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Vehicle Battery Gauge Proper Voltage
By valterra, Section Storage Posted on Sat Mar 29, 2008 at 10:25:58 PM MST
What voltage does a vehicle battery gauge measure?

Sounds like a stupid question. But a buddy of mine let me scavenge through his junkyard. I got some instrument panels and when I hooked my SLA up to the battery gauge, the needle pegged, and the magic blue smoke escaped! No big deal moneywise, but what did I do wrong?
My DMM hooks up to each pole of the batteries and doesn't complain. But these things apparently do NOT like 12vdc!!
Do they hook up in series somehow?

Vehicle Battery Gauge Proper Voltage | 14 comments (14 topical)

Re: Vehicle Battery Gauge Proper Voltage (3.00 / 0) (#1)
by kurt on Sat Mar 29, 2008 at 04:44:26 PM MST

was it an amp meter or a volt meter?? cars can have both older cars had amp meters newer cars tend to have volt meters.....

IRC inst.
just a personal rant carry on.

Re: Vehicle Battery Gauge Proper Voltage (3.00 / 0) (#2)
by valterra on Sat Mar 29, 2008 at 05:05:16 PM MST

Good point. They both say "Charge" and have a battery icon and a "D" on the left and a "C" on the right.

I figured it was voltage because it didn't give any indication of scale. For example +20 amps or something.

[ Parent ]

Re: Vehicle Battery Gauge Proper Voltage (3.00 / 0) (#3)
by valterra on Sat Mar 29, 2008 at 05:07:03 PM MST

For Voltage, I'll look for the standard 13.8 meters. If these are ammeters, they're not too helpful because they are not marked in any useful way. I mean, is it a 60 amp scale or 600? You know what I mean.

[ Parent ]

Re: Vehicle Battery Gauge Proper Voltage (3.00 / 0) (#4)
by jimjjnn on Sun Mar 30, 2008 at 02:02:21 AM MST

If the meter said C on one edge and D on the other,it was an ammeter not a voltmeter
Denver,CO
[ Parent ]

Re: Vehicle Battery Gauge Proper Voltage (3.00 / 0) (#5)
by valterra on Sun Mar 30, 2008 at 03:24:43 PM MST

Okay - now I'm confuzled. I have two different ammeters that I pulled out.

When I hook them in series with a small load (small b&w 12v television) one of the meters barely moves and the other one just pegs all the way over. I'd expect them to just barely move.

What's the deal with the other one? I know that you can't see them to diagnose, but one would think (perhaps wrongly) that a vehicle ammeter would not peg itself over a load less than 1 amp.

[ Parent ]

Re: Vehicle Battery Gauge Proper Voltage (3.00 / 0) (#6)
by Waterlogged on Sun Mar 30, 2008 at 06:27:19 PM MST

Some vehicles used a shunt type ammeter. Fords, I believe. I had a Dodge, and drove a Ford wrecker at work. I noticed the difference and looked at the wiring diagrams. That was many years ago. I don't remember all the details on the ford, but the Dodge wiring ran all the power in or out of the battery(except the starter) through the ammeter. When I replaced the 37 amp alternator with a 90 amp alternator, it started the wiring on fire. That was a good time to replace the ammeter with a voltmeter.
Rod

[ Parent ]

Re: Vehicle Battery Gauge Proper Voltage (3.00 / 0) (#8)
by valterra on Sun Mar 30, 2008 at 08:43:46 PM MST

I guess I still don't understand. I didn't know there was any way to hook them up except in series with the load. What am I missing?

[ Parent ]

Re: Vehicle Battery Gauge Proper Voltage (3.00 / 0) (#9)
by commanda on Sun Mar 30, 2008 at 10:48:49 PM MST

The current shunt probably isn't part of the meter assembly. In fact, if you think about it, it almost certainly isn't, since a cable carrying from 30-60 amps (think very heavy cable) doesn't run through the dashboard.

Amanda

[ Parent ]

Re: Vehicle Battery Gauge Proper Voltage (3.00 / 0) (#10)
by valterra on Mon Mar 31, 2008 at 06:36:38 AM MST

Thanks Amanda. That's too bad, since these only cost me the price of my time.

Harbor Freight has some 40? A meters for 2.99. I was just hoping to get away with these, since I'd like to use 4 of them in various places (3 different generators and along the outgoing bus)

[ Parent ]

Re: Vehicle Battery Gauge Proper Voltage (3.00 / 0) (#11)
by valterra on Mon Mar 31, 2008 at 06:47:58 AM MST

When I said get away with "these," I meant the freebies.

A vehicle's voltmeter shouldn't give me any trouble, right? Since a voltmeter uses super high resistance so as to NOT allow the current to pass through it?

Worst case scenario would be just waiting until those digital multimeters at harbor freight go on sale for $3.99. They'd look fancy anyway.

But I just like seeing the needles for some reason. Easier to see "movement' that way, as the current rises and falls. I mean, "Cutting Edge of Low Technology," right? Seems as if I'd heard that somewhere... :)

[ Parent ]

Re: Vehicle Battery Gauge Proper Voltage (3.00 / 0) (#12)
by commanda on Mon Mar 31, 2008 at 11:18:47 AM MST

A vehicle's voltmeter shouldn't give me any trouble, right?

Famous last words.

The voltmeter in a car is nearly always an expanded scale (doesn't start at zero) which requires extra circuitry. May be inside the meter, may be hidden in the dash panel somewhere.

And I agree about using analog meters. Much easier to interpret at a glance good/not so good/bad.
And if you color code the display, much easier to explain to non-technical people.

Amanda

[ Parent ]

Re: Vehicle Battery Gauge Proper Voltage (3.00 / 0) (#14)
by valterra on Mon Mar 31, 2008 at 06:58:07 PM MST

okay. So pulling one out of a car could be a bad idea because I wouldn't know if extra circuitry was involved. But then THIS should be okay then:

Voltmeter:

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=95779

[ Parent ]

Re: Vehicle Battery Gauge Proper Voltage (3.00 / 0) (#13)
by Waterlogged on Mon Mar 31, 2008 at 06:43:46 PM MST

On my 1974 Dodge Ramcharger 4x4 truck, and others, the 30+ amps did run through the dash board. It was 10 awg wire, and connected to the ammeter with ring terminals over studs. If it used a shunt, it was built into the gauge. The current went through the firewall, and back, and that is where the fire occurred. Chrysler had some quality problems with their wires and connectors, and armed with the wiring diagram, I replaced a lot of wiring. I learned a lot about how they were wired. In all fairness, I did replace the original 37 amp alternator with a 90 amp alternator, and rev the engine to assist the winch which was rated to draw almost 600 amps. The heavy electrical load, caused the voltage regulator to make the alternator go to full output, and I quickly learned something Chrysler seems to also have learned. I haven't seem a similar design in years.
I wired my alternator output direct to the battery, and put a voltmeter in the dash. If the voltmeter reads above battery volts, the system is charging; if volts are low, the system is not charging.
Rod

[ Parent ]

Re: Vehicle Battery Gauge Proper Voltage (3.00 / 0) (#7)
by commanda on Sun Mar 30, 2008 at 08:30:57 PM MST

I'm no auto-electrician, but................

In my experience, the meter in the dash is just a meter, and the shunt(ammeter) or voltage divider(voltmeter) is elsewhere; sometimes part of the dash assembly, sometimes not.

I've also seen automotive meters which work on the bi-metallic(heat) principle; so the gauge only ever moves really really slowly.

Surely a proper MU45 moving coil meter isn't that expensive. I buy them brand new for less than $10 Australian each. You can even buy digital multimeters for similar.

Amanda

Vehicle Battery Gauge Proper Voltage | 14 comments (14 topical)

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