Big Rig Progress - Photos - and a couple questions...

[N8UH]

Hey All!

I've been making some progress on the big rig as of late. As usual, my plans had to change a bit. I'm housing all of the "modern" iron in a rolling chassis that I fabricated. I made it nice and low, so it'll slide under a desk and quietly do it's job. The true buzzardly stuff will be in a separate rack, away from all of this new-fangled technology.  I'm still in the "Finding just the right spot for everything stage", but I'll get there.  When I button this thing up it'll be covered in Lexan panels to keep things visible and out of reach.

Photo Gallery for the project:

http://gallery.me.com/tbkmedia#100099

Anyway, as can be seen in the photos, I'm building this thing to (hopefully) work without breaking a sweat in amateur service. Massive rectifier stacks for the bridge, 10H 1A choke, and 120uF (!!!) 4KV cap. The power supply will be shared by the Mod section and PA section. If I calculated things right, the voltage should be around 1.7KV, give or take, with less than 1% ripple under load, and regulation looks excellent on the Duncan simulator.

I initially questioned the cap, as it's labeled "Energy Storage", but after searching the forum, that doesn't seem to be an issue.

But, quite obviously, I'm going to be needing a serious step-start or soft-start scheme to go with this thing. I imagine a simple resistor/relay scheme would work ok, but I see that Mouser has some beefy 40A Triacs... Hmm. A nice voltage ramp-up on the primary would be pretty slick... Has anyone tried a system like this, or am I over-engineering things again here... 

Any comments or suggestions would be greatly appreciated! Thanks!

TK

[KA2DZT]

Tim,

Are you sure this supply is going to be big enough??

The thing looks great, really nice job.

That cap is really going to pull some current on start-up.  Hopefully, you don't pull down the grid when you fire this thing up.  I'll let you know if my lights dim, here in the east.

You'll need a step-start for sure.

I'm not following what your circuit is.  I see three large irons and one smaller iron.  Maybe you could put up a schematic of what this rolling rack contains.

Fred

[The Slab Bacon]

Tim,
       "Energy Storage" type caps need to have the voltage de-rated a bit for power supply filter service, but a 4kV rated energy storage cap should be OK-Fine at 1700v.

A FWB into that massive cap will definately need a step-start setup of some type.

Last and most important, you will need a good, stiff bleeder stack, both for regulation and to pull that cap down quickly when you kill the incoming power.

But......................That thing looks like it will never break a sweat in amateur service.

Now, like a girly magazine centerfold, we want to see the "MONEY SHOT". Post some pix of the RF deck! ! ! ! ! ! !   

[W3GMS]

Tim,
Your off to a great start.  I like you quality of workmanship. 

If you want a non relay approach to your step start, I used a Triac across the inrush Thermistor.  That scheme worked very well.  To drive the Triac, I used a zero cross opto isolator to drive the gate.  The beauty was that it only turned on the triac at the near zero voltage cross time, rather than hitting it at the peak of the AC input.  A simple sequencer was made with an LM-339 voltage comparator.  Many thousands of these were shipped without an issue.  An SSR could be used as your main AC on/off function.  Hit the SSR with a 5V level, then after the inrush period, enable the opto to short our the inrush thermistor.  During normal run time, the thermistor is cold since its shorted out by the triac, yet it can and is made to handle the inrush limit you set by its value prior to turning the Triac on.     
Have fun with your build project!

Joe, W3GMS 

[W7TFO]

Hey Tim,

Looks good.  I'm glad to see all the stuff from me has a good home!

Yes, cover that beast to keep toes & pets out...

73DG

[K9PNP]

Fine looking job.  Don't worry about the over-engineering.  If you build it so that not even the military could break it it's good enough.

[W7TFO]

Fine looking job.  Don't worry about the over-engineering.  If you build it so that not even the military could break it it's good enough.

,,Yeah, but there is still Tim...

73DG

[N8UH]

Fine looking job.  Don't worry about the over-engineering.  If you build it so that not even the military could break it it's good enough.

,,Yeah, but there is still Tim...

73DG

Heh Heh... yeah, there is still that... But if I'm able to somehow break this thing, there will definitely be a crater involved. 

Thanks all for the feedback and info so far.

Fred: The rack contains both the power supply and the modulation iron for a modified Heising setup. Everything else will be in another rack. So the 2 big hunks 'o iron are a Dahl 5KW Modulation transformer and matching reactor.

Slab: Well, I haven't started the RF deck build yet. So wait for next month's issue. 

Joe/GMS: Excellent idea. Sounds simple and elegant. The only thing missing would be a big power-on KERCHUNK!!! Maybe I'll just use a big contactor instead of an SSR.

[WA1GFZ]

SSRs leak a little current in the off mode so they are never totally off BEWARE

[KC2ZFA]

good job !

but that 5KW mod xfmr may refuse to pass a measly 1700V through its secondary 

[flintstone mop]

Keep pictures of the RF final confidential.............Especially if you are using tubes with handles..........nice heavy duty stuff there. We won't tell.....cuz it would be another TALL ship in the sea of AM radio.
Fred