First off, I am NOT an electrician, and I am NOT advising you to do ANYTHING. That said, I'm pretty sure 100 feet is still within the range of a normal pack from one of the larger sets. Those I believe are 24 volt DC, and measured in milliamps, not amps. BIG difference. The wall packs that you plug into your walls have up to 120 volts and 20 amps at their disposal, but they only use a tiny fraction of that. I looked at a few on the bay, and DC volts are between 14 and 22, and about 14 milliamps. Keep your volts in the lower range. The lower the volts, the longer you can run the cars. The higher the volts, the quicker they overheat. So, basically, you need 14 milliamps times 3 = 42 miliamps, maybe a bit more. The cars won't use more amps than they can handle, it's you and everyone else that need to be safe. You could hook up 8,000 milliamps and you wouldn't burn out the cars, but if anyone touched the rails, they might get thrown across the room. And yes, that does happen. I watched my best friend's kid sister fly into a couch 10 feet away. No, I didn't know she had a fork in her hand in front of a wall socket. Scared the crap out of all of us, except her. She had a dazed look on her face, then she laughed. If we hadn't yelled in surprise when it happenned, and told the adults, we may have tried it too. After all, she did laugh.. Back to your powerpack issue. HO train powerpacks, the bigger ones, should have plenty of power for your track. And, it's adjustable on some, which have 2 separate throttles, so you can dial back the power for kids and novice racers. I've also heard of some people just hooking up a 12 volt car battery hooked up to a trickle charger. You'll definitely get a few hours of racing out of it before you need to recharge, or just leave the trickle hooked up. That'll negate some of the drain. You can get a used battery from most junkyards, and a trickle charger for under $40. Ask around. Reviews of tracks that use 12 volts always say their cars ran nice and smoothe for hours. And I need to say this again, just in case you decide to set your beer on top of the battery, then dump it on both terminals while holding on to the mailbox-- I am NOT an electrician, and am NOT giving you electrical advice.