I'd like to wire one into my diesel glowplug system but the problem I have is the 4 glowplugs are powered by 12v to a busbar. Is there any way of connecting an ammeter to the postive side of the circuit?

 

Cheers

 

Vijay

What do you want to wire in, a volt gauge? If you want to see if a certain part is getting 12v you will need to test across the said part at both Pos & Neg terminals.

Are you testing the plugs?

I want to see what amps the glowplugs on my diesel are pulling so I can see when one stops working (ergo I see a lower amp displayed as they are joined on a busbar)

You need the meter to be in series with the circuit, so you would need to wire the 4 supply cables into one side of the meter and the other side to the bus bar. In theory you should be able to do the same on the negative path as well, as long as the meter is in series it doesnt matter.

The downside of an ammeter, as mentioned above, is that it has to be in series, positive or negative side, probably doesn't matter as long as the polarity is right. But this means that all the current is pulled through the meter itself which does make it a weak link in the chain. There may be smarter ways of doing this with a modern, non-intrusive multi-meter as a temporary solution, or you can connect it in parallel with a shunt, to reduce the reliance on the ammeter itself.

 

Do you really need this on a long-term basis or just for a bit of short-term fault finding ? Clouds of smoke on start/slower starting, is usually a good indication of when a glowplug is failing, and even with an ammeter in place you still have to work out which of the plugs has gone.

Edited August 28, 201411 yr by AndyP

Andy I think the multi meter option won't work, I'm pretty sure the clamp metres only work on ac currents. Also connecting in parallel with shunt won't work as all the current will flow through the shunt and not the Meter.

 

What sort of current would be expected in the glow plug circuits.

You're probably right about the clamp meter, but an ammeter in parallel with a shunt will measure the current that runs throiugh the shunt, that's my understanding anyway.

the 4 glowplugs are around 50 amps in total. I bought a 100a digital ammeter (panel type) with a 100a shunt but it can only be connected on the negative side of the circuit. That's no good to me as the engine/glowplugs are earthed.

Sorry Andy I was getting slightly confused, The shunt idea actually measures the volt drop across the shunt so if you were using a muti meter it would be voltage you measured and would then need to calculate the current based on the fixed resistance of the shunt and the volt drop. I forgot that for panel aplications you can get a shunt and meter that are calibrated together to display current ( though what the meter is actually reading is voltage ).

 

As for the unit Vijay has, I am still not sure why it must be on the negative side, the current will be the same at each part of the circuit. It probibly wont matter but assuming the battery supplies a constant voltage the resistance of the shunt will cause a reduction in the current flowing through the glow plugs which if they are just coils will mean them not getting as hot.

Sorry Andy I was getting slightly confused, The shunt idea actually measures the volt drop across the shunt so if you were using a muti meter it would be voltage you measured and would then need to calculate the current based on the fixed resistance of the shunt and the volt drop. I forgot that for panel aplications you can get a shunt and meter that are calibrated together to display current ( though what the meter is actually reading is voltage ).

 

As for the unit Vijay has, I am still not sure why it must be on the negative side, the current will be the same at each part of the circuit. It probibly wont matter but assuming the battery supplies a constant voltage the resistance of the shunt will cause a reduction in the current flowing through the glow plugs which if they are just coils will mean them not getting as hot.

 

Thanks for the clarification.

I really have no idea why it has to be on the negative, both ammeters worked fine on the negative side and both blew when connected to positive :(

 

Every wiring diagram I've seen suggests that it should be connected to the negative....................