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[safe]

Do you own one of these?

My digital camera seems to not be able to focus down to sizes that small (like the circuit board) so I probably can't get a very clear picture to you for you to attempt to do it over the internet.

Have you done something like this before? (as he asks the doctor if he's ever done "open heart surgery" before and the doctor replies: "Heck No, but darn, it sure would be fun to try!" )

 

[Leeps]

Well if the controller has a shunt, you could just hook up a potentiometer as a voltage divider, the output of which would go to the comparator in the controller. This would allow you to raise the current limit. Other wise to drop the current limit you would have to intercept the reference voltage going to the comparator and put the potentiometer there.
might be easy might not be, all depends on how things are laid out in the controller and how easy it is to identify what goes where.
Joe

 

[safe]

Fechter

Assuming that there was no need for an LED and the shunt was "borrowed" from an Ammeter then could the "Boost Control" circuit be made any more simple?

At this point I'm thinking of simply owning a 40, 60, 100 amp controller and switch them around depending on what I feel like doing for that day. (rather than risk destroying them through "surgury")

From TNCScooters:

The YK42-2 is a 40 amp controller. ($40)
The YK42-3 is a 60 amp controller. ($40)
The YK42-4 is a 100 amp controller. ($40)

...and with the Deans Connectors it's simply "plug and play". (these three controllers would be used on my two new projects which are a 750 Watt motor that is "overvolted" and a 1200 Watt motor, they would share a battery pack that would also get swapped back and forth)

But I'd RATHER have a "Boost Control" circuit and with your expert knowledge and experience having BUILT one it would be wonderful. A full article with pictures of what you do would be fantastic!

Pleeeeeeeeeeeaaaase...... 8)

 

[fechter]

I know, I know,
It's still on the to-do list.

Making a controller's current limit adjustable is usually just a matter of attaching a few wires and resistors.

Unfortunately, I don't have any controllers like yours, so I can't specify any details. If it was a Vego controller, no problem.

For an external current limiter add-on, Mr. Electric built and tested some that worked fine. The current mode throttle is a new design that has not been tried yet.

Hey, Nick,
got any pictures of the current limiters you built?

 

[mr.electric]

No pictures of the limiter circuit I only have a box of broken brake levers and bent handlebars from the scooter wrecks before I added the current limiter. The circuit fit on a 2" x 2" board and could have been made significantly smaller if I had worked more on the layout. The circuit worked very nicely.

 

[safe]

It would be much better to have one 100 Amp controller and be able to fine tune the "boost" to what I want for a ride (or an individual hill or a straight away) than to have to swap controllers all the time.

I'd love to see a "boost control" circuit to imitate... (that I knew worked already)

 

[Matt Gruber]

i use a pot for that
probably fechters idea

 

[safe]

i use a pot for that

You understand the differences right?

What I want is a "current limit" adjustment so that the limit might range from 100 amps down to 25 amps in the controller. There are two ways to do this:

1. Take apart your controller, learn the circuit, modify the circuit.

2. Create an "external boost control" circuit that takes a reading of the current going to the motor (through a shunt or Hall Effects sensor) and then selectively decides when to turn down the throttle voltage whenever the actual current exceeds the desired current.

Which type of modification did you do?

 

[Matt Gruber]

It would be much better to have one 100 Amp controller and be able to fine tune the "boost" to what I want for a ride

**********(or an individual hill or a straight away)***********
POT WORKS GREAT FOR THIS(NOT THE KIND U SMOKE)

than to have to swap controllers all the time.

I'd love to see a "boost control" circuit to imitate... (that I knew worked already)

 

[safe]

You didn't answer the question:

Did you do option #1 or option #2?

 

[Matt Gruber]

i use a pot for that
probably fechters idea

#0 (before 1&2)

it is not as good as 1 or2 but i use it NOW every ride. i like it, but i also like a manual camera where i set the speed and fstop.

 

[fechter]

I have a tested design for that, Safe.
Add-on adjustable current limiter that goes inline with the throttle wires.

There are some options.
Do you want a control that you can change while riding?
What range do you want on the control?

I have a schematic and I'm working on a layout, but they're not in this computer, so I'll post later. I need to straighen up some things in the drawings first too.

 

[safe]

New Question

Fechter

You've said that depending on how you might hook up a "Boost Control" circuit it can either allow the PWM "effect" or it could EXCLUDE the PWM "effect". Is this a correct recollection on my part?

If I could design a pedal assisted motor "hybrid" that had an automatic "trigger" that once you started to pedal then the "Boost Control" would know to "engage" and limit hub breaking torque then I could have more freedom in gear selection. I might turn up the "boost" for a speed ride or turn it down for a range ride. Having the PWM effect "off" all the time is to my advantage on a geared bike because low end torque just turns your bike into a "space heater" anyway and produces a higher risk of hub breakage. (there's more actual power elsewhere so you never need the PWM effect)

 

[xyster]

(there's more actual power elsewhere so you never need the PWM effect)

Because VoltsIn X AmpsIn = VoltsOut X AmpsOut + heat, the higher motor-side torque is a direct and inevitable consequence of PWM. How do you control the controller's voltage output without PWM? A variable resistor is the only way I know of that doesn't require messing with rewiring batteries on-the-fly. A resistor would be a hugely wasteful heater.

 

[safe]

Because VoltsIn X AmpsIn = VoltsOut X AmpsOut + heat, the higher motor-side torque is a direct and inevitable consequence of PWM. How do you control the controller's voltage output without PWM?

Well that's where Fechter jumps in to the rescue. PWM actually increases the "apparent" current above the level that one would "expect" for that voltage. So the "easy" way to compensate would be to lower the voltage in a proportional manner to compensate for the PWM effect. This way you could keep a "flat line" for torque (easier to gear with) rather than the curve that spikes up near the low rpm's. PWM has this "effect" of INCREASING the "apparent" current limit in the very areas that turn motors into "space heaters" like I learned about yesterday.

Fechter says this CAN be done and some controllers already do it. I'm just wondering if the "Boost Control" circuit could serve a second purpose which would be to protect the multispeed hub from overload.

Like "killing two birds with one stone."

The "actual" PWM current limit is not flat...

 

[fechter]

With a variation of the current limiter add-on circuit, it could be used between the motor and controller to keep the torque constant.

You would still have a problem if you hit a bump while under throttle and the motor spins up while the wheel is not in contact with the road.

 

[safe]

With a variation of the current limiter add-on circuit, it could be used between the motor and controller to keep the torque constant.

Excellent! So I can make plans for maxing out the motor on the top end and not worry about a low rpm torque nightmare. Cool!

You would still have a problem if you hit a bump while under throttle and the motor spins up while the wheel is not in contact with the road.

Those things don't happen much on the street. On the dirt I could see it as a problem and I know on some dirt bikes they used to place little rubber "shock absorbers" into the rear sprocket so that a sudden "catch" like that didn't overload the system. If I can "solve" the "big question" about PWM then the less likely things are less of a threat. When you drop PWM you cut your "threat level" from about 100 Nm (just surviving) to around 40 Nm. (very conservative)

 

[safe]

I'd like to see this "Boost Control" circuit built someday...

 

[Toorbough ULL-Zeveigh]

I'd like to see this "Boost Control" circuit built someday...

And I would like to see,
a poem as lovely as a tree.
Yet here we be, tee-hee-hee.

Haven't you heard?
Desire is the root of all unhapiness!

 

[Reid Welch]

My god, if e-bikes come to do all our thinking
then this insider hobby ceases to be fun.



I like Model T type tech.
It's good to crank

a bike, by heck


=Silas E Fiker=

 

[safe]

Motor Current Limited "Boost Control"

If it's possible to measure the motor side current as the "baseline" in "Boost Control" rather than the battery side current (like a standard controller does) you can limit the heat you produce and prevent excessive torque from damaging an internally geared multispeed hub. This adds extra value for such a circuit. The charts show the dramatic difference in heating that you get between the two types. When you run gears there is no reason to allow strong but wasteful low rpm torque... because you can shift your way out of it... so this design would be ideal for anyone who uses gears with their motors. Hub motors are better off with the existing battery side current limiting scheme.

At peak power both are the same... but at low rpms the geared bike rider will "know" by feel that they need to downshift. It would be important to gear for the worst case scenario hill because there will be no low end torque to draw from. It will "feel" like a "peaky" race bike in that all the power will be in the peak part of the effficiency curve.

Heating would essentially disappear as a problem... :wink:

The units are in Watts.

Note: If you add "Controller losses", "Heat Losses", and "Power(Out)" together you get "Power(In)". So these charts demonstrate how well you use the energy you have. The standard battery side current limiting scheme is not the most efficient choice.

 

[eP]

Hi

Note: If you add "Controller losses", "Heat Losses", and "Power(Out)" together you get "Power(In)". So these charts demonstrate how well you use the energy you have. The standard battery side current limiting scheme is not the most efficient choice.

Your chart is a little wrong. Controller losses are much higher when controller work at low duty and at the same average current limit than if it work at high duty at the same limit.
So green belt i wider at low rpm and narrow at high rpm (high duty) and almost zero when average current = motor's no load current.
You also keep in mind that no load current is more than zero, so red area (heat) dont reach zero at max rpm. Red at the max rpm end should be much higer than green (green is almost zero) as motor's Rm (hundreds mOhms) is usually much higher than controler's Rcontr (less than 10 mOhm) -current is the same as duty is 100% at WOT.

regards

 

[safe]

Your chart is a little wrong. Controller losses are much higher when controller work at low duty and at the same average current limit than if it work at high duty at the same limit.
So green belt i wider at low rpm and narrow at high rpm (high duty) and almost zero when average current = motor's no load current.
You also keep in mind that no load current is more than zero, so red area (heat) dont reach zero at max rpm. Red at the max rpm end should be much higer than green (green is almost zero) as motor's Rm (hundreds mOhms) is usually much higher than controler's Rcontr (less than 10 mOhm) -current is the same as duty is 100% at WOT.

You are probably right. When it came to controller losses I just plugged in the published value (usually 95%) and so I take 5% of the total input current and arrive at an estimate. It's a complicated matter to model correctly and since the value is small I figure this estimate is "good enough".

I wanted to avoid hassling with formulas like:

Can you blame me for not wanting to go any further?

 

[safe]

These charts should be more "normal" to read since they are individualized. The other charts combined everything together and might have given the wrong idea. Controller losses are not a significant factor in the overall picture of what is going on.

Heat is tied to current.

At the no load speed the current is small, so the heat is small. In the standard battery current limited controller the current rises at low rpms even though the power is falling off. The torque increases at low rpms, and the heat goes up along with it.

With a motor current limited controller the low end torque is small and the current can't get high enough to cause excessive heat. So if you are using gearing you can avoid heat altogether by shifting your way out of it. You just have to be ABSOLUTELY sure that you have gears that cover everything because if the rpms drop you have no torque to bail you out.

Just think of one of the old two-stroke race bikes... like a 125cc dirt bike... and how the powerband tends to be rather "peaky".

 

[Beagle123]

It seems to me that I already have a boost control because I just "floor" it all the time. My boost control's limit is 40 amps.

What's the difference between the boost control, and using the controller's upper limit?

Really, I'd like to have a simple on/off switch.

I wanted to just connect my battery cables directly to the motor with a switch inbetween. I've learned that is an explosive situation.

So, my next wish is to have the simplest possible controller:

I'd like to taake the component that limits the current (I beleive its a mosfet and use an on/off switch to it. Then you have two speeds, off and full throttle. I know that is not very desireable because of the jolt you'll get when you press it. I imagine you could pad the shock with a large capacitor.

I saw it in a movie once.

(Are you getting the feeling I don't know anything about electrical engineering?)



I really think its a good idea because when you ride, its good to have two modes: "go faster" and "coast." I think it would be a very effecient way to ride because bikes are very good at coasting. I drive an old BMW that has a mpg guage on the dashboard. When you add coasting into your driving you can practically double your gas consumption. Thnk about when you have to pedal your bike. It's much easier to pedal then coast that to pedal constantly. Anyone using this bike probibly would not want to "floor it" all the time.

I want to use this idea in conjuction with a variable speed transmission, so when you press the "go" button, it will automatically be in the right gear, cushioning the initial jolt more. Also, the power could be set to a lower amount-- just enough to get you up a decent hill in 1st gear. This should be plenty of power for faster speeds. The lower power would drain the batteries more slowly giving added range.

I'd love it if the thing could recover some of the 5% energy loss too!

Is this a crazy idea?