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1
So I finally got my act together and did some probing on the buck QCW. One hint to electronics experimenters,
don't buy cheap 9 volt batteries from Amazon. A box of 10 PKCELL batteries stored in the refrigerator has two
batteries left usable after 1 year.

There are two scope captures. One shows primary current (red) buck voltage (blue) and Vce (green) on the low side transistors.
Note the very low transients on the Vce compared to the phase shift.



The second shows a detailed look at the ZVS switching of the transistors. Very smooth and it looks this nice over the entire ramp.

2
Electronic circuits / Re: Eaton PowerWare 20 kVA UPS teardown
« Last post by Mads Barnkob on October 16, 2018, 11:09:33 PM »
I've worked on a few Eaton boards (design / modify), though I don't recognize anything in this one, maybe it's older than the designs I've seen.

Nothing really to say, just thought that was interesting, and, I guess, maybe you'll get lucky some day and tear down one that I recognize! ;D

Tim

It seems that quite a lot of this model gets thrown out within the last few years, so they have matured for replacement, if you worked on newer stuff, I will see that in some years ;)

You got quite of lot of re-usable parts out of this one Mads.
Shame about the terminal blocks getting busted up, still could be worse.

Out of interest, do you just give any wiring/cables you don't need to the junkyard, or just toss it back into the cabinet ?

Yeah its much more of a shame when its the IGBTs that are cracked. Part of staying good friends with a scrap dealer is that when i take stuff apart, i sort stuff i get loose in iron, cable and copper, thats like free labor to him and i was doing it anyway to get things out. Nothing lost, all to gain :)
3
I also did a teardown of a Kone elevator VFD and it seems to be the exact same unit, except mine was older.

Technological advances especially in the silicon / integrated 3 phase IGBT bricks made all these "small" drives very cheap to produce, there is no longer any real expensive parts to hold back a design or race it to the sky in price, at least not for consumer products, which a small elevator falls under in my view.

4
Electronic circuits / Re: Royer induction heater and high current power supply
« Last post by Max on October 16, 2018, 10:30:07 PM »
I'm a little late to the party, but hopefully not too late  ;)


Yes, you would just have to derate the current, I am not sure by how much, but looking at a similar capacitor type from Vishay http://www.vishay.com/docs/13057/phawo-ks.pdf

Where current ratings are given for a 1500V capacitor at 3000, 5000, 8000 and 10000 Hz, I extrapolated the derating further for the yellow marked numbers, these are just a guess.



So that would make my NWL rated at 680 A, should be derated to something like 400 Arms at 40 kHz.

Actually I don't think that these values are that useful; they come from different capacitors with different capacities. Vishay doesn't indicate it, but a quick calculation based on Urms, Irms and the frequency gives the following values (sorted by voltage):
   Urms [V]    Irms [A]      f [Hz]     C [uF]
25016806001783
250264010001681
25026403000560
25025605000326
25024008000191
250228010000145
60012671502241
60017003001503
15002640300093
15002560500054
15002333800031
150022671000024
245020001000130
3000667150236
30001333300236
30002000600177

As you can see, your diagram is based on capacitors with 24uF to 93uF.

I'd like to point to another reference. Celem (manufactor of induction heating capacitors) indicates voltage and current deratings vs frequency for their capacitors. Take the example of a 6.3uF 600V 600A capacitor. Here's their diagram:

(their other capacitors look quite similar)
As far as I understand it, you simply have a maximum voltage and a maximum current which must not be exceeded. To do so, you have to derate the other value respectively. This would mean, that as long as you keep the voltage low enough so that the current does not exceed the maximum rating, you can go as high in frequency as you want (and vice versa for lower frequencies).
Now this seems quite simple and there're two situations where I think that this rule is too simple:
  • First, as visible on the diagram from Celem, around the point of maximum power both current and voltage are derated and I'm not quite sure why. Also this does not concern all of their capacitors.
  • Secondly with frequencies much higher than the nominal frequency I could imagine that the dielectric losses rise, too. Which means you'd have to decrease the current. However, I couldn't find such an example at Celem, where the maximum current always remains constant over the whole upper frequency range.

Kind regards,
Max
5
Dual Resonant Solid State Tesla coils / Re: Building of my first tesla coil
« Last post by Skylex86 on October 16, 2018, 10:01:05 PM »
Hello

other question:
how to calculate the current that will pass through the primary coil?

because I would like to be sure that the IGBTs will resist


kind regards
alexis
6
Uspring,

I understand what you are saying. I'm coming to the suspicion that snubber implementation is a black art which few can master.
Currently the snubber I have on the bridge is four 2.2uF film caps mounted as close as physically possible to the IGBJTs. The buss
capacitor is a 10,000uF unit of unknown ESR. The leads from the cap to the bridge are 12AWG and about 4 inches long.

Do you think that it would help to place a 20uF film cap directly across the electrolytic?

Cheers.
7
Electronic circuits / Re: Offgrid 48V solar to 24V battery setup
« Last post by station240 on October 16, 2018, 02:57:07 PM »
Victron have not unreasonable pricing
https://www.victronenergy.com/solar-charge-controllers

I rewrote the instructions at the top of the page to be clearer.

In our MPPT model names,  the first number is the maximum PV open circuit voltage. The second number is the maximum charge current.
For example MPPT 75/50, maximum PV open circuit voltage 75V.  maximum charge current 50A.
8
Electronic circuits / Re: Royer induction heater and high current power supply
« Last post by kamelryttarn on October 16, 2018, 02:35:32 PM »
There hasn't been much progress this summer as I have had other things to to but I have thought a lot about the project and I still want to get back to it. I bought some thick, soft tin toil which I hope will give each and every SMD cap ok contact. In order for the small SMD caps to stand upright and to make it easier to mount them I made a small frame that I intend 3d print in some plastic. Don't know if I need to use some special kind of filament but I will start with regular PLA and see what happens. The frame holds 144 pcs of 1210 SMD caps.
9
Printed Circuit Board / Re: looking for PCB creating software
« Last post by station240 on October 16, 2018, 01:56:34 PM »
has anybody tried designspark

https://www.rs-online.com/designspark/pcb-software

Been using DesignSpark for about a year now, as a replacement for Eagle after the buy out broke a lot of my libraries.
Use it with Library Loader, which is part component database website, part conversion software.

Free + no limitations for what I'm doing with it.

One neat trick I only just found, you can copy paste whole PCB designs between projects. So no need for panelization software.
10
Electronic circuits / Re: Eaton PowerWare 20 kVA UPS teardown
« Last post by Hydron on October 16, 2018, 01:15:17 PM »
Aha, I recognise a lot of stuff in this video.

A few years back I came across the toss-out pile of a UPS company that was moving premises and scored a bunch of PCBAs that match what Mads has here (along with a lot of other goodies) - nice to know what they were actually out of!
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