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Author Topic: DC ammeter on lamphouses- a must or not? Dave Macaulay Film God Posts: 2321 From: Toronto, Canada Registered: Apr 2001 posted 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.  |  IP: Logged Luciano Brigite Master Film Handler Posts: 277 From: Sao Paulo, SP, Brazil Registered: Jan 2002 posted 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..  |  IP: Logged Tim Reed Better Projection Pays Posts: 5246 From: Northampton, PA Registered: Sep 1999 posted 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.  |  IP: Logged

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