Engine runs before Mars light turns on


malletman

malletman

Alcohaulic
Ok, here is what I have. Older PFM brass NKP Berkshire, Pittman open frame motor, 1 amp draw at stall, half to three quarter amp during normal operation. I installed a Minitronics Mars light circuit but the engine is up to a decent speed before it activates, not bad for an open frame motor eh! I need to drop the voltage to the motor by 3-5 volts so the mars comes on before she starts to move. My electronics knowledge isnt the best. What Ohms value do I need to achieve this? I know I can pair up the resistors to handle the motor amp load. Thanks in advance. Mike
 
What voltage is the mars light? If it's 12 volts, then dropping the voltage to motor doesn't seem to make sense to me. You'll have a motor that runs more slowly with less power and mars light still isn't going to come on any sooner. If the mars light is running off less than 12 volts, you need to apply Ohm's law. There's a site at http://home.cogeco.ca/~rpaisley4/LEDcalc.html that helps you calculate the type of resistor you need for the current you need to start mars light operating. I'm not familiar with the Minitronics Mars light so I can't give you more specfic help but it sounds like you need to have some kind of constant voltage lighting system for the mars light to function properly.
 
What you might consider doing is putting 12V worth of battery in the tender (look into rechargeable? 2 9V will give you 18 and you can use a voltage limiter to drop that down if need be.) and have separate wiring that will enable you to turn on the mars light and headlight independently. This will also enable you to have a constant intensity headlight on DC.

As far as charging the battery, I would wire it to power pickups from the wheels and have a spot you can park the engine where only the tender wheels get power, then have a switch that has three positions (on, off, charge)

I am no electronics expert myself, but I think that this could be accomplished without too much difficulty...
 
mars light comes up to full brightness at around 4-5 volts, circuit is rated 4-14volts dc. Engine is at a nice branch line speed before the mars gets its act together. I have a better circuit coming soon, I will probably just wait till it arrives. Minitronics has some good stuff, this isnt one of them.
 
Without a constant voltage lighting system, the mars light will never activate until it gets the minimum voltage. If the mars light used a 1.5 volt LED or bulb, you could use a resistor to drop the voltage so it would come on at 1.5 volts, but a 4 volt incandescent bulb just won't light until you give it enough volts. I'm sure the kit was made for engines with a constant voltage system in place, with a broad enough voltage range so it didn't require a dropping resistor.
 
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