nuckolls.bob(at)aeroelect
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 Posted: Mon Jan 04, 2010 9:15 am Post subject: Question about 16V POLYFUSER Radial Leaded Resettable PTC |
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At 09:41 PM 1/3/2010, you wrote:
Go to http://tinyurl.com/yzs2u65 and review the
discussions on Exp Bus and Greg Richter's polyswitch
based products.
The polyfuse has been around for 30+ years. We
looked at them for general circuit protection in
the GP-180 program at Lear. We looked at them
at least twice that I know of at Beech/Ratheon/
Hawker-Beech. In no instance were we able to
integrate these products into either legacy or
current design goals for TC aircraft.
These devices are intended for integration inside
a product where their unique issues of wiring
(20AWG solid wires soldered to ECB), mounting for
vibration resistance, self-resetting, etc could
be smoothly integrated into the product.
None of the studies lasted more than a couple
of days before we agreed that they're fine
in a clock radio or toaster . . . or even
some automotive applications.
My cars use poly-fuses in series with the
window lift motors. They are used in lieu
of limit switches for actuator travel. In this
case, the lift mechanism hits a hard mechanical
stop at travel limits whereupon you are expected
to release the switch. But if you continue to hold
the switch for say 30 seconds. You'll find that
the motor mysteriously goes dead. You'll have to
wait a minute or two for the polyswitch to cool
off before the system ops return to nomral.
Interestingly enough, the polyswitch does not
protect the window lift motor feeders from the
bus. There's still a fuse in that slot.
They're a fine product and perform as advertised
in gazillions of situations. But they were never
intended for and do not integrate well into
general protection of power distribution feeders off
a bus. This is especially true of aircraft when the
owner-operator wants to be aware of any fault that
generates a trip so that the difficulty can be
accommodated (plan b) and fixed on the ground.
The only instances I've observed attempts
to pull this off are on EXP-Bus and on Richter's
proposed product described in the articles
cited in the above literature search.
Bob . . . [quote][b]
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