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another multi battery question...

Old 01-02-2003, 03:42 AM
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I have two batts for each engine in a dual yami setup. Each engine's batts are connected together with a common ground, but the two pairs aren't grounded together. I assume(yikes) that the engine share a common somewhere on the boat, maybe through the water or that aluminum angle iron that protects the transom lip. Since this does not seem to be a very good ground, is there any benefit or danger to grounding the circuits together, either at the engines or at the batts? I think that they also share a ground at my fuel management gauge ( which is giving me fits).
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Old 01-02-2003, 07:02 AM
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Yikes!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

OK, I'll grant you that its quite possible that somehow somewhere in the jumble that is factory wireing there may be come common line connecting the two banks of batterys, or maybe you just hit it lucky and water in the bilge is acting as a conductior. So, what's that mean? Well, it means that some very skinny wire is doing a job that would normally be given to a battery cable that's about as thick as your thumb. Is that important? Depends on how you feel about heat - and lots of it.

Of course its is possible that amoung the miriad of ways a multiple engine mulitple battery boat could be wired that there is no mutual connection on the negative side and one needed. In that case there is absolutly no harm done by having them connected via a battery cable. But of course there is a down side to making a proper connection with a real length of battery cable, and that is that it could cost you as much as $10 to have the cable made up. So, you gotta ask yourself is there a down side to not putting a connecting battery cable on there. Well, you know that when electricity finds its own path it has the nasty habit of moving material along with the electrons. A sort of a do it yourself electroplating takes place if you rely on bilge water to do the transfer for you, taking very expensive metal from one device and putting it all over another. A second down side, and this one assumes you have some wire connecting things through something like a fuel gauge, is that zillions and zillions of electrons will share that same pathway and that will get that wire awfully hot - maybe hot enough to get you a new boat amid clouds of smoke (unlikely but quite possible).

So, you know what to do. Just have a cable made up. I prefer to do it the solder and seal method but any real auto parts store will sell you the cable, sell you the lugs for the ends, and crimp them on for you while you wait. After that you will need a half inch wrench to put them on.

Whoops, there's something I haven't ranted and raved about for years. You have, I have assumed, tossed those wing nuts that come with batterys and replaced them with nylock stainless steel nuts, haven't you? That alone is the very best and most important $0.40 investment you can make in your boat. It would be worth it if it cost 50 times that much.

Thom

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Old 01-02-2003, 07:35 AM
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Thom, if you saw the setup, you would be proud. I have a source for marine sundries so cost is not the object. Everything is tinned 600v marine, soldered, shrinkwrapped with the goo inside and on and on...There is separaton of each bank, that is: one aux batt powers my switch panel exclusively and is wired to that batt accordingly and the other aux batt powers the fuse panel for my electronics only. Of course, each batt is grounded to it's mate, but the two pairs share no common ground..In effect I'm running two separate systems.. except for the incidental crossover.
So, I will put a common ground between the two banks and sleep soundly from now on...
Thanks,
Pete
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Old 01-02-2003, 08:10 AM
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guess i better 2x check also,I have the same setup.

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Old 01-02-2003, 09:45 AM
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OK Thom, I have warned you about my ignorance when it comes to electrical issues before but I am venturing out again. Are you saying that the negative grounds on the batteries should be connected via a battery cable? Mine are not but I have two batteries and a single OFF BOTH 1 2 Perko switch that might be connected together inside the switch. I guess that would accomplish the same objective. OK, here is my question:

This winter I am converting to a two switch set up that will have two Perko OFF BOTH 1 2 settings. Does that mean I need to install a cable between the negative posts on my two batteries or will that again be taken care of inside the switch.

Thanks in advance for your help.

Kirk

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Old 01-02-2003, 09:56 AM
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The Black, or negative, or ground wires are NOT connected to the Perko (or any other brand) of battery selector switch. Only the RED, or positive battery cables are fed to/through the battery selector switch(s).


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Old 01-02-2003, 11:55 AM
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Ocnslr already took care of one of your questions quite nicely, so I'll hit the other. Yes, I am saying that if you have two banks of batterys (which might be one battery each) they should be connected together on the negative side. That is for just the reason that Pete brought up.

Its possible and even likely that somewhere in your electrical system there is a negative wire that somehow crosses over from one of your independent battery systems to the other. A ground wire from a fuel tank sender would be a good expample of a place where it might happen. If this is the case then in the event of a short at the battery terminal for one of the batterys it is quite possible that that one skinny wire becomes the grounding circuit for the entire boat. So there you could have something like a typical 16 gauge wire now trying to move the electons that are comming from stuff like a VHF, a GPS, a Radar, maybe a CD player, a couple of lights, a bunch of instruments, and maybe a pump or two all at the same time. If it does that little wire is going to light up like a 300 watt light bulb, much to the detrement of anything near it.

Thom

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Old 01-02-2003, 12:56 PM
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Thanks to both of you, just gives me something else to do over the winter. I wish everything on my list was this easy.

Kirk

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Old 01-02-2003, 02:11 PM
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Now I'm totally consued and alarmed about that glowing red skinny wire. I have three batteries and two (Yamaha) engines. There are two big black cables connecting the negative posts of each engine battery to a stud terminal post near the battery boxes and a big cable connecting the port engine battery negative to the house battery negative. The negative connections from the engine wiring harness go to that same stud terminal post. Another big cable runs from the post up to the console and provides the ground for all the electronics, etc.

Since all three batteries' negative terminals are connected with large cables, I assume I am okay?
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Old 01-02-2003, 02:25 PM
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Saltdog, that's how I'd want mine wired if I were you.

Thom

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Old 01-02-2003, 02:39 PM
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Thom -

You bring up a most excellent point about those wingnuts that come on the posts of the batteries. They could loosen from temperature change, vibration, corrosion, etc and cause serious electrical or safety problems if used as is (especially if they are only tightened by hand).

However, there is a simple solution without having to replace hardware. Simply take the wingnut off and distort it a little bit to convert it to a prevailing torque locknut. That way, you don't have to find the wrench to install or remove it.

As long as it can't loosen, it should be okay - right?
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Old 01-02-2003, 03:46 PM
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For added contact and protection I use stainless lock washers on the batt stud, then the cables, then a slim stainless washer, then the locknut. Coat liberally with corrosion blocking grease. I feel the lock washer bites into the lead and the lug for a clean contact.
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Old 01-02-2003, 04:19 PM
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Stainless steel has about 40 times the resistance of copper. I envision your battery current running thru star washers before the battery terminal. Not good!! Lead is actually a much better conductor than stainless.
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Old 01-02-2003, 05:08 PM
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Thom...take a look at my post below...under "Wiring Quandry". Is this what you are saying? Looks to me that all two or three batteries share a common ground, right?

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Old 01-02-2003, 06:12 PM
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I can't win for trying. Out with the stainless washers...
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Old 01-03-2003, 07:47 AM
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guys, the batteries are most likely connected together through the engines themselves. Specifically from the engine ground on the block to the steering shaft that ties/slaves them together.

Current will follow the least resistant path, and this will offer much lower resistance than a oddball ground wire up in the harness somewhere.

However that oddball ground wire can cause an undesirable ground loop, where some electronics are at a higher voltage than others. The dash gauges usually dont feel this, but it can be a real pain if you have multiple units (gps,autopilot)talking to each other.

Take the time to run a "real" ground connection between the batteries. Then do your best to run all grounds for your electronics back to one place. Preferably to a neg. battery post.
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