Troubleshooting a fan speed controller UPDATE

Thread Starter

Tonyr1084

Joined Sep 24, 2015
5,215
Back in June I was asking about a flyback diode to go onto a 12 volt blower. I think that subject has been covered. So I've built this circuit below, you may have seen it. Here's what it IS doing and what it is NOT doing:

First, it consists of a dimmer control out of a 1989 Toyota car - the dash board dimmer lights. First question you may have is "Does the dimmer work?". Answer - Yes. It's PWM and it is PWMing. Checked it with the scope. Its output varies between 5% and 95% with full on and full off at either end of the pot. So it can switch to full on or full off or somewhere in-between the 5% and 95%. However, my IGBT doesn't seem to be doing anything. Is my thinking wrong? Applying power to the gate via the Sink doesn't turn the test lamp on. Have I got the wrong IGBT? Or just wired wrong?

I've cut the 1KΩ resistor out. No change. I've jumped the resistor (what was V+) to Neg. No change. The IGBT is IRG4PSH71K and I'm not good with data sheets, but it looks like it takes about 15 volts to turn on. Yes? No? I've set my supply to 15 volts but it still doesn't do anything. Tested the light bulb with the PS set to 15.9 volts. Upon connecting the 12 volt tail-lamp the lamp lit but the voltage dropped to 6.2 volts. When I connect the blower (after verifying the circuit works) it will be powered from a 12 volt car battery.

I'm at a loss. Stuck.

Note to moderators; if this is in the wrong category - sorry. I only know I need help.

Variable Blower1.png
 
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MisterBill2

Joined Jan 23, 2018
7,272
First, I would check that the power source is able to run the motor. Then I would verify that the rest of the wiring is able to power the motor. A motor that draws 36 amps at 12 volts is effectively a 1/3 ohm resistor, and so to provide any worthwhile powr to that motor the resistance in the rest of the circuit needs to be very small. So the problem may have nothing to do with the motor. try using that same circuit with a small lamp bulb and see if it works with that
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
5,215
try using that same circuit with a small lamp bulb and see if it works with that
Applying power to the gate via the "SOURCE" (not sink) doesn't turn the test lamp on.
Tested the light bulb with the PS set to 15.9 volts.
I may have failed to make clear that I was using a test lamp to verify the circuit before stepping up to the big motor. But in response to your suggestion - yes, I've tried that. Even tried connecting directly to the PWM sink. The bulb didn't light.

Before building the circuit I tested the PWM dimmer and it worked. So I'm not sure exactly why it's not working now. I plan on completely disconnecting the IGBT and going directly to the bulb. And yes, even the bulb works. I'm wondering i f it's my power supply. It's an old school training supply with a 120 VAC input through a Ferro-resonant isolation transformer that then goes to an Auto-transformer. From there you can have a varied AC or DC supply. The DC is through a full wave bridge with caps and a coil to buffer the output.

When testing the lightbulb itself setting the voltage to 15 VDC then connecting the bulb, the voltage drops - depending on which filament I use - to either 9 volts or 6 volts. So the supply is not a regulated device, just a variable device. And like I said it's from a school electronics lab from very long ago. There is NO solid state in it at all. In fact, the MOST technological component is the isolation transformer.

The PWM dimmer IS doing its job. The scope proves that out.
 
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Thread Starter

Tonyr1084

Joined Sep 24, 2015
5,215
I think what I'm asking is how to turn the IGBT on. My assumption is that it takes a voltage on the Gate to conduct current from the Collector to the Emitter. That's why I put it as a follower. This is my first experience with IGBT's. A few years ago I may have messed with a MOSFET and I believe it worked. However, due to the high current needs of the blower I've tried substituting in the IGBT in place of the FET. Obviously I need to learn more about it.

If you've looked at the data sheet, I'm not sure if I read this correctly, but the Qge turn on voltage is 47 volts ? ? ? If that's the case then this particular IGBT isn't going to work. In that case I'll have to go back to the FET but try and find one that can handle the motor current. No sense in building a circuit that can't handle the amperage.
 

shortbus

Joined Sep 30, 2009
8,043
How fast is the PWM switching? IGBT's don't like fast switching. Why the 1K ohm resistor from the positive voltage to the gate? Shouldn't that be to ground? Why pick an IGBT that's rated for 1200V when only using 12V? I don't see your concern to find a mosfet that will switch 36 amps, they are available to work into the hundreds of amps.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
5,215
@shortbus Couple things: First, this IGBT is something I got out of a pool / spa controller. I have a few of them. I also have a number of FETs out of the same source. The FETs that I have can not handle the current I anticipate. So having something as big as the IGBT solves the problem of the potential current draw of the motor at startup.

In testing the circuit I have cut the resistor out - had no affect. I jumped the resistor to ground - no affect. Left the resistor completely out of circuit - again, no affect. As for the value of the resistor, someone, somewhere, I don't recall exactly where, commented on my original design using a 10KΩ resistor, that it was way over valued.

Finally, the PWM speed? Haven't looked at that yet. I'll set up the board and see if I can figure out the answer to that. I'm not very experienced with an O-scope. Sweep rate, how many divisions - etc. But I'll give it a shot. Will have to get back with that part.
 
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Thread Starter

Tonyr1084

Joined Sep 24, 2015
5,215
PWM rate: Scope set to 1 µS, scope shows 2.6 major divisions Positive edge to positive edge. However, I think I've discovered the problem: Output from source is only 29 mV. I might have hooked it up backwards initially. Oops! Looks like this project just came to a crashing halt.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
5,215
Having opened the PWM module, there's a large transistor looking device marked K972 (next line) 8. Below that is a symbol of the manufacturer that looks like a target with points at North, South, East and West. It MUST be a transistor. Trouble is it's riveted in and I'll have to go get the drill and remove it. Will take some time though. Once loose I'll check to see if the transistor (assumed) is open. If I had to guess I'd say it is an NPN transistor. The 30 mV output is coming from the PWM board through the Base to the Emitter. The Collector is probably where the failure is (due to inadvertently reverse polarity hookup). Yeah, I think I did that. Doesn't take long to blow something out, does it?!
 

MisterBill2

Joined Jan 23, 2018
7,272
Quite possibly a 2SK972. but I have also seen model numbers starting with just K. 2SK types are N-channel FET devices. That looks like a Hitachi label.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
5,215
Judging from the PCB picture, the "Out" is a SINK. But if it's a FET then how can I be getting 30 mV on the "Out"? Unless it's gone short internally.

[edit] got 30 mV by testing it the wrong way.
 
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Thread Starter

Tonyr1084

Joined Sep 24, 2015
5,215
Since I'm using this PWM dimmer to control the IGBT can I replace it with a 2N7000? If not - why not? I'm not asking it to handle any high amounts of current such as dimming dashboard lights, it's only providing a pulsed signal to the gate of the IGGY.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
5,215
OK, I really need to slow down and rethink this whole thing. The PWM Dimmer works just fine. Using the "Out" as a "Sink", I can light and control brightness with the dimmer just fine. So back to the original question - - - What am I doing wrong? Could my IGGY be bad? I'm NOT getting any control through my IGGY.
 
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Thread Starter

Tonyr1084

Joined Sep 24, 2015
5,215
IGBT is working fine with DC. When I touch 12VDC to the gate, using the Iggy as a follower (Power to the device under control, through the iggy to ground as shown in the diagram) it switches on. So maybe it's an issue with the speed in which the dimmer is on. HOWEVER, when I turn the dimmer to full brightness there's a pure DC signal present. The iggy should come on. No??? Could the 1KΩ be too much? I don't want to draw too much current with a lower resistance.
 

Dodgydave

Joined Jun 22, 2012
9,651
IGBT is working fine with DC. When I touch 12VDC to the gate, using the Iggy as a follower (Power to the device under control, through the iggy to ground as shown in the diagram) it switches on. So maybe it's an issue with the speed in which the dimmer is on. HOWEVER, when I turn the dimmer to full brightness there's a pure DC signal present. The iggy should come on. No??? Could the 1KΩ be too much? I don't want to draw too much current with a lower resistance.


2SK972 is a Nfet.


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