Originally Posted by ghoffman

OK, I understand now, 3.73A sounds about right for a 5955. Thanks for the clarification.
I found this about Polyfuses.
So, if I am reading this correctly, the hotter they get, the less current they need to trip. And, it seems they don't reset until they cool off. This is a great idea for some things, but could be disastrous on a flight vehicle

Yes, the difference between 22C and 60C is about 0.2A. The resetting takes a few seconds.

Originally Posted by hpdrifter

Yes, the difference between 22C and 60C is about 0.2A. The resetting takes a few seconds.

The poly fuse does not reset in a few seconds...
That is incorrect information....
I will post video later today that will completely disprove our friend Ed..

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.

Originally Posted by KMatch

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.

See Buckeyeflyer, maybe we're both right!


Holding servo stalled at 3.74A/75C for 60 sec raised the temp by 1C only.

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!!!

When power is removed, the heating due to the leakage current will stop and the PPTC device will cool. As the device cools, it regains its original crystalline structure and returns to a low resistance state where it can hold the current as specified for the device.[6] This cooling usually takes a few seconds, though a tripped device will retain a slightly higher resistance for hours, unless the power in it is weaker, or has been often used, slowly approaching the initial resistance value. The resetting will often not take place even if the fault alone has been removed with the power still flowing as the operating current may be above the holding current of the PPTC. The device may not return to its original resistance value; it will most likely stabilize at a significantly higher resistance (up to 4 times initial value). It could take hours, days, weeks or even years for the device to return to a resistance value similar to its original value, if at all.

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.

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.

Originally Posted by JoeT

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.

Definitely a strong NO on my next radio being a Jeti.

Originally Posted by dhal22

Definitely a strong NO on my next radio being a Jeti.

How is Servo Balancer and Wireless Trainer going, done yet?

Originally Posted by Esprit Model

Why would I even get to that point? We have Telemetry and Telemetry Alarms for any of the 80 data streams I am recording. Seems VERY stupid to drive overheated car and keep driving it till engine explodes. You HAVE Voice, Vibration Alarms, Data Logging, RED Temperature Data Display and ding ding still nothing for some “experts”.

But we can always count on one “Joe” who can get there. You cannot fix STUPID

https://youtu.be/--Z8FDwBkxA

So that being said ZB what temp do you set the alarm?

Originally Posted by JoeT

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.

Can I get an Amen..... Now Ed this guy knows what he is talking about...

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.

Just out of curiosity do the Spektrum Powersafe RX’s have the ability to isolate a shorted or stalled servo? I think I remember reading they have the ability to isolate a shorted battery. What do they use to accomplish this?

Originally Posted by camss69

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.

Please read the article Joe T posted. It is very good...
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..