50cc equivalent motor setup help.

Hi, my first post and fist steps in to the world of ebike/moped-ing.
Forgive my ignorance and that did not sieve through the whole forum for double posts, a whole forum of information can be intimidating when you take your first steps in it.
As a european/dutch citizen, I have been very familiar with bikes and mopeds,
The whole e-bike thing is working quite well here, the moped side not really, you see the occasional scooter, but I'm not interested in those stunted dwarfish things
Like I said, I am a moped enthousiast , own a fully restored kreidler florett (1968), and had my fair share of hondas in my teens.
I own a design and construction company, (furniture and the likes), so welding and electronics can be done.

I would like to build (from scratch) an E-moped (so spoked wheels, large tires, etc.), legality will be an issue, but not in this moment of time.
I would like to have moped speed 45kmh.
My question:
What would you guys recommend for a basic rear wheel setup (motor, battery, controllers)to get an e-moped up to the 45kmh range with +-26" wheels, no pedal assist.

50cc is about 3 horsepower right, so just your basic 2500 watt motor should do the trick. Motors are rated in RPM per volt so if you buy a 10 kv motor and run it at 48 volts you will have a tire that is spinning at 480 rpm because 10 times 48 = 480.

You can use a rc drive calculator like this one to determine what that rpm would mean as far as top speed will be at any given tire size/motor kv.

Here's the catch, higher kv motors have produce more watts per motor weight so you can get a lighter weight motor with the exact same power if you put a big gear reduction on it or use tiny wheels. Like you can use little 12 inch wheels instead of 26 inch wheels and save a lot of money and motor weight.

All that being said if you use 48 volts and 26 inch rims like you were saying you were wanting, you will need your typical 9-12 KV hub motor rated for about 3 kilowatts and a speed controller rated for about 70-90 amps. You will want something like xt-90 antispark connectors soldered to your battery and speed controller so you can connect the two together. Your battery will need to be something in the ballpark of at least 40 amp hours to get any kind of range.

In Texas, and some other states, a "Moped" can have no more than 2 horsepower. That's 1500 watts peak (750 watts = 1 horse power), and good for ~55kph
An electric motor is rated by it's nominal wattage, not it's peak wattage. So a 500 watt motor could easily match a 50cc in speed, while also producing many times more torque. But you'll probably want a bigger motor.

Your goals for a 50cc replacement are easy. The battery, that another issue.

You said you wanted "up to" 45 km range, but whats the minimum range you would accept? See, electric motors run slow and with soft starts are super efficient. a small battery used with slow speeds and a soft touch on the throttle might get you 45km, but the same battery might be drained on a single run around the block if you ride it hard and fast. With an electric bike, you need to build them to meet your minimum standard. That is, the range you need to be able to get every single ride.

The way we figure that is to say something like "I need to get to work 11km away and back and maintain 32km for the ride whole ride". From that, we can calculate the size battery you will need to ensure the bike can always make it with a comfortable reserve. In this case, a 22km round trip at 32 kph would need a minimum 440 watt hour battery. That translates to a 48v 9.2 Amp hour battery.
With a battery that size, you will often be able to go much further, but you should always be able to go 22km at that speed.

The math works out to 22 watt hours of battery capacity needed per kilometer at 32 kph.
And if you didn't already know, Volts X Amp hours = Watt hours.

As to what motor and battery to get and from where, that depends on where in the world you are.

thank you both for all the insightful information, I'm taking it all in
Dutch (the netherlands, holland if you must) law states that an electric moped (45kmh speed limit with a 5km overhead, so legally absolute maximum 50kmh) can have an electric motor with a nominal maximum continuous power output of 4 KW (hope I translated this correctly).

Since we have a lot of bike lanes combined with moped use here, the maximum speed is often 30kmh here, so I,m taking your battery comments to heart.

That rating of a 50cc moped as a '3hp,' a 80cc lawnmower as '5hp,' that's a mathematical model based on the displacement, the actual performance is noticeably less. More typical of a moped is about 1.6hp/1,200w. So that 1,500w motor in Texas should do you just fine. Though I'd like that 4kw better.

So let's work at your 30kh as 1,185,000 INCHES in an hour. How many times do you want that wheel to go around in an hour to match that speed? Would a 20 inch mean 18,840? Meaning 314/minute? If the motor was to be running at 3,000rpm at that speed, what gear ratio do you need? Does an 11 tooth pinon on the motor with a 105 tooth sprocket on the wheel sound good?

A 26 inch wheel drops to perhaps 14,520 revolutions in an hour, 242 per minute. That 11 tooth pinion would need to be matched with a 135 tooth sprocket. If you use that same 105 tooth as the 20 inch wheel, you get up more about 40kh, though the acceleration isn't as good.

(fellow dutch here)

i currently have both a blue and yellow plate moped (25 and 50kph) and they both run with a 1.5kw motor.
1.5 is usually plenty, you can boost it up to 2.5+kW wich will outaccelerate almost everyone. (more is not recommended)

gettin a battery that can deliver a solid 40~60 amps is needed no matter the capacity.
i went all out and build a 87Ah battery that gives me 180km range on the 25kph mode and 120 or so on 50kph.
but that was a 1000+ euro investment so if you don't need insane range i would oopt for a smaller battery.


ps: just buy a secondhad electric with busted batteries on marktplaats for 200 euro and build your own battery (or commision someone) for something like 500 euro, replace the cheap chinese controller for a decent one wich you can program yourself and for less then a 1000 euro's you have a moped that will last you for years.

flippy said:

i currently have both a blue and yellow plate moped (25 and 50kph) and they both run with a 1.5kw motor.

Click to expand...

Hi fellow dutchman!
Thanks for the information
I'm very curious as to what motor you use.

just the stock hub motor that was supplied with the mopeds.

currently i am rebuilding the fast one to take the battery from the (older) slow one as the battery boxes are slightly differently welded (due to chinese cheapness) so i am making my own aluminium one for both and also solving the water ingress problem of the battery box.
when that one works properly i will take apart the motor of the slow one and probably rewire it for more torque and make it more of a project while the missus can drive the fast one to work every day.

i suspect that if you have a motor to spare (thay are all basically the same) and you do some mods and rewire work and replace the controller and have a capable battery you can make a really ludicrously fast accelerating moped that still complies to all laws.
but that said: the slow one limited to 30kph is capable of breaking the dreaded rolling bench as it accelerates so fast it instantly breaks the belt of the rollers inside the bench :lol:

The 4kg mid wind 500w bpm motor using a 3.5kg dolphin pack with integrated 20A controller will do 44.4kmh on the flat without over heating. The 12ah pack will last 25km at that speed. At 25kmh you will get 65k. You could always carry a spare for when that's not enough.

just build a bigger fixed battery. cheaper and more wears out a lot less. and where do you plan to keep a 12Ah battery as a spare?

I don't believe in carrying more battery than needed. They last years anyway. Here we have the longest average commute in Europe with a 25kmh round trip. Which could be done at full power with the above.

I don't know where he would keep it. He hasn't built the bike yet. I'm showing him a motor that could complete his task though, with performance expectations from a specific sized battery.

Do you have a motor suggestion he can actually use?

we already had some back and forth with PM's. he has a 3kW hub motor he can buy from someone.
otherwise a decently sized regular motor setup can be used to replace the existing motor and keep the chain drive. plenty of those on the market.

regarding battery size:

round trip is something you want to have spare power for. forgetting to charge or not able to charge can cause a lot of problems you can solve very simple during construction and give you a much more pleasant experience of the years. constantly worrying if you can make it is not very comforting.
going from a single 15Ah to a single 30Ah for example is also a lot cheaper then getting a second 15Ah battery and gives you the abillity to have 2 round trips for example
when the battery starts to wear you lose range and losing 20% on a 15Ah battery will hit you much harder then 20% on a 30Ah battery and will ensure that you can make the trip with capacity to spare.
bigger capacity also reduces wear and gives you bigger overall lifespan and not to mention more power if you so desire on a later stage. (like we all do)

Battery placement will not be a problem, since I plan on building my own frame, this project for me is all about exploring the possibilities and limits of building my own moped, meijsmotorman has successfully got a relatively small production of retro mopeds through the dutch/eu law swamp, since I'm quite good at building stuff and own a design an production company, it is relatively easy to build and fabricate a frame, which Ironically is more easy to get street legal than a bicycle with a motor slapped on.
I had some great answers from the RDW (The dutch institute for control of road using vehicles, papers and such.) They gave me answers and information (to my surprise) how to go about and what to comply to. One can make a road legal frame, it will be legal once approved by the RDW and it will get stamped "zelfbouw" which means own fabrication.
You have to supply the frame unpainted for inspection, have a material, motor numbers etc and weld list. But that is do-able.
What I'm interested in and why I'm thanking you all for the avalanche of information, is a simple setup that will work will give me the desired 45kmh and which in time maybe is replicable, which I can use for testing with minimal hassle, and is flexible enough to try different setups, hence the rear wheel motor on 26" or 24" rims, lots of tire options and lots of mountainbike gear to chose from, no chain or drivetrain makes the construction that much easier, battery should go where a tank ought to be, moto and mountainbike forks are there in abundance as well as headsets, stems, etc.
I'm not interested in off road use, I want road use.
Blablabla.

After some considerable time on the internet.. and on this forum.
i've decided to shop local and new, so it is tax deductible for me.
The best options locally are a magic pie 5 1000w rear motor, laced in a 26" wheel.
http://www.devi-motion.com/webshop/e-bike-kit/p-1/D1000778--magic-pie-5--kit-48v-1000w-26%22-front.html
Also to my surprise there are a lot of 18650 cell supplier in the neighborhood (20km away).
Some stock Panasonic 3400 cells already in parallel
http://www.batterijservice.nl/en/pack-8-panasonic-inr18650b-unprotected.html
This gives me a nice starting setup. (still checking if these specific panasonics are giving me enough continuous drain)

Now I still need to find the correct BMS and charger for this setup, I could use some help with that, where to find a good quality bms, either in europe, or via postage, it's still a bit muddled, but I'm getting there
Should be a 13s 48v, still a bit unsure about the amps, what determines the amps you need; the continuous current of the motor?

i would not reccommend that setup with those 7 cell pre made sets. you need something much stronger then the (copper?) tabs alone.
you need to have the cells spaced apart slightly and have them in a holder. the copper will move and crack after a while as it hardens due to viberation. having a holder will reduce any load on the tabs to zero and prevent potential fireworks when a cell dies or a tab cracks.

you can get 5x5 holders so you can make big packs really strong for cheap on ebay.

here is a pic of one of 3 blocks i have made before i put the nickel strips on them:


you can also get the cells for even cheaper here:

http://www.nkon.nl/rechargeable/18650-size/panasonic-ncr18650b-made-in-japan.html

highly recommended celler/seller.

also: that 1000W motor is WAY too wimpy you need 2500 at least in order to get along with traffic. that results in 60~80 amps during acceleration depending on the phase amps.

starting to build my frame, all square tubing.

finally having some components to build my motor setup I have a few questions remaining:
I currently have a battery: 48v 10p 13s built out of panasonic batteries pack 33.5Ah, maximum continuous drain 67A
The bms on this should do 90A
my Kelly Kls-s controller has limit of 300a,
My Crystalyte h4080 motor has a maximum current of 50A

My questions:
-how many amps should my battery fuse be?
-How many amps should my contactor be? (I will build a precharge capacitor in the whole)

Projects updates are due (am at my third iteration of the frame as of current)

Because people tend to like pictures, and this took me a while to find; include is a picture of the mini xlr plug wiring for the hal sensors of the crystalyte motor, wire colors match the kelly controller.

the contactor needs a precharge resistor. putting in a capacitor is the opposite from what you need to do.
a 50A contactor is enough. you will not swich under power so the contactor will not wear a lot.
a 120~150A fuse would be best. the battery is capable of reaching that current and allows the BMS to trigger at 90~100A without blowing the fuse.

flippy said:

the contactor needs a precharge resistor. putting in a capacitor is the opposite from what you need to do.

Click to expand...

Thanks again Flippy, yeah resistor of course.

I now have here a 50v/50a continuous 75a peak switch, can this replace the contactor and start switch?

sjofels said:

I now have here a 50v/50a continuous 75a peak switch, can this replace the contactor and start switch?

Click to expand...

Hi there, this switch cannot replace a contactor I'm afraid. A contactor is designed to switch in a controlled environment so that the sparks are unable to oxidise. A contactor will also be controlled by your BMS so that it can safety disconnect your battery in whatever conditions you deem appropriate. But you will need at least under/over voltage protection and if you can, over temp protection.

You should have the switch as well though. If you google precharge wiring it's dead simple, you should just need a biggish resistor and a diode, easy peasy wiring too. It's just to avoid a big surge while your controller capacitors are charging.

Hope this helps

his BMS has internal switching. no contactor needed.
the green resistor supplied with the controller needs to be put over the contacts of the switch in order to keep the caps charged. not using the resistor will instantly destroy the controller.
personally i would not bother with the swich or a contactor on a bike and just have a 150A slow blow fuse after the BMS as a secondary protection.

I now have a 140a 50v boat battery automatic fuse, water resistant, which is a bonus.
Have been working on the frame and battery compartment a little more.

This compartment forms the 3rd leg of the frame main triangle, more attachment points to the frame will be added.
Pictures:

Hi another question : can I use 2x6mm2 wire instead of one 10mm2 wire?

defenetly not recommended as any difference in resisitance would cause one wire to carry the brunt of the current, lowering it's resistance and taking all the current and burning out both eventually.

if you use high grade copper wire you can probably get away with 8mm2 but i would not use smaller if you want to pull some serious currents.

wire distance is very short, you should try hooking up the battery terminals directly to the controller wires with the supplied connectors.