DIY Sparkie

[dmck]

Instantaneous starting current may be quite high, you may have to go 80-100.

Try the 50 & 60A first... before you buy a BIG one...

[dmck]

slight change to isolation switch wiring...

Duckys wiring.jpg (12.37 KiB) Viewed 534 times

otherwise you will NOT be able to totally isolate house-battery but still have instruments etc working

[dmck]

Ooops.... yes you can... by operating the 'house' cct breaker...

[Kimtown]

Be damned careful. Attached is a wiring diagram from a major component manufacturers 2021 catalogue. Wire it like this and you could be in big trouble if either battery fails......
It is IMPOSSIBLE to isolate a faulty battery and have motor and instruments operating on the remaining good battery.
BEP FU wiring diag.jpg

I think we should all carry jumpstart kits. A lot goes into a quality wiring system.

I always keep my little USB jump pack with me when boating. Needed to use it dozens of time lol

[ducky]

slight change to isolation switch wiring...

Duckys wiring.jpg

otherwise you will NOT be able to totally isolate house-battery but still have instruments etc working

Let me mull that one over. Been a long day at work so it hasn’t sunk in just yet.

It’s 3 independent isolation switches linked up with bus bar Having it the way I had it gives me the option to crank the outboard with the “house” battery without paralleling to the crank battery, along with giving direct charge off the outboard alternator if I ever needed to bypass the ctek for any reason.

But I’ll take it on board and have a think over the coming day or so

[dmck]

I hadnt taken in to account the 'house battery' circuit breaker... which you can use as another isolater.

[dmck]

You should be able to TOTALLY isolate either battery and run-the-ship on the other one.

[ducky]

Putting this out there cos I assume it isn’t common knowledge. Mercury (and presumably other manufacturers) have put out a statement saying they won’t warrant any lithium batteries connected as crank batteries in addition to the advice to not have an isolator between outboard and battery.

This is because a disconnection with the motor running can cause motor problems (lithium have a battery management system BMS that can disconnect the battery in the event of an issue)

So looks like I’ll be going lead acid for the crank battery, plus some wiring changes to remove the ability to isolate the motor from the crank battery