Clap on current probes work one of two ways.[list=1][*]Cheapest is a transformer where the primary (the "wire") is one turn. Unfortunately this only works with AC and not DC like a car.[*]The steady magnetic field around the wire is measured with a hall effect sensor and associated electronics. Expensive and not something you would have found in cars in the 60's[/list=1]

Just because the Westach gauge looks aircrafty doesn't mean it's accurate. It may well be (and probably is) but as far as I know, it's not a certificated unit; you can put it into a homebuilt (i.e. licensed experimental) but not a normal- or utility-category certificated aircraft.

so, even if the volt meter is a glorified idiot light, if monitored occasionally, it could prove useful.

my 'idiot light', while it would glow red at pre-ignition and during initial top-up right after the engine lit, gave me no indication that the alternator had died on the way to Watkins Glen. ??

Bill K

A voltmeter and ammeter are excellent if used as a diagnostic tool at specific points in an electrical circuit. However, with few exceptions, there are no factory specs for current. In a permanent installation in an IP, they just provide an overall view of the electrical system.

Voltmeter: Provides overall status of voltage; deficit, source and charge level. Same as the red light except with numbers. During normal operation, if system voltage is less than high 13s and higher than mid-14 volts, there's a problem.

Ammeter: Depending on the installation, it shows only overall system current flow. If cranking, current drainage from battery could be 100, but unless it's a shunt type ammeter, you don't want to install it in the starter circuit. In normal operation, there should never be a drain if the alternator is working correctly. The voltmeter is of more value here.

A permanently-mounted ammeter, even one that constantly monitors the circuits with the ignition OFF), may not indicate a milliamp drain due to insufficient gauge resolution and/or how the gauge is connected into the circuit. In addition, most vehicles have circuits that are constantly or intermittently ON (radio presets, alarm, clock, etc.).

Between the two, a voltmeter provides more user information, especially in a car with limited instrumentation space. The voltmeter upgrades built into an existing factory gauge save space and are nice. Here's mark914's version.

http://forums.pelicanparts.com/uploa...1174240266.jpg

Sherwood
(no affiliation)

so, even if the volt meter is a glorified idiot light, if monitored occasionally, it could prove useful.

my 'idiot light', while it would glow red at pre-ignition and during initial top-up right after the engine lit, gave me no indication that the alternator had died on the way to Watkins Glen. ??

Bill ,

The idiot light is a voltmeter, if charging voltage drops below battery voltage, it lights up. What exactly happened to your alternator and did the battery also have to be replaced ? I have cars with ammeters and cars with voltmeters. Most of the ammeters are wonky and not completely accurate and I usually switch to a voltmeter when upgrading the electrics or wiring. I also find the little handheld cigar lighter voltmeters handy, most of them are quicker and more accurate than analog gauges and you don't have to cut a hole in you 55 XK140.

Paul

I suggest a VDO expanded-scale Voltmeter, available here:

http://www.pelicanparts.com/cgi-bin/ksearch/PEL_search.cgi?command=show_part_page&please_wait= N&make=POR&model=911M&section=ELgage&page=2&bookma rk=8&part_number=VDO-323041

For the DIY types,here are a couple of articles to build Digital DC Ammeters:

Compact 0-80A Automotive Ammeter -- whole article, free:

http://siliconchip.com.au/cms/A_30551/article.html

Current Clamp Meter Adaptor for DMMs article [purchase online]:

http://siliconchip.com.au/cms/A_30669/article.html

Yo Ronin...what/who is the source of your dual amm/volt mtr please?

the more i think about this the more i want this dual ga Westach. So far i think one dual and a sw to control 2 shunts?


great entertainment imo :D


the pic here http://www.westach.com/gauge_images/2DA10-21.gif



home page www.westach.com

finally did the install on the voltmeter.

a belated thanks for all the replies.

I tried a matching VDO in the 2 1/16th inch size, and it would not fit the console without interfering with the air conditioning controls and the remote microphone, so I downsized to a 1 1/2 inch Stewart-Warner.

fits perfectly, and only needed two connections, as it is self lit.

Bill K

http://forums.pelicanparts.com/uploa...1180399925.jpg

http://forums.pelicanparts.com/uploa...1180399960.jpg

The only vehicle I've been in with an ammeter was a B-52H.