Hi all, when I used to want to fire up a 1000w compact source iodide lamp, I used to drag out a 1000w SON choke and run it in parallel with a 400w SON choke.
That combo gave the required lamp current of about 15 amps but it had some issues, namely it was a PITA wiring it all up and now the gear I used to use are now in their own enclosures which rules it out completely now.
I've decided to build a dedicated gearbox for running these lamps but I'm not sure on what gear to use.
I've read somewhere that 3 x 400w SON chokes will give the right lamp current? Obviously I just want to confirm before I got and plop £45 each on some 400w SON chokes!
Any info would be nice so I can crack on!

I did a quick impedance calculation of the system you want to build and your 3x 400W HPS choke solution should work indeed. For its proper operation, the CSI 1000W needs a ballasting impedance of 11.5 Ohms on 230 V 50 Hz mains. One 400 W HPS choke has a total impedance of 35 Ohms, so three in parallel results in a total ballast impedance of 11.7 Ohms, which is close enough.

However, that being said, keep in mind that those choke ballasts are designed for an operation at 4.4 A and pushing that current to 5 A (due to the CSI's low arc voltage) will increase the ballast's power dissipation by 30% (64.5 W vs 50 W per choke), which can result in a significant overheating, especially if you pack all three ballasts together in a compact enclosure...

Thanks for that.
I'm not really concerned about overheating the ballasts and realistically this will only get used for no more than maybe half an hour at at time.
I only have two lamps so it's not like I'm going to put them into proper service

No problem. An intermittent service won't be a problem then. Otherwise it would be a really good idea to couple heatsinks to those ballasts and possibly add a few fans.

Bang! And my wallet takes a hit...