If this is the wrong place for this question, my apologies. I am using some 6.5v 68ma grain of wheat bulbs on my layout, powered by a 18v model rectifier dc train power pak i had with no other use. I tried these bulbs at first on the power packs accessory terminal first and it was apparently too much and blew the bulb. ok then. So i then put a few on the dc power terminal. Initially they work fine with me using the speed controll of the power pack as a dimmer, thereby i figured using less power and i had no issues until once i added the 6th bulb, it didnt want to power any of the bulbs. If i take that 6th bulb off, the other 5 are fine. Im no electric goo roo and Im learning. So, what kimd of power supply do i need for these bulbs so that I can use several without having to use so many power supplies? Obviously being a 18v power supply if i didnt “dim” the others Id blow them out. I know this isnt the right way to do this hence why Im asking.
Depending on how many bulbs you will end up using you could get a 5 or 6volt wall wart. If you bought a sack full of the bulbs like I do buy a 5 volt power switching supply off eBay. The bulbs will be slightly dimmer but will last for ever running on reduced voltage.
1 amp = 1000ma, multiply the 68ma by the number of bulbs to size the power supply.
If you are using these in buildings, less than full power should be good. So try this. Hook 4 of the bulbs in series. That’s
----O--------O--------O------O------
hook the free ends to the 18V terminals. The should light, but not insanely bright.
Now if you need more than 4, hook another 4 up just like the first 4, and hook the free ends of those to the power pack terminals, combined with the wires from the first 4 lights. This puts each group of 4 in parallel with the other group of 4.
Depending on the capacity of your power pack, you should be able to run at LEAST 5 strings like this, 20 bulbs in total, and probably closer to 10 strings, 40 bulbs.
If they are too dim, try strings of 3 bulbs each, that’s a lot closer to the 18V rating of the power pack and may be too bright though - that “18V” output may well be a couple of volts higher with a light load. So try strings of 4 bulbs first.
