KB356: DH165A0 - Headlight brightness

This article was last updated on Jan. 20, 2012, 9:48 a.m. | Print Article | Leave Feedback

I am installing a DH165A0 in an Athearn SD70.

The head light outputs are a nominal 30 ma (with the link cut).

The bulbs were of course a bit lower in their current demands and were very bright for a short while.

Is there any way to lower the current output from 30ma or do I need to add a resistor in line with the bulb to drop the voltage output?

Of course if it is supposed to be a regulated current output this might be a problem.


The DH165A0 has a constant current source for F0F and F0R, so a series resistor will simply increase the terminal voltage at the selected fixed current.

To drop the lamp current, add a resistor in parallel with the lamp to bypass some of the current selected, calculating value for the resistor: (R = Lamp Voltage / amount of current to divert).

If the resistor is too small a value it will bypass more of the current and the lamp will be dimmer.

You can try a number of values to get the best "fit".

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