  My question is can I use two 50A shunts in parrallel to feed my ammeter that uses 75 mv inputs.  the shunts are marked 50a 75 mv.  I would buy a shunt as needed but since I have these laying around I thought this may be a solution.

Thanks in advance for your input.

Marko

[Rover]

You won't be able to measure 100A. In series they will drop 150 mv, so your meter will peg at 50A (75 mA)

[Rover]

75 mV...
sorry about that

[TomW]

You could parallel them and read one which would "more or less" show 1/2 the current flow.

Problems could be that the flow does not exactly split evenly but for a good idea of current flow it would be OK.

You would need equal cabling to each shunt and equal shunts, terminals, etc.

Not the best way but could use what you have.

I would think for our purposes in RE it is good enough.

Others may think otherwise. I would do it that way under the circumstances.

Just from here.

Tom

[xmarkox]

I think I understand what you are saying thats why I thought using the shunts in parallel would work. ie current division as in kirchoffs law.  Is my thinking bass ackwards. 

Thanks again for your reply,

Marko

[TomW]

I think I understand what you are saying thats why I thought using the shunts in parallel would work. ie current division as in kirchoffs law.  Is my thinking bass ackwards. 

Thanks again for your reply,

Marko

In theory it should work.

Variables creep in with hardware like connection integrity, etc.

Worst case is it reads high or low but with identical shunts it should be plenty good enough for tracking something like .
RE sources.

Shunts are simply low resistances. Very low so connection differences may affect the readings.

Again, I would try it myself if it was me.

[Rover]

"You could parallel them and read one which would "more or less" show 1/2 the current flow."

Yep TomW is right , but the reason I didn't mention it is that the resistance of the shunts is so light , you would have to be really carefull with the splits to parallel, and the joins . I think the deviation could be much higher than expected from the extra wires etc..

This is 4 connections (split to the shunts, join out... shunt to meter join from shunt, and split back) ....

Although you could calibrate it with another meter to get a reference..... still a pain , as you would have to do mental math each time you looked at the meter.

[ghurd]

I think it would work fine.

To reduce error, make sure the input and output wires have relatively the same length.
Like incoming wire to Shunt #1, jumper to Shunt #2.
Outgoing wire on Shunt #2, exactly identical jumper wire to Shunt #1.

G-

[xmarkox]

Thanks so much for your help. I see the problems and as i prototype and things work I can always invest in he shunt that is absolutely correct.  my only hesitation is it takes so long to get things on ebay and i don't like to wait when i'm in hot pursuit of an idea. mainly
i did not want to release the smoke in my ammeter/wattmeter/controller.

Thanks again.

You guys are great!

Marko