Teardown of Danfoss VLT6000 4kW Variable Frequency Drive

[Mads Barnkob]

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A teardown of a Danfoss VLT6000 4kW VFD, a run down of the current paths in the system and I show which parts I find to have a value.

Datasheet on the unit: https://www.danfoss.com/en/products/ac-drives/dds/vlt-and-vacon-legacy-drives/vlt-6000/#tab-overview

[rikkitikkitavi]

Cant watch it, it reminds me to much of the two 37 kW units and the 75 kW units that I bingedived from my previous work and spent a good evening with beer , recovering ferrit-toroids, LEM current sensors, some drive Xformers, all IGBTs (halv bridge units) , rectifiers , capacitors and of course the heatsinks.

It made up a pretty large and heavy box of stuff.

That I unfortunately misplaced during a housemove so it went to the recycling station instead.

Kicking myself repeteadly I still havent forgiven me. Damn it.

Good teardown though. Unfortunately IGBT development have now reached so far that even in quite large units the IGBTs are in sixpacks or sevenpacks (brake chopper style) and thus smaller chips perhaps not so good for coiling en massive scale. But the rest is still useful. The modules that are soledered to the thick-copper-cladding-double-sided-PCB are a b-tch to desolder though.
I recommend dremel of the PCB so there is less heat conductive material, but carefully to prevent damage.

[klugesmith]

Has anyone else here noticed that VFD makers write very conservative rules about re-forming electrolytic capacitors?
A think I discovered last week, while investigating best practice for consumer electronics that's been without power for 10 or 15 years.

We all know that ancient vacuum-tube gear needs attention to reforming, or replacing, old caps.

Now it appears that if you have a modern VFD, which has been in "spares" stock for one year or more, it seriously needs attention to reforming before being put into service.  Is that a thing that's familiar in the trade? 
https://library.e.abb.com/public/cf2c9be9fc666ebbc1257729002bd7be/Guide_for_capacitor_reforming_Rev_G.pdf

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I guess it's the equipment makers who would hear about it, if un-reformed drives fail soon after power-up in 1% of the cases, because of capacitor that is statistically weak at maintaining its form.

[shrad]

From experience with a former employee, they are stocking spares during approximately two years and every now and then they throw them away to avoid having bad ones in spare

[klugesmith]

That could get expensive if you are talking about 100 kW drives!  (Hmm . . . how big are the drives in Tesla automobiles?)

Mads, how did the unit in your video come to be on your autopsy table?

[Mads Barnkob]

That could get expensive if you are talking about 100 kW drives!  (Hmm . . . how big are the drives in Tesla automobiles?)

Mads, how did the unit in your video come to be on your autopsy table?

I was not aware that shelf-life was so short, which is ridiculously short, compared to some systems I have worked on/made service on/restored, they could be 30 year old systems, with some spare parts being just as old or at-least nearing 20 years. I guess it just comes down to things are not made as they used to be

I fetched this drive from a scrap yard, I assume it was thrown out due to upgrade or maybe defective, but it has no visible signs inside of being defective.

[klugesmith]

Excellent video, Mads, as usual.
Here are a couple of VFD factoids just found on the Internet.

For the electrolytic capacitor reforming question, I looked up VFD's by Siemens.  That brand has been respected for industrial electric motor stuff since 19th century.  Got a manual for today's BT300 series VFD's for HVAC applications:
https://www.controlmanagement.com/content/products/BT300/catalog/1-VFD-Techdata_149-711_CA.pdf

Perhaps for historical reasons, the "preferred numbers" for nominal VFD sizes seem to be based on horsepower instead of kW.


As for the re-forming, this series uses film capacitors instead of electrolytics.  I bet that's because Marketing said the product would have a competitive boost, if customers did not not have to worry about reforming.


My guess is that reforming is important for _all_ electrolytic capacitors stored for years without bias.  That doesn't mean they usually fail, if rated voltage is applied with nothing to limit the leakage current.  It means the probability of failure (say, 1%) is unacceptable, in major applications like VFD's, where people are paid to buy and manage spares stock, and one's reputation for reliability must not be blemished.

It's funny that the no-electrolytics feature is presented in a section about how it's green to buy Siemens. 
Because 'lytics have toxic stuff inside.  They go on to discuss the CO2 reduction because the product shipping weight is lower than the competition.  As if the CO2 emissions that depend on electrical efficiency, during the life of the product, aren't a million times greater. :-)