Conversion to eBike

  • This page is about the conversion of a set of two ATB's to eBikes or ATEB's.
  • The bikes are described here: Review ATB low cost high fun.

  • This project will become fun (I hope).
  • I was really not informed about ebikes at all before.
    • This page should give people planning something similar a basic understanding.
    • It will take some additional hours to prepare your own project - unless you go this way...

What we want

It turns out that "what we want" is different from "what we get", read on.

  • A cost effective solution. Two parts are not cheap: the battery and the ordered wheel assembly.
  • Rear drive, keeping existing brake disc and spur functionality.
    • Actually, front drive is easier to service and for very low power applications (equals low weight) an option.
  • Enough power for terrain, steep hills, 500W is fine, brush-less. However, a powerful motor (1500W) has a longer lifetime.
  • Limited total weight gain. That one is hard to achieve, but not an excuse to just add unlimited kilograms.
  • A battery with loose 18650 elements, powerful for a proper range.
  • Easy conversion. But tinkering will be necessary from time to time.
  • Proper quality. Time will tell.
  • Support when pedalling but also power without pedalling.
    • This is not an excuse for irresponsible behaviour, when driving more than 20 km/h:
      • Technical defects like tire punctures or a breaking fork become life threatening.
      • Fellow road users do not expect speeding ebikers so please, cram this in your head: cyclists are vulnerable.
    • It is just very relaxed!

Battery

Why make your own battery pack? The cheap packs have lousy cells, the ones with proper cells are very expensive, even on aliexpress.

Buying battery cells on the net is dangerous, chances are that you get imitation. Too good to be true? Don't buy!

Go for 18650 form factor. Batteries equal weight. So you want batteries with high capacity, more than 3000 mAh. After searching for a proper size I ended up with a great deal: 110 cells for $344. Form factor 18650, brand LG, type F1L, capacity per battery cell ~3400mAh.

Choosing a voltage means going for 48V or 36V. I chose 48V which seems to be the trend (2017).

Things to consider

  • 18650 cells are dangerous, DON'T UNDERESTIMATE! Shorting can result in explosions. Work with batteries with safety in your mind.
  • Wh (Watts during an hour) are more interesting than mAh (milliamperes during an hour).
    • A cell of 3.7 V and 3400 mAh does have an amount of energy of 3.7 * 3400 / 1000 = 12.6 Wh. This means that this cell can deliver 12.6 Watt during an hour. Let's consider two cells, totalling 25.2 Wh:
      • In series two cells are still 3400 mAh, but 7.4V.
      • Parallel two cells are 6800 mAh, and only 3.7V.
    • So, concluding, the amount of mAh is only interesting when you know the voltage.
    • When you build a battery of 48 V, based on 3400 mAh cells, with 52 cells, the amount of Wh is 3.7 * 3400 / 1000 * 52 = 654 Wh, not bad!
      • Calculating backwards, this equals a 48 V battery of 654 Wh / 48 V = 13.6 Ah (Amperes for an hour), or,
      • this also equals a 36 V battery of 654 Wh / 36 V = 18.2 Ah.
      • To give you an idea, it also equals a 12 V car battery of 54 Ah.
      • And that is the reason to stop thinking in Ampere-hours and always calculate Watt-hours.
  • About weight: a cell is <50 grams. 52 cells are ~2.5 kg without housing and BMS. Not that much.

  • A word about nickel conductors:
    • Take care that you use pure nickel and not nickel plated metal.
    • About "how much" nickel: 1mm2 is okay for 5 Ampere, 7.5 A as max, but 10 A gets warm.
      • A strip of 7 mm * 0.15 mm = ~1 mm2.
      • A 1.5 kW motor on ~50 V is peaking at 30 A. So you need 6 mm2 conductors, at least 4 mm2 if peaks are very short.
    • It may help you to draw arrows on nickel strips to see how currents are divide over strips, in order to find weak spots.
    • If you need more conductivity, just layer up extra nickel.
    • Nickel is not used primary used because of it conductivity, that is a common misunderstanding. Resistance in ohm.m: Copper = 1.68*10−8, Aluminium = 2.65*10−8, Nickel = 6.99*10−8 (Iron = 9.71*10−8, Steel (carbon) = 14.3*10−8, Steel (stainless) = 69*10−8).

Getting 48V

  • If you chain 13 cells of 3.7V, you get 48.1V
  • So if you put 4 chains parallel you have still 48V, but more capacity.
  • Each 4 cell block is connected, see below.
  • This configuration is abbreviated as 13s4p.

48v-battery-block.svg

Multinationals Suck

I bought a really nice set of 110 batteries, enough for two bikes. But multinationals think they can form cartels for price-fixing, don't pay taxes and believe they are obliqued to terrorize competition. This is a text from a supplier:

Due to LG/sanyo/panasonic/ sony/samsung/sony is International brand ,We'll use blue shrink wrap to cover it to avoid custom issue
Like this sample photo .Please find enclose
After get cells ,please remove blue shrinkwrap, that's all

Yes, it gets that bad! Politicians, read this.

Battery Management System (BMS)

Construction

A solution that is easy to service means: No spot welding of nickel strips on batteries. By the way, batteries with pre welded strips have similar prices as without. They can be used in several battery containers.

The promising solution: http://vruzend.com/ This system contains end caps for individual cells with nuts. Easy, not expensive. However it is a brand new product (2017) and I expect it to have some start problems. I love this system but it looks like it is not available right now. This means I have to think of a different solution...

Tinker part... HPL plates with holes for compression springs, nickel strips between cell and spring (only one side), ceel standing between plates, plates pulled together.

Drive chain

On Aliexpress.com, there are not many suppliers of complete wheel sets. I ended up with three options, one 1500 W from Conhismotor and two from Pasion E Bike, 1500 and 500 W. The 500 W solution was a Bafang motor. What kept me away from it was the small size in relation to heat production. There are several stories about this on the net. So the final solution for choosing a 1500 W assembly was based on price and wheelsize. Both directed me to Pasion E bike on details. The price difference was very small and in my case, a 29" wheel was offered. The difference between 700c and 29" is merely the width of the rim, 29" is bit larger while rim diameters match.

Pasion contacted me and proposed to deliver from Germany to the Netherlands. Great news, no extra VAT and import duty's, paying ~100 euro's less. It took only 5 working days to receive all. General impression: More than okay, even a cutlery set included - no kidding!

About Tyres

For now I am going to use the included tyre, it is certainly not bad, a Maxxis Page, 29"*2.1, max pessure 4.5 Atm, 65 psi. Current tyres: 29"*2.35 for mud processing. Not sure what the future brings, I like tyres like Schwalbe Marathon because profile on a straight road is not interrupted. Anti leak features are nice too. On the other hand, a can of "Cyclon Tyre Repair Gel" or something else is always an option. Books are written on tyres... More later... maybe.

Electronics

Assembly

Bookkeeping

1 dollar equals 0.86 euro...

Description

Price

Batteries 3400 Ah, a set of 110 pcs for 2 bikes, per bike

148

Wheel assembly complete, brake sensors hydraulic: PASION E BIKE 48V 1500W Conversion Kits for 29" Rear Wheel

347

BMS charge, discharge = 15A, 50A

16

54.6V 4A Lithium Li-ion Battery Charger

22

Multiple GX16 connectors

10

Vruzend battery system

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