Add resistor in line with throttle to limit top speed?

[michielk]

Hello,

Optional intro
I'm starting a new build soon (electric kickbike). I would like the option to limit the top speed to keep it road legal (27kmph, 17mph). My controller needs the optional display to do this, but I would like to keep the setup clean/simple and not use the display. If I understand correctly the throttle is actually a potentiometer, so a kind of variable resistor to send a voltage of 0-5V for a 0 to 100% throttle control. I understand that I would need to experiment with different resistors to get the speed correctly.

Actual question
Can I limit the top speed by adding a small resistor between throttle and controller?

For example
Stock: 0-100% throttle = 0-5V output
Add resistor: 0-100% throttle = 0-4V output, so limit to 80% throttle

It would then be easy to create a switch of some sort to go from 80 to 100%.

thanks for confirmation

 

[amberwolf]

Some threads that have the info you're after:

https://endless-sphere.com/forums/search.php?keywords=throttle+resistor*&terms=all&author=&sc=1&sf=titleonly&sr=topics&sk=t&sd=d&st=0&ch=300&t=0&submit=Search

https://endless-sphere.com/forums/search.php?keywords=speed+throttle&terms=all&author=&sc=1&sf=titleonly&sr=topics&sk=t&sd=d&st=0&ch=300&t=0&submit=Search

https://endless-sphere.com/forums/search.php?keywords=limit+throttle&terms=all&author=&sc=1&sf=titleonly&sr=topics&sk=t&sd=d&st=0&ch=300&t=0&submit=Search

Not every thread is relevant, but the titles generally indicate which ones will be. THere are quite a few other threads that have posts in them that would help too, but you'd use different searches to find those.

 

[TommyCat]

Sorry being late to the party... but for future searchers.

Shown for a hall sensor throttle, but should work the same with a potentiometer type throttle.

For other throttle testing and modification tips... see this THREAD.



Regards,
T.C.

 

[dogman dan]

Throttles are usually a hall sensor, but it does vary the voltage back to the controller.

Great diagram, but I'd want to add one more thing. A toggle switch or at least a jumper wire plug that could allow a bypass of the trim pot. If you have hills to climb, you will still want full power then. Maybe even a pushbutton, mash it and get a few seconds of full power, then resume riding at legal speed.

Many controllers have a three speed switch option. The switch could then just be in a secret place, instead of on the bars.

 

[oded]

I made a mistake and installed a way too powerful controller on my e-dirt bike. The bike can not be ridden like this as a small twist of a throttle causes the bike to launch like a rocket.

Until I get a lower watt controller, I can trim the end point voltages, creating a much tamer power delivery curve, and reduce the amps drawn.

I do that by adding resistors as instructed here. Am I missing something?

Sent from my LM-G850 using Tapatalk

 

[TommyCat]

I'd note that some controllers allow for maximum amperage or RPM restrictions if a display is used. And if available would be a handy alternative or something to easily try first...

But if a hall sensored throttle output modification is needed as mentioned above to drop the WOT signal output voltage. Note that only one resistor is typically used in series on the 5vdc positive voltage supply wire which drops the input voltage. (or potentiometer as seen in the diagram above...)

This graph showing the results of adding different resistances which lowers the input voltage and thus effecting the output, and other specifics and details are found in this thread...
Guide to Hall Sensor Throttle operation, testing, and modification.

 

[spinningmagnets]

you might also research the controller, to see if it has a "throttle ramp" adjustment. You would still get max throttle, but it would take a few seconds to get there, instead if full power being instant.

I'm interested to see how this throttle resistor idea works out. Cheap and simple.

 

[ZeroEm]

Need to write you up in Endless Sphere's history member controller is two powerful.

by oded » Sep 29 2021 2:06pm

I made a mistake and installed a way too powerful controller on my e-dirt bike. The bike can not be ridden like this as a small twist of a throttle causes the bike to launch like a rocket.

Until I get a lower watt controller, I can trim the end point voltages, creating a much tamer power delivery curve, and reduce the amps drawn.

I do that by adding resistors as instructed here. Am I missing something?

Sent from my LM-G850 using Tapatalk

 

[oded]

The bike is my son's Oset 24 trial dirt bike. It's a 48v 1.4kw brushed motor bike. Slow speed charectaristics are very good (also due to the brushed motor).

Replaced the stock faulty 1000w controller with a basic crude 1500w controller, and the bike can not be ridden like that due to excessive power and sensitivity.

I was thinking about adding a 10k pot variable resistor to the throttle's red wire, and play with it.
Not sure if another resistor should be placed on the ground black wire.
The first 1/8th twist do not power on the motor, and that's ok, but if it will help flatten the curve, I'll gladly do that.
Just looking to tame the bike and make it less brutal and amp hungry.

10k variable resistor is fine?

And yes, I also can't believe I'm trying to reduce the bike's power. It's not like me

 

[TommyCat]

I was thinking about adding a 10k pot variable resistor to the throttle's red wire, and play with it.

10k variable resistor is fine?

Yes, the 10K size will work nicely. And highly recommended verses trying different sizes of resistors... definitely easier!

Not sure if another resistor should be placed on the ground black wire.
The first 1/8th twist do not power on the motor, and that's ok, but if it will help flatten the curve, I'll gladly do that.
Just looking to tame the bike and make it less brutal and amp hungry.

A hair trigger on a powerful dirt bike, with all the jolts and bumps may not be for everyone. But as shown in the next graphic, will also flatten the curve a bit. (might as well use a 10k Pot here also...)

As per #3 "double Dipper Mod"... yep, you know from where. :wink:

 

[spinningmagnets]

Awesome info, Tommy Cat.

https://electricbike.com/forum/foru...r-throttle-operation-testing-and-modification

 

[oded]

Tommy cat, your input is priceless. Thanks.

According to the double dipper mode, do I really have to connect the ground wire to the 2nd pot (leg 3 of the resistor)? Circled it.

Also, adding a resistor to the signal green wire only (without bridging it to the other wires, or adding a capacitor) will not make difference?

 

[TommyCat]

Glad to help. :thumb:

Also, adding a resistor to the signal green wire only (without bridging it to the other wires, or adding a capacitor) will not make difference?

Good question.

Yes, certainly the addition of a resistor in the signal line will drop the output voltage accordingly. But unfortunately it also drops it for the entire range of throttle operation. Thus introducing even more throttle lag or hesitation on start up as you have now. The uniqueness of having the resistance on the input voltage side of the hall sensor, is that this added negative effect is avoided.

According to the double dipper mode, do I really have to connect the ground wire to the 2nd pot (leg 3 of the resistor)? Circled it.

Even better question...

One that is addressed in THE THREAD directly above the graphic you posted. 8)

"November 24th, 2019: Using my controller in actual operation trying both options I can see no electrical downside to ether wiring usage. I have used the top diagram (with use of ground) with no problems at all and had stopped there. But recently I was questioned as to if the ground was actually needed. So doing more tests I determined that the ground connection was not necessary as far as my controller's operation was concerned. This would seem to be more desirable, as it requires fewer wiring modifications. So I added it here. The choice is yours."


Data that I used to make the comparison...

Since it seems to induce less voltage supply voltage drop, and is more efficient at dropping the output voltage. I continue to use the original wiring graphic with ground in quick postings.
Using the ground connection may be just a hair better, but specs for both are awfully close. Again... your choice.

 

[SlowCo]

Great thread, thanks for the info :thumb:

 

[oded]

Thanks TC,
I'll post my results in few days.

 

[oded]

good news - works very well!

started with adding a 10k potentiometer to the red +5v wire (when throttle is disconnected it measures 7.3v for some reason).
power was limited as I was hoping. however, the more I increased the resistance, the wider the dead band in the throttle's twist became. so, I went with TC's "double dipper" mode, and installed a 10k potentiometer on the black ground wire as well. that helped and I got rid of the excess dead band.

needed to replace the 10k pots with 1k for finer tuning.
settled on red wire 0.72 ohms, and black wire 0.17 ohms (I may be wrong with the units). when switching the power on, these resistance measurements change.

this is the controller I am using -
https://electricscooterparts.com/hookup/SPD-601500Awiring.htm

will have to take it for a real test drive, but it seems to work well.

Thanks!

 

[TommyCat]

Great news!

I'm curious... what are the final tweaked voltages of the throttle's signal wire after your modding?
With my small input voltage drop testing, never had the bottom drop too. Wondering how close you are to the sensor's minimum input voltage spec.

 

[oded]

Did not measure the signal wire's voltage since it stayed intact. Didn't have to cut this wire, so I can't tap to it in order to measure its voltage.

If it's important to you TC, I can cut, measure and re-solder. Let me know.

Seems that adding the pot to my +5v wire is behaving like adding the pot to your signal wire. Both caused the bottom voltage to drop.

 

[TommyCat]

Thanks for the offer, but I say leave well enough alone.
But if someday the chance arrives that it's possible, would be interesting to know for the reasons you mention.
That is a very straightforward and basic controller!


I wanted to thank all for the positive comments on the Hall Sensor Throttle Thread. Always nice to hear some feedback!

@spinningmagnets Doubly appreciated from a distinguished author of several E-bike articles that have helped me in pursuit of knowledge of components and operation. And an inspiration to offer something back for others.

But as always, any helpful comments or suggestions to make it better are welcome. :wink:


Best regards,
T.C.

 

[m3vuv]

Hello,

Optional intro
I'm starting a new build soon (electric kickbike). I would like the option to limit the top speed to keep it road legal (27kmph, 17mph). My controller needs the optional display to do this, but I would like to keep the setup clean/simple and not use the display. If I understand correctly the throttle is actually a potentiometer, so a kind of variable resistor to send a voltage of 0-5V for a 0 to 100% throttle control. I understand that I would need to experiment with different resistors to get the speed correctly.

Actual question
Can I limit the top speed by adding a small resistor between throttle and controller?

For example
Stock: 0-100% throttle = 0-5V output
Add resistor: 0-100% throttle = 0-4V output, so limit to 80% throttle

It would then be easy to create a switch of some sort to go from 80 to 100%.

thanks for confirmation

Firstly the throttle is NOT a potentiometer its a hall sensor,with my bike i put about 3 small skhotty diodes in series with the throttle sensor output wire ,each diode dropped the signal voltage from the throttle down by about -3v for each diode in series,i had a 4 position rotary switch too switch in the voltage drop needed so had 3 levels of power!and a bypass position,hope that helps!.

 

[amberwolf]

Firstly the throttle is NOT a potentiometer its a hall sensor,

Some are. Two well known ones are Magura and Domino, but there are plenty of cheap ones.

 

[m3vuv]

having diodes switched in series with the throttle signal wire using a box mounted rotary switch works well as you can adjust the max power on the go without trying to alter a trimmer pot,try doing that when riding!.

 

[E-HP]

having diodes switched in series with the throttle signal wire using a box mounted rotary switch works well as you can adjust the max power on the go without trying to alter a trimmer pot,try doing that when riding!.

Or just use your wrist to adjust max power without having to mess with switches.

 

[m3vuv]

my wrist is stronger than my willpower tho.