Today's Message Index:
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1. 09:53 AM - Re: resistance in solenoid (Eric Page)
2. 11:42 AM - Re: resistance in solenoid (user9253)
Message 1
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| Subject: | Re: resistance in solenoid |
alfuller194(at)gmail.com wrote:
> In the original post, the device in question was described as a 'continuous'
solenoid.
>
> Is that relevant, or am I just being pedantic?
The primary difference between continuous and intermittent duty solenoids is in
their coils. Continuous duty generally have higher resistance coils designed
to draw less current and therefore heat up less. They're designed to be on all
the time without overheating. Intermittent duty solenoids have lower resistance
coils that draw larger current. This makes them close "harder" at the expense
of greater heat, so they can't stay on continuously.
There is often a difference in their contacts as well. Intermittent duty solenoids
are often rated for much higher surge current than continuous duty. Their
aggressive closing velocity and pressure helps them carry higher loads.
The ones we use as battery contactors are continuous duty, while our starter contactors
are intermittent duty. Whether or not to run starter currents through
an already-closed battery contactor is open to debate, but I'm not doing it.
There are ways to protect the starter circuit against unwanted activation without
doing so (one example: a small automotive relay interrupting the starter
switch circuit, with its coil in parallel with the battery contactor's coil,
so that it pulls in at the same time as the battery contactor).
Does the OP's aircraft route starter current through the battery solenoid? If
so, could that have burned its contacts, causing a high resistance connection?
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=516720#516720
Message 2
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| Subject: | Re: resistance in solenoid |
The OP sent me a private email. He indicated that there are two continuous
duty contactors, only one used at a time. Which ever one is energized will
carry starter current and aircraft load. He said the engine cranks just fine.
I assume there is a separate starter contactor. I do not have a schematic. He
measured the voltage drop across each continuous duty contactor when it was
independently energized. He measured 0.82v across one contactor and 0.42v
across the other contactor with the voltmeter probes on each large stud and
with the contactor energized.
I suggested that he turn each contactor on and off 100 times in an attempt to
wear away any contact oxidation, then repeat the voltage measurements.
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=516721#516721
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