Dear Sir,
It must be bad luck to break a leg, then.
Cordially yours, Gerard Pawlowski
Roughly, a 9V alkaline will run an N scale engine for 5-6 hours till it's dead[assuming 100-200 ma draw for the engine, and 600-800 ma hours for the battery].
An easy way to do this is to get a portable auto power pack. These are used for powering laptops, cell phones, TVs or anything else designed to operate on car power. They have a gel cell battery inside (sealed battery as above). In this case an advantage of them is they include a UL approved charger. So you should be able to charge it or use it but just not both simultaneously. One advantage of this method is that you can switch power supplies easily.
An important thing to do is to put a fuse (1 or 2 amps should do nicely) in the DC circuit. Most car adapter cables include this in the cigarette plug. If you don't it's quite easy to fry various components in a short circuit. In fact, due to the ease of shorting out the track it's best to have a reset-able overload protection. This can be either a circuit breaker or a solid state throttle with over current protection.
One possibility is to just use a model throttle from MRC, disconnect the transformer and connect the power from the battery after the bridge rectifier. There are also throttle circuits available that use DC power.
PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.