So I have a 600 W high pressure sodium ballast that I'm using as a regulator for a series circuit that I have. Is it works decent.  My issue is though that it's in an enclosed can and because of that it gets very very hot. I'm thinking about just submerging it in oil. I've heard that mineral oil can be harmful to the varnish on the ballast, what other alternatives are there? I know some types of varnish will be dissolved by the mineral oil while others won't, and some types of mineral oil will be harmful while others won't.

For something small like that, I'd look into using some epoxy based transformer potting before I'd consider oil. No mess once cured and you can get some that will conduct heat away pretty well.

And for the oil to really work as a transformer cooling medium, the winding would need to be specifically designed for (with spacers forming channels within the winding for the oil to flow through,...).


With this use, you have to make sure no winding is loaded above the current it was designed for. It does not matter what exact function the contraption will have nor how it is connected, nor what real power it is transferring, for the heat what matters are the losses and their vast majority comes from the current passing through the ohmic resistance of the wire the winding is made of. And don't forget there is a square law between the current and dissipated power (Ploss = I^2 * R), so even a seemingly small current increase (e.g. 10%) leads to way larger power losses increase (21% for that example).

Oil cooling of a transformer which has not been designed for it won't help that much. These ballasts use to be designed to be thermally tightly coupled together, so if you manage to add extra cooling to the core assembly (thermall conductive pad between the core and a bigger metal acting like a heatsink,...), it will cool down the winding as well.

OK, then I'm thinking maybe some sort of aluminum heatsink meant for a computer or something.  I wouldn't want to use anything solid because if anything were to happen I wouldn't be able to remove it.