Shunt Resistance.

longwood

10 µW
Joined
Dec 9, 2020
Messages
6
The shunt inside my PhaseRunner is 1ohm, 75A. I damaged my CA in a fall and trying to get by until the replacement arrives.

The PR has the two shunt wires exiting it, I have the WP connector pigtail.

I have a cheap shunt display from Amazon, without the shunt (used it on another project) It only works with .75ohm and 1.5 ohm

Is it possible or can it be as simple as using resistors in one side of the shunt feedback wires to bring the resistance to correct value and zero it?

I did what I could to google this, how ever it's not a hot topic. Or I do not know the correct terms to look it up, or it's a really stupid question. :confused:

Thank you for any help, just would be nice to have a battery gauge and ah idea in the mean time :)
 
The resistor must be able to handle full dissipation power of the shared load based on the current... , but yes, this in theory works... but... but however, finding a resistance to place in parallel accurately might be tough to find.

Formula for resistors in parallel is 1/Rt = 1/R1 + 1/R2 + 1/R3 + ...

So if you have two, 1 ohm, resistances in parallel, the equivalent circuit resistance is .5 ohm, and each resistance will share the full current evenly. Must be able to dissipate the energy of the resistor.. most resistances are not much more than a 10w or 20w, for a large aluminum cased resistor, wire wound. Little board mount resistors are in the range of 1w. You must calculate the current traveling through this circuit to be able to know the dissipate energy in the resistance.

So you have a 1 ohm shunt resistance, in the phase runner... and you want it to be 750mOh ( .75 ohm) or 1500mOh ( 1.5 ohm) ...


If you add a resistor of 3 ohms into this circuit, parallel with the 1 ohm..., the equivalent circuit resistance is now .75 ohm.. ( aka 750 mOh) .. but the resistor must take all dissipate power or else it will burn.. Dissipate power based on voltage ( number of volts) through the resistance...

So if you find a EXACTLY 3 ohm resistor, that can handle full power of the controller and not burn, yes this would work. The PR probally has a special metal bar shunt inside. A small wire wound resistor would be hard to find.. in the power capability that you want... but a bar style resistance would work, but is needing a very good meter to calculate exactly 3 ohms.. measure.
 
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