IREM EX-170 switching rectifier v/s traditional IREM N3 etc.

[Jerry G. Axelsson]

Hello dear colleagues,

I am looking into upgrading a pair of rectifiers to a modern switching rectifier such as an IREM EX-170 in favor of an IREM N3-150 (from the year 2006)

I have heard postive details about a switching rectifier in comparions to an older traditional types such as the IREM N3.

Comments have been: Improved arc stability, longer bulb life, less power consumtion, easily adjusted current via remote.

This would be for an archival facility which runs analog film on a daily basis.

Any feedback or experience concerning this matter would be appreciated.

[Steve Guttag]

On the N3 series, if you keep the filter capacitors good, you should get very good lamp life. Typically, for a linear rectifier like the N3, the quality of the lamp life is mostly determined by incoming power (crap in, crap out), filter capacitors and controlling in-rush current. Irem does this with their A1 relay board (formerly the RA relay on earlier versions). It allows a boost voltage for the igniter while not charging the main capacitors up to the higher voltage. So, once the voltage rises to somewhere around 40V the relay kicks in, dropping the main capacitors out (but they're still charged), letting the boost voltage rise. Once the lamp ignites, the voltage will drop immediately and the relay will drop out putting the main filters back on line. So long as all of that is working, your lamps should have a good life. If you look at the electrodes at the end of the lamp's rated life...do they look clean? If so, you're good and changing rectifiers will not solve anything.

I have not had issues with Irem's EX series of switch mode rectifiers either. Typically, the "ripple" from a switch mode supply is much higher frequency so, again, looking at the electrodes, you'll see what may appear like fine sandpaper on the anode surface.

Here are things to consider with the two types. With a conventional supply, most everything is field serviceable. You need diodes, possibly every 20-years a fresh set of capacitors, maybe a contactor (keep the connections good) and maybe an A1 relay (I had better luck with the A1 relays than the RA relays of yore). You can keep that rectifier going, almost indefinitely.

The switch mode supply works until it doesn't. You are pretty much beholden to Irem for its support if it gets too deep into a failure. The life cycle of the semiconductors/chips used in a switch mode supply are shorter (how long manufacturers make those components) than things like a DO-5 package diode (or whatever is used in your rectifier). The power efficiency is better on the switch mode supply, for sure. I'd be surprised if that was the major driving factor in selecting them though. And yes, there are some benefits to electronic control, if you are going to ramp the power. Then again, I've found that xenon lamps don't like to go back down in power once they've been driven at a higher power for any length of time. There is a range that they'll behave but you can't go from 130A and down to 100A and not expect some stability issues.

So, if you do make the switch, keep the N3s around to put back on line if one of the EXes goes down (or have a spare EX or 2.

[Jerry G. Axelsson]

Thank you Steve for an excellent summary.