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Twin honda battery/ground between panels?

H

hairdresser100

Contributing Member
Hi All,

I have twin 1997 BF90A outboards on my boat and I read somthing in the Honda factory service manual that I need to learn more about.

It reads, if you install twins you CAN NOT run them both off one battery so I installed two batteries with two 1,2,all switches.

It also says if you do need to run both engines off ONE battery you must disconnect the negative wire that grounds the two Honda control panels together that's located on your dash.

What is this all about????

If I did run the engines using only one battery what did I screw up???? I notice one volt meter jumps to 14 volts and stays there like a rock but the other one is sluggish and drifts around a little depending on RPM...but is always above 12 volts and stays at 14 when on plane.


My email is [email protected] (not spam or ....)

Thanks
 
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sounds like it causes a problem with the alternators charging the same battery could possibly hurt a voltage regulator.
 
I do not remember discussing using only one battery in any of the classes I have attended except maybe in passing....Just what I read in various rigging instructions. Basically, one battery per motor.

I can give you some thoughts based on my engineering background....the regulator will look at the battery to sense if the charge is down, then it will actively charge the battery. If two regulators are trying to do the same thing, they are not only looking at the battery but also each other. They are going to be confused and will most likely not charge the battery correctly. They may also temporarily charge...not charge....charge....not charge etc. The transient voltages and currents may be what could cause some damage....but who knows for sure? Considering, most regulators have some diode in its output circuit, it should protect the regulator from damage, but it does seem like it could weaken over time and finally give up.

Those are my thoughts on that.

I hope you used diagram #2 http://www.perko.com/images/catalog/pdf/Fig%208501-8504%20Inst%20(8500INS1).pdf in wiring your new switches. Just make sure that when you are running the engines, run engine 1 on battery 1 and engine 2 on battery 2. If one of the batteries go dead, you can turn the switch for that engine to ALL or BOTH to "jump" the batteries to start the engine. Once the engine runs and the battery gains some charge, you can turn the switch to the proper setting. Do not turn the battery switch to OFF as the motor is running...that can blow the regulator.

The ground is common between the two engines only at the battery negative or negative buss bar. I do not know of any Honda book that says to connect the grounds of two panels of the two engines at the console. It may be something I missed.

In general, each engine wiring and gauges should stand isolated from the other engine and the general boat wiring (nav lights, radios, etc should have a separate fuse panel and grounding system all the way back to the battery).

I would like to know what manual you got that information out of.

Off the top of my head the only exception that I can think of is a jumper for lighting the gauges. That lead can be jumpered to the switch for the nav lights. The ground is not jumpered.

Well you asked "what time is was" and I think I almost told you how to build the watch.

Mike
 
The way I understand it is this:

When you are using an alternator in a charging system, it needs the battery to supply "reference" volts to "tell" it when to charge and when to not charge. A fully charged, 12 volt, automotive, wet cell, battery should have a static charge of 12.6 volts. The voltage regulator on MOST systems is set to have the alternator charge the battery at 2 volts above "reference" so that, in this case, we would see a charging voltage of 14.6 volts at the alternator output terminal. This is done so that the alternator will have the reserve capacity to run your electrical system while, at the same time, keep the battery charged.

If you were to introduce another alternator and voltage regulator in parallel with the first one, this is what is likely to happen:
When you start the first engine, you will probably not notice anything out of the ordinary and the battery will "excite" the first alternator and charge normally. However, upon CRANKING and starting the second engine, THAT alternator will momentarily see voltage on the order of less 14.6 volts from the already charging first alternator and the regulator will allow it to start charging. This is because there is a voltage "slump" due to the cranking starter. But, when the engine starts and the starter load is taken away, the voltage will rise again and then there will be a "conflict" between the two regulators. Whichever one sees 14.6 volts first will stop charging and the other will charge until it sees 14.6 volts and then it will stop charging and then the other will start because the battery in not yet at 14.6 volts

This could actually work like this for a while but what we need to understand is that this "switching" is taking place pretty much at the speed of light or as rapidly as the electrons can make their way through the stator. This rapid "pumping" of voltage and current through the field circuit and stator coils does not happen without a penalty. As this high speed "oscillation" is taking place, it will cause, among other things, heat to build due to the "ramping" up that the current has to do to overcome the inherent resistance within the coils. Faraday's law covers this aspect I believe.

In addition to rapidly overheating the alternators themselves, the constant and rapid build up and collapse of magnetic fields in and around the coils will set up some fairly powerful inductive voltage spikes on an order that the system just wasn't designed for and that the solid state circuitry in the voltage regulators may not be able to handle. The diode banks in the alternator will also be subjected to these spikes along with the inordinate heat and may fail as well along with, maybe, even the engine computer.

So, have you damaged your system? Maybe. But, like I said, it could operate like this for a little while (I think) and there might not be any damage. You just don't want to do it again.
 
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Thanks Mike and jgmo!!

Yes on the #2 battery for sure, even though Blue Sea thought I was WAY off base and advised other ways.

I bought the factory Honda BF90A manual and on page #378 it talks of "BATTERY." Top right. This looks to be the rigging section. It clearly stated one battery per engine and if you need to get home on one disconnect the neg wire between the two "switch panels."

jgmo,
Thanks for the great response, I understand and appreciate it. I think the worse thing I did was run the two battery switches on "all" when I should have had port on 1 and stb on 2. This was done for years until I read the manual cover to cover and found that sentence. It still charges but I'll have to dig deeper with a volt meter to really test things more thoroughly. I don't think "all" followed the rule of one engine, one battery!!!?? What do you guys think?
 
if you can copy and post the wiring diagram of the system you have....its also important to know what kind of boat you are running....each battery is grounded to the motor its wired to and if its a metal boat then those two grounds are connected..the wire between the two panels may be just to pick up ground for both panels and save from having to run two wires to the back of the boat...without a wiring diagram i dont know what the ''all'' position of the switch does....if everything works going by the book consider your self lucky and stay by the book on switch posiitions...what the ''all'' position actually does is the question here...good luck..
 
HI Papyson,

Figure #2 http://www.perko.com/images/catalog/...(8500INS1).pdf is how it's wired.

When you see above, the two switches have a battery 1,2, and all positions. When the two switches are both on all it's two engines charging two batteries. Not sure if the engines can tell if it's two batteries though...

It's an aluminum plate work.

I'm under the dash now looking for this common ground wire to be sure I even have it. Someone else rigged this boat so...

Thanks,
 
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I also add my kudos to Professor Jimmy. Always well worded.

It's interesting....none of my manuals go to page 378. I have access to all the manuals on the 90A since it was made including one on a disk and downloads from Honda. All but one have page numbers that are part chapter number and page ( like 2-35) for Chapter 2 page 35. Only the one on disk has regular page numbers also because of the pdf.

If you live outside of the United States, there may be different manuals for your country. So I can not find that statement in my manuals....even doing a computer search on the pdf version of the Service Manual and one in the rigging manual. All I can find is "one battery per engine".

As for jumping the grounds under the dash to save on running ground wires back to the engine....the Honda wiring harness has all the grounds that it needs for each engine. No extra grounds need to be run from the dash to the engine. Once again....everything in the Honda wiring harness should stand on its own. No additional taps should be made in the wiring.

Mike
 
how many terminals are on each of these switches?i am having trouble understanding the all position function and its not shown in the diagram...does this position have anything to do with the starting or is it just for the charging systems?
 
The ALL just connects the positive terminals of both batteries. In this situation, it is used to "jump start" the engine associated with a dead battery.

In single engine applications with two batteries, the switch is set to ALL to charge the second battery. There are also voltage sensing relays to automatically connect both batteries together for charging once the starting battery is fully charged.

Mike
 
After further considering what might have taken place when you were running the two systems "connected", it could be assumed that one charging system kept the other "suppressed" by supplying enough voltage to keep the regulator switched off. That would explain why you did it for so long and there were no ill effects. At least, that's the best explanation I can dream up at the moment.
 
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