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18 010

Examensarbete 15 hp

20 Juni 2018

Uppsala Universitet

Electronic project - heat lock for bikes

Mauricio Ramirez Zavala

Teknisk- naturvetenskaplig fakultet

UTH-enheten

Hus 4, Plan 0

Postadress:

Box 536

751 21 Uppsala

Telefon:

018 - 471 30 03

Telefax:

018 - 471 30 00

Hemsida:

http://www.teknat.uu.se/student

Abstract

Electronic project - bike heat lock

Mauricio Ramirez Zavala

This project explores the idea of implementing an electronic device that can melt away ice from frozen bike locks. It narrates the process of starting with no knowledge of how heating works and ending with a manufactured and soldered PCB with limited heating capability. Resistance heating and induction heating was studied in the initial phase of the project. Which proceeded into designing the complete schematic of the induction heater. A prototype was built which advanced further to the development of tools and ways to measure inductance, resonant frequency and temperature before the tests of the performance. When the performance tests were done the induction heater was optimized and later designed in eagle. A PCB circuit was ordered which later was soldered until completion. The result was an induction heater in PCB form with limited functionality compared to the data of the prototype, due to faulty layout of the circuit. The performance of the end result was 20.02 degrees C to 33.20 degrees C in 11 minutes. The data from the prototype suggests that the induction heater can melt the ice from frozen bike locks since the performance was 21.96 degress to 62.02 degress C in 4 minutes. Any rise in temperature over the boiling point of water 0 degrees C is good but tests in real winter conditions needs to be done to definitively confirm success. The mayor problem is whether a battery can provide with the required energy without getting to big or expensive. If the answer is yes then the induction heater of this project can be used regularly but the manufacturing costs would still be high.

Tryckt av: Uppsala

ISSN: 1654-7616, 18 010

Examinator: Hana Barankova

Ämnesgranskare: Ladislav Bardos

Handledare: Olle Svensson2

Electronic project - heat lock for bikes

By: Mauricio Ramirez Zavala

Supervisor: Olle Svensson

Uppsala

June 24, 2018

3

Abstract

This project explores the idea of implementing an electronic device that can melt away ice from frozen

bike locks. It narrates the process of starting with no knowledge of how heating works and ending with

a manufactured and soldered PCB with limited heating capability. Resistance heating and induction heating was studied in the initial phase of the project. Which proceeded into designing the complete schematic of the induction heater. A prototype was built which advanced further to the development of tools and ways to measure inductance, resonant frequency and temperature before the tests of the performance. When the performance tests were done the induction heater was optimized and later designed in eagle. A PCB circuit was ordered which later was soldered until completion. The result was an induction heater in PCB form with limited functionality compared to the data of the prototype, due to faulty layout of the circuit. The performance of the end result was20:02C to33:20Cin 11 minutes. The data from the prototype suggests that the induction heater can melt the ice from frozen bike locks since the performance was21:96Cto62:02Cin 4 minutes. Any rise in temperature over the boiling point of water0Cis good but tests in real winter conditions needs to be done to definitively confirm success. The mayor problem is whether a battery can provide with the

required energy without getting to big or expensive. If the answer is yes then the induction heater of

this project can be used regularly but the manufacturing costs would still be high. 1

Contents

1 Introduction3

1.1 Backround

3

1.2 Objective

3

1.3 Limitations

3

2 Theory4

2.1 Properties of water

4

2.2 Developed power in an electrical circuit

4

2.3 Total capacitance for series and parallel configurations

4

2.4 Total resistance for series and parallel configurations

4

2.5 Resonant circuit

5

3 Experimental Apparatus and Procedure

6

3.1 Method

6

3.2 Resistance heating

6

3.3 Induction heating

7

3.4 Mazilli oscillator the induction heater

8

3.5 Inductance measurement

9

3.6 Temperature sensor

11

3.7 Experimental setup for system tests

14

4 Result14

4.1 System performance

14

4.2 Optimization and the final eagle PCB design

17

4.3 Solidworks CAD

20

5 Discussion21

6 Conclusion24

7 Appendix24

8 Acknowledgement37

2

1 Introduction

1.1 Backround

At winter the bikes are sometimes rendered unusable due too the locks being frozen. Which is a problem

when the need to travel is present. One solution would be too implement electronics that can heat up and

melt the ice. Which would allow travel.

1.2 Objective

The objective of this project is to construct electronics that can heat up bike locks that are frozen. An

effective way to heat up frozen bike locks will allow people to travel at winter without frozen locks. People

may also save money since they can use the bike instead of the bus for travel.

1.3 Limitations

The bike lock itself will not be constructed, a bought, regular bike lock is used in tests. A fully embedded

system is not in the scope of this project, the construction of the heating device and the studies of it"s

properties are of interest. No tests in real winter conditions were made with the heater device. To quantify

the result so that analysis can be made the performance of the heater in room temperature is measured

instead. 3

2 Theory

2.1 Properties of water

The boiling point of water is 273.15K and the relationship between Kelvin and Celsius is C water= (Kwater273:15) =)Cwater= 0C

2.2 Developed power in an electrical circuit

Joule"s law for thermal power is given by the formula:

P=V I=I2R=V2R

(1)

Rewriting equation

1 yields the needed resistance for a giv env oltageand p ower R=V2P (2)

2.3 Total capacitance for series and parallel configurations

The resultant capacitance in a series arrangement is given by the formula:Cs C s=CnP n(3) The resultant capacitance in a parallel arrangement is given by the formula:Cp C p=X nC n(4)

2.4 Total resistance for series and parallel configurations

R s=X nR n(5) Resultant resistance for a parallel arrangement is given by: 1R p=X n1R n=)Rp=1P n1R n(6)

If resistances are equal then equation

6 b ecomes: 1P n1R n=Rnn (7) Relations between frequency f,angular frequency!, and period T f=1T =!2(8) Equations and the statements declared are taken from physics handbook [ 1 4

2.5 Resonant circuit

+V ocZ RC L

Figure 1: Resonant circuit

The resonant circuit (fig

1 ) consists of a combination of R,L and C elements. Having a frequency response similar to the one appearing in figure 2 . Note that the response is at maximum for some frequencyfr

and that the response will be near maximum for a particular range of frequencies. The frequencies to the

far left and far right are of small currents and, for all practical purposes, have little effect on the systems

response. When resonance occurs due to the application of the proper frequencyfr, the energy absorbed by

one reactive element is the same as that released by another reactive element. Thus the maximum current

appears when the sum of the impedances of the elements are equal and cancel each other out when Z

L=ZC=)i!L=i1!C

. With fixed values on the elements resonance happens at the frequency yielded from equation 11 4 Z

L=ZC=)(9)

!L=1!C =)(10) 2=1LC =)42f2=1LC =)f=142pLC (11)

Rewriting equation

11 yields the ind uctanceat the resonanc efrequency L=1!

2C=)(12)

L=1(2f)2C=)(13)Figure 2: Resonant circuit

5

3 Experimental Apparatus and Procedure

3.1 Method

The method under the project was an iterative work procedure. The initial main problem that needed to

be solved was, how can you create heat with an electronic device? The problem at hand was then solved

by either the study of literature, the web or the help of the advisor. With each problem solved, another

appeared and the process had to begin anew. Each renewal, leading to the advancement of the project.

3.2 Resistance heating

The first problem was to determine a way to develop heat with an electronic device. Research was carried

out via the internet. Resistive heating was explored firstly. The key idea with resistive heating is whenever

an electric current flows through a material that has some resistance. Power is dissipated in the form of

heat. The resistive heating is the result of collisions between charges. [ 6

The initial approach was to write code and have an arduino (a micro controller) monitor and control the

resistance heater. A mechanical switch was connected to the arduino which functioned as a power switch

for the resistance heater. If the arduino read the switch as high, it set the mosfet"s base to high, which in

turn allowed current to flow and the electric heater to turn active. To monitor the development of the heat

a temperature sensor was planned to be implemented. The arduino code was in large extent inspired by the

following reference [ 7

With the heating system layout mostly done the only thing remaining was the power output of the resistance

heater. The initial desired power was 5.2W and with a power supply of 12VDC the required resistance was

calculated through equation 1 7

R=1225:2= 27:7

Whether one resistor could handle the power delivered without malfunctioning remained a problem. It was

solved by connecting 12 resistors in parallel to distribute the power and minimize the power load on each

resistor [ 7 ]. The result was a resistance ladder with a total resistance of 33012
= 27:5 , which dissipated a power ofP=12227:5= 5:2Win heat.

A quick assessment of the heat was made through touch and it was deemed to low to melt ice in a quick

manner and thus the resistance ladder was abandoned in search for a resistor that could handle more power

without malfunction.

Research at the internet indicated nichrome wire as an excellent solution for the insufficient power dissi-

pation of the previous resistance ladder. Nichrome is an alloy produced by a mix of nickel, chromium and

occasionally iron. Its properties include resistance to heat and is highly resistive causing it to heat even

when exposed to small electrical currents [ 8

The usage of nichrome wire at a specific heat application needed specifications on wire length and wire

diameter. Research was done on the relation between wire geometry, voltage and developed temperature.

Eventually a nichrome wire calculator was found and used [ 9

But a problem arose the resistance heater had to be dimensioned to fit the dimensions of the lock, which

at that time was unknown. The initial plan was to create the lock mechanism through the means of CAD-

solidworks but that gave rise to another problem. How would the resistance heater manage to get inside

the lock itself. Even if the pathway of the nichrome wire was made inside the lock in CAD, how would 6

you actually get it inside. The problem was challenging and the idea of heating the lock from outside was

more appealing. Resistance heating was eventually abandoned due too the problem of getting the nichrome

wire inside the lock. Heating the lock from outside became the solution which in practice meant induction

heating.

3.3 Induction heating

Induction heaters has built in circuitry that provide alternating electric currents to an electric coil (the

induction coil). The induction coil becomes the heat source since it induces an electrical current into the

metal part to be heated, the workpiece. No contact is required between the workpiece and the induction

coil. Furthermore the heat is restricted into only developing heat inside the workpiece. This is because the

alternating current (ac) has an invisible magnetic force field which only interacts with metals [ 10

When the induction coil is close to the workpiece, the lines of force concentrate in the air gap between the

coil and the workpiece. The induction coil functions as a transformer primary, with the workpiece to be

heated becoming the transformer secondary. The magnetic field of the inductor induces an equal opposing

electric current in the workpiece, the workpiece then heating up due to the the dissipated power from the

resistance [ 10

The frequency in the ac plays a role in how much heat that is developed. The currents flowing in a cylin-

drical workpiece will be most intense at the outer surface at higher frequencies due to the skin effect,

while the currents at the center are negligible. Which leads to a span of different resistances depending

on the frequency of the ac [ 2 ]. The rate of heating depends also on the magnitude of the induced current,

the specific heat of material, the magnetic permeability of the material and the resistance of the material[

10

Hysteresis losses also contributes to the development of heat. It occurs in magnetic materials such as steel,

nickel and a few other metals. When magnetic parts are being heated, by induction, from room temperature

a phenomenon occurs. The alternating magnetic flux field causes the magnetic dipoles of the material

to oscillate as the magnetic poles change their polar orientation. This oscillation is called hysteresis and

contributes to the development of heat [ 10 7

3.4 Mazilli oscillator the induction heater

The idea of using a mazilli oscillator as induction heater was inspired by various projects found on the web.

The parameters of the components were largely inspired by RM CYBERNATICS schematic design [ 11 ]. The zener diodes and pull down resistors for the gate protection were inspired from Marko"s design [ 12 ]. The connection between the choke inductors and the induction coil were inspired from DIY King [ 15

The mazilli circuit is displayed in fig

3 . When power is applied atV+current flows at both sides of the choke

coils (Lc1andLc1), reaching the drains of both mosfets. A voltage will simultaneously appear at the gates

(G1andG2) through nodeN. Because no mosfet is manufactured equal to another, one mosfet turns on a little faster(sayQ1for example). Which eventually pulls down the drainD1to ground. As that happens the schottky diodeDs2rob the current from gateG2thus pulling it also down to ground.

Turning its mosfet off. The LC-tank formed by the induction coil(Li) and the capacitors leads to the voltage

proceeding to rise and fall sinusoidally.D1will be close to zero volt whileD2will rise to its peak (its

mosfet is off). Then fall back down as the LC-tank reaches its half cycle. When the voltage atD2passes

through zero volt, the gate currentG1is robbed and the mosfet turns off allowing the voltageD1to rise and

sustaining the second half of the cycle. The same process repeats again and the oscillator continues cycling

and thus creating a sinusoidal voltage across the induction coilLi[16]. In order to prevent the oscillator from drawing huge peak currents and exploding,Lc1andLc2are added

in series withV+as chokes. Their only function is to limit the current spikes while the LC-tank limits the

current. The resistorsR1andR2limit the current that charges the gates since too much gate current can

cause damage. The resistorsR3andR4pull down the gates down to ground to make sure that the mosfets to not get stuck on[ 13 ]. The zener diodes prevent the gate voltage from exceeding 5.6V [quotesdbs_dbs23.pdfusesText_29

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