Building "The Big Unit", balanced power device

[ThomasW]

People have ask for a separate thread about this device so here we go......

2 of the 800Va Avel Lindberg transformers will fit in the Hammond chassis (PE#320-840). It's a steel chassis, but it will flex from the 26 lb weight of 2 transformers.

To stiffen the chassis and add a little class, I used a powder coated rack mount front panel. (PE#262-112). These are made from pretty thick steel and as a result are a little trickey to machine.

I wanted the greatest number of outlet for this device so I went with snap-in AC receptacles. That of course drastically increased the amount of machining. In hindsite I should have used 3 standard duplex 'Modula' receptacles. Doing that would have not only given me better quality outlets, and only required making 3 large rectangular cutouts.

Anyway, here's the chassis and front panel with all the machining completed.



The small rectangles cut in the front panel and chassis are for individual power switches for each of the transformers.

[David Meek]

Here We Go

Thomas, you ready for a question or thirty?

What I'm considering is a bit larger chassis in black anodized aluminum. The internals will be basically the same as your big unit with the only mods being cosmetic. I'd like to have the power switch on the front and that's it. On the back I'd like 8 outlets but 6 will do in a pinch, whether singles or duplexes, doesn't matter. Anyway, that's it as far as generalities.

[David Meek]

First up - the chassis:
After following up on your suggestion, I'm looking at the Par-Metal model 12-19155B, 15" deep by 5.25" high black anodized aluminum chassis. The back plate is .06" (1/16th") thick. What will it take for me to properly cut the holes in it? A Dremel tool w/jig, or . . ? The front plate is .125" (1/8th") and about the only thing I'd want there, if possible, is a single (or maybe a double - one for each transformer?) on/off switch. However at 1/8th" thick, what'll that take - a professional job?

I haven't ordered the chassis yet, so there's room to maneuver if we need it.

Oh, would it be beneficial to upgrade to the EMI/RFI shielded unit? Or is that an unecessary enhancement?

[ThomasW]

The all aluminium chassis are quite flexible. You might consider the "10" series where the front and back are alu and the rest is steel. Also you don't really need a chassis that tall for the PE transformers, they're pretty short. My chassis is only 3" tall. If you do opt for a shorter chassis you'll need to shorten the transformer mounting bolts.

For metal working I use the following, spring loaded center punch, elec drill/titanium coated bits for starter holes, jig saw with Bosch metal cutting blades, Dremel with a diamond impregnated blade (these are cheap from Harbor Freight Tools, and TONS of various metal files.

I cover the chassis with masking tape and to all my layout drawing on it. If I screw up the drawing it's not big deal to peel of the tape and start again

I wouldn't worry about the shielded chassis unless your house has high tension wires in the back yard.

Are you going to use any of the EMI/RFI filters? If so, you might want to buy everything execpt the chassis, do a layout and buy the chassis last.

If you use the 'Modula' style duplex AC outlets there's only one large restangular cut per outlet. Trying to make the standard "D" style cutouts is really a pain. And after trying the individual chassis mount outlets I don't recommend those.

I uploaded a couple new pics of the unit at it's current state of assembly.
HERE'S a link, they're at the bottom of the page.

[David Meek]

The all aluminium chassis are quite flexible. You might consider the "10" series where the front and back are alu and the rest is steel. Also you don't really need a chassis that tall for the PE transformers, they're pretty short. My chassis is only 3" tall. If you do opt for a shorter chassis you'll need to shorten the transformer mounting bolts.

All righty then, I'll go with the shorter chassis. I'm surprised that the aluminum flexes more than the steel. In that case (pun intended), I will go with your model.

For metal working I use the following, spring loaded center punch, elec drill/titanium coated bits for starter holes, jig saw with Bosch metal cutting blades, Dremel with a diamond impregnated blade (these are cheap from Harbor Freight Tools, and TONS of various metal files.

Okay, I'm good to go with the exception of the center punch. That should be easy enough to get.

I cover the chassis with masking tape and to all my layout drawing on it. If I screw up the drawing it's not big deal to peel of the tape and start again.

Now THAT'S a good idea! :T

I wouldn't worry about the shielded chassis unless your house has high tension wires in the back yard.

No transmission type lines, but there is a "neighborhood" type power line that runs along/above the back fence. A possible issue there?

Are you going to use any of the EMI/RFI filters? If so, you might want to buy everything execpt the chassis, do a layout and buy the chassis last.

Absolutely, I'm using the EMI/RFI filters - that's a big part of the attraction. As I'll now be using the same chassis you are, I'm going to duplicate your "big unit" as much as possible. Hmmm, guess I'll be doing some ordering tonight.

If you use the 'Modula' style duplex AC outlets there's only one large restangular cut per outlet. Trying to make the standard "D" style cutouts is really a pain. And after trying the individual chassis mount outlets I don't recommend those.

Hey, I do like the idea of the rectangular duplexes! Much simpler cuts, and also, that way the back of the unit will match my house outlets. It's all in the accessorizing, you know?

[ThomasW]

Spring loaded center punches keep the drill bit from 'walking' when starting a hole in metal

Standard power lines aren't a big deal, transmission lines are problematic.

The Hammond chassis is a pretty tight fit for all this stuff. Using the Par-Metal would give you greater front to back depth that can't hurt. The cost difference isn't all that great. Having used the Hammond I'd recommend going with the Par-Metal. Since it's all separate pieces as opposed to a 5 sided box with an open top, it will be easier to machine.

[David Meek]

A Par-Metal chassis it is then.

[Glen B]

First up - the chassis:
After following up on your suggestion, I'm looking at the Par-Metal model 12-19155B, 15" deep by 5.25" high black anodized aluminum chassis. The back plate is .06" (1/16th") thick. What will it take for me to properly cut the holes in it? A Dremel tool w/jig, or . . ? The front plate is .125" (1/8th") and about the only thing I'd want there, if possible, is a single (or maybe a double - one for each transformer?) on/off switch. However at 1/8th" thick, what'll that take - a professional job?

I haven't ordered the chassis yet, so there's room to maneuver if we need it.

Oh, would it be beneficial to upgrade to the EMI/RFI shielded unit? Or is that an unecessary enhancement?

I used a Par-Metal 10 series chassis for my balanced power project. Since the big transformer was 60lbs, I reinforced the chassis with a steel plate which I epoxied to the bottom panel and supplemented with small bolts/nuts. To make the holes in the rear panel, I first cut a rough-shaped hole then removed most of the excess metal with a nibbling tool. I then followed that up with my Craftsman rotary tool and bit and finally a deburring stone.

To have a surface on which to trace the holes I needed to cut and help protect the rear panel from getting nicked and scratched by metal shavings, I covered the surface with masking tape. After I completed work on the holes, then I removed the masking tape. I also covered the outer surfaces of the chassis (especially the front panel) with masking tape until all assembly work was complete.

I have not encountered any problems with airborne EMI/RFI in the three months since the project has been completed.

[beboram]

Where are the by-pass caps attached? +ve to -ve, +ve to Ground or -ve to ground?

Can the same supression effect be achieved by simply soldering the cap inside each equipment?

[ThomasW]

They go between the line and the neutral. And personally no I wouldn't put them inside the components