VCCS questions

[jnbsystems]

I'm concerned about the connections to some of my pieces, which is why I was looking at the higher voltage transformer. Although they are very small, some of the parts I have may only have the wire wrapped around them in one place. I am still trying to work out the total surface area of these little buggers. I have them drawn up in Autocad, and I'm trying to cheat by using the software, instead of actually measuring them (without much luck, I must admit ). They have several complex shapes, external threads, holes, o-ring grooves, etc. I will probably just end up using estimating and trial-by-error.

I will look at addressing the enclosure issue, since I've done some panel assembly and industial electrical work.

I'm curious about the heat sinks. I would think there is some way of calculating surface area for the power devices, assuming things like max power handling, ambient air temps, convection vs forced air cooling, etc. I've looked at quite a few various sizes, ranging from very small to very big. What is the best way to do this? It will aid in figuring enclosure configurations and such.

[Fibergeek]

Yes the exact shape/size of the heatsink can be calculated, but none of you will like the math.

In Jnbsystems case; his worst case power dissipation would be 29V x 6A = 174 Watts. In the case of a VCCS used for anodizing, the worst case only occurs at maximum current (6A) and at startup, where the output voltage will be very low, and the VCCS has to absorb most of the 29 V. Fortunately this condition only exists for a matter of minutes, after some anodize forms, the required voltage goes up, taking some of the load off of the VCCS.

I noticed at MPJA a heatsink; 9206 HS, that is already drilled to mount three TO-220 packages, it costs about $5. TO-220 is the package that we will select for the MOSFETs. If you used this heatsink with a small 120 VAC fan; or even better, a small blower, moving air along the fins, you should be fine. MPJA has suitable fans and blowers.