I’ve got the crazy idea in my head to run an Apple IIc system completely from battery power, so I could take it on the road. I know it’s possible – there’s already one person selling a pre-made kit. That’s a nice solution, but the pictured setup involves an automotive jump-start battery that costs around $150. Would something simpler be possible?
The Belkin Residential Gateway Battery Backup pictured above is designed to keep your VOIP phone or similar device working during a power outage, but it’s found a second life as a popular portable 12V supply for electronics projects. Inside the Belkin unit is a 12V/7.2Ah lead-acid battery. It charges from a standard AC wall outlet, and has a DC barrel plug for connection to the powered device. Hack that off and attach a 12V car cigarette lighter receptacle, or other connector of your choice, and you’ve got a nice little portable power source.
Is 7.2Ah enough to do anything interesting? To answer that question, we need to know how much power an Apple IIc requires. My Apple original AC adapter says it outputs 15V @ 1.2 amps. The IIc can accept any DC voltage between 9V and 20V, so the Belkin’s 12V should be fine here. 15V @ 1.2 amps is 18 watts, and to get the same power at 12V we would need 1.5 amps. That tells us the maximum power the AC adapter can deliver, based on what’s printed on its case.
What about the average power? That’s much more relevant, if we’re trying to estimate the possible run time while connected to a battery. I used a Kill-a-Watt to measure the AC adapter’s power draw from a wall outlet, and it was 12 watts while the IIc was idle doing nothing. So the adapter draws 12 watts from the wall, and delivers something less than 12 watts to the IIc, depending on its efficiency. I don’t know if it’s a switching regulator, or how efficient it is, but I’ll be generous and assume it’s 75% efficient and delivers 9 watts to the IIc. If my reasoning is correct, that means a IIc at idle would draw 0.75 amps from a 12V battery (9 watts).
Back to the Belkin unit: its 7.2Ah battery should theoretically be good for 9.6 hours of runtime, assuming the average power draw of the IIc is close to the idle draw of 0.75 amps. 9.6 hours seems a bit hard to believe, but I’ll go with it for the moment.
Now what about a monitor to use with the computer? Fortunately I’ve got an old portable DVD player with a composite video input that I know works with the IIc. And the DVD player runs off 12V! I haven’t measured its power draw, but I don’t think it can be more than the IIc itself. I’ll assume it’s equal to the IIc’s draw, so the total battery runtime of a IIc with DVD player / monitor would theoretically be 4.8 hours.
If the Apple IIc used any type of standard DC power connector, I’d give this a try right now. Instead, I need to go digging for a female DIN-7 plug. Why must every vintage Apple system include some kind of obscure connector? 