StarDestroyer.Net BBS

My power cord is pretty much kaput, I'm pinching it really tight, and I was was thinking about looking around the house for a cord that fits. How bad of an idea is this? What numbers do I want to match up?

If you match voltage and current you'll be fine, but be sure you're matching output rather than input ratings.

Pinching the cord implies you know where the circuit is broken. Why don't you just strip, solder, and tape it?

Feil wrote:Pinching the cord implies you know where the circuit is broken. Why don't you just strip, solder, and tape it?

Dude, he doesn't even know the two basic descriptors of power adaptors. If he tries to solder the cable, he can easily mess something up, fry the adaptor and/or the laptop.

I would have to ask for a clarification, though: by "power cord", do you mean the thick cable going from the outlet to the adaptor cube, or the one going from the cube to the laptop's power jack?

If its the cable going into the transformer (the little brick, also called "power brick" in my manual) than usually you can find a cord fitting to that in any electronics shop. Mine actually is a radio cable because it was longer than the cable I got for my eeepc.

If its the cable going to the laptop from the transformer, than you're fucked unless you have extensive soldering experience and a shadowed cable. Those cables are a bit special, having something that my electrician (or rather, electric engineer) dad refers to in Hungarian, as "shadowed" (protected? having a layer of unused cable threads around the cable that actually supplies the power). They're fiddly things to solder together so you may have to get another transformer for your laptop. In that case, you can get an universal transformer. Just match on the Vs that is on the laptop and it should be fine.

Those universal adaptors are usually shit, though (won't keep a stable voltage), and I've seen more than one laptop get fried by them. It's usually better to just get a new adaptor with the proper parameters.

PeZook wrote:Those universal adaptors are usually shit, though (won't keep a stable voltage), and I've seen more than one laptop get fried by them. It's usually better to just get a new adaptor with the proper parameters.

Quality ones do work, but you will have to be careful that you get one that is outputs the right voltage and can provide enough current. The technically correct term for that "power brick" is "power supply", by the way. It does exactly the same thing as the power supply inside a desktop computer, except that it outputs only a single voltage1 and unlike desktop power supplies, laptop ones are not standardized so that manufacturers can sell more expensive original replacement parts.

1 Incidentally, there has long been suggestions to replace the standard desktop ATX power supply, which outputs 12 V, 5 V and 3.3 V, with a PS that outputs only 12 V, since that would make more sense in modern desktop computers as well, but systemic inertia and backwards compatibility requirements have prevented that thus far.

Feil wrote:Pinching the cord implies you know where the circuit is broken. Why don't you just strip, solder, and tape it?

I read "pinching" as in he's pinching his pennies. As in, he's on a limited budget.

lance wrote:My power cord is pretty much kaput, I'm pinching it really tight, and I was was thinking about looking around the house for a cord that fits. How bad of an idea is this? What numbers do I want to match up?

On a power adapter there will typically be two ratings. I have a laptop power adapter in front of me that I'll use for an example, which has the following printed on it:

INPUT: 100-240V* 50-60Hz 1.5A
OUTPUT: 19V* 4.74A

The input voltage range indicates the range of voltages that the adapter can handle; so as long as the wall socket provides a voltage between 100V and 240V, the adapter is fine. Same with the frequency range; this adapter was clearly intended to be usable internationally. The amperage rating indicates that this adapter may require as much as 1.5A; this can be useful if you're trying to determine how much of a load you've placed on a given circuit, but for purposes of compatibility with your laptop you won't need to consider it.

The output voltage rating indicates the voltage the adapter will provide to the laptop. This is a very important figure to match; your laptop will expect a certain voltage and your adapter should provide that voltage to it. The amp rating indicates the maximum amperage the adapter is designed to provide to the laptop - but it can provide less current as well. The laptop that this adapter was bundled with lists an input requirement of 19V 4.2A - so this adapter exceeds that requirement by 0.54A.

*The input voltage has a symbol for AC next to it, indicating that it accepts AC power. The output voltage has a symbol for DC next to it, indicating that it outputs DC power.


To sum up: Your laptop requires a specific voltage and a minimum of whatever amperage it requires. Your replacement adapter should match that voltage, and meet or exceed that amperage.

Don't forget that if it's a circular DC jack into the laptop whether it's center positive or center negative...

Uraniun235 wrote: To sum up: Your laptop requires a specific voltage and a minimum of whatever amperage it requires. Your replacement adapter should match that voltage, and meet or exceed that amperage.

In reality 5% variation in output voltage is quite acceptable, though. So if the nominal output voltage is 19V, the laptop will work just fine with anything from 18 V to 20 V as long as the amperage exceeds the requirements. In fact the power regulation circuitry on the laptop will probably accept even greater variation upwards in voltage just fine, but since you can't be 100% sure about that, I wouldn't use anything more than say 10% upwards (i.e. 21 V in this case). The critical thing in most cases is not the nominal output voltage but ripple voltage. Better quality power supply will minimize ripple.

Even more important is simply component quality. Poor quality PS may fail catastrophically due to bad capacitors. It can result in a serious overvoltage that the laptop's regulation circuitry can't handle and you end up with a bricked system.

Marcus Aurelius wrote:In reality 5% variation in output voltage is quite acceptable, though. So if the nominal output voltage is 19V, the laptop will work just fine with anything from 18 V to 20 V as long as the amperage exceeds the requirements. In fact the power regulation circuitry on the laptop will probably accept even greater variation upwards in voltage just fine, but since you can't be 100% sure about that, I wouldn't use anything more than say 10% upwards (i.e. 21 V in this case). The critical thing in most cases is not the nominal output voltage but ripple voltage. Better quality power supply will minimize ripple.

I don't want to scare anyone, but be sure to get a voltmeter (you can buy one in every hardware store, they are quite cheap these days) and actually measure the output voltage of the adaptor you want to use. Recently I had two adaptors which were supposed to output 12 Volts but when I measured them it was actually 16 volts, so double-check everything even if it says so in the adaptor's sticker.

Tolya wrote:Recently I had two adaptors which were supposed to output 12 Volts but when I measured them it was actually 16 volts, so double-check everything even if it says so in the adaptor's sticker.

It could be that the adaptors were totally off, but more likely they just have poor load regulation. In an adaptor with poor load regulation, there will be a large difference between the voltage it puts out under zero or light load and the voltage output under its rated maximum load. Building an adaptor that puts out the same voltage regardless of load gets rather complicated & expensive, in this day & age not everyone's going to build one to those standards.

It was the part that connected directly into the computer that I was pinching. Which is apparently called a power supply. A buddy of mine has a universal one that I'm borrowing until the part that I ordered comes in. I matched all the numbers on the power supply so it should be a fit unless the connector is the wrong size.

Thanks for the help

Zixinus wrote:If its the cable going to the laptop from the transformer, than you're fucked unless you have extensive soldering experience and a shadowed cable. Those cables are a bit special, having something that my electrician (or rather, electric engineer) dad refers to in Hungarian, as "shadowed" (protected? having a layer of unused cable threads around the cable that actually supplies the power). They're fiddly things to solder together so you may have to get another transformer for your laptop. In that case, you can get an universal transformer. Just match on the Vs that is on the laptop and it should be fine.

The English term is "shielded cable," with the insulated power or signal cables surrounded by an unused conductive layer that serves as a Faraday cage to insulate the current from interference.

aerius wrote:

Tolya wrote:Recently I had two adaptors which were supposed to output 12 Volts but when I measured them it was actually 16 volts, so double-check everything even if it says so in the adaptor's sticker.

It could be that the adaptors were totally off, but more likely they just have poor load regulation. In an adaptor with poor load regulation, there will be a large difference between the voltage it puts out under zero or light load and the voltage output under its rated maximum load. Building an adaptor that puts out the same voltage regardless of load gets rather complicated & expensive, in this day & age not everyone's going to build one to those standards.

Yes. For reliable results some kind of load simulation should be used. However, full size laptops usually draw enough current that the power supply should be switched-mode design in any case, which typically have better regulation and will not even work with zero load. Modern universal laptop power supplies are switched-mode and automatically detect if a load is present. Linear power supplies have terrible efficiency, so you really should not use them at all for electronic appliances, although many of the cheaper general-purpose universal adapters are linear. For a laptop you should use a PS designed for laptop use unless you really know what you are doing. As for unregulated PS...(usually the cheapest third party adapters). They are good only for loading your rechargeable flashlight, if that. Avoid like plague.

Terralthra wrote:
The English term is "shielded cable," with the insulated power or signal cables surrounded by an unused conductive layer that serves as a Faraday cage to insulate the current from interference.

Ah, its good to know that. Thank you for mentioning it.

aerius wrote:It could be that the adaptors were totally off, but more likely they just have poor load regulation. In an adaptor with poor load regulation, there will be a large difference between the voltage it puts out under zero or light load and the voltage output under its rated maximum load. Building an adaptor that puts out the same voltage regardless of load gets rather complicated & expensive, in this day & age not everyone's going to build one to those standards.

One of those adaptors was actually a crappy charger used to power something I long forgot about, so no surprise there. However, the second one was supposed to be a big good amateur charger (blue box with a handle kind of thing) with many different outputs: separate +/- for 6V and 12V and a separate cord for Delta Peak fast charging of NiMh batteries (with switchable 1A/2A/4A output) so I was really pissed off when I learned its 12V output is 16V and its 6V is actually 8V

The company that manufactured it is Conrad.

aerius wrote: It could be that the adaptors were totally off, but more likely they just have poor load regulation. In an adaptor with poor load regulation, there will be a large difference between the voltage it puts out under zero or light load and the voltage output under its rated maximum load. Building an adaptor that puts out the same voltage regardless of load gets rather complicated & expensive, in this day & age not everyone's going to build one to those standards.

In twelve years of fixing laptops, we've never seen an adaptor that puts out a full 4V over the stated level under no load and didn't come with a fried laptop. Of course, they're all heavily loaded with electronics (the decent ones, at least), so Tolya's example might be somewhat different.

PeZook wrote: In twelve years of fixing laptops, we've never seen an adaptor that puts out a full 4V over the stated level under no load and didn't come with a fried laptop. Of course, they're all heavily loaded with electronics (the decent ones, at least), so Tolya's example might be somewhat different.

Of course not, since even a semi-decent switched-mode power supply would not put out so much overvoltage and it would require a pretty broken design for a linear power supply. Of course many modern powers supply designs may have both a switched-mode and a linear regulator in series in order to eliminate ripple.

For Tolya:

http://www.produktinfo.conrad.com/

My guess is that the cheapo charger is an unregulated PS, which are practically always shit. As for the Conrad device: provide load with a small light bulb (car signaling, large flashlight or similar) and re-measure the voltage. Also check if you find info above.