Help with DC adapter - Page 1
Forum section: electronics / beginners

author: jj5
author_rank: Unknown
timestamp: July 20, 2023, 03:10:06 am
content: Hi there. I needed a 19.5V DC adapter so I purchased one of these:19.5V 2.31A AC Adapter Charger for HP Split 13 X2;HP Stream 11 13 14 Series;Pavilion x360 x2 11 11t 13 15;Elitebook Folio 1040 G1;P/N 721092-001 PA-1450-56HA Power Cord.The adapter arrived today and looks like this:The problem was that when it arrived it had the wrong sort of adapter, like this:So I decided to attach my own adapter, like this:But when I cut the adapter off and stripped the wire I found three wires, not two as I was expecting:I plugged in the adapter and used my multimeter to measure voltage across the wires, but I couldn't get any reading. Not sure where the problem might be. Figured I should ask because I don't want to short anything out doing experiments on wires I don't understand...So my questions are: which two wires should I expect to be able to attach to my new adapter? Do I need to short any of these wires to enable power through the device? Why are there three wires?

author: gnuarm
author_rank: Super Contributor
timestamp: July 20, 2023, 03:21:28 am
content: These days most laptops have a comms signal for the computer and the power supply to exchange information. The power brick tells the laptop it's max power or something equivalent and the laptop decides if it is going to charge from it. That's the third wire.Until the laptop tells the power brick to turn on, you will get no power from the brick.You bought the wrong type of power supply.I can't see from your photos what is going on with the pins. Normally the connectors on these bricks will have an outer barrel, an inner barrel and a pin in the center. Does the connector you cut off have the center barrel and pin?

author: jj5
author_rank: Unknown
timestamp: July 20, 2023, 03:27:01 am
content: I used my continuity tester to check the wiring of the three wires to the original adapter which I cut off. The outside was to black, the inside of the barrel to red, and the pin to white, as far as I could tell (it was hard to be sure my multimeter probes were properly positioned). Is there anything I can do to get a useful voltage out of this thing? I already cut the adapter off so I think a return is out of the question!

author: gnuarm
author_rank: Super Contributor
timestamp: July 20, 2023, 03:47:38 am
content: Quote from: jj5 on July 20, 2023, 03:27:01 amJust tell them that was how you received it and sound angry that they are ripping you off! lolYou would need to figure out the protocol of the interface and build something that will do the same thing. My guess is the power brick has something in it like a one-wire device with its data. That would require some sort of very simple MCU in your adapter to talk to the brick. It would have to run off the power on the white wire, since there is none on the red wire.I assume you realize you will need a small perf board to solder the wires to, etc.

author: jj5
author_rank: Unknown
timestamp: July 20, 2023, 03:53:53 am
content: Thanks Rick! I would really love to figure out how to reverse engineer this thing, just for the sake of the exercise. I can put the three wires into a breadboard for experimenting. How do I go about figuring out the protocol? Should I use my scope to see what happens between the white and black wires when I power-on? Can you help me figure out the protocol? If you can instruct me I will do what you say!

author: jj5
author_rank: Unknown
timestamp: July 20, 2023, 04:12:50 am
content: I've got this thing wired up, what's the first step?

author: gnuarm
author_rank: Super Contributor
timestamp: July 20, 2023, 04:24:14 am
content: Quote from: jj5 on July 20, 2023, 03:53:53 amThe easy way is to look it up on the Internet. Use one of the laptop names and look for a power supply protocol.Otherwise, you need to know the timing details which would be hard to figure out by exploration. When you plug in the power brick, what voltages do you get on the red and white wire assuming black is ground?

author: jj5
author_rank: Unknown
timestamp: July 20, 2023, 04:55:46 am
content: When I plug the power in the red black pair jumps briefly to 12V but then settles into open circuit. The white black pair goes to 15.44V.

author: jj5
author_rank: Unknown
timestamp: July 20, 2023, 05:14:10 am
content: Hey Rick, I made a quick video to show you what happens when I measure voltages on the wires:https://youtu.be/ApvlTKbqNNc.

author: gnuarm
author_rank: Super Contributor
timestamp: July 20, 2023, 05:29:15 am
content: Quote from: jj5 on July 20, 2023, 04:55:46 amI don't know what you mean by "open" circuit. The voltage is zero on the red line, then goes up to 9.3, then 1_.__ I think the meter is overvoltage on the red wire. I'm guessing your meter is 3.5 digits, so that setting probably maxes out at 19.99V and you are seeing a bit more than that. Try changing the range to 200V max.

author: MrAl
author_rank: Super Contributor
timestamp: July 20, 2023, 05:46:29 am
content: Quote from: jj5 on July 20, 2023, 03:10:06 amHi,Some of these just use a resistor or thermistor or just a switch so the battery can tell the wall wart to shut off if something is wrong. Unfortunately, it would vary by manufacturer as to what method they use so you'd have to find out from them or find it on the web. If you could get a working genuine wall wart you could test it but that could be very difficult and if you get it wrong, it could turn dangerous as these types of battery packs are nothing to play around with. Better to get a working wall wart by far even with the extra cost. A fire could cost you a lot more.

author: jj5
author_rank: Unknown
timestamp: July 20, 2023, 05:48:10 am
content: Oh, yes, you're right! It's delivering slightly more than 20V so I needed to go to the next level. Seems to me like there's 20V across the red black pair. Not sure why I couldn't read that before. Maybe I can just hook this up and it will work. I will try that again...

author: MrAl
author_rank: Super Contributor
timestamp: July 20, 2023, 05:50:59 am
content: Quote from: jj5 on July 20, 2023, 05:48:10 amJust be careful the wrong protocol could make charging dangerous.Why didn't you just buy the right adapter.

author: jj5
author_rank: Unknown
timestamp: July 20, 2023, 05:57:22 am
content: QuoteI'm a novice and I misunderstood. The multimeter goes to "1" when it's overloaded. I thought that it went to "1" when it was "open circuit", that is, zero volts. But of course that's not how it works. At least I'm learning...

author: gnuarm
author_rank: Super Contributor
timestamp: July 20, 2023, 06:12:14 am
content: Quote from: jj5 on July 20, 2023, 05:57:22 amSo, what is the voltage? Is it about 20V? Does it remain at 20V? That would be odd, but it might only let you draw a low current before shutting down, or the comms sets a higher current.

author: jj5
author_rank: Unknown
timestamp: July 20, 2023, 06:22:44 am
content: Quote from: jj5 on July 20, 2023, 05:57:22 amThe reason I made this mistake is that when the multimeter is in resistance mode it shows "1" when there's an open circuit (i.e. no load). So just the confusion of a novice getting used to using his equipment.

author: gnuarm
author_rank: Super Contributor
timestamp: July 20, 2023, 06:37:27 am
content: Quote from: jj5 on July 20, 2023, 06:22:44 amSo, what is the voltage?

author: jj5
author_rank: Unknown
timestamp: July 20, 2023, 06:41:10 am
content: Quote from: gnuarm on July 20, 2023, 06:12:14 amYes, it's about 20V. I put a load across it using a 1M potentiometer and it delivered voltage for a while but I burnt out the pot (magic smoke!) when I decreased the resistance too much.

author: gnuarm
author_rank: Super Contributor
timestamp: July 20, 2023, 07:29:07 am
content: Quote from: jj5 on July 20, 2023, 06:41:10 amOk, are you good to go?

author: jj5
author_rank: Unknown
timestamp: July 20, 2023, 07:35:44 am
content: Quote from: gnuarm on July 20, 2023, 07:29:07 amNot sure yet. I will hook this thing up to a better load for testing but won't be able to get that done today. I will let you know how I go tomorrow! Thanks for your help!

author: ozcar
author_rank: Frequent Contributor
timestamp: July 20, 2023, 07:29:17 pm
content: What do you intend to power with this adaptor?

author: jj5
author_rank: Unknown
timestamp: July 21, 2023, 01:45:41 am
content: Quote from: ozcar on July 20, 2023, 07:29:17 pmI want to use it to power aRIDEN RD6006power supply.

author: MrAl
author_rank: Super Contributor
timestamp: July 21, 2023, 05:34:05 am
content: Quote from: jj5 on July 21, 2023, 01:45:41 amHi,Oh, that's a very different application. It should work one way or another as long as you don't exceed the max input voltage.The problem with wall warts to charge Li-ion batteries (a lot of laptops) is that those batteries are dangerous if not charged exactly right so better to have the right wall wart to begin with.Li-ion batteries can catch fire or worse explode and burn out like a blow torch for several minutes if not charged right, and charging is the most dangerous time. There are lots of videos of this on the web that illustrate what can happen.Power supply regulators generally do not complain about the input supply except for certain types like for example some Li-ion charger controllers which require a 5v only input.

author: gnuarm
author_rank: Super Contributor
timestamp: July 21, 2023, 06:27:48 am
content: Quote from: jj5 on July 21, 2023, 01:45:41 amWhy don't you just buy a power supply that works from the mains power, instead of needing yet another supply to power the other supply???

author: ledtester
author_rank: Super Contributor
timestamp: July 21, 2023, 07:20:42 am
content: Quote from: gnuarm on July 21, 2023, 06:27:48 amThe RD6006 is a buck converter that has a configurable CC mode which is what I bet the OP is relying on to charge the li-ion batteries. Another forum member has developed an alternative firmware which improves the UI and adds more features. More info is available at:https://www.eevblog.com/forum/testgear/ruideng-riden-rd6006-dc-power-supply/msg4971583/#msg4971583

author: jj5
author_rank: Unknown
timestamp: July 21, 2023, 08:00:58 am
content: Quote from: gnuarm on July 21, 2023, 06:27:48 amMy other bench supply is aTENMA 72-10505, but I also have two of these Riden RD6006, and I've got them now, so might as well use them than replace them!

author: jj5
author_rank: Unknown
timestamp: July 21, 2023, 08:03:27 am
content: Quote from: ledtester on July 21, 2023, 07:20:42 amTo be clear: I am not charging li-ion batteries. I'm just powering the Riden RD6006 so I can use it for a bench supply.Quote from: ledtester on July 21, 2023, 07:20:42 amCool! I will check that out, thanks very much.

author: jj5
author_rank: Unknown
timestamp: July 21, 2023, 08:05:14 am
content: Quote from: gnuarm on July 20, 2023, 07:29:07 amI am indeed. Thank you again for your help! I have rewired the HP AC adapter and it is now powering my Riden RD6006 providing 19.94V:So I'm not sure what problem I had in the first place when I made the initial post on this topic. I didn't read any voltage, but there is voltage. Probably operator error!

author: MrAl
author_rank: Super Contributor
timestamp: July 21, 2023, 02:21:18 pm
content: That's interesting. I have a PC board power supply also that needs an input from another power supply.The reason I got that one was so I can get more than one voltage from the main power supply. So, I can vary both now to get voltages from 0v to about 30v DC. Without that second power supply regulator board I would only have one voltage 0v to 30vdc.If I get a third PS controller board, I can have three outputs all independently adjustable from 0 to 30vdc. I use mostly light current levels, but they will go up to around 5 amps which is more than I usually need.

author: gnuarm
author_rank: Super Contributor
timestamp: July 21, 2023, 05:10:29 pm
content: Quote from: jj5 on July 21, 2023, 08:05:14 amYou aren't done until you've drawn some significant power from the unit. It might be that the brick puts out a minimal amount of power until the protocol verifies the compatibility of the brick with the laptop. Let us know when you've drawn an amp or two.

author: jj5
author_rank: Unknown
timestamp: July 22, 2023, 12:15:32 am
content: Quote from: gnuarm on July 21, 2023, 05:10:29 pmOkay, will do. But what is the best way to do that? I don't yet own a programmable load. Can you recommend a programmable load which is cheap and would be good for this job? I would like to own a programmable load and maybe I could use this as an excuse to buy one... or otherwise how do I introduce a load for testing?

author: gnuarm
author_rank: Super Contributor
timestamp: July 22, 2023, 12:25:54 am
content: Quote from: jj5 on July 22, 2023, 12:15:32 amhttps://www.ebay.com/itm/275384331361?hash=item401e2f6c61:g:GUsAAOSwxOFizUaY&var=575829112157

author: jj5
author_rank: Unknown
timestamp: July 22, 2023, 01:07:17 am
content: I was thinking I might get one of theseEBD-A20H Battery Testers, what do you think?

author: jj5
author_rank: Unknown
timestamp: July 22, 2023, 01:11:23 am
content: Quote from: gnuarm on July 22, 2023, 12:25:54 amThanks! I will get 12Ω 25W for testing 12V at 1A and 6Ω 25W for testing 12V at 2A. Will that be good enough do you think?

author: gnuarm
author_rank: Super Contributor
timestamp: July 22, 2023, 01:27:38 am
content: Quote from: jj5 on July 22, 2023, 01:11:23 amHow high will your output voltage go? Why can't you test 2A with one resistor? I would get the higher wattage resistors. The rating is just a number. 24W into a 25W resistor will get really hot. I had some 1 ohm resistors in series running around 5 amps, so 25W each, and 50W parts got hot enough to char wood if left running overnight. That's hot! Now, I bolt them to an aluminum plate to act as a heatsink.

author: jj5
author_rank: Unknown
timestamp: July 22, 2023, 01:40:37 am
content: Quote from: gnuarm on July 22, 2023, 01:27:38 amProbably not more than 12V. This is just a bench supply for playing with digital electronics. I'm expecting to use 5V, 9V, and 12V. Also the occasional small voltage for testing LEDs.Quote from: gnuarm on July 22, 2023, 01:27:38 amWell I can. I just figured I would test in stages... not necessary you reckon? Just go straight for the maximum?Quote from: gnuarm on July 22, 2023, 01:27:38 amThanks! I will get 6Ω 100W for testing. Will that do?

author: gnuarm
author_rank: Super Contributor
timestamp: July 22, 2023, 02:39:15 am
content: Quote from: jj5 on July 22, 2023, 01:40:37 amYou can change the power level by adjusting the voltage. If you want to test multiple power levels at the same voltage, then use different resistors.QuoteIf it works for you, it works for me.

author: MrAl
author_rank: Super Contributor
timestamp: July 22, 2023, 02:48:21 am
content: Quote from: jj5 on July 22, 2023, 01:40:37 amA 100 watt incandescent light bulb will give you low Ohms like around 8 or 10 Ohms at 12v.

author: gnuarm
author_rank: Super Contributor
timestamp: July 22, 2023, 03:09:33 am
content: Quote from: MrAl on July 22, 2023, 02:48:21 amYou can't buy them in the US any more. At least, they are hard to find. A 75 W incandescent bulb should work though.

author: BILLPOD
author_rank: Frequent Contributor
timestamp: July 22, 2023, 01:31:44 pm
content: Automotive bulbs work fine for low voltage loads. My headlight bulbs draw approx. 5 Amps on low beam, and 7.5 A on high beam, at 12 VDC.

author: MrAl
author_rank: Super Contributor
timestamp: July 22, 2023, 04:10:21 pm
content: Quote from: gnuarm on July 22, 2023, 03:09:33 amYes you really have to have one already. Some of us do.

author: gnuarm
author_rank: Super Contributor
timestamp: July 22, 2023, 07:43:56 pm
content: Quote from: BILLPOD on July 22, 2023, 01:31:44 pmYou need to be careful with light bulbs. They have very low resistance when cold, which rises when they start to heat up. Do not count on them having the resistance you need. If you manually adjust the controls, they should be fine.

author: jj5
author_rank: Unknown
timestamp: July 28, 2023, 11:29:38 am
content: Quote from: gnuarm on July 21, 2023, 05:10:29 pmHey Rick. My 100W 6Ω resistor arrived today and I finished the testing. Turns out the AC adapter in question could deliver more than its 45W maximum rating. The write-up for my testing ishere. Thanks very much for your help with this one!

author: gnuarm
author_rank: Super Contributor
timestamp: July 28, 2023, 11:42:32 am
content: Quote from: jj5 on July 28, 2023, 11:29:38 amI found I was able to read your web page in Reader View in Firefox. Otherwise, the color scheme would have made it very difficult for me.

author: jj5
author_rank: Unknown
timestamp: July 28, 2023, 11:45:13 am
content: Quote from: gnuarm on July 28, 2023, 11:42:32 amYes, I'm sorry about that. It was designed as a bit of a joke, but it's not very practical. I should probably change it. In the mean time thank goodness for Firefox Reader View.

author: jj5
author_rank: Unknown
timestamp: July 28, 2023, 11:55:16 am
content: Quote from: gnuarm on July 28, 2023, 11:42:32 amI fixed this now. Thanks for your feedback!