Help replacing AC powerplug

I need ya'lls help on this one:

I have a friend at school who has an HP laptop, the model I'm not sure of. Anyways she was complaining about her charger not charging her laptop and having the battery just go dead on her. Of course this is a common problem among laptop users. I asked her if the plug on the computer was loose and she said no, it is the AC adapter. Longer story shorter, she gave me the ac charger, and i figured i could splice a new barrel plug on the end. It turns out this is a barrel plug with 3 poles: The outside barrel, a TINY pin in the middle, and then the entire inside of the barrel. The outside is ground, the center pin tests 14 volts, and the inside of the barrel tests 18.5 or so volts. The tester tests good, no shorts in the wires. That being said, I have two questions:

A) What is the 14volt positive center pin for? If it's not important, can I B) change the plug on the adapter as well as the motherboard plug over to something standard and just wire in a 2 plug barrel male and female and call it a day? If that is possible I may do that.

The # on the adapter is a PPP0009L
HP Part #: 384019-001, Replace with HP Spare: 391172-001

Thank you all for the help!

 

Not important??? Then why would HP have gone to all the bother of putting it there?

Maybe the charger is faulty, like the lady says, maybe it isn't. 18.5 volts is pretty close to the 19 volt standard.

I would think the cost of a charger relative to a pc is pretty low so if you don't have access to the service details and parts don't mess.

You will end up causing a bigger problem.

 

Well I figured it could have been some type of sensing pin or something. I thought it could have maybe been a smart charger that could power two different things. Like I said, I dont know what the deal is, it tests a consistent output of 18 and change just like my HP charger does, and varies 1/100th of a volt every 30 seconds on the multimeter, so it really does point towards the computer end.

I just need to know if the computer needs that center pin. If not ill break out my soldering gun, heatshrink and plug ends and go to work on the conversion.

 

Sounds to me like the AC adapter is fine. My guess is the either battery is bad (they do tend to lose their 'chargability' over time) or the charging circuit in the laptop is bad (this is actually more common than you might think). The only way to know for sure is to buy a new battery and see how it charges, or send the laptop to a qualified repair center where they can do board level component replacement and micro-soldering.

 

Well, its actually neither of those. If she takes the battery out while plugged in the computer will stay on til she wiggles the cord. So she told me the adapter/cord assembly deal was bad, so i checked it and it checks out. Thats what lead me to believe that it was the port. Ive replaced many laptop DC plugs, and can do it flawlessly, but i just really needed to know what the hell that tiny pin was for, and why it has 14v on it. haha

 

Hi, That third pin is the "Saftey" ground from the third pin on the AC Plug. All part of the government standard to protect the user in case of a short from the 120/220 volt hot lead to the case. Maybe?

Luck, Jim

 

You're talking about the AC side of the adapter. that is not my problem. Im talking about the center pin inside the DC barrel plug that goes into the computer. Its a type I have never seen before. Like I said, a multimeter tells me it has 14 volts on it...for what reason, i have no idea...so thats what im trying to figure out. I appreciate your reply though!

 

Hi again GMan,

I just checked with an Ohm Meter and the third pin in the adaptor output plug is definitely connected to the ground pin in the AC plug. For saftey the voltage from the adaptor is referenced to "safety" ground so would show voltage same as your 3 pin AC outlet in the wall.

Jiim

 

good advice take it

The middle pin is monitoring circuit that keeps the battery from being overcharged

 

Thanks jlphlp & chaimjm, I appreciate yalls replies.

Chaimjm, Why would they suddenly need something like that center pin to prevent battery overcharging, since they've been using traditional 2-pole barrel plugs up til now? That is the dumbest thing ever. I figured it may have something to do with something like that though.

Jlphlp, Thanks, I would try the ohm meter trick but I had already given the adapter back a few hours ago. So you're saying that tiny center pin ohms-out with the 3rd round ground pin that goes in your wall socket? Man, i wish I would have tried that. My house has 3 pole plugs in the walls, but since the house is old only pos & neg are hooked up, so im guessing that may have skewed my testing.

Thanks for the replies!

 

I suggest you find out and understand a bit more about domestic wiring before you have a serious accident somewhere along the line.

I am sure you have AC, not DC, domestic mains in Mobile.

 

Hi again GMan,

I under stand 'Yall'. I'm from Northeast Louisianna now in the Chicago area. The third pin really has nothing to do with battery charging. It's still just there to blow your circuit breaker if the AC Hot manages to short to the frame. Could only happen maybe if the transformer in the adaptor burned up. Not likely to hurt you in a Laptop. You do need to do something about the 2 prong plugs. Check an outlet and see if your wiring is in conduit. The conduit is usually used in modern house wireing as the ground in lieu of a green wire. If so an electrician can check it out and tell you if it only requires 3 prong self grounding outlets be installed. I call it "saftey" ground as my guys confused it with common in schematics etc.

More good Luck,
Jim

Sorry I missed your reply to Chaimjm. If the house has three prong plugs chances are that they are self grounding to the conduit thus perfectly OK in most regions of the USA. If self-grounding there will be a strap from the green ground lug to a mounting lug to connect the ground to the comduit.

Jim

 

LOL @ studiot. I know my fair share about electronics, believe me. I know how my house wiring works. In the walls there is only a white and a black (hot and ground) and the metal work box is not grounded to anything (bad i know). Thus, the green colored screw on the back of all the plugs in the house is just not connected to anything. But none of that is my problem! My problem lies on the DC side of the charger, specifically the barrel plug. What sets it apart from the normal barrel plugs that goes into your computer, aside from size/diameter, is that inside that barrel plug there is a VERY tiny pin (the size of a sewing needle) in the middle.

No worrys, I have given the adapter back already. I am still curious as to the purpose. I have just written HP total care an email so maybe they can tell me.

 

I understood from the outset that you were interested in the connector to the laptop from the power supply, not the connector from the domestic mains to the power supply.

From you description / measurements (a picture would have helped) I and others were not convinced with the stated deduction that the charger was at fault.

Some battery packs contain internal electronics to support the 'smart' function. Some of these require additional power supplies. There are even laptops that will not turn on unless the correct battery and its electronics are in place. So I was not suprised to learn of a 14 volt additional supply.

Without specialist equipment and data these cannot be tested. You have actually done well to get ordinary multimeter connections without shorting anything.

In view of the fact that you were considering modifying someone else's equipment I suggested that in this case discretion may be the better part of valour. There are no brownie points for risking a few dollars saved on a proper repair against possibly a few hundred dollars damage if it goes wrong.

As regards to your domestic wiring, I understand that you have the old American 2 wire alternating current system. The correct terminology for these wires is phase or line and neutral ( not earth or ground).
Most certianly not positive and negative. DC mains went out of favour in the 1890s, although there were some ultra high voltage superconducting distribution mains laid in New York in the 1990s.
The lack of ground in the old system is not as unsafe at the US voltage of 120 as the bigger bite carried by the European 230 volt standard. But is can still cause serious injury if treated with disdain.

Have you come across the old adage "It's the volts that jolts, but the mils that kills"?

Perhaps you will post HP's reply if you ever receive one?