Sanding down Hammond transformers

[leoparleur]

Hi,

Since the quality finish on Hammonds transformers is not quite nice, I'd like to know if I can sand down the sides and top of the cores to redo the painting.

I'm asking because I do not know much in transformer design and aint sure if each core plate is isolated from one to another and if it will short circuit them if I sand down to metal.

All comments appreciated as if I should or not do it.

Thanks!

[DF96]

My understanding is that each lamination is poorly insulated from its neighbours, but as all these weak barriers are in series the result is a higher resistance so only small eddy currents. Sanding the ends could create dead shorts so increasing eddy current losses. I would leave it as it is. If you don't like looking at it then add a perforated cover.

[bob91343]

I don't believe you will cause a problem, especially if you use sandpaper and not emery or a file. Metal filings aren't good. Tighten the mounting screws before you proceed. Sand lightly, just enough to do the job.

Note that the mounting screws have insulating washers. Don't compromise that insulation.

[leoparleur]

DF96, bob91343,

Thanks for your replies gentlemen it was very helpfull and answered my question. I will sand them down beeing carefull to only remove the small impureties that built up in the original finish (not to bare metal). I would have liked to remove every thing and start from new with a nice copper finish but I dont want to take any chance and alter their performance.

Thank you!

[Zero Cool]

I know of one MFG that does this to every exposed transformer without ill effects. has been doing it for years and even has a full time employee that does not but this! they sand the sides flat and smooth then repaint!

[metalsculptor]

Why sand it down, the usual technique to pretty up industrial hardware is to use body filler or spray putty then sand down that till it is smooth. As for the insulation between the plates, it is common practice to weld a lamination stacks together evidently with no ill effects (this is done on one side of the stack only) so I cannot see a bit of sanding causing problems.

[Tony]

the rough surface you see at the edges are caused by the insulation varnish used in making the traffo, the vendor did not see it fit to smoothen them up before painting.....

but you can make it smooth if you want to repaint, sandpapering will do...then apply gray primer and then the black paint....

[DF96]

You won't see copper however much you sand the laminations, as they are made of iron/steel.

[db!]

Dip the affected side in a very shallow tray (Don't fill it more than a couple mm's) of lacquer thinner; the varnish should be soft enough to scrape off after an hour. Just make sure you don't get any on the windings, bobbin or wires.

[leoparleur]

Originally Posted by Zero Cool

I know of one MFG that does this to every exposed transformer without ill effects. has been doing it for years and even has a full time employee that does not but this! they sand the sides flat and smooth then repaint!

I have emailed Hammond today to have their expertise on that. The sales rep told me I could sand down to metal but I'll try to speak to an engineer tomorrow for approval. I want to make sure this in no way will affect the performance. The rep also proposed to have the transformers sent back to the place where I purchased them and they would take care of all the shipping expenses (mine and the store). Not bad, but I'd rather not go through that hassle and wait a week or two. I haven't mentionned either to you guys that the varnish (not paint) on the 193M choke end bells is peeling off very easy. It's supposed to be baked. If I gently touch with my fingernail, air penetrates between the metal bell and the lacquer coat. It's sad that they don't use the same finish as the OPT and PT, this one is very nice and clean. Check my picture...

Thanks!