rectifier box

[kitestrings]

Greetings,

I thought I'd post a link to this here, rather than rewrite/repost it.  I would be obliged to any comments.  Generally, it is a 15' axial build.  We have 2-250V Classics and are looking at a similar configuration to Ryan's (neighbor's) 17' install.

http://fieldlines.com/board/index.php?PHPSESSID=c7b8057e0f1af1e98e787b5053cd9c46&topic=145892.0

Thanks,

~kitestrings

[boB]

One thing you were asking that maybe wasn't answered on Fieldlines was that if what you want to transfer heat from is already electrially isolated, use thermal grease between the thing (for instance, typically a SSR), or if it's a transistor or triac that isn't isolated, use the sil pad by itself.

Any time you can get away from the thermal goop, it's good cause it's messy.

Bridge rectifiers are usually isolated to the grease is probably good between those and the heat sink.

boB

[kitestrings]

Thanks boB,

Bridge rectifiers are usually isolated to the grease is probably good between those and the heat sink.

You're referring to potted bridges?  Otherwise, I'm not sure as I follow.

I was late getting back to this, but my follow up today:

The sil-pad is marketed as a "thermally conductive insulator".  I suspect it is a challenge to do one or the other well.  For this size material, it had the lowest thermal impedance that I could find (.41  deg C-in^2/W @50psi).  Your point is well taken though Dan, that the thermal peformance is best under higher pressure.  I'm going to start by swapping out the screws for (hex) cap heads.  the latter has a max torque before deformation of 15-16 in-lbs vs. 9-10 fo rthe screws.  If we're still not satisfied we can go larger, or use insulated metal fasteners.

The material is suprisingly tough, however, notice it also has a breaking resistance of 30 lbs/in (5 kN/m).

The original heatsink design used 35 amp diodes on our 12-volt system, and I rarely saw the temperature of them be more than mildly warm to touch.  In our design, they are 85A diodes (1,200 PIV), but the load is split between the two rectifiers (so the amperage will be in a comparable range).  I'm further assuming that at the higher voltages that the Classics will allow that there will be less amps, and therfore less heat than if direct tied, but maybe this is not the case?  Maybe it is simply a function of power?  In any event, increasing the passive cooling seems easy enough, and adding fan cooling if it becomes necessary.

Jim once described the stud mounted diodes as a "brute force approach....[that was] perfect for wind."  I like it simply because you can swap out one or two if they get hammered in a lightning surge.

Clockman, thanks for sharing the pics.  What is the meter and digital display indicating?  It looks good, except for I'd be nervous having it all mounted in a wood box.

No one has said, "Stop you damned fool"! so I gues I will press on.  Thanks again.

~kitestrings

[Grizzo]

Good info

[mike90045]

There are also mounting pads made of ceramic (BeO) and Anodized Aluminum (with voltage resistance specs). The ceramic is brittle & toxic, the anodized aluminum is tougher, but needs smooth surfaces to not cut through the anodized insulating layer.   Both have low thermal resistance.