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I'm considering replacing a 300W / 500W R7 halogen fitting with one of those 12v HID car fittings, (and obviously customising the halogen lamp housing) I'm also trying to do it on a budget. I'm looking to change five video lights.

I COULD buy a large lead acid battery of about 28AH, (bulb has inrush of 10A, but working current of around 3.5A @ 12v, so batt could last 7 - 8hrs) but ideally, I would prefer to work with 240V.

So my next idea - and the one that I'm a little concerned about - would be to use a 240V to 12V power supply, such as a PC PSU or similar. Since most items are SMPSU these days, I'm wondering if the output would 'collapse', (ie not even start up) if it's suddenly asked to provide 12v @ 10A to ignite the bulb at the onset. (If it was asked to provide 12v@ (say) 1A at startup, it could possibly build up a reserve in the output cap/inductor to supply more current at a later stage, but to jump straight to 10A ....)

It also seems to be a lot of 'work' electronically, converting 240v to 12v, and then 12v through ballast to control lamp. I've found a few 240v to HID ballasts ... but then read that the "ballast must be matched to a particular bulb"

Anyone worked with these lamps? I'm doing this to a) reduce heat of lamp as I've read that HID run cooler than 500W halogen, and b) get more light output for less current.

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  • \$\begingroup\$ Difficult to say that all SMPSes with sufficient continuous rating will cope under inrush but many will. Do some experiments and you will see. \$\endgroup\$
    – winny
    Commented Jan 22, 2017 at 11:57
  • \$\begingroup\$ Also, theare are R7 metal halide bulbs and purpose made ballasts for them operating on 230 V. No hot restrike though. \$\endgroup\$
    – winny
    Commented Jan 22, 2017 at 11:58
  • \$\begingroup\$ Forget about HID lamps in that power range, there are 30W LED fittings for R7s sockets which operate on 240V and replace a 300W halogen bulb. HID is still a thing for >5000lm though. \$\endgroup\$
    – Janka
    Commented Jan 23, 2017 at 21:02

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A 40W ( 3.5A @ 12V ) HID lamp is equivalent to 70W halogen lamp in terms of light output, so it is not really a replacement for a 300W lamp. As for the SMPS question : any good quality computer power supply rated for 350-400W should easily provide 10A of current at 12V rails ( inrush or continuous )

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