# Incandescent Bulb Question



## Bwells (Mar 30, 2014)

I am trying to connect 4 bulbs in series. All bulbs are 1.5 volt. Two are grain-of-wheat and the other two are marker lights, which I guess are GOW also, they are not LED. I have a voltage of 6.63 DC and when connected I measure 2.5 volts across each GOW and .89 volts across each of the two marker lights. I am under the assumption that each bulb would receive 1.6 volts. I thought of mA ratings, the GOW have a mA rating of 30 however I can't find the rating on the markers, not in the paperwork that came with the lights nor on Tomar Industries website. I assume there must be a large difference between the two. I assume this is where my problem lies. Any thoughts? Thanks.


----------



## gunrunnerjohn (Nov 10, 2010)

The GOW bulbs obviously have a considerably higher current rating, so their resistance is lower. If you have a basic meter, put 1.5V on one of the markers and check the current it consumes. Do the same thing with the GOW bulbs, you'll probably have your answer.


----------



## Bwells (Mar 30, 2014)

Okay, thanks John. I'll see if I remember how to do that. I may just move to plan B, whatever that is.


----------



## gunrunnerjohn (Nov 10, 2010)

Set the meter to current, move the positive lead to the current plug, and put the meter in series with the circuit.


----------



## Bwells (Mar 30, 2014)

Okay, I did that. The GOWS measure 70 mA and the markers measure 80 mA. The stated rating of the GOWs of 30 mA is different than that I measured. No big deal as I was expecting a major difference between the two bulbs. 1/100th of an amp seems somewhat negligible however the readings don't lie. It is apparent that my plan is flawed so I switched to plan b. I reconfigured the resistors on my LM317 to produce 3.02VDC and series the two markers and then series the two GOWs and then paralleled the two. Perfect solution and I don't understand why this didn't pop into mind a while back. Oh well, live and learn!!! Thanks for the help, Brian


----------



## Bwells (Mar 30, 2014)

double post


----------



## gunrunnerjohn (Nov 10, 2010)

I suspect that the rated voltage of one of them is different as you wouldn't have had such extreme voltage spreads with that small a current difference. 

Your solution is the right one in any case, no chance of dissimilar voltage drops killing things.


----------

