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Newbie question Battery charging output on Merc 15

T

tomf

Regular Contributor
"Hi all,

thanks for the br

"Hi all,

thanks for the brilliant forum, reading through the archives has been a great way to get info on Mercury outboards. I just acquired a Belgian-made 1993 Merc 15 (serial #09768069) and have been getting it ready to run by replacing a few broken parts left over from the previous owner.

My question (and apologies if this is blindingly obvious): is there a battery charging output on this outboard? And if there is, where would that be located, and what does it look like?
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The parts listing and drawings for this model can be found here: http://www.mercruiserparts.com/selectDocs.asp?doc_nbr=811286

I know the previous owner had some sort of 12V setup, but the boat was such a mess of disconnected wiring, that I'm not sure if he just had a separate battery or whether it was charging from the engine.

Any hints appreciated!"
 
Part no. 17 under electric com

Part no. 17 under electric components is a rectifier so the output for charging would be the red wire coming off it. If the wiring is that bad there is a chance that the rectifier is blown. The easiest way to check it is to hook it up then check the voltage at the battery with the motor off then again with it running. You should see an increase in voltage as RPMs increase.
 
"Perfect, thanks! I'll che

"Perfect, thanks! I'll check it out when I get to the boat over the weekend. In the meantime, ordered a stack of Merc shop manuals and repair guides, so I expect to be up to speed on the tech side in no time.
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Seems like a nice little engine so I look forward to taking care of it, hopefully for a long time."
 
"Tom, if this "wasn't&

"Tom, if this "wasn't" an electric start from factory, the charging system will not be there - it sells as an option.

Even if it is there is just a 5 amp system - and you only get the 5 amps at wide open throttle.

I have the system on my 15 horse and while it will keep a battery topped up (that is fully charged) while running a fish finder/gps or nav lights, it will not replentish a battery if you have used it all day to run an electric trolling motor.

My opinion - if it's not there, it isn't worth the cost of installing, even doing the work yourself unless you get the parts for next to nothing..."
 
"OK, thanks, Graham. In that c

"OK, thanks, Graham. In that case, it's probably not there, but I'll double check anyway, as I haven't had time to get familiar with the motor yet.

My intended use would be primarily for keeping the battery full for the lights, as currently I use neither a fish finder nor electric motor.

So probably I'll have to just resign myself to topping up the battery at home and lugging it to the boat when needed... Yippee, yet another gadget to be charged along with the mobile phone, laptop, GPS, digital camera, video camera and cordless screwdriver.
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"Well, I decided I'll try

"Well, I decided I'll try to go ahead and install this setup anyway, even it the charging output is so nominal. I figure it's better than nothing if it will at least keep the battery topped up...

I found what looks like the correct alternator and rectifier in the bargain bin of the local outboard salvage shop. But before I start tearing the engine apart, here are a few questions for you guys familiar with the system:

1. Can you tell from the attached photo whether these will even fit a '93 15hp Merc? My shop manual's drawings were pretty vague but these components were most like the pics. The alternator doesn't have any numbers on it, but it apparently came from a 20hp model. The rear of the rectifier says: VARO R363 7243

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Mercury rectifier and alternator"">

2. Is the removal of the 15hp flywheel a major hassle, and/or does it require special Mercury tools? I have neither a Strap wrench (91-24937A1) nor a Flywheel puller (91-13661A1), but would something from a regular auto tools supplier do the trick? I don't want to get into something that will be difficult to back out of or that will risk damaging the engine.

Hints appreciated, as always!

Tom"
 
"Tom, the alternator/stator in

"Tom, the alternator/stator in your pic is exactly what you are looking for. It fits everything from the 6 horse upto and including the old 18/25 models.

You can remove the flywheel with most automotive tools, I have used a steering wheel puller in a pinch and it worked fine. It can be fairly tight if it hasn't been off before (or for a while), a few taps on the top of the crank with pressure applied from a puller usually persuades it to let go.

This is easy to install, going in the "blank spot" under the flywheel, but you will have to pick up 3 screws from Merc to fasten this down. The old ones that get removed from the ring on the existing stator are too short to go through the charging stator and make it all the way down to the plate.

Stop at a Merc dealer and pick up 3, part number 10-4000123 - they go for about 50 cents a piece and may have to be ordered in. Install them with a touch of Loc-Tight when you do put them in - you don't want something vibrating loose under the flywheel...

The rectifier may be toast. These things fry if the motor is ever run without a battery hooked up. With no battery these things kill themself with the power they produce - it has to go somewhere, or they fry.

If it is shot, an aftermarket rectifier (pretty much universal for Merc's that use a rectifier only) is generally available for between 25-35 bucks....

If you are going to fashion up a harness to feed the battery you can simply use 10 or 12 gauge automotive wire. The factory harness for this is certainly not heavier than 12 gauge (more like 14 or 16)...."
 
"Excellent, thanks!

I'

"Excellent, thanks!

I'll test the rectifier for proper continuity/non-continuity between the terminals as soon as I can get to my volt-ohmmeter. If it looks kaputt, I can probably just exchange it, there was a pile of these at the shop & the guy said I can come back and change it if it doesn't work. In the meantime, I'll try to find the screws somewhere."
 
"I have to ask... Will leaving

"I have to ask... Will leaving your running lights on when there isn't a battery on board be enough of a draw to bleed the charging circuit, or is this going to blow the bulbs???"
 
Not exactly sure what you mean

Not exactly sure what you mean. With no battery there would be nothing to power the lights unless your motor has either a voltage regulator or lighting regulator.

What motor are we talking about here???
 
"I think T means whether it wo

"I think T means whether it would be possible to run the lights directly off the rectifier if the battery were not onboard. I guess this theoretically would work, but wouldn't be very practical since the lights would only shine properly with the throttle wide open?

At least for the 15hp/5A alternator+rectifier system discussed above, if you need to run the engine without the battery, isn't it easiest just to unscrew the yellow and grey wires from the rectifier terminals and tape them up so they don't accidentally short out? Then reconnect once the battery is back."
 
"That's what I was trying

"That's what I was trying to get from him - if that was his exact question.

Because, yes, it can be done. However, the normal rectifier must be replaced with a "lighting regulator" - it is not capable of charging a battery but does allow you to power running lights.

Running a motor with a rectifier WITHOUT a battery hooked up will immediately fry the rectifier - you need the battery in that set up to act as both the regulator and capacitor since the rectifier throws out "unregulated" power - simply trying to feed the power to "assessories" will not suffice.

The the lighting regulator does that all in one and is a decent option if you want to travel light - you just can't have both on a small Merc setup...."
 
"Copy that, thanks Graham. By

"Copy that, thanks Graham. By the way, speaking of unregulated power, what kind of battery do you use with your 15hp and the 5A rectifier setup?

Since my projected current draw will only be a couple of amps (1 running light + depth sounder + maybe GPS), I would love to be able to use one of the small and compact sealed batteries suitable for cyclic use. However, I noticed that my shop manual cautions against using sealed or maintenance-free batteries with a constant unregulated charging output, as it may cause the electrolyte to boil and damage the battery.

Can you advise what kind of battery would be best here, or is the above not an issue with the small output power produced by the alternator? (My knowledge of 12V boat electrics is still very close to zero...)

cheers,
Tom"
 
"Hi y'all, I'll bounce

"Hi y'all, I'll bounce this back to the top --

Any advice on what kind of battery would be best with the unregulated 5 amp Merc charging system?"
 
"Tom, I have been running a gr

"Tom, I have been running a group 24 dual purpose (deep cycle/starting) on that particular system for a few years now with good results.

Any marine battery should be fine as long as it is the normal acid cell - don't try a gel battery, it doesn't like the unregulated power - kills them quick.

Have also used an old car battery and even the small 12 volt utility (motorcycle size) from my snowblower over the years with no adverse affects - but have found the standard marine group 24 to stay topped up quite well running gps/vhf and nav lights (as required)..."
 
"Cool, thanks again! Will be i

"Cool, thanks again! Will be installing the alternator/rectifier/battery combo in a few weeks once I can get to the boat, so I'll start looking for a battery in the mean time."
 
"OK, one more dumbo question f

"OK, one more dumbo question from "Boat Wiring 101".
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- So once I have the battery set up, I connect all peripherals to the battery via a switch/fuse panel, with all positive leads going to the battery (+) terminal and all device grounds returned to the (-) terminal.

- The red (+) wire from the rectifier will run to the battery (+) terminal for charging. The rectifier is of course grounded to the engine.

Q: With the above, so far I just have a single (+) wire connecting the rectifier to the battery. Should the engine ground be connected to the battery ground with another lead? The user manual mentions (+) and (-) cables from the optional charging system going to the battery, but at the moment I of course have only one (red) wire coming from it.

Thanks in advance!"
 
"Yes, you got it Tom. You run

"Yes, you got it Tom. You run a wire from the negative post on the battery to just about any convenient spot on the powerhead (of course ensure that the connection is decent - ie. a clear spot free of paint/oil etc).

Most times for stators/rectifiers up to about 9 amps, I would run the negative back to one of the rectifier mounting bolts (and hook it up between the powerhead and the rectifier - kinda sandwiched in there). On some of the larger powerheads they will have a dedicated (post) tapped right in to the front of the powerhead, close to where the wiring comes into the cowl..."
 
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