[Healeys] fuel pump condenser

[Alex]

Just to clarify, you will not harm a capacitor, even a polarized 
electrolytic type, by "testing" it with an ohmmeter (continuity tester) with 
the leads reversed. You can, however, harm an electrolytic cap if it is 
installed backwards in a circuit. Some can even explode.

Years ago I was troubleshooting a Heathkit stereo amplifier that a customer 
had newly assembled. The electrolytic cap in its power supply blew up like a 
firecracker. Fortunately for me I was wearing glasses, so the bits of paper 
and aluminum landed on  my eyeglass lenses and not in my eye. Turns out the 
cap was marked backwards! The customer had installed it "correctly" 
according to the markings as per the kit's instruction manual. That was a 
rare bird---but almost cost me dearly.

Also, digital multimeters with capacitor test functions typically reveal a 
cap's value. They do not check for leakage. Only a capacitor tester that 
applies voltage to a cap can do that, which is why I always have an ancient 
Eico capacitor tester in my shop. Using it you can apply DC voltage to a 
capacitor under test, and watch the instrument's "magic eye" green tube to 
see how it reacts. I often find bad caps this way in radio sets that I 
repair, especially the old Sprague Black Beauty types.  Ditto for 
electrolytics.

Finally, the best "test" for a suspect cap is substitution.

== Alex in Maine
     "The Blue Mainie," 1960 Austin Healey 3000 BT7
     "Conkling," 1946 M.G. TC #1321
     Former owner 1957 A-H 100-6, 1967 A-H BJ8,
     1965 MG Midget
     http://home.roadrunner.com/~alexmm



----- Original Message ----- 
From: "Bob Spidell" <bspidell at comcast.net>
To: "Richard Kahn" <tahoehealey at hotmail.com>
Cc: <healeys at autox.team.net>
Sent: Wednesday, April 02, 2014 12:00 PM
Subject: Re: [Healeys] fuel pump condenser


> Condenser = Capacitor
>
> I think some (expensive) DVMs have a capacitor check function. A 
> capacitor/condenser is basically a current sink, at least until it becomes 
> saturated with electrons. So when you apply voltage/current to a 
> capacitor, it will appear as a dead short for a brief instant, then appear 
> as an open circuit. Conversely, the capacitor will discharge its electrons 
> when its leads are shorted or a load is placed across them. You can test 
> for a shorted capacitor with the voltage and/or continuity function on a 
> DVM--if it's shorted there will be no voltage (just like crossing the tips 
> of the leads). If it's open, well, that's where you need a capacitor check 
> function.
>
> I seem to recall you can test with an 'old school' moving coil 
> voltmeter--when the leads are applied to the capacitor the indicated 
> voltage will rise a bit slower than an open circuit.
>
> Note some capacitors--notably electrolytics, which are sometimes used in 
> (older) SU pumps--are polarity sensitive. Apply the leads backwards and 
> you can/will destroy the capacitor (probably leading to a short 
> condition).
>
> Bob