Need more voltage

Thread Starter

Jeff262

Joined Sep 19, 2021
4
Is there any way to get this to rise to max output to atleast 3.9v? I am trying to get my son's scooter to smooth out the start up throttle but keep the top end on the hall effect speed controller which needs 3.9v or greater for top speed. Thanks jeff
 

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Papabravo

Joined Feb 24, 2006
18,978
The best you can do at the emitter of the transistor is 0.7V less than the voltage on C1. That's it, that's all she wrote and there isn't any more.
IMHO that is a pretty lame circuit.
 

DickCappels

Joined Aug 21, 2008
9,078
This is a work-around.
Take an oscillator and use its output to drive a half-wave voltage doubler, like this:
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In my experience NE555's are disappointing when trying this to increase +5V because of the internal voltage drops at the '555's output. The ICL7660 is CMOS and designed to drive this kind of load.
 

MisterBill2

Joined Jan 23, 2018
12,697
A direct bypass connection from collector to emitter will provide more voltage by avoiding that 0.7 volt drop.

But it is not clear just exactly what "smooth out the startup throttle" means, nor how this relates to a hall effect speed controller. And a word of caution is that adding any delay to throttle controls is usually a poor choice because it usually leads to operator over-shooting the target speed. And any delay on slowing the reduction of a speed request is unsafe.

This is once again a case of being only given a very small amount of information about the perceived cause of some condition. Providing more information will always lead to getting more applicable advice, instead of guesses.
 

Thread Starter

Jeff262

Joined Sep 19, 2021
4
It more of a torque issue with the motor on low end, I had the change the gearing to reduce top end speed but now with the larger main gear and slower speed it likes to "pop a wheelie" when the kids give it full throttle which max speed is only 8 mph
 

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MisterBill2

Joined Jan 23, 2018
12,697
How is raising the maximum speed voltage going to improve that problem??
The circuit shown is a speed command delay circuit.
What I see is that because of the intentionally added delay in "throttle" response the operators twist the control to max at startup. so the real solution is to remove that gentle-start circuit so that they get the speed that they want without going to max speed in an effort to start up.
This is an example of an intention to avoid a problem causing a worse problem. A safety feature causing unsafe operation.
 

Halfpint786

Joined Feb 19, 2018
40
How is raising the maximum speed voltage going to improve that problem??
The circuit shown is a speed command delay circuit.
What I see is that because of the intentionally added delay in "throttle" response the operators twist the control to max at startup. so the real solution is to remove that gentle-start circuit so that they get the speed that they want without going to max speed in an effort to start up.
This is an example of an intention to avoid a problem causing a worse problem. A safety feature causing unsafe operation.
If the operator cranks the throttle and the delay circuit still allows it to pop a wheelie, I don't think a lagging response causing overshoot is the issue. My scooter had this safety feature and the slow acceleration was annoying, but in this case here, the delay isn't too long, it's not long enough. The obvious solution is to increase the size of that capacitor, not removing the entire circuit (which gives the kid even more torque). Changing that capacitor value (or turning TP1 to a higher resistance) does not affect the maximum or minimum voltages available, it merely slows the time the voltage takes to reach those limits.

Or am I misunderstanding all this? Are you saying that the initial rapid rise to 0.7v is the problem? In that case, could you just swap that transistor for a cheap op amp voltage follower?
 
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MisterBill2

Joined Jan 23, 2018
12,697
Just like driving a car, if you step on the gas and the acceleration is not as much as you want, the inclination is to step on it a bit more. That is a rather basic reflex. Are youngsters likely to be much different? Certainly this feature is a C.Y.A. move by the producer to prevent anything close to responsibility for any injuries, that much is certain.
Certainly delaying the response is simpler than reducing the acceleration, but the result is different. Who would buy a car with a 5 second o to 20MPH throttle response? Nobody that I know.
 

DickCappels

Joined Aug 21, 2008
9,078
It looks like the circuit has adjustable lead via the 144 ohm pot. Not sure that helps much, but the pot in that location is a good idea to help tweak in the response.
 

ro80rob

Joined May 2, 2022
2
Am I missing something here? The answer is probably, but here goes anyway....

You changed the scooter's gearing to reduce the top end speed, but now find that the extra torque at startup due to the revised gear ratio means it can give your favourite child whiplash at startup?

Surely you should return the gearing back to the setup it left the factory and just add a potentiometer/resistive divider in the throttle control line to limit/set the maximum speed.
 

MisterBill2

Joined Jan 23, 2018
12,697
Another option is to teach the riders about not popping the throttle all the way so fast. we learn to start up without any tire squealing quite early in the game. One simple thing would be to add a stronger return spring to the throttle linkage. That might be all it takes.
And still another idea is to add a wheelie bar to the scooter.
For white knuckle excitement not much beats having the throttle not close after a fast startup with a new stronger engine, and doing a half-block wheelie because of no kill switch, no rear brake, and no way to let go of the bars wit the front wheel up in the air. eventually it came down and I could choke it with my hand until the engine died and then slow it with the front brake. Turned it around, an easy bump start, and idled back in first. It seems that neither of thethrottle return springs had been installed yet, nor the kill switch wire, nor the foot pegs. But the engine survived because it did not over rev. None of the neighbors had seen such a wheelie on a funny bike before.
At 8 or 9 MPH I think the kid will be OK, and any wheelies will be less exciting.
 
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