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Old 07-28-2015, 10:34 AM   #1
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continuity tester


I just bought a continuity tester. Does anyone know why I cannot test a 100w incandescent bulb with it? The tester light does not light when I touch the probes to the bulb. Is it too dim for me too see?

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Old 07-28-2015, 10:58 AM   #2
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Battery powered continuity tester? The filament of the bulb probably has too high of a resistance to allow this tester to work. You need a ohm meter to measure the resistance of the filament .

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Old 07-28-2015, 11:15 AM   #3
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will it light up for anything? Could be the battery? Dare I ask if your touching one on the end and one on the threads?
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Old 07-28-2015, 11:37 AM   #4
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Go to Harbor Freight and buy their $5 DMM. Or, wait for the coupons and get one free.

It's much more useful than a continuity tester.

IMO....a continuity tester can get you in trouble unless you know exactly what you are checking.
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Old 07-28-2015, 12:11 PM   #5
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Here's an analogy:
You have a garden hose in your back yard connected to a faucet to run a waterwheel. Open the faucet, water flows through the hose and the waterwheel turns. If 3 year-old Little Timmy steps on the hose, you might see reduced water flow and the waterwheel might slow. Now if 250 pound Big Tim steps on the hose, you'll probably have no water flow at all and the waterwheel will stop.

When Little Timmy steps on the hose he presents a small resistance to the water moving through the hose. When Big Tim steps on the hose he presents a large enough resistance that no water flows at all.
What does this have to do with your continuity tester? The filament (coiled spring looking thing) in the bulb is the electrical equivalent of Big Tim; there just isn't enough power from the battery in your tester to overcome the resistance of the filament.

The light bulb dissipates 100 watts of power at 120 volts. But you don't have 120 Volts from your tester. If your tester uses 2 size AA or AAA batteries in series, that's only 3 Volts. Not enough to dislodge Big Tim. Nor would 6 or 9 Volts.

A Volt/Ohm Meter (VOM) set for high Ohms (Ω) would confirm circuit continuity and tell you the approximate resistance (Ohms Law gives me 144 Ohms resistance).
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Old 08-10-2015, 09:15 AM   #6
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Quote:
Originally Posted by ddawg16 View Post
Go to Harbor Freight and buy their $5 DMM. Or, wait for the coupons and get one free.

It's much more useful than a continuity tester.

IMO....a continuity tester can get you in trouble unless you know exactly what you are checking.
A word of warning there. A meter is much more useful but they come in all qualities. A cheap meter can explode on you with household current. It would be great for the filament test but I would get my face near it testing an outlet. I have one of HFs meters as a freebe with something else and compared the accuracy with my Fluke 87V and it was very close. But still, use with caution.
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Old 08-10-2015, 10:45 AM   #7
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Quote:
Originally Posted by Rango View Post
A word of warning there. A meter is much more useful but they come in all qualities. A cheap meter can explode on you with household current. It would be great for the filament test but I would get my face near it testing an outlet. I have one of HFs meters as a freebe with something else and compared the accuracy with my Fluke 87V and it was very close. But still, use with caution.
Explode on 240Vac? I'd like to see that.

Sorry, but I don't buy your negative assessment of the HF meter. Yea, it's cheap, but it works. My son has used it to measure house voltage with no issues.

And I don't know of 'anyone' who has had an issue with it. Do I expect it to out perform my Fluke 179? No. But do I trust the HF meter to tell me if I have 120Vac +/- 2 v at an outlet? Yes.
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Old 08-10-2015, 11:15 AM   #8
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Quote:
Originally Posted by ddawg16 View Post
Explode on 240Vac? I'd like to see that.

Sorry, but I don't buy your negative assessment of the HF meter. Yea, it's cheap, but it works. My son has used it to measure house voltage with no issues.

And I don't know of 'anyone' who has had an issue with it. Do I expect it to out perform my Fluke 179? No. But do I trust the HF meter to tell me if I have 120Vac +/- 2 v at an outlet? Yes.
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Old 08-10-2015, 02:21 PM   #9
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That "test" was performed by connecting the multimeter to the meter base on an amperage setting. It created a phase to phase fault. You would expect the meter circuitry to be the weak link.

The video was created to sell fused leads.

That would not have happened on a voltage setting.
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Old 08-10-2015, 05:24 PM   #10
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Quote:
Originally Posted by Oso954 View Post
That "test" was performed by connecting the multimeter to the meter base on an amperage setting. It created a phase to phase fault. You would expect the meter circuitry to be the weak link.

The video was created to sell fused leads.

That would not have happened on a voltage setting.
I believe the point was what could happen with a mistake with an inexpensive meter. Even pros make mistakes, certainly someone buying a $10 will.
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Old 08-10-2015, 06:13 PM   #11
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That 'cheap' meter has a fuse in the current range. The fuse will blow.

In the above 'staged' video, I'm guessing things were modified in order to create the drama.

I've put my meter across 480 with it in current mode. Yep....blew the fuse. But the only indication I had that it was happened was the lack of a reading. It didn't blow up.
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Old 08-10-2015, 06:29 PM   #12
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Does the HF even have a fuse? I haven't looked, I won't be using mine for that. But I have seen the discussion on eevblog a few times. For example:

http://www.eevblog.com/forum/chat/sm...a-cheap-meter/
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Old 08-11-2015, 06:56 AM   #13
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Quote:
Originally Posted by ddawg16 View Post
... In the above 'staged' video, I'm guessing things were modified in order to create the drama...
Exactly! An explosion being heat and pressure, is visually uninteresting and usually with little flame or smoke, unless an appropriate fuel is present. Movies and TV, being visual, have no way to represent heat or pressure so their explosions nearly always include a fireball created by adding gasoline, napthalene, etc. But we are "primed" to expect such added visual components.

YouTube, is also a visual medium so draw your own conclusion.

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