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bertrv6(at)gmail.com
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Posted: Fri Nov 16, 2007 11:37 am Post subject: Hello

Hi'



My question is I hope a simple one.   My Intrument pannel is according

with Van's Plan, for my RV6A.



I have the shunt connected from the Mater Relay, to the shunt to the Main

Bus...(Battery Connection is on my Exp2bus from Control Vision)



  There are the two small screws on top of shunt, these two are connect

the wires to the Ammeter  (18 guge wires)   the Ammeter has then, on

connection + Pluss side and on- Nweg. side.



But the two screws on the shunt are always Hot....that is one I connect the

two wires one for each side,  they are always hot...



Is this Correct?  where is the one for Ground???? I do not think it should be

that way no?   But yet the Shunt is always hot on the big bolts No. 8 wire...





Your comments appreciated, before I pout my new Ammeter...



thanks



Bert



rv6a



do not archive

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Ed Anderson

Joined: 10 Jan 2006
Posts: 475

Posted: Fri Nov 16, 2007 12:58 pm Post subject: Hello

Hi Bert,



I don't have the plans in front of me and its been over a decade, but I may 

be able to help you.  I assume your shut meter is dedicated as a load meter 

and is not dual function as a voltmeter.  It probably looks something like 

this.



In which case, it sounds like you have an external shunt and YES, both ends 

of the shunt should be hot.



DO NOT GROUND ANY LEAD OF THE METER (OR SHUNT)  - That would send amps 

through the meter (for a few millionths of a second) before it destroyed the 

meter.    Here is why:



First, unlike a voltmeter which must have one end on the "hot" wire and one 

end on a "Ground" to measure the voltage potential difference between the 

hot wire and ground (the common reference) the Amp meter does not use a 

ground because it is not measuring a difference in current - so it does not 

reference it to ground.



What you do with an externally  shunted amp meter is insert the shunt in the 

power line and connect the meter's leads to each end of the shunt.  The amp 

meter needs a shunt (sometimes inside and sometimes outside the case) like a 

heavy strap/bar of metal (usually copper), one end of the shunt is attached 

to battery or source  and the other to your load (or use) end of the 

circuit.



The amp meter generally only measures a few micro or perhaps  milliamps of 

current that flows through it while the vast major of the current flows 

parallel to the meter internals through the large metal strap -the shunt. 

The scale of the meter is generally shown in amps but its actually has only 

a very small amount of current flowing through the meter housing itself. 

That amount is, however, proportional to the large current flowing through 

the shunt strap so for example - when 1 microamp is flow through the meter - 

the needle is pointing to a "1" on amp scale.  So 99.999% (or more) of the 

current flows through the strap and .001%(or less) flows through the meter 

but with the scale marked to represent the actual amps flowing through the 

shunt.



So the answer is both end of the shunt should have voltage - or be HOT.  If 

it is like the meter in the photo then it will show + or _ amps, So if you 

hook it up the wrong way, it will just have the needle pointing the wrong 

way and you can easily reverse the leads to correct it.



DO NOT GROUND ANY LEAD OF THE METER - That would send amps through the meter 

(for a millionths of a second) before it destroyed the meter.



Hope this helps.

Ed



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_________________
Ed Anderson
Rv-6A N494BW Rotary Powered
Matthews, NC
eanderson@carolina.rr.com

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