18 replies to this topic

[Spider]

I don't know if there are available in the Auto World, but see if you can find a Meter that uses an external Shunt.

 

This has many advantages, not the least of which is you are not running huge cables to the Meter and back again. They are generally way more tolerant to overloads and even if the Meter does burn out, everything else still works.

 

The Shunt is basically a Resistor (of VERY low resistance), the circuit for current measurement is connected through that, then off either side of it, smaller signal wires are run to the Meter.

 

I have seen Digital versions for Cars.

 

By chance, I was just now looking through the VDO Catalogue and these guys do have an Ammeter that uses a Shunt

 

http://newenglandins...art-no-190-504/

 

While this is 150-0-150, it's only a matter of changing or even modifying (which is dead easy) the shunt to change that.

[tiger99]

The advantage of using a Hall effect sensor over a shunt is that it introduces no voltage drop whatsoever, as the existing bunch of brown wires are simply threaded through. Also, none of its terminals are at unfused battery potential, unlike both ends of a shunt.

 

I suppose I should find the time to design the proper thing, with the appropriate sensor and other bits on a small PCB, since I can't find anyone making one at the moment. The sensor end is the easy bit. I don't know how to go about making the dashboard indicator as it needs to be a voltmeter, reading maybe +2 to -2 volts, and in a standard Smiths casing. A digital or LED bargraph version would be simpler.

[Spider]

I wouldn't disagree with you tiger on the hall effect ammeter, but I've not seen anything like that (off the shelf) for the auto industry.

 

I do recall seeing an article in an electronics magazine a few years back for one though, but it had a digital display, great in the workshop, useless on the road.

[tiger99]

Yes, I have found these too. Disappointing.

I suppose a standard ammeter could be rewound with a coil of many turns of fine wire. Presuming it was 60-0-60 with 1 very thick turn, a coil of 60000 turns of very thin wire, upwards of 40swg, would give it 1mA full scale, ideal for use with a Hall sensor. Or 6000 turns would give 10mA which is good enough.

I don't know the internal construction os a Smiths ammeter, so don't know how feasible it would be.

You can of course still buy analogue meters but not in a size that would be immediately useful. Someone has missed an opportunity...

I suppose the modern way is to use simulated analogue pointers on an LCD screen. Can be good, but the aesthetics are wrong if you already have an array of Smiths dials.