CHRISTMAS LED STRING TESTER

Too many times, the devices you bought for the old kind (incandescent) of Christmas lights do not work with the new LED Christmas lights. But there are tricks you can use to get these devices to work with many kinds of strings of the new lights.

This tester can be used to find out how to get the desired results with LEDs:

DANGER

DO NOT BUY OR USE THESE BULBS

These imported candelabra-base LED bulbs have enlarged metal ferrules (indicated in diagram) that are connected to the screw shell. An unsuspecting person touching or changing this bulb can contact this live metal part.

  ELECTRICAL SHOCK HAZARD!  

DO NOT USE THIS KIND OF BULB in Christmas light strings or in any socket where the ferrule is exposed. An unpolarized plug on the light string, Christmas lights connected in series, or an open neutral wire in a light fixture can leave the ferrule connected to the live side of the power line.

• What are "special devices"?

  Special devices designed to operate incandescent Christmas lights in any of the following ways:

  • Making the lights chase in sequence
  • Creating interesting patterns in lights (e.g. the GE Gala set)
  • Making lights dance to music
  • Mixing colors using red, green, and blue lights
  • Making lights slowly fade up and down
  • Making lights shimmer or behave like candle flames
  • Making light patterns in a grid (e.g. as on a disco floor)
  • Making light patterns move up and down or around and around a tree
  • A master control system that lights an entire house with many patterns
  • A MIDI (Musical Instrument Digital Interface) controlled system of lights changing to music
  • Converting power from a car to operate the lights
  • Doing more than one of these functions
• What are the ways that LED light strings fail to work with special devices?

  There are several reasons the LED strings fail to work with special Christmas display devices

  • The lights do not pass both directions of alternating current, causing the special device to stop passing power or to pass it wrongly.
  • The special device rectifies the alternating current to direct current, causing part of the LED string to fail to light, or causing too much current to pass through the LEDs (designed to have a rest during part of the AC cycle), burning them out.
  • The special device rectifies the alternating current to direct current, so any switching power supply in the string will not run. The string will not light.
  • The string does not draw enough current to make a normal TRIAC dimmer work.
  • The string has a low power factor, causing phase errors in the special device. This can make the lights stick on, blink on and off, stay either full on or full off, or fail to light.
• How many kinds (electrical) of strings of LED Christmas lights exist?
  

  There are at least 8 different kinds of LED strings:

  • H1: A half-wave string that passes only one direction of the AC cycle.
  • H2: A dual half-wave string that passes one direction of the AC cycle through half of the string and the other direction of the AC cycle through the other half of the string.
  • F1: The string has a full-wave rectifier that sends both directions of the AC cycle through the same LEDS in the same direction. This is the most compatible LED string for special devices.
  • F2: The string has a full-wave rectifier with a filter capacitor that sends both directions of the AC cycle through the same LEDS in the same direction. This is the second most compatible LED string for special devices.
  • B1: The string has a bidirectional LED in each bulb. It passes current in both directions of the AC cycle through the LEDS.
  • D1: The string has a half-wave voltage doubler that uses both directions of the AC cycle to double the voltage through the LEDS. This requires a full-wave AC power source.
  • S1: The string has a switching power supply to power the LEDs (It does not flicker. But most special devices cannot power it).
  • C1: The string has its own special controller that could have any kind of power supply. But it has its own controlling functions that make the lights do things.
  • M1: Each lamp in the string has its own special controller that makes the light do things. These must not be connected to other controllers except on-off timers.

  Note that any of these different kinds can have several series sets of LEDS in parallel (as seen in the F1 and F2 diagrams) or just a single series (as seen in H1). The number of sets in parallel does not change the kind of circuit.

• What happens if the light string is incompatible with the special device?

  Look for any unexpected behavior:

  • The string fails to light.
  • A fuse blows
  • Half of the string fails to light.
  • All or part of the string is too bright (and can burn out early).
  • The lights flash on and off rapidly (when they are not supposed to).
  • The lights are either fully on or are off (in a device that fades brightness).
  • The light string (or an individual light) burns out.
  • Part of the special device burns out.
• What can be done to make LED lights work with special devices?

  In most of the cases, making the load look like incandescent lamps will make the device work with the LED lamps.

  Note that this does NOT work when the LED string has a sophisticated power supply.

  A Converter-Driver works in almost all cases, but it is more expensive.

• What can make LEDs look to the special device like incandescent lamps?
  

  Add a small incandescent load to the circuit:

  Make a load using two incandescent lamp sockets wired in series and spliced into a short extension cord connected between the special device and the LED light strings. The page author used candelabra-base sockets mounted on an electrical junction box.

  Be sure that all connections are well insulated, with heat-shrink tubing, electrical tape, wire nuts, or liquid tape.

  Use TYPE A for normal dimmers.

  Use TYPE B if the device puts out pulsating DC (see below). May not work with all strings.

  Use TYPE C or TYPE D if the special device puts out full-wave rectified DC, but the string is half-wave.
  - If this is true, the string will be brighter on the special device than it is in a standard power socket.
  - The TYPE C load limits string current.
  - The TYPE D load limits string voltage.
  - The TYPE C load also needs a calculation for x in the TYPE A Load.

  Use TYPE E for strings that draw too much current and burn out too quick.

  Use a fuse in either TYPE A or TYPE B that lets the string or lamp work normally, but will blow if the string or lamp shorts out.
  - No fuse is needed for TYPE C, D, or E.

  Use the following tables to determine the minimum size of the incandescent bulbs needed to use the LED strings.

  CALCULATING VALUES
  LOADED CORD TYPE A				LOADED CORD TYPE B						LOADED CORD TYPE C
  NEED LOAD = x/2				FIND CAPACITOR y						FIND LOAD z
  One Bulb x (W)	Two Bulbs Each (W)	Hot Bulb Each (Ω)		Cap y (μF)	Xc @ 60 Hz (Ω)	LEDs (mA)	Est Load (Ω)	Std Bulb Load (W)		LEDs (mA)	Hot Bulb Res (Ω)	Bulb volt drop (V)	Std Bulb z (W)
  4	2	7200		1	2653	4	3316	4		20	2880	57.6	5
  5	2.5	5760		2	1326	8	1658	10		40	1440	57.6	10
  7	3.5	4114		3.3	804	13	1005	15		60	960	57.6	15
  10	5	2880		5	531	20	663	20		*	*	*	*
  12	6	2400		10	265	40	332	50		*	*	*	*
  15	7.5	1920		20	133	80	*	*		*	*	*	*
  20	10	1440		33	80	132	*	*		*	*	*	*
  25	12.5	1152		50	53	200	*	*		*	*	*	*
  30	15	960		100	27	400	*	*		*	*	*	*
  40	20	720		200	13	799	*	*		*	*	*	*
  60	30	480		330	8	1319	*	*		*	*	*	*

  * Beyond the scope of LED Christmas Strings - Use a method other than Loaded Cord Type B or C.

  CALCULATING VALUES
  LOADED CORD TYPES A, D, AND E													LOADED CORD TYPE D WITH STRING
  Lamp properties							Series properties						ALL	Lower series t&t value of t
  Rate 120V (W)	Bulbs t and u			Bulb t	Bulb u		Rate 120V (W)	2 Bulb Series Values					Upper Rated (W)	t to set current
  	120V (mA)	hot (Ω)	cold (Ω)	60V (mA)	50V (mA)			120V (W)	120V (mA)	hot (Ω)	cold (Ω)			0 mA	10 mA	20 mA	30 mA	40 mA
  4	33.3	3600	450	16.7	13.9		4	2	16.7	7200	900		5	4	†	†	†	†
  5	41.6	2880	360	20.8	17.4		5	2.5	20.8	5760	720		6	5	†	†	†	†
  6	50.0	2400	300	25.0	20.8		6	3	25.0	4800	600		7.5	6	4	†	†	†
  7.5	62.5	1920	240	31.3	26.0		7.5	3.75	31.3	3840	435		10	7.5	5	4	†	†
  10	83.3	1440	144	41.7	34.7		10	5	41.7	2880	360		12	10	7.5	5	4	†
  12	100	1200	180	50.0	41.7		12	6	50.0	2400	300		15	12	10	7.5	5	4
  15	125	960	120	62.5	52.1		15	7.5	62.5	1920	240		20	15&20	15	12	10	7.5
  20	167	720	90	83.3	69.4		20	10	83.3	1440	180		25	20	15&20	15	12	10
  25	208	576	72	104	86.8		25	12.5	104	1152	144		30	25	20&25	20	15&20	15
  30	250	480	60	125	104		30	15	125	960	120		40	30&40	30	30	25&30	25
  40	333	360	45	167	139		40	20	167	720	90		*	*	*	*	*	*

  * Beyond the scope of LED Christmas Strings - Use a method other than Loaded Cord Type D.
  & Between standard lamp sizes - use one of each in the series.
  † Below the scope of LED Christmas Strings - Use a method other than Loaded Cord Type D.

  Calculating for load TYPE D

  • The series forms a voltage divider when combined with the current drawn by the light string(s).
  • The upper lamp u wattage is adjusted so the voltage across it is 50 volts.
  • The lower lamp t&t series and the string(s) should have 120 volts across them.
  • If a single-direction half-wave string is used, calculate for the direction of current flow in the string.
  • If current flows in opposite directions are unequal, calculate for the direction with the higher current.

  If the special device has a minimum wattage rating, use that in the left column of the tables.

  CAUTION: Do not exceed the Device Max power capability of the special device.

  If the special device does not specify a minimum wattage, use trial and error, starting with the largest size in the table that does not exceed the output capabilities and working down until the special device misbehaves. Then go up at least 20 percent from the value that made it fail, to make sure the special device does not intermittently fail.

  Because the two lamps are in series, they should rarely burn out. But keep some spares, because they may ban all incandescent lamps.

  The load lamps do not need to be part of the display. They can be hidden in any out-of-the-way place. But make sure they have ventilation air and do not touch other materials.

  This TYPE A load will be referred to as a loaded cord.

  An output with this TYPE A load device connected to it will be referred to as a loaded output.

  The capacitor in the TYPE B load must be non-polarized.

  Experiment with bulb z wattage in the TYPE C and TYPE D loads to make string brightness the same as the string plugged into a standard power socket. Bulb z might not reach full hot resistance.

• What devices has this loaded cord trick worked for?

  These loaded outputs have worked for the page author for the following:

  • An old-style thermal flasher
  • A chase-light sequencer
  • A color-fader sequencer
  • Two different dance-to-the-music color organs
  • A candle-flame flicker simulator
  • A lamp dimmer
  • A GE Gala set with the light strings cut off* and the ends of the extension cords with the loads spliced into the cut ends from the controller,
    - The output is full-wave rectified DC and requires Loaded Cord C.
    - Note that each socket is fused and marked as being for only LED Christmas lights.
    * The incandescent light strings were already damaged. The page author wanted to keep the functionality of the set, but use LED lights.
• What if none of the string lights when connected to a loaded output, even though the load lamps light?
  • If the string does not work when plugged directly into a wall outlet, the string is bad or the fuse is blown.
  • If the string works when directly plugged into an outlet, but not on the loaded output of the special device, a DC string may be plugged in backwards. Turn the plug of the string over.
  • If the string still does not work on the loaded output, but works in a wall socket, it has a switching power supply. It will not work with the special device.
  • If the plug is polarized and will not go in the other way, try turning the plug over at the special device end of the loaded cord.
  • If neither plug can be turned over, see the question about "The DC string has the wrong polarity" below.
• What if the lights of the string are brighter on the special device than they are when plugged into a standard power socket?
  • Do not use them this way or their lives will be shortened.
  • The special device outputs full-wave rectified DC. The LED string is half-wave.
  • Use Loaded Cord D to fix the problem.
• What if the lights of the string are brighter than they should be and burn out quickly when plugged into a standard power socket?
  • Do not use them this way or their lives will be shortened.
  • The string is mismanufactured or is made for the 100V power of northern Japan.
  • The string has a capacitor current load instead of a resistor. Surges destroy LEDs.
  • Use Loaded Cord E to fix the problem.
    • If the string is made for northern Japan, the series load E must absorb 20 volts at probably 20 mA. This needs a resistive load of 1000Ω cold.

      This load E requires a 4W and a 3W lamp in series.

    • If the string passes too much current or has a capacitive load the series load E must absorb 10 volts at probably 20 mA. This needs a resistive load of 500Ω cold.

      This load E requires two 7W lamps in series.

• What does "turn the plug over" mean?

  Pull the plug out of the socket, turn it half a turn, and plug it back in, so the two prongs are inserted into each other's slots.

  Note that this does not work if the plugs are polarized or a three-prong plug is used.

• What does it mean that the plugs are polarized?
  

  The neutral blade of the plug is wider than the live blade. This is made so the neutral blade is always plugged into the neutral slot in the outlet.

  The plug will not fit into the socket the other way.

  Three-prong plugs with the safety ground pin are also polarized.

  This was done so that the screw shell of an Edison-base light bulb socket is always connected to the neutral.

  This prevents someone from accidentally contacting a live screw shell of a light bulb when changing bulbs. It is a safety device that should normally not be defeated.

  In the case of LED Christmas lights, there is no agreement between manufacturers of the polarity of a string that works on only half of the AC cycle (or on DC).

  • Many strings do not have polarized plugs.
  • Some string manufacturers do not standardize the polarization of their strings.
  • Often the polarization of the plug does not match the DC polarization of the device feeding the light string.
  • Some strings pass current to half of the lights on each half of the AC cycle.

  The surgeries on light strings listed below change the polarity of part or all of the string without changing the polarity of the outlet at the end of the string.

• What if only half of the string lights up when it is plugged in to the loaded output?

  If this occurs, the entire string needs AC, but the special device output is DC. See below.

• What needs to be done to fix a case where only half of the string lights?

  There are several possibilities:

  • Replace LED string with one that works on DC (e.g. has full-wave rectification).
  • Replace the special device with one that provides an AC output.
  • Use the TYPE B loaded cord (see above). Note that this does not work with some strings.
  • Do surgery on the LED light string to make it work on DC. See Surgery.
  • Build a relay device or a TRIAC Converter-Driver that converts one kind of output into the other.
• How can I build a Converter-Driver?
  

  Use the wiring diagram at right:

  • The plug on the left goes into any special device.
  • The plug on the right supplies power to the strings or lamps.
  • The TYPE A load and full-wave rectifier should work with any special device.
  • Build the TYPE A load and choose bulbs to fit your special device.
  • Choose the triac to be able to drive the load you have with capacity to spare.
  • This circuit can be built to drive loads much larger than the special devices can drive.
  • This circuit provides electrical isolation between the special device and the load circuit.
• Can a tool be built to test special device outputs and light strings for load and polarity?

  Yes. The following circuit can do this.

  ---

  THE CHRISTMAS LIGHT TESTER

  ---

  The tester can test all of the following:

  • The special device output
  • The LED string of Christmas lights
  • Connection between the special device and the LED string of Christmas lights

  Features of the Tester:

  • The grounded (3-prong) power plug PS (orange) to be plugged into a grounded outlet.
  • A grounded (3-prong) socket SD (white) for powering the special device.
  • An ungrounded (2-prong) plug SD (white) for the output of the special device. The plug is ungrounded so it will fit either a grounded or an ungrounded output socket. If the special device is not used, the SD Plug and the SD socket must be connected together.
  • A grounded (3-prong) socket LS (orange) for the light string. The grounding comes from the PS power plug.
  • Switches for DC simulation (A and B), loading (C), and AC restoration (D and E).
  • Green LED lamps for observing the AC and DC output characteristics of the special device.
  • Red LED lamps for observing the AC and DC characteristics of the power feeding the light string.

  Instructions:

  

  

  

  • Build this to power line safety standards. Everything should be insulated and no live parts may be exposed.

    The device was built into a 3-gang plastic electrical box with a 3-gang cover.

    The plastic nailing ears were cut off the electrical box.

    Holes were drilled in the "back" if the electrical box to mount the lamp sockets.

  • Use an output fuse sufficient to let the string or load to operate, but to blow if the string or lamp draws too much current because it malfunctions.
    If the string has a fuse in its plug, use twice the value of that fuse.
    If many different strings will be tested, use a 1/2 amp fuse.
  • Testing the output of a special device:
    1. Turn off all tester switches (A and E off, B, C, and D to center).
    2. Plug the PL plug of the tester into a power socket.
    3. Plug the special device into the SD socket of the tester.
    4. Plug the SD plug of the tester into the special device output.
    5. Turn on switch A.
    6. Turn on the special device.
    7. If both green LEDs light, the special device puts out AC.
    8. If only the + green LED lights, the special device puts out positive DC.
    9. If only the − green LED lights, the special device puts out negative DC.
    10. If neither LED lights, turn on switch C1 and repeat the test.
    11. If neither LED lights, turn on switch C2 and repeat the test.
        DO NOT use C2 if the device is rated for only miniature lights.
    12. If only the + green LED lights or of only the − green LED lights, the special device puts out some kind of DC. If so, continue with the next tests:
    13. Turn on switches C1 and D1.
    14. If only one green LED lights but both red LEDs do not light, the special device puts out pure DC. A TYPE B device will not work.
    15. If only one green LED lights but both red LEDs light, the special device puts out pulsing DC. A TYPE B device can possibly work.
    16. Use Table A below for more comprehensive tests.

    The first photo shows a simulation of a loaded AC source using switches A, C2, and E.

  • Testing a string of LED lights:
    1. Turn off all tester switches (A and E off, B, C, and D to center).
    2. Plug the PL plug of the tester into a power socket.
    3. Plug the SD plug of the tester into the SD socket of the tester.
    4. Plug the LED string into the tester SL socket.
    5. Turn on switches A and E. All of the LEDs in the string should light.
    6. Turn off switch A.
    7. Turn on switch B+. If half of the string lights, that half uses positive DC.
    8. If entire string lights, the entire string can use positive DC.
    9. Turn on switch B−. If half of the string lights, that half uses negative DC.
    10. If entire string lights, the entire string can use negative DC.
    11. If entire string lights in both B+ and B−, it has a full wave rectifier.
    12. If the string stays dark in B+ and B−, its switching supply can't use DC.
    13. If the string stays dark in A, B+, and B−, check the string for defects.
    14. If each half of the string lights in different tests above, turn off switches A and E and turn on switches B+, C1, and D1. If both halves of the string light, then the TYPE B loaded cord will work with a pulsing CD special device.
    15. If half or none of the string lights in the above test, try different combinations of C1 and C2 and of D1 and D2. If both halves of the string light in any of the combinations, then that combination should be used as a starting point for design of the loaded cord.
    16. Use Table B below for more comprehensive tests.
  • Testing a string of lights with the output of a special device:
    1. Plug the string into normal power and notice its brightness.
    2. Turn off all tester switches (A and E off, B, C, and D to center).
    3. Plug the PL plug of the tester into a power socket.
    4. Plug the special device into the SD socket of the tester.
    5. Plug the LED string into the tester SL socket.
    6. Plug the SD plug of the tester into the special device output.
    7. Turn on the special device.
    8. If the test of the special device output required switch C1 or C2, turn on that switch.
    9. Turn on switches A and E. If the string lights normally, it will work with the special device.
    10. If the string lights brighter than it was on normal power, unplug it immediately. A TYPE C loaded cord will be needed.
    11. If the string stays dark or acts up, turn on switch C1 (if it is off). If the string lights normally, it will work with the special device with a TYPE A loaded cord.
    12. If the string still stays dark but the load lamps of the tester light, try switch C2 if the special device can handle the load.
    13. If half of the string lights, Turn off switch E and turn on switches C1 and D1. If the string lights normally, it will work with the special device with a TYPE B loaded cord.
    14. If half or none of the string lights in the above test, try different combinations of C1 and C2 and of D1 and D2. If both halves of the string light in any of the combinations, then that combination should be used as a starting point for design of the loaded cord.
    15. If the string still stays dark, it can't be used with the special device.
    16. Use Table C below for more comprehensive tests.

    The second photo shows a simulation of a loaded pulsing DC source using switches B+, C1, and E.

  TABLE A - TESTING POWER SOURCES AND SPECIAL DEVICES
  CONNECTIONS			SWITCHES					LEDS		OUTCOMES
  SOCKET SD	PLUG SD	SOCKET LS	A	B	C	D	E	GRN	RED	OBSERVED LIGHTING EFFECT	MEANING AND NOTES
  SD Pow	SD Out	none	A	off	off	D1	off	+ −	+ −	AC before and after capacitor	Outputs AC
  SD Pow	SD Out	none	A	off	off	D1	off	+	off	Positive DC unknown type	Outputs positive DC
  			A	off	C1	D1	off	+	+ −	Positive pulsing DC	Outputs positive pulsing DC
  								+	off	Positive steady DC	Outputs positive steady DC
  SD Pow	SD Out	none	A	off	off	D1	off	−	off	Negative DC unknown type	Outputs negative DC
  			A	off	C1	D1	off	−	+ −	Negative pulsing DC	Outputs negative pulsing DC
  								−	off	Negative steady DC	Outputs negative steady DC
  SD Pow	SD Out	none	A	off	off	D1	off	off	off	No current supplied	Not working or needs a load
  			A	off	C1	D1	off	any lit	+ −	Small load makes current flow	Needs a small load
  			A	off	C2†	D1	off	any lit	+ −	Large load makes current flow	Needs a large load
  			A	off	C2†	D1	off	off	off	No current supplied-	Not working
  † Do not use position C2 if the device is not rated for use with anything larger than miniature light strings. Use C1.
  TABLE B - TESTING LED LAMPS AND LIGHT STRINGS
  CONNECTIONS			SWITCHES					LEDS		OUTCOMES
  SOCKET SD	PLUG SD	SOCKET LS	A	B	C	D	E	GRN	RED	OBSERVED LIGHTING EFFECT	MEANING AND NOTES
  Plug Together		String	any	any	any	any	any	any	any;	RAPID FLASHING OR MALFUNCTION*	TURN OFF A AND B IMMEDIATELY*
  Plug Together		String	A	off	off	off	E	+ −	+ −	String should work here	Works on normal AC
  Plug Together		String	off	B+	off	off	E	+	+	String lights normally	Full-wave rectified string
  								+	+	Only half of the string lights	Each series is half wave
  								+	+	String does not light or malfunctions*	Switching power supply needs AC
  			off	B+	C1	D1	off	+	+ −	Entire string lights	Pulsing DC uses loaded capacitor
  								+	off or +	Entire String is off or part is dim	Can't use series capacitor
  Plug Together		String	off	B−	off	off	E	−	−	String lights normally	Full-wave rectified string
  								−	−	Only half of the string lights	Each series is half wave
  								−	−	String does not light or malfunctions*	Switching power supply needs AC
  			off	B−	C1	D1	off	−	+ −	Entire string lights	Pulsing DC uses loaded capacitor
  								−	off or +	Entire String is off or part is dim	Can't use series capacitor
  * This malfunction can damage the light string if not stopped immediately.
  † Do not use position C2 if the special device is not rated for use with anything larger than miniature light strings. Use C1.
  TABLE C - TESTING SPECIAL DEVICES WITH LED LAMPS AND LIGHT STRINGS
  CONNECTIONS			SWITCHES					LEDS		OUTCOMES
  SOCKET SD	PLUG SD	SOCKET LS	A	B	C	D	E	GRN	RED	OBSERVED LIGHTING EFFECT	MEANING AND NOTES
  SD Pow	SD Out	String	any	any	any	any	any	any	any;	RAPID FLASHING OR MALFUNCTION*	TURN OFF A AND B IMMEDIATELY*
  SD Pow	SD Out	String	any	any	any	any	any	any	any;	ALL OR PART OF STRING IS TOO BRIGHT‡	TURN OFF A AND B IMMEDIATELY‡
  SD Pow	SD Out	String	A	off	off	off	E	+ −	+ −	String works normally	Output is normal AC
  SD Pow	SD Out	String	A	off	off	off	E	any	any	RAPID FLASHING OR MALFUNCTION*	TURN OFF A AND B IMMEDIATELY*
  			A	off	off	off	E	off	off	No current supplied	Won't work or needs a load
  			A	off	C1	off	E	+ −	+ −	Small load makes current flow	Needs a small load
  			A	off	C2†	off	E	+ −	+ −	Large load makes current flow	Needs a large load
  			A	off	C2†	off	E	off	off	No current supplied-	Cannot drive this string
  SD Pow	SD Out	String	A	off	off	off	E	+	+	String lights normally	Full-wave rectified string
  								+	+	Only half of the string lights	Each series is half wave
  								+	+	String does not light or malfunctions*	Switching power supply needs AC
  			A	off	C1	D1	off	+	+ −	Entire string lights	Pulsing DC uses loaded capacitor
  								+	off	Entire String is off	Can't use series capacitor
  SD Pow	SD Out	String	A	off	off	off	E	−	−	String lights normally	Full-wave rectified string
  								−	−	Only half of the string lights	Each series is half wave
  								−	−	String does not light or malfunctions*	Switching power supply needs AC
  			A	off	C1	D1	off	−	+ −	Entire string lights	Pulsing DC uses loaded capacitor
  								−	off	Entire String is off	Can't use series capacitor
  * This malfunction can damage the lights and the special device if not stopped immediately.
  † Do not use position C2 if the special device is not rated for use with anything larger than miniature light strings. Use C1.
  ‡ This can damage the lights. Use loaded cord C.

• How do the different kinds (electrical) of LED strings behave with special devices:

  The following are the usually expected results.

  TYPE	Normal AC	Pulsed DC	Steady DC	Pulse w/ LOAD B	TRIAC Dimmer	Diagram
  H1:	Works Normally (or try LOAD A)	One Way Turn plug over ovetvolt LOAD C	One Way Turn plug over ovetvolt LOAD C	no Does not pass AC.	Use LOAD A if dimmer malfunctions
  H2:	Works Normally (or try LOAD A)	Half set lights LOAD B, surgery ovetvolt LOAD C	Half set lights (Surgery only fix) ovetvolt LOAD C	Maybe - Half of string might stay dark	Use LOAD A if dimmer malfunctions
  F1:	Works Normally (or try LOAD A)	Works Normally (or try LOAD A)	Works Normally (or try LOAD A)	Maybe (Unnecessary)	Use LOAD A if dimmer malfunctions
  F2:	Works Normally (or try LOAD A)	Works Normally (or try LOAD A)	Works Normally (or try LOAD A)	Maybe (Unnecessary)	Use LOAD A if dimmer malfunctions
  B1:	Works Normally (or try LOAD A)	Works Normally (or try LOAD A)	Works Normally (or try LOAD A)	Maybe - Half of string might stay dark	Use LOAD A if dimmer malfunctions
  D1:	Works Normally (or try LOAD A)	no - Can damage power supply	no - Can damage power supply	Maybe - Might be dim or stay dark	Use LOAD A if dimmer malfunctions
  S1:	Works Normally (or try LOAD A)	no - Can damage power supply	no - Can damage power supply	no - Can damage power supply	Try LOAD A if dimmer malfunctions
  C1:	Works Normally (or try LOAD A)	no - Can damage power supply	no - Can damage power supply	no - Can damage power supply	Try LOAD A if dimmer malfunctions
  M1:	no - No controller on/off timer OK	no - No controller on/off timer OK	no - No controller on/off timer OK	no - No controller on/off timer OK	no - No controller on/off timer OK

• How can the tester be used to do the different kinds of electrical LED string tests?

  TABLE D - TROUBLESHOOTING LIGHTS AND SPECIAL DEVICES
  SYMPTOM	POSSIBLE CAUSE	WHAT TO DO	MEANING
  Unintended rapid flashing*	Special device won't drive LEDs	Try the test box with switches: A, off, C1, off, E)	Special device needs incandescent load
  		Try the test box with switches: A, off, C2†, off, E)
  		Try loaded cord A (above).
  		None of the above work.	String can't be used with special device
  String is dim or won't light	Special device won't drive LEDs	Try the test box with switches: A, off, C1, off, E)	Special device needs incandescent load
  		Try the test box with switches: A, off, C2†, off, E)
  		Try loaded cord A (above).
  		None of the above work.	String can't be used with special device
  Only half of the string lights	Special device has a DC output	Try the test box with switches: A, off, C1, D1, off	Special device emits pulsing DC Capacitor reconstitutes AC
  		Try the test box with switches: A, off, C2†, D2, off
  		Try loaded cord B (above).
  		None of the above work.	Special device puts out steady DC
  All or part of string too bright	Full wave device with half wave string	Try loaded cord C	Special device emits steady or full-wave DC
  None of the above tests work	Special device can't drive string	Get a different string of lights	String can't use special device output
  * This malfunction can damage the lights and the special device if not stopped immediately.
  † Do not use position C2 if the special device is not rated for use with anything larger than miniature light strings.

• Can the tester check for failures in LED Christmas lights?

  Yes. Do the following:

  1. Turn off all tester switches (A and E off, B, C, and D to center).
  2. Plug the PL plug of the tester into a power socket.
  3. Plug the SD plug of the tester into the SD socket of the tester.
  4. Plug the LED string into the tester SL socket.
  5. Turn on switches A and E. All of the LEDs in the string should light.

  If part of the string does not light, there is a failure in the string. Often a bulb is burned out, shorted, or loose.

Links:

Links:

Fun with Christmas Lights

Christmas Light Devices

Make Christmas Lights Shimmer

Sequence your Christmas Lights

Light Bulbs, Spectra, and Vision