Author Topic: High DC Voltage needed for project  (Read 835 times)

0 Members and 2 Guests are viewing this topic.

Offline Technobabble_

  • Contributor
  • Posts: 37
  • Country: us
  • Self-Certified Fabricobbler
High DC Voltage needed for project
« on: March 05, 2018, 09:35:23 am »
(Note: I am well aware of the dangers of high voltage, and am reading up on general safety practices. If there is a specific article that you recommend I read, please let me know.)

Hello,

I want to recreate this dielectric elastomer project: https://softroboticstoolkit.com/book/dea-bill-materials

For the project, the lab used a XP Power high voltage amplifier (https://www.xppower.com/portals/0/pdfs/SF_AG_Series.pdf). They are ~$200 US, way out of my budget, and I was unable to obtain a free sample. I need something to substitute this module.

According to the website, they needed at least 5 kilovolts to operate the actuator.

Options I currently looked at:

1. Using one of these "taser" modules (https://www.amazon.com/Boost-Power-Module-Voltage-Generator/dp/B00JVJDEZE) i.e. a pulse generator, and rectifying the output.
2. Salvaging an old flyback transformer. This option is the one I know least about.
3. Using a Cockroft-Walton multplying circuit. This option likely cannot be used alone, since the circuit can only double the input with every stage.

Am I researching in the right direction? What do you recommend?

Thanks.
 
 

Offline Buriedcode

  • Frequent Contributor
  • **
  • Posts: 957
  • Country: gb
Re: High DC Voltage needed for project
« Reply #1 on: March 05, 2018, 12:43:04 pm »
Those modules discharge a (relatively) high voltage cap into a simple transformer, as such produce brief pulses of very high voltage and rather high current several times a second.

Because its essentially a current source, its output voltage is determined by the spark gap on its output. I suspect it can reach over 50kV but you will not be able to control this with any degree of accuracy.  They're great for just making quick and dirty (and scary, and impressive) sparks, but for a testing instrument, I wouldn't trust it.  I also wouldn't trust its reliability, as tasers are not meant to be used regularly, or for more than a second or two at a time.

A tv/monitor flyback will do, but can be tricky designing a driver for it, although the web is FULL of them.  I'm willing to bet one could easily get 5kV without a multiplier or a high input voltage.

that xppower module says the 5kv module outputs 0.2mA. This is tiny.  You could probably use a CCFL driver with a couple of multipler stages afterwards to get your 5kV at several milliamps.  A tv flyback and one of those sparky modules is complete overkill for the requirements.
 
The following users thanked this post: Technobabble_

Offline Jwillis

  • Frequent Contributor
  • **
  • Posts: 296
  • Country: ca
Re: High DC Voltage needed for project
« Reply #2 on: March 05, 2018, 06:30:43 pm »
Danger! Will Robinson Danger! I hold no responsibility for any injury incurred!

You could scavenge a couple of similar micro wave oven transformers and parallel them.Each one would kick out 5kv .In series they could give you 10Kv.
Remember they have to be similar.
 
The following users thanked this post: Inverted18650, Technobabble_

Offline ikrase

  • Regular Contributor
  • *
  • Posts: 134
  • Country: us
Re: High DC Voltage needed for project
« Reply #3 on: March 05, 2018, 06:32:50 pm »
MOTs are scary, more so than many other HV sources.


5KV is a pretty low amount of voltage and the current needs probably are not too much. I would search Ebay for a lucky deal on an HV supply
 
The following users thanked this post: Technobabble_

Online Gyro

  • Super Contributor
  • ***
  • Posts: 3656
  • Country: gb
Re: High DC Voltage needed for project
« Reply #4 on: March 05, 2018, 09:29:40 pm »
Yes, definitely avoid the 'taser' zapper things, they put out evil waveforms and voltage and current levels. You're almost guaranteed to cause dielectric breakdown of your elastomer.

Likewise MOTs. It's just not worth the risk of playing around with something of that power rating, no matter how experienced you are! Also far too bulky and heavy compared to the alternatives. You can't put the secondaries in series either, one end is grounded.

My vote would be to go with a flyback circuit followed by a voltage multipler - say 1-2kV on the flyback and a 3 - 5 stage multiplier. That way, you minimize the insulation requirements on the transformer, and also relax the voltage rating of the capacitors and diodes to something easily obtainable. This is the way most insulation testers and modest output 5-10kV supplies tend to do it. The most economical and safest all round.
Chris

"Victor Meldrew, the Crimson Avenger!"
 
The following users thanked this post: Technobabble_

Offline mav_iqdirect

  • Contributor
  • Posts: 13
  • Country: us
Re: High DC Voltage needed for project
« Reply #5 on: March 05, 2018, 09:39:17 pm »
You could use Cockroft-Walton multiplier. We have successfully used such circuits to achieve 20KV.   :-DMM
 
The following users thanked this post: Technobabble_

Offline Technobabble_

  • Contributor
  • Posts: 37
  • Country: us
  • Self-Certified Fabricobbler
Re: High DC Voltage needed for project
« Reply #6 on: March 06, 2018, 07:57:35 am »
Is a new flyback transformer out of question? Is there a supplier of new flyback transformers at a reasonable cost?
 

Online Gyro

  • Super Contributor
  • ***
  • Posts: 3656
  • Country: gb
Re: High DC Voltage needed for project
« Reply #7 on: March 06, 2018, 08:12:57 am »
You could try using one  from one of these 15kV kits, they're certainly cheap enough... https://www.ebay.com/sch/i.html?_odkw=15kv+converter&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313.TR0.TRC0.H0.X15kv+inverter.TRS0&_nkw=15kv+inverter&_sacat=0

Rewinding the primary with a higher number of turns (to reduce the turns ratio) should bring the output voltage down to something more sensible, hopefully the cores aren't glued. No guarantees.

Another cheap alternative might be a CCFL inverter transformer.
« Last Edit: March 06, 2018, 08:19:20 am by Gyro »
Chris

"Victor Meldrew, the Crimson Avenger!"
 

Offline Buriedcode

  • Frequent Contributor
  • **
  • Posts: 957
  • Country: gb
Re: High DC Voltage needed for project
« Reply #8 on: March 06, 2018, 09:06:20 am »
Is a new flyback transformer out of question? Is there a supplier of new flyback transformers at a reasonable cost?

Unless I have missed something, you only require 5kV @ 1mA (probably higher voltage though).  That's 5W.  Lets call it 10W tops. A tv/monitor flyback - if that is what you are referring to - is completely overkill often for 40W+ throughput - often much more.  It seems much of the chat is either for much higher voltage (20kV+) and/or higher current.

What are the actual requirements?  Does it need to be regulated? adjustable? current limited? Min/max output voltage/current etc..

Although it would work I feel that if you use a large flyback (as in tv/monitor flyback, not just a flyback converter which can be any wattage) and use one of those self oscillating drivers you'll end up burning everything it goes near, as well has providing a perfectly lethal high voltage supply (as in likely to kill, not as in mains which can possibly kill).
 

Offline Technobabble_

  • Contributor
  • Posts: 37
  • Country: us
  • Self-Certified Fabricobbler
Re: High DC Voltage needed for project
« Reply #9 on: March 06, 2018, 03:43:53 pm »
Isn't this similar to the "taser" ignitor internals? What is the differance?
 

Offline james_s

  • Super Contributor
  • ***
  • Posts: 6562
  • Country: us
Re: High DC Voltage needed for project
« Reply #10 on: March 06, 2018, 03:46:07 pm »
You might check the 4HV forum, lots of guys building HV power supplies. It's actually fairly easy to build a self oscillating converter that will produce several kV using a self wound ferrite transformer. Be careful, this stuff can be lethal.
 
The following users thanked this post: Technobabble_

Offline Technobabble_

  • Contributor
  • Posts: 37
  • Country: us
  • Self-Certified Fabricobbler
Re: High DC Voltage needed for project
« Reply #11 on: March 06, 2018, 03:47:06 pm »
Specs:

Minimum: 5 kilovolt output. Max: ~10kilovolts.
Current: No more thean 1 milliamp.
Adjustable voltage.

I've already obtained a flyback transformer from an old CRT TV. I agree, it's probably overkill. I may look for a smaller one in an old air ionizer and/or a laser printer.
 

Offline james_s

  • Super Contributor
  • ***
  • Posts: 6562
  • Country: us
Re: High DC Voltage needed for project
« Reply #12 on: March 06, 2018, 04:00:57 pm »
That ought to be quite easy to achieve. You might have a look here, might be one of these projects you can use, if nothing else for inspiration. http://uzzors2k.4hv.org/
 
The following users thanked this post: Technobabble_

Offline Buriedcode

  • Frequent Contributor
  • **
  • Posts: 957
  • Country: gb
Re: High DC Voltage needed for project
« Reply #13 on: March 07, 2018, 02:02:35 am »
Isn't this similar to the "taser" ignitor internals? What is the differance?

Although this is probably a bit off topic, I never could resist telling folk how (I think) things work :(

Generally tasers - and I'm assuming these taser "modules" - work by charging a high voltage capacitor up, and discharging it through a cheap potted transformer.  Potted because its secondary can develop well over 50kV, can even be 100kV if the insulation holds.  And cheap because its primary only has a few turns, and its core is just a block of laminated iron.  There are two stages involved, no voltage multipliers although I guess they could use one or two stages.

So first the input voltage is stepped up to 400-1kV to charge a -0.5-3uF cap. This is usually done with a flyback converter as that's the most efficient way to step up voltage and charge a cap (since its a current source).  It is charged via the primary of the second transformer, and there is a spark gap that, when the cap reaches its target voltage shorts across the cap and primary, effectively dumping the caps energy into the second transformer. So it gets stepped up again.

The upshot is, its output is far from DC.  Its low duty high power, high voltage.  So brief millisecond pulses, at several hertz, and possibly at hundreds of watts per pulse (but low average power of 10W).  It makes then great for sparkers and to cause muscles to contract violently to use up muscle energy stores, but pretty terrible for any kind of lab supply. 

Its output pulse frequency depends on several things, input voltage (how quickly it charges the cap) humidity (which determines breakdown voltage of the spark gap) etc..  I bought a couple for novelty value, but they scare me.

There are other "kits" on ebay/amazon that aren't potted modules and just have a transistor, and a high voltage flyback transformer rated for 20W tops.  They have a feedback winding that allows it to be self oscillating, so whilst you can't control the turns ratio as the transformer is made for you - you might be able to add feedback to its sort of regulated.

https://www.ebay.co.uk/itm/15KV-High-Voltage-Generator-Step-up-Transformer-Igniter-Coil-Module-DIY/282659520031

that sort of thing.  But at 15kV again its over kill.

For 1mA a 1kV transformer with a few multiplier stages could easily provide the required current at DC as well as at a level of safety has it is inherently limited to a few mA (so it'll sting, but won't be as dangerous).  Two of us have mentioned CCFL inverters so far :)
 
The following users thanked this post: Technobabble_

Offline Technobabble_

  • Contributor
  • Posts: 37
  • Country: us
  • Self-Certified Fabricobbler
Re: High DC Voltage needed for project
« Reply #14 on: March 09, 2018, 09:10:15 am »
Clarification:

CFL's run on high frequency AC voltage. Are you saying to rip out the transformer from the cfl inverter and rectify it, or use the entire board? I don't see the added benefit of using th entire board.
 

Offline blueskull

  • Supporter
  • ****
  • Posts: 10233
  • Country: cn
  • Power Electronics Guy
Re: High DC Voltage needed for project
« Reply #15 on: March 09, 2018, 09:16:00 am »
If you only need a few kV, and virtually no current, then just get a CCFL xfmr and run it as a flyback choke, followed by a voltage multiplier.
 
The following users thanked this post: Technobabble_

Offline james_s

  • Super Contributor
  • ***
  • Posts: 6562
  • Country: us
Re: High DC Voltage needed for project
« Reply #16 on: March 09, 2018, 01:16:33 pm »
I'm a fan of Royer oscillators, they're simple to build, self resonant and work quite well. There's a common design referred to as a "Mazilli" ZVS flyback driver, I've built a few and they work well. Most of the components are non-critical and it scales well from miniature up to >1kW.
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf