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1. 12:18 PM - Re: Re: Clearance Delivery Diode Leakage (Robert L. Nuckolls, III)
2. 08:49 PM - Any ideas where to get electric motor brushes? (rparigoris)
Message 1
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| Subject: | Re: Clearance Delivery Diode Leakage |
At 07:10 PM 12/31/2020, you wrote:
>
>
>user9253 wrote:
> > Check for electricity on the main bus using a test light.
> > The light will not illuminate. That means there is no voltage on
> the main bus.
> > Leave the test light connected to the main bus, then measure the
> voltage with
> > the digital meter again. The main bus will now have zero
> volts. The diode is OK.
>
>
>I see....The test light (load) on the main buss drains the residual
>voltage and kinda make the diode seal better like a check valve
>with differential pressure would.
No, leakage through the reverse biased diode is
relatively constant irrespective of the load. Consider
the attached drawing. The red boxes represent your
ship's battery and the diode under study. I've
depicted a reverse leakage resistor RL2 around the
diode.
To read 0.4v across a 10M resistor in series (your
voltmeter) describes a ratio:
RL2 + 10M 10M
---------- = ----------
12V 0.4V
Solving for RL2
RL2 + 10M = (10M x 12V)/0.4V
RL2 = [(10M x 12V)/0.4V] - 10M
RL2 = 290,000,000 ohms which
represents a parasitic (leakage)
load on the battery of
12/290M ~ 41 NANOAmps
For this leakage to take say, an 18AH battery
down to 1/2 capacity would require . . .
9,000,000,000 nAHr/41nA = 220 Million hours
or roughly 25,000 years.
The value for leakage current is generally
always cited on data sheets for diodes but it's
so tiny that only in very specialized, small
signal applications is it significant to the
design. We CAN measure it, as you have done,
but in the airframe, its more of a curiosity
than a concern.
Also, reverse leakage varies widely with temperature,
applied voltage and batch-to-batch variations.
Going back to the drawing I show another 'leakage'
resistor (RL1) that is internal to the battery.
All batteries have one of these and depending
on chemistry and temperature, it too will discharge
the battery. Most secondary SLVA and Lithium products are
good on the shelf for 1-2 years.
I suggest that leakage inside the battery is
of far greater concern than diode leakage(s)
outside the battery.
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"
Message 2
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| Subject: | Any ideas where to get electric motor brushes? |
Hi Group
I need some brushes for the exciter on my Monarch EE lathe. Was making some aeroplane
parts and it quit.
Sizes needed:
3/8" x 3/8" and worn out length is 1.060", it has a shunt and terminal (need 4,
will buy 8)
1/2" x 1/4" and worn out length is .495", it has a shunt and terminal (need 2,
will buy 4)
Any ideas where I can purchase from?
Thanks
Ron P.
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