PWM Idle mod on MS PCB 3.0

IvarS · Post by **IvarS** » Mon Jul 31, 2006 12:38 am

I was previously running PWM idle on my 2.2 board with the Bosch -516 valve. I have however moved on to 3.0 now and am having some problems. The firm who made me the MS 3.0 assured me the FIDLE transistor was upgraded to control PWM but it didn't work. It turned out to be a ZTX450 (max 1.0A)

The instructions below explain how to install a ZTX650 (max 2.0A) on a 2.2 board but not on a 3.0.

http://megasquirt.sourceforge.net/extra/pwmidle.html

My question is: Can I install the ZTX650 in Q4 instead of the ZTX450 and expect it to work? Installing a TIP-transistor seems like a lot more work. I just replaced the R16 and Q5 on the 2.2 and it was fine, does the 3.0 board not allow this?

superchargingmachine · Mon Jul 31, 2006 5:05 am

I don't run a V3.0 but on the 2.2 board removing the 2N2222 and poking the correct tabs of the TIP122 in the holes and soldering it in place worked fine.

I would think just pulled the ZTX450 and replacing it with a ZTX650 would be fine if you don't need more than 2A.

IvarS · Post by **IvarS** » Mon Jul 31, 2006 6:42 am

Ok, I will try that! Worst thing that can happen is that I've spent $1 and it still doesn't work.

snillet · Post by **snillet** » Mon Jul 31, 2006 7:21 am

There is some difference regarding the flyback circuit but i do not have the schematics in front of me right now and i do not have time to check it either...

But if the 2N2222 is connected in the same way as on the 2.2 board there shouldn´t be a problem i guess

.

IvarS · Post by **IvarS** » Wed Aug 02, 2006 4:33 am

Just replacing the Q4 with a BD139 doesn't work. When I did this to the 2.2 board, I also had to replace R16 1k with a 510R. What resistor does R16 correspond to on the 3.0 board? Or is a TIP-transistor my only option?

Post by **jsmcortina** » Wed Aug 02, 2006 4:53 am

The flyback also needs uprating. The V3 board as-is will not survive with PWM operation - the flyback zener is fine for an on/off relay operation but the energy from continual PWM operation will overheat it.

You'll have to check the schematics to see the base resistor in question.

James

IvarS · Post by **IvarS** » Wed Aug 02, 2006 8:19 am

Ok, I've bought a TIP121 now as it seems to be my easiest way to get it working. The TIP121 is rated to max 5A, does it really need heatsink to operate my Bosch 2-wire valve @ less than 1.5A?

IvarS · Post by **IvarS** » Wed Aug 02, 2006 11:41 am

Will mount it on the case and wire it into Q4, have been told Darlington transistors need to be mounted on some kind of cooling flange.