# Motor controller freewheel diodes



## major (Apr 4, 2008)

jehan12413 said:


> Does anyone have experience with connecting the freewheel diodes or one large diode directly across the motor rather than in the controller? Electrically the result should be the same.


Hi jehan,

Offhand, I'd say it is a bad idea. I am pretty sure you need to keep the diode as close as possible to the switch. Electrically the result will be different due to the inductance in the motor leads. Hopefully we'll see another opinion about it. I'm not an expert on power electronics, just a long time user 

major


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## Tesseract (Sep 27, 2008)

jehan12413 said:


> Does anyone have experience with connecting the freewheel diodes or one large diode directly across the motor rather than in the controller? Electrically the result should be the same.


If you do that the switch will blow up after one cycle. The inductance of the switch/fwd interconnection is critical in a buck converter; the farther you separate the two devices the larger the voltage spike produced when the switch turns off.




jehan12413 said:


> I am replacing the freewheel diodes in my controllers with higher rating units (600 volt) but after searching many sites and hundreds of parts I just can't find the right polarity. I'm presently using MUR2020R which is a reverse polarity( TO220 case with anode tied to case and left hand lead) The 1560 has the 600 volt rating I want but the cathode is tied to the case as well as every other unit I have been able to find. Any help would be appreciated.


After a cursory search it does appear that what you are looking for does not exist or, at least, is one rare bird.


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## EVfun (Mar 14, 2010)

A Curtis controller, right? I don't know of anybody who has obtained those diodes except by salvaging them from another dead controller.

Would it be possible to have a smaller set of diodes inside the controller to catch the spike while the main freewheel current is handled by a large diode at the motor?


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## Weisheimer (May 11, 2009)

jehan12413 said:


> Does anyone have experience with connecting the freewheel diodes or one large diode directly across the motor rather than in the controller? Electrically the result should be the same. I am replacing the freewheel diodes in my controllers with higher rating units (600 volt) but after searching many sites and hundreds of parts I just can't find the right polarity. I'm presently using MUR2020R which is a reverse polarity( TO220 case with anode tied to case and left hand lead) The 1560 has the 600 volt rating I want but the cathode is tied to the case as well as every other unit I have been able to find. Any help would be appreciated.


It sounds like you already have the MUR2020R diodes but if not, they can be obtained at www.Digikey.com as
MUR2020RGOS-ND for appx (US)$2.09 each.
I have never found any larger capacity "reverse polarity" TO-220 diodes
that are Fast with soft recovery. 
If this is a Curtis controller (and it sounds like one) you could consider ditching the outer case and fabricating a new enclosure with an additional heat spreader for "outboard" diodes and then use a normal format device in a TO-247 body or perhaps a modular device.

Cheers
Mark


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## jehan12413 (Feb 4, 2010)

Mark, thanks for the advice, that's what I am thinking of doing as the controllers are mounted on a large heat sink with lots of space around the sides. I'm just not sure how close to 200V I can operate while still using the MUR2020R diodes.


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## Weisheimer (May 11, 2009)

jehan12413 said:


> Mark, thanks for the advice, that's what I am thinking of doing as the controllers are mounted on a large heat sink with lots of space around the sides. I'm just not sure how close to 200V I can operate while still using the MUR2020R diodes.


I wouldn't push it too far. 200V is the maximum rating. you could switch to another diode using an outboard scheme with a separate heat sink.
You'd have to use a new outer case and fabricate a new buss bar assembly and such, but it might be fun. Don't forget the CAPS are 200 v rated as well.
You can replace them too, but at the end of the game, you are really making your own controller now!
If you are going to go that far, at least consider the advantages of using a better current limiting circuit, using a micro-controller and etc before making your decision.
Take a look at:
http://ecomodder.com/forum/open-revolt-open-source-dc-motor-controller.html
you're going to need glasses if you read the whole thing though. You will see some folks are making other kits from that design as well, and others are just using the controller board to drive what they choose,
including IGBT modules. I think that there may be a thread on this board about the controller as well, I think that it is called "open source controller" or something close to that.
and the parts list, schematics, code, etc is:
http://ecomodder.com/wiki/index.php/ReVolt
Paul and Sabrina sell the controller board and pre-programmed micro-controller at:
http://www.paulandsabrinasevstuff.com/store/index.html
though they are on a short break at the moment (he is a school teacher).
Tesseract has a thread called "so you want to build your own controller" and it is very informative too.
I'm not really trying to push you away from your goal, I'm just pointing out some alternatives.

Cheers
Mark


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## jehan12413 (Feb 4, 2010)

Mark thanks for the information. Actually the only original parts are the freewheel diodes! I have several of these controllers which I have been using for several years with great success (under 200 volts), I just want to build one now to operate above that voltage.
If anyone else is doing this I just found some diodes! They are MR2406FR (600V 24A) and americansemiconductor.com has them, the catch is they are $15 each. If anyone has any suggestions as to where to get a better price I would appreciate it. No luck with digikey.
Thanks


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## Weisheimer (May 11, 2009)

jehan12413 said:


> If anyone else is doing this I just found some diodes! They are MR2406FR (600V 24A) and americansemiconductor.com has them, the catch is they are $15 each. If anyone has any suggestions as to where to get a better price I would appreciate it. No luck with digikey.
> Thanks


That is interesting except for the price! I saw them about 2 years ago but they didn't give a price or have any stock then, so I had thought that the device was "end of life".

Cheers
Mark


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## pyrogaz (Jan 3, 2010)

Quite a few with 600v+ rating at Farnell's, always a compromise between ratings, recovery time and price but 600v,30A, 60nS for under £3 seems reasonable and that was just a quick glance, I'm sure there's better deals in the list

http://uk.farnell.com/jsp/search/browse.jsp?N=1004178+365256+365255+538468+5056536+5056629+5056619+5056617+5056609+5056602+5056578+5056572+5056564+5056550+5056540+5056522+5046235+5046243+5046206+5046180+5046189&No=0&getResults=true&appliedparametrics=true&locale=en_UK&catalogId=&prevNValues=1004178+365256+365255+538468+5046218+5046224+5046235+5046243+5056536+5056629+5056619+5056617+5056609+5056602+5056578+5056572+5056564+5056550+5056540+5056522&filtersHidden=false&appliedHidden=false&originalQueryURL=%2Fjsp%2Fsearch%2Fbrowse.jsp%3FN%3D1004178%26No%3D0%26getResults%3Dtrue%26appliedparametrics%3Dtrue%26locale%3Den_UK%26catalogId%3D%26prevNValues%3D1004178


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## Tesseract (Sep 27, 2008)

pyrogaz said:


> Quite a few with 600v+ rating at Farnell's, always a compromise between ratings, recovery time and price but 600v,30A, 60nS for under £3 seems reasonable and that was just a quick glance, I'm sure there's better deals in the list...


The anode needs to be connected to the case/left-hand lead of the TO-220 package... Add that to the filter - if you can, otherwise you'll probably have to open every datasheet - and I'm betting your results drop to zero.


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## pyrogaz (Jan 3, 2010)

http://www.fairchildsemi.com/ds/FE/FES16JTR.pdf

Seems to have option of anode left and case.


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## Tesseract (Sep 27, 2008)

pyrogaz said:


> http://www.fairchildsemi.com/ds/FE/FES16JTR.pdf
> 
> Seems to have option of anode left and case.


Indeed it does... Many manufacturers still indicate that "reverse polarity" versions are an option, but that doesn't mean they are available off the shelf. Did you actually try to find if any of the parts in that series are available with the R suffix? I did, and it appears that Mouser has the 600V (FES16JTR) part in stock... it is marked as EOL but they have ~500 left.

FES16JTR


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## Weisheimer (May 11, 2009)

Tesseract said:


> Indeed it does... Many manufacturers still indicate that "reverse polarity" versions are an option, but that doesn't mean they are available off the shelf. Did you actually try to find if any of the parts in that series are available with the R suffix? I did, and it appears that Mouser has the 600V (FES16JTR) part in stock... it is marked as EOL but they have ~500 left.
> 
> FES16JTR


It looks like a good alternative, though I am not sure that it will have the "soft knee / soft recovery" needed for this controller. The data sheet doesn't note anything about that, and the curves don't either. I'd check it out a bit further before I'd use it. Did you look at the data sheet, and if so, what were your thoughts about soft recovery?


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## Tesseract (Sep 27, 2008)

Weisheimer said:


> It looks like a good alternative, though I am not sure that it will have the "soft knee / soft recovery" needed for this controller. The data sheet doesn't note anything about that, and the curves don't either. I'd check it out a bit further before I'd use it. Did you look at the data sheet, and if so, what were your thoughts about soft recovery?


A good alternative to the MUR2020R that was originally installed in the controller? I would say it's a step backwards, actually. You get a higher PIV, but at the expense of a higher Vf, unknown recovery characteristics and unless you also replace the MOSFETs, the input capacitors and modify the power supply to run on a higher voltage, you will still be stuck with the same absolute voltage rating.


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