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How do I reduce the speed of a 12v childrens car

Ylli

Jun 19, 2018
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That's where I was going, BUT...... Since you can not measure any resistance between the green wire and either of the other two, I have to agree with kellys_eye and BobK that the throttle block is not a simple potentiometer, but rather an active device. The voltage divider will need to be added in the output leads (green & yellow) of the throttle block.
 

duke37

Jan 9, 2011
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Is the device an LVDT? , linear variable differential transformer. These have two coils which have variable coupling depending on the positon of a core.
They need an oscillator to drive them and a phase locked detector to obtain the output.
 

kellys_eye

Jun 25, 2010
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This is what is needed:
No it isn't. That's wrong.

Using a new potentiometer, cut the green wire and the bit of green wire that's still connected to the PLUG should connect to one of the outer terminals of the new potentiometer.

The bit of green wire that's going off to the controller box should now connect to the middle terminal of the new potentiometer.

The remaining outer connection on the new potentiometer should connect to the yellow wire on the plug (without removing it from the plug).
 

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Ylli

Jun 19, 2018
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Kellys_eye is correct if you are doing your surgery at the connector that the accelerator plugs in to. If you are making the changes at the connector that is attached to the accelerator, then the stub of green going to the connector goes to the pot wiper, and the green coming from the accelerator goes to the top of the pot.
 

Tha fios agaibh

Aug 11, 2014
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Very Nice @kellys_eye, but what value should this pot be?

I'm not familiar with the voltage output of this hall effect sensor.
I'm thinking if this pots value is too low, it would drag down the return voltage regardless of the wiper position.
 

73's de Edd

Aug 21, 2015
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Sir surreyman . . . . .

If the two parts telescope freely within each other BUT you see no mechanical coupling between the two halves, which would be a condition which would relate to a potentiometer being contained within the wired half.
Find the half without any wiring and consider that it is going to be containing a hollow rectangular formed magnet encased within it.
That half would be receiving the moving portion of the other half (with the wiring) on the inside of it.
The portion / half with the wired connections will be having a LINEAR type hall effect sensor within it.
That portion is connected to the control electronics .
I am just going to assign the electronic portion as being A section with B section containing the magnet.
The spring loaded accelerator linkage is holding the two parts separated ENOUGH , such that the magnet is not having any effect upon the other sensor containing half.
As the accelerator is pressed there is THEN the point of strong enough initial magnetic flux influence, such that there is then being a change in the output from the hall sensor .
Its voltage changes in unison with the depth that the hall sensor is pressed into the hollow magnet.

The three wires on the sensor . . . . .

  • One will be a ground wire
  • There will be a power supply voltage for the hall device on a second wire . . .usually + 5Vdc. . .you seem to be finding +4.35 instead.
  • The third wire will be the voltage output of the hall sensor, which will vary in accordance to how deep he sensor is inserted into the other magnetic side.
All of this info can easily be confirmed by initially pulling away the sensor half and thereby getting access to the central core of B half that A passed into.
Use a small standard steel / iron bladed screwdriver and insert its blade into the hollow and you should feel the pull of a magnet surround.

Further dynamic testing . . . . .

That would confirm the actual type of accelerator sensing incorporated.
You can then lift the drive wheel up from ground contact such that you can then test the unit at a standstill.
You then power up the unit and use the DC voltmeter probes very end tips in to get their access to the connector at the end wire crimps to run sequential tests until you find the 5V supply. That voltage presence PLUS its polarity should establish that the meters black lead is properly on the supply ground line to the sensor. You keep the negative lead where it is, on ground, and move the red lead over to the third wire which should be the sensors variable output.
Now, with you safely being able to vary the accelerator pedal, should reveal a variance of the sensor lines voltage with the accordingly different accelerator pedal positions.

The fix . . . . .

The same previously described methods of limiting extreme mechanical travel types of max speed could still be utilized.

Or the mentioned electrical series insertion of a select resistor value to limit top speed could be used .
HOWEVER, with the use of a hall device and the inherent high impedance that it will be dumping into at the controller, I feel that a different . . . . . . two resistor voltage divider technique . . . . will be needed instead, rather than just an inline series resistor..

We STILL don't know the requested motor connection wire count or if being of a heavier gauge of wire than the somewhat minimal RED wire pair seen back at the battery terminals.

We see the 48 VDC spec on the units controller, with the norm on ebikes, small motorcycles or scooters using 36 or 48 volts battery power sources .

Leaving suspicion that this controller is found to be able to operate on down at a 12VDC level. but with you already confirming that it certainly will not operate at 8VDC.

Thasssssit . . . . .

73's de Edd
.....
 
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kellys_eye

Jun 25, 2010
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Very Nice @kellys_eye, but what value should this pot be?
I'd start with a 100k linear pot - that should be enough to prevent loading of the hall effect output but be low enough to allow current draw to the speed controlling circuitry without causing problems.

Without full technical details this is going to be a suck-it-and-see situation but the cost of a pot is minimal in relative terms.
 

Tha fios agaibh

Aug 11, 2014
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I was thinking like
@73's de Edd,
Jack-up the drive wheels off the ground and brace the vehicle from movement in a safe manor and take some voltage measurements of the sensor output at min, midpoint and max with the vehicle in use.

From there you at least have an idea of where you want the reference voltage to be.
 
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