In-line voltmeter on dash? Suggestions?

[Early_S_Man]

Mark,

If you contemplate using 10% carbon resistors, then don't bother with that panel meter, or even the lesser expensive $18 units available from Hosfeld and other sources!

My point about the basic accuracy issue is that the $7.50 LCD unit, at +/- 0.3 Volts (worst case) ... is no better than the VDO analog gauge, which I have used and fully recommend as an excellent meter! You can easily and accurately see the Voltage fall-off after an alternator warms up to the full underhood temperatures!

When I assembled a 19.99 Volt panel meter, I used a 0.1% metal-film resistor and a 10-turn wire-wound Bournes trimpot, and checked the accuracy of the divider with a 6.5 digit Fluke 8500A lab-grade bench meter ... on my garage workbench.

[Joeaksa]

Warren,

I am real glad that there are guys like you on this planet, because when you get to this level of working with electronics, its way over my head!

After building several Heathkit projects (TV, yes it worked) and working a bit on ham radio and computers for years, I know my way around to a limit on electronics.

That said, to do what you and Mark are talking about is best left to others who know what they are doing! Its more than I want to take on at this level. I will just buy the other gauge and give it a try. Its more accurate than the idiot light no matter what.

JoeHahn, Sorry... I remember some past emails with you and had forgotten. You could take the car to a good alternator shop and they can put a tester on the system that should tell if your diodes are in good shape or not (hope this is possible?). Next time I come to Cleveland I will help you take it out!

JoeA

[MBAtarga]

Warren,

I certainly respect your input, but the reason I brought up the tolerance on the resistor bridge is that others reading this post may not realize the importance of the tolerance of the components. Also, the supply voltage requirement of +5V is not going to be met unless a regulator is used.

In summary, I didn't want someone thinking they can purchase the LED unit and 2 resistors and expect it to be accurate, much less even work off the +12V vehicle voltage.

[Nifty]

I would recommend installation of an anolog voltmeter such as the VDO cockpit guage referred to. Digital guages are great if you want an accurate check on the volts but not that good for checking rate of change. An ammeter will tell you the state of the alternator but a voltmeter is better as it also gives an indication of battery status. Because I had concerns over the charging circuit on a previous vehicle ('74 911S) in installed a VDO guage. VDO recommend direction connection to the battery terminals (with a fuse in the +ve line) so that you are directly measuring battery volts. Otherwise the load on the circuit you tap into will influence the reading. I shifted the hazard warning lamp pushbutton to the other side of the dash strip and then installed the VDO guage where the pushbutton came from. The result was very neat, and did not look out of place. Sorry but can't provide a pic now.

[mod]

Thanks for Joeaksa's picture I was able to locate the exact voltmeter display. http://www.skingcompany.com/detail.asp?product_ID=1044

It's about $15 with $5 shipping. It seems to be a good one as it is small, and does not need any other voltage supply other than the intrinsic 12V from the car. They have 7 left after I purchased 2. But I was told they can get more.

[Joeaksa]

Mod,

That is exactly what mine looked like before I mounted it on my tach gauge. Good to see someone is making this unit again and assume that its the same outfit in Taiwain/China/Japan et al.

Sure is nice to know what your charging system/Alternator is doing in real time instead of just the red light that came with the car.

Thanks for passing it along to us!

Joe

[stlrj]

This might be what you need:

http://www.autobarn.net/powpvm804.html

Joe

[carnut169]

I like Jeff's suggestion. I have the Escort 8500 which will double as a voltmeter. No installing, drilling, cutting.... plug it into the cig lighter, set it up, and you are done. Has some other pretty nice features as well. I have yet to get a speeding ticket since I purchased it 6 months ago (that is saying something).

[R22tech]

Ditto on the escort 8500:

It seems like with these other suggestions it's comparable to killing an ant with a hammer! All to save a buck or two....hundred.

Besides, don't Porsche owners NEED a radar detector, even if they don't speed, to alert them to a possible "Porsche profiling" ticket?

[v9ff]

Originally posted by Joeaksa
I found this gauge at Fry's electronics two years ago. It was a cigar lighter type gauge and worked fine for a while. After a bit I got tired of looking at the center of the car to check the voltage and took it apart. Now it is attached to my tachometer and in the direct line of sight. It also covers up that worthless "shift gauge" that the factory put in the mid-80's cars. Yes I know that the wiring looks like hell but it was a temp installation... two years ago!

Is this how I should wire my new voltmeter?

[JP911]

I wired my analog voltmeter into a switched circuit in the fuse box and it works great. I mounted it, with it supplied mouting bracket in the center console.

[v9ff]

Originally posted by JP911
I wired my analog voltmeter into a switched circuit in the fuse box and it works great. I mounted it, with it supplied mouting bracket in the center console.

Could you edumacate me on this... I'm not that savvy with automotive lingo. What's a switched circuit? I know where the fuse box is.

[jabb]

A switched circuit is a circuit or wire that becomes energized when the key is turned to the on postion.

[JP911]

What Jab said.
If you wire it into a non-switched circuit the voltmeter will read voltage all the time, regardless of whether or not the key is in the on position or in your pocket. An example of a switched circuit would be defroster or windshield wipers. An analog guage will also have a wire for lighting which can be tapped into a dash lighting wire (like one of the lights on the dashboard) so that when you turn on the lights, the guage will be lit like all of the other guages in the car.

[jasonq]

I did the very same thing joe did with the hacking a cigarette lighter voltmeter, only i installed mine next to the ingnition switch, looks nicer, but less visible.

here is a link to where you can get it for 17 bucks:
http://www.cetsolar.com/voltmeter.htm

later,
jason

[v9ff]

Originally posted by v9ff
Is this how I should wire my new voltmeter?

Would this wiring design work? Would this set up be unadvisable?

If not, which switch circuit fuse position should I use?

Thanks!

[JP911]

I'm no expert with things electrical, but in lieu of connecting the voltmeter directly to the battery (cannot be switched) then the fuse box is the next best thing. It's not hard at all to run a wire from the trunk to the dash.

[v9ff]

Okay... so I should connect from a switched fuse to the (+) then (-) to a body ground, right?

[Early_S_Man]

Steve,

The circuit you posted will work just fine!

[JP911]

That is correct. Run a red wire from the fuse box to wherever it is you plan to mount the guage and a black (or brown) wire from the guage to a grounding point. Connect the lighting wire to a light wire somewhere behind the dash. You can use a tapping connector for the light connection. I used 16 guage wire (may be overkill) for the install.