A Review of an Economical Digital Time Switch from Q0010

7 April 2014

Introduction

Bought a digital time switch from Q0010 last week for about SGD $12/= to replace my present mechanical time switch which has been used to control a 3-litres Jojirushi water air-pot that  draws about 3.0 -3.5 amperes.  The digital time switch has no other name on it except “Timer” on its cover.  It is made in China 

Differences between Digital and Mechanical Time Switches

The main difference is in the construction. 

The mechanical time switches on the left have gears and wheels that are driven by an electric motor synchronised to the electrical mains.  These wheels rotate a time dial that can be programmed to activate a level that will turn on or off a micro-switch to control the electricity supplied to the socket outlet.

The digital time switches on the right have no gears, wheels and moving parts.  The timing is driven by a digital clock much like an ordinary quartz alarm clocks except in this case,  instead of activating a mechanical switch that turn-on the alarm circuitry,  the digital time switches have electrical relays that control the electricity supplied to the socket outlet.

Dismantling the Digital Time Switch

It is quite easy to open the casing of the time switch by first finding the two “catches”,  one at each end of the time switch as shown,  then use a small screw driver to carefully pry open the casing which will “pop up” from its base readily. 

The Electronics and Components 

The digital time switch has 3 components 

1)     the switch socket outlet assembly

2)     the supply unit and the output relay

3)     the time clock and display screen

Description of the Circuits 

The supply for the electronics is obtained through a simple transformerless power supply unit that consisted of a 400 volt supply capacitor,  a power limiting 1 ohm resistor and a full wave rectifying bridge.  The power supply unit is supplying a 24 volts dc supply to run the relay circuits as well as 1.2 volts to charge the Nickel Metal Hydride  (Ni-MH) battery and also to run the time clock and display unit as shown in the attached.

The time clock and the programming electronics are hidden behind the display screen’s circuit board

The relay has a name plate rating of 16 ampere @ 240 volts.  The unit has a spare battery chamber which is not used,  probably left over from the older design that used AAA rechargeable batteries. 

The Rating of the Time Switch

Although the name plate of the time switch has a rating of 13 amperes,  the driving electronic has relay rating of 16 amperes. This,  however,  does not mean the time switch can be used for appliances with current rating of  13 amperes so long as it is less than 16 amperes.   This is because most of the appliances have inherited electromotive force (emf)  during starting up or switching on.   For example,  appliances with electric motor can induce current sometimes as high as 12 times the rating of appliances for as long as 10 seconds during starting up.  That back emf induced could easily damage the time switch if there are frequent start-ups even though the rating of the appliance is less than 3 amperes.  As a rule of thumb,  it is not advisable to load more than 4 amperes for most appliances with or without motor start ups.

Heating up of the Time Switch

Time switch will heat up although its electrical components consume little or no electricity.  This is because there are always resistances in the socket outlet's  connection and the wiring.  A typical resistance of 0.3 ohms in the connection circuit will give up about 2.7 watts of heat if the current is 3 amperes.  Try touching an electric light bulb of about 3 watts,  one would always find it warm to touch.     

Comparing to Mechanical Time Switch

This digital time switch was running cooler than the mechanical time switch probably for 2 reasons

1)     The mechanical one consumes slightly more power;

2)     The mechanical one is a bit old giving rise to higher contact resistance.

Programming

The programming is quite straightforward.  The unit has 8 buttons in 2 lines.   The top ones (3 to 7) are for adjusting and setting the weeks,  hours,  minutes and an R/Recall button to cancel or recall the program.  The bottom ones are for setting of clocks and do the programming with an extra button for manual/auto  turning on and off the time switch.

As usual,  the manual coming along with the unit is written probably by a technical guy who assumed everyone if fully versed with function of the time switch.  It is only with trial and error can one started to understand what was written in the manual.  Fortunately,  nothing will destroy the time switch if one is playing around with the buttons without the unit connecting to any power mains.

The Life Span of Battery

All rechargeable battery has a certain life.  For Ni-MH battery, it is not more than 5 years;  after which,  one would have to replace it.  The unit is supplied with a button or coin type of battery which is often seen in laptop/desktop computers for the CMOS circuits.   The battery is not readily from the neighbourhood store.  One might be able to get them  from Sim Lim Tower at a cost of about SGD$6/= each.  Fortunately,  the unit came with a spare battery chamber that one could easily convert the button or coin battery into an AAA Ni-MH battery if one is familiar with soldering.  The AAA battery is easily and readily available from local stores.

Delivery

The track and trace list of Q0010 shows that the unit was prepared for shipment on 31 March and reached the delivery partner by 1 April who delivered it on 3^rdApril.  The cost of delivery is another SGD$4/= or about 30% of the unit cost.

Conclusion

This time switch is a worthwhile investment.  It works very well compare to the mechanical time switch with flexibility of weekly programming which a mechanical time switch cannot offer.   The only snag is that it came with a button or cell Ni-MH battery which is not only expensive to be replaced,  it is also not readily available.   The alternative is to replace the whole unit or convert the battery to the AAA type;  fortunately,  this problem only comes after 5 years.

Manuals

How To Repair Electronic Equipment with Button Switches

3 April 2014

Introduction

These “critters”,  button switches,  are often used in our electronic equipment whenever there is a button designed to be pressed either to reset a program or to do the programming.

These buttons are cheap but they are often not lasting especially those in the cheaper electronics equipment such as door bells or some remote controls. One would need to press the buttons extra hard in order to sound the door bell or to activate the remote control.

Why?

There are 2 reasons:

1. The current that passes through the buttons is not enough to overcome the “dirt” building up at the contacting point. When the contacts of the button are making or breaking, there will be “sparks” no matter how small, these “sparks” will usually “blow” the dirt building up in the contacts.   If the current is too small,  the sparks created will not be able to "blow" off the "dirt".

2. The current that passes through the button is too strong, hence,  causing sparks to “eat away" the metal of the contact surface and therefore, building carbon resistance enough to prevent the passage of the current.

How to Repair?

First, remove the buttons carefully,  making sure the circuit board is not damaged, then

1. Replace the buttons

This is the best option.

2. Open up the button and then clean the contact. 

This will require some skills to break open the cover and then reseal it after cleaning. Not often successful

3. Pass a small current through the button using a torchlight battery with as many pulsation clicks as possible  (i.e to click the button switch as quickly as possible, say 20 clicks) until the ohms meter measurement across the button switch shows consistent low resistance readings. Do not leave the button switch  close for too long as this will short-circuit the battery.

Method 3 may not necessary work when the contacts of the buttons are completely charred and worn. In that case, the only workable solution is to replace the button switch.   However,  method 3 may be a quick method as it could be done "in circuit"  when one can isolate the switch from the circuit. In the case that one torchlight battery cannot do the job and the button switch came back with the same problem,  try maximum 2 nos of batteries working in series.

I Saw Missing Malaysia Airlines Flight MH370 In Water – Woman says

26 March 2014 

Introduction 

Malaysian flight  MH370 went missing on 8 March with 239 people on board.  It was en routed from Kuala Lumpurto Beijing.  The experts now pin-pointed the plane's location to be about 2,500 km west of Perth,  Australia.  Till date,  there is still no sighting of the plane nor its debris.  This article is not offering any expert view but some arguments and pictures from another angle. 

The Johor Housewife

A Johor housewife, Mrs Latife Dalelah, claimed that she saw an aircraft  half submerged in the waters  at about 2:30 pm  Malaysian time (same for the rest)  when she was returning to Kuala Lumpur after a pilgrimage to Mecca on 8 March.   The news said that she took Saudis flight SV2058 that left Jeddah at 8.30am but actually,  she took Saudis flight SV2798 and not SV2058 as shown in the attached. 

 

Flight Path of SV 2798

According to flightradar’s flight history,  Saudis Airline SV2788’s flight path is as shown.  On 8 March 2014,  SV 2798 took the red dotted path  flying over Chennai of India.

Using the flight data found at flightrada24,  one could determine that flight SV2798 was  above Chennai at around 1300 hour (5:00 UTC).  It then jumped to show SV2798 at the marked location at 1500 hours as there was no data in flightradar24 for 2 hours between the two time intervals on 8 March.    If one interpolates the time and distance,    one could find the rough location where  Mrs Latife Dalelah sighted the airplane at 14:30 hours.    It was at a distance almost perpendicular to the site where Tomnod map 4543, 5239 and other maps were located.  

The same is shown on  a google earth map where Tomnod maps were tagged.

Update:

For those interested in finding out the co-ordinates of the various Tomnod maps using Google Earth or Google Map can download this file.   It will load and appear automatically in Google Earth or map. To get the co-ordinates,  click the "direction" at the bottom.

 What is Tomnod map?

Tomnod is a website where it allows volunteers to spot and tag any object using satellite images.  So far,  some of the maps showing possible debris findings were circulated around in various forums and twitted around as shown in the Appendix.
 

Can one see object from a plane flying at around 35,000 feet?

Many web articles said can.  One of them claimed that we could see a 737 plane or smaller ones from 30,000 feet and  777 is almost twice the size of 737.  He assumed that one should have a normal vision, or vision that was corrected to be normal.   

This website offered a calculator that says that human eyes can see an object about 250 miles away from 35,000 feet.  This is  roughly the distant from where  Mrs Latife Dalelah was to the Tomnod maps.

 

The Satellite Pinging 

The experts used doppler effect of the satellite pinging and the 4 pings to pin-point the where-about of MH370.  Although this Doppler effect of satellite pinging was never used before to locate a plane,  many,  including the Malaysian PM,  have accepted it beyond reasonable doubts.  This Doppler effect concept appears to go against Mrs Latife Dalelah’s plane sighting because the plane was not moving after it had crashed. It could not have been providing the satellite pings with Doppler effect throughout the next 4 hours.   The only logical explanation that can hold some water is that the aircraft’s  satellite pinger might be floating after the crash and was transmitting the signal although the quality, strength and also the frequency of the signal could be affected after being partly submerged in water.    

Conclusion 

There could and just may be possible that Mrs Latife Dalelah had seen flight MH370.   If that is the case,  the multi-nation search now carrying out in the southern Indian Ocean west of Australiawill be futile and will  turn up no result.

Update 1:  Check the vision of the lady  26 March

 

Someone in a forum suggested that lady's vision should be checked as she was over 50.  This suggestion is reasonable but in the first instance,  someone must accept her story.  BTW,  how much would it cost to send a plane there to check it out?

 

 

Update 2:  How deep is the seamount  26 March

 

The seamount or the mountain under water where the Tomnod maps are located is called the "ninetyyeast ridge" in the eastern Indian Ocean as shown.  It is about 5000 km in length,  stretching from the Andaman islands all the way to Western Australia.  According to this echogram from this article,  the ridge is still very deep,   around 1,500 to 2000 metres.  Therefore,  it is likely that any plane landed there would have sunk after sometime.

 

 

 

 Update3 : Picture from the Plane 28 March

 

A Chinese forumer took a photo of Lanzhou airport from a plane.  He said  he was about 10,000 metres (or about 32,800 feet) high and about 200 km away when he took the following  picture with his  Canon digital camera that  has no focusing function.  The parking planes can be seen roughly. 

 

  

Update 4:  Timing of the sighting - 28 March

 

Mrs Latife Dalelah saw  the plane floating in the water at 2:30 pm Malaysian time and the Malaysian's military radar spotted the plane flying around Andaman sea and disappeared from the limit of its screen around 2:15 am,  about 200 miles North West of Penang.  There is an approximate 10 hours between the two locations.  Although the plane might take another hour to fly to the crash site,  the timing is against  Mrs Latife Dalelah's plane sighting unless the plane could float in the water with air pockets in the fuselage and the wings for about 9 hours.

 

 

Update 5: Can Plane float in the water? - 28 March

 

Plane will eventually sink when landed on water.  The time taken will depend on the condition of the aircraft,  how it is damaged as well as the pressure within the aircraft and whether there are still air pockets large enough to hold up the plane.  In the history of aviation,  most planes landed on water sunk within an hour.  However, on 23 November 1996,  there was an Ethiopian Airlines Flight 961 (a Boeing 767-260ER) floated in the Indian Ocean for some time until the 50 survivors were rescued. 

 

============================================================

Appendix I:  Tomnod maps

1)  Tomnod map 4534 and 5239 

Tomnod map 4534 and 5239 contain some satellite images debris that were suspected to be from MH370.   

5239 appears to show the 2 engines of the Boeing 777

It matches the dimensions of Boeing 777 when a 777 was superimposed as shown in the following picture. 

 

Isn't the engines supposed to have sunk? 

It may be because the plane actually hit the seamount as it crashed (see google earth map)  and the plane did not sink immediately when the satellite image was taken.  The waves or ripples created on top and around the right wing suggested some very big boards as large as a wing of a plane was submerged underneath the water.  Just like what was seen here for this plane

 

Map 4543 which shows some debris that appears to match one of the logo of MAS airline “Malaysia” although many said the fonts were not the same.  It may have been distorted due to the poor resolution of the satellite images 

 

Other debris found around the area   

 

 

 

 

Bed Cooler for Ng Teng Fong Hospital

12 February 2013

Introduction

The 700-bed Ng Teng Fong hospital at Jurong East is set to open in December 2013.  It will serve the 900,000-strong residential and business community in the West of Singapore.  It shall have green surroundings and spacious wards with a view of  several rooftop gardens.  However,  what most patients need is also a good rest and a good night sleep for quick recovery in the hospital;  it is always hard to get one in a hot and humid environment like in Singapore.  

Is it acceptable?

The report said that the spacious wards in Ng Teng Fong hospital will have natural ventilation except for those in private wards.  Those who was bedridden before will testify that this is far from acceptable. What about those who are suffering from bed sore?   

What can be done?

One way is to provide air-conditioning for all the wards.  But this will not only make hospital stays  more expensive but also not acceptable because it is unhygienic to share recycled air.   Furthermore,  individual control for air-conditioning is not possible except for the private rooms.  Howvewr, Air conditioners cannot solve bed sore problem unless the heat from the bed can be extracted.   Other methods such as provision of water bed and ripple bed will not help also.   The alternative is to provide bed cooler,  one for each bed.

 

What is a Bed Cooler?

It is a small air conditioning system that will cool only the bed.  It has a cooling  sheet or jacket spreaded between the bed sheet and the bed.  The cooling sheet may have embedded flexible tubes or otherwise that will allow cooled air or chilled water to be circulated to the bed to extract the body heat.  The simple ones used a cooling fan blowing into the cooling sheet;  the more complicated ones use chilled water for cooling.  The latter is preferred because it can provide better and efficient cooling.   

What are the Advantages?

Bed coolers will not only provide affordable cooling,  it is also hygienic as water is used as a media in a closed loop system.  It will work well in natural ventilated wards.  Bed coolers can save up to 90% of the air conditioning bills.  If they are operated together with existing air conditioning,  it can save up to 50% of the energy bills as the temperature of the existing air conditioning can be raised.  The system can be designed to be controlled remotely,  individually and/or centrally  to suit the patients’ cooling requirement.  

Bed sore is one of the biggest problem in hospitals as most hospital use  PVC covered mattresses and pillows for hygienic reason and ease of cleaning.   Patients are often strapped with tubes or illnesses making them difficult to turn their backs and bodies around like ordinary people.    Prolonged staying in the bed in a position will cause bed sores.  Although the nurses can help,  they are often very busy.  Bed coolers can help to solve this bed sore problem,  save labour as well as energy cost.

Why our Hospitals not using them?

It may be because bed cooler is a relatively new concept that has never been used in hospitals.  Many are not sure just how they would fit into the hospital's operation. Bed coolers are quickly perceived to have operational  problem;  for example, how to ensure that the cooling system can be quickly connected and disconnected when the bed is always on the move.  

Bed Cooler,  a Proven System?

Bed coolers are actually nothing new.  They are just miniature size of a chilled water cooling system that has been used in cooling large buildings. They can be part of the existing air conditioning  system with addition of  inexpensive controls and minimum maintenance. 

As for the  quick connection and disconnection of chilled water piping for beds on the move without making a mess on the floor,  there are proven  quick connectors that one can use to ensure safe connection and disconnection without any water spillage or leakage.  Such quick connectors have been used in car racing sports  to fill up the petrol for the racing cars within minutes or seconds.    

Additional Cost

The bed cooler can make use of the existing chillers often installed as a standard in air conditioning buildings.  The additional cost for the new building will not be much;  even for existing buildings,  it would be possible to add bed coolers without additional chillers as the burden of bed coolers  should  be offset by reduced air conditioning load.   The additional cost will therefore be the PVC water jacket which will cost less than $20/= each when purchased in bulk.  There will be additional cost for quick connectors, small pumps, heat exchanger,  tubing and flow controls which a rough estimate indicates that it will not cost more than  $400 per bed including installation. 

 

 

Conclusion

It is good for hospital to have all the features and facilities that are designed for healing but what is the use if the patient cannot get a good rest or a good night sleep in a hot and humid environment of Singapore.  Bed coolers will not only save energy bills, it can also save labour cost and solve bed sore problems.  It is also more hygienic than the ordinary air conditioners.

]
Update :  19 August 2014

Just read  that Tan Tock Seng Hospital had retrofitted their hospital's subsidised  wards with  air conditioning.   This indicates that there are demands even for existing hospital to retrofit its wards for better comfort of the patients.  However,  the air conditioning provision will not be able to solve the bed sore problem because the air conditioning cannot reach the bed and take away the body heat built-ups;  only bed coolers can.   

The retrofitting of the air conditioning to existing building will cost at least 200% more than bed cooler,  requiring extensive retro-fitting work and closure of the wards for some long period.  As for the bed cooler,  one will need only a bottom corner space to run horizontal PVC trunking for piping and controls.,  the installation should take less than a week.

References

Cut Cooling Bills by 90%

Spot Cooling Cuts Aircond Bills by 50%

DIY Bed Cooler

Bed Cooler, a Worthwhile investment

tinyurl :  https://tinyurl.com/y8g4c5xu

What VIX Can Tell Us?

29 Jan 2014

Introduction 

VIX is a volatility index that tracks the trends of the US markets.  It runs inversely proportional to the USindexes.  When VIX goes up,  the general US market indexes like DOW JONE (DJI) ,  S&P500 (SPX) and Nasdaq (IXIC) will trend down and vice versa.   Many investors like to view VIX in daily chart but it would be more meaningful to view VIX in another form.  This article will show how and why. 

Original form

When VIX is shown in its original daily form,  it simply shows the inversion between indexes between say SPX and VIX.  Nothing in the chart can show how one can use VIX to predict  the direction of SPX.

Transformed

If one were to transform VIX by showing only the 20-day,  50-day and 200-day simple averages,  one can use it immediately to show whether it is strong buy or strong sell or just simple buy and sell.

Why?

When VIX is shown in its original form,  the noises of daily movement prevented the trends from revealing.  The average function smoothen out the noises.    One can also use many other similar smoothening technique or technical analysis tools to chart VIX’s direction and predict where the USmarkets will go next.

The Significances

1. The reversal of VIX’s 20-day will indicate the reversal of SPX.  It will also indicate if it is buy or a sell;
2. The 200-day will chart the general direction of the SPX.        SPX will trend up when the 200-day trends down. When the 200-day going flat or trending the other direction; be ready to press buttons;
3. When 20-day or 50-day rebounds from the 200-day,  it could be time for a strong buy or sell;
4. If there is a cross between 20-day,  50-day and 200-day, it has some special meanings.  When the 20-day or 50-day fluctuates around 200-day, it does indicate some weakness to come in the main indexes.

Where the US Markets are Heading?

The US markets should register a strong buy as it rebounded recently from the 200-day;  however,  the 200-day has been going flat with signs of going up;   therefore,  it should limit the further rise of SPX;  also,  the VIX’s daily closing price is running very close to the red 2-year trendline with no sign of trending down.  

With the 20 and 50-day now turning up,  the SPX will be ready to trend down.  When the 20-day crosses the 200-day and subsequently corrects and rebounds from the 200-day,  be ready for a plunge.

Disclaimer:  Please note that this article concludes its finding from analysing the charts.  As the market sentiments will change and so will be the trading pattern,  it is therefore advisable for traders to consult to seek further technical assistance if they should use these findings.

What’s Wrong With this Chart?

25 January 2014

Introduction

Shown in the chart are the DOW’s Transportation Index (^DJT) and DOW’s Commodity Index (^DJC) superimposed over the past 20 years.  There are obvious divergences and convergences between the two index.  Divergences usually happened just before any crisis and the index will converge soon after that.  Recently,  we see divergence with  ^DJT taking off mid 2011 and ^DJC going the other direction.   Lets examine closely what are the causes and  implications

Relationships Between

DJC and DJT

DJC is an index that tracks all the commodity futures that are traded in US.  DJT much Like DJI, the DOW JONES Industrial Index, consisted of about 20 US companies such as FedEx that deal with airline and rail transportation. 

As more produce like iron core, corns etc come on-stream,  more transportation will be needed.  Rightfully speaking,  the better the performance in DJC,  the better will be the performance of DJT and vice versa.  However,  there are rare occasions that over production causes  commodity prices to slump and affects only the commodity price index;  similarly,  a rise in fuel cost will cut transportation companies’ profit.

DJT and DJI

Some argued that DJT was more related to DJI than DJC.  This is because companies in DJI rely on transportation shipments to stock and sell their goods.  When DJI companies anticipate a positive performance, they will increase production of goods that will be needed to be transported between different outlets.  The two indexes inter-twine each other most of the time.

Actually,  DJI,  DJT and DJC are in a value chain except DJC is based on commodity futures indexes whereas DJI and DJT are based on stock prices of the companies.  If the external factors such as QEs are removed,  these 3 indexes should go hand in hand.

Present Development

As can be seen from the chart,   DJT took off mid of 2011 whereas DJC went the other way.  It is obvious that DJT is tracking along with DJI  whose prices have been affected by Bernanke’s QE programs.   

Why?

One reason could be because US are still heavily depended on import of commodities and the production of commodities overseas are more affected by supply and demand rather than the US’s QEs.

Where would the Prices go?

The chart shows that ^DJT and ^DJC wondered around sometimes but they always  converged and move in tandem afterwards.  It can also be seen that whenever there is appreciable divergence between the two indexes,  a recession soon follows;  they will  converge again by the time the recession is over. This happened in around year 2000,  2008 and mid 2011.  Year 2011 was an exception where an intended recession was saved by Bernanke's Operation Twist and QE3.

We are now in year 2014 where one can see the great divergence again between DJT and DJC.  It is therefore likely that these 2 indexes will again converge in the future.   But before the  convergence,  would we not see another recession?

Sealing of Openings for Window Unit Air Conditioner

22 November 2013

Introduction 

Some high rise apartments in Singapore, especially those older types, are in-built with openings for installation of window type air conditioning unit.   With the advent of inverter split air conditioning unit that can save energy,  many apartment owners have converted from the windows unit  to split air conditioner unit.  The AC installer will simply seal up the window unit openings and walk away,  leaving the owners having to face all sort of maintenance problems.  This article will describe how best to seal these openings.

What’re the maintenance problems?

The AC installer will usually seal the opening with a nice painted 3 mm plywood board,  nailed on the timber frames from inside the apartment.  This board will rot in time and allow rain water to sip onto the carpets or parquet floorings during heavy rains.  A small ledge left outside will attract not only birds to nest but also small plants to grow;  also,  the thin plywood board offers no security as they can be easily kicked open. 

What're needed? 

1. A piece of 20 mm thick plywood to cover up the hole;
2. One lots of about 30 numbers of 30 - 35 mm self-taping screws;
3. 4 number of 100 mm self taping screws
4. Few  lengths of 25x25 timber strips
5. Weather sealing strips
6. Necessary tools such as power drills,  drills,  screw drivers etc..

What precautionary measures?

Assuming that one would have to fix the heavy 20 mm board from inside the apartment to cover the opening from outside the apartment,  one necessary measure is to ensure that the board would not accidentally drop and hit some passerby beneath the openings.   This can be done by fixing ring hooks onto the board and tie strings to hold the board throughout the installation.

Installation steps 

1. Cut the 20 mm plywood to a size slightly larger than the hole;
2. Fix the ring hooks and strings,  then put board to the hole and mark up the size of the hole on the board;  alternatively, one can measure the hole and mark the board;

1. Remove the board and cut 4 number of the 25x25 timber strip to  place them exactly in the inner dimension of the opening and screw the timber strip to the board;
2. Protect the board by painting water proofing paints or seal it up with weather board or otherwise to prevent water coming into contact with the plywood;
3. Place weather sealing strip around the 4 sides of the board;
4. Prepare 4 numbers tensioner and install them onto the timber frame as shown,  making sure that the 100 mm screw is free to move and can be screw onto the 25x25 timber strips;
5. Fix the board in place and screw the 100 mm until the board is pulled in and sit tightly fitted to the timber frame with the weather sealing strip fully compressed to form the water seal;
6. Fix the 25x25 timber strip to the timber frame and remove the tensioners if necessary.

The Completed Work 

Makita Cordless Power Drill DC7100

20 November 2013

The Makita Cordless Power Drill is a handy tool.  Its power unit consists of a 7.2 volt battery pack and a fast battery charger.   This article describes how to replace the battery and repair the battery charger.

 What’s Needed

1)     For replacement of battery 

a)     Soldering iron,  solders and some connecting wires

b)     4 Nos  of 18650 Li-ion batteries.  Can also use some of the good batteries in Laptop for this purpose

 

c)     Remove the end cap of the battery pack and withdraw the batteries

d)     Solder the 18650 batteries,  2 in parallel then put them in series to make up a total voltage of 7.4 volts.  Pay particular attention to positive and negative battery terminal and make sure there are correctly wired;  also pay attention to how the resistor is connected. 

e)     Once soldering is completed, wrap the batteries with shrinkable plastic and re-assembled the batteries to the battery pack casing.

2)     For repair of the power charger 

In addition to the soldering iron,   one will need a multimeter that can measure the workings of the A1015 transistor and the 2P4M SCR thyristor.  These 2 components are likely to be at fault.  .  One would need knowledge of electronic repairs for this task.  Use the attached circuit diagram to troubleshoot.

2P4M Thyristor