Hi all,

Well I'm about to embark on my first ebike build, I've spent weeks researching and using calculators and I'm more confused then before I began!

The one must have feature of the bike is a 50km (30 miles) minimum range with light pedaling.

I would like it to be able to travel between 25-30kmh (15-19mph) while not attracting attention so a small motor would be preferable.

I weigh 80kg (177lbs) and the terrain is virtually flat but with possible strong headwinds.

My limited knowledge has led me to the following and before i purchase them I wanted to know if they would meet the above requirements? I'm open to suggestions but limited to about $1000. These are all sourced from conhismotor.com

48V 350W Mini Motor
48V 25Ah LiFePO4
BMS 60A (120A at peak)

Thanks

You wouldnt need either 48 volts or 25 AH batteries to meet your criterias.
36 volt & around 12 AH { 12 is a little overkill even ** would surpass your goals, a 20 AH battery could use up your budget alone.
What is your doner bike like, are you interested in FWD or RWD .
My first build was a Conhis EBay special- not total junk but I would consider getting a quality motor & seperate { not in hub ** controller & doing a build from there, or spend a minium of 2 grand on factroy build .https://www.tdcm-motor.com heres a link for a quality water proof motor.

Welcome to the BikeForums gogreenpower,

Ok, the motor you're considering is, at best, probably only rated for about a 12-20 maximum amp draw imo. Average e-bike conversion kits run 36 or 48 volt batteries at about a max of 22 amps. Fortunately, most e-bike kits also come with controllers that limit the maximum amps that the motor can draw. For instance, the motor you mention is rated at 350 watts. Watts = Volts x Amps (i.e. 350 watts closely = 48 volts x 7.3 amps). This means that you'll reach the motor wattage rating while drawing just over 7 amps.

Meanwhile, it is very important that you, at the very least, take the following considerations when building an e-bike:

1. The battery must have both a "continuous" and a "maximum" discharge rate that falls within the draw specifications of the motor/ controller combination.

2. The motor should be rated for the voltage you intend to supply it with (some, but not all, bicycle hub motors can be "over-volted" to a some degree (i.e. a motor with a "36v" rating can often be used cautiously with a 48 volt battery).

Also keep in mind that most electric bicycle batteries have a built-in BMS that is specifically calibrated for the battery itself (i.e. there is, of course, little or no reason to use an additional BMS, if the battery you purchase already has one built-in).


Here's an e-bike calculator that might help with some of your calculations:

https://www.radiocontrolinfo.com/RCca...e.php?a=4#bike

Anyway, my guesstimate (partly using the above calc) is that you should achieve both the speed and the range you're looking for (minus the "headwind). The speed of this headwind could very well upset these "calculations" to a lessor or greater degree. However, this headwind issue could be somewhat "canceled out" if you have a similar "tailwind" going the other way. I'll also add that you might off-set this headwind if you have the option of pedaling harder.

I also agree with Scaliboy62 in that you could probably run a 36 volt battery with a 12-20 AH capacity rating.

Good luck with your build, and let us know how it turns out.

what are the prices for the tdcm motors? i couldnt find any. i understand motor quality but what major differences can a decent controller make over a kit controller?






ok, so found a kit with a 36v 350w motor with a 36v 20ah Lifepo4 (i wont go any less) battery.

by my reckoning there should be no issues with the supplied controller with a 23A/43V cut off, the battery with a 20A rated discharge current, instantaneous max of 60A and max continious of 40A. and with the motor drawing at maximum torque 16A??

The average 36v (12 cell) LifePo battery should fall "within" the following specifications: Voltage : 38.4V(working) 43.2V(peak) 30.0V (cut-off).

You wrote: "by my reckoning there should be no issues with the supplied controller with a 23A/43V cut off, the battery with a 20A rated discharge current, instantaneous max of 60A and max continuous of 40A. and with the motor drawing at maximum torque 16A??"

Can you post any links to the motor/controller/battery?

Otherwise, it sounds like your talking about a ("mini") 36v 350w (internal) geared hub motor. If so, then I reckon that this motor, depending on the load (weight/incline/wind etc), will draw maybe 5-7 amps under average conditions, with a maximum of about 12-18 amps under peak (5-10 second duration) loads. Note: you should, of course, avoid stalling your motor with the throttle on. Such "throttle on stalls" can damage the motor windings and/or the plastic internal gears (if equipped), etc.

My 36v geared hub motor has held up very well while drawing approximately 16-18 amps max (level ground, mild to medium winds, with a 210 lb. rider weight @ ~ 17mph/27Kph.

Below is a link with some general LifePo info:

https://www.cycle9.com/wp-content/upl...ery-manual.pdf

Motor

Controller

Battery

the reason i wanted the range is to get to and from work and i couldnt get the bike near any power points to charge it there, but I just came across some easily removable batteries, which i could charge at work ready for the trip home. I like the look of this one, it looks just like a water bottle, which suits the low key look im after, although at 10AH i dont know if that would do it, or this slightly different one, 12AH version.

The controller, motor, and batteries show in your links look to be well matched with each other.

The advantages of the 2nd and 3rd batteries are, of course, easier initial mounting and their built-in detachable/locking design. This should make for easier re-charging at work and better anti-theft security. These features might make this battery style the best choice in your case (the "detachable/locking" feature of my 36v LifePo battery has proven to be very practical over time).

Further info and/or questions might be:

1. Your estimated average speed (the system shown in your links should provide a (no-pedaling) top speed of 25-30kmh (~15-19mph).

2. Both the average and top speeds of the headwinds you expect to encounter, and for what distance.

3. Your average* (non-motorized) "light pedaling" speed?

4. How hard/fast* are you willing to pedal during peak loads (i.e. strong headwinds and/or running at or near 3/4 throttle).

* As determined with the use of a properly calibrated bicycle computer or suitable GPS device, etc.

The info might better help determine your best battery/controller/motor choice.

Ok thanks for the help so far, I have a couple more question before I purchase my gear.

1. What would be the major differences from running all 36V gear (36V 350W motor, 36V 20AH Li-ion) to running all 48v gear (48V 350W motor, 48V 20AH Li-ion) at full throttle?

is it just a top speed gain or is there a distance gain as well?


2. If I ran the afore mentioned 48V system at 3/4 throttle, would it be true to say that it would be roughly the same speed as a 36V system at full throttle, while gaining a 25% extra in the range stakes?

or am I being far to simplistic in my thinking?

Q 1. Generally speaking, and with all things being equal, an increase in voltage = an increase in speed, while an increase in amps = an increase in torque.

Various "real world" findings in regard to "36V vs 48V" range/distance performance tend to bounce "back and forth" between the two (all else being equal). Either way, the difference between the two is probably negligible as long as the individual motor efficiency ratings remain nearly equal (motor efficiency is, of course, very important in regard to performance). However, I feel that operator "technique" often has a larger impact on range than will the 12 volt difference between a 36 and a 48v system (all else being equal).

Q 2. This is a very good question. Much of the controversy over "36 vs 48v range", as mentioned above, seems to be born from this "throttle position" theory. Some say that yes, slightly better range can be achieved with careful throttle use on a 48v system. Others often counter this theory by stating "the more power you have, the more power you'll use."

I would, at this point, base your "36 or 48v" choice more on headwind and just how much, and for how long, you expect to encounter it. Meanwhile, you seem to be settled on running a 20AH battery capacity (which imo is a good idea, if you're expecting prolonged moderate headwinds of more than 15 mph). My general thoughts on ebike range and power are that it's probably better to have a little too much than it is to not have enough. Like you mention, you can always use less throttle...

OK, so after weeks of mental anguish I ended up going for a 36v system with a 20ah li-ion removable battery, the donor bike has turned up, accessories are in the post, now waiting for it all to arrive.


I'll post some before and after pics once I have everything.


And thanks for all the help.

Definitely looking forward to reading/seeing more about your build. Btw, if anyone asks, tell them you're running a "250 watt system" (wink, wink). You might even consider putting a small "250 watt max" sticker on the hub motor just in case the authorities become interested in your ebike (just tell really nosy types that you have a "36 volt 6.5 amp max" system). It's also a good idea to "pedal all the time" (except, of course, when you're braking/stopping/coasting).


Have a good holiday weekend.