Should the boat die if you take off a battery cable?

[jasun]

Will the boat run directly off the alternator if it is running and you disconnect one of the battery terminals?

[2500HD]

I believe it should, just like a car the alternators job is to keep the engine running and charge the battery. The battery's job is to power accessories and start the engine.

[haugy]

It should. I can be running and switch over from one battery to another without any issues.

Correct me if I'm wrong (never was good at electrical crap): But the alternator is there to run the boat, and any residual left over is to charge the battery. The battery's main purpose is to start the boat, running accessories is the secondary role. Once the boat is running it shouldn't be pulling from the battery, unless you have huge stereos that draw more than the Alt puts out. Then it will run the boat off the Alt, but it will also pull from the battery which will run it down over time.


EDIT: Damn too slow!!! I was busy typing long novels. :D

[Jetlink]

Ok, I always thought that the battery supplied power to the electrical system and the alternator supplied power to the battery to continually top off the battery as it were.. Granted I might be messing this up with aircraft electrical systems but that is how every electrical system on any airplane works.

[dirtydawg]

an engine will run without a battery no different than jumping a dead battery with a good one, once the engine starts you remove the jumper cables and it continues to run. I agree with Jetlink. Battery runs accessories/ Alt charges battery.

[Wylietunes]

Will the boat run directly off the alternator if it is running and you disconnect one of the battery terminals?

1st off, its not good for the alternator to see an open field, i.e. no battery to charge, so taking the cable off for long could actually short out what was a working alternator.

To answer your question, yes, if you pull the B+ cable from the battery, without disconnecting the alternator cable from that main battery cable. If you pull the ground cable, you can very well disconnect the ground side of the very components that are needed to run the engine and the engine will shut off.

In haugy's case, he probably has a make-before-break switch. This is one that the rotating pole piece makes contact with the next post position before breaking connection with the current post. This prevent that open field condition. Not all marine dual battery switch are make-before-break though.

All loads do actually pull from the battery, in theory. The batteries job is to carry those loads and the alternators job is to keep up with those normal loads and replenish what is used from the battery during starting.

[haugy]

1
In haugy's case, he probably has a make-before-break switch. This is one that the rotating pole piece makes contact with the next post position before breaking connection with the current post. This prevent that open field condition. Not all marine dual battery switch are make-before-break though.


Interesting point. It's just a Perko switch. I've never seen inside one. But It goes battery 1 (9 o'clock position), OFF (12 o'clock), battery 2 (3 o'clock). So I would think it would close the connection completely. But I just don't know. I've seen the ones with "both" in between the batt 1 and batt 2. I bet those are like what you are talking about.

[Wylietunes]

Interesting point. It's just a Perko switch. I've never seen inside one. But It goes battery 1 (9 o'clock position), OFF (12 o'clock), battery 2 (3 o'clock). So I would think it would close the connection completely. But I just don't know. I've seen the ones with "both" in between the batt 1 and batt 2. I bet those are like what you are talking about.

If you can rotate clockwise and pass through OFF to get from 1 to 2, then no, yours is not a make-before-break. Its actually opening the battery circuit when it hits off, before closing again when it hits 2.

If know what model Perko, I would look up the specs on their site and it should tell you.

[haugy]

Yep, that's what I was saying. I meant open the connection, not close it. All you electrical nerds can pounce now. :D

[jasun]

Thanks for all the input... Had 2 batteries on the boat (not both hooked up) and one had died trying to start it. Used the other to start it and tried to hook the dead one back up to charge it and when I pulled off the - terminal, the battery died.... Just wanted to make sure it wasnt a bad alternator..

From what Wylie is saying, it is a very good possibility that it would have died from removing the - side..

Thanks again!!