1156 lamps on DC layout.

[edwardpa]

I am in the process of building a layout and plan to use DCC. Because of budget restraints I am wiring for DCC but testing the track work with a DC throttle. There are six power districts protected by 1156 automotive bulbs.

Heres the problem: when you run older multiple unit Athearn locomotives the bulbs come partially on. This limits top speed and surges between districts (lamps heating up). Will this be a problem with DCC?

[Vail and Southwestern RR]

As long as the method of power distribution the bulbs should behave about the same under DCC, though they might kick in a bit sooner since there is a bit of power disapated in the decoder.  If the power staion is up to it, you can put two bulbs in parallel, and double the current before they kick in.

[selector]

..or maybe a single bulb that draws more amps?  My understanding is that the glowing filaments mean the bulbs are getting an increasing voltage as you dial it up enough to get these older motors to their amperage druthers for actual work.  In DCC, the track voltage is fixed by the system at somewhere between 15-17 volts (HO) in most cases...it varies.   You are dialing up in DC and putting more amps through the rails as well for the motor.  That is a slow signal for the lights to do their thing, too.

[jfugate]

Do you have train length blocks already? How many locos do you have on your typical train?

If you already have train length blocks and will be using those same blocks with DCC, then the bulb performance will be similar. You don't want the bulbs to glow if you can help it, so you need to keep the amp draw of your train down under about 75% of the bulb total amp limit.

An 1156 bulb has a 2.1 amp limit, and the fact the bulb is glowing dull orange means you're running more than 1.5 amps through the bulb already. You need to move to a bulb arrangement that increases the amp limit. You can find a list of bulbs and amp combinations here (scroll down).

Ideally, you raise the limit high enough that your typical train is not affected (the bulb doesn't glowe), but keep the limit low enough that a short has the least amount of amps flowing through it.

The bulbs are cheap, so one way to handle it is to just start working your way up the bulb combination list on one test train block until it no longer glows -- and you've found your magic bulb amp limit that's just enough. Once you've found that magic combination, you can outfit your entire layout's train blocks with that combination.

[edwardpa]

Thanks Joe for the link; it was very helpful!

I'm going to use the 1157 bulbs with the filaments wired in parallel, remotor some of the older locos and add more bulbs to make the power districts smaller. Thanks again.