nuckolls.bob(at)aeroelect
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 Posted: Thu Feb 17, 2011 10:56 am Post subject: Wiring diagram question for Pitot Heat On indicator light |
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At 10:59 AM 2/17/2011, you wrote:
| Quote: | --> AeroElectric-List message posted by: "plevyakh" <hplevyak(at)mac.com>
Thanks Bob...that helps.
Can you comment on use of the 18AWG fuselink in the Pitot Heat.pdf schematic in place of a 15amp fuse?
Why wouldn't I just use a 15amp fuse at the bus to protect my wire? |
The cold resistance of a heated pitot tube is about 1/2 that of the
warmed up condition. Here's some data I gathered on a 28v tube.
Cut the resistance values by about 1/2 for a 14v tube.
[img]cid:.0[/img]
Further, from the time power is first applied until the
tube reaches operating temperature can be 20-60 seconds
depending on environmental conditions. A 100w tube will
nominally draw 7A at 14v, a 150w tube will be 11A.
Inrush during warm up can by 2x those values. The duration
of that inrush is protracted compared to a motor or
incandescent lamp. Hence the suggestion for a 'robust'
circuit protection. You can put in larger fuses too.
Suggest 30A for fuse. A 15A circuit breaker would probably
stay in . . . but be prepared to upsize if you get
nuisance trips.
Bob . . .
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