Film-Tech Forum ARCHIVE: Irem Switcher

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Posted by Rick Glaus (Member # 1259) on 03-06-2007, 04:59 PM:

I am currently looking at a 6000 watt Big Sky with and Irem rectifier and switcher. I was told these draw about 1/3 the power my current 4000 uses. My question is how reliable these switchers are. Has anyone had any experience good or bad with them. Thanks for any help

Posted by Mark Gulbrandsen (Member # 72) on 03-06-2007, 05:24 PM:

It is correct that switchers do consume alot less power. They can be upwards of 70% efficient while iron core rectifiers are at best about 30 to 40% efficient. The thing I find that helps prolong a stwitchers life is to have proper surge protection on the panel that feeds the switcher... not on the buildings main panel! Other devices in said building can also cause surges and they need to be dlet with at each booth panel. Switchers and the switching transistors in them do not like high voltage or fast high voltage spikes spikes... low voltage can however be tolerated and some designs the switcher automatically compensates for lower power conditions... the resulting ripple which is at about 35 khz is of no matter to the lamp at all. With proper installation of a switcher lamp life can be very long and the switcher can be extremely reliable.

Mark

Posted by Steve Guttag (Member # 268) on 03-06-2007, 06:05 PM:

IREM lists their standard rectifiers (N3 and G3) series at greater than 80% efficientcy.

The switch mode rectifier for 6KW is listed at 90%.

Both numbers seem reasonable to me.

Note too, the N3-180 is listed at less than 3% ripple while the EX-170/G3 is listed at less than 1%.

I strongly disagree with Mark regarding switcher ripple of no concern to the lamp. Lamps run with a switcher type supply (IREM or Strong, that I've seen) have a rather characteristic look on their anode after a time...the flat spot gets these very small, yet uniform rough texture to it. This is in contrast to a ripply conventional rectifier that will leave big "snot" balls on the anode.

My best performance remains a low ripple conventional supply. Christie's seem to do VERY well at keeping lamps going though there seems to be nothing particularly special about their design...IREMs seem to chew up lamps for me faster...particularly if you run them near their top of range...keep them in the sweet spot and they can do well too.

Posted by Mark Gulbrandsen (Member # 72) on 03-06-2007, 07:00 PM:

quote: Steve Guttag
IREM lists their standard rectifiers (N3 and G3) series at greater than 80% efficientcy.

I'd say they are very definately pushing that spec a bit too far. A good friend of mine back in the Midwest who happens to be a transformer engineer claims that the best an iron core tranny will do is in the 30% to 40% region with the very best silicon steel being used for the core laminations. The Irem with its movable core would actually be less efficient than a fixed transformer like Christies or LP. Measure the current draw yourself...they hardly figure out to 80% efficiency with the core fully in place which should be the most efficient operating point.... that spec is very definately more than likely a typo. The rectification section of an Irem if it utilized high speed diodes might approach that efficiency but there is simply too much heat dissipated in them to be near that efficient.. and they don't use high speed diodes.

The switcher might be that efficient... a quick check with the amp clamp at both ends would allow you to at least somewhat calculate that... also factoring in the heat generated along with those measurements... there is always some. I bet its no where near that 90% rating, more like 70%.

Mark

Posted by Steve Guttag (Member # 268) on 03-06-2007, 07:27 PM:

Are you just referring to transformer efficency? Christ they are very high...often over 90%. You can find that on just about any web site on dry type transformers.

Much of the heat given off is in the copper itself. So take a 6KW system that uses a standard rectifier of what Irem claims is 80% efficient. In that case, you would consume 7500-watts of power lighting 6000-watts for your lamp and leave 1500-watts to heat up your space. Now ask yourself, does a conventional 6KW rectifier feel like a 1500-watt heater element or even a 1500-watt xenon lamp has been left inside it in terms of how hot it gets?