ORIGINAL: dondeaida
Well... Simply forget the resistor thing (just turn off or unplug the power supply when not in use) ATX Switching mode power supplies these days are designed so that it will not be damaged as long as there is a very very little load present and since all ATX power supplies have a fan in it, a small load is always present. This makes "max power save mode" possible in which all data in RAM is saved to harddisk and basically the computer shuts down (Some ATX supplies even shuts down its own fan and still no damage) A very small additional load should wake up from this max save mode to full power via implementations like mouse break or wake-on-lan. This means charging batteries alone should wake up ATX to full power (It may not in rare cases, explained later)
Bottom line: You do not need a resistor. And if you are a worrying type, do this (even though you do not need to do this) : Hook up the batteries BEFORE you plug in the ATX to the wall and when charging is done, unplug ATX from the wall first and then take those batteries out.
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If you still cannot live without a resistor and need a heat source
in cold weather, hook it up to 5v. This is because motherboard works at 5v and it is this 5v load that brings ATX supply to full power (mouse break, wake-on-lan are all 5v based) But the fan in power supply is 5v on the first place, so basically most ATX are ever-ready and you do not need a resistor in 5v line.
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In rare cases ATX power supplies will not wake up at 12v load (A very few ATXs' can't convert 12v load into 5v load) In this case, you do need a 5v load but a small one will do (resitor is not a good idea anyways since it creates lot of heat. use a led or a fan instead. CPU fans are 5v)
hrm... I know you are trying to be helpful and conribute and help people out, and I commend that =) I'm just not sure how accurate all this info is.
when you put your computer in standby, none of the info is on the hard drive, it's all in the ram, and that is why you need to keep power to the computer and you can't unplug it. Yes it is true that some computers turn off the fans during this because it only consumes about 9 to 20w of power. With something like hibernate it writes the info the hard drive and completely shuts the machine down. You could completely disconnect and take out the power supply, put in a new one, power it on, and be right where you left off.
The 5v rail that all the stuff like WOL or WOR your mouse keyboard WOUSB and all that sort of stuff runs on a completely different rail. The 5v standby rail, which is usually rated something like 500mA to 3A or so.
Most power supplies have a fail safe ciruit in them when you don't have something hooked up to the 5v rail, it wont power on. This is to prevent shorts and frying your mobo, or causing a fire or something along those lines. Most power supplies will not run without a load on the 5v rail. I don't think a 5 to 20mA LED or a 0.20A computer fan will be enough of a load on the 5v rail to switch this protection circuitry, but I've never tried it, so I guess it could be
The main reason people are putting resistors on the 5v rail, is because this is how the PSU controls the votlage of the 12v rail. The more load that is on the 5v rail, the higher the 12v rail goes. With no load it runs right around 11v if your PSU will turn on, and if you are drawing more than a couple of amps to charge your packs you could get below 11v pretty easily. This is what's called an undervolt. If you have an expensive charger it will either pause charing, sound an alarm or turn off, or somtehing like that. If you have a less expensive charger, it could just fry it. Also running on a lower voltage basically causes more heat to build up in your charger because of conversion and inefficiency factors.
Hopefully that makes sense =)
Basically a bunch of EE's and people with electronic circuitry background would not be writing a how to guide telling you to put in this resistor if there wasn't a good reason for it =) and telling you that you have to put it in if it's not required. Some would atleast explain it is optional and what it's function is.
If you can get your PSU to run without a resistor on the load, then that's great =) and if you also have a charger that doesn't mind the lower voltage and doesn't get hot on it, then something like this would definately work for you.