This is topic DC ammeter on lamphouses- a must or not? in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.


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Posted by Luciano Brigite (Member # 1104) on 05-21-2003, 07:18 PM:
 
Hello all,
I'm on the final stage of setting up a pair of GK President lamphouses and I've been wondering lately if the current metter is really a must or not. these LH's doesn't have any metter nor have any cutting in the panels to fit one. The rectifiers also doesn't have the metters ( both rectfiers made by myself).
The reason I'm asking about it is because the prices of them.
I know that there are some direct metters ( that won't need a shunt) but they're hard to find. the standard ones ( that requires a shunt) I can find easy, for about $25.00 each. but the kick comes with the shunt.. it'll cost around 3 times the price of the panel metter .
the only direct ammeter I have right now is marking 40 amps all alone ( and no.. it's just there standing on the bench hooked to.. nothing) and the std type ( with shunt) is only up to 75A.
my last resource is the metter from a peerless, it'll go up to 110A but will look odd on the Gk lamp.. but I have only one..and two LH's
any hint?
Thanks!
 

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Posted by Gordon McLeod (Member # 33) on 05-21-2003, 07:40 PM:
 
All the GK presidents I ever worked on had a ampmeter
 

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Posted by Paul G. Thompson (Member # 655) on 05-21-2003, 08:19 PM:
 
It would be a very good idea to have an ammeter on the lamphouse. If calibrated, it can be a very good troubleshooting aid in case something went wrong. It also gives a very good idea if you are operating within the current parameters of the bulb.
 

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Posted by Luciano Brigite (Member # 1104) on 05-21-2003, 08:48 PM:
 
Hello,
That's a little strange but none of my Gk president or the ones I saw/worked with have/had ammeters and the manual I have for it also doesn't show any nor has any mention of one anywhere ( the manual I found here on Film Tech).I have pictures of it but when I tried to scan, my scanner went poop on me. I ended taking a picture of the picture with the webcam, then sorry for the poor image, it's from the rear of LH where an ammeter should be located, it's before I took it down for re-paint/rebuilt and xenon conversion. The two fuse blocks on the lower left are gone and it's there I'm planning to put the ammeter. the black square at the top is a dark green glass and was kept there.

 

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Posted by Paul G. Thompson (Member # 655) on 05-21-2003, 10:52 PM:
 
It may have been an option, or someone removed them.

I personally feel very uncomfortable operating a carbon arc lamp or a Xenon lamp that is not equipped with an ammeter.

One never knows what idiot may have come in the booth and said, "Duh, what a pretty knob. I wonder what it does?" and they give it a "spin" to see what it does. Then they forget where it was.....or just leave it in a new setting.

Seen it!
 

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Posted by Stan Gunn (Member # 554) on 05-22-2003, 01:19 AM:
 
The President lamps were never fitted with amp meters.
They had a floor standing unit with the rect switchs, volt and amp meters.



 

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Posted by Dick Prather (Member # 1136) on 05-22-2003, 01:27 AM:
 
Mayby the GK President lamps sold to North America had them. I agree with Gordon that all the ones I have seen had the meter. They were all in Vancouver, British Columbia and vacinity. The one I have in my basement has one.
 

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Posted by Leo Enticknap (Member # 534) on 05-22-2003, 01:58 AM:
 
Also, make sure that if you do have an ammeter, it is of the correct sort and working properly. At one cinema I worked we couldn't work out why lamps were only lasting 1,000 hours or so before dying of a badly blackened envelope and/or a charred anode lead.

After months of head-scratching, the answer turned out to be that the ammeter was of the wrong sort, and giving a reading which was way too low. We thought we were running the lamp at 65-70 amps when in fact it was doing 110-120. Needless to say, that explanied why we were nuking the bulbs, and also why the picture looked nice and bright!
 

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Posted by Stephen Furley (Member # 1277) on 05-22-2003, 02:42 AM:
 
Paul wrote:

quote:

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I personally feel very uncomfortable operating a carbon arc lamp or a Xenon lamp that is not equipped with an ammeter.

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quote:

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I'm sure the apt operators didn't increase the curreny beyond what was needed to get 16FL

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In retrospect I'm sure we did. Screen luminance is a bit difficult to judge subjectively and without a spot photometer, especially when lots of (differently graded) prints are passing through (so in effect you're trying to judge a moving target) and we'd never seen that screen with a lower illumination level.

Needless to say the difference was startlingly obvious when the correct ammeters were in and the current was back down to 70, though...

It's for that reason that I'd be very cagey about ever operating a lamphouse without a verifiably kosher ammeter: if you suspect that something's wrong with the power supply, there is no other way of checking it objectively unless you have a light meter (which most cinemas don't) or you're willing to take the cover off a live rectifier and poke a very high-spec multimeter up its innards. Call me a wuss if you like, but I think I'd pass on that one!
 

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Posted by Gordon McLeod (Member # 33) on 05-22-2003, 09:03 AM:
 
If you notice that black bar below the rear view port with the two holed that is where the surface mount meter went the two stud of the connection went through two porcelain bushings andthe shunt was mounted across the back
Considering how many were sold (very popular lamphouse and very efficient) I would be suprised that they were not on all of them
 

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Posted by Jim Spohn (Member # 1547) on 05-22-2003, 10:16 AM:
 
In a pinch, amp-clamps will give a pretty good idea of how many amps you are pulling. (Yes they will work on DC) You might also find an ammeter on an old carbon arc lamp, it will have the proper shunt on it for the meter. The shunt goes across the meter and the meter goes in series with the load....Jim
 

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Posted by Luciano Brigite (Member # 1104) on 05-22-2003, 05:47 PM:
 
Hello again,
thanks for all the information until now.
The black bar bellow the rear view port has the switchs for the inspection lamp and the feed motors, what they control is written on that bar.( that bad pic. I posted isn't showing it clearly).
I have a clamp meter,bought it mostly to take dc current readings after reading somewhere here in the forum about that same situation Leo mentioned ( I believe it was his own post i read at the time about it) anf after had about the same problem once with a bad ammeter ( it'd stick at about the 70 amps while the real current was reaching the end of scale, 100A).
The only ammeter I have that'll fit the 2000W bulb range is one from a peerless lamp ( up to 110A), but I have only one, it's working ok and is in good shape. I'm looking for another one ( or maybe for a new pair of them) if I can't find.. I'll have to find a place that sells ammeters for a fair price.
Thanks!
 

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Posted by John Spooner (Member # 1565) on 05-23-2003, 12:23 PM:
 
Dear Luciano and interested parties.
Here is a picture of an original Gaumont Kalee President carbon arc lamp (with Kalee 21 head).
The amp meter was mounted on the pedestal directly under the lamp.
John S.
 

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Posted by Dave Macaulay (Member # 813) on 05-23-2003, 10:32 PM:
 
Since you have a clamp-on meter you can easily make and calibrate a shunt.
Get any old ammeter for external shunt.
These are almost always 50mV full scale, although there are oddities. If you find one with the scale range you want, great... but you should be able to find one with the face removable so you can simply paint over the numbers and add what you want.
Assuming you want 150A full scale, just over a foot of (preferably solid not stranded) #4AWG wire would be a fair starting point (you want 0.000333 ohms and #4 copper is 0.000293 ohms/foot) then either prune it until it's correct or cut it to read a bit high then attach your meter lead as a tap like an adjustable resistor. The #4 wire is way small for lamp power normally but this foot long piece will only disipate 7.5 watts at 150A current and will get warm but not super hot.
If you want to coil the wire to save space, be careful to make a magnetically neutral coil or you may distort the lamp arc. Doubling the wire in half back on itself and then coiling the resulting pair of wires achieves this. Don't make any really sharp bends, this changes the copper crystal structure and raises the resistance considerably.
 

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Posted by Luciano Brigite (Member # 1104) on 05-24-2003, 12:45 AM:
 
Thanks for sharing that picture John
it's always good to see an all original GK setup in that nice clean condition,wish I'd find one just like that somewhere where I live. The pair I have ( model 12) doesn't have the original pedestal nor the sound head, only the main mechanism, spool boxes and lamp. it was also repainted a yucky gray , one is now fully re-painted,not like the original gold color but somewhat close. ( pics of them to come ).
Also thanks for the info about the shunt ,Dave. I might try that pretty soon, I just found 4,brand new dc ammeters I bought for a now long dropped project for a bench power supply and they're left forgotten in the parts's cabinet, they're 10 and 15 A max.. but with that info you posted here a new shunt and a X10 marking on the panel seems a good way . Will post the results after I give it a try..well.. that if I don't forget to do it..
 

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Posted by Tim Reed (Member # 137) on 05-24-2003, 05:06 PM:
 
Humm, that lamp's a new one on me. Can't say there are many of those in the states.

Regardless, there are small/portable setups that have the ammeter on the rectifier. E.g., Kneisley Pup, Strong Super Trouper spotlight.
 

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