24 volt starters....or....electricity 101

[Foolwitools]

Hi Guys!

I usually run my boats from my 16' runabout. I made a boatstand that fits across the gunnels in the back.........works out pretty well. anyhow ................

I use the big boat battery for the little boat starter. just got a sullivan 12/24v starter and wondering about the best way to rig a 24v supply.

If a run another 12v car battery in series with the big boat battery( leaving the big boat hooked up to only one battery), I know I'll get 24v. Question is, when I use the little boat starter, is there any chance of some kind of electrical feedback that might fry the big boat electrical system?

Thanks, Bob the Fool

 

[snowdog-2112]

Fool,

I would think that a full-size marine battery would supply a sufficient amount of current to crank any engine at 12 volts. Try that first and if it's not enough, then move up to 24 volts.

Just my $.02

Snowdog

Team Snowdog: keeping it simple!

 

[Foolwitools]

Snowdog,

A new sullivan starter on a freshly charged, 730 cold cranking amp car battery has a heck of a time turning over my .82 outboards. always gotta loosen the glo plug. Haven't even tried to start the 1.0 yet..........

Bob the Fool :blink:

 

[izitbrokeyet?]

Wow bob...you and I must talk sometime

For about 2 years I ran most of my boats from a 16ft Boston whaler

I gotta tell you up front.....you're not going to start that 1.0 cubic inch without 24 volts of potential across your starter....no matter how many amps you've got, it'll take at least 15,000 watts of power to put on that motor to get it rolling

power=Watts(W)=Volts x Amps

Given Amps at 730 and watts at 15,000 you can rearrange the above to see

15,000/730= 20.54Volts minimum

That's a huge motor....that takes allot of starter energy to get it rolling

Have fun

That 1.0 P/S you got was pretty impressive in size......looked like it belonged in a large Chainsaw or somethin :blink:

 

[jasonspeedy]

Fool,

I'll agree that most of my posts are lighthearted and not at all based any reality, but I know a thing or two about electricity. First, forgetting about any other factors, the RPM's generated at the starter with 24 volts are much appreciated by large motors (at least in my experience). Now, if you double the voltage potential, you will be demanding twice as much current from the source, which shouldn't be problem for the following reason: you now have 2 twelve volt batteries in series, and by having two batteries you have doubled the amount of physical media used to generate the current, in short , you should have the same theoretical lifespan as with 1 battery delivering 12 volts (assuming all batteries are of the same amp/hour rating). Now , I thought you mentioned something about putting a second battery in series with your marine battery. Don't do that. The problem lies in the fact that the amp/hour ratings of these two batteries wouldn't be the same (unless your second battery was identical with the first). The starter will try to suck the same amount of current from each battery simultaneously; if they're mismatched you get into a lot of theoretical crap about internal resistance, etc...which becomes a large problem when one of the batteries is trying to kick the bucket (smoke, fire, etc...) Just get two identical 12 volt batteries and wire them in series, it will save you a lot of heartache. I have 2 11amp/hour batteries in series, and I can go a long time in between rechargings. Best of luck, JOB.

 

[nitrotoys]

Hey Bob, I did up a nice little starter box, I will take some pics of it if you would like or draw you a wiring diagram.

Its real simple, I used QD plugs. But when doing a OB i had to reverse the leads in the connector.

Or start IB with the starter from the front of the boat.

Hey WARNING, hang on to that BIG BIT(H When your using 24 volts.

 

[Jerry Wyss]

I use Two Twelve volt lawn tractor batteries that are similar tied in series with a heavy construction type Female replacement

connection and with a Male connector on the end of the Model Starter. The Full Size boat motor can be connected to One

of the batteries and be OK, but as soon as you hit the button on the Model starter I think your Full Sized motor will get

a Shot of 24 Volts. You would have to have a easy way to disconnect one "Leg" from the Full Size motor while your using

the model starter. I think this is correct, and be sure to use heavy wire on this stuff , a fire in a boat out in the middle

of a lake is a scarey thing. Jerry

 

[Preston_Hall]

I really doubt you would have any trouble. Just simply disconnect the secondary from the primary when not in use to assure safety of both electrical systems. This would only be a one wire disconnect. The secondary shouldn't feedback through the primary system. But even if it did, the primary system (16' boat) is off. Therefore no current passing through the 12V system.

Ideally the batteries should be matched. Will you ever know the difference? I doubt it.

I'll also add that my 24V sytem doesn't affect my $15 12V fuel pump connected to it.