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I am trying to develop a simple 6-8 Volt lamp soft start circuit for my 1939 Chris-Craft. The boat originally had a 6 volt electrical system. In order to facilitate starting, I went to an 8 volt electrical system. This has worked fine for everything except for the 6-8 volt light bulbs.

At idle the system voltage is ~ 8.7 volts. While underway the voltage can go as high as 10 volts. If you turn on any lights while underway, the inrush will eventually burn out the bulb(s) in a short period of time.

I have taken a first cut at the "soft start" circuit using an IRF530 MOSFET. I would appreciate any assistance in fine-tuning this circuit in circuit-lab so I can see if I am accomplishing my goal.

https://www.circuitlab.com/circuit/8n3r44/6-8-v-lamp-soft-start/

Have a play with this:

:)

What I'd do is tap off +6 volts off the third cell of the batteries and use that to feed the lights. You can usually drill a small pilot hole into the lead cell terminal and put in a self-tapping screw.

Be sure to put a circuit-breaker or fuse in that 6V feed line!