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Buck Converter for lights?

PostPosted:Mon Nov 06, 2017 1:56 pm
by Bjorn
First post here (hope its in the right spot) and new to upgrades. I tried to search but did not find anyone trying this. Makes me think its not a good idea. Has anyone tried to use a buck converter so they don't have to add a yet another battery or buy expensive led 18 volt lights?

Re: Buck Converter for lights?

PostPosted:Mon Nov 06, 2017 2:32 pm
by Hammer-fm
Definitely. You can get them on Amazon/ebay/etc. or buy them from a vendor like Mltoys (nicely packaged):

Most of the cheaper ones are rated only up to ~30V, but most people are running less than that so that's sufficient. (MLtoys does not list a maximum but says it's for 18V or 24V vehicles).

I've personally used this XL4016-based one successfully (rated to 40V, so can even use it with 3x 12V batteries):

Re: Buck Converter for lights?

PostPosted:Mon Nov 06, 2017 2:54 pm
by Bjorn
Even a blind squirrel finds a nut now and then... I just got the same model buck converter off ebay ;)

Re: Buck Converter for lights?

PostPosted:Thu Nov 09, 2017 9:10 am
by Bjorn
I have seen where some people are adding multi-meters displays to the dash. I likes the idea and they are fairly cheap so why not. I followed the link (
) and purchased one. It only has three wires comping out of the back so it does not have a separate harness for display power. The problem is every diagram I look at online shows the neutral going to the battery and the yellow wire going to the motor and removing the wire from the battery to the motor. This cant be correct (I assume). Do I need a shunt? I would appreciate any help... I would REALLY appreciate a wire diagram : )

Re: Buck Converter for lights?

PostPosted:Thu Nov 09, 2017 4:32 pm
by Hammer-fm
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)
Wire Connection:
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."

Re: Buck Converter for lights?

PostPosted:Fri Nov 10, 2017 8:03 am
by Bjorn
You're awesome. thanks!

Re: Buck Converter for lights?

PostPosted:Fri Nov 10, 2017 4:55 pm
by Hackish
I bought the 10A version of that unit. Had an internal shunt but I maxed it out pretty easily. The important part is that it seemed to be relatively accurate for the $5 I paid (shipped).