# How do I reduce the speed of a 12v children's car?

1. ## Re: How do I reduce the speed of a 12v children's car?

Originally Posted by surreyman
thankyou so much- that is very clear- i will keep you informed when it arrives! really appreciate your help
HI - so it arrived and has three wires- red/ white/ black - i joined the black and white wire together at the end of their lengths they were supplied with - thus leaving me with two wires that i joined into the jeep red wire.(see pic) . Then off for a test drive- sadly with the control knob fully turned to the left the jeep works as normal- if i turn it just a fraction away from fully left the jeep just doesnt work - this is the same the more i turn it .

2. ## Re: How do I reduce the speed of a 12v children's car?

Strange!
What are the markings on the new control?
Can you turn it full 'not working' direction and measure the voltage across the original control please. Black meter probe to the yellow wire and tell us the voltages on each side of the red wire you cut.

I will try to help but I'll be out of action for a few days after today I'm afraid.

Brian.

3. ## Re: How do I reduce the speed of a 12v children's car?

Originally Posted by betwixt
Strange!
What are the markings on the new control?
Can you turn it full 'not working' direction and measure the voltage across the original control please. Black meter probe to the yellow wire and tell us the voltages on each side of the red wire you cut.

I will try to help but I'll be out of action for a few days after today I'm afraid.

Brian.
hi, so the markings on the new control are 'B10K' . So o put the black voltmeter wire into the yellow and connected the red voltmeter into the red 'cut' wire . the side that was joined to the red wire on the new control stays a constant 4.34v no matter whether you turn the control up or down. When i connect the red voltmeter to the other side of 'cut' red (the one thats joined to the black/white of the new control) it shows 0.7v and rises progressively to 4.35v as i turn it up to full. Should this all be in the green wire ?

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Originally Posted by surreyman
hi, so the markings on the new control are 'B10K' . So o put the black voltmeter wire into the yellow and connected the red voltmeter into the red 'cut' wire . the side that was joined to the red wire on the new control stays a constant 4.34v no matter whether you turn the control up or down. When i connect the red voltmeter to the other side of 'cut' red (the one thats joined to the black/white of the new control) it shows 0.7v and rises progressively to 4.35v as i turn it up to full. Should this all be in the green wire ?
i seem to recall the green wire was the one that voltage altered as the pedal was pressed?

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4. ## Re: How do I reduce the speed of a 12v children's car?

It would be on the green wire but only if the pedal was hard down. In that position it is basically joined to the red wire and should carry the same voltage. The green wire should never go higher than red because that is it's source of voltage but it should be lower by an amount determined by the pedal position.

I wish I knew the full specification of the control box, it would make things far simpler than remote guesswork!

It is just possible the new control has what we call a 'log taper', 'log' in this case meaning logarithmic. There are two main types of potentiometer, log and linear. Linear means the voltage from the wiper (middle contact) is proportional to the rotation, mid position for example gives half the voltage output. Log potentiometers are mechanically the same and they are usually used as volume controls, the mid position giving half volume. That isn't the same as half voltage though because human hearing is very sensitive in quiet conditions but relatively insensitive to changes at high volume, the rotation follows the characteristics of normal hearing rather than absolute amount. The reason I mention all this is that if your new control is indeed logarithmic, all the adjustment will be at the very end of rotation, exactly what you are seeing. There is a very simple fix to see if I'm right, just swap the wire to the middle contact over so it connects to the other end wire. It will make the control work in reverse but may let you use the part of rotation that give a more gradual effect.

Try it and let me know what you find. I will not be able to reply for a few days but I'm sure others here will do their best to help until I return.

Brian.

5. ## Re: How do I reduce the speed of a 12v children's car?

Originally Posted by betwixt
It would be on the green wire but only if the pedal was hard down. In that position it is basically joined to the red wire and should carry the same voltage. The green wire should never go higher than red because that is it's source of voltage but it should be lower by an amount determined by the pedal position.

I wish I knew the full specification of the control box, it would make things far simpler than remote guesswork!

It is just possible the new control has what we call a 'log taper', 'log' in this case meaning logarithmic. There are two main types of potentiometer, log and linear. Linear means the voltage from the wiper (middle contact) is proportional to the rotation, mid position for example gives half the voltage output. Log potentiometers are mechanically the same and they are usually used as volume controls, the mid position giving half volume. That isn't the same as half voltage though because human hearing is very sensitive in quiet conditions but relatively insensitive to changes at high volume, the rotation follows the characteristics of normal hearing rather than absolute amount. The reason I mention all this is that if your new control is indeed logarithmic, all the adjustment will be at the very end of rotation, exactly what you are seeing. There is a very simple fix to see if I'm right, just swap the wire to the middle contact over so it connects to the other end wire. It will make the control work in reverse but may let you use the part of rotation that give a more gradual effect.

Try it and let me know what you find. I will not be able to reply for a few days but I'm sure others here will do their best to help until I return.

Brian.
Hi so i swapped the white middle wire (was connected to the black on the poteniometer ) and connected it to the red on the potentiameter with it all still in the line of the cut red wire on the jeep (basically swapped sides on the middle white wire. This time the knob works the other way around (ie full power is turned far right rather than left) - bad sadly the same thing happens- turn it fractionally to the left and the jeep doesnt work

6. ## Re: How do I reduce the speed of a 12v children's car?

Originally Posted by surreyman
Hi so i swapped the white middle wire (was connected to the black on the poteniometer ) and connected it to the red on the potentiameter with it all still in the line of the cut red wire on the jeep (basically swapped sides on the middle white wire. This time the knob works the other way around (ie full power is turned far right rather than left) - bad sadly the same thing happens- turn it fractionally to the left and the jeep doesnt work
HI, are you back yet?

7. ## Re: How do I reduce the speed of a 12v children's car?

Originally Posted by surreyman
turn it fractionally to the left and the jeep doesnt work
It sounds as though the potentiometer is a very high ohm value. This means that resistance in your circuit quickly increases as soon as it has the slightest length of resistive carbon track in it.

8. ## Re: How do I reduce the speed of a 12v children's car?

It sounds as though the potentiometer is a very high ohm value. This means that resistance in your circuit quickly increases as soon as it has the slightest length of resistive carbon track in it.
If the car has a 2.38K pot in it for the accelerator then using a 10K pot was a mistake at 1/10 of the rotation it already nearly 50% of the original pot's range. I would have used a 1K ohm pot to try this solution out, which I don't think will work quite as well as others seem to think.

Primarily because you don't want to increase the ohmic value much higher than 2.38K (assuming this was the car's stopped position). At the other range is full speed, so you really want to limit the range of the accelerator to 2.38K (stopped) to 1K (max speed). This matches the symptoms as the turning the new pot even fractionally causes the car to stop working, i.e. tuning the pot 1/10 will result in the accelerator range changing to 2.38K+1K= 3.38K to 1K. Now you have to depress the accelerator through the first 1K of the range to even start getting it to move. If you were to set the pot to 2.38K you would have a car that never moves as the combined accelerator and pot are already at the maximum stopped position even when the accelerator is depressed completely.

What you really need is a way to cut in 1K ohm of extra resistance in the path, increasing it from 0 to 1K as the accelerator goes from stopped (2.38K) to full speed (0 ohms). Can't think of any way to do that with just passive components.

9. ## Re: How do I reduce the speed of a 12v children's car?

If the car has a 2.38K pot in it for the accelerator then using a 10K pot was a mistake at 1/10 of the rotation it already nearly 50% of the original pot's range. I would have used a 1K ohm pot to try this solution out, which I don't think will work quite as well as others seem to think.

Primarily because you don't want to increase the ohmic value much higher than 2.38K (assuming this was the car's stopped position). At the other range is full speed, so you really want to limit the range of the accelerator to 2.38K (stopped) to 1K (max speed). This matches the symptoms as the turning the new pot even fractionally causes the car to stop working, i.e. tuning the pot 1/10 will result in the accelerator range changing to 2.38K+1K= 3.38K to 1K. Now you have to depress the accelerator through the first 1K of the range to even start getting it to move. If you were to set the pot to 2.38K you would have a car that never moves as the combined accelerator and pot are already at the maximum stopped position even when the accelerator is depressed completely.

What you really need is a way to cut in 1K ohm of extra resistance in the path, increasing it from 0 to 1K as the accelerator goes from stopped (2.38K) to full speed (0 ohms). Can't think of any way to do that with just passive components.
so if i use a 1k rather than 10k potentiometer do you think that would work?

10. ## Re: How do I reduce the speed of a 12v children's car?

I'm back.
It is so frustrating when we could probably fix the problem in five minutes of "hands on" but even time zone differences here can delay replies by many hours.

I think my next suggestion would be to buy a 1K fixed resistor and wire it across the ends of the new potentiometer to see what happens. It will drop the effective value from 10K to a little under 1K and still allow some adjustment although the speed limit adjustment will no longer be as linear as before. You can try replacing the control with a 1K linear one or try the resistor first. If it doesn't work with the fixed resistor it certainly won't work with a variable one.

Brian.

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11. ## Re: How do I reduce the speed of a 12v children's car?

If after all the good community efforts, sweat and tears you are ready to give up; replace the traction wheels with smaller diametre ones.

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12. ## Re: How do I reduce the speed of a 12v children's car?

Originally Posted by betwixt
I'm back.
It is so frustrating when we could probably fix the problem in five minutes of "hands on" but even time zone differences here can delay replies by many hours.

I think my next suggestion would be to buy a 1K fixed resistor and wire it across the ends of the new potentiometer to see what happens. It will drop the effective value from 10K to a little under 1K and still allow some adjustment although the speed limit adjustment will no longer be as linear as before. You can try replacing the control with a 1K linear one or try the resistor first. If it doesn't work with the fixed resistor it certainly won't work with a variable one.

Brian.
Hi, so you think buy a 1k fixed resistor join it to my 10k variable potentiometer? And not just buy a 1K variable potentiometer? Could you show me on ebay what to buy and i will get it. Many thanks

13. ## Re: How do I reduce the speed of a 12v children's car?

You have two options, one is to replace the 10K potentiometer with a 1K one so you get 10 times less adjustment, given that it seems too 'coarse' to adjust correctly it should make matters better. The other is to wire a fixed 1K resistor across the existing 10 K potentiometer. when you connect resistors in parallel (across each other) the resulting value is lower so 10K and 1K in parallel will give about 910 Ohms but don't forget the potentiometer is 10K maximum so it can still be adjusted down to zero.

If you are buying components anyway, it probably makes more sense to buy a 1K linear potentiometer: https://www.ebay.co.uk/itm/Single-Li...9akw:rk:7:pf:0

I have no affiliation with the seller, make sure you select 1K if you buy from them.

Brian.

14. ## Re: How do I reduce the speed of a 12v children's car?

Originally Posted by betwixt
You have two options, one is to replace the 10K potentiometer with a 1K one so you get 10 times less adjustment, given that it seems too 'coarse' to adjust correctly it should make matters better. The other is to wire a fixed 1K resistor across the existing 10 K potentiometer. when you connect resistors in parallel (across each other) the resulting value is lower so 10K and 1K in parallel will give about 910 Ohms but don't forget the potentiometer is 10K maximum so it can still be adjusted down to zero.

If you are buying components anyway, it probably makes more sense to buy a 1K linear potentiometer: https://www.ebay.co.uk/itm/Single-Li...9akw:rk:7:pf:0

I have no affiliation with the seller, make sure you select 1K if you buy from them.

Brian.
hi- i have ordered a 1k one- so i discard the 10k one and wire it in in exactly the same way?

15. ## Re: How do I reduce the speed of a 12v children's car?

Yes, exactly the same. The physical position of the pins is what matters, the outside two are the ends of the internal track and the middle one is the wiper that moves along it.

Brian.

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