Right place to connect Voltmeter?

[xterra]

Today seems to be my day for questions. This time it's electrical.

 

Where should I connect a new digital voltmeter to get a correct reading? Or is my in-dash voltmeter the one that's wrong?

 

I'm prepping for a swap to a '93 gauge cluster and got a digital voltmeter to replace the one I'll be losing. It was a simple install where the lighter used to be, and I used the lighter power connections.

 

My problem is I don't know which numbers (below) are right - or even where I should really be checking.

 

key in the "ON" position, but not started:

- in-dash gauge reads 14 (needle jumps immediately when I turn the key from ACC)

- new gauge reads 12.4

- Fluke meter at the battery also reads 12.4.

 

Started, at idle:

- in-dash gauge reads 15

- new gauge reads 13.1

- Fluke meter at battery reads 13.0 (so close enough)

 

When driving:

- in-dash gauge read 16

- new gauge reads 13.7

 

So is the in-dash gauge giving a bad reading and the Fluke and the new meter are right?

Or is there somewhere besides the battery that I should be checking with the Fluke that might be closer to the in-dash gauge?

 

If it makes any difference, it has (what appears to be) the original alternator - and the battery is about a year old.

 

Thanks all for your advice!

[Terranovation]

The alternator keeps the battery charged while running and the battery is only a year old so that's fine. You'll get three to four years life out of a battery from my experience.

The fluke meter is probably more or less accurate and the dash volt gauge is probably really old so it's not going to be giving you accurate readings. I always check my battery with my multimeter when I'm checking oil etc.

[Slartibartfast]

The readings your meter and new gauge are giving you are what battery voltage should be, and I'd be inclined to trust a good meter over the factory gauge. If the charging system was running up to 16v I think you'd be having battery issues. I guess you might get a higher voltage reading right off the alternator but only if there was a problem with the cable between the alt and the battery.

 

Terranovation, that's odd, I've seen them go much longer than that. The one in my '95 has May of '09 stamped on it and still works fine. The battery in my mom's Honda had at least seven years on it when we replaced it (as a precaution) and my cranking amp tester whatsit says it's still up to spec. (I use it around the shop to test motors and things.) Maybe your climate's tougher on batteries than mine?

[Terranovation]

Yeah, Australia is what we say 'bloody hot' even this year, during June when it's supposed to be winter we have had 23 degrees Celsius and lots of sun. In summer we can get consecutive days of 40 Celsius and above. The hottest it's ever been here in Perth was 48 Celsius so that one time we were the hottest location on the planet.

[Precise1]

Xterra, your old in-dash meter is off, reading high. I wonder if there is a pot on back to adjust/calibrate it?

Your multimeter and new gauge are accurate. Not only do they both show the same readings, those readings are in the appropriate range for a properly functioning battery/charging system, the in-dash is not.

 

I would connect the new gauge at the battery, because this is where you will get the the most accurate and important data. Patching in downstream from the battery could be affected by various connections, resistance of the wires, and various draws. You really do want at the battery info...

 

B

[xterra]

Thanks, y'all

 

Although it's really tempting to just leave the new voltmeter connected as-is, it looks like I'll be running a couple extra wires into the engine bay along with all my other prep work.