Building an E-Bike: basic questions

The idea for this post is to ask some questions that hopefully will be graciously answered by those more experienced in these matters and will perhaps assist others who are interested in going down this path. IE building an E-Bike to suit their personal preferences.


Presumably I need to determine how I think I will use my E-bike so my first question to the forum is;

1.) What parameters do you think are important to take into consideration when starting this process? (know of an existing answer how about a link?)

And

2.) How would you go about prioritizing these parameters?

There are many on this forum with far more technical knowledge than I and my experience is limited to SLA power only but prioritizing, to me at least, is fairly easy. With the right priorities building the bike should fall into place.

First, to me, is range. 60 MPH does no good if it only last a mile and you need to go fifteen.

Next is speed. How fast do you need to go to get there and what are the laws in your area governing the speed. Here in FL if we go over twenty MPH we're not officially a bicycle and then subject to all sorts of rules and regulations a bicycle can't possibly meet.

Third is budget. No budget, no bike, big budget, big bike. A Crystalyte Sparrow on a Wal Mart frame can probably be done for less than $500.00. One of the members here just found a Mongoose on Amazon in the $300.00 range. Bigger motors generally mean bigger dollars. Lots of range equals more SLA's or more dollars for more expensive battery technology.

I've been asked many times to help folks choose a boat and my answers are always the same: What do you want to do with the boat? Cruise? Fish? Travel protected or open water? How much are you willing to spend? Biking, any sport/recreation/avocation is similar, you get what you put in and precious little more. I believe your question will generate a lot of individual comments from learned individuals and will greatly aid you in your search.

Good luck. One thing I've learned for sure and I've had an electric bike, two electric scooters and a electric golf cart for a LONG time and that is now that I have a electric bike capable of 30+ MPH it is a LOT OF FUN. Also a lot to learn and that's where this forum is indispensable.

Mike

gwsaltspring said:

The idea for this post is to ask some questions that hopefully will be graciously answered by those more experienced in these matters and will perhaps assist others who are interested in going down this path. IE building an E-Bike to suit their personal preferences.


Presumably I need to determine how I think I will use my E-bike so my first question to the forum is;

1.) What parameters do you think are important to take into consideration when starting this process? (know of an existing answer how about a link?)

And

2.) How would you go about prioritizing these parameters?

Click to expand...

First step, define the performance parameters you'd like for speed, range and hillclimb ability. Then check your bank account and review step one again. :lol:

It might be easier if people could post up some example performance targets along with an approximate dollar budget and type of bike, and then we could give some possible solutions.

Dog has been promissed a walk and is going insane barking at the door with her leash in her mouth.. so i'll revise this in a short bit..

There is no " One Way " to do this, but here goes:

Crystalyte or Hub motor setup :

1- Do you already have a bike.. or are you buying one ?

- If you already have a bike, you know your wheel size.

- If you do not already have a bike.. start with the motor then find a bike that fits it and the parts/batteries/etc

2- Batteries : What's your budget ? and how much will you use this bike?

Rarely, weekend joy rides, occasional use.. : SLA

Frequently, Job-commuter, means of transportation.. : Nimh/Nicad

Obsesive compulsive disorder Rider, long range and big budget : Lithium

3- Consider your weight, terrain, weather, and figure out how fast you honestly want to travel 80 % of the time....

Ok.. i have to go.. Be right back ( 30 minute run on the e-bike with the dog and she'll leave me alone for a second.. )

Missed an important detail:

How mechanical is the user? Is the person going to be installing the system themselves, or paying to have the work done? What seems easy to the more technical and mechanical crowd here, may be outside the ability of the average person.

Since your considering the crystalyte I hope its alright if I include couple of basic questions I have.

How do you decide on the number of windings?

Presuming that the price is about equal or otherwise not an issue, what factors guide your choice between say a 406 & a 409?
I take it that the lower number means less back emf therefore higher top speed. From ebikes.ca:

If you take the same motor and wind it with twice the number of turns of copper, then k will double, so the motor will require twice the voltage to reach the same speed, but it will only need 1/2 the current to output a particular torque. Notice that the power input (V*I) for a given torque and speed is the same in both cases. The power lost in the copper is the same too, since twice the number of turns means twice the length at half the wire area, so 4 times the resistance. Power loss goes as I2R, so halving the current is exactly cancelled by a 4-fold increase in R. The important point here is that rewiring the motor for a different K value does _not_ change the motors fundamental performance in any way, provided that the same total amount of copper is used.

I know if you choose the model with the highest rpm rating then it won't have very much torque for hills. Other than that, I don't know how to differentiate between the models in the middle ground.
As Justin points out the winding doesn't alter the motors fundamental performance. Therefore isn't it preferable to go with the model that has the highest torque rating & get the speed back with higher voltage rather than the other way round? I notice most have gone in the middle of the pack with the 5304. Is that partly because of the volume sold it costs less & is more readily available than the other variants?

How do you choose the proper voltage/current controller?

Again leaving the price out of it because I understand why higher power components costs more.
The voltage rating makes some sense because of the low voltge cutoff that the controller is preset for.
As for current, why would you not go for highest amp model available?
The way I see it, it's worth the few extra bucks to get highest I/V controller because you can always adapt it to run lower.

So my conclusion is a 5305 with a 72V 40A contoller, or something approaching that if money is factored in. I know there must be someting wrong with this logic, I just don't see why. If this were true I'm sure someone else would have taken this route by now. Any guidance would be very much appreciated & think others may find useful as well.

I totally agree I use a 72v 35A controller at 48V 20A for the reliability and it can be easily adapted to different motors and batterys.
If you are capable of lowering the current limit to your battery capacity or lower then go with the highest voltage/Amperage controller you can get.
I believe this does waste some power but well worth the reliability

I think everything comes down to budget, speed and weight

As for the choice of winding a 408 has (higer torque) quicker excelleration from stopped than a 406 but the 406 has the higher eventual top speed so it depends on wheather you have to stop often imo.

So my conclusion is a 5305 with a 72V 40A contoller, or something approaching that if money is factored in. I know there must be someting wrong with this logic, I just don't see why. If this were true I'm sure someone else would have taken this route by now. Any guidance would be very much appreciated & think others may find useful as well.

Click to expand...

I see nothing amiss with this logic. I'm also of the opinion overall performance is best served by employing the highest-winding motor that can attain the desired top speed using the highest voltage possible within the constraints of battery budget, motor/controller specs, weight, and physical size. A 408/9/11/12 at 72 volts is preferable to a 406 at 48 volts. The only condition I might choose the 406/48v combo was if I absolutely could not afford, or fit on the frame, 72 volts worth of batteries.

That sheds some light on why there's so many winding options, the available payload or acreage for batteries. Particularly the sheer number of 1.x volt cells it takes to reach 48V let alone 72V. You can get up and running with a smaller pack if you go with a low wind motor & don't need volcano climbing capability. I see that now, thank you for that.

So I would anticipate that as lithium takes over with it's lower cell count to reach the same voltage level that the lower wind count motors may eventually be discontinued. Still I don't see the 5305 as being very popular but see quite a few people here with a 5303 & even a 5302 (Ypedal?).

You guys crack me up

Kind of like herding cats, as it doesn't take much effort for a thread to go off topic.

Thanks to all who have responded so far, I'm finding the replies very helpful.

Anyone else want to play: Answer the beginners question?

As a refresher:

1.)What parameters do you think are important to take into consideration when starting this process? IE building an e-bike to suit our personal preferences

2.)How would you (go about, approach) prioritizing these parameters?

I hope to paraphrase the responses if I can, then ask for some feedback before moving onto some more questions.

Cheers Greg

gwsaltspring said:

1.)What parameters do you think are important to take into consideration when starting this process? IE building an e-bike to suit our personal preferences

Click to expand...

The Primary parameter is your intentions. "whatcha guna do wit it?"
If you live in tebet, and you're going to be replacing your Yak to go up the mountians, Or in the tropics, and using it to haul virgins up the valcano to appease the gods, your needs are going to diffrent than if you live in, well, say.. Kansas.

gwsaltspring said:

2.)How would you (go about, approach) prioritizing these parameters?

Click to expand...

Well, first of all, check your shoe. if there's no Yak dung on the sole, you're probably not going to need a bike that can replace a yak.
Now check around your village for a stockpile of virgins. If you find some, let me know, but if you don't happen to see any, and the volcano gods haven't erupted for it, then you probably won't need to be hauling anything up a volcano either.
So you can rule out the slow but powerfull torque happy Mountian and volcano climbing motors.

Now look around you. Do you see anything? anything at all? You do? then you're not in Kansas. Had you been in kansas, you would have needed the fastest posable motor, for getting the hell out of Kansas, but if you live anywhere between the volcanos and kansas, you'll probably need a motor that falls in the mid range of power and speed.

Right then, on to the next part of the newbie questions.

Thanks DS, LOL

Cheers Greg