Ammeter

[plainsman]

Have been reading on the forum of the usefulness of an ammeter. Seen a few on sale but not sure what scale range i need. 60-60, 80-80 seem to be common. My alternator is rated at 90 amp 12v. What size ammeter and shunt do I need? Prefer a cream faced analog type to match other instruments (Temp, volts) Advice on type and possible source much appreciated.

[nicknorman]

Have been reading on the forum of the usefulness of an ammeter. Seen a few on sale but not sure what scale range i need. 60-60, 80-80 seem to be common. My alternator is rated at 90 amp 12v. What size ammeter and shunt do I need? Prefer a cream faced analog type to match other instruments (Temp, volts) Advice on type and possible source much appreciated.

The ammeter should be able to read correctly at the maximum normal load, so with a 90A alternator that would be the minimum. If you have the likes of an inverter rated at over 1kW or so, it would need to be larger. Use a shunt -type, not a direct reading type, to avoid having high current cables routed to the ammeter with inherent voltage drop at high loads and possible safety issues.

 

Of course a digital one is far easier to read accurately, eg to determine when charging current has fallen to a couple of % of battery bank size, if not so aesthetically pleasing for you!

Edited July 16, 2012 by nicknorman

[plainsman]

The ammeter should be able to read correctly at the maximum normal load, so with a 90A alternator that would be the minimum. If you have the likes of an inverter rated at over 1kW or so, it would need to be larger. Use a shunt -type, not a direct reading type, to avoid having high current cables routed to the ammeter with inherent voltage drop at high loads and possible safety issues.

 

Of course a digital one is far easier to read accurately, eg to determine when charging current has fallen to a couple of % of battery bank size, if not so aesthetically pleasing for you!

 

Thanks for the info. I am unable to find a supplier of 100 amp ammeter - any ideas? Also if I "upgrade" my alternator to say 120 amp, is it correct I must have an alternator reading 120amps?

 

Regards

[bottle]

Any ammeter (shunt) must be able to cope with the maximum(or more) amperage available.

 

or yes.

[NB Willawaw]

Lots of cheapy Chinese ones on Ebay or you could use the Nasa BM-1 Battery Monitor for 100A or BM-2 for 200A.

[Tony Brooks]

Any ammeter (shunt) must be able to cope with the maximum(or more) amperage available.

 

or yes.

 

 

Also do not forget that if you have a heave load item like an inverter and the ammeter is wired in the usual way it should be capable of registering the maximum discharge as well.

[smileypete]

Have been reading on the forum of the usefulness of an ammeter. Seen a few on sale but not sure what scale range i need. 60-60, 80-80 seem to be common. My alternator is rated at 90 amp 12v. What size ammeter and shunt do I need? Prefer a cream faced analog type to match other instruments (Temp, volts) Advice on type and possible source much appreciated.

Depends on budget, Blue Sea, Smiths or VDO will have something, but at a price.

 

If you end up going for the cheap 3 1/2 digit Ebay ones it's good to get one that can run off the same supply, and goes up to 200A.

 

cheers, Pete.

~smpt~

[Keeping Up]

You can tell a lot from a moving-needle ammeter that you cannot tell from a digital meter, by watching the patterns in the way it moves, especially if you have a moving-needle voltmeter as well. Although if you want accuracy you need to be digital.

[plainsman]

Depends on budget, Blue Sea, Smiths or VDO will have something, but at a price.

 

If you end up going for the cheap 3 1/2 digit Ebay ones it's good to get one that can run off the same supply, and goes up to 200A.

 

cheers, Pete.

~smpt~

 

Thanks for this Pete. I Have tried Blue Sea et al but nothing to match my existing cream/magnolia faced instruments. Looks like I'm going for digital on Ebay, this will be a nearer match to a Smartgauge when I get one!

 

Thanks everyone for your help

 

Regards

[smileypete]

Thanks for this Pete. I Have tried Blue Sea et al but nothing to match my existing cream/magnolia faced instruments.

 

Just for a laugh, sit down, THEN click on the following link...

 

http://www.vetus-shop.com/vetus-ammeter-cream-12v-and-24v-100a-with-shunt-p-1166.html

[plainsman]

Just for a laugh, sit down, THEN click on the following link...

 

http://www.vetus-shop.com/vetus-ammeter-cream-12v-and-24v-100a-with-shunt-p-1166.html

 

Yes - I sat down, opened the link. Now I can't get up, breathless!!

[Simon R]

Just for a laugh, sit down, THEN click on the following link...

 

http://www.vetus-shop.com/vetus-ammeter-cream-12v-and-24v-100a-with-shunt-p-1166.html

 

Very expensive and I doubt they are really high quality. I mostly use military surplus meters, the quality is of a different order, but it is has been hard to find meters for big DC amps. I needed a couple at 100-0-100 amps and one at 200-0-200 amps. They are hard to find and the shunts can cost a lot. Westach in the US make some pretty ones but there's a guy in Ukraine who is selling Russian ones on ebay that look like good quality - military grade shunts and, he says, the meters are used on the Moscow Underground.

 

I've taken the plunge and ordered a few. I'll report on how they are when they arrive. Here's a link, do a shop search for 100A, 150A or whatever:

 

ebay ammeters link

 

 

Simon

Edited July 21, 2012 by Simon R

[Simon R]

Some more links for meters:

 

This guy has a lot of meters made by Crompton, mostly for AC circuits. I've dealt with him quite a bit and he's very helpful. These are very heavy duty meters - metal body, nitrogen filled, toughened glass, many have war department markings:

 

thexmod

 

(Beware of the frequency meters, they need a special transducer which costs hundreds from Crompton, unless you can design and build your own).

 

I've also had some good quality meters from here, it's a bit of a luck dip but sometimes they have what you need:

 

surplus sales Nebraska

 

Simon

[Arthur Brown]

RS have stock of several shunts and meters. Get a 75mV shunt rated for the current that you need and a 75mV meter movement to suit, or a 75 - 0 - 75mV meter for centre zero applications.

 

Some currents only flow one way -notably the alternator, others notably the battery can pass current both ways (charge and discharge). Be careful where you put the meter so that you read the current that means something to you. Reading the current draw of the starter motor is little help but knowing that the start battery is charging sensibly is very useful.