MEP 002 hot Q3 transistor

[dangier]

Today I had been running a load test breaking in the new pistons and re-installed rings on my latest 002 and noticed the q3 transistor on the AC power regulator board (5020), is very hot running at 60hz. Could not hold my finger on it for very long. Is this normal as it has a heat sink or am I heading for a replacement? All other components on the board feel cool. I had previously replaced the r11 resistor and cr2 diode as they were burned. Unit is now making good power and had a 240v load bank up to about 6960 watts load (576w inductive/6384w resistive), without the engine lugging down. Load meter showed around 120%. Ran this way for about a half hour, then back to 5000w for an hour and half. Probably could have increased the load in smaller increments using work flood lights, but was worried about the q3.
This is the one with the cracked pushrod tube. Cleaned the crack and sealed with rtv until I can get a replacement tube. No oil leaks during a 2 hour run.
Thanks,
David

 

[PeterD]

... Could not hold my finger on it for very long. Is this normal as it has a heat sink or am I heading for a replacement?...

Not a very scientific test! One's finger is not well calibrated but most semiconductor devices are rated at about 70-100 degrees Celsius which will burn your finger very quickly. Military rated semiconductors may even be rated higher (Military grade: −55 °C to 125 °C (sometimes -65 °C to 175 °C)) and one may assume this is a military grade device.

That said, devices can and will fail when they wish, and are surprisingly smart: they know when they are most needed and will typically choose to fail at that time.

(Consider getting a temperature measuring device such as a contact-less IR or a good contact based one, and measure the real temperature.)

 

[glassk]

I would say a contact one in this case

 

[n1oty]

This is normal for heat-sinked transistors. This is why they are heat-sinked to begin with!! You should see how hot the power transistors get on some of my 12 volt power supplies when under load.

John

 

[dangier]

Appreciate the responses. I have a Fluke thermometer, but when I picked it up, the sensor wires were broken at the plug. My finger was a back-up (calibrated from my refrigeration days). I know it was at least 120+ (read by the speed I pulled my finger off it), and i did not take into consideration that these are military units and are built to take abuse. I did know these are heatsinked, but the metal is not much of one (flat plate).
Guess I will let go as-is and see what happens. Isn't that why we have two or more generators just standing-by?
Thanks,
David