Volt amp meter problem

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wjyates

Member

• Sep 22, 2013

• #1

I bought a volt amp meter for a project I'm working on. problem, I have no access to the - load wire only the + wire
pic attached. would it be possible to use the shunt on the + side. or replace the shunt with a current loop so I can then read current off the + side or should I just buy one that will work on the high side

 

Last edited: Sep 22, 2013

cowboybob

Well-Known Member

Most Helpful Member

• Sep 23, 2013

• #2

Is this what you are trying to accomplish?

 

dr pepper

Well-Known Member

Most Helpful Member

• Sep 23, 2013

• #3

You need to check the meter, some measure the difference in voltage accross the shunt, others from ground to the non ground side of the shunt, or maybe the + leg of the supply to the load.
Do you have a suggested wiring diagram for the meter?, is the shunt in the + or - line?, if the + then your idea may not work without extra circuitry.

 

W

wjyates

Member

• Sep 24, 2013

• #4

can you guys not see the diagram I posted. anyway it shows the shunt on the - side. but like I said I have no access to
the - wire. may have come up with my own idea. I have a sencing circuit from another project. I'll run it off a shunt from the + side and then to my meter

 

dr pepper

Well-Known Member

Most Helpful Member

• Sep 24, 2013

• #5

Yes that might work, the o/p from a differential amp amplifying the v drop across a shunt in the + side shunt can be fed to the meters i/p for a shunt that would normally be in the - side.
The i/p impedance of the meter is probably high enough for an op amp to drive.

 

W

wjyates

Member

• Sep 25, 2013

• #6

hay doc, it seems like you,re the only one paying attention. just to let you know my project now works great. with a little tweak of the output resistor on my sensing circuit it now reads within .1 of an amp + or -

thanks for your input

 

dr pepper

Well-Known Member

Most Helpful Member

• Sep 25, 2013

• #7

No problem, I'm sure theres more than just me paying attention, must be a quiet day.

0.1a isnt brilliant accuracy wise, it depends what you want to do if your motor pulls a lot of current it might not matter, a % or so is probably the best to be expected from most meters like this.