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Efficiency of adjustable 3 terminal current regulator?
Efficiency of adjustable 3 terminal current regulator?
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Old 1st August 2018, 04:06 AM   #21
TMM is offline TMM  Australia
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Hard to beat a PPTC resettable fuse for what you want to do. http://au.element14.com/bourns/rht20...ettable%20Fuse

This will allow you to draw 2A more or less indefinitely. 4A for 20seconds, 8A for 2 seconds etc. If you trip it then you have to reduce your current draw to near zero to reset it.

As for "protecting over and above the fuse", maybe not. If the goal is to never burn things down then a fast blow fuse is the best option. As for being less annoying, a PPTC is definitely yes. I don't think you will find any air compressor that uses less than 2A. The small compressor I use to inflate car tyres uses >10A. Upgrade your wiring/socket in that case.

Last edited by TMM; 1st August 2018 at 04:13 AM.
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Old 1st August 2018, 04:22 AM   #22
leadbelly is offline leadbelly  Canada
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Many thanks.

As for what I meant by "over and above" I realize that was a poor choice of words. I was not hoping for a device to provide a higher level of safety than a fuse, I was looking for a circuit that would essentially protect a higher current device from blowing the fuse if plugged in.
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Old 2nd August 2018, 05:56 AM   #23
PRR is offline PRR  United States
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Quote:
Originally Posted by leadbelly View Post
Is the crossword all done? Are the other threads boring?
Yes. Yes.

Quote:
Originally Posted by leadbelly View Post
...devices on my utility trailer behind my car. Things like USB chargers, trouble lights, travel coolers, air compressors. Some are over 2A, but there's always trial and error ...
OK. Some of those things probably should not sit at say 4V 2A, they may be unhappy. You want a fold-back current limiter. Up to 2 Amps, it passes freely. Exceed 2A, and it folds-back to maybe 0.1A at zero V. This will prevent damage. Done right, when you remove the culprit, it comes back to full voltage without user action.

Of course you want green and red LEDs so you know that it cut-out, not that the appliance is sick.

Since the real limit is wire heating, it should have some time-constant appropriate to wires. Several seconds of a 5A start-up on a 2A wire will not burn the wire.

BTW: Harbour Fright sold me a trailer harness with "2 Amp" wire. Moderately plump plastic with incredibly thin conductors inside. It maybe carried 2A when new. But a year on the shelf, it all went bad. The plastic was not fully cured and rotted the conductors multiple places.
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Old 2nd August 2018, 06:00 AM   #24
PRR is offline PRR  United States
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bjt - How can I calculate knee current for this foldback current limiter - Electrical Engineering Stack Exchange
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Old 2nd August 2018, 08:12 AM   #25
leadbelly is offline leadbelly  Canada
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Quote:
Originally Posted by PRR View Post
Yes. Yes.



OK. Some of those things probably should not sit at say 4V 2A, they may be unhappy. You want a fold-back current limiter. Up to 2 Amps, it passes freely. Exceed 2A, and it folds-back to maybe 0.1A at zero V. This will prevent damage. Done right, when you remove the culprit, it comes back to full voltage without user action.

Of course you want green and red LEDs so you know that it cut-out, not that the appliance is sick.

Since the real limit is wire heating, it should have some time-constant appropriate to wires. Several seconds of a 5A start-up on a 2A wire will not burn the wire.

BTW: Harbour Fright sold me a trailer harness with "2 Amp" wire. Moderately plump plastic with incredibly thin conductors inside. It maybe carried 2A when new. But a year on the shelf, it all went bad. The plastic was not fully cured and rotted the conductors multiple places.
Many thanks.
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