Hi All,
Was just watching episode #512 about the overheating regulator in the Rigol 832 and I recall a similar problem with their DC loads as well. I have worked many years in the industrial electronics area and it is amazing how common this problem actually is and not just with regulators but many electronic components.
The problem I have found mainly from the point of view that electronic products are mainly designed for either European, US or Japanese environments, the closest to us being European with a 220 to 230V nominal supply which is usually 240V or less at maximum. Australia on the otherhand is usually closer to 250V especially now with the prevailance of solar. For example in the lab at work I get about 247V on 2 phases and 249V on the 3rd. This is within spec, here at home it is about 245V normally but when the solar is going full tilt in the summer it gets upto 250V. I have also worked on equipment from mining areas over in WA and some areas out there can get up to 265V. Anyhow long story short, the voltage is pretty high.
The problem with this excessive voltage is it does put a lot of stress on some components, in the case of some Rigol products with linear power supplies this is excessive heat in the regulators even though in the case of the DP832 the heatsink is also inadequate. Other common problems I've seen with equipment is rapid heater element aging, burned out encapsulated transformers, premature electrolytic capacitor failure and bootstrap/voltage balancing resistors in power supplies going open, oh and on older equipment, rapidly burning out indicator lamps.
So how I get around this problem is actually quite simple, non invasive and considerably lengthens the life of many products. What I do is use a 300VA toroid transformer (or any transformer with the same ratings will do) with a 30V secondary, I connect this as an auto-transformer so I get about 220V coming out at the tap connection (Provided the transformer windings are connected with the correct phasing). This setup is good for upto 2400VA of load, I pretty much run everything in the lab through a couple of these, I also have a 3 phase unit too but I generally use that to test our products at lower voltages (385V @ 40A) that we export to Europe. I also make it a point to ensure that Neutral is common to both the mains and load sides of the auto-transformer and I also have a 2 Pole 10A C curve circuit breaker on the load side. Really important, check the output voltage before you use this, if the voltage is higher than the incoming mains then the transformer is incorrectly phased and you will need to either swap the primary leads or the secondary leads but not both.
I'm not sure what the mains voltage is where Dave is but assuming it is around 245V then dropping the voltage down to about 220V should reduce the dissipation in that LM317 by about 20% so the heatsink will still be way too hot IMO but that and the junction temperature will have come down by quite a bit. This should also reduce the dissipation in the series pass elements too as the DC bus voltage for each channel will have come down too therefore the series pass element doesn't need to dissipate quite as much.
I don't have a DP832 but plan on buying one in the next week or 2 so I will try it with and without the auto-transformer and see what the difference is and will make a further post then. If anyone else wants to try this out you can also test it using a variac (which is a variable auto-transformer) and just wind the voltage down to 220V and see the result.