TIP3055 NPN transistor thru put

[Oxford]

A new IRF510 MOSFET met all the tests:
battery voltage 12.01
volts across the 10 ohm in parallel heaters 10.72
volts across the source and drain 1.19

I also took out the V+ hook up to the gate and pulsed the MOSFET from a 2N2222 and observed 1.9 amps being drawn thru the heaters.
The Mosfet can dissapate 20 Watts. Why would I not use the darlington with a 65 watt dissapation??

Thanks,
Roger

[Oxford]

Looks like I'm talking to myself but actually I'm going to post a JPEG image as suggested earlier to describe my efforts at assembling a percent time on controller.



Apparently I have to use the MOSFET to turn on the Darlington instead of vice versa. The darlington does have more ampacity.
My objective is to fine tune the timer circuit to control heat on the two 10 watt heaters.
comments are solicited.

Thanks for the help,
Roger

[Bigglez]

A new IRF510 MOSFET met all the tests:
battery voltage 12.01
volts across the 10 ohm in parallel heaters 10.72
volts across the source and drain 1.19

Excellent!

I also took out the V+ hook up to the gate and pulsed the MOSFET from a 2N2222 and observed 1.9 amps being drawn thru the heaters.

Excellent!
A diagram would really help us...

The Mosfet can dissapate 20 Watts. Why would I not use the darlington with a 65 watt dissapation??

Because you are confusing device performance
limitations with circuit performance.
The power dissipated by the FET is governed
by the load current and the RSD(on) of the
Fet that you picked. A lower RDS(on) would
reduce the power dissipated in the FET.
Comparing that with the bipolar (single or
darlington connected) the power will be greater
because the bipolar device can not reach the
same level of stauration peformance as a
PMOSFet.

For the IRF510 at RDS(on) = 200milliohms
IF driven hard on.
Using your data: P= V*I = (12.01 - 10.72)*2.2
=2.83Watts
A TO220 package in free air is only good for about
one watt of dissipation (regardless of FET, Bipolar,
Darlington, or Triac or other structures).
*** You will toast this part at 2.83Watts ***

A better FET would help, and multiple FETs (but
not bipolars or Darlingtons) can be connected
directly in parallel to spread the heat over several
devices.

[Bigglez]

Looks like I'm talking to myself

If my help is not wanted I can spend my
time doing something else...

[Bigglez]

This circuit as drawn can't possibly work!

[Bigglez]

Looks like I'm talking to myself

I feel the same way!

Apparently I have to use the MOSFET to turn on the Darlington instead of vice versa. The darlington does have more ampacity.

For the last time. Please do not use any Darlington transistor
in your design while we are helping you with a PMOSfet
solution.

The FET is superior in every way (power dissipation,
efficiency, switching speed, freedom from thermal
runaway, freedom from charge storage delays, ease
of driving, cost) compared to a 1970s technology
Bipolar transistor.

[Oxford]

I was posting too maany replys to prove that I had learned how to upload an image. I did not mean that I wasn't getting attention. Sorry.
The Darlington is out. Of course the MOSFET drive the heaters but it does get hotter than the darlington and quick.
It sound like a MOSFET with better ratings for the job or two in parallel is the next order of business?
I think that one good MOSFET is better than two, because if one of two fails the other one should fail with more heat and fanfair!
I may have a technical error in the drawing but it ran for more than 10 minutes as drawn with heaters on. Please give me a hint.

Roger

[Bigglez]

The Darlington is out. Of course the MOSFET drive the heaters but it does get hotter than the darlington and quick.

Good!

I may have a technical error in the drawing but it ran for more than 10 minutes as drawn with heaters on.

Going back over the recent posts I see that you
tested the first FET with an LED and found it
was dead. The replacement FET of the same
part number is not able to run the heater load
without a heatsink of its own, according to
your test data.

It sound like a MOSFET with better ratings for the job or two in parallel is the next order of business?

Yes. There are lots of candidates, here's my pick.
Here's the IRF3704 data sheet

Here's a test circuit to use with the new FET:


Pressing S1 will turn on the heater 100%, and
light the LED. Measure and record the voltages
for the supply and the voltage across the heater.

[Oxford]

Ordering IRF3704 from mouser
Roger

[Bigglez]

Ordering IRF3704 from mouser
Roger

Okay, but when I checked Mouser
it was substituted to a back ordered part.
I found it in stock at Digikey (PN IRF3704ZPBF-ND).

[Oxford]

This my final posting in this subject. The drawing (JPEG) is intended to show a tested circuit with the parts suggested by those that helped me on this forum achieve a functioning project.
The 2K resistor should be reduced in size to about 1K in order to have the reference pot work more in the mid range. The desired external temperature range is about 170 degs F.
I finally used 24 " rope heaters in parallel drawing a total of 2.74 amps. This is a little on the weak side because it takes about 15 minutes to reach the comfort range.
The ideal rope heater should wrap snuggly around a 3/8" brass tube 4" long (solder a 7/16" brass washer on each end as a stop). Tie the heater to stop unwraping. Grind a path thru the washer for the leads.Place the thermistor in a 1/4" brass tube and insert it into the opening in the brass washer. Stuff the assembly into the 1" ID of the handle bars......
It works!



Thank you for the help,
Roger