Discharge Lamp Testing

[djpaulboy]

Hi guys,

 

Is there a way of testing the output from a lighting fixture that takes an ARC discharge lamp? I have several fixtures that take the MSD 250 bulbs but won't strike with new bulbs fitted.

 

Cheers,

 

Paul.

[Jivemaster]

Very little can be done, and that done very carefully.

 

The lamp runs at vaguely around 70 - 150v BUT the start trigger may well run at 25 -50 KV and can have an RF component too, Poking fingers toward a 25KV source is a poor choice. Also a discharge lamp misused may fail explosively, modern housings are designed to take the impact but your fingers wouldn't be the same again.

 

Does your lantern need a reset after fitting a new lamp, some do.

[Thunderlight]

Three component's simply Ballast, Capacitor and Igniter. It will more than likely NOT be the Cap as when the Cap goes it just makes the incoming supply noisy but the lamp will still strike!! The Ballast is next as all the current running the lamp has to pass though it! When this goes they usually show signs of burning, however not always the case!! The Igniter is last before the lamp and is the kiddie that provides that nasty belt of high voltage to start the ark in the lamp!! These go quite often!! The Cap will be just across the incoming live and neutral to the lamp driving circuit eg: Ballast incomer and lamp,Igniter neutral!

 

The best way to test the system is to remove the lamp and Igniter making sure you know exactly where the wires go!! As Jivemaster says wrong connection and these things go bang big time!! You should be left with the out going wire from ballast to Igniter and the main neutral. Test across these for voltage when the lamp should be striking and the voltage you should get depends on weather the fixture uses a transformer to run the lamp or if it runs on mains voltage!! You'l have to look for that yourself although again like Jivemaster says most MSD's and HTI's use 70-150v!

 

If you get a good voltage then it's either lamp or Igniter!! If your lamp's new and your ballast is giving voltage then it's a good chance it's the igniter that's Knackered!! Whatever you do though for god sake don't test on the lamp terminals with the Igniter in circuit, it will blow your test instrument or more importantly YOU!!!

 

It's not for the faint hearted testing these so if you do not feel confident with what I've just rambled then it's probably best to send it to someone like myself who works with these allot!

 

 

Hope this helps! Tom

[csg]

we can simplify this quite a bit - I take it from your statement that the fixtures will run with old lamps fitted - but fail to start new lamps?

 

If this is the case, then the fault lies with the ignitor. New lamps require a slightly higher strike voltage and when a coil type ignitor ages, their peak voltage will fall. Whilst this may be adequate for an older lamp, it is often noticed as a problem when the fixture is re-lamped.

 

This used to be an occasional issue back in the days of golden scans - when the fixtures were getting on, often on re-lamping we would have to replace the ignitor for this very reason.

 

If the ballast is a wirewound choke, the chances of a fault here are very low.

[Jivemaster]

Do you have access to spares for your lanterns?

 

Switch them OFF and unplug them then wait an hour, then open the case and find and swap the igniter. Check it's wired properly and fully close and screw the case together before testing. The ballast will limit the current and voltage under normal running conditions, without a running lamp the volts could be closer to mains.

[PaulDF]

With the supply disconnected, capacitors discharged etc a wire wound ballast can be simply tested using a simple multimeter set to ohms range, there ought to be a fairly low resistance (in the region of a couple of ohms). If it is open circuit it is goosed. Similarly if it is down to earth (you ideally need an IR tester AKA megger to test this) then it is goosed.

[Thunderlight]

This is true to an extent Paul but doesn't test coils down to each other which will alter inductance that some starters require!! Although there is no easy way to test coils to each other anyway!!

 

We normally just test the voltage from the ballast to starter as the nature of the work we are doing means we have allot of light fittings to get through!! But the safer more time consuming way is to completely strip the unit and conduct continuity/ insulation resistance testing! Plus no live testing permits needed!!!

 

If it's down to earth then it's going to be blowing fuses/ tripping RCD's anyway so that soon pin points a major problem!

 

Tom

[djpaulboy]

Thank you for all the responses guys. I didn't expect so much information.

 

I will try testing the transformer and ballast as per your guidance, but after that I will probably abandon them.

 

The units a MAD ITM 250r lights from a nightclub we were trying to get going again. All functions work except they will not light with old or new bulbs fitted.

 

Someone prior to me had fitted them with Sound Lab bulbs mind you and I am sure they may have contributed to the failure of the lamp gear.

 

Cheers.

[Jivemaster]

Do a quick approximation of the costs of the project and the profit to be made, only you can determine the amount of money to be viably spent. Would a new unit be cheaper.

[PaulDF]

This is true to an extent Paul but doesn't test coils down to each other which will alter inductance that some starters require!! Although there is no easy way to test coils to each other anyway!!

A ballast is in essence just a long piece of wire wrapped around an iron core. Testing the end to end with a an ohm meter will show if it has gone open circuit, as a normal meter uses DC for measuring resistance inductance won't come into it.

We normally just test the voltage from the ballast to starter as the nature of the work we are doing means we have allot of light fittings to get through!! But the safer more time consuming way is to completely strip the unit and conduct continuity/ insulation resistance testing! Plus no live testing permits needed!!!

I'd be concerned doing this as at that point if the lamp is trying to strike there will be thousands of volts present.

If it's down to earth then it's going to be blowing fuses/ tripping RCD's anyway so that soon pin points a major problem!

 

Tom

True, if they have overheated to the point of the insulation breaking down you can usually smell (and taste) them too!

[Thunderlight]

A ballast is in essence just a long piece of wire wrapped around an iron core. Testing the end to end with a an ohm meter will show if it has gone open circuit, as a normal meter uses DC for measuring resistance inductance won't come into it.

 

Yes you can't measure Inductance on a normal meter that's what I said, however the large ballast on these fittings do religh on their inductance to run or more importantly start! After all that's another reason the cap is there to balance the inductive load out!

 

 

I'd be concerned doing this as at that point if the lamp is trying to strike there will be thousands of volts present.

 

 

Not on the ballast side after the starter yes. There is an exception to this rule in that lamps with internal starters will leave a short burst of volts on the ballast leg but after 2 mins of being switched on this will have been shot and dispersed! Although yes I would agree if I wasn't using high voltage rated test gear I would always take the starter or lamp out of circuit!

 

I think we have probably blitzed this subject now anyway!http://www.blue-room.org.uk/public/style_emoticons/default/smile.gif

 

Tom