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Author Topic: VRA meter  (Read 4086 times)
Harv
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« on: March 01, 2015, 04:47:52 PM »
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This may be a long shot, but can only try.

I'd like to get my hands on an old VRA (volts, resistance, amps) meter, similar to the one shown in the early workshop manuals:


I can meaure volts with my Jaycar-special voltmeter, but struggle to measure heavy DC amps. I'd also like the resistor setup to play with generators.

Any old autosparkies got an old VRA (dead or alive) they would part with?

Cheers,
Harv
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ardiesse
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« Reply #1 on: March 04, 2015, 05:46:11 PM »
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Harv,

Technology marches on steadily, and test equipment is generally better, cheaper and more accurate these days.  Now that I've done the throat-clearing -

I'd recommend a clamp-style ammeter, but check to see that they will measure DC amps.  Otherwise, Jaycar sells high-capacity current shunts.  One that'd be ideal for testing generator output is the QP-5412, which is rated at 50 mV drop for 50 A current (hence 1 milliohm).  A multimeter set to the millivolt range will read amps directly with this shunt.

I've mucked around with a few generators and regulators recently, and I improvised a variable resistance out of resistance wire.  But it's a bit dodgy, and I always used to burn my fingers adjusting the resistance.  I'd suggest making up a lamp bank with a few 21 W indicator bulbs and switches, to connect across the generator rather than in series with it.

And a partially discharged battery is always a great help too.

All that said, nothing beats the old-school feel of quality moving-coil instruments.  Just don't drop them, and don't get them wet.

Rob
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Harv
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« Reply #2 on: March 05, 2015, 08:02:17 AM »
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Thank Rob - appreciated.

I came to the same conclusion... easier to get modern gear, DC clamp meters are pricey, and hard to find a decent load bank.

I'm going to try to find an old VRA if I can... if nothing else it will give Dad something else to teach me (he worked many hours with one when he was on the tools).

Cheers,
Harv
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