MOS68X's new sealed/dry cell

[mos68x]

[mos68x]

Hey Gary, I'm trying to make a DIY DC shunt that can handle a ton of power. I have brass flat stock here that I'm going to use for the main part of the shunt (1/8x1/2), but I need the formula to find the distance for the 1mV drop for every amp passed through the bar if I know the resistance for a set distance. Yes, I could use an approximate method but I want to be exact, so I was hoping that you had a formula for that since Google pulls too many links that aren't related.

[SeaMonkey]

for some clues.

[chemelec]

[mos68x]

[chemelec]

You will NOT find a Formula for the Actual Resistance of your Brass bar.
So you need to determine it this way:

Take a VERY Specific Length of that bar!
Get a Power source that will deliver 10 Amps through that bar.
Varify this with your Fluke 87.
Now Measure the Voltage across the bar.

Basically the Formula is just "OHMS LAW".

E
------
I x R

So from this, Volts/Amps = Resistance

Now More Examples:

200 amps, times .01 Ohms will give a 2.0 volt reading across the shunt.
But be aware that this is Also a 2 Volt LOSS at 200 Amps
Or
200 amps, times .001 will give a .2 Volt reading.
Much LESS waste.

Contacts to the Bar MUST BE SOLID to get correct readings.
And there are Ways to Avoid Solder Resistance problems.

I will do up some Drawings for you to Explain all this process in DETAIL.
(Later Today or Tomorrow!)

[mos68x]

[mos68x]

[chemelec]

[chemelec]

Here is a Good Way to do this:



NOTES:

The Higher your Known Test Current the Greater the overall Accuracy.

As to the Length or Size of the Shunt:
Any Length that will allow reasonable Readings as Shown.

IF your SHUNT is TOO LONG, you will need to Adjust the Control Down LOW, Or BETTER YET, SHORTEN the SHUNT.

IF you Can't get it to Adjust to these Readings, You need a LONGER Shunt.

Since Two SEPERATE Connections are made for the Power Connections and the Meter Connections, There is No Error from solder connections as mentioned in that other article.

Different Materials will have Different Resistances for the Same Area.
And Some materials Change Resistance GREATLY with Temperature.

Other QUESTIONS?, Just ASK.

Gary

[mos68x]

With the posted pictures I understand what you were suggesting with the pot so I'll do that since I think I like that way better than the way shown in the video. Thanks that should help greatly. If I had an accurate way to measure high amps now I would certainly set it up for higher amps, but for the time being I think I'll set it up like you showed in the picture. Besides, it probably would be better for me to calibrate it for the current that I'm using right now, since your way also allows for me go back and recalibrate it later for higher amps when I need it.

I was looking to make this shunt bar as short as possible so I think I'll still play with it later to see how long of material I'm looking at cutting off. Besides I'm in the middle of redoing my reservoir, and right now it looks good. Got the "top" glued on with an 1/4 NPT 3/8 barb elbow in it for the gas to go to the safety bubbler, with the inlet and outlet barbs for the cell itself.

Just for clarification, for calibration you are saying to use a 1K ohm pot, right?

[chemelec]

[mos68x]

[mos68x]

[chemelec]