Reducing throttle by 10% using resistor?

Spacey

Spacey

100 kW
Joined
May 15, 2010
Messages
1,464
Location
United Kindom
Hi all,

now I've built a couple of legal...and yes I actually mean real UK legal spec bikes i.e 250W 15.5mph.... or is it 16mph?

Anyhow the bikes just want to do 18mph.... they only just touch 18mph with no wind and a flat road, most of the time they are on 17mph but they absolutely have to be at the most 16mph.

So I was thinking that as you can not program these tiny 6fet controllers would it be possible to put a resistor in the main throttle signal wire to stop the max volts being 4V and reducing it to say 3.6V so that the top speed is reduced by 10%

Would this work? :?
 
It defiantly should. Why can't your program the controller though?

Any ways, this is a really good idea for folks that want a throttle limiting rather than speed limiting. Most likely to let people try their bikes with out them throwing themselves off in a wheelie. (Looking at you here LFP)

Best bet would be to use a pot to trim it to the exact resistance you need while the bike is on a stand, and then replace the pot with the correct resistor.
 
Oh I have all those toys but these are legal schmegal builds that use controllers that can not be programmed...think $20 36V 12A max 7A continuous. No programming cable and opening them up is fine but getting it back together is one hell of a job with the anti contact tape on the fets. These builds had to be done as cheap as could possibly be whilst maintaining reliability and legality.

I could just doctor the speedo's wheel measurements lol.....er...maybe not :twisted:

I have a lot of resistors from some audio projects and quite a few pots so will put one on the green signal wire and see what happens :)

Any idea of ball park figures?
 
I'd think if you limit the throttle, you are also limiting the maximum watts at the same time, not something you really want to do when you only have 250Watts to work with.
 
Pretty sure that the speed throttle just tells the controller what speed you would like to go....not how much power to apply. So unlike a petrol engine if you tell it to go 30mph which could be half throttle it will apply all the power it has to to get you up the hill at 30mph.

With electric controllers it is your desired speed not desired power. So if I take the top speed down by 10% it will still give me the full 250W to get to 16mph and then whatever it needs to to hold me at that speed :)
 
I think El_wato is correct. Your basically trying to cap the throttle. So imagine if you just turned it half way. I don't think it's linear, so it wouldnt be half power, but you get the idea.

And the amount that your talking about cutting it down by is so little, you probably won't notice.

For balpark range, use a resistor divider calculator to drop 4v down to 3.5v... then raise it until you hit the legal limit.
 
resister diver calculator...sounds complicated.
Surely if I tell the motor to go 90% of speed it will give me the maximum power to get to 90% of speed.

My 66V 40amp Lyen controller set to 73% speed gives me full amps up to that speed and then dies down once it gets there. Regardless of what I set my top speed to I can always get full power up to that speed.
 
I don't have an answer for you.

Spacey said:
... but they absolutely have to be at the most 16mph.
Click to expand...

But I'm curious. Do they (the ebike police) actually test the top speed of each ebike in the UK? If so, do they take into consideration of the rider's weight? Or the mechanical efficiency of bike? That is unlubed chain, unlubed hubs, crooked wheels, etc...
 
Does your euro law say "250w output" or "250w input"?

And does it say it's the mfg's rating for the motor? Or does it specify how and where this 250w is measured with/at/from?

I'm curious, because in the USA, it says a motor that is not rated for higher than 750w output (as in mechanical horsepower out of the motor).
 
Ok, here's your law apparently.


Euro Union - E Bike Definition: Cycles with pedal assistance which are equipped with a auxiliary electric motor having a maximum continuous rated power. Maximum Power Output 250w. Max Speed 25km/h (15mph). Use and travel regulations – UK specific must be ridden by someone at least 14 years of age. Weight and voltage requirements for Ebikes sold in the UK.


250w maximum power output. That means starting from a stop, you're legal to dump >20,000watts into the hub (because output efficiency is 0% on any motor at zero RPM), and then taper power down as speed increases and the motor begins to have some efficiency.

I don't know what hub you're running, but if it's only going 15mph, I bet you never see over 80% efficiency at any point no matter what happens, so make sure to figure that into your calculations on the acceptable power to draw.
 
Spacey said:
resister diver calculator...sounds complicated.
Surely if I tell the motor to go 90% of speed it will give me the maximum power to get to 90% of speed.

My 66V 40amp Lyen controller set to 73% speed gives me full amps up to that speed and then dies down once it gets there. Regardless of what I set my top speed to I can always get full power up to that speed.
Click to expand...

Yes, but give it %10 throttle, and you'll notice that it will not give you 40 amps any more.
 
You know, a lot of low end kits like the ampedbikes/cell_man/ebikekit 250-350w geared motors have an option for this.
It is a blue/gray wire that usually hangs loose.. it is used as a speed control. You plug that in, and it goes euro legal, to 15mph i believe.

This problem is already solved, if we are talking about basic geared kits and not infineons etc..
 
This is a joke, right? You can't actually be worried about going 18mph if the limit is 16 with your tax dollars go toward paying someone along with the equipment they need to enforce such a minor infraction.

Rules are meant to be broken anyway, especially silly ones.
 
John in CR said:
This is a joke, right? You can't actually be worried about going 18mph if the limit is 16 with your tax dollars go toward paying someone along with the equipment they need to enforce such a minor infraction.

Rules are meant to be broken anyway, especially silly ones.
Click to expand...

If you knew who I worked for you would understand :oops:
 
neptronix said:
You know, a lot of low end kits like the ampedbikes/cell_man/ebikekit 250-350w geared motors have an option for this.
It is a blue/gray wire that usually hangs loose.. it is used as a speed control. You plug that in, and it goes euro legal, to 15mph i believe.

This problem is already solved, if we are talking about basic geared kits and not infineons etc..
Click to expand...

At 36V that speed restricter goes 8mph, I believe on the kits I have it only works for 48V. It is a grey cable with only one contact.
 
The EU regs state...

250 continuous output maximum before the windings burn out....., so you cannot legally run a 1000w motor at limited amps

the use of a button for "boost" or off road setting is considered not ,to be in line with "ebike" definition within the EU...

Stupidly, the UK is the only country in the EU able to use a throttle, but only at 200W output....all the rest have a rule that the power must be cut if the peddles are not turning...
 
So you are some kind of civvy police liason officer.....

I think it doesnt matter that much. I can't see any coppers whipping out a mutimeter and clampmeter to find out if you're breaking the law. I reckon the main thing is to make sure your bike "looks" legal. get one of those "200W MAX POWER!!!!" stickers.

plus in the UK +/- 10% is allowed for most speed related laws.
 
Yeah, pretty much what I was thinking... on pull away I can dump 12amps into the hub but it settles down to 5 to 6amps at around 17mph which is just under 250W.... but that is from the controller so at the wheel it's probably 180watts. UK law is output from back wheel so I could up this a bit.

I thought the speed limit was 15.5mph not 15mph? There is the allowance of +/- 10% inaccuracy of speedo's which would get me to 17mph nicely :twisted:

maximum continuous rated power. Maximum Power Output 250w
Click to expand...

I had thought that maybe this meant an overall average but as you say it would seem it is when the bike settles down it must not produce more than 250W at the rear wheel and go no faster than 15mph.

Dialing back the speed by 1.5 mph is not deal breaker really in the speed department. Cheers for the info LFP :)



liveforphysics said:
Ok, here's your law apparently.


Euro Union - E Bike Definition: Cycles with pedal assistance which are equipped with a auxiliary electric motor having a maximum continuous rated power. Maximum Power Output 250w. Max Speed 25km/h (15mph). Use and travel regulations – UK specific must be ridden by someone at least 14 years of age. Weight and voltage requirements for Ebikes sold in the UK.


250w maximum power output. That means starting from a stop, you're legal to dump >20,000watts into the hub (because output efficiency is 0% on any motor at zero RPM), and then taper power down as speed increases and the motor begins to have some efficiency.

I don't know what hub you're running, but if it's only going 15mph, I bet you never see over 80% efficiency at any point no matter what happens, so make sure to figure that into your calculations on the acceptable power to draw.
Click to expand...
 
Aren't three speed switches simply adding resistance to the throttle? Or is there more to em? I'm trying to create a makeshift three speed switch for my 72v 40a controller.. it doesn't come with it, and the torque and top speed is just crazy that I'd like two speeds, one that makes sense and the one 100% when I feel and want the thrill
 
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