Troubleshooting a fan speed controller UPDATE

shortbus

Joined Sep 30, 2009
8,594
Why? Because
But you seem to be not understanding that the PWM won't work like you want. Your IGBT will always be on even when the PWM is off. This is because of how a gate on a mosfet or IGBT works if there is voltage on it and it can make a reference to the source or emitter it will be on, no getting around that it's just how they work. Maybe you could incorporate some kind of optoisolator into the gate circuit but doing it like your doing is a futile job.

I guess it's time for me to bow out of this, since the only one else that understands is Wolf.
 

shortbus

Joined Sep 30, 2009
8,594
@shortbus I've already explained that the drain current for that FET is 25 amps. 100 amps peak at a duration of 10µS or less
And I explained to you how the amps your driving or sinking have nothing to do with the amps in the mosfet. see again what I said in the second part of post #46 to you.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
6,000
Well Shortbus, sometimes I can be thick headed and stubborn. Until I learn for myself I might not learn.

When I was a child I was convinced of an absolute fact that if you pulled all the buttons out at the same time on the (old style) car radio and then push them in at the same time - I'd get Santa Clause. Not making that up! I believed that to be a 100% true fact. That is until my mother left me in the car listening to the radio. She warned me against pulling out those buttons. AS SOON AS SHE WAS OUT OF SIGHT I pulled those buttons out and pushed them in. To my astonishment (and education) it didn't work. So this may just be one of those things I have to prove to myself. Believe me, if (or when) I discover that you're right I'll come back and publicly state so. I've learned many lessons in life. One of those lessons is to be able to admit when you're wrong. But sometimes we (all of us) believe something to be one way despite others telling us repeatedly it's not that way at all. So forgive me if I have to learn the hard way. Just sometimes that's the only way I can convince myself that it doesn't work.

Incidentally, what you said in post # 46 - if the gate gets charged up then it would stay on - that didn't happen with my lamp tests. In my lamp tests the light never came on. Maybe because the capacitance was never getting a chance to charge high enough. But in manual testing, the lamp lit only when I struck 12 V directly to the gate and extinguished as soon as the power was removed. Doesn't mean I can discern the discharge time, but if what you say is true, the gate should have been turned on until I discharged it. Maybe that's part of the reason why I'm being so stubborn with this.

[edit] I would be happier if you didn't go away. Honestly, I value all input that is not derogatory in nature. I can take constructive criticism.

And Happy New Year y'all. I MIGHT build my circuit to the latest drawing before the end of this year. But there are a lot of things to be done that don't involve me sitting at my workbench testing out circuits. And maybe I have enough time to correspond with y'all, and that may be enough time to actually do the mod's. But one more issue I will be raising when I'm ready to move to actual blower testing; concerning the fabrication of heat sinks.
 

Chris65536

Joined Nov 11, 2019
270
From Post #46:

Your thinking like I did when first working with mosfets. That the D-S amps was the amps through the thing you're switching. But that isn't what "amps D-S" means. It means the voltage times the RDSon.
I=V/R, not V*R. That result doesn't sound right either, as it implies the RDSon for this fat MOSFET is 2.4 ohms. The datasheet says 0.04 ohms max.
 

Chris65536

Joined Nov 11, 2019
270
But in manual testing, the lamp lit only when I struck 12 V directly to the gate and extinguished as soon as the power was removed. Doesn't mean I can discern the discharge time, but if what you say is true, the gate should have been turned on until I discharged it.
This is what lead me to think you might have the collector and gate swapped. That datasheet unbelievably does not show the pin numbers!
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
6,000
@Chris65536 PG 8 of the data sheet gives GDS (left to right) and GCE (left to right) in green underneath the face view. And I believe there's a fast recovery diode in the body. (figure 1 of data sheet) When power is applied to S it flows directly to D regardless of the state of G. In that case the test light is always on.

Screen Shot 2019-12-30 at 9.32.57 AM (2).png
 

MisterBill2

Joined Jan 23, 2018
8,808
But most blowers are under some type of restriction, but he is going to use this blowing into open air little or no restriction. Fuses in cars many(most?) times control more than one thing and are rated for all things being on at the same time. A better way to tell is to look at the motor leads, and figure the amp handling capacity of the wire.
30+ amps is an entirely reasonable value for an automotive blower at full power. It has been my observation that some are specified at 32 amps with a regulated 12.00 volt supply. That is an inspection check value, and so very realistic. In addition, like the TS states, the dimmer control assembly has no heat sinking and thin board traces. They used a higher power FET to avoid needing any heat sink, and also for handling the turn on surge. So indeed, why dig into a functional and quite compact module that works?
 

MisterBill2

Joined Jan 23, 2018
8,808
With more airflow, some types of blowers take even more power. I have seen that in the past. It all depends on the specific design of the blower. MY shop-vac goes much faster with the hose blocked because then the airflow stalls and the blower stops being such a load. So NEVER presume that allowing free flow will unload a blower.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
6,000
Thank you @MisterBill2. The fact that the air is nearly completely unrestricted is the basis for the amperage measured during testing. Also thank you for covering the points about the size of the FET in the module. This evening I will probably give the circuit some more build time. Just been too busy this morning with chores and other things.

And heat sinking the IGBT will be a separate post.
 

Wolframore

Joined Jan 21, 2019
2,283
Oh, that's the kind of thing we use to forge metal... just be careful you don't melt your fireplace... we may have a working blower by next year :D... have you tried using a hair dryer? 120V would be more efficient and easy to control using an SCR or triac.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
6,000
@Wolframore No, hadn't thought of that. But then again, a hair drier won't run on 12 volts, and dragging 120 VAC around melting snow and ice isn't the wisest thing I could be doing with my time. Perhaps some time I'll indulge the idea of a blower powered from a battery with a fuel pump and a fuel injector blowing across a spark plug all powered from a 12 volt battery mounted on a cart. The remote thought is to build this into a pipe and blow the hot exhaust on the ground thus melting ice. If it melts snow fast it may become my new snow blower (of sorts). And I'm sure the fire department will love me for it. But hey! Nice thing is I'll also get rid of those pesky leaves that blow into my yard from the neighbor's tree.

Oh, and another thing about the hair dryer - noisy!
 

MisterBill2

Joined Jan 23, 2018
8,808
The most impressive snow melters I have seen were an older turbojet engine mounted on a flat-car used to melt ice off of frozen track switches, and a crazy mechanic with jet fuel in a compressed air paint sprayer. The 20 foot fireball would clear snow from in front of a hanger quite rapidly. Please note that I DO NOT recommend the jet fuel or av-gas in a paint sprayer method of snow melting. But it is very impressive to see. It is also specificly BANNED on many USAF bases.
 

MisterBill2

Joined Jan 23, 2018
8,808
I think that I saw a saturation voltage of 2.4 volts on the one graph. I was looking at the graphs onn the data sheet because I did not see any listing of Vce sat. Just a plot towards the last page of the data sheet.
 

MisterBill2

Joined Jan 23, 2018
8,808
Very interesting article! However, how does that apply to the 2SK972 MOSFET in the dimmer? It's rated 25A and if anything, the thermal issues described in the article would reduce that. If the TS was concerned the 25A rating wouldn't be enough, how would this argue that it would be OK?
RIGHT!! My thinking from the start was that the 25 amps rating was on an ultimate heat sink, perfectly coupled and never getting hotter. so that 25 amp part was about right for the ONE AMP of those cluster lights. An it will probably be OK for the drive circuit for that IGBT. But then, I do know a bit more about some parts of automotive design thinking.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
6,000
At present, I've put together a perf board circuit that fits into a small box. The initial point of this build is to prove out a working circuit. But I'm likely going to have issues with heat. I probably will have to rethink the enclosure for the addition of heat-sinking abilities. Have scrounged several different heatsinks from computers and other stuff. The IGBT does not have a mounting hole but rather it's a clip design for mounting; so perhaps one of those scrounged heatsinks will do. If not - a scavenged LED lamp with aluminum housing and heatsink fins can probably be made to work well.

Over the four years I've been here I've learned a few things. Thank you all for that. Even the arguments and disagreements is a source of greater wisdom and critical thinking. This has probably been the best year so far for learning new things, and everyone's input has been greatly appreciated (least say the very few that I've put on the ignore list). So Happy New Year wherever you are. Today is the warm before the storm so I'll probably be busy pulling down Christmas decorations from on the house. My sleigh and reindeer with the frog driving - that's got to come down. Expecting 4 to 10 inches tomorrow (boy I wanted to say "next year").

Looking forward to an even better year; and I hope I've made a similar contribution to others. Again, thank you all. And Happy New Year.
 

shortbus

Joined Sep 30, 2009
8,594
Very interesting article! However, how does that apply to the 2SK972 MOSFET in the dimmer? It's rated 25A and if anything, the thermal issues described in the article would reduce that. If the TS was concerned the 25A rating wouldn't be enough, how would this argue that it would be OK?
OK, the heat sinking wasn't brought up until recently. But that doesn't mean that the mosfet wouldn't work to do the job if it was heat sinked, it would. I was under the assumption that the module had heat sinking covered probably by it's mounting in the car, many things do that they use mounting to a panel instead of what most people think as a heat sink, the little aluminum finned thing. Many motor controls do that, using the panel as the heat sink.

All of that said it wouldn't be that hard to unsolder the mosfet and run wires from the through holes out to a mosfet mounted to a heat sink. Or for that matter to the IGBT he is so in love with.
 
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