VCCA Home Forums TECHNICAL - GENERAL Electrical - 6 volt Ammeter Basics

Not sure if this should be posted in the 6V or 12V forum.

A couple of questions about ammeters in general.

1) Is an ammeter voltage sensitive? For example, if a 6V car is converted to 12V (yes, I am trying to discourage that but the owner is pretty sure he needs it) will the existing ammeter function correctly with no changes to it?

2) What happens to an ammeter if more current is passed through it (either way)than it is designed to register? For example, the ammeter in my '37 Master Coupe shows a range of -15 amps to + 15 amps. What happens if a charging load of greater than 15 amps is passed through the meter? The same situation could happen if terms of discharge load if all the lights, heater fan, and cigar lighter are on without the engine running.

Thanks for the education!

While I am not electrical engineer I have never found a ampmeter to be voltage sensitive but excess amperage tends to let the smoke out then they no longer operate.
Tony

The ammeter is simply a soft iron bar embedded in a brass holder with a needle with counterweight for mid position. The principle is very simple magnetism. Compass needle and a wire carrying an electric current. http://physics10aps.blogspot.de/2011/08/magnetic-effects-of-electric-current.html
There a no tiny little coils that can smoke. Twice design current load will only bend the needle.
To avoid this you can bypass the ammeter terminals with a short wire. Try to find out the right wire gauge to half the needle movement. Try AWG 12.
Tino

Hi Rusty,

There is something wrong with the electrical or mechanical system in a 6 volt car that could cause someone to assume the electrical system should be changed to 12 volts. If the owner is hot rodding the car, or adding 21st century technology then changes would be justified.

What are the owners reasons for wanting to change?

Thanks, Mike

P.S. It is my opinion that 90% of the vehicles of our vintage need to have their complete electrical harness replaced if they have been subjected to normal driving conditions in the 30's through 50's. I will be glad to post pictures of my old harness to validate my concern.

I agree with Mike's comment about old wiring. I recently rebuilt/refurbished the gauge cluster on my project '46 1/2 ton. I was surprised to find the original cloth covered wire to be so worn in many places. The wiring, all of it was going to be replaced anyway, but after seeing the state of deterioration, I would be reluctant to trust any wiring that old without careful and thorough inspection. Even then, I'd likely still replace it.

I converted my '53 3600 to 12 volt years ago...Had no problems with the original 6 volt ammeter...The pain comes with all the other stuff that will need to be changed out...( right down to the heater fan motor ) It's not worth it...There is nothing wrong with a 6 volt system, as you probably well know...In any event, I wasn't happy with the 12 volt system...Can't recall why, but I did change it back to 6 volt...At any rate, tell him to take it from a glutton for punishment...Stick with the 6 volt system...

Hello to all,

Thanks for the responses to my questions as well as the encouragement to stay with the 6V system. That is my strong preference but I have to remember that it is not my vehicle and $.

Yes, he is doing a complete new wiring harness. It did not take very long to convince him that was essential after he handled the old harness.

Guess I'll brake down and start working on a new harness...The other day I switched on the lights and the horn went off...! Kind off embarrassing to say the least...Wrapped a little tape around the offending short...lol

I am NOT an expert on electricity but my personal experience has been that more current than an ammeter is designed to tolerate can damage them. I've been told that it makes no difference as noted in one of the posts above but consider this.

I put a 6v 60 amp alternator on my '38. At first all was good but over time I would experience difficult hot starts at times where I had to crank longer than normal to start the car. Once the car started the alternator would slug 60 amps through the system back to the battery. A few times of that and now my ammeter no longer indicates accurately. I can start the car with no load other than the ignition and the ammeter shows a charge. ANY load in excess of that, even simply turning on the dome light, and the ammeter drops to discharge. I've checked the output to the battery with the ammeter showing discharge and everything but the ammeter is working correctly. I ended up putting a voltmeter under the dash and have driven successfully for several years now with my ammeter showing most times full discharge but I've never run the battery down.

I agree with all that there's nothing wrong with running a 6 volt system . Just keep your battery charged up.

12 volts should not harm a 6 volt ammeter because a 12 volt system operates on less current than a 6 volt system. That's why you see heavier cables on a 6 volt battery vs a 12.

The ammeter is connected in series with the hot side and measures current (amps) passing through.

RR
former US Navy AE2 ( aviation electrician)

I have a question for who ever can give me the right answer.
I replace a cut-out (regulator)on my 32 chevy 6volt system. Does anyone know is you have to do the wire thing to short out the cut-out??

If all you do is replace the cut-out on a working generator then it is not necessary to short around the cut-out and polarize the generator. However it may be necessary to adjust the point gap in the cut-out. It does not hurt to polarize the generator. If the generator was not generating then polarizing is a good step. If still not generating then the generator needs to be checked for the problem.

It's only really a question of right, wrong or justification on the show judging field. On the road, drivers that from time to time must rely on readily available parts, it is a matter of direction. 6v is fine but it all boils down to plunging head long into the 19th century technology of alternating current. Another turn in the road, 6v or 12v, is away from external mechanical voltage regulators. Love them or hate them they are inefficient and potential fire hazards.