Power to voltmeter
#1
Power to voltmeter
I did something I'm no too comfortable with all of a sudden. I'm using the IGN terminal on the fuse block to power my HEI so I thought it was a simple solution for the voltmeter as well (sunpro gauges). I pig-tailed them together and soldered them up nice but now I'm wondering if that's a bad idea. The voltmeter reads a hair over 14v and she seems to run fine, but still.....
Thoughts?
Should I run a wire directly to the bat terminal on the alternator for the voltmeter? It's externally regulated. I looked and looked under the dash but couldn't find the oft-suggested gray wire.
EDIT: Now I'm confusing myself. The gray wire is for the lamps w/dimmer I think.
Thoughts?
Should I run a wire directly to the bat terminal on the alternator for the voltmeter? It's externally regulated. I looked and looked under the dash but couldn't find the oft-suggested gray wire.
EDIT: Now I'm confusing myself. The gray wire is for the lamps w/dimmer I think.
Last edited by Macadoo; July 31st, 2014 at 12:05 PM.
#9
IMO, you should never hook anything to battery power than can short out. Can you say smoke & possible fire? You can piggy back on to any fuse on the block that is hot in Run. A voltmeter draws virtually no current at all. Be sure to tap on to the fused side.
#10
Not sure, gut feeling. Something about the HEI being a high power output unit sharing it's input. But it was just a feeling not experience.
So I have to admit I don't know how to tap the fuse block. Is it tapping into the wire on the backside of the block?
So I have to admit I don't know how to tap the fuse block. Is it tapping into the wire on the backside of the block?
#11
The current draw of a voltmeter is about zero, by definition...
if it passed much electricity it would be an ammeter.
#15
The key with a volt meter is to decide what you want to monitor, ie: where you want to connect it.
As stated, the power stud on the horn relay is considered the "zero point" so to speak, of the power supply system, so it is a logical place to connect. The supply on the back of the alternator makes, sense, too.
You can connect to any of these, and to prevent the chance of a horrible short, just fuse the voltmeter supply wire.
And, Yes, by definition, volt meters draw so little current as to essentially not be drawing any.
- Eric
As stated, the power stud on the horn relay is considered the "zero point" so to speak, of the power supply system, so it is a logical place to connect. The supply on the back of the alternator makes, sense, too.
You can connect to any of these, and to prevent the chance of a horrible short, just fuse the voltmeter supply wire.
And, Yes, by definition, volt meters draw so little current as to essentially not be drawing any.
- Eric
#17
Duh.
What was I thinking?
They are good sources to connect to, but not without putting a relay between the post and the meter, controlled by the ignition.
The fuse block can have a fair amount of resistance from subtle corrosion, so may not be the best electrical connection point, but tapping off of it in the right place (IGN or ACC lug, for instance) will give you switched, fused power.
I've always prefered a source switched to the ACC side, as it leaves the gauge on if you are sitting in the car running the radio, and you can see if the battery is draining down before it's too late.
Also, either of these can be very useful for this:
- Eric
Last edited by MDchanic; July 31st, 2014 at 08:01 PM.
#18
As always Eric(s), the info is appreciated.
Umm, dumb question maybe but how do you know which end of the fuse is fused (output)? I would assume it's the right-hand side but I have nothing to base that on.
Umm, dumb question maybe but how do you know which end of the fuse is fused (output)? I would assume it's the right-hand side but I have nothing to base that on.
#19
#20
That brings up a point I was thinking when I first read this earlier today: exactly what would you want to monitor? The voltage that the alternator is putting out or the voltage that your accessories are actually seeing? They can be different. If you monitor the alternator you may not be seeing the reality on the other side of the firewall, but you'll know what your alternator is doing. Does this really help you? Depends upon what you want to know, right? Is my battery getting charged, or are my accessories getting full power? If you monitor inside the firewall and have full voltage, then you know everything is OK. If you don't have full voltage, then you know it and can fix what's wrong.
#21
No matter where you tap into with the key on, it will be within a few millivolts of what the electrical system is seeing. The voltage will fluctuate between around 12.5v and 14.5v depending on whether the lights are on and the alternating is charging.
#22
That brings up a point I was thinking when I first read this earlier today: exactly what would you want to monitor? The voltage that the alternator is putting out or the voltage that your accessories are actually seeing? They can be different. If you monitor the alternator you may not be seeing the reality on the other side of the firewall, but you'll know what your alternator is doing. Does this really help you? Depends upon what you want to know, right? Is my battery getting charged, or are my accessories getting full power? If you monitor inside the firewall and have full voltage, then you know everything is OK. If you don't have full voltage, then you know it and can fix what's wrong.
#23
In my car last month, I found that my battery wasn't charging - I had 14.5V at the alternator, but 13.25V at the battery.
Grounds were good, but there were losses in the wiring from the alternator to the horn relay, from the horn relay to the starter, and from the starter to the battery.
I cleaned and replaced wires and terminals and now there's less than 1/10th of a volt difference, but the same thing can happen throughout the electrical system, and especially at the fuse box, where those steel terminals love to corrode.
My point? You could be reading 13V at a fuse box tap, think you've got a problem, and the alternator can be feeding 14.5V to the battery.
You can connect the volt meter anywhere, but at least check to be sure that you know whether your readings reflect the actual voltages you are interested in monitoring.
- Eric
#25
Well as it turns out, I was looking for a bad connection that wasn't. Yes I was concerned about sharing the power source but the meter was also acting odd. Working sometimes and not others. I'd check for juice at the meter and sometimes it would have it and other times it wouldn't. I picked up some spade doublers and taps and that ironed out the power issue but I also discovered the meter is bad. I have to tap on it firmly to get it to read (which only works some of the time). Now, since I bought the triple gauge set I assume I either uninstall the oil and water gauges in order to return it or purchase the single voltmeter. Kind of a no-brainer but still.....
Thread
Thread Starter
Forum
Replies
Last Post
KZ442
Interior/Upholstery
5
April 10th, 2009 03:16 AM