Another kid's toy, electrical help required, I'm stumped

Deschodt · 07:52 AM

My youngest has a modified 18V powerwheel Jeep, it stopped working, but this has me scratching my head.. I mention it's modified (added a 6V battery to the 12V in series) but that's not the issue there, it's been modified for years and most folks go 24V).

I verified power at the gas pedal (18V), and after the gas pedal 3 wires come out, Red(+), black (grd) and orange (sharing a connector with Black). Not sure what orange is.. If I measure voltage there between the red and orange+black spades with a multimeter, I get 6/12/18V depending on how hard I press the pedal, so far so good ! Should work.

Now the speed selector is between those wires and the motors, Reverse/Forward one wheel, FWD 2 wheels and it is suspect (made of switches and relays, and corroded), so I decided to bypass it altogether and have the car permanently on the faster mode (both motors forward). here's the rub:

If I connect the 6V battery directly to the motors at the wheels individually, they run.
If I connect both motors together (++/Grg grd), and wire them to a battery, now they both run together... So far so good.

If I connect them to the gas pedal wires, which I just verified have 18V with the gas pressed, nothing.... What...the..Hell ?

Same if I connect even just one motor to the gas pedal wires, nothing... How can I get 18V there confirmed by a meter, and no results at the wheels, while a direct battery connection to the wheel works ? I swear electricity is voodoo to me... Is it possible to see the right voltage but not enough "oomph" to turn the motors at all? I checked continuity and saw no obvious shorts... might rewire it all unless you guys have an idea...

dad911 · 10-02-2017, 07:55 AM

Gas pedal may be a signal, might not be able to handle the current. Are the wires to the gas thinner?

sammyg2 · 10-02-2017, 08:19 AM

Maybe some of this will help, maybe not ....
(thermal protector ..)

https://service.mattel.com/instruction_sheets/78538pr-0920.pdf

https://service.mattel.com/instruction_sheets/W9418pr-0920.pdf

https://www.youtube.com/watch?v=8XMysrUnNHg

Power Wheels Troubleshooting & Service Center - Fisher Price

https://www.youtube.com/watch?v=Ymdws6b2Z-k

Deschodt · 10-02-2017, 08:32 AM

Thanks.... This is indeed the "vehicle" that turned my kid into a scandinavian flick artist ;-)
I was surprised as I excpected there would be some sort of gearbox, but the gear selector is actually a tab that pushes 2 captive "light switches" on and off, it's clever, purely electrical, no gears at all..

Unfortunately given the age of the thing and the mods, the above docs are not relevant. My real puzzler is why I see 18V after the gas and they turn to zero V once connected to the motor, while the motor works independantly if directly wired..

I guess I'll rewire as Dad911 suggests... Made no sense to me except wiring...

aschen · 10-02-2017, 08:47 AM

are you sure all the current is meant to go throught the pedal? I dont know what these things use for speed control, but I suspect not. The pedal could (probably) activate a relay or a solid state speed control that passes the drive current to the wheels. This device could be fried from the over voltage.

See also: the headlight switch in you car activates a relay, dosent pass the full current. I think 10min of googling will get you the schematic. If you find it share and we can help. If the switch is meant to pass the full power than You are right to assume wiring or a fault connector.

dad911 · 10-02-2017, 08:58 AM

FWIW, I've purchased Powerwheel parts here: Repairing your Power Wheels car is easy with help from us. Parts are available and the experts to help | Hobbymasters

I have some motors and gearboxes if it helps, we used them for robotics.

I'm surprised the motors can take 18v. Don't stall them.

Deschodt · 09:25 AM

Quote:

Originally Posted by aschen

are you sure all the current is meant to go through the pedal? I dont know what these things use for speed control, but I suspect not. The pedal could (probably) activate a relay or a solid state speed control that passes the drive current to the wheels. This device could be fried from the over voltage.

Yes, there are no other wires. Wires go from battery to the pedal, then pedal to 2 light switches that activate the motors either forward or in reverse + one wheels vs 2 wheels, there are zero relays or circuit boards I can see unless there is something inside the pedal. That is the bit I am bypassing (the selector).. ... Nothing is fry-able except wiring I guess, the motors both still work... the pedal still works too as it gives me progressively more voltage as I press harder... I'm stumped as to why I'd see correct voltage out of the pedal but once I connect that output to a motor I get nothing... must be wiring then, it shows V but cannot take the load ???? Still when I plug those pedal wires to a motor the V goes to zero. Again direct battery, they work...

Quote:

Originally Posted by dad911

I have some motors and gearboxes if it helps, we used them for robotics.
I'm surprised the motors can take 18v. Don't stall them.

Oh yeah, there's a whole hobby of pushing those to 24v + , my 18V mod was a joke and both motors still work fine, either the pedal is lying to me or it's a wiring issue... Thanks for you offer but my motors are good as far as I can tell and there is no real gearbox there. Frankly this thing has lived a good life, wore out a front end hitting sidewalks (replaced) and 2 sets of rear wheels worn to the max - I'm ok trashing it but I'm annoyed I can't figure out what's going on ;-) This should work ;-)

dad911 · 10-02-2017, 09:41 AM

If you are measuring voltage with no load (motors disconnected) then no voltage with a load, there is a connection somewhere in the circuit with "High Resistance". Likely corrosion.

T77911S · 10-02-2017, 10:12 AM

first off a meter is not a load and does not require much current to measure 18v. on the other hand the motor is a big load and requires LOTS of current.
you may just have a bad connection

(thinking on it some more and trying to figure out what you have)
one other thing, you need a good ground on the other side of the motor back to the batteries

wildthing · 10-02-2017, 10:17 AM

Measure current...

Deschodt · 10-02-2017, 01:04 PM

I chatted with an expert and he thinks the gas pedal switch is toast, it should read 18V period and not 6/12/18 as I press it, it's an on-off switch and it'snot acting like one.... I ordered a replacement pedal switxh and will also rewire all the connections bypassing the shifter... Thanks guys, that twice this week with kids' toys !

1990C4S · 10-02-2017, 01:49 PM

Quote:

Originally Posted by wildthing

Measure current...

but measure with caution....the motors current likely exceeds your meter's fuse rating.

dad911 · 10-02-2017, 01:58 PM

That's why I recommend clamp-on ammeters. (must be DC)

I've also seen too many people try to measure current like voltage, across the terminals.

T77911S · 10-03-2017, 04:24 AM

i thought the gas pedal would be like a rheostat (variable resistor). where you would have 18v going into it but the gas pedal would vary the voltage coming out.