Film-Tech Forum ARCHIVE: Acceptable Ripple Current for 7k Lamps

This is topic Acceptable Ripple Current for 7k Lamps in forum Large Format Forum at Film-Tech Forum ARCHIVE.

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Posted by Bob Brown (Member # 1205) on 05-09-2004, 12:59 PM:

Anyone know what the acceptable range of ripple current allowed for the 7K SR projection system using the Miller rectifiers? I am starting to get arc flicker just after 100 hrs.

I checked the ripple current at the rectifier and I am getting a reading of 200Mv.
For the record I am using OSRAM XBO Lamps. Power settings on the rectifiers are set at 160 amps 43 volts

Posted by Gordon McLeod (Member # 33) on 05-09-2004, 01:51 PM:

Sounds like you are ok for ripple at that level though it would be better to measure the ripple current rather than the ripple voltage

Posted by Adam Martin (Member # 641) on 05-09-2004, 02:42 PM:

With Osram 7K lamps, I've always seen flicker start at around 200 hours.

I thought you guys were going to give Christie 7K lamps a try?

Posted by Bob Brown (Member # 1205) on 05-09-2004, 03:20 PM:

Adam, Been there done that, no difference. I think the next move for IMAX is installing some filters on the rectifiers in hopes that it will help. Grand Rapids is really bad, and mine here in Lansing are starting to have the same problems as in GR.

Posted by Phil Hill (Member # 371) on 05-09-2004, 04:12 PM:

You may be over-cooling the lamp...check the lamphouse exhaust airflow.

>>> Phil

Posted by Mark Gulbrandsen (Member # 72) on 05-09-2004, 05:37 PM:

To think that Imax is still using converted arc welding rectifiers is a gas..... there's much better available than that for that current level of operation, and it comes right off the shelf!

You also need to pay as much attention to inrush current as the ripple current. As Gord says only measure it by the current method as this is the only meaningful measurement. Many rectifiers will exhibit different levels of ripple at differing operating levels. I also agree, switch to the Ushio's and give them a try.... overall, I can't think of anyone that gets very decent life span out of a 7kw lamp. Probably the best 7kw life span I've seen though is with all Christie stuff... lamp, rectifier, lamphouse.

Mark

Posted by Gordon McLeod (Member # 33) on 05-09-2004, 05:43 PM:

typically the Millers have proven themself to be an excellent rectifier
With the Ultra80's I usually get about 700hrs on the 7K lamps before they get changed

Posted by Mark Gulbrandsen (Member # 72) on 05-09-2004, 08:58 PM:

I agree thry're good rectifiers, but I am just amused that Imax hasn't developed their own when you look at all the other developments thay've done.

Mark

Posted by Steve Guttag (Member # 268) on 06-19-2004, 06:20 AM:

Gord,

Whos 7K lamps are you using?

Steve

Posted by Gordon McLeod (Member # 33) on 06-19-2004, 04:33 PM:

We are using OSRAM's right now and before we had Superior Quartz
The rectifiers are strong switchers with Ultra 80 lamphouses and lots of cooling

Posted by Steve Guttag (Member # 268) on 06-20-2004, 12:24 AM:

I've gotten more life out of Christie CXL-70SC lamps is why I'm asking...generally Christie's are getting 2-3 times prorated warranty life presuming the power is clean. In the case of a 7K, that would be 1000-1500 hours.

The 6K lamp is another trick...it is more light efficient than the 7K and tends to last longer.

Steve

Posted by Dick Vaughan (Member # 540) on 06-24-2004, 03:00 AM:

We use Christie /Ushio 7kW here in our SR projectors in Bradford .

Usually pull them around the 800-850 hour mark but have had them run to 1000 with no problems. Much better than Osrams