Super small YAG laser cavity

[Branson33]

Maybe you guys can help me though? I am using a tiny EMCO 4kv 5ma power supply to charge a 800 joules capacitor bank to 1kv. That takes about 5 whole minutes. Is there a much faster way to charge the capacitors? Like 5-10 seconds at most? I want to be able to fire it rapidly not every 5 minutes. I was thinking about using a variac to power a microwave transformer and rectify the output to dc at about 1200 volts 250ma, or possibly take wall outlet voltage and current and multiply it and rectify it at the same time. If you have any clue what to do I’m all ears at this point

 

[Alaskan]

Don't take power from the mains and multiply rectify it, very dangerous. Just buy a flash tube HV power supply on ebay, they can be had cheap from time to time.

https://www.ebay.com/sch/i.html?_fr...ly.TRS0&_nkw=flash+tube+power+supply&_sacat=0

 

[Branson33]

Okay thank you Alaskan, yeah I was just wondering if that was even possible at all, but now that I think about it, that’s even a dumb thing for me to do lol, I have looked at getting this though 37393 Freed Transformer 115V-1400V 115V-700V 300mA
It outputs like 200 some ma of current, would that be enough to charge them to 1000 or so volts quickly? I know it has a higher voltage rating, but I have a kilovolt meter I will be using to monitor voltage across the caps just to make sure they don’t go over. Does this sound like a decent idea?

 

[Alaskan]

That transformer, once rectified, will put out a lot more than 1400 volts, with a full wave bridge rectifier without a choke, the capacitor could charge up to 1.6 times that voltage without a load on it. You could use a variac to adjust the input voltage to bring it down. honestly though, the thought of your messing with high voltage like that scares me, better to buy a used flashlamp power supply.

 

[Branson33]

I do have a variac I could use to lower it substantially but that would also lower current. I’m not ignoring your flashlamp power supply suggestion, I’m just exploring all options right now. If you look again at the transformer I linked it also says 300ma DC on the second winding, does that mean the secondary is already rectified to DC and not AC? I’m confused why they would put it on there if it was not

 

[Alaskan]

It's a simple transformer, AC out.

 

[Branson33]

Alright thank you, so here is what I’m thinking I will get this module 202172802791 it’s rated for 20kv 2 Amps I believe, get a simple MOT, using a variac I will tune down/or up the output depending on my needs and the current is about 500ma so plenty to charge the caps for a shot every 10 seconds or so I think. Problem is how do I keep it from arcing... also what size smoothing capacitor would I possibly need?

 

[Alaskan]

Using a trigger coil, it won't arc if you don't exceed its design flash voltage, they are not supposed to arc at the design voltage and require a trigger coil voltage to get it to flash. i would not trust that 20 KV bridge to be good, if one of those diodes are bad, you will pay a lot more to replace it than the whole thing costs. If you want to risk it, at that price, not too bad, but be aware if you use a full wave bridge with only capacitive filtering, the unloaded peak voltage the capacitor charges to will be about 1.6 times the RMS AC voltage being fed into it, under load about 1.4 times which is moot for this application, as you will charge the caps to peak. If you want 1000 VDC, the AC into these diodes will need to be 625 volts for a top voltage of 1000 VDC when the capacitor is fully charged. A bleeder resistor across the capacitor, depending upon the resistance, will dampen the peak charged voltage a bit, but i would put one across it to save you from getting zapped later, if charged the day before and getting across it somehow. Using a variac you can adjust to the dc voltage you want but be careful, if using an electrolytic capacitor, i wouldn't charge it to its top voltage rating, keep it 25 percent below that. i had one blow up on me a few days ago, as they age, or if used old surplus stuff, the more likely for a failure if running at their rated voltage, accidentally exceed that voltage too far and they get hot and build up pressure until they blow. Although some electrolytic capacitors have over-pressure vents, if the pressure builds up too fast, they won't stop an explosion.

i built a 2kv high voltage power supply some years ago and put a safety bleeder resistors across the capacitor, just as a double check before working on it, after turning it off a few minutes, i measured the voltage across the capacitor and it was fully charged! a brand new out of the box wire wound bleeder resistor i had just received from Mouser electronics had an open! there was no resistance due to that failure, that could have killed me if I had assumed the resistor was good.

 

[Branson33]

Alright, I won’t trust those then I’ll find some different ones. And I’ll be sure to use the Variac to pt about 600 volts on the diodes to get 1000 out of the rectifier. Also here is what confuses me.... so let’s say the MOT is rated at 2000 volts 500ma...alright so I am using a variac and I set the voltage To 600 volts out on the secondary of the MOT.... since the voltage on the secondary goes down does that also mean that the current goes down with it? Or will the current stay the same or even rise?

Also you are starting to scare me Alaskan with those stories I really need this power supply please no more stories that will make me rethink this whole laser thing

 

[Alaskan]

Anyone who works with HV needs to remain scared a bit, stop being that way and become too casual with it and you may end up dead.

For most HV flashlamp power supplies, the discharge when the lamp arcs will take the voltage across the capacitor way down and the transformer will immediately begin to supply high current to charge it back up, but the current from the transformer will reduce to a very small amount, once the capacitor is charged all the way back up. You could use a very heafty high voltage transformer and diodes which when you flash the lamp it continuously arcs, or immediately charges back up for another flash right away to the point you can keep flashing the lamp so often it overheats and cracks. CW YAG’s are designed for a continuous arc, but as far as i know, are water cooled to keep the lamps from cracking. i'm not up to speed on much when it comes to these flashed rods, but have worked with HV, built a 4 amp 3800 VDC HV supply some years ago. Perhaps someone else can chime in with more info.

E: When working with high voltage, keep one hand in your pocket, it may save your life, let that voltage cross from one arm through your chest to the other and your heart stops.

 

[paul1598419]

I have seen many exploded electrolytic capacitors in my lifetime. Was one the blew a hole through the top of a console TV back in the 1970s. They were metal cans with multiple caps inside and the metal top went though the wood cabinet. This was only a 400 volt capacitor too. If you are going to play with high voltages, you need to learn how to do it safely. If you don't, someone will find you dead someday, slumped over your high voltage circuit.

 

[Alaskan]

I don't like the idea of a minor, even if in high school, messing with HV unsupervised.

e: 20 years ago i zapped myself with 2500 VDC, but had my hand in one pocket, burn mark charred into my finger and arm muscles were hurting after the jolt, but didn't go through my heart, went through my torso and feet to ground.

 

[Branson33]

Alright I’m going to go with a 1190 volt @277ma transformer on that one website. The MOT just scared me way too much and I think I can wait the extra 5 seconds to not kill myself like the 10+ amps if short circuit into your body...not my kind of thing...but I’ll get that transformer, hook it up to that diode rectifier I showed you, I contacted the one guy and he said it is brand new so might as well try to get it, and finally hook it straight up to the capacitor bank, I don’t think I need a filter capacitor on the output of the rectifier because the cap bank basically acts as that and a power supply correct?

 

[Alaskan]

You will want to filter the bridge rectifier output, look for an oil filled capacitor, they are safer in my opinion, can be run to full voltage rating. The problem is the rectifier output won't allow enough peak current for the flash, the correct capacitor will. edit: you need to figure out what size of inductor in microhenries you need for a given capacitor size in microfarads, or you could blow another flash lamp.

See: http://donklipstein.com/xeguide.html

This might work for you, I believe these are mica capacitors which can also be run to the full voltage rating, if you need double the capacitance, order two and parallel them: https://mi-lasers.com/product/pulse-forming-network-for-ssy-1-nd-yag-laser-head-2/

Schematic: https://mi-lasers.com/wp-content/uploads/pftr1sch1.pdf

Remember, using a full wave rectifier diode bridge, the capacitor will charge to 1.6 x the AC RMS output voltage of the transformer.

This is nice but $$$: https://www.ebay.com/itm/HOYA-LCSM-...acitor-for-MEDLITE-C6-LASER-2262/152728811364

 

[diachi]

https://www.electronics-tutorials.ws/rc/rc_1.html

 

[Alaskan]

Yea, youngin out pacing his knowledge, wanting to buy and try before fully researching the tech enough, is how he blew out that SSY-1 flashtube putting HV on it without an inductor to limit the current surge.