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Xenon short arc lamp starter circuit

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haxor5354

Wed May 21 2014, 08:41PM

Registered Member #2063 Joined: Sat Apr 04 2009, 03:16PM
Location: Toronto
Posts: 352

Hi all, its been a while since I've been on 4HV.
I've been messing around with xenon short arc lamps recently trying to make a search light.
The power supply requirements for a xenon short arc lamp is rather high.
it must be able to put out ~10KV to strike the arc then supply ~40v 50-100A to maintain the arc.
The HV supply must not kill the high current supply, vice versa.
The attached image is a schematic of my starter circuit, I've tested it, it seems to work okay.
I've used four 12v small SLA batteries in series as my high current DC supply.
Is there anything wrong with my circuit if I use an arc welder as my high current supply?
In theory, the microwave oven cap should absorb any HV spikes that couple potentially damage the high current supply right?

schematic

Sulaiman

Wed May 21 2014, 10:00PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

I'm not sure but I suspect that using a.c. to power the arc would
result in the arc being 'lit' for 1/2-cycle then extinguish
requiring an eht pulse each 1/2-cycle of the a.c.
PLUS the inductance of the eht winding of the pulse transformer would act as a 'balast'
which is probably a good thing as it will limit the arc current.

If the arc does extinguish each 1/2-cycle then a bridge rectifier
(combined with the eht winding inductance)
would keep the arc alive.

haxor5354

Wed May 21 2014, 10:09PM

Registered Member #2063 Joined: Sat Apr 04 2009, 03:16PM
Location: Toronto
Posts: 352

Xenon short arc lamps are polarity sensitive, so they have to be powered by DC, or else you'll destroy the electrodes.
stick welders output DC right?

Steve Conner

Wed May 21 2014, 10:11PM

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

The circuit shown should work, but you may not even need to go to those lengths. If you have a Tesla coil, try just firing it in the general direction of the lamp.

Some short arc lamps are designed for AC, some are designed for DC. The DC lamps have a positive electrode that is larger than the negative one with more heatsinking. If you use an AC lamp on DC or vice versa, you'll overheat one of the electrodes.

Sulaiman

Wed May 21 2014, 10:21PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

d'oh .. forgot the welder would be d.c. .. shouldn't be a problem

haxor5354

Wed May 21 2014, 10:43PM

Registered Member #2063 Joined: Sat Apr 04 2009, 03:16PM
Location: Toronto
Posts: 352

The microwave oven cap should in theory absorb HV spikes that might damage the high current supply right?
the last thing I want is to blow up a welder.

it seemed fine when I was using SLA batteries as my high current supply.
but batteries are less susceptible to damage from HV spikes I would imagine.

Ash Small

Wed May 21 2014, 11:56PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Most small stick welders output AC. A rectifier is no big deal. Other than that your circuit looks pretty much OK to me.

haxor5354

Sun May 25 2014, 07:55PM

Registered Member #2063 Joined: Sat Apr 04 2009, 03:16PM
Location: Toronto
Posts: 352

I tested my circuit again yesterday, but this time I used a rewound high current MOT as my high current supply.
I connected a neon test light in parallel with the output rectifier, and I can see a faint glow from the neon bulb.
therefore there must be some transient high voltage spikes during ignition right?
will it be enough to kill an arc welder or not?
if so, can I use some MOVs to suppress the HV spikes that might damage my high current supply?

Ash Small

Sun May 25 2014, 08:24PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

haxor5354 wrote ...

I tested my circuit again yesterday, but this time I used a rewound high current MOT as my high current supply.
I connected a neon test light in parallel with the output rectifier, and I can see a faint glow from the neon bulb.
therefore there must be some transient high voltage spikes during ignition right?
will it be enough to kill an arc welder or not?
if so, can I use some MOVs to suppress the HV spikes that might damage my high current supply?

You can wind a choke on some ferrite (two windings on one core, wound so that the spikes cancel out).

This will block any spikes that get past the capacitors.

Look at mains emi filters for more details.

haxor5354

Sun May 25 2014, 09:07PM

Registered Member #2063 Joined: Sat Apr 04 2009, 03:16PM
Location: Toronto
Posts: 352

so, like this? schematic here

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