500 amp Shunt

[Shadow]

I'm getting things lined up to hook up a Tri-metric into my system. It calls for a 500 amp shunt. I have numerous shunts from 50amp, to 200 amp. So can I stack a couple of 200amp and a 100 amp to get the required 500 amp? Or is it more complicated than that, and would never get past the... shunt police?

[Nando]

You can parallel them if the connections to the cabling is really tight and as shown in the photo you included.

Clean the surfaces well, and make them flat or if possible use pure copper flash to insure tight conduction.

Hard and tight with the bolts handling.

Nando

[Shadow]

 Thanks, Would it help to use heat sink compound between the surfaces?

[Nando]

Don't you DARE to do such a thing, automatically you will damage the connection.

the heat sink compound has insulation capabilities to certain extent.

Nando

[willib]

http://www.nwpwr.com/products/meters/tri-metric.htm

their shunts look a LOT smaller than yours

[Volvo farmer]

Yah, you sure those shunts of yours are 50MV?

[boB]

Where is the sense terminal going to go ??

Maybe they're hidden on the dark side of the shunts in this picture ?

boB

[Drives]

White heatsink compound is a poor insulator of electricity, and a good conductor of heat.

http://www.cool-amp.com/cool-amp.htm

This stuff works the best, but I have used Noalox, and Penetrox with good sucess.

On Hockey Pucks, and Stud mount devices, I use Noalox or Penetrox.

The key is getting flat mateing connection points to bolt to each other.  Surface area is important for proper "low resistance" conduction of current.

Over the Christmas Hoilday I supervised an install of a Heat Treat Furnace that had transformer connections rated to handle 4000amps continuous at 150 degrees C....the cool-amp product ensured a nice cool connection the doesn't even show up on a IR Thermograph picture.

I also strongly recommend stainless steel hardware.  I have had bad problems in the past with cheap galv. and even zinc bolts.

[Shadow]

The bottom two are 200amp 50mv, the top one is 100 amp 50mv. I had thought of using brass bolts as terminals, maybe stainless be better? There are screws to mount the sensor wires.

[Drives]

Brass screws for the sensor wires is standard.  You could use large brass bolts to bolt the whole thing together...I just worry they might stretch over time and start a loose connection.  Your call, go brass, and check tightness at least twice a year, or go stainless, and check it at 3-5 year intervals.  

If you don't have the brass bolts handy, I am guessing the stainless would be cheaper?  Do I hear a trip to the hardware store anyone??  :-)

[Drives]

My first sentence was supposed to read "White heatsink compound is a poor conductor of electricity".  Rather, it is an insulator.  

Thank God I am not being graded on this!  :-)

[TomW]

boB;

See those tiny holes near the inner side of each end piece?

Threaded for machine screws and thats the sense connection.

Cheers.

TomW

[Ungrounded Lightning Rod]

You'll also do well to put the power terminal on one side on TOP of the stack and on the other side on the BOTTOM.  Clean the terminal and shunt interface just as you did the between-shunts interfaces.

Be sure both meter wires are connected to the same shunt.  (It's hard to fail on this given that the top shunt covers the meter terminals on the others.)

[TomW]

Dean;

See subject!

Tom

[maker of toys]

one dodge we use for making better connections to 100KW+ electromagnets is to embed a soft silver mesh between the cable lug and the bus / contact block.

there is also a rub-on silver-plating compound and a "silver goop" (for excluding oxygen and improving conductivity) made for this kind of project. . . (the most common oxides of silver conduct much better than the common oxides of copper, brass or aluminum.)  I'll try and remember to get the brand-name tomorrow.

we also use hard (phosphor?) bronze bolts.  (not brass and DEFINITELY not stainless)  sometimes we use O.F. copper barstock and rivet things together. . . but that's not as common; usually a rivet is the last step before a vacuum brazing operation.

tinning the shunt blocks with 60/40 solder before assembly, then re-heating them to reflow the solder might help, too. I'd do this before attaching the cables, and use a stainless bolt for this stage, then do the final wiring with bronze.  If you go to this extreme, make sure to wash ALL flux residue off before the reflow step. A sealed pocket of still-active flux is an invitation to a melt-down.

-Dan