method to protect power supply from HV arc starter? - Page 1
Forum section: electronics / projects

author: coppercone2
author_rank: Super Contributor
timestamp: August 14, 2024, 05:32:06 am
content: I am interested in using a lab power supply with some kind of HV sparker to use it to try to control arcs. Like a pilot arc.Getting the arc into the circuit seems easy enough, but I am worried about protecting the power supply. Say a sorensen.Like if i wanna put a BBQ starter on it with a coupling transformer.My first thought is foil capacitor of moderate size. and a TVS diodeis that enough?

author: moffy
author_rank: Super Contributor
timestamp: August 14, 2024, 07:14:47 am
content: With the HeNe lasers we used the 10kV HV pulse transformer was just placed in series with the 1.5kV HV, no real protection, but then the HV was only a few 'ma'. The HV would discharge through the tube into some 200V JFETs that had some series balast resistors, I can't remember there being a single failure of one of the JFETs.

author: LaserSteve
author_rank: Super Contributor
timestamp: August 15, 2024, 05:35:44 am
content: Traditionally we use a resonating or ringing ignitor and a beefy symmetrical LC low pass filter network at a minimum of 1/5th of the ringing frequency.Find the "Cermax lamp engineering guide" by Excelitas as an example.In my case I typically have 2 series Ls, one each in the hot and cold sides, Then some really beefy HV caps in shunt, one before the Ls and one after it, plus a blocking diodeSTEVE

author: Xena E
author_rank: Frequent Contributor
timestamp: August 15, 2024, 07:44:08 am
content: Depends on the actual Voltages involved.I've done HIgh frequency HV impressed on LV DC for fuse failure mode testing with CM choke from the DC and Neon on the hot side.

author: Psi
author_rank: Super Contributor
timestamp: August 15, 2024, 08:00:54 am
content: Is your HV going to be in series with the low voltage powersupply, or across it?If across it you need to isolate your powersupply with a diode. So the powersupply can output DC but not receive HV in.If in series then a TVS diode that clamps to the max voltage of the powersupply sounds like a good plan.

author: coppercone2
author_rank: Super Contributor
timestamp: August 15, 2024, 08:32:39 pm
content: Hmm I did not think to put it across it.what are the pro and cons? The welder put it in series. But I don't see why to add the complexity if its just a pilot arc

author: Psi
author_rank: Super Contributor
timestamp: August 15, 2024, 10:20:16 pm
content: The problem having the HV in parallel with the supply is that any HV ringing will produce a negative pulse that a series diode won't block. (Since normal supply voltage coming out of the supply looks the same as reverse polarity flowing into the supply). So you'd need to block the positive HV and also clamp any negative ringing.With the HV in series it's easier to deal with using a TVS diode across the supply. It efficiently turns the supply into a short from the HV perspective, except for the TVS voltage drop which is tiny compared to the HV.For this sort of application in-series is the normal way to do it. I just wasn't sure which way you were trying to do it, so thought i'd ask.

author: Xena E
author_rank: Frequent Contributor
timestamp: August 15, 2024, 11:56:31 pm
content: Series definitely

author: coppercone2
author_rank: Super Contributor
timestamp: August 16, 2024, 12:53:17 am
content: so 1 TVS diode and the coupling transformer is enough? I can wire the diode across the psu trerminals?This would be like for a starter from a lighter or maybe a BBQ if that is too weakThe point of this is to try to study welding type things

author: LaserSteve
author_rank: Super Contributor
timestamp: August 17, 2024, 03:10:27 am
content: A "ONE POINT" piezo start may be very unsuitable. One of the ugly trurths about about arcs is the formation of an emissive "cathode spot" can require far more energy then a single Townsen discharge can provide. You have to transition through Townsend to Glow to Abnormal Glow to Arc.

author: coppercone2
author_rank: Super Contributor
timestamp: August 17, 2024, 03:11:47 am
content: its easy enough to try if its safe with 1 diode