250V AC Capacitor across input

[JonathanAnon]

Hi lads, I'm looking at a spotlight that is getting 0 voltage on it's 240V lightbulb rails... but I'm a bit confused.. There is a large 20uF capacitor marked as 250V AC across the live and the neutral, just after the fuse.. After a quick google, I've discovered that this is to prevent arcing when it is switched on, but there really isnt a huge amount of information on using a capacitor in parallel on an AC circuit. Can anybody clarify this for me...

I assume that I can just pull this out of the circuit and switch on and it will work away the same.. or is there a large possibility of arcing with this type of circuit.. i.e. a spotlight..

I think the cap may be causing the problem even though it checks out fine with the ESR meter.

[budm]

Re: 250V AC Capacitor across input

What kind of lighting system is this? Arc lamp? Gas Discharge?
Can we see this spotlights?
There are safety caps that are used across the line, or line to ground, or neutral to ground.
https://cdn.badcaps-static.com/pdfs/...b8818c3858.pdf

http://www.kemet.com/kemet/web/homepage/kechome.nsf/file/KEMET%20Kollege%20Presentations/$file/EvoxRifaRFIandSMD.pdf


Then the PFC cap which is used across the line, which is more likely to be in your case if it has high inductive circuits.

[JonathanAnon]

Re: 250V AC Capacitor across input

Hi Bud, it's a Spot 150XT

Spot 150XT Manual



It's C1 in the diagram below...

[budm]

Re: 250V AC Capacitor across input

That is the Arc Discharge stage lighting system.
Read here:
http://www.lrc.rpi.edu/programs/nlpi...l/abstract.asp
http://www.mjguide.com/tutorials/Lighting/583.htm
http://www.ehow.com/how-does_5692618...ide-lamps.html


http://en.wikipedia.org/wiki/Arc_lamp

Since this cap is enlcosed in very hot enviroment, they do fail quite often.

[JonathanAnon]

Re: 250V AC Capacitor across input

There is only 30 volts on TL1's input, and zero on it's output... The AC voltage across C1 measures 30 volts also... I've pulled out the thermistor at RV1 and replaced with jump wire, so that is not the cause.

I've tested the C1 and it checks out okay with the ESR meter, but I'm still thinking it could be the fault.. I'm thinking of pulling out C1 and putting it parallel to a regular 100W bulb (and in series with a fuse ;-) ) to see if it works properly out of circuit..

[budm]

Re: 250V AC Capacitor across input

Rv1 is inrush current limiter to reduce the current surge when you first power up the unit, after that you should have full AC line voltage on that cap, you must have high resistance in the current path from the AC line input.
Check the AC voltage drop across the power switch contacts 1 & 2, and 3 & 4 they should be 0VAC, also check the voltage across the fuse, it should also be 0VAC.
That SW1 switch should be high in-rush current capability type.
By the way, is the Thermal fuse 100c F2 OK?

[JonathanAnon]

Re: 250V AC Capacitor across input

The fuse at F2 checks out okay.. I've also pulled out RV1 and replaced with jump wire for the moment, so there is 0 ohms along that whole section from the + of C1 to the input of TL1.

What you think of my idea of my idea of putting C1 in parallel with a regular 100W / 250V lightbulb to see if it charges to 250V (only reaching 30V in the above circuit).. ?

[budm]

Re: 250V AC Capacitor across input

C1 is not causing the voltage to be only 30V, it is hooked up right across the power line, it is bad and causes the voltage to drop down from 230v to 30v, the fuse would have blown by now.
Did you check the voltage across the closed contacts of the switch like I suggested you to do?
You can also bypass the power switch.

[kaboom]

Re: 250V AC Capacitor across input

It's a power factor correction cap.

What you have is simple choke ballast for the lamp. An "ignitor" fires the lamp. When the voltage across the lamp is over a certain point, the path from the ballast to neutral is closed, then opened. This continues, rapidly, until (hopefully) the arc is established in the lamp.

The lamp will work without the cap. It's only there to cancel the inductive portion of the incoming current. Rather than, say, 400VA/165W (allowing ballast losses), you end up closer to 165VA/165W.

The resulting line current at 230V, not including control power, is ~720mA with the cap, 1.74A without. This assumes an uncorrected power factor of .4125.

The thermistor is used to eliminate very high inrush that would otherwise occur if the power switch should close at the top or bottom of a half-cycle.

What are you reading the 30V with? A high impedance meter? Try tracing the circuit with a lightbulb and going back through til you find line voltage.

Also, from what two points were you measuring voltage? Eliminate that switch entirely and hook a line cord right to the ballast tap and lamp/ignitor common. Don't need the DMX, control tx or PFC cap for this. You're gonna do the same thing as if you were testing a metal halide fixture.

Look at some ballast diagrams- it may make it clearer for you.

-Paul

[budm]

Re: 250V AC Capacitor across input

I already told him to check that power switch or bypassing it, but he did not do it so far.

[JonathanAnon]

Re: 250V AC Capacitor across input

It's a power factor correction cap.
What are you reading the 30V with? A high impedance meter? Try tracing the circuit with a lightbulb and going back through til you find line voltage.
-Paul

http://www.kewtechcorp.com/products/multimeters/kt115

That's my DMM, apparently used by the guys in the ESB (out national electricity supply board).

I'll have a read through the stuff above and have another look at it tomorrow.

I already told him to check that power switch or bypassing it, but he did not do it so far.

I havent had a chance to check that yet, bud, I was playing with the band all weekend. I'm not ignoring your advice on that one, I'm really just trying to work out the best troubleshooting procedure for something like this, rather than specifically trying to just get this one item fixed...

That switch seems to be buried somewhere in the unit that isnt as visible as the other items.. To be fair to the manufacturers, every item on the schematic is very well labelled making troubleshooting much easier..

[sam_sam_sam]

Re: 250V AC Capacitor across input

I work on these type of lamps before you ether have a bad ignitor a bad ballast

There is easy way to trouble shoot these Iam not trying to be funny here But you have to have
If you have a know good spare ignitor try it if the lamp light then the ballast good

I have found a lot of bad ballast that you can not just ohm these out and say they are good or bad it dose not work that way

I have two bad ballast where I work that compare to a working ballast it should work but these two do not work and I am using a know good spare ignitor

I would also jump out the switch as well just to make sure that this also not one of you problems

If you want to be real bold you could take apart the ignitor and look on the board and see if you can find the firing doide there will also be a cap and a resistor 5 watt or better and choke coil that what is on most ignitor board that I have seen you can do this as along as they did not use black or clear or any other color goop to cover the hole board

The firing doide is the part that gose bad most of the time if the wattage of the lamp is from 35 to 100 watt you can find this part at Digikey I do not have a part # for you right now I keep about ten of these in my part bin I repair these boards

Here is where you can buy a ignitor from here http://www.bltdirect.com/products.php?cat=602

I hope this helps

[JonathanAnon]

Re: 250V AC Capacitor across input

okay got some time to look at this today...



I disconnect the rest of the circuit and checked the input voltage after the fuse... It measures 240V AC so there is no voltage drop across either SW1 or F1

I connected the fuse and switch back to the circuit, and then cut the parallel connection to XS1 / RV1 / C1 to eliminate them from the circuit.. I switched back on the light and tested the voltage at the input of TL1 and it still measures 30V....

There are two wires going to TL1, input and output... Would it be okay to join them together to cut TL1 out of the circuit and see if the bulb lights up.. ?

[budm]

Re: 250V AC Capacitor across input

"I disconnect the rest of the circuit and checked the input voltage after the fuse... It measures 240V AC so there is no voltage drop across either SW1 or F1"
You have to have a load at the output side C1 will be the load or just put a lamp in place to use it as an indicator, you can have high resistance on the switch, the out put will still be reading 230v since there is not load and your meter has 10Mega Ohms input impedance. Hook C1 and RV1 back in place and check the voltage drops between SW1 pin 1 and the right side of F1.
You can prove my point about the reading with out the load by doing this, get a 1000 Ohms resistor and connected to the Line side of the power, black probe of the meter on Neutral side, Red probe on the output side of the resistor, your meter will still show 230V, that 1000 Ohms is used to simulate the line resistance.
Why don't you just bypass the switch and se what you get? Switches, fuse, connectors are not mounted on the circuit board, right?

[JonathanAnon]

Re: 250V AC Capacitor across input

Again I wasnt ignoring your advice Bud, it was physically difficult to jump both... however I managed to jump everything out.... as in my photoshopped image below..



I noticed that sometimes the voltage was 70V, sometimes 40V and sometimes 240V so given that everything else was jumped out, I tried to follow the voltage further down the line..... And ... would you believe it.... the wire from output of TL1 to F2 was shorted.... jumped a wire from TL1's output to F2 and the light comes on....

Gonna leave it on test, but I think that's the fault...

[budm]

Re: 250V AC Capacitor across input

But the wire on the wire on the right side of the TL1 is supposed to be connected to the thermal fuse F2, so I do not understand by what you mean that the wire was shorted.
If the wires are connected as shown, I would expect TR1 transformer pin 1/2 and pin 6 will have steady 230 volt which the cap is also connected in parallel through the thermistor current limiter.

[JonathanAnon]

Re: 250V AC Capacitor across input

Sorry, I meant that the wire is open not shorted...



TL1 is physically at the bottom of the device behind the LCD interface. The fuse F2 is up beside the light, so the wire between them is cable tied the whole way along the arm which moves about a lot.... I assume that through wear and tear it failed...

From the schematic in my first post (the original schema, not the one I photoshopped), the 250V cap is only across the line to the ignitor TL1, not to the main transformer...

[budm]

Re: 250V AC Capacitor across input

So basically the diagram was wrong? What does the correct diagram look like?

[twbranch]

Re: 250V AC Capacitor across input

I apologize but I do not see where C1 is across N and L. It is hooked up to N and PS4-2.

[budm]

Re: 250V AC Capacitor across input

It has inrush limiter RV1 in series with it to reduce inrush current, but he said that the diagram is not correct. You need to click on the picture to see the diagram.