Can you hijack the HF section of a commercial SM HV CCPS? For driving a custom HF HVPS (Recycling) / High Voltage / Forums

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Can you hijack the HF section of a commercial SM HV CCPS? For driving a custom HF HVPS (Recycling)

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LutzH

Sun Feb 14 2010, 11:33PM

Registered Member #1721 Joined: Sat Sept 27 2008, 08:44PM
Location:
Posts: 136

Hello:

To start with, yes I know, and yes I agree that it is better to build the HF source specifically for a given HFHV transformer to drive it. This fact aside, theoretically: If you wanted to tap into the HF section of a commercial switch mode HVCCPS what would be the best way to do it? The power supply in question is a Kaiser Systems OEM 1.5KV/1KW CCPS. Here are some basic facts about it:

I have figured out that it is IGBT based, and it uses a PWM parallel resonant topology, feeding a ferrite core final transformer, which is rectified for the final DC output. It is built to tolerate indefinite short circuit, and even no load conditions, and the output is current limited. The frequency is about 20-30KHz. It was originally designed to charge laser capacitors to 1.5KV.

At first glance, I can think of several potential approaches to hijacking the HF section to drive a separate home built ferrite core HV transformer from it:

1. Tapping into the primary feed of the final HFHV transformer in the PS, while leaving the stock transformer still in the circuit so that you would possibly still have some voltage regulation in the PS. Maybe even adding a resistor so that the stock transformer sees some load for better regulation, if this even makes a difference. Basically soldering in two extension wires to the home built HFHV transformer.

2. The same as #1 except doing it so that the existing 1.5KV ferrite core transformer primary is in series with the primary circuit of the home build HFHV transformer. This would seem on the surface to give some current limiting, and some protection from any reflected load situations, encountered from the home build HF transformer circuit.

3. Designing the home built HFHV transformer with a 1.5KV primary, and tap into the HFHV circuit right before the final output rectifier section. Again the same two variations as outlined above could be done: 1. Which just connects to the HFHV terminals at or before the rectifier board input of the PS, and 2. Where now the HV secondary coil of the PS HF transformer is in series with the primary of the homebuilt HF transformer.

My question in a nutshell is: Has anyone ever tried this and managed to do it in a way to preserve some of the the regulation features of the stock power supply, and used them to their advantage?

Although many purists hate this kind of idea, (Sorry, absolutely no offense is intended) there are so many of these type of high power units in the surplus market now, why not re-cycle if it is possible? Especially when its free! I mean we recycle all the time with components, and with transformers, cores, etc. Why not recycle an entire power supply as a HF driver? Thank you in advance for your thoughts....Lutz

Steve Conner

Sun Feb 14 2010, 11:45PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

I think either would work, the only bad thing is connecting the new transformer in series with the old one. To my mind that would seriously limit the power output, because if one of the transformers is unloaded, it'll stop current from passing through the other one too.

I don't think CCPS are "regulated" as such, they just shut off once the capacitor reaches the voltage you set.

LutzH

Mon Feb 15 2010, 01:22AM

Registered Member #1721 Joined: Sat Sept 27 2008, 08:44PM
Location:
Posts: 136

Thanks Steve:

Yes I see your point if the PS transformer is not loaded it is basically a choke, and little current will flow. What about connecting it in this manner: With the primary winding of the stock PS 1.5KV transformer in series with the home built one, and then shorting the secondary of the PS 1.5KV one?

Could it then functionally be the HF equivalent circuit of a shorted MOT primary being used to limit the 60 Hz power into an old x-ray transformer? I am just asking because then it would seem like the operating conditions which the PS now experiences, would be closer to what it was originally designed for? In other words the primary of the shorted PS transformer could now provide some current limitation, to help protect the IGBT's

The only potential problem that I see here is: If the PS feedback regulation taps off of this section, then it may cause a problem. If it sees the short as an empty cap, then no problem, it will just run at full power. I suppose that you could also isolate this feedback connection, and then supply it with a seperate reference control voltage to help regulate it.

I suppose that by using the PS HF from the secondary, and then designing the HFHV transformer with a 1500V primary, this could provide the same intended end result also. Maybe this is the overall safest approach for the PS circuit?

My main concern ref. the direct use of the HF which now goes to the PS HV transformer is: The stock 1.5KV HFHV transformer is very different from the one which I am building. My core is way larger, and it has a very different turns ratio, so a direct replacement would seem to be PS suicide. If however the stock transformer were left in the circuit, then at least there is a chance that the HF circuit of the PS could function somewhat normally.

My main concern is that I would want the PS to survive as much as possible, so anything which increases the survival odds would be worth implementing, this is what I am mainly looking for :)

Thanks.....Lutz

Conundrum

Tue Feb 16 2010, 01:17PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

Hmm.
Surely you'd be better off starting off with a working power supply removed from an old laptop or xbox ?

one trick I've also used is to find a small lighting transformer of the tungsten halogen variety (available in units up to 250W) and use the output from this to drive the transformer.
usually the frequency is determined by output load and a pair of resistors which can be replaced easily.

regards, -A
#include "CheapLoanscall1-800-SUCKER.h"

McCluskyCustom

Thu Feb 18 2010, 08:40AM

Registered Member #2538 Joined: Sat Dec 12 2009, 06:56AM
Location: San Luis Obispo, CA, USA
Posts: 10

I'm a fan of completely replacing the xfmr. I agree with Steve about adding in series limiting the power output. And if you short the secondary to use the leakage to somewhat ballast the drive, this could help the lifetime of the IGBTs, but will possibly burn out the current xfmr. Depending on the secondary resistance, you may have significant secondary currents that generate heat in the xfmr, and if run too long, poof!

Since resonant power topologies depend so much on the magnetic components, changing/modifying the xfmr setup may prevent correct operation. That being said...

Depending on your experience with magnetics, if you could design your homemade HFHV xfmr with a similar primary inductance, and equal or lower leakage inductance, then you could simply replace the current xfmr and still get the power throughput and topology-inherent protection. Of course, this would require gapping your core appropriately. If you were able to make your xfmr with lower leakage, then you could simply add a series inductor with a value that adds to your leakage to get the leakage of the original xfmr. Depending on the control scheme, it may "self-correct" within a range to appropriately resonate with whatever magnetizing and leakage inductance you have. If you do option #1 or #2, you may change the frequency too far out of whack, but it would really depend on the control scheme. Try it!

Easiest: Add your xfmr in series with the shorted PS xfmr.
Best: Design your transformer so the primary looks to the circuit nearly identical to the PS xfmr.

Oh, and option 3 sounds the safest as far as ensuring power supply longevity.

I like your idea of recycling the driver like this, but no, I haven't done this, so Good luck!

LutzH

Tue Feb 23 2010, 08:40AM

Registered Member #1721 Joined: Sat Sept 27 2008, 08:44PM
Location:
Posts: 136

Thanks Folks!!!

These great ideas will keep me busy for a while, at least I hope so or I will be busy scavenging the good parts still left. I really like the idea of trying to match the original transformer inductance as best as possible, this just makes sense on an intuitive level. Thank You....

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