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How do I test a lapotop power cable
Hi all,
What do I need to test a laptop cable? Often there is no LED on the adapter, and I'm often left wonder well is it a broken cable, a broken adapter or is there something broken inside the laptop. Usually I find the cable is at fault. thanks for any advice, cheers! |
#2
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How do I test a lapotop power cable
One way to get or make a wire ended low powered 12V lamp say a couple of watts and use that has a 'dummy load', you can of course use a test meter, connect to the end making sure you are not shorting the bare wires and you should be OK.... .... the only other way is to connect the lead to the machine, holding the plug steady waggle the wire and see if it goes off broken wire, the wire breaking because of the stress of pulling... you can then hold the wire steady and waggle the plug to check for a faulty socket or loose fitting plug again usually caused by stress of pulling and pushing. Pulling at the wire is not the correct way of removing the lead from the machine for obvious reasons, do not be tempted to use high wattage lamps should you take this route of trying the lead... with a lamp the wire polarity, that is the +ve and -ve doesn't matter. davy |
#3
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How do I test a lapotop power cable
"someone_else" wrote in message ... Hi all, What do I need to test a laptop cable? Often there is no LED on the adapter, and I'm often left wonder well is it a broken cable, a broken adapter or is there something broken inside the laptop. Usually I find the cable is at fault. thanks for any advice, cheers! ok .. I had an idea that a multimeter would help me so I have one on order ... should be easy enough to figure out how to use.. |
#4
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How do I test a lapotop power cable
someone_else wrote:
"someone_else" wrote in message ... Hi all, What do I need to test a laptop cable? Often there is no LED on the adapter, and I'm often left wonder well is it a broken cable, a broken adapter or is there something broken inside the laptop. Usually I find the cable is at fault. thanks for any advice, cheers! ok .. I had an idea that a multimeter would help me so I have one on order .. should be easy enough to figure out how to use.. Failures can be due to a "short circuit" or due to an "open circuit". A short circuit overloads the switching power converter. An open circuit prevents current flowing to the load. Your LED symptoms are telling you something. The LED inside the adapter end, could be monitoring the single voltage which feeds the laptop. The LED could be connected to the 18V rail, through a current limiting resistor in series with it. So it may be giving you direct feedback about the output. The adapter could fail to produce any output, due to a primary side or secondary side circuit problem inside the "brick". That would require a new adapter, as getting inside it, may not be that easy. If the cable is frayed, near the laptop end, the wires could short temporarily. The adapter may have overcurrent protection, which causes the LED on the adapter to go out. Overcurrent protection means the adapter does not get hot when it gets shorted. It might get hot if operated at its rated load. So there should be some protection from short circuits in the thing. That helps to reduce the possibility of a fire. Inside the laptop, there is probably some means to prevent an external electrical failure, from draining the battery in a spectacular way. Perhaps a diode or equivalent, only allows current to flow from the charger barrel connector input, rather than back out of it. But if the center connector pin on the laptop end, broke, and touched the other conductor, that would cause the LED to go out. That could be your short circuit. So the short could be at the laptop connector, or anywhere along the adapter barrel plug and cable. If the connector inside the laptop end broke, it could also fail open circuit. The laptop wouldn't get any current in that case, but the adapter LED would likely stay operating. Your symptoms don't match that case. So that leaves a short in the cable somewhere, or some kind of failure in the AC to DC bits inside the brick. Typical tests a person would do on an adapter, would consist of two tests. These tests are intended to prove the adapter operates over its ratings range. 1) With adapter unplugged from load, verify the open circuit voltage. The adapter is likely regulated DC, and it might deliver a steady 18V whether the load is zero amps or 3.5 amps. An open circuit test verifies the switching converter inside the brick, is doing something. The LED should come on. If the switching regulator is "weak", it might still pass this test, and the LED might be on. 2) load test. If the adapter is rated 18V at up to 3.5A, then a person could devise a load test. This tests that the adapter meets its stated rating. Doing the math, 18V / 3.5A = 5.14 ohms. Nine of the following resistors in parallel, would give a 5.55 ohm load, with a 90 watt dissipation rating (point a fan at the resistors, to cool them off). There should be some clearance around each resistor for air flow. The slightly higher resistance value I get by using just nine resistors, means the load test will be testing the adapter at slightly less than 100% of its rating. I don't want the final load resistance value to be lower than 5.14 ohms. http://www.radioshack.com/product/in...ductId=2062292 The load test verifies the brick still delivers the rated power. If the LED goes out during the load test, then the adapter should be replaced. It could very well be a problem with the switching regulator inside the brick. During the load test, you can also verify the regulated output voltage is still at 18V or whatever. Different brands of adapters, will operate at different voltage and current values. There are 65W adapters and 90W adapters. There can be subtle differences between them. You can adjust the arithmetic above to suit. The only thing I don't like about that load test above, is the resistors are wire wound. That means there could be a slight inductive kick when the load is applied or disconnected. I would leave the load connected before plugging and unplugging the adapter, during the load test, to reduce the insult to the adapter. The adapter may have "slow start" output, which would reduce inductive kickback. Once the adapter is disconnected from the wall, then I'd disconnect my home made load. I use resistors like that, for a home made ATX power supply tester. I point an 80mm fan at my resistors, during the test. I load test new ATX power supplies, before I use them, but not at their rated power. (I run for a couple hours, to verify there aren't any infant mortality problems with my new product. I check the voltages during the test.) A laptop is more likely to use all the watts that the adapter can provide, so getting closer to the rating makes more sense for those. (You don't need to run the load test for two hours on the laptop adapter - even 30 seconds is enough to prove it still runs at close to full load.) Since an ATX supply has multiple rails, it is more difficult (and expensive) to devise meaningful load tests. I selected a total loading of about 100W or so, for my tester, suitable for most power supplies I might buy. It isn't intended to be stressful to the supply and wasn't part of my plan. It allows me to check the voltages before actual usage, without danger to a new motherboard. (An example of a home ATX power supply tester.) http://groups.google.ca/group/alt.co...b?dmode=source To make a reliable connection to a barrel power plug, you could use something like this. Otherwise, it could be difficult to hold a load in place without the contact being intermittent. http://search.digikey.com/scripts/Dk...ame=CP-048H-ND HTH, Paul |
#5
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How do I test a lapotop power cable
"Paul" wrote in message ... someone_else wrote: "someone_else" wrote in message ... Hi all, What do I need to test a laptop cable? Often there is no LED on the adapter, and I'm often left wonder well is it a broken cable, a broken adapter or is there something broken inside the laptop. Usually I find the cable is at fault. thanks for any advice, cheers! ok .. I had an idea that a multimeter would help me so I have one on order .. should be easy enough to figure out how to use.. Failures can be due to a "short circuit" or due to an "open circuit". A short circuit overloads the switching power converter. An open circuit prevents current flowing to the load. Your LED symptoms are telling you something. The LED inside the adapter end, could be monitoring the single voltage which feeds the laptop. The LED could be connected to the 18V rail, through a current limiting resistor in series with it. So it may be giving you direct feedback about the output. The adapter could fail to produce any output, due to a primary side or secondary side circuit problem inside the "brick". That would require a new adapter, as getting inside it, may not be that easy. If the cable is frayed, near the laptop end, the wires could short temporarily. The adapter may have overcurrent protection, which causes the LED on the adapter to go out. Overcurrent protection means the adapter does not get hot when it gets shorted. It might get hot if operated at its rated load. So there should be some protection from short circuits in the thing. That helps to reduce the possibility of a fire. Inside the laptop, there is probably some means to prevent an external electrical failure, from draining the battery in a spectacular way. Perhaps a diode or equivalent, only allows current to flow from the charger barrel connector input, rather than back out of it. But if the center connector pin on the laptop end, broke, and touched the other conductor, that would cause the LED to go out. That could be your short circuit. So the short could be at the laptop connector, or anywhere along the adapter barrel plug and cable. If the connector inside the laptop end broke, it could also fail open circuit. The laptop wouldn't get any current in that case, but the adapter LED would likely stay operating. Your symptoms don't match that case. So that leaves a short in the cable somewhere, or some kind of failure in the AC to DC bits inside the brick. Typical tests a person would do on an adapter, would consist of two tests. These tests are intended to prove the adapter operates over its ratings range. 1) With adapter unplugged from load, verify the open circuit voltage. The adapter is likely regulated DC, and it might deliver a steady 18V whether the load is zero amps or 3.5 amps. An open circuit test verifies the switching converter inside the brick, is doing something. The LED should come on. If the switching regulator is "weak", it might still pass this test, and the LED might be on. 2) load test. If the adapter is rated 18V at up to 3.5A, then a person could devise a load test. This tests that the adapter meets its stated rating. Doing the math, 18V / 3.5A = 5.14 ohms. Nine of the following resistors in parallel, would give a 5.55 ohm load, with a 90 watt dissipation rating (point a fan at the resistors, to cool them off). There should be some clearance around each resistor for air flow. The slightly higher resistance value I get by using just nine resistors, means the load test will be testing the adapter at slightly less than 100% of its rating. I don't want the final load resistance value to be lower than 5.14 ohms. http://www.radioshack.com/product/in...ductId=2062292 The load test verifies the brick still delivers the rated power. If the LED goes out during the load test, then the adapter should be replaced. It could very well be a problem with the switching regulator inside the brick. During the load test, you can also verify the regulated output voltage is still at 18V or whatever. Different brands of adapters, will operate at different voltage and current values. There are 65W adapters and 90W adapters. There can be subtle differences between them. You can adjust the arithmetic above to suit. The only thing I don't like about that load test above, is the resistors are wire wound. That means there could be a slight inductive kick when the load is applied or disconnected. I would leave the load connected before plugging and unplugging the adapter, during the load test, to reduce the insult to the adapter. The adapter may have "slow start" output, which would reduce inductive kickback. Once the adapter is disconnected from the wall, then I'd disconnect my home made load. I use resistors like that, for a home made ATX power supply tester. I point an 80mm fan at my resistors, during the test. I load test new ATX power supplies, before I use them, but not at their rated power. (I run for a couple hours, to verify there aren't any infant mortality problems with my new product. I check the voltages during the test.) A laptop is more likely to use all the watts that the adapter can provide, so getting closer to the rating makes more sense for those. (You don't need to run the load test for two hours on the laptop adapter - even 30 seconds is enough to prove it still runs at close to full load.) Since an ATX supply has multiple rails, it is more difficult (and expensive) to devise meaningful load tests. I selected a total loading of about 100W or so, for my tester, suitable for most power supplies I might buy. It isn't intended to be stressful to the supply and wasn't part of my plan. It allows me to check the voltages before actual usage, without danger to a new motherboard. (An example of a home ATX power supply tester.) http://groups.google.ca/group/alt.co...b?dmode=source To make a reliable connection to a barrel power plug, you could use something like this. Otherwise, it could be difficult to hold a load in place without the contact being intermittent. http://search.digikey.com/scripts/Dk...ame=CP-048H-ND HTH, Paul Thanks all, I am enjoying playing with my multimeter .. a friend of mine has bought at least four replacement adapters for his laptop .. I just tested one of his 'bad' ones .. it's good! .. so I guess I'll be taking his laptop to bits soon .. |
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