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Paper Number

HYBRID POWER PACK (ULTRA CAPACITOR + BATTERY) FOR TWO WHEELERS FITTED WITH STARTER MOTOR

VIJAY CHHEDA & VERNEKAR D.Y. Chheda Electricals & Electronics Pvt. Ltd, Pune (India)

Copyright © 2008 SAE International

ABSTRACT

Self-Start Two-Wheelers, including motorcycles and scooters between 50 - 200 cc capacity, use standard Lead Acid battery of 5, 9 and 12 Ah rating as energy source. Battery is a well-known energy source but cannot supply large amount of power in short time. The size of the battery is decided based on the starter motor requirement. Deep discharge at the time of cranking reduces the life of the battery drastically as compared to normal use. Extra factor of safety is provided for cold weather cranking performance, poor maintenance and end of life performance in view of deep discharge. Hence it is heavy and bulky. On the other hand, Ultracapacitors can supply large burst of power for short time but can not store much energy (hence limited number of starts). It is seen that in Hybrid Power pack (Ultracapacitor + down sized Battery) the major power requirement at the time of cranking is taken by Ultracapacitor resulting in reduced load on the battery thereby making it possible to be downsized. This paper describes how a Hybrid Power Pack utilize the strengths of both, resulting in a unit which is economical, maintenance free, low in weight with good cold start capability.

1. BACKGROUND

Two-wheelers are an integral part of life in developing countries like India, China, SE Asia, etc. The usage & function of two-wheeler is similar to car in developed countries. The traffic and road conditions, the short travel distances involved, moderate weather conditions, high fuel costs and the limitation of consumer spending power is the reason for the popularity of the Two-wheelers (Motorcycles, Scooters/Scooterette, Mopeds) in India, as shown in Figure 1.

Figure 1: Vehicle distribution in India (for 2007-08)

The production of Two-wheelers in India, in the year 2007-08 is 8 million and expected to grow at the rate of 8% in the coming decade [1].

75% of the two-wheelers manufactured in India are of ‘Kick-Start’ type, that is, they are without Starter Motor. They are fitted with 2.5 Ah battery to meet the safety related loads, such as Horn, Direction Indicator and Brake Lamp etc. Our first paper published at SIAT2007 [2] describes how Ultra capacitors can be used successfully to replace lead-acid battery on ‘Kick-Start’ vehicles, ensuring the safety features operational at all times throughout the life of the vehicle without maintenance hassles and cost of periodic replacement of Battery.

This product, as shown in Fig. 2 & 3, (called as ‘BSU’, in short for ‘Battery Substitute Unit’), was launched in Indian market and is well received.

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Figure 2: Battery Substitute Unit (BSU)

Figure 3: BSU fitted on Two-wheeler

This paper describes how Hybrid Power Pack (Ultra capacitor + Battery) can replace the bulky 5 or 9 Ah lead acid battery used on two-wheelers fitted with Starter Motor.

2. INTRODUCTION

In the recent past, with the increase in purchasing power of Indian customer, preference for two-wheelers fitted with Starter Motor is on the increase. More than 25% of the two-wheelers manufactured, that is about 2 million two-wheelers manufactured in 2007, are with starter motor. Any how, two-wheelers of more than 150cc are fitted with starter motor as kick-starting such engine is physically demanding on the part of user.

The Ampere-Hour (Ah) rating of the battery used on two-wheelers depends mostly upon the engine capacity, as, the rating of the starter motor needed goes-up with the engine capacity. Apart from cranking the engine, the battery has to take care of normal loads like turn signal, horn and brake light etc. Typical loads on a 5 and 9 Ah lead-acid battery fitted on a two-wheeler with starter motor are as shown at Table 1.

TABLE 1: TYPICAL LOADS ON BATTERY

Load ON 5Ah

BATTERY (W)

ON 9Ah BATTERY

(W) Remarks

Horn 24 24 Safety feature

Direction Indicator

21.7 21.7 Safety feature

Brake indicator

lamp 20

20 Safety feature

Dash Board Neutral indicator

1.7 1.7 Indication

Starter Motor

150 350 Functional

Total 216.4 417.4

All the above loads are intermittent in nature. It may be noted that the Battery (or any on-board energy storage device used) should be able to meet the Starter Motor load right in the beginning, even under worst environmental conditions. For this the battery has to be maintained in working condition, at all times.

Battery is a well-known source of energy but must be over-sized to deliver current rapidly enough for acceptable starting performance, as their ability to deliver such currents drops-off sharply under adverse freezing environment. Thumb rule says, for every 10°C (16°F) below room temperature, for worst-case low-temperature operation, we have to increase the battery capacity by 10%. Hence they become bulky.

Further, the ‘Cycle Life’ of Lead Acid battery depends upon ‘Depth of Discharge’ (DOD). On an average the cycle life of a starter battery is about 1000 cycles, when subjected to deep-discharges, such as, at the time of cranking the engine.

On the other hand, Ultra capacitors can supply large burst of power for short time but cannot store much energy and hence can give limited number of starts, as compared to battery. They can be charged and discharged quickly over thousands of time without appreciable deterioration in capacitance. An effort made to utilize the strengths of both has resulted in a unit, which is economical, maintenance free, low in weight with good cold start capability. This paper describes how Ultra-capacitor along with a small maintenance free VRLA (Valve Regulated Lead Acid)

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battery can adequately replace the 5 or 9 Ampere-hour bulky lead-acid battery used on two-wheelers resulting in obvious advantages.

3. ULTRA CAPACITOR

As the name suggests it is a capacitor with large capacitance. It polarizes an electrolytic solution to store energy electro-statically. Though an electrochemical device, no electrochemical reactions are involved in its energy storage mechanism. This mechanism is highly reversible, and allows the Ultra capacitor to be charged and discharged hundreds of thousands of times, without any appreciable loss in its capacitance. Electrochemical Double Layer Capacitors (Ultracapacitor/Ultracaps/Super capacitor), with its short charging & discharging time, is ideally suited for the intermittent loads. [3] Starting with the introduction of ‘Coin/Button Cells’ in the ‘80s to the present mega-ultra-capacitor units, the industry has come a long way. In the ‘80s and ‘90s, manufacturing of Ultra-capacitors was primarily an art. With the advance in technology, automated assembly techniques have replaced the labour-intensive aspects of manufacturing. As a result, costs have decreased substantially.

3.1 COMPARISION BETWEEN ULTRA CAPACITOR & BATTERY A Lead Acid Battery is an electrical storage device that uses a reversible chemical reaction to store energy. It uses a combination of lead plates/ grids and dilute sulfuric acid as electrolyte, to convert electrical energy in to potential chemical energy and back. Thus, it is slow in charging and slow in discharging. Ultra capacitors store energy electro-statically. They can be charged or discharged very fast, in seconds. Table 2 shows the comparison of Ultra capacitor and Battery. [5] TABLE 2: COMPARISON OF ULTRA-CAPACITOR & BATTERY

Sr.No. Parameter Ultra-Capacitor Battery

1 Expected life, years More than 20 1 to 3

2 Charge – discharge

cycles More than 500,000 1000

3 Power density,

W/Kg 4000 300

4 Energy density,

Wh/Kg 3 to 5 80 to 100

5 Charge control Not needed Needed

6 Ability to discharge

completely Yes No

7 Self discharge High Low

8 Flat discharge

curve No Yes

9 Maintenance free Yes No

10 Weight Less More

11 Damage proof

against short circuit Yes No

12 Environmental

friendly Yes No

13 Operating

temperature range Wide Narrow

4. HYBRID POWER PACK (HPP) 5AH

4.1 TWO-WHEELER ELECTRIC CIRCUIT

Any typical electrical circuit diagram of two-wheeler fitted with Starter Motor and powered by magneto is as shown in Figure 4

Figure 4: Typical electrical circuit diagram of a Two- wheeler with starter motor

The magneto (1) is the power source of the system. This is a device in which permanent magnets, fitted on rotor are used as field to generate electric power in coils placed on stator. There are two types of coils on stator, namely ‘Source coil’ (2) used for generating the spark in spark plug (3), to ignite the fuel mixture in the IC engine of the vehicle. CDI unit (4), along with ‘pulsar coil’, help in advancing the spark with speed and load, for achieving better fuel efficiency

The Lamp-coil (5) is designed to meet the vehicle’s A.C. loads, such as Head Lamp, Rear Combination lamp etc. Lamp coil output is also used for charging of Battery (6), with the help of ‘Regulator & Rectifier Unit’ (7), which maintains the output voltage, at all vehicle speeds &

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under variable load conditions, within 14.2 +/- 0.2 VDC. Fuse Unit (8) is used to protect the Battery from full discharge and possible permanent damage, due to any short to ground taking place throughout the vehicle wiring.

4.2 HPP CIRCUIT DIAGRAM

Figure 5: HPP Circuit Diagram

As shown in Fig. 5, this is a simple arrangement in which 12 Ultra-capacitors of 2.7 V, 25 Farad rating, are connected in series-parallel combination, resulting in 12V, 8.33 Farad Ultra-capacitor (UC) unit. The UC unit relives the battery of the demanding short duration, high current starting load. Thus, the 12V, 1.3 Ah VRLA battery connected across the UC unit is able to substitute the 5Ah lead-acid battery.

The voltage across each cell in a series string must not exceed the maximum continuous working voltage rating during charging/discharging, as sustained over-voltage can cause an Ultra capacitor to fail. Resistor (2) is the cell voltage equalization resistor, whose value depends upon Equivalent Series Resistance (ESR) of the Ultra capacitors [4]. If reverse voltage is applied to Ultra capacitors, capacitor life is shortened and serious damage may occur. To protect the Ultra capacitors from such damage, a Diode (3) is connected in reverse. For ease of replacement with existing lead-acid battery on vehicles, the +ve and –ve terminals (4 & 5) are designed suitably. This circuitry is embedded in appropriate Epoxy compound (6) to protect it from the vehicle vibrations, greasy environment etc.

4.3 DESIGN CONSIDERATIONS

The selection of battery and Ultra-capacitor values is guided by the following considerations; Why not only UC Unit? From practical considerations, the energy source should be able to give minimum of 5 to 7 cold-cranking starts on

the vehicle. This calls for a 12 V, 70 Farad unit, that is, 12 Ultra-capacitors of 2.7 V, 210 Farad rating. This will make the HPP commercially un-viable in comparison with the 5 Ah lead-acid battery used. 12V, 1.3Ah VRLA battery along with UC unit meets this requirement adequately. Why 2*25F UC in parallel instead of single 50F? Equivalent Series Resistance (ESR) has decisive influence on the current shared by UC Unit and battery. The ESR value of series-parallel arrangement results in lower effective ESR, resulting in UC Unit taking higher share of peak load current. Why maintenance free VRLA Battery? Flooded lead-acid batteries call for regular maintenance, such as topping-up of Acid and Distilled water, cleaning of +ve & -ve terminals eroded by the acid, maintaining the air-vent clear for easy escape of gases produced etc.

4.4 CONSTRUCTION

The size and shape of the HPP Unit is maintained same as the existing 5Ah lead-acid battery for ease of replacement on vehicle. The epoxy molded UC Unit is housed in the upper portion. This is not easily accessible to the user, as it is expected to last for the life of the vehicle without need for any maintenance. Maintenance free, VRLA battery is supported on two vibration absorbing pads at the bottom and held firmly in place by hook & loop wrap strap. This arrangement ensures that vehicle vibrations do not affect VRLA battery. The battery is housed without any cover for ease of replacement as and when required. Fig 6 shows the Rear & Front view of the HPP Unit.

Fig 6: Rear & Front view of HPP

4.5 ADVANTAGES TO USER

• No regular maintenance needed:

Sealed, maintenance free VRLA battery does not require any regular maintenance, only replacement once in 2 to 3 years. UC Unit is designed to work for the life of the vehicle without any maintenance.

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• Low replacement cost:

Once in 2 to 3 years the user has to replace only the VRLA battery, which is much cheaper than 5Ah lead-acid battery. As on date, in the open market, the price of a 1.3Ah VRLA battery is about Rs.210 as against Rs.950 of 5Ah lead-acid battery

• Low initial cost:

The price of HPP works out to about 90% to that of 5Ah battery, in the open market.

• Extended Life of Battery:

As about 60% of the peak-power demand is met by UC Unit, battery is not subjected to deep-discharge, resulting in extended life of battery.

• Better cold weather performance:

Ultra-capacitors work satisfactorily up to minus 40°C without appreciable drop in capacitance. Hence HPP has better cold cranking capability at minus 10°C as compared to lead-acid battery.

• Reduced weight:

The weight of 5Ah battery is about 2.15 Kg and that of HPP is 0.93 Kg. This will help OEMs in their effort to reduce the vehicle weight to achieve better fuel economy figures.

• Environment pollution:

Hazardous materials such as antimonial lead and sulphuric acid are used in the manufacture of lead-acid batteries. Improper disposal of batteries leads to poisoning of potable water, pollution etc. By use of smaller VRLA battery the ill effects are reduced to that extent.

5. TESTS & RESULTS

To compare and confirm the suitability of HPP as substitute for the existing 5 Ah lead-acid battery on two-wheelers, the following tests were carried out.

5.1 ENGINE STARTING TEST

This test is done on various 100cc Self-Start vehicles, fitted with 5 Ah lead-acid battery, like Honda Activa, Honda Dio, TVS Scooty pep+ etc., to confirm that functioning of HPP is on par with that of battery. Here Starter Motor is made ‘ON’ for 3 seconds during which the engine fires. The summery of the test results is at Table 3. Fig 3 shows the typical voltage and current plots taken on Honda Activa scooter, using 5 Ah battery and HPP as power source.

TABLE 3: ENGINE STARTING TEST RESULTS

5.1.1Observations -

• The starting performance of the vehicle with HPP is on par with that of lead-acid battery

• Major portion of the peak load is taken by UC-Unit. This will result in longer life of the VRLA battery used

Fig 7: Honda Activa Starting plots 5.2 ENGINE CRANKING TEST During engine start test, the role of power source and Starter Motor is for smaller duration, say for 100 to 150 m-seconds. Cranking the engine for longer time, without allowing it to fire, puts the power source to real test and we get insight of its response. In this test the engine is cranked for 8 seconds, without allowing it to fire and plots of Voltage and Currents are taken. For test results refer Table 4. Typical Voltage and Current plots are shown at Fig. 8. TABLE 4: ENGINE CRANKING TEST RESULTS

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Fig 8: Honda Activa Cranking plots

5.2.1 Observation:

• From the Voltage plot it may be seen that; as expected, the terminal voltage at the end of 8 seconds, with HPP is lower at 10.2V as against 11.8V of 5Ah battery. However, in the subsequent tests it is confirmed that, the terminal voltage gets back to its full value fast as the charging time of UC Unit is quite low.

• From the Current plots it may be seen that; - As the internal resistance of UC-Unit is very low (less than 1/3 of VRLA battery), it un-loads its power during initial 300 m-seconds, when the demand is high. During rest of the period, power for cranking is met by VRLA battery

- 61% of the peak load is taken by UC Unit. Low load on VRLA battery ensures longer life of the battery - The peak currents with HPP are lower as the starting voltage is higher, an added advantage over battery system.

• Engine starting and cranking trials at minus 5 and minus 10°C are yet to be done to confirm HPP’s better performance at low temperatures.

5.3 QUICK CRANK TRIALS Due to any reason if the engine does not start, users keep cranking the engine repeatedly. To study the response of HPP under such conditions, this test was conducted in the following manner; 5.3.1 Test Cycle:

• Crank for 2 seconds – Rest for 4 seconds

• No charging during this test

• Find out number of crank cycles possible

• Refer Table 5 for the test results

TABLE 5: QUICK-CRANK TEST RESULTS

5.3.2 Observation:

As the stored energy in HPP is lower, only 28 cranks were possible. This is one of the limitations of the HPP. However this should be acceptable, as we do not expect more trials by the user, practically.

5.4 LIFE CYCLE TEST

The next important question is, on the vehicle how long HPP will last, as its stored energy in comparison with 5 Ah lead-acid battery is low. To find out, test as shown in Fig. 9 was derived.

Figure 9: Life test Cycle 5.4.1 Test Cycle 3 second Starter Motor ‘ON’ – 30-second engine ‘ON’ – 10-second system ‘OFF’ Total Cycle time: 41 seconds Initially the test was planned for 2000 cycles expecting HPP to last less than that. However, test was concluded at 3200 cycles as HPP continued to work without any fall in terminal voltage. The speed setting of the Magneto, which charges the power source during engine ‘ON’ period, was adjusted to 2200 rpm. This test cycle is devised to simulate the worst case possible during city driving condition. Terminal voltage of the power source was taken at the end of every 50 cycles, along with voltage and current plots. The plot of terminal voltage Vs Test Cycle is shown at Fig. 10.

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Figure 10: Life Cycle Test Results 5.4.2 Observation: Like in lead-acid battery system, no drop in terminal voltage is observed with HPP system. This indicates that the designed energy of HPP is adequate to run the system without degradation, in comparison with lead –acid battery 5.5 HPP SELF-DISCHARGE TEST The self-discharge rate is the measure of how-much batteries discharge on their own. Flooded cells in lead-acid batteries typically use lead alloyed with Antimony to increase their mechanical strength. But this also increases the self-discharge. Gel and AGM (Absorbed Glass Mat) cells, like in maintenance free VRLA battery, use lead alloyed with calcium, which reduce gassing and self-discharge. At room temperature, drop in terminal voltage per day of a lead-antimony battery is 3 times more than that of a lead-calcium battery In case of HPP, apart from self-discharge of VRLA battery, the self-discharge of UC-Unit is added as it is connected in parallel to the battery. Hence it was necessary to confirm the effect of self-discharge of HPP on system working. The fall in open-circuit voltage of fully charged 5Ah lead-acid battery and HPP unit was monitored for a month. The findings are shown graphically at Fig.11 below.

5.5.1 Observation

• The drop in terminal voltage due to self-discharge of HPP is 3.6% per month and that of 5 Ah lead-acid battery is 2.3% per month.

• Though the self-discharge rate of HPP is higher, the terminal voltage at the end of 30 days is higher than that of lead-acid battery. This is because the terminal voltage of HPP is always higher than that of lead-acid battery. Thus, even after 30 days of self-discharge, HPP unit could easily crank the engine.

Figure 11: Drop in terminal Voltage due to self-discharge 5.6 FIELD TRIALS

HPP was fitted on 16 different customer vehicles and monitored regularly, since July 2006. These vehicles have covered approximately 1, 60,000 Km without any noticeable problem. In one vehicle, the UC-Unit failed as the charging voltage crossed 28V due to the failure of Regulator-Rectifier Unit, on the vehicle.

6. HYBRID POWER PACK (HPP) 9AH

The circuit is similar to as shown at Fig. 5, above. Here 12 UC of 2.7V, 50 Farad rating are used, resulting in UC-Unit of 12V, 16.67 Farad. The rating of the VRLA battery used is 12V, 3.3 Ah. This unit also has under-gone the same tests as that of 5 Ah HPP. The test results and field trials confirm that the 9 Ah HPP can replace the existing 9 Ah lead-acid battery on two-wheelers.

CONCLUSION

• Based on the field trials and experiments, it can be concluded that HPP as a Battery substitute matches all performance requirements of ‘Self-Start’ Two-wheelers.

• Users are benefited with maintenance free, lower weight system with better cold-start capabilities.

The replacement cost over the years is also low.

• The product also contributes towards lowering of Environmental Lead pollution

• As per survey of electrical systems across different brands of vehicle, HPP can directly

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substitute, without any modification for over 70% of the existing Self-Start vehicles.

PRESENT STATUS

• 5 Ah HPP is launched in the Indian open-market in September 2007 and 9 Ah HPP will be launched in January 2009

• One of the leading Indian two wheeler O.E, has shown keen interest in this product and is undergoing extensive testing by them

FUTURE OUTLOOK

• Price of Ultra-capacitor is coming down and that of lead-acid batteries on the rise. This will make HPP commercially attractive and also help in improving the product further.

• Along with the introduction of HPP, it is possible to improve the electrical system efficiency by re-designing of Magneto, introduction of Re-generative Braking etc. Work is under progress on these lines.

• Work is underway to use HPP for Self-Start of four wheelers & Gen-sets

REFERENCES:

1. Automotive Components & Manufacturers Association

(ACMA) ‘website: www.acmainfo.com’.

2. Chheda V.J. & Vernekar D.Y., ‘Ultra-Capacitors as

Battery substitute on Two-Wheelers’, SAE paper

No.132, presented at SIAT-2007.

3. NESSCAP product literature ‘What is Electric Double

Layer Capacitor?’(EDLC)

4. NESSCAP ‘Ultra capacitor Technical Guide’

No. 2003.7

5. EPCOS literature No. KO UC PM

CONTACT: Mr. VIJAY JAGDISH CHHEDA Managing Director Chheda Electricals & Electronics Pvt. Ltd 14, Hadapsar Industrial Estate, Pune- 411013. (INDIA)

Phone: +91-20-26817780, 26876950 Mobile: +91 98220 50939

E-mail: ignition@vsnl.com

Mr.Chheda has done his Masters in Manufacturing Engineering from Carnegie Mellon University, USA, in 1991. In 1995, Mr. Chheda founded Chheda Electricals & Electronics Pvt Ltd for manufacture of auto electrical & electronic parts. The company has made rapid progress due to strong focus on innovation & quality and has grown to USD 25 million turnover .The company has made strategic investments in R&D to develop new technologies in the field of electrical & electronics for motorcycles. BSU is one of the products evolved as a result of development of new technologies.

Mr. D.Y. VERNEKAR General Manager Chheda Electrical & Electronics Pvt. Ltd.

14, Hadapsar Industrial Estate Pune- 411013. (INDIA) Phone: +91-20-26817780, 26876950

Mobile: 9370147623 E-mail: vernekar@masterignition.com

Mr.Vernekar is B.E. (Electrical) with 38 years experience in Design & Development of Auto-Electrical systems.