Construction of an electronics box

Construction of an electronics box

BAG OR BOX?

IS IT WORTH GOING TO EASY?

If not the most difficult, then certainly the most labor-intensive stage when assembling an electric bicycle is the construction of a battery and electronics box. Of course, you can go easy, like I did in my first project, and use a textile bag mounted in the triangle of the bicycle frame. At first glance, this seems like a cool and aesthetic solution. Unfortunately, realities quickly verify the idea as good only for a moment. While it looks really neat and does not arouse much interest in bystanders, it turns out that such a bag has, unfortunately, several key disadvantages. The choice of solid bags is limited, and when we hit a nice model, we won’t fit too much into such a bag. In my case, the bag fits 78 cells of size 18650 (13S6P), 48V 18A controller, 5v power supply, cables and charging socket. I will not stuff more if I wanted to. This set weighs about 4 kg and this bag was certainly not designed for such a load. Once, I even managed to break the attachment strap when I drove into a larger hole on a dirt road. The most glaring fact for me is that the textile clamps fastening the bag to the frame and the bag itself at the point of contact with varnish can scratch all the paint into bare metal. At the end I leave the questionable watertightness of the bag itself in case of stronger rainfall.

I prefer solid box

In my subsequent projects it was certain that I would not use a textile bag anymore. I decided to make a box of polyester resin laminate and fiberglass mats. On thematic forums you can read a lot about how people make containers from this material. There are as many methods and formulas as there are makers. Most often, however, visually such boxes are very “heavy and rough” and I did not like them. I will not post pictures of boxes that I do not like, because their authors might feel offended, and it is not my goal to insult someone. I hope that everyone who reads my scribbles knows what I mean by writing “heavy and rough”.

I set a goal that my boxes must optically match the bicycle based on a regular frame. It is known that such a frame is made of pipes or more modern hydro-molded profiles. The cross-sections of such sections are max 50mm, and our box has the widest point around 130mm (you can’t do more because the cranks would hook the edges of the box). If I put in a nearly rectangular box, there would be a significant change in width around the frame tubes, which would not look good to me. Therefore, I decided to add bevels, running parallel to each of the tubes of the triangle of the frame. This solution, unfortunately, reduces the space inside the box, which we have to use for battery and electronics, but it fits much neatly with the entire bike. Practice shows that despite the reduced capacity of the box, you can easily stuff the 45A controller and about 1200Wh battery, which in an e-bike design based on a classic frame is sufficient to cover a distance of about 100km.

Let's go design!

Therefore, I have assumptions, it’s time to begin the project that will be supported by 3D CAD software.

1. I start by measuring the arms of the triangle formed by the frame. At this stage, you can help by cutting out a cardboard template, fitted to the frame and measuring its sides. I measure the dimensions inside the frame.

2. From the middle of the frame, I take a photo of the whole bike, which I then place in the software. Using measurements and photo as a background I created the rest of the project.

3. At the moment, I am mainly guided by visual aspects and I try to do everything to make it as pleasant as possible. I try to remember to leave about 10mm of space around the container, so as not to bother with its subsequent installation. At the first design of the laminated box – for “Pienius bike”, unfortunately I left too little space and I had a problem with the seal connecting both halves. Under the upper tube, the derailleur cables and the brake hose run and are almost in contact with the box. In the second design of the resin container for “Minion bike” I have already corrected it.

4. When theoretically everything looks OK, I proceed to check what I can fit into the modeled box. At this stage, you can still make small adjustments to the project, which can result in adding the additional battery section in or take one out.

Time to roll up your sleeves 🙂

Method one

1. Okay, the battery and controller are in the box, it’s time to finish the project and start construction. Theoretically, I made both boxes using the same method – by laminating. However, the devil is in the details. The „Pienius bike” box was made first and then I came up with the idea that I would make the mold based on inside dimensions for it, and after thar i will stick everything with resin and fiberglass mat. I did a template made of cardboard and adhesive tape. Such 3D PUZZLE.

Horror

2. I think the devil in its own person was sitting on both my shoulders and told me to follow this path. In so far as assembling the mold and laminating did not cause any major problems, but finishing this SHAPELESS THING (that looked like ham/gammon) that i laminated, required countless hours (at least 10 hours) and many sand papers for an orbital sander. After the this part, my garage was suitable for thorough cleaning. The foil I hung up to separate the dirty part from the rest did not help. Dust from grinding laminate settled everywhere, in every smallest, furthest, smallest corner of the room was a minimum half a millimeter layer of fine dust! Dust that you couldn’t just sweep away. Everything with Ania cleaned the next X hours and even the walls had to be wet cleaned … Anyway, see for yourself.

3. After initial sanding, I applied a layer of colored gelcoat to fill larger holes and sand again. Theoretically, this was to result in a navy blue substrate, however, I sanded a lot of it again, and I lost my nerve for the next layers of gelcoat.

4. After grinding, I halved the whole with a mini-grinder with a cutting disc. I tried to cut on a drawn line, but it is impossible to get two identical halves with this method. Fortunately, the whole is connected by a rubber gasket, which will mask the larger shortcomings of the cutting line. Somehow it all managed to bring order to order. After the first adjustments, it turned out that even it begins to fit.

5. In the workshop where I used to work, I managed to add some mounting plates to the box. Made of 1.5mm thick sheet metal with M5 welded nut and several spacers. Then I fixed it in the place for a water bottle. It takes a little bit of effort to adjust it all, but in the end it all worked out. While fitting the box to the bicycle frame, I roughly marked a point for holes, and then I first drill with a small drill d3, and then drilled to d6, taking care that the laminate did not tear. Then i adjusted the box on the mounting plates. At the top of the box I used a bracket printed on a 3D printer fitted to the bicycle frame.

6. It remains to fill the shortcomings that remained and paint in the target color. Unfortunately, I was not able to finish everything to high aesthetic level, my impatient nature won. It would be good to fill everything up twice, because after painting you can still see the irregularities of the laminate. However, I already wanted to put it all together so left it as it turned out. It’s time for ready assembly and adjustment of the rest of the equipment and for affixing the finishing labels of the whole design – laser cut from 1.5 mm thick aluminum sheet. I ordered colorful acrylic sprays and colorless matt lacquer at a popular auction site, choosing similar colors to the bicycle frame.

Time for the second method!

As they say “The first pancake is always spoiled”. Having learned all the hardships associated with laminating resin on the interior mold of the box for “Pieniuś bike”, I came to my senses.

1. I made the second box, this time for “Minion bike” by laminating the two halves separately (unfortunately I don’t have photos from the whole process …). Left and right forms, this time mapping the outer surfaces of the box, I also made of cardboard, of course, all previously modeling in CAD 3D. Corners with a radius I glued with pulp available in every shop with artistic products. I smoothed the exact radius in the cellulose mass with a disc, printed on a 3D printer, with a diameter corresponding to the corners.

2. This time sanding after lamination was just a cosmetic. In an hour I sanded both halves. In several places, you also had to use putty to level the surface on which there were cavities from air bubbles. The contact surface of the two halves was ground by sticking sheets of sandpaper on the table top and the whole half of the box was scrubbed on this surface with sandpaper. I consider such a laminating solution with a projection in the form of external planes to be recommended.

3. The box colors have also been chosen according to bicycle frame and ordered acrylic sprays. In addition, I also bought a colorless spray with a structure effect that is painted first. It gives the entire surface a sandblasted structure. This eliminates the visual effects of laminate unevenness and the whole looks very aesthetically pleasing. Finally, all the electronics had to be adjusted to the inside of the container again, and finally secured everything with mounting foam.

It's good 😀

I consider the goal almost achieved. It looks good, houses the equipment that I need. The mounting foam holds all the components inside as it should, and thousands of kilometers after verses are not able to loosen anything. Such a box can be opened if necessary by unscrewing one half (it is best to rethink the arrangement of components in this regard). The only drawback is the problematic fitting of the two halves relative to each other – even on seals. It is difficult to press perfectly so that there is a tight connection. Unfortunately, there is a risk that in unfavorable weather conditions water will get into the box through not tight connections at the top of the box. To minimize this risk at the joint, on the gasket, I additionally stick black insulating tape.

Bicycles with such boxes look really great. I highly recommend this solution to everyone, as the final e-bike based on a regular frame, with powers up to 3kW and a range of about 100km. If someone needs more (range or power), then better go straight to the custom frame.

Pieniuś i Minion
PIENIUŚ left / MINION right

We have also third way!

30.08.2018 – we have and third way. But what I will describe, you just have to watch it. I say we have, because it was created with the participation of Radek, from the TABA ON BIKE channel. The largest electric ebike channel in Poland.

Stay tuned 😊 :

FB group e-BIKEL-owcy technically about electric vehicles

Group e-BIKEK-owcy

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e-Bikes in the light of the law

e-BIKes IN THE LIGHT OF THE LAW

not everything is allowed

Before you start your adventure in the e-bike world, you must know that as a constructor (or rider in principle) you are not allowed to do everything. The law restricts and very strictly legal riding of electric bicycles.

That’s why it’s worth learning the definition of an e-bike that looks something like this:

“A vehicle with a width not exceeding 0.9 m moved by the muscular strength of a person riding this vehicle; the bicycle may be equipped with an auxiliary electric drive driven by pedal pressure, powered by a voltage of not more than 48 V with a rated continuous power of not more than 250 W, whose power output gradually decreases and drops to zero after exceeding 25 km/h.”

Road - offroad mode

What electric bicycle ride is legal?

The above law, in relation to riding an electric bike, clearly says (this applies to Poland):

  • The bike can only support us up to 25km/h. Above this speed, we are dependent only on the strength of our own muscles. To think that without assistance, with wind and downhill, you can accelerate even to 35 – 40km/h). Hmmm there would be a ticket for this 😉?
  • Riding on the throttle grip is prohibited. No matter whether thumb or other. So what remains for us is the motorbike, of course, that you have age-appropriate permits 😜.
  • Watts no more than 250 W.
  • Remember – voltage not higher than 48 V.

You may have problems

If you do not comply with any part of the above provisions, you may have problems.

[At least when traveling on public roads and during possible inspections 🙂 ]

Limit the power of your e-bike

- MPe computer

Take care of your and others’ safety and limit the power of your electric vehicle. All this in 2 seconds. See the MPe computer offer in our store:

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Li-ion battery – testing

LI-ION BATTERY – TESTING

Testing the battery

is it necessary?

YES !

The lithium-ion battery requires performance checking right after construction and from time to time during operation.

Why should you test

Li-ION batteries?

The characteristics of li-ion cell operation and their ease of damage require adequate battery protection, e.g. by using a BMS (Battery Management System). This device, like any other, can break down or have a factory defect that can damage the battery or cause a fire! Therefore, it is necessary to check the operation of the basic security functions.

What to check?

Lithium-ion cells don’t like:

  • overcharge – above 4.25V

  • excessive discharge – below 2.5V (3V is used because very little capacity remains between 3V and 2.5V, and it is safer)

  • excessive temperature – above 65 degrees Celsius

In addition, it’s worth knowing what capacity our battery has. As you know, over time and subsequent cycles of charging and discharging our battery will have a smaller capacity, and at some point it may turn out to be insufficient.

How to do it the easiest way?

On this blog I deal with the issue of electric bicycles, which is why I will be referring to them. The battery can be tested directly in the bike with proper precautions and frequent voltage control with a meter. During charging, we check the voltage of each section on the BMS plug and make sure that none of them overcharges above 4.25V. Finally, BMS must disconnect the charger when one of the sections reaches a dangerously high level of charge

Next, while driving, every few kilometers we stop and check the voltage on each section and when we reach the level of approx. 3.3V / section, we compact the measurement frequency to check if BMS cuts off the power in the area of 3V / section.

You can also try to remove one of the wires from the BMS plug. This simulates a sudden drop in voltage on the battery section and at this time the voltage should not go to the motor controller.

Most BMSs have thermal protection, which should be attached directly to the battery cell. If this is not the case, we can add our own thermostatic fuse and plug it into, for example, the controller’s e-lock or brake circuit. After exceeding the maximum temperature, the fuse will cut off the controller power supply, and thus the current consumption from the cells, and thus prevent further heating by discharging.

How do I test the battery?

Unfortunately, testing while cycling takes a long time, requires our constant commitment and is unpleasant. You can test one battery like that, but when we make more bikes / batteries, we must go a step further. I decided to build my own discharg station. Thanks to this, I can test the battery without leaving my home. In addition, the discharger is useful when you want to discharge the battery for some purpose, and do not want to go cycling (e.g. to store the bike during the winter or when we perform maintenance charging to level the battery section).

The discharger controller saves on the SD card the measurement results from which a discharge graph can be generated. It is possible to monitor the temperature of four sensors, and for each one you can set a different discharge disconnection threshold. The testing process is also interrupted when the packet reaches a voltage below the number of sections * 2.5V (BMS should cut off the battery earlier).

I built my discharger based on:

  • Arduino Nano micro-controller with display and SD card modules
  • 30A ACS712 current sensor
  • power resistors 50W 4.7Ohm (25 pcs 5s5p) total 1250W
  • switch on MOSFET (currently I have used IRF 3205, but its max voltage is 55V, therefore it is suitable for max 13S package. I plan to change the transistor to be able to test packages above 13S. I will update this description when I find the right transistor and test it)

The construction cost was about PLN 200 (~$50).

I have a schematic diagram, PCB design and arduino code, but it is all in a very early beta version, so for now I will not put them here.

Below is a video in which I show the process of testing the battery, using a discharger.

(Polish version)

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Li-ion battery – assembly process

LI-ION BATTERY - ASSEMBLY PROCESS

Spot welding yourself?

Spot welding of batteries for an electric bike is quite an ardous task. However, it pays back to do it on your own, because on this element we can save the most money. For example, the battery, which spot welding I will present, cost me around PLN 450 (~$115). Its capacity is about 570Wh (48V 13S6P, 12Ah), which is enough to cover about 50-70km by bike with an 18A controller (max 850W).

How to do it

and what will we need?

I will show you the whole process in the video below. Also, I will show there the tools I used. You will need a spot welder, and you can read about my spot welder in the PREVIOUS POST There is also a schematic diagram of its electronics there. The cells I used come from dismantling a larger package, but they have nominal parameters – they are like new. The whole idea of welding is the same for all cells, and the ones I used were SONY 18650V3 2150mAh and I was able to buy them for PLN 4 / pcs (~$1). I used about 4 meter nickel tape at a price of 5.5 PLN (~$1.3) per one meter.

(Polish version)

Photo Gallery

bms soldering

(Polish version)

Estimate

  • SONY 18650V3 2150mAh cells (unpacked) 78 * 4 PLN (~1$) = 312 PLN (~$78)

  • nickel steel tape 8×0.15 4mb * 5.5 PLN (~$1,3) = 22 PLN (~$5.5)

  • triple holders 52 * 0.7 PLN (~$0,175) = PLN 36.4 (~$9)

  • BMS 13S 20A PLN 66 (~$16.5)

  • connectors and cables PLN 10 (~$2.5)

    Total PLN 446.4 (~$111)

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Bionx motor – modification

BIONX MOTOR - MODIFICATION

Start by watching the episode about conversion on our YT channel 🙂:

WHY THIS MOTOR?

  1. I recommend this motor to DIY enthusiasts who build a bike up to 1500W.
  2. This motor is cheap to get on the aftermarket because people import bikes with these systems as damaged, convert them to regular bikes and sell wheels as unchecked or damaged. It is very possible that they are actually damaged, but it does not bother us at all!
  3. Most often in these systems controllers that are inside the engine break down, and we throw this controller away!
  4. The engine is light (about 4.5kg), gearless (which makes it maintenance-free),
  5. has hall sensors (better start from zero than sensorless).
  6. Looks good and pushes well up to 1500W 🙂.

WHAT'S MODIFICATION ALL ABOUT?

We convert this motor to an external controller and add thermal protection against overheating, and replace the bearings with new ones.

Such a converted motor can be connected to any BLDC motor controller / controller that supports hall sensors (most of it has). The power in electric bikes is maintained mainly by the controller, so we are not limited only to statutory 250W.

This engine will pull up to 1500W without damage. It’s not recommended to push this motor beyond 1500W becouse it has relatively small magnets and coils. It means that it will not produce much more more torque and will heat.

WHAT WILL WE NEED?

Fortunately this list is not long:

Heat Gun / burner
vice
LIYCY cable 8×0.25mm2 (1.5mb)
1.5mm2 wire with silicone insulation (3×1.5mb)
polyester cable braid
cable ties
shrink tubes
bearings 6003 with C3 clearance 2 pcs
thermal protection 145 degrees C
LM35 temperature sensor
heat conducting glue above 200 ° C
car spray black semi-matte (for rims, bumpers etc.)
hammer
sockets / bushes for knocking out and driving in of bearings
water spray, cloth

Good luck 🙂!

GALLERY

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