How to wire an Amp meter?

[Seah0rse]

Some while ago I bought this amp meter on Ebay. As it came with no instructions I am unsure how and where to wire it. From what I have found out, it seems I need a Shunt and that it should be fitted to the 'low side'. I guess I will have to choose whether to measure charge or discharge too. There are also two bare wires, one with a bolt and one soldered to the casing on the back. What are they for? Presumably the casing one is earth but as there appears to be no internal illumination I am lost on the bolted one.

Thanks for advice

 

[Bassplayer]

An ammeter has to be wired in series with a supply line. Most of them that can read high amperages will need a shunt. The problem is that all ammeters are different! You may need to do some research to find the correct one.
Why a shunt? Because the meter will only cope with a few amps, so the shunt will take most of the current, but because it runs in parallel the current readeing will be correct, assuming the shunt is the correct one.
I personally hate ammeters as they can and do fail, leaving you with no electrics. Whereas a voltmeter doesn't interfere with things.
If you really need to know current consumption, I would use a clamp-on inductive ammeter for checking.
Hope this helps a little.

 

[davidej]

I think that this one has an internal shunt. That is why it has such large terminals. Thus you have to wire it directly into the boats wiring.

Assuming that you don't want to measure the starter motor draw or the alternator output (which I think would be impractical with this type of meter), I would wire it into the common negative which feeds the busbar behind the switch panel.

This would show you the current draw on the service battery - but not the amount that was being replaced by the alternator.

It it was mine - I think I would re-sell it and buy a proper one which will show a net draw and a percentage of capacity used.

 

[nigelmercier]

Honestly? Just use it for testing purposes. It isn't really suitable for being installed.

 

[vyv_cox]

Honestly? Just use it for testing purposes. It isn't really suitable for being installed.

I agree. Far better to buy one of the combined amp/volt meters sold on Ebay from Hong Kong. They are digital, show positive and negative currents and will show volts at the press of a button. Around £25 for the meter and shunt, consumption is minimal, LCD display. I have two, useful and reliable.

 

[Seah0rse]

Honestly? Just use it for testing purposes. It isn't really suitable for being installed.

Fair enough! I accept that.

 

[VicS]

Nice to come by useful bit of kit but I agree with the above thsi is really not suitable


Get you self a nice -60 to + 60 amp or similar and wire it in so so that it shows both charging and discharging currents but excludes the starter motor current.

If you are prepared to locate it near the battery then you do not need one with a shunt.

It you want to locate it on a instrument/switch panel then you will need one with a shunt.

It easy to say all this but it may not be quite so straightforward in practice

Take a look at the section on instruments in the boat electrical notes

at http://www.espares.co.uk/

 

[nigelmercier]

really not suitable...

But we know who to ask if we need to measure 300A!