Author Topic: Right gear for CDM-T?  (Read 2554 times)
Roi_hartmann
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Right gear for CDM-T? « on: April 30, 2015, 06:55:21 AM » Author: Roi_hartmann
Hi everyone!

Im repairing Philips Decoflood that I got sometimes ago. Ballast was shorted badly and inside of the fixture was pretty dirty from smoke. Ive cleaned it up inside of the fixture(glass still has something in it, was unable to remove the dirt yeat). Now Im trying to find new gear. Im not so familiar with MH gear and was wondering if this ballast and ignitor is OK?

Its a SON ballast but current is very close to what old ballast had, 0,98A. Also need help to verifyi can I use ignitor in the picture as well.

Intended lamp is CDM-T 70W
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dor123
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Re: Right gear for CDM-T? « Reply #1 on: April 30, 2015, 10:48:14 AM » Author: dor123
CMH lamps intended to be operated on a HPS gear (Both ballast and ignitor).
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Ash
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Re: Right gear for CDM-T? « Reply #2 on: April 30, 2015, 06:00:31 PM » Author: Ash
Choke is probably ok

Ignitors can vary. This one is superimposed so its got good chance to be ok, but if it is not, it can be harder for it to start the lamp or to restrike it when hot after a power interruption
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Re: Right gear for CDM-T? « Reply #3 on: May 01, 2015, 12:46:43 AM » Author: dor123
Ash: There are 50/100hz semi-parallel ignitors (Philips SN 58 for example), which are suitable for CMH. Not all semi-parallel ignitors, are like the Eltam ES-50 (Low frequency pulses)
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Please forgive me if my choice of my words looks like offensive, while that isn't my intention.

I only working with the international date format (dd.mm.yyyy).

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Re: Right gear for CDM-T? « Reply #4 on: May 08, 2015, 01:45:50 AM » Author: Medved
If your lamp could be close to the ignitor, these superimposed ignitors are the "safest" choice, because they are completely selfcontained (pulser + pulse transformer), so you are not risking ballast-ignitor mismatch as with the semiparallel ones (there are two topology types, same looking wiring, but completely incompatible with each other).

Generally the MH's are rated for 3..5kV ignitors for really reliable starting (down to freezing temperatures,...), however if you don't mind a bit longer hot restrike time, in my experience even the "1.5..2.5kV" types (originally intended for HPS) work well too, at least at normal room temperature.

The rated current of the MH is a bit lower, but it will be that lower on the same ballast with the MH, because the MH has a bit higher arc voltage (when compared to a new HPS; the MH does not increase it's arc voltage that much as HPS uses to do)
« Last Edit: May 08, 2015, 01:48:16 AM by Medved » Logged

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marcopete87
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Re: Right gear for CDM-T? « Reply #5 on: May 09, 2015, 10:43:33 AM » Author: marcopete87
see the choke as mercury ballast, D goes to ballast, N to neutral and La to lamp.
Usually, CMH lamps are rated for electronic ballast, but they works well with magnetic.

I have an question for Medved: what kind of ignitors are avaiable?
Usually i use this kind of ignitor, but sometimes i see 4 pin ignitor which take two ballast taps.
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Re: Right gear for CDM-T? « Reply #6 on: May 09, 2015, 02:33:58 PM » Author: Medved
see the choke as mercury ballast, D goes to ballast, N to neutral and La to lamp.
Usually, CMH lamps are rated for electronic ballast, but they works well with magnetic.

The "Electronic only" is the case just for the 22W version, those need active arctube temperature stabilization and that feature is beyond the reach of the simple magnetic gear.
The 35W and above are officially rated as well for a series choke ballasts, common with HPS lamps (I'm talking about EU-like 230V market only, this does not apply for the US nor CAN, there the HPS spec's are way different).


I have an question for Medved: what kind of ignitors are avaiable?
Usually i use this kind of ignitor, but sometimes i see 4 pin ignitor which take two ballast taps.

The ignitor depicted here is the superimposed type. It contains everything necessary to generate the required high voltage pulse without even needing the ballast inductance for it (so no inductive kick; it would work with any ballast type, include a resistor; but the limit is the lamp here). It's distinctive characteristic is the way how it is connected: "Cut" the wire from the ballast to the lamp and insert the ignitor there.
It is the type usable as well with US ballasts of any type, when remote ballast configuration is required (where the ballast to lamp cable exceeds the ballast specification). In that case the internal ignitor inside of the ballast is deactivated and the superimposed type is placed inside of the fixture close to the lamp. The long cable is then between the ballast and the ignitor. It works just because that ignitor does not need any cooperation from the ballast at all, so the capacitance of the cable to the ballast is no problem at all (with the original ignitor build into the ballast it tend to attenuate the HV pulses).

Other ignitor I have in my hands is the semiparallel style represented by e.g. SN57. The "ignitor" box is just a 750V (for MH; or 500V for the HPS) pulse generator, feeding tap on the ballast winding in 20% from the line input. The ballast coil then act as the 1:5 step up transformer, so transforms the 750 or 500V to about 3.5 (for MH) or 2.5kV (for just HPS). The main workings (a capacitor in series with a triac) of the ignitor is connected between the tap and Neutral, the connection to the lamp is just a voltage sensing (it senses thge voltage there and based on that determines if the lamp had ignited or not yet, so eventually triggers the triac at the correct moment).
This ignitor system requires the ballast to work together with the pulser box: It forms the switched resonator circuit to boost the 230V to the 750V peak (however it is not sensitive to the actual inductance, it just has to be of sufficient quality), plus uses the turns ratio to transform the pulse to the final 3.5 or 2.5kV.
Because it generates the pulses without any significant losses, it is able to generate rather high energy pulses at every mains half cycle, so it's main use is as high energy, long range ignitor.
Interesting note: If you have a lamp that needs just 750V, you just connect the "tap" and "lamp" terminals of the ignitor box together and connect it behind the ballast parallel to the lamp. It will work exactly the same way as designed, just without the additional boosting, so the ignition voltage would be the 750V (so e.g. to operate US probe start MH on an European series choke MV ballast)

Then in the literature (and if I remember well in one catalog as well) I've seen another form of a semiparallel ignitor: It uses practically the same pulser part as uses to be part of the superimposed ignitors, but it lack the step up pulse transformer, but uses the ballast choke with tap instead. With this type the tap has to be in 6% (for 3.5kV MH ignitor; or 8% for the 2.5kV HPS one) from the lamp end.
Here a capacitor is charged via a resistor (and an filter inductor) till the breakover voltage of a SIDAC (or something similar made of thyristor and few other components), so aboput 200V, then the SIDAC turns ON and discharges the capacitor to the 6% or 8% section of the ballast, so it gets transformed to the required 35. or 2.5kV. As all the circuit is connected around the HV end of the ballast, the inductive filter makes sure the charging resistror does not eat up the HV enmergy.
As the capacitor is charged via a resistor, the pulse energy is rather limited, so these are not suitable for remote ballasts (maximum ballast to lamp is 2m).
Even when the wiring appear exactly the same as with the previous "SN57-like" topology, this is different arrangement, requiring the tap on different position. So you must make sure you have correct ballast/ignitor combination, components of those two styles are not compatible at all (however ballast suitable for both could be made - having two taps, one in the 20% from the line input and second the 6% from the lamp end, then you should make sure you use the correct tap according to what type is your ignitor).
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Roi_hartmann
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Re: Right gear for CDM-T? « Reply #7 on: May 12, 2015, 04:01:26 AM » Author: Roi_hartmann
Thanks to everyone.  :D Now its just to assembly new ballast and ignitor to fixture. I will be postin pic once Im finished.
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marcopete87
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Re: Right gear for CDM-T? « Reply #8 on: May 21, 2015, 05:54:35 PM » Author: marcopete87
Thank you again, Medved!
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