- Thu Nov 09, 2017 4:32 pm
Yeah, looks like it needs a shunt, based on their description:
"Three-digit 0.28 " LED dual display, red display for voltage, blue for current, needs an extra 50A shunt for measuring current.
(Does not include shunt, if need,please check the item ASIN:B00BYO72Q6)
COM: Black wire,Power Supply - , Measure Voltage -
PW+: Red wire, Power Supply +, Measure Voltage +
IN+, Yellow wire, Measure current input. if use the voltmeter function only, please connect the Yellow wire and black wire together to avoid the Interference "
For accurate measurement, you would buy a 50A/75mV shunt and then connect :
Black wire => Shunt negative
Red wire => battery positive
Yellow wire => Shunt positive
In a stock power wheels, the "original" black wire that went to battery negative would connect to the Shunt positive.
The Shunt negative would then connect to the battery negative.
This ensures all of the motor current goes through the shunt. DO NOT connect the meter's black wire to the battery directly because then it will incorrectly report the current value. It needs to connect to the negative lead of the shunt.
Note: this 3-wire connection means it will incorrectly report the voltage by an amount equal to the IR drop of the wire between the shunt and the battery -- if you have 3' of 14-ga wire, that's ~12mohms, and if you're pulling 20 amps, that means it will be off by 0.24V (the meter will read lower than the real battery voltage) This is why some of the other ones have 4 wires -- making a true-differential connection for the shunt.
I wouldn't be concerned about -- just realize it's there.
(after looking up the part reviews, I see that "SoCal Flyer" posted a nice review that included a description of his wiring, which is correct but slightly more detailed).
"Only gave it four stars because was it was delivered without any documentation, nor did any appear to be available on Drok's website, so it took a few minutes of Googling to find something. Briefly, attach the negative side of your DC source (battery or whatever) to one end of the shunt using one of the two screws provided, and connect the black lead to the other screw at that same end. On the other end of the shunt, attach the negative side of your load, whatever it is, and connect the yellow lead to the second screw on that same end. Now connect the red lead to the plus side of your DC source along with the plus side of your load, and you are good to go.
I strongly recommend attaching the yellow & black meter leads directly to their own screw points on the shunt, with no other wires on those screws. Reason is the "Amps" meter circuit is reading some very tiny voltages dropped across the shunt and if even the slightest additional voltage drop gets introduced into the black/yellow amp meter circuit it will throw your amps reading way off calibration, far beyond the range of the (very tiny) variable pot on the meter circuit board. Wired as described, my readings were virtually dead on without need for adjustment."
F-150 - 24-36V with homebrew 100A variable-speed motor controller, 4x 775 motors (no, it's NOT all-wheel-drive--look up 'quad damage' in the gearbox section for more info!)
Pink Rocket Princess Mustang - 15mph, 36V, 4x 775 motors, homebrew PWM controller rev 2....
Hurricane - 24V w/50A step-down controller, 775 motors