Adding a second battery

[Sanlen]

Sorry for the late reply - we had our national holiday in Sweden and payed a visit to our youngest son who is serving in the Navy on one of our latest ships - the stealth version. We got a private tour - I must say it is a impressive ship .

The Dynastart is a DC starter/alternator and will take no harm if the DF lead is disconnected. It will just spin free when the engine is running.

I prefer this type of main switch (in metal), although the equivalent type in plastic is ok.

It is great if the latest BM-1 can show starter battery voltage - then drawing #2 should be correct. Now I will get myself one of these

[dahlke]

I disconnected the DF lead in both ends (reconnected in the picture below). Today I had planed on taking the motor for a spin - as I'm still waiting for my headsail. When I switched on the engine I noticed the yellow light was on (according to the manual that is the oil pressure warning light). I had a look at the wiring. See the below images Wire 1 goes to the yellow light and the brown wire (number 2) goes to the dynastarter (marked D+). If I reconnect the DF lead the yellow light turns off.

Would the yellow light in my boat in fact warn me if something was wrong with the oil pressure? On the relay it says ("D+/61"). What does "61" refer to?

I had a look at an exploded view of the MD6a (see below). Looks like there is a pressure sensor next to the oil filter. Is that what monitors the oil pressure?

Looking at my engine there is a green wire going from this sensor (pressure sensor) to one of the red lights. Wouldn't that indicate that on my boat the oil pressure light is red and not yellow as described in the manual?

[Bob McGovern]

Just a guess here, & hopefully someone w/ more experience will add a better opinion. Looks like from the diagram your oil pressure sensor borrows its 12vdc POSITIVE(+) from a pigtail attached to the Dynastart's charging output leg. This is a handy place to tap in, since the oil pressure sensor only has to be energized when the engine is running. So in Boolean terms, IF pressure switch closed (open?) AND Dynastart producing amps, THEN turn on oil pressure lamp.

So my guess is, you can transfer the oil pressure sensor pigtail to the alternator output terminal (Alt +) & obtain the same result. If fire shoots out of it, I never said that.

[dahlke]

Just a guess here, & hopefully someone w/ more experience will add a better opinion. Looks like from the diagram your oil pressure sensor borrows its 12vdc POSITIVE(+) from a pigtail attached to the Dynastart's charging output leg. This is a handy place to tap in, since the oil pressure sensor only has to be energized when the engine is running. So in Boolean terms, IF pressure switch closed (open?) AND Dynastart producing amps, THEN turn on oil pressure lamp.

So my guess is, you can transfer the oil pressure sensor pigtail to the alternator output terminal (Alt +) & obtain the same result. If fire shoots out of it, I never said that.

I just reorganized my post a bit There was some text in the bottom that might easily be overlooked There is only one wire going to the pressure sensor (a green one) and it connects directly to one of the red lights (on the positive side). Does that make any sense?

[Sanlen]

I disconnected the DF lead in both ends (reconnected in the picture below). Today I had planed on taking the motor for a spin - as I'm still waiting for my headsail. When I switched on the engine I noticed the yellow light was on (according to the manual that is the oil pressure warning light). I had a look at the wiring. See the below images Wire 1 goes to the yellow light and the brown wire (number 2) goes to the dynastarter (marked D+). If I reconnect the DF lead the yellow light turns off.

Would the yellow light in my boat in fact warn me if something was wrong with the oil pressure? On the relay it says ("D+/61"). What does "61" refer to?

Normally I would say that the yellow light is your charging lamp. Since you have disconnected DF your Dynastart doesn't charge and thats why the light is on.

Edit: I just got unsure about where you should connect the cables - I have to check in my old manuals I'll be back.

[Sanlen]

I found this nice wiring diagram for the MD6A. You should be able to connect the lead from the yellow lamp (#1 in your picture) to D+ on your alternator instead. And yes, the yellow lamp is the charging lamp
I hope you can read the diagram, image resolution is bad.

[dahlke]

Thank you all so much for helping me figure this out