DC electric problem

Lee Kaufman · Post by **Lee Kaufman** » Dec 26th, '07, 19:51

I need the help of someone that understands batteries and DC electrical systems.

Here's the deal.

I have a 6hp Nissan long shank outboard in the motor well of my CD25. I had an alternator (read coil with rectifier) installed. When I measure the output of the motor in neutral I get something in the vicinity of 14.4 volts at something less than full throttle. When I put the motor in gear the output falls to about 10 volts at full throttle. After extensive discussions of this situation with Nissan tech support, I am told that everything is working properly and that at 10 volts the battery is being charged.

I realize I have posed questions about this matter on the board before but I am still not certain what should be happening here.

Will a battery charge from a source from which the voltage is lower than the current charge in the battery (i.e. will 10 volts charge a battery that is registering 12.4 volts)? It was always my understanding that it wouldn't but, I am not sufficiently certain to argue the point with a professional technician.

I am also told that, due to the size of the boat, the motor is unable to achieve the rpms for which the motor is rated. They suggest switching from an 8 pitch prop to a 6. The idea is that this will let the motor operate at higher rpms and the alternator to put out more power.

The alternator is rated at 6 amps. I realize that this is not much but, on a typical day of sailing I am not using much power on a C25. I typically motor 2-3 hours in a day of sailing. Shouldn't that put at least 12 amp hours into the battery while a handheld gps, listening to a VHF, a depth gauge, and tiller pilot would not draw near that much?

I hope there is someone out there that understands all of this stuff and can explain it until a novice can understand. I definitely need “DC Systems for Dummies”. I'll certainly appreciate any help anyone can give. I'm “bumfuzzled”.

M. R. Bober · Post by **M. R. Bober** » Dec 26th, '07, 20:24

First off, I am not an expert. That having been said... If your Nissan guy can fully charge a 12 volt battery with 10VDC output from your alternator, he should move up to cold fusion. I don't believe your battery will ever reach full charge from that alternator.

The tiller pilot can draw quite a bit from the battery depending upon conditions.

Good luck,
Mitchell Bober
Sunny Lancaster (where when it comes to DC systems "anode" the answer) VA

seadawg · Post by **seadawg** » Dec 26th, '07, 23:10

After reading your post Lee a couple of question came to mind. Could the outboard motor alternator (+) and (-) polarity be reversed? Does the alternator and (-) lead to the battery have a common ground? Are you measuring alternator output voltage with the battery connected in circuit? I am not familiar with outboard motor alternators but Mr Bober is very correct...10 volts will not charge the battery. It sounds like the outboard needs to be in gear before the alternator spools and when the motor is in neutral you are actually measuring battery voltage. If so, I would question the accuracy of your volt meter. I sincerely hope these ideas and thoughts don't confuse you more. Cheers Charlie

Russell · Post by **Russell** » Dec 27th, '07, 00:38

Lee Kaufman wrote:After extensive discussions of this situation with Nissan tech support, I am told that everything is working properly and that at 10 volts the battery is being charged.

Hate to say it, but the nissan guys couldnt figure out your problem so they simply lied to you to send you on your way. There is no way an altenator running at 10v is doing anything for your batteries. Yes the ideal voltage is going to be 14.4 or whatever your type of battery is rated for. But it will charge at less then ideal voltage, if your battery at rest reads 12.4, it will accept a charge from a source at 12.5 it will just be very inefficent but it will charge. But 10volts? Thats entirely unacceptable and maddening that Nissan support would pass you off like that and tell you its actually charging.

Now, why would your altinator drop to 10v at full throttle when it easily puts out 14.4 at less then full throttle? Kind of an odd situation, here are things off the top of my head, I know a fair amount about DC electrical work, but honestly nothing about outboard altinators.

1) Regulator failure, the built in regulator on the altinator has gone screwy.

2) Overheating, the altinator is quickly overheating, which causes output to drop drasticly.

3) Horribly undersized wiring. This is hard to imagine at 6 amps though, but as amperage increases on an undersized wire, voltage drop increases.

4) Similar to above, badly corroded wiring or connections, massive voltage drop as amps go up. But geez, 6 amps? Its hard to imagine but not out of the question. But reguardless in either situation, voltage would never drop below the batteries rest state voltage.

5) One thing that gets me, 10v? If your batteries at rest, with the engine off, are above that, then there is no way a properly functioning altinator would ever read lower then that. If your batteries are indeed at 10v at rest, then well, you need new batteries. But if the voltage reading is lower then rest state for the battery, then for some reason the altinator is draining your batteries (but that doesnt explain why its 14.4 at idle).

They may be right in that you need a new prop, but there is no way thats causing your voltage problem. Do they really expect you to beleive that running at idle your engine is acheiving higher revs then when in gear and full throttle? I dont care how poorly proped your outboard is, thats just silly.

Personally, I think all things point to a faulty altinator and/or its built in regulator. Its internal circutry is screwed up causing it to drain your batteries, or its overheating inappropriately, or some combination of all sorts of things.

Its an interesting problem reguardless, I would love to be your neighbor right now and come over with a multimeter to troubleshoot it and scratch heads. Please tell us all what the problem ends up being.

The Patriot · Post by **The Patriot** » Dec 27th, '07, 08:14

Lee Kaufman wrote:I ... When I measure the output of the motor in neutral I get something in the vicinity of 14.4 volts at something less than full throttle. When I put the motor in gear the output falls to about 10 volts at full throttle ... Will a battery charge from a source from which the voltage is lower than the current charge in the battery [?] ...

The alternator will not charge the battery if it its actually pushing 10 volts. Still I wonder what the state of your battery is, and how long it has been in a particular state of charge, if you are not charging it via the outboard. In other words, have you been draining the battery with regular use for some period of time, and if so, where is the recharge coming from? Do you take it off the boat to charge, do you run the outboard out of gear, etc.? Also, does the outboard have electric start?

If your battery is reading 12.4 or 12.6 or thereabouts after much use, the charge is coming from somewhere. Also, do you see 10 volts at the alternator all the time, after running for a considerable period of time, etc.? I have zero experience with charging from an outboard, but is it possible that the alternator cuts back after the battery appears fully charged to the regulator? Perhaps this is a seriously dumb question, but I thought I'd give it a shot.

D Rush · Post by **D Rush** » Dec 27th, '07, 08:42

A 12v battery will not charge if the Alternator is outputting 10V.

IMHO - The issue here seems to be is the outboards alternator and regulator operating properly.
the outboards charging system (alternator and regulator) has specs for the electrical load it can handle at a specified RPM.

If in neutral the outboard is spinning at a certain RPM, the output voltage is 14.4v and the electrical load ( the battery, wires, lights and radio) is constant. Everything is fine. the system is handling the electrical load, and the battery is charging.

If the electrical load remains the same, and the outboard is put into gear, the RPMs drop, the output voltage drops then I would think the issue would be that the alternator is not spinning fast enough to produce the correct voltage or the regulator is not regulating the output.
The outboards alternator specs should specify an RPM at which it produces a regulated output. say 60W @ 1000rpm (just made these numbers up) 60W = 12V x 5A meaning at 1000 RPM the outboard would produce 12V with a 5A (amp) load.

If the electrical load remains the same and it sounds like it does. Then the RPM are not high enough or the alternator / regulator is not producing according to their specs.

Troubleshooting - With no or little electrical load is the alternator/regulator producing 12v or more when the outboard is in gear?
What are the outboards RPMs when in gear? (I'm not sure how you'd figure that out)
If the Nissan Techs are talking "load", is it electrical load or outboard load (prop pushing against water to propel the boat)

I hope this helps.

Bumfuzzeled? - must be an electrical term

Lee Kaufman · Post by **Lee Kaufman** » Dec 27th, '07, 22:22

Wow! What a great bunch of folks and great questions. Let's see if I can elaborate:

1)Could polarity be reversed? How can I tell? A friend had a Tohatsu (same motor – different name). He said his polarity was reversed. Could be.

2)Common lead? Yes.

3)Measuring out put voltage w/ battery connected? The 14.4 & 10 volt measurements are at the pigtail from the alternator without it being connected to anything.

4)Accuracy of voltmeter? I checked the digital voltmeter against that at the dealer and against a known good battery. Tech suggested radio interference w/ digital meter so I bought an analog meter w/ the same result.

5)Undersized wiring? The wiring from the alt to the rectifier is like 16 gauge while the wire from the rectifier is 12 gauge.
6)corroded wire/connections? New connections.

7)If battery at rest is 10V . . . It is now at 12.4V but was fully charged & tested good. It is not connected when the alt is reading 10V.

8)Where is the recharge coming from? I have recharged it at intervals w/ a charger.

9)Elect. start? No.

10)Alternator specs should specify an RPM? The only info I have found is 12volts/ 60 watts with no RPM specified.

11)With no load is it producing 12 volts? With no load it is producing 14.4 volts

12)Outboard RPM when in gear? Although the manufacturer claims 5500 RPM the most I can get in gear is 3800 RPM w/ 124 pounds of thrust with the factory 8 pitch prop. With a 6 pitch I get 4300 RPM & 165 pounds.

13)Tech is talking load? They are talking outboard load.

14)Bumuzzeled refers to my brain load.

seadawg · Post by **seadawg** » Dec 28th, '07, 10:46

You have certaintly isolated the problem to the outboard motor/alternator system. Without knowing exactly whats going on inside the outboard/alternator combo it is hard to proceed with the troubleshooting. If it were me I would try to locate a maintenance manual for the outboard to get an internal electrical drawing and perhaps if we are lucky a troubleshooting procedure. Cheers Charlie

marilou · Post by **marilou** » Dec 28th, '07, 10:50

The "alternator" on the small Nissan is really a Generator/Dynamo with a rectifier. It produces about 5 amps, I believe. Most alternators will produce 50 + amps. and change the amount according to needs, and charge of battery. The Nissan "alternator" is more like a trickle charger and is intended to be able to produce electricity for - like running lights. A battery charger will produce about 2 amps in trickle charge, 10 amps for overnight charge, 50 amps to turn starter motor.

To determine polarity - connect your digital voltmeter to leads from motor - if you get a (-) reading your polarity is reversed. Sounds like your's is correct.

Connect a 12 volt test lamp to leads - if you light up you are producing electricity.

If, you can connect your running lights directly to leads, without your battery, and they work, the "alternator" is working correctly, I believe.

Lee Kaufman · Post by **Lee Kaufman** » Dec 28th, '07, 10:54

Thanks, Charlie

The owners manual has a wiring diagram at:

http://www.nissanmarine.com/tech_talk/o ... nuals.html

The motor is the NSF6A2

The alternator is also described as an accessory near the end of the manual. It all seems very simple. The tech went through each of the components and maintains each one is working as it should. At this point I am inclined to believe that the motor is just not capable of getting the RPM necessary to generate sufficient voltage. But what do I know.

seadawg · Post by **seadawg** » Dec 28th, '07, 11:11

I understood you to say in your first post that motor output voltage in neutral was 14v and just by shifting the motor in gear the voltage dropped to 10v and this all with nothing connected to the output of the alternator. Maybe the alternator needs a load to function correctly. Marilou mentioned connecting a load, maybe a nav light bulb and then measure the voltages. Also we need your outboard motor model number to look up the maintenance manual on the website you provided. Charlie

Russell · Post by **Russell** » Dec 28th, '07, 11:22

Indeed for an altinator to function correctly it needs to be connected to something that will consume the power it produces. Its possible since its not connected to anything, that when you put it in gear and it wants to put out amps, but those amps have nowhere to go, the altinator is simply shutting down at those higher revs.

What voltages do you see when the altinator is actually wired to your battery?

Lee Kaufman · Post by **Lee Kaufman** » Dec 28th, '07, 11:33

When the alt is connected to the battery, it is reading the voltage of the battery (e.g. 12.4 volts). Does this mean that the alt is actually putting out the necessary voltage but it can't be measured without the battery connected? Will the only way to tell then, is to run the motor in gear and then let it rest and compare it to the voltage at rest before running and see if the voltage has increased?

Charlie, the model number is

NSF6A2

seadawg · Post by **seadawg** » Dec 28th, '07, 11:55

Ok, Were on to it now! I did find the manual and electrical drawing for your motor. The specs say the rectifier out is 12V @60W. then amps out = 60/12 = 5 amps. There should be a rise in voltage at the battery with the motor in gear but it probably won't be much. For example with a standard inboard engine alternator the voltage could rise to say 13.75 volts when charging at 20 amps or so. You will probably see maybe .5 volts or so. If you don't get this probably the internal diode is bad or the installation is faulty. You may need to replace the whole rectifier option. Nissan may supply you with one as a troubleshooter. I don't know how much the option costs. If you don't get this rise in voltage at the battery you need to find out about these troubleshooting options with the factory. Cheers, Charlie

Lee Kaufman · Post by **Lee Kaufman** » Dec 28th, '07, 12:19

Let's see if I have it.

Connect the voltmeter to the terminals on the battery and take a reading with the motor off. Then start the motor and put it in gear at full throttle. Expect to see an increase in voltage of about .5 volts. If this happens we will assume that the system is functioning properly.

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