# strange scope image ??



## dcb (Dec 5, 2009)

*Re: strange scop image ??*

you might want a diode across the motor....











and of course probing bus voltage would answer your capacitor sizing question. Might as well probe gate voltage too. I am assuming you are probing the collector here, might want to clarify.

also, 1500w is barely enough for a moped.


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## kimjessen (Oct 27, 2014)

*Re: strange scop image ??*

the diode in alredy be in use....
Motor sizes are I realize.
it is only to get a little experience.

gate = 6v

collector = 29v


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## dcb (Dec 5, 2009)

*Re: strange scop image ??*

what I mean by probe, is put a scope on it, and tell us what the units are on the screen. You are leaving out so many important details?!?


anyway, it doesn't look too out of the norm:









from here:
http://linuxgazette.net/179/radcliffe.html

when your duty cycle approaches %100, it never settles down to the bemf value perhaps.


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## kimjessen (Oct 27, 2014)

hi dcb!
it makes sense.
I shall just study more closely.
I need an additional probe for my scop to come up with the right images, that i get within the next few days.


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## dcb (Dec 5, 2009)

also, not sure what 6v means, but igbt's typically operate at about 15v gate voltage, with a quick drain diode to bypass the gate resistor for shutoff or a negative voltage.

https://www.fairchildsemi.com/datasheets/FG/FGH40N60UFD.pdf
lists typical gate voltage as 15v, the max threshold is 6.5 which is greater than 6v. If you look at figure 4, transfer characteristics, you are barely moving any current at 6v. 

The gate is essentially a capacitor, that you need to charge and discharge quickly (without overdoing it). If it is turned on/off slowly, the igbt body becomes a linear device for the turn on/off time, and can burn out.


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## kimjessen (Oct 27, 2014)

Hi ..
Thanks for the input, I saw just after on voltage.
My signal generator only goes to 10V.
I need to have done a driver stage so I can get up on the 15V. then I try again.
Many thanks for your help.


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## kimjessen (Oct 27, 2014)

Hello dcb!
I have seen the same image multiple locations and it seems like it's ok.

Today I had made it so that I use 15V pulse input, it seems as if the motor run a little more smoothly.

I've got an extra probe and here are the pictures. top is the collector and the bottom is the gate

with the extra probe, it all looks quite ok now.


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## dcb (Dec 5, 2009)

awesome! looks like you are off to a great start! Don't forget to read and UNDERSTAND those datasheets for all them parts 

plus look around at some other diy motor controller threads and schematics and concerns and yadda yadda.


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## kimjessen (Oct 27, 2014)

Hey Thanks for the roses.
Now I just find a real motor 15-20Kw would be appropriate.
And yes there must reading a lot more.
Does anyone have a cheap DC motor lying around. just like that. ;-)
again many thanks for the help.


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## kimjessen (Oct 27, 2014)

hi so now my project is dying.
maybe.
Here in Denmark, there must be an EMC test on the finished project or an explanation that there is no EMC. problem, an EMC test costs about 5000usd.

it is too expensive for my budget ..
is there frequencies in pwm modulation where you are pretty sure that you do not have problems.
if engine squeal does not matter I just need to find an easy solution. so I do not have to make the test 
any suggestions 

Kim Jessen


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