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United States, UT, Park City
Joined Mar 2009
143 Posts
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Yes, the difference between 22C and 60C is about 0.2A. The resetting takes a few seconds. |
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I would imagine as a general rule, any device tripped due to temperature won't reset until cooling down and since ambient temp is a factor, when combined with a high current servo, this cool down period may take quite some time. If it trips in a cooler environment due mostly to an overloaded circuit I suspect the reset time may actually be a few seconds but in the wamer climates I can see it taking longer.
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United States, UT, Park City
Joined Mar 2009
143 Posts
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See Buckeyeflyer, maybe we're both right! Holding servo stalled at 3.74A/75C for 60 sec raised the temp by 1C only. |
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Poly fuses can take weeks to finally get back to it's original resistance values:
See here: https://en.wikipedia.org/wiki/Resettable_fuse Polyfuses are are great, but not for this application!!! Quote:
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Also PTC's may remain latched until all power is removed. Cooling or ambient temperature or the addition of a heat absorption device will affect how quickly a PTC (Poly Fuse) returns to 80% of resistance state. Meaning you still won't get full voltage to whatever it was powering.
Here's some interesting reading: https://www.littelfuse.com/~/media/e..._paper.pdf.pdf From this document, there are several factors involved. Temperature (ambient) + cabin temp: Can affect recovery time and load which trips the poly switch. Current: If power is still flowing the poly fuse, it can remain in it's tripped condition. And (not in this document, but documented in a video) When the CB200 is tripped, and the fuses reset, the PWM Signals get out of sync which causes unpredictable movement of servos / control surfaces. |
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I would rather land on fire with a possibility of control than have a defective device force a crash for questionable reasons. I suppose folks with high end planes feel warm and fuzzy with the "protection" but it looks like this form was released before its time.
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Esprit Model | |
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Melbourne, FL, USA
Joined May 2007
586 Posts
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So that being said ZB what temp do you set the alarm? |
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Can I get an Amen..... Now Ed this guy knows what he is talking about... |
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ZB does bring up a good point, there is a temp sensor inside the CB that is alarmable... I realize this won’t help with a high current situation causing the poly fuse to trip but it should give you some warning or reason for caution if you are starting with a high ambient temp. You could also use it to know if you need to direct airflow over the CB and if your deflected airflow over the CB is working.
On question for Joe and Buckeye flyer, when you say the poly fuse tripped at a lower load every time, were you tripping it back to back with no or little recovery time? Or were you allowing the CB / Poly fuse time to recover (fully get back to ambient temp) and then tripping it again. If it was back to back with no recovery time that’s a little less concerning. If it returns back to “normal” after returning to ambient that’s a much better situation. |
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Once the poly fuse it’s tripped it will not come back to normal operating Range. The chemistry could take days to get back to normal.. |
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