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Evaluating Used HMIs for Purchase


Bradley Mowell
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What should one watch out for when buying a used, larger HMI par without a warranty?

If the unit strikes fine, what would it be a good idea to check before making the purchase?

Lens and reflector condition? Cable damage? Any particular issues with ballasts? Bulb condition? Etc.

Thanks.

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I'd post pictures here and ask.

Be very clear what type they are. Magnetic ballast HMIs can cause serious problems with rolling shutter cameras, no matter what anyone tells you, and it's not necessarily fixable with shutter speed adjustments. Electronic ballast types are better. Types with the option to select flicker free or silent mode are best. The flicker free modes may make the lamp head buzz. HMIs not intended for film and TV work may only have, in effect, flicker free mode and they may always make the lamp head buzz. Check if it's hot startable or not. Non hot start lights are a pain.

All you can really do is try it. If you don't have a flicker meter, shoot video with your cellphone, right into the light so that the phone camera shuts down to minimum shutter timing. If there is an issue with flicker this may reveal it as venetian-blind stripes in the image. It's not completely reliable but it's better than nothing.

Also look for types which take bulbs which are hard to find. A while ago there were lots of 1200W HMI PARs being sold, mainly old magnetic ballast types, which used the 1200W PAR64 which is very expensive or may even now be completely unavailable. Check prices and factor a new bulb into your price calculations. If the bulb is very old it will drift toward blue-green and go dim. If the bulb is old, or if you're not sure, replace it. If it fails catastrophically in use, the explosion may damage lenses and reflectors. Look for signs of arcing or electrical discharge around the bulb socket and anywhere else in the head where there's cables. Hot startable lights may use very high voltage to achieve reliable starting and if they are faulty or abused this can cause damage.

Otherwise, it's the same as buying any other electrical item. Look for signs of damage to cases and cables, particularly to the cable that connects the ballast to the head. They're expensive and tend to get thrown around a lot. If appropriate, check that the interlock on the door works (it should refuse to start with the door open). Check the lens isn't cracked and that there are no signs of heat damage on the inside (this can happen with certain types which are not rated to run in certain positions).

If you're in a jurisdiction where there's a standardised electrical safety test, ensure it passes, or at the very least ensure continuity of grounding between mains power connector and all of the exposed metal parts on ballast and head.

P

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Magnetic ballast hmi:s may have visible arch flicker depending on the bulb type and burning position. In most cases you would want a high speed electronic ballast for all shoots unless you dont have any choice.

I just purchased couple of old 575 hmis for low budget docu and 16mm indie stuff. They were 8 times cheaper than similar output led light so I can live with the downsides. But if price is not the main criteria, then I would avoid the magnetic ballasts.

The easiest way to see if a bulb is likely good or not is to look the glass of it. A newish bulb has pretty clear or perfectly clear glass and you can clearly see the electrodes. A old bulb has eroded and hazy glass and the bubble may asymmetric and the electroded much further apart. I would not bother with the old bulbs, just calculate the price of the new bulb to the total price of the hmi set and replace the old bulb right away before using the hmi for work

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14 minutes ago, aapo lettinen said:

The easiest way to see if a bulb is likely good or not is to look the glass of it. A newish bulb has pretty clear or perfectly clear glass and you can clearly see the electrodes. A old bulb has eroded and hazy glass and the bubble may asymmetric and the electroded much further apart. I would not bother with the old bulbs, just calculate the price of the new bulb to the total price of the hmi set and replace the old bulb right away before using the hmi for work

Brand new bulb on the left and the old bulb from a eBay HMI on the right. If the bulb in your second hand HMI looks like that on the right, then get rid of it and buy a new bulb right away (it can be used still but has colour shifts and has striking problems and increased risk of exploding. You don't ever want a bulb explode in you HMI light if there is any way you can avoid it... may damage the fixture quite a bit like Phil said)

51274945446_b056abdd46_h.jpg

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Strike the lamp and burn it for a good hour. 

Measure current draw and ensure that it isn’t excessive. Drawing excessive current can be a sign of other problems developing. 

Inspect lamp and lamp holder. Look for any pitting, burns or signs of arcing. Check the lamp seats properly into lamp holder. 

Inspect all plugs and sockets for damage, corrosion and burns. This is usually particularly telling on the feeder cable. 

Open up the ballast and check for corrosion, signs of water ingress and check general condition. Moisture and dust in any combination is a recipe for expensive repairs. 

Overall you are looking for signs of care and ongoing maintenance. Aging HMIs that are in a bad way can be particularly expensive to keep going. 

Edited by Matthew Parnell
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