Occasionally I come across someone asking about putting those 90w T17's on a rapid-start circuit. A few years ago, I even did some experiments with F96/HO and VHO ballasts. I had determined they weren't compatable because the T17 lamp voltage is too low (about 60v if I recall). Recently, I acquired some more VHO ballasts and T17 lamps...this time I tried a GE F48T12/VHO ballast. The lamp was still overdriven because the T17 still has a lower operating voltage than a F48 VHO but I then realized there was an even BIGGER problem....

Ok, initially, when I did the experiment,  the ballasts were 525v OCV so lamps started quickly. When I tried using the GE ballast....which despite the label, has ONLY 280 OCV. the lamps glowed dim with bluish ends. I then removed a wire from each end of one lamp and manually PREHEATD it and presto....they both came on! So, I realized the filaments have high resistance. I did measurements and sure enough, the 4v filament current was too low (wrote it down and lost it). This is the same behavior as, say, a 15 or 20w lamp on a regular 30 or 40w RS ballast. That's why PH exclusive lamps, such as 14-20w require about 9v filament current, aka trigger-start.

From all of this, I would have to say that in order to run a T17 "Rapid Start", they will have to be in a "Trigger Start" situation. Naturally, my first thought, since the T17's have similar voltage to regular 20w lamps is to get about 5 or 6 20w trigger start ballasts and carefully connect them in parallel. That means the wire pairs will have to be right polarity or the filament voltages will become shorted.

In the future, I may try something like this.

 If that lamp have such low arc voltage about 60 volt you need about 1500 mA to light it.
  so I would try light it on 100 watt 55 volt HPS ballast with no ignitor and use them on preheat configuration
  that should be close to the voltage spec of your lamp.

If that lamp have such low arc voltage about 60 volt you need about 1500 mA to light it.
  so I would try light it on 100 watt 55 volt HPS ballast with no ignitor and use them on preheat configuration
  that should be close to the voltage spec of your lamp.

How would I wire it in a preheat configuration? I have plenty of 100W HPS ballasts laying around..

Phase to Ballast's Phase terminal

Ballast's Lamp terminal to one Lamp pin

Lamp pin on the other end of the lamp to Neutral

Tap on the ballast (for the ignitor) do not connect, isolate it

Remaining 2 lamp pins (one pin from each end of the lamp) to a switch. To start, connect power, then flip the switch ON for a few seconds and then OFF



Also, for 60V 1500mA lamp you can try 4 F20T12 chokes in parallel (but check the current, if they underdrive the F20T12 they will underdrive the F90 as well, so maybe you'll need to add a 5th choke)

So I tried it, the preheating works but the ballast doesn't seem to provide enough current to strike the arc..

Would putting two HPS chokes in parallel be a bad idea?


Would resistive ballasting be an option? If so how many watts of bulbs would I need? I have no clue how to calculate that..

The ballast gotta be about right in current. It is not your problem. Maybe the impulse voltage is too low, but those T17's were made to be started with 4 pin starers, which starting pulse is as low and inconsistent as it gets, so that would be a non issue. Is there something in your circuit that we dont know about ? - Such as capacitor connected to the ballast ?

Don't try with 2 chokes in parallel, as this will also double the preheat current, and if you do manage to start the lamp, it will get double the arc current

 These lamps are pain to start.  try holding button
 down few seconds then push it in  and out to create
pulsing voltage spike from inductive kick from the ballast
 
even 4 x 20 watt choke will work.  problem was
starting curent way too high that you need had some
 more resistance across the starter switch.  or you will blow cahode. 

  you may have boost the OCV up a bit
by taking a 120 to 12 volt transformer
and boost the voltage up a bit.  it cause
lamp is being so long as that longest  and
lowest arc voltage preheat tube  the US.
i am afraid incandescent wont work
unless you have 240 volt ocv, as  it lacks
inductive kicks for 120 volt ocv.

A US 70w S62 55v HPS ballast without the ignitor might actually be a close match since US 70w S62 HPS lamps run at 52v 1.4a.