Re: Larger Starting Capacitor?
- From: "Jerry Foster" <jmfoster711NOSPAM@xxxxxxxxxxxxx>
- Date: Mon, 4 Jun 2007 15:24:43 -0700
Well, I "was" going to correct the top posting, but, since it has gone on
for a while...
You can often "heal" an electrolytic by powering up the cap at low voltage
and
gradually increase it to its full rated voltage. How long it will last is
anyone's guess...
But I somehow doubt that a 4 uF AC capacitor is necessarily an
electrolytic...
And I'm not quite sure what the function of this capacitor is... 4 uF at 60
Hz has
a reactance of around 660 ohms. One would expect a capacitor to have a
reactance
of, maybe, 20 ohms to resonate a start winding. Of course, it is not
necessarily a
good thing to go all the way to resonance. Maybe the idea is just to shift
the phase
a bit. Then, one might expect a reactance of, guessing wildly, maybe 100
ohms.
I would tend to suspect a 4 uF cap is for noise suppression or maybe power
factor
improvement. Recall that the OP described the cap as being "on it." It
didn't say,
as most of the respondents have assumed, that it is in series with a
winding. 4 uF
in series with anything isn't going to allow for much current. It may well
simply be
in parallel with the entire motor...
Jerry
"Robert Swinney" <judybob@xxxxxxxxx> wrote in message
news:4664372c$0$14977$4c368faf@xxxxxxxxxxxxxxxxx
Sorry about the double post. What I intended to say is while John'svoltage.
suggestion good in general terms it may be misleading when checking larger
value capacitors. Electrolytics have a way of "healing themselves", so to
speak. They can be totally ruined in so far as working at their rated
voltage and still appear to be ok on a simple ohmmeter test. A formal
capacity tester shows leakage, or the lack thereof, at some working
can
Bob Swinney
"Robert Swinney" <judybob@xxxxxxxxx> wrote in message news:...
John sez:
"> I have been using ohm meters fro measuring caps for many years. You
secondget a good idea if the cap is good or not by doing a couple simple
tests. First understand that you are using the ohmmeter as a charging
instrument with the ohmmeter indicating the rate of current flow into
the cap. The first thing you do is short out the cap. Then hook up the
leads to the cap and watch the incication on the meter. The meter will
go up and then back to infinite. Its the timing or length of the time
it takes to charge the cap. that is proportional to the value of the
cap. Measure a good one and compare it to the unknown one. The
testtest is to hold the leads on the cap and charge it to full capacity.
Then take the leads off and wait a half minute and then put the leads
back on the terminals. If the meter goes up and then back down the cap
is leaky. Granted these tests are not like using a precision capacity
meter but they work for a general indication of good and bad caps."
"John" <amdinc@xxxxxxxxxxxxxxx> wrote in message
news:46638207.3E879A12@xxxxxxxxxxxxxxxxxx
"Martin H. Eastburn" wrote:
Remember the ohmmeter is for resistors and can be used as an simple
on other parts.
Caps are the hardest since the meter shows if it is open or shorted or
very leaky.
It doesn't show if the cap has capacitance at all. If it is leaky
at voltage or when hot.
John
.
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