Ammetres & Shunts

Interesting info about voltage loss.
Not being an Auto Sparkie, I wonder is it possible to locate the shunt in the neg wire immediately prior to the neg battery terminal thus having all "return current (amps)" going through the shunt.
Will this eliminate the possibility of voltage loss in the positive wire?.

Just wondering thats all.

Regards,

Scrubby.

Its really nice to know how much current is going into the aux batteries but for reasons of simplicity I don't use a shunt. The "ammeter" is simply a millivoltmeter measuring the small voltage difference across the shunt. Why not simply measure the small voltage difference across the thick wire and fusible links between the two batteries?

I run a measuring wire from the pos terminal of each battery to a digital voltmeter (2 decimal places) in the cab. With a flick of the switch I know the voltage of each battery but also the voltage difference between the two terminals. That voltage difference is proportional to the current. So in my vehicle, I know that a 0.10 volt difference equals 5 amps going into my AGM battery in the canopy (thats what I measured with a clamp meter).

So putting it simply, if the voltage difference is not much, then the aux battery is approaching full charge which is all I want to know.

Hi Scubby

Any voltage loss will be minor but it does not matter where the shunt is connected it will still create the SAME voltage loss in the circuit.
If the shunt is in the starter circuit ,which I would strongly advise against, a by pass switch as suggested by Paul would be required
The shunt would :
[A} present a significant voltage drop in the starter motor circuit due to the very high amperage involved
[B]put both the shunt & the meter at a very high risk of burning out unless both were rated @ many hundreds of amps
BUT relying on memory to operate a switch would be very dicey

Any problem with the bypass switch could lead to the shunt carrying excessive current .
There is really little point in having it in the starter circuit
I STRONLY ADVISE AGAINST HAVING IT SO FITTED


Peter

HI Murray

Sorry ,but no way will any fuse protect a miilivolt meter if it cops 12v or any heavy excess voltage
Yes the cables can be very light & fuses are a good idea, as a normal protection of cables
Actually one of the advantages of the 4 terminal type is the meter really cannot suffer excess voltage due to bad load connections to the shunt,




RE, having the shunt in the negative lead, yes, agree that does reduce the risk of a fault to earth, however I would expect the shunt to be mounted & insulated so this could not occur no matter which line it is fitted in .


Peter