Rebuilding Mac Portable batteries with caps

Whether or not you need the caps depends on what kind of power supply you plan on running the Mac from. Generally, the lower the frequency of the power supply, the more capacitance you'll need. In other words, a linear supply that operates at 60 Hz will need a lot more capacitance than a switcher suppy that operates at 24kHz. I realize that you'll use a "DC" power supply but very few power supplies put out a pure DC and you need a pretty pure source of DC to prevent glitches in the logic of the Mac. That's one of the biggest reasons that switching power supplies were developed originally. The high frequencies that they run at means that you can filter out the hum and still have a power supply that's not the size of a refrigerator! This is assuming that the load is steady. However a computer isn't steady due to drives starting and stopping and the like. Because of that, you'll need even MORE capitance! In any event, you certainly won't be able to cram enough caps inside the Mac to adaquetely filter it. If I were you and I wasn't concerned with portability, I would run the Mac off of some kind of large battery, perhaps even a car battery or a battery out of an old UPS. Of course, you'll have to find something that is the right voltage. However most most computers that use lead acid batteries run off of either 6 or 12 VDC so that makes it easy. FWIW I have a couple of old Mac portables and they seem to be real power hogs. (That's probably why they use lead acid batteries instead of NiCads.) My small HP power supply won't run them. Even with the drives off, it will only run them with a partially charged battery to take up some of the peak load. It won't run at all when the batteries are dead. And forget it when the drive kicks in! My 2 cents worth, Joe At 02:56 PM 5/16/01 -0700, you wrote: