Tip & How-To about Measuring Tools & Sensors

Is a Voltmeter worth the investment?

One of the handiest inventions known to man is the voltmeter, which often also comes with an ammeter (current meter), and ohmmeter (the setting that measures continuity, or resistance of components). The voltmeter will let you know the condition of your battery on your car, and also if your alternator's charging the battery with a good output. Always measure from the the positive battery terminal to the frame of the car (or negative post if the frame is unaccessible), unless you're an experienced mechanic. Measuring the alternator output with the output wire disconnected can blow diodes in the alternator. Measuring at the battery posts will tell you all you usually need to know, however measuring from the positive post to the frame of the car will let you know if the negative ground clip is corroded (you will get a lower reading).
Aside from cars, voltmeter's can be set to the AC voltage setting (VAC) to measure outlet voltages in the house. Sockets do get broken and go bad, or wires can oxidize, and vibrate loose over time, and a low voltage reading (approx. 50vac) will tell you that. Setting the voltmeter to VDC (direct current voltage) will let you check computer power supplies, cell phone, ipod, and GPS chargers, and any other device that uses a power supply. Added bonus is that you can measure all batteries, no matter the type or size. Batteries usually show a bit higher than their rating (e.g. 1.5 volt battery might measure 1.56 or higher), and most AA batteries will work down to 1.25 V or maybe 1.17 V, depending on the current "draw" of the device (technically referred to as "load").
The last, but certainly not least function, is the handy ohmmeter. Ohms is a measure of resistance based on the primary formula E=IR (voltage equals current times resistance). It is most often used to measure continuity of cords, wires, connectors, and fuses, and a small resistance reading (maybe 50 ohms, and also probably an erratic reading, can indicate corrosion or contamination, which can usually be cleaned by sprays or slightly abrasive material (sprays or pencil eraser on gold-plated contacts- fine emery cloth is good for resistors, capacitors, and larger wires).
There is no big trick to using voltmeters, but you do have to remember NEVER, EVER measure voltage with the meter set to OHMS. This will usually fry the ohms circuit, or, if equipped, take out a fuse. If you measure AC voltage on a DC setting, or vice versa, you will just get erratic, erroneous readings. Don't use the DC Current or AC Current settings unless you understand what you're doing. They're for more technical analyzation, and usually only technicians and engineers use them.
You can get voltmeters at surplus stores, Walmart, Lowe's, Radio Shack, and online. I like the digital meters myself, they're easier and faster to read than the analog (meter) type. I've fixed everything from problems with my automobile, computer, accutron watch, and a $750 voltage module in a friend's car with just a voltmeter, so to me it was worth the $20 I invested over 12 years ago. These days you can find them for $5 at surplus stores, less than $20 at most places, and they make handy gifts for all around do-it-yourself handymen/handywomen!

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3 Answers

Battery light on and off

The battery light means the alternator is not charging the battery. The charging system would need to be checked out when the light is on.

Feb 07, 2014 | 2001 Pontiac Montana

1 Answer

The microwave trips the breaker when used twice in a row.

First, verify that the appliance is the problam or not.

Get a clamp-on ammeter, such as this one: https://www.walmart.com/ip/Digital-Clamp-Multimeter-AC-DC-Voltmeter-Ammeter-LCD-Ohmmeter-Tester-Meter/272114348?wmlspartner=wlpa&selectedSellerId=7754&adid=22222222227092377675&wmlspartner=wmtlabs&wl0=&wl1=g&wl2=c&wl3=213509462359&wl4=pla-346089952276&wl5=9001910&wl6=&wl7=&wl8=&wl9=pla&wl10=115794707&wl11=online&wl12=272114348&wl13=&veh=sem

This can tell you right away if the appliance is drawing too much current.

A loose connection in the screw terminals on the outlet can cause the appliance to draw excessive current. If you house was built in the 70's, you might have aluminum wire. Sell the house and move since aluminum wiring is no longer legal to install due to the extreme fire hazard aluminum wire presents. Seriously, if you have aluminum wiring, then every junction needs to be checked. Every screw terminal, every wire nut.

Finally, you could have a bad circuit breaker. If the clamp-on ammeter says your appliance is drawing 10-Amps and the 15-amp breaker trips, then replace the breaker.

WARNING- If you don't know what you are doing around lethal voltages, hire an electrician.

Oct 28, 2017 | Frigidaire Microwave Ovens

1 Answer

glow ignitor

To do this safely, you'll need a "clamp-on type ammeter" or "amprobe" . They look like this:
The nice thing about "clamp on type ammeters" is that they do not require physical connection to or disconnecting of any wire(s). Instead, simply set the scale for the most current you expect to see, clamp around ONE wire and adjust the scale as needed & read the meter for the most accurate reading.

There are available in various sizes and by other manufacturers - that offer a wide range of prices. Amprobe is the name of a particular company that invented this years ago - and makes this one - and other electrical test equipment. A search for images of "Amprobe" returns these.

Jul 11, 2013 | Admiral Gas Dryer AGD4675YQ

1 Answer

will not hold charge and voltage gage is not working

Is the alternator putting out a charging current when running? Measured at alternator then at battery. If no at alternator, replace alternator if high mileage, if low mileage replace regulator. The part the harness plugs into.

If yes at alternator and no at battery, check for continuity across ammeter and check the voltmeter for a short. The ammeter should read essentially zero ohms and the voltmeter should read about 15,000 to 40,000 ohms when measured with an analog ohm meter.

If those check okay, check for a wiring fault or a blown fuse on the power distribution block or a broken fusible link. Fusible links can be checked by gentle tension on them, those that have failed will pull apart.

Jan 18, 2012 | Cars & Trucks

1 Answer

Readings of Ammeter and Voltmeter.

The voltmeter will display 3V and the ammeter will show a small amount of current this is the current being used to swing the needle or in a digital meter the current used to get a sample.

May 07, 2009 | Kitchen Appliances - Others

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