pete10uk Posted June 7, 2013 Share Posted June 7, 2013 Morning all Apologies this is a PS question in the sound forum, but my use for it is sound related. I have a netbook used for sound stab playback which I'm plugging in to a battery operated sound system, the netbook battery life is far less than the that of the PA so I'm wanting to introduce a battery to power the netbook. I have used a cheep universal 12v - 19v adaptor for use with a different laptop for a few years which has worked fine, so I ordered a second unit for the netbook, however when it arrived non of the power plugs fitted the netbook. No problem I thought, I popped down to maplins, picked up the correct plug and I'm in the process of hard wiring it in as it no longer needs to be universal. The problem has come actually connecting up the wires, the cable on the PS is very hard to solder as the copper is coated in some sort of clear resin, this can't be soldered direct and I've tried scraping, burning and general ignorance however every time I think I've done it when tested the unit just blew the fuse. I thought that the heat of the soldering iron was melting the insulation resin, so I thought I would open up the unit and swap the cable. On opening the unit I have noticed that there is the + & - wires soldered to the board which I expected but wrapped inside the + is a small group of copper with red resin on it, this is soldered to the board on a pin labelled ifb, which seems to go to a LED via a resistor. The group of red wires seems to be insulated from the +, I've checked to see if there is a resistance between them but it doesn't seem so. Any one have any ideas as to what this does and how? Cheers Link to comment Share on other sites More sharing options...
timsabre Posted June 7, 2013 Share Posted June 7, 2013 It is probably a feedback signal which allows the power supply to compensate for voltage drop in the cable, in which case it would need connecting to the + cable at the plug end. However there is really no way to tell for sure from your description - you would need to check the wiring of the original netbook psu which I presume you don't have. The best way to solder that enamelled wire is to scrape some of the enamelling off with a craft knife, then use the biggest hottest soldering iron you can get hold of to tin the wire. If your soldering iron is too wimpy you just melt the cable. Link to comment Share on other sites More sharing options...
pisquee Posted June 7, 2013 Share Posted June 7, 2013 Some laptop PSUs (certainly true of Dells) are three wire, with an extra pin to tell the laptop which power supply you are using - if the laptop can't detect which PSU is in use, then the laptop will run in a low power mode (slower) and will not charge the battery. Link to comment Share on other sites More sharing options...
timsabre Posted June 7, 2013 Share Posted June 7, 2013 Some laptop PSUs (certainly true of Dells) are three wire, with an extra pin to tell the laptop which power supply you are using - if the laptop can't detect which PSU is in use, then the laptop will run in a low power mode (slower) and will not charge the battery. True, but this type has a 3-pole plug on the computer - how many terminals are there on the plug? Link to comment Share on other sites More sharing options...
pete10uk Posted June 7, 2013 Author Share Posted June 7, 2013 Some laptop PSUs (certainly true of Dells) are three wire, with an extra pin to tell the laptop which power supply you are using - if the laptop can't detect which PSU is in use, then the laptop will run in a low power mode (slower) and will not charge the battery. True, but this type has a 3-pole plug on the computer - how many terminals are there on the plug? This just has the 2 pins. I have managed to test the cable again after cleaning off the lacquer and the + and the red strands are shorted at the plug, I like the idea or the voltage especially as when I've cleaned up around the contacts the pin is actually labelled vfb. I have changed the cable and shorted the + & VFB out and all seems to work. Thanks for the help Link to comment Share on other sites More sharing options...
DrV Posted June 7, 2013 Share Posted June 7, 2013 Vfb = "voltage feed back" ...probablyDave Link to comment Share on other sites More sharing options...
mrboo Posted June 8, 2013 Share Posted June 8, 2013 what make of laptop? Link to comment Share on other sites More sharing options...
pete10uk Posted June 8, 2013 Author Share Posted June 8, 2013 It's all sorted now. We figured out what VFB was connected it up and it's all working ready for a weekends work. It is a Asus Eee netbook, annoyingly though I did find a 12v charger dedicated to it on eBay for £7.50. So the £20 spent on the universal adaptor, the trip to maplins and the couple of hours sorting it out we're pointless. I'll use my contraption this weekend then it will just be a spare as the connector on the dedicated one is less chunky and less likely to rip the socket out, which is also sold on eBay so is a possability. Thanks for the help Link to comment Share on other sites More sharing options...
bigclive Posted June 8, 2013 Share Posted June 8, 2013 One thing to note about the extra voltage drop sensing wire on these PSUs is that if it goes open circuit the voltage can shoot up to levels that cause equipment damage. The early Tom Tom sat navs were apparently bad for that. Link to comment Share on other sites More sharing options...
timsabre Posted June 8, 2013 Share Posted June 8, 2013 One thing to note about the extra voltage drop sensing wire on these PSUs is that if it goes open circuit the voltage can shoot up to levels that cause equipment damage. The early Tom Tom sat navs were apparently bad for that. This is presumably the reason it was blowing the fuse, when he didn't have the Vfb connected. Link to comment Share on other sites More sharing options...
DrV Posted June 8, 2013 Share Posted June 8, 2013 One thing to note about the extra voltage drop sensing wire on these PSUs is that if it goes open circuit the voltage can shoot up to levels that cause equipment damage. The early Tom Tom sat navs were apparently bad for that. Standard practice to prevent that is to put a resistor from + to +sense (vfb) of a value low enough to ensure that the error amp sees the output voltage but much higher than the expected lead resistanceSay 22 ohms or so DaveE2A the resistor goes at the psu end of course, preferably inside the psu Link to comment Share on other sites More sharing options...
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