Vintage Lighting Tarnex for restoring old wiring ballast

[ship]

So the ceramic cores to these copper spring resisters were too badly damaged to just epoxy back together. This fixture got dropped in destroying both the casters (TBD separate project & just as interesting in unique casters) and the ceramic support for the heater resistance as it were for sustaining the arc. Have the ceramic glue, but waiting on McMaster to special order the bonding agent recommended from spec. to properly glue back together these parts of the resistor core support. It's over a hundred years old and too fragile to thoroughly clean the broken parts. Bonding agent will be needed before doing I'm thinking at this point, Cotronics Resbond #940LE I have a lot of experience working with to glue the parts back together with. The other choice was #907, have a can but years since, it's solid now. Can't see buying another given the other in two part is still fresh and will work.

In the mean time in not starting the light fixture itself yet, I have time to work on the core winding - especially while waiting on a replacement cover for the ballast to be welded up. Took well over an hour to sand blast the housing for this ballast, than more hours to cut 1" 16ga box tubing into angle iron so as to make a cover. Why cut box tubing into angle iron? Because normal steel angle iron would be rounded over on the concave side and not work. Waiting to get the original box back with new cover from the welding shop.

Tarnex... You can see how oxidized and heat burnt etc. these copper coils are in the photos. This has to add resistance to heat dissipation, if not given the skin effect of current flow, resistance to current flow which would not help either. For bling factor and current flow, given I cannot re-produce the coiled springs of the resistors... I'm going to try to dip them in Tarnex. Following the instructions... a plastic or stainless mudding tray for both the chemical and one or more for water rinse after, than a hanging rack to drip dry. The aluminum turkey pan I bought today would be bad. Alternate and perhaps for the water in having more volume is a plastic try to dunk in for water is to use a plastic tub for more volume on at least the last dip.

Pre-tried oven cleaner and lime away/CLR in areas & did nothing.

So, prepping to try this... any final words electrically before the Tarnex does it's thing, rinsing twice, than spraying to drip dry with electrical contact cleaner with lubricant? Thoughts our concerns? Think this will help electrically. Note coil in the center looks like it's broken but it's just the photo and a gap in how the coils are hung.

 

[ship]

No broken sections of the wire, should work especially if I remove carbon from the surface in causing resistance. Still curious about why the third coil was not used in wiring to it. This especially given it's basically a variac dimmer in adjusting to local voltage - or perhaps in the last use the local voltage was good enough? Or on the other hand, given a AC/DC fixture, the fixture was last used for DC voltage and the third coil was not needed?

Could really use some advice on this question before I plug it in.

 

[FMEng]

The coils are not likely copper. More likely something like nichrome, which will never look shiny and clean. Their appearance has no affect on their electrical performance. Resistance and heat dissipation is what a resistor is supposed to do. I would not attempt to clean them.

 

[JD]

Agree with FMEng above, Nichrome steel is what is used in almost all high power resistors to this day. Best example, storage battery load testers. Copper would never work. Even new, Nichrome isn't shiny, and generally after the first use, resembles what is in the pictures. Over the years they increase in value as the wire becomes a bit thinner, and thus the current in the circuit decreases.

 

[Dover]

I would try contacting a company called Powerohm, they make resistors of all kinds with ceramic cores like you need. They may have some that will work as replacements.

 

[ship]

Thanks all for replies. I seem to have a small stock of mud trays and large stock of Tarnex at the moment. I really am thankful for the info above. As for the ceramic... that I can fix without replacement. The ceramic supports the coils in recesses and while badly broken I think can be repaired safely. This I have a lot of experience with.


Almost a shame in that I have this dipping operation all ready to go. But glad I asked, got help and stopped. Were it not for a rush L21-30 twofer project tonight, I will have dipped before checking in.

So if I understand the above correctly for theory, the third coil / variac (as it were) attachment to might not have been needed given the over the years use of this type of wire I have never heard of before, in adding resistance by itself?

Have another carbon fixture where the loading was in shining up - copper - or was that by way of cleaning? This noting it won't work again in many as perhaps noted above failure points of the wiring within the resistor as per cited above.

 

[ship]

Sprayed thoroughly for drip dry the removed coils with "Sprayon #EL'2001 Electrical Contact Cleaner & Lubricant. The normal stuff I use on up to resurfaced 5Kw lamp sockets. Another coat or two in going brown/black instead of black/white. Thanks again for the advice, but removing the buildup and or corrosion I think also important. Did dipping of various clamps/bolts of brass/bronze in CLR, yet to polish, but will help conductivity. Waiting on primer for broken ceramic supports to the coils before I high temp. ceramic glue them back together, than re-wire. I can do this I think properly and well in repair I think from here on the resistor part of the light.