Voltmeter - what am I missing?

[Soundguy]

Pat.. my guess is there is about 30 different connectorsinline before power gets to that aux lamp wire.. and who knows.. this may be off a tap on an ignition switch.. and they aren't known to be robust.

A simple 5$ addition of a relay will 'solve' his problem of the voltage difference he is seeing, and not expecting.

soundguy

 

[Dyer retired]

Larry,

I looked at the installation instructions, the only paperwork that came with the gauge (a Cyberdyne brand,) and it doesn't have any information about how much current it draws. The display is very bright and I suspect that it would be a rare occasion that I forget to turn it off. I put the toggle switch close to the key and have been shutting the gauge toggle off before I shut the tractor down. My multimeter across the battery when the engine is running is reading 14.46 volts and my gauge is reading 14.3, jumping to 14.4 volts now after the engine has been running for awhile. I'm satisfied that I'm only getting a slight drop in the reading on the gauge, compared to the multimeter.


Pat,

I have been able to test the battery post and clamp connections as you suggested, one probe on the post and one probe on the clamp, and am getting triple zero readings. Same result on both posts, so I take that to mean that those clamps are clean, tight, and performing as they should? I like the alligator clips suggestion and will be getting a set that fit over the probes....these tests will become much easier once I have those. I looked more closely at the 20 amp fuse where I had posted that there were 5 or six wires fed into/out of that. Well, that estimated count from memory was faulty and the I'm finding 1 hot wire feeding into one female side of the blade fuse 20 amp box and 3 wires coming out the other female post, one of those wires is the wire that I had originally tapped for the gauge. Now for the latest.....I pulled the 20 amp blade fuse out, just to look and see what the cluster of wires looked like from the fuse side. I couldn't really tell much from that, so I plugged the fuse back in snug. I tested the battery posts, key and engine off, and got a reading on my dmm of 12.73 volts. I then decided to recheck the voltage drop on the wire that I initially used (before wiring direct) and got the one volt drop. I turned the key on and first checked the two battery posts again and got a 12.32 volt reading. I then touched the positive probe to the unused wire and got the same reading of 12.32 volts. What happened? The only thing that's happened is that I've taken the fuse out and plugged it back in? Dyer, retired

 

[CCWKen]

I'm really getting concerned about you guys. I'll be down right scared when you want to know if you have 20.1 or 20.6 psi in your tires.

 

[mjncad]

Steve,

It's a digital mulitmeter....if that's what you're asking.
If you're asking about the gauge, there is a picture attached to post #6, and it is also digital. Since my first post, I've wired the gauge directly to the battery with a toggle on/off switch and am gettng much more accurate readings...checking against the readings with the multimeter. I was hooked in after the key initially and got the full volt drop with that installation, so I went direct to the battery instead. John

John:

I've only scanned this thread, so if I'm repeating what someone else has written, my apologies.

That being said; the problem could be the gauge's accuracy tolerance. Just because it's digital, doesn't make it accurate. I had a digital LCD give away clock I received when the defunct company I worked for at the time had its 100-year anniversary. This clock would gain 30+ minutes each month and it was digital. It was useless and went in the trash. That was in the 80's before Made in China became the corporate in thing to do.

 

[Steve_Miller]

I might as well jump in here and give my two cents worth as well. When you hooked your meter to the accessory wire the meter is such a light load (probably a very high resistance) that even though you are now completing the path for that circuit, the load (ie. milliamps at best) is light enough that any contact resistance (ignition switch, relay contact resistance) is still significant because of the loading. If you do a simple experiment by adding a marker light (signal light, park light) or something in parrallel to the meter should help load the contacts in the circuit enough to get a more accurate voltage reading. An even simpler test may be to hook the meter to a loaded circuit (marker lamps)and see if you get any different readings. It may prove nothing or it may make all the difference in the world. As patrickg stated, the sum of all voltage drops equals the source. With light loading in your circuit, resistance can be your enemy. Every time you turn your key on you may get a slightly diffrent voltage as the resistance can change each time the contacts make. Sound simple? Better yet, does it make any sense?

Steve

 

[Soundguy]

The only thing that's happened is that I've taken the fuse out and plugged it back in? Dyer, retired

Dirty fuse holder connections?

soundguy

 

[RobJ]

I'm really getting concerned about you guys. I'll be down right scared when you want to know if you have 20.1 or 20.6 psi in your tires.

hehe, me to.

I always amp gauge, simpler, and tells you what the charge rate is.

 

[Dyer retired]

John:

I've only scanned this thread, so if I'm repeating what someone else has written, my apologies.

That being said; the problem could be the gauge's accuracy tolerance. Just because it's digital, doesn't make it accurate. I had a digital LCD give away clock I received when the defunct company I worked for at the time had its 100-year anniversary. This clock would gain 30+ minutes each month and it was digital. It was useless and went in the trash. That was in the 80's before Made in China became the corporate in thing to do.

I tested the gauge before I installed it by running the hot and ground leads directly to the battery posts and got the same reading as my multimeter in key off, key on, engine running at idle, increased rpm's, etc......so I think the gauge is accurate. At least accurate enough for me. I was concerned about the 1 volt drop when hooked to the spare wire for the rear light hookup. I've since wired it directly and am satisfied with the readings I'm getting, but am also using this opportunity to try and learn a little about this stuff. It interests me and I'm picking up a lot from the TBN help I'm getting. Dyer, retired

 

[Dyer retired]

Dirty fuse holder connections?

soundguy

Soundguy,

Would that account for the voltage drop I was seeing? The drop doesn't seem to be there now though and that's the only thing I've done beyond testing. John

 

[Dyer retired]

I'm really getting concerned about you guys. I'll be down right scared when you want to know if you have 20.1 or 20.6 psi in your tires.

Ha! I'd agree that it seemed picky whining about 1 volt, but wondered what good a voltage gauge was that gave an inaccurate reading? Then, after some very helpful responses, I got nervous that there was a potential problem with the circuit I tried originally to tie into, but really just find it all interesting. I don't think I really needed a Voltage gauge, but it's fun to have, looks good, and will let me know if my new alternator upgrade is working down the road. John