Testing for current leakage

Anonymous-0

Well-known Member
O. K. I read and copied this about 8-10 years ago. Now I can not find it. It was a home made tool a guy had rigged up to test for slow current draws. He had put a light bulb in series to see if there was any small current draw. On this tractor it took a week at least for the batteries to go dead. There was something unusual about the size of the bulb he used. Anybody have any comments or suggestions? Thanks in advance. J.
 

The lower the wattage, the sensitive the lamp will be to low current flow.
For all a multi meter costs these days. A good one with volts AC & DC, DC amps up to 10amp and ohms for $20.
 
Those tiny 12 volt incandescent automotive marker/indicator lamps (seems like No 94 ???) are fairly low wattage and it wouldn't take much current to see a dim yet still visible glow. If one terminal is on hot 12 volts and the other a dead ground she glows bright, but if theres a resistive connection she may glow dim or not at all depending on how much resistance.

Even a cheap ammeter gives a fairly accurate answer however. Heck a round 20 amp tractor dash mount type of ammeter has decent resolution at lower currents, that would work better then a test lamp. And theres even inductive meters you just hold up against a wire to read current flow.

John T
 
Harbor freight sometimes give away, as a free
gift, a cheap digital vom. I have about 6 new one
hanging on pole barn wall. They go as high as 10
amps and down to the micro amps.

There was a time I had a senior moment, mesured
120vac on the ohm's scale. One big snap and meter
was shot.

I used one to find a very small current drain that
would take 13 days to drain a battery. It was the
tiny light next to the mirror on visor that
wouldn't turn off. Drain was only a few milli
amps.
George
 
I've always used the regular old test light. The clear plastic pointed ones with a small (smaller the better) incandescent lamp.

If the lamp doesn't glow at all, that's great. If it is a very faint glow it's probably a memory circuit in the clock or some electronic device, would take months to even begin to drain the battery.

A bright glow means something is draining the battery.

Volt meters are too sensitive. They can pick up insulation leakage, send you on a senseless chase that means nothing.
 
A digital multimeter will do the trick, but you need to understand your electrical theory before you start to do leakage tests. Otherwise you'll end up blowing the (often expensive) fuses in the meter.
 
At the vocational school, all our VOM's had a ATO/ATC type automotive fuse holder soldered into one of the leads. That way, if a fuse blew, it was the cheap automotive fuse and was easy to get to and replace.
 
In my 50 or so years of electrical troubleshooting (from amateur high school hobbyist up through BSEE and 40+ years as an EE)

I've also used a test lamp,,,,,,,,, and I've used an Ammeter,,,,,,,,,,and I've used a Voltmeter but never had a problem with a meter being "too sensitive" but can see how Billy Bob may have a problem with that as you mentioned lol

Best wishes

John T
 
well John I must be a Billy Bob since I have only been working as an electrican then as a HVAC controls guy since 1977 and have seen and used plenty of didgital VOM's that are "too sensitive". The master Electrican who taught me in 1976 complained that his high end digital VOM was "too sensitive" so he must have been a Billy Bob also. He did teach when and where to use a Digital VOM, where to use a Analogue VOM and most importantly when a set of test lamps in series was the best indicator.
Also John, Honeywell Inc where I attended tech schools at as an employee also taught me when a Digital VOM was "too sensitive" and how to work around this in the field. So Honeywell must have been full of Billy Bob's also
Ron
 
Fun post, all I can say then is Hi Billy Bob lol, no harm or bad intentions intended of course and I apologize if any offense was taken. I use that term light hearted in jest for the types out there (you know who they are) who wired their house over a case of beer and now think they are experts lol. If a person such as you or others who understand electricity use a meter and know what theyre doing and how to interpret the readings its not a problem AGAIN HOWEVER if Billy Bob who has no idea what hes doing tries that its likely a miserable failure. I still cling to my old Simpson 260 Analog yayyyyyyyy

God Bless best wishes and thanks for your input

John T
 
Evel, I think most EE's will take issue with the idea any instrument is "too sensitive". The real issue with digital multimeters is they have high input impedances (typically 10 megohms) which can cause confusion if you don't understand the consequences of input impedance.

Analog VOMs typically have sensitivities of around 10 kilohms/volt. That means on a 20 volt scale, the input impedance is about 200K ohms. That's plenty high for most electrical work, but low enough to drive you nuts when working on electronic gear. So VTVMs (vacuum-tube voltmeter, even though later VTVMs were actually transistorized) were developed to meet the needs of electronics techs. These had sensitivities of 100K ohms/volt or more. When digital voltmeters came out, manufacturers standardized on 10 megohm input impedance, probably because that matches the input impedance of an oscilloscope with an "X10" probe.

Normally higher input impedance is better, but high-impedance instruments are sensitive to noise. In electrical work, this is most noticeable if you try to measure voltage on an open circuit; what appears to be "good" voltage might just be noise.

You can always "downgrade" your digital multimeter to analog sensitivity: Just place a 100 kilohm resistor across its input.
 
I can remember when my old Simpson 260 was widely used (still proudly have mine) and then they started improving sensitivity and resolution and ability to measure extreme low voltages etc and likewise the price "improved" (increased) lol In my navy electronic component testing days there wasn"t hardly anything as too sensitive, its in part a matter of if the user knows what hes doing and what it is hes trying to measure and the expected readings and voltages and in certain applications the more sensitive the better, i.e. never too sensitive provided. In modern cars some memory chips may draw such low currents they are barely measureable while in an old tractor its probably easier to trace down faults. STILL it makes a difference if its Billy Bob or an experienced electronic tech or engineer that is using the meter and if its really too sensitive or not.

I always recall the EE 101 definitions, an "Ideal" Voltmeter would have infinite resistance while an "Ideal Ammeter would have zero resistance, and you or I know why also!!!

As always fun sparky chattin with ya

John T
 
(quoted from post at 12:00:01 07/10/14)

......You can always "downgrade" your digital multimeter to analog sensitivity: Just place a 100 kilohm resistor across its input.

Mark,

Great tip - I learned something tonight.

Thanks
 
Hi John,

I, too, have a Simpson 260, which it seems I forgot to return to my employer at some point in my career. It sits unused in my tool chest. It didn't work the last time I tried it; I suppose corrosion got to the switch contacts. One of these days I'll try to resurrect it. I'm not sure how old it is; it's been in my possession for 35 years. It was a great instrument in its day, but that day was nearly half a century ago. It's big, not particularly accurate and somewhat delicate.

The meter I actually use is a Fluke 77, which I purchased at great expense in 1992. It rattles around in my tool bag until I need it. It's been dropped and otherwise abused and hasn't given me a bit of trouble. Every ten years I have to replace the battery. If it ever fails, I'll buy another Fluke, although probably one with more functions than the 77. (I'd like frequency and maybe true rms.)

With decent digital multimeters selling for less than fifty bucks, everybody should own one.
 
Ken, my suggestion to downgrade your multimeter with a resistor was made somewhat in jest, although it will work for voltage measurements. The important thing when troubleshooting is to treat every measurement with a healthy dose of skepticism. If the reading doesn't seem right, figure out why.
 
Thanks for all the good comments! I do have a "cheap" meter as well as a Fluke that is classified as more of an industrial meter. My former employer gave it to me after a major project they had. I taught a fundamental using a meter class one time. All 10 in the class had a Fluke meter their employer had purchased for them and they all had blown fuses when we went to use the Amp side. Yes fuses were around $10.00 about 8 years ago. Again thanks for all the good information. I wanted the light because I can not see the meter to read it when I do some of the checks. Thanks again! J.
 

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