What is it???

**Eaglewood** · Feb 18, 2024, 06:31 PM

Hi, I need help from experienced brain trust. I have had this tool that I suspect is part of battery/circuit testing. Can anyone tell me what it is? It was given to me 50 years ago and has been in my tool box ever since.

Dick

**BuffaloJohn** · Feb 19, 2024, 11:58 AM

Does the large hole fit over a battery terminal (the lead post kind)?

The bar underneath is screwed to the two posts. If you remove the screws, is the shorter post insulated from the body?

It looks like it is missing something that attaches to the rectangle with a bottom bump.

It doesn't show up on an image search. If you don't get an answer here, you can search on reddit r/whatisthisthing

**mklotz** · Feb 19, 2024, 01:17 PM

The brass piece is reminiscent of a shunt. If it was associated with "battery testing" as the OP suggests, a shunt would be useful to read the battery current using nothing more than a voltmeter.

Check to see if the 'shunt' is mounted to the metal frame in such a way that the battery current could be made to flow through the shunt and possibly emerge from one of the knoblike structures on the top of the frame.

**BuffaloJohn** · Feb 19, 2024, 01:24 PM

Originally Posted by mklotz

The brass piece is reminiscent of a shunt. If it was associated with "battery testing" as the OP suggests, a shunt would be useful to read the battery current using nothing more than a voltmeter.

Check to see if the 'shunt' is mounted to the metal frame in such a way that the battery current could be made to flow through the shunt and possibly emerge from one of the knoblike structures on the top of the frame.

I asked those same questions, but the bar is rather large to be a shunt, would get rather hot I would think...

**IntheGroove** · Feb 19, 2024, 02:33 PM

Definitely not electrical related. The hole fit over something and an arm of some sort fit over the center post. The knurled knob held something else...

**Eaglewood** · Feb 19, 2024, 08:21 PM

Thanks for the inputs. The shunt is isolated from the aluminum body as is the vertical stud and threaded knob. The large hole goes on the bat. post and the vertical post accepts the cable I think. Current can flow through the body and if the knob is tightened pass through the shunt to the cable. Must be some sort of accessory for troubleshooting with a meter. It would be great if I could use it to test current but would need some direction.
Dick

**BuffaloJohn** · Feb 19, 2024, 10:20 PM

Originally Posted by Eaglewood

Thanks for the inputs. The shunt is isolated from the aluminum body as is the vertical stud and threaded knob. The large hole goes on the bat. post and the vertical post accepts the cable I think. Current can flow through the body and if the knob is tightened pass through the shunt to the cable. Must be some sort of accessory for troubleshooting with a meter. It would be great if I could use it to test current but would need some direction.
Dick

If you have an ohm meter that would have low enough resolution, you could measure the shunt. First measure the leads touching and then measure the shunt and take the difference. My guess is that you will find it nearly zero. Most people don't have low resistance measurement capability.

If you have a constant current source, then you run the curent through the shunt and measure the voltage across the shunt.

What if you don't have a constant current source, then what you do is find a low resistance (and stable) device and load a power supply with this low resistance device in series with the shunt.

What kind of device might you have? An incandecent bulb. Find a low wattage bulb and make a circuit with a power source, the bulb, and the shunt. Don't get shocked - be careful. What you have created is a voltage divider with two resistors. Now you need to measure the total voltage across the two loads and across each of the resistors. The current through the bulb and the shunt is the same. The resistance across the bulb should be much greater than the shunt, so you can estimate the resistance of the bulb and thus calculate the current and knowing the voltage and current through the shunt, you now have it's resistance.

Here is an article with schematics and formulas to calculate this voltage divider:

https://en.wikipedia.org/wiki/Voltage_divider

**BuffaloJohn** · Feb 19, 2024, 10:21 PM

Might this be a disconnect?

**IntheGroove** · Feb 20, 2024, 01:37 AM

If it was a shunt there would be a non conductive component. I think it is part of a jig of some sort...

**mklotz** · Feb 20, 2024, 08:36 AM

If BuffaloJohn is correct, and I think he is, in use the VM used to read the current would need to be attached between the frame (which is attached to the shunt by the left hand screw in the photo) and the wire to the load which is attached to the thumbscrew. The tab sticking out of the left side of the frame would be a convenient place to make the VM attachment to the frame.

If the OP knows of any 'hams' (amateur radio operators) near him, they may have equipment suitable for measuring the resistance of the shunt.