Battery Isolator ~ Part Deux

[spharis]

Yeah, but what happens when you are running along, fuse blows by the battery, and the alt was excited, and the battery leaves the circuit.......ouch......If I had a fuse on my main battery line, or anywhere between my alt and my battery, it would be removed. Your ignition has a breaker on it, or it should anyway to keep the starter from being used if it is popped. Newer alternators also have protection diodes integrated into them so they correct AC current. The one you fried probably did not. Because of this the, what could possibly happen save a catastrophic failure (like a crash into another boat) that could cause the main battery line to require fusing? Everything in it is protected at the component, so there is not a need to fuse the wire. If there is a fuse on the main battery wire, it is probably huge, like 150A or something. There is no component in your electrical system that can dish out that much amperage, so whats the point of even putting it there? The highest output components you have are your alt, and your battery. Some starters pull 200A+ when turning as well. What's the point in having a fuse that large, IMO it only adds the potential to fry your alt if for some reason it does pop, which is likely never. That would equivelent to internally fusing the battery....just no point to it.

One thing you do want to do Razz is make sure the relay activate circuit (the little lugs you have to tie to the ignition) is fused. Those need to be on an acc line, or added to a breaker or something somewhere; or just add a low amp inline fuse on it.

[Razzman]

One thing you do want to do Razz is make sure the relay activate circuit (the little lugs you have to tie to the ignition) is fused. Those need to be on an acc line, or added to a breaker or something somewhere; or just add a low amp inline fuse on it.

Your talking about the small +/- takeoffs on the iso right? What amp fuse we talking here?

[tarheeler]

You have a fuse inline from your battery to your starter, where does your alternator cable go, to the the starter lug?

correct. it is a 90 amp fuse. one time when i reversed the cables by mistake it blew the 90 amp fuse the instant the last cable touched the battery and did not distroy the fuse. all the mercruiser engines i have seen from 1998 on up have thes fuses and maybe the older one do also.

[Razzman]

correct. it is a 90 amp fuse. one time when i reversed the cables by mistake it blew the 90 amp fuse the instant the last cable touched the battery and did not distroy the fuse. all the mercruiser engines i have seen from 1998 on up have thes fuses and maybe the older one do also.

Well my '95 doesn't or my alt wouldn't have cooked as i did the same thing.

[spharis]

Well my '95 doesn't or my alt wouldn't have cooked as i did the same thing.

Your new alt wouldn't have cooked either. They (should) have a recifying diode in them. The fuse really is an unecessary part in there, and save from hooking up cables backward, I don't know why it even has a purpose; maybe if you have your key on and you hook them up backward.....I really can't think of a reason outside of a human error, like during jumping or something. This isn't something that is gong to protect anything during normal operation. If you change your starter, you may have to upgrade that fuse. Some starters pull major amps, like 200+. Still, in either case, fusing the integrator is completely unecessary in a boat. I would remove any fuse between my battery and my alternator as well. That's just me. I think I have a higher case of losing the fuse while running, than of hooking up cables wrong or smething.

Your talking about the small +/- takeoffs on the iso right? What amp fuse we talking here?

Yes....something small, it is just to close the coil in the integrator. Maybe .5 to 1 amp.

[tarheeler]

starter and fuse. fuse is number 7

[spharis]

Thats looks like a solenoid breaker/fuse, not the starter cable line part. Most of our boats have a breaker on the ignition components further up the line that does the same thing. It looks like the below is how that one works, but I am not sure from this angle. That looks like an external solenoid to make the starter gear engage. Maybe not, but I really cant tell. It wil go to one of those two points, depending on the style. Either way there is no way your starter cable is going through that little thing. It will be attached to the main lug, and will be bypassing that little box. That looks like a fancy relay or something. Do you have the location of where you found that drawing?

The starter solenoid works just like Razz's battery combiner. It has an input lug, and an output lug. Both are very high amp. There is a circuit that uses low amp to close the coil between them. In the starter case, the ground is on the backside of the starter (that hanging cable) and grounds to the engine block via the case bolt usually. The smaller lugs are tied to the key's start lug back at the dash ignition switch. When the key is turned to start, the low amp signal closes the huge coil between the lugs.

That box looks like it goes elsewhere, maybe to the ignition, but it definately is not inline with the main power wire. The starter current draw would melt that.