Dealy-bob between the alt and battery

erps · #1 (**permalink**) 09-25-2006

Was looking for some help on identifying this dealy-bob in our "new to us" boat. It's attached between the alternator and the battery and has a third "ground" terminal. I thought it might be a battery isolator at first, but I've ruled that out. I'm starting to think that it's some sort of a electrical noise suppression thingy.

Does anyone know what it is?

Thanks,

Ray

Faster · #2 (**permalink**) 09-25-2006

This is a bit of a W.A.G, but it appears to have a transformer coil so could well be an external rectifier, converting the AC output of the alternator to DC to charge the battery. This function is most usually integral to the alternator, but if this is an older vessel it may well be a separate component.
Thoughts, anyone?

Zanshin · #3 (**permalink**) 09-26-2006

I think it is a rectifier as well (couldn't be a coil as in 120V60cycles to 230V50Cycles or vice-versa, could it?). A quick check with a common voltmeter that every boat should have should sort that out.

erps · #4 (**permalink**) 09-26-2006

Thanks for the ideas. Some additional information. This dealy-bob is wired in parallel with the main wire to the battery. The alternator is a conventional 100 amp alternator externally regulated. The battery terminal lug has two wires attached to it, one is the main cable to the battery, then there is a second wire that attaches to this thing. I checked to see if the battery terminal on the dealy-bob was wired to the second battery bank (thinking it was a battery isolator switch) but it wasn't. It's wired to the same battery that the alternator is charging. That's what made me think it was some sort of a noise suppression thing (to cut down on electric noise to the radios) I could disconnect it and the alternator would still charge the battery bank it's attached to. (I have two alternators that charge two separate banks)

Ray

Zanshin · #5 (**permalink**) 09-26-2006

I can see a red plaque attached to side of the "dealy Bob" -> does that contain any text that might explain it?

gc · #6 (**permalink**) 09-26-2006

My guesses.
1) This is an older boat with a lot of history.
2) Maybe the second alternator was added well after original delivery.
3) The original alternator (or maybe the add on)had a noise suppression device (this thing)
4) Someone decided (maybe rightly) that it had burned out and bypassed it straight to the battery, but left it in place.
5) Maybe it was a home brewed noise suppression inductor - and not adequately designed so it burned out.

All of these are just random thoughts, trying to generate ideas you can explore.

feetup · #7 (**permalink**) 09-26-2006

The black thing on the right is most definately a transformer, and a transformer of that size will have only one task, that of converting one voltage of alternating current to another, either higher or lower. There is no use for a transformer in a rectifier so that rules that out. The transformer could be used as an inductor, or a choke, both of which woul lead to the noise suppressor guess.
How about another clue. What does the red tag say?

Feetup

hellosailor · #8 (**permalink**) 09-26-2006

The black "blister" on the side of the gizmo is pretty clearly a transformer shield, and the only reason to put a transformer in that line would be RFI (radio frequency interference) noise suppression.

That also fits in with the wiring. There are different ways to do suppression, (i.e. capacitors as well as transformers or coils) this one would indicate the positive lead out form the alternator is being interrupted and the AC component of the signal being clamped to ground right at that box. The base is big enough that there's room for other components, that might be a very nice & effective little box.

Positive INput, Positive OUTput, Ground. Three leads.

It might or might not actually be doing anything, since RFI is sometimes caused by things like a bad alternator diode (either failed or failing) and that might have been replaced over the years. I'd say this means you should check the alternators, especially the diodes, and check for RFI. You should be able to bypass the gizmo (connect the two hot leads) very simply, and if you don't get any RFI, it is no longer necessary.

Couldn't hurt to leave it there? Unless, of course, IT shorted out. So if there's no RFI when it is bypassed, I'd either remove it or bypass it.

erps · #9 (**permalink**) 09-26-2006

Thanks for all the ideas. Regarding the red tag visible in the picture, I went back and looked at the orginal picture and zoomed in on it. The only thing I can read off the tag is "Caution". The tag is in plain view and I'm sure I read it while on the boat scratching my head, wondering what it was. I don't recollect that the tag had enough information to reveal its purpose to someone like me anyway, but I'll stop by the boat tomorrow and check it again.

Ray
S.V. Nikko

hellosailor · #10 (**permalink**) 09-26-2006

"the red tag visible in the picture"
Must be the ectoplasmic containment vessel switch. (Punning on "ghostbusters".)