Alternator coil for Mercury 8HP outboard to charge battery

tommays · Sep 9, 2009

On that size motor the MAX output is 6 amps BUT thats at full motor speed with 3 amps being more likely which will keep your lights on but take forever to recharge a battery

dserrell · Sep 9, 2009

Ahoy Scott,

Do not think you will need the starter kit, if all you want to do is install the alternator kit? While you have the mast down you can use the existing wiring, however new wiring would be nice! An LED light uses 9 times less current than an incandescent light, so going with LED is much better. On Pachebella, our 89' Compac 19/3 we have a Garmin 90 sonar unit which displays the battery voltage. This has been very useful in determining how effective the alternator and solar panels have been in charging the battery. Was quite surprised at how well each charges the battery. I'll forward pictures! Have a great day!

David

Timo42 · Sep 9, 2009

Just added the alternator coil and rectifier kits to my 6hp Tohatsu, the rectifier is available separately from the starter kit and you need it to change the a/c output from the alternator to d/c that the boat uses. I cobbled together a puller in a couple of minutes, took less than an hour to add the kits.http://www.tohatsuoutboardparts.com/Electrical-Kits.html
Here are pics of the different kits. This is the cheapest place I found,

Tim

dserrell · Sep 9, 2009

Ahoy Scott

The rectifier converts the AC current put out by the stator to DC current, which will charge your battery. I did not need a starter kit on the 5hp Mercury, but of course they don't make a starter kit for size motor. I'd check with Mercury technical and they can tell you if you need the starter kit too! The alternator kit came with a stator and rectifier. Can't figure out how to send you an email with pictures? dserrell@yahoo.com

David

Stu Jackson · Sep 9, 2009

If the LED light is such a low draw

then you would be wise to consider these options:

1. do the alternator thing and get solar
2. forget the alternator thing and get better solar

In most cases folks bought the engines WITH the alternator and didn't have to add it. They did this way before the LED lights became available, BECAUSE by far the biggest draw on their boats was the danged anchor light! What we did years ago was diss the anchor light for a nautical traditional lamp oil fired fresnel lens anchor light that hangs off the backstay. Electrical draw = ZERO!

Since you'll be getting the anchor light electrical draw down about that low with the LEDs, if you do an energy budget you'll find you have almost no need for that extra 3A from the engine especially if you're gonna be hardly motoring at all. And to get that 3A you'd have to motor for over an hour because of battery acceptance!

Plus, if you don't take much OUT of the battery bank(s) you have, the battery acceptance will be so high that it'll be difficult to put anything back in. Battery acceptance is much like what it says: the ability of a bank to absorb more "input" or charging amperage. As a bank gets to within 15 to 10% of fully charged (like when you don't take much out of it) it becomes very hard to push much back into it. So if you're always running the boat on a weekend after having it charged all week in the 85% already charged range, the engine will do little good because the bank just won't accept the charge, or any charge for that matter.

From a financial and battery efficiency charging point of view, you would do better to spend a little more on solar than the alternator kit.

txtowman · Sep 9, 2009

how many $$ worth of solar would be required to replace the 3 amps on a cloudy day?

dserrell · Sep 9, 2009

Ahoy Txtowman,

When your out sailing in a small sailboat that has a cabin for sleeping, its nice to have the ability to charge the battery or batteries. The choices for charging a battery are by a generator, which is noisy and bulky for a small sailboat. The motor's alternator, which can charge the battery, but perhaps not much. Solar panels which can charge a battery depending on the output of the solar panels. A wind generator, but they are big, and expensive for a small sailboat. Possibly a water turbine, which works while the boat is moving. What's the best solution for charging a battery on a small sailboat, if your are planning to spend a few nights out, or perhaps a few weeks out? Something is better than nothing. The motor is equipment you must have, so adding an alternator to it seems realistic. Next, would be solar panels, if you can find a place to mount them, and if they can actually charge the battery, not just maintain it. I added an alternator and solar panels. They have worked well on our small saliboat. We've been out for weeks at a time, without having any battery issues. Recently trailered down to Key Largo and sailed to Key West. When were out for that period of time we have to have a method for keeping the battery charged. We have an LED anchor masthead light, so that helps! Would like any suggestions for improvements we could make!

David

kenn · Sep 9, 2009

Our 1983 5 HP Suzuki came with the charging (alternator) coil already installed. According to the service manual, it's a simple unregulated alternator + bridge rectifier, and for charge regulation, it simply relies on the fact that the alternator can't put out more than 5 or 6 A. In fact the manual recommends that you use the charging coil with conventional flooded-cell batteries rather than AGM or sealed gel-cells, because the flooded-cell type are a bit more tolerant of overcharge.

I've installed a DC voltmeter so that I can have an idea of the state of the battery, and I simply disconnect the charging coil if the battery's decently charged. A friend of mine has put in a relay and a resistor on his boat: when the battery is charged the relay switches in a resistor that limits the charging current to a safe "trickle" level.

I'm also gonna add a 5 or 10 W solar panel next time one is on sale.

Rob Hessenius · Sep 9, 2009

You cant add electric start to a 2003 Mercury 8 hp, 2 cycle, I added the charging system to my exact same motor. I go on trips of various lengths of time up to 10 days. Beyond using the autopilot and the stereo, I minimalize my dc usage. I also carry a small 1k Honda generator to fully charge up the batteries as need.

walt · Sep 10, 2009

I have a charging alternator on an old 8 hp Honda and it just doesnt contribute much to charging the battery. Its supposed to be 60 watt (ie, 5 amp or so) but at the normal speeds I run the outboard, I only get maybe 2 amps out of it. If I run it for an hour (which I do if I go out on a light or no wind day), that is only 2 amp hours of charge. The self discharge of a wet cell battery might be 3 to 4 amp hours per week so I may not have even kept up with self discharge let alone generating extra to use.

Compare this to a 20 watt solar panel (which is a reasonable size on a smaller boat). Assuming a good mounting location, a good rule of thumb (from someone posting on this BB, cant remember who it was) is that on a daily basis, you will get between .25 to .5 times the panel watts in amp hours. Ie, for a 20 watt panel, you will get between 5 to 10 amp hours per day. The panel contributes this every day the sun is shinning. Ie, in a week, you could expect maybe 7 days * 5 amp hours per day = 35 amp hours. If you use the boat one day per week, the solar panel contributed way more than the outboard. I would take the money you intended to spend on the alternator and put it all towards a solar panel and charge controller. Finding a good place to mount the panel is very important - partical shading can easilly reduce the numbers given by 30% or more. Way in the back on the stern railing like the picture posted previously is a good place.

kenn · Sep 11, 2009

wonkodsane said:
What do you folks think about the wire? Should I try to clean up and re-tin the ends of the marine wire I have or just get new wire? I'm looking at about 40 feet, four conductors.

Test all conductors for continuity and to see if there's any shorts or resistance to the mast. Also, if the wire is pinched, damaged, cracked or worn anywhere along its length, probably best to replace it.

Otherwise, if there's enough slack that you can safely trim back an inch or two at the ends, cut the worst wire back by an inch and strip 1/4" to check. If the wire's in good shape there, just cut all wires back by the same amount, tin and re-attach.

Even if you have to cut back several inches at the mast-head to get past the corrosion, it's probably easier to splice some extensions on, than to run a new wire. Just be sure you can do proper twisted and soldered splices that you can weatherproof with sealant and heat-shrink tubing.

Stu Jackson · Sep 11, 2009

Wire replacement

How old is the wire? What is it: tinned or other? What do you need the four conductors for? And, given the discussion, I wish you luck with your decision. I know it's your boat, your choice. I'll just murmur in your ear, once again: solar, solar, solar... Walt's #13 pretty well nailed it. Your pocketbook...

dserrell · Sep 11, 2009

Ahoy Scott,

Like Stu said solar, solar, solar! I purchased the 5.5W 458mA solar panels for Pachebella a a cost of $49.95 each, and the Solar Grip mounting brackets for $26 each, however they were on sale. Just looked on the internet and found the Silicon Solar 5.5W 458mA panels are still $49.95, and on Amazon the Solar Grip mounting brackets are $39.99 each. One panel in additiion to the alternator would be great! On Pachebella we have a Mega-Tron Deep Cycle Marine Battery 550CCA, and between the motor's alternator and the solar panels, the battery stays charged. We use the battey lots, because the fixed VFH radio and sonar stay on while we're under way. The Autohelm 1000 does take currrent, but I haven't figured out how much! The LED mast light barely draws any current. Its the stereo that takes some current, as well as my daughter's, TV, MP3, DVD, etc. She'd have air conditioning on our Compac 19/3 if she could talk me into that. Like others have said, your existing wiring may work just fine, if you check it out and clean up the ends. Good luck!

David

PS I'm a trailer sailor, so the solar panels can be removed from the stern pulpit in less than 1 minute. They were installed so that the bottom sections of the Solar Grips remain clamped to the stern rail, and the top sections stay bolted to the panels. I added connectors in the wiring, so the panels can be unpluged and removed for trailering!

Napa Ed · Sep 11, 2009

cut and re-tin the wire? Huh? if it's modern marine conductor, it is already tinned, just trim the ends and use heat shrink crimp connectors as needed. If it's old copper "marine" then throw it out and start new.

walt · Sep 11, 2009

If you use the old wire, make sure you always have a fuse on the battery side so that a short (you dont know about or is about to happen) doesnt cause the wire to burn up.

One thing that has been noted in the previous posts is that these smaller outboards dont have regulators. This makes for a simple systems (good thing) but has several drawbacks. First, the charging system wont "properly" limit charging to the battery even when the battery is full. Normally no problem because the current is low to begin with. The second effect is that the output current is much more dependent on engine RPM. A normal alternator/regulator has a feedback mechanism (drives the alternator coil harder at lower RMP) that tends to keep the output current much more independent of RPM.

I wonder if anyone else has measured the current they get out of one of these smaller outboards? As mentioned, in normal "one half throttle" motoring on a sailboat, Im getting around 2 amps out of a 60 watt non-regulated alternator - and as far as I know, it is working fine - but the motor is almost 20 years old so cant be sure. I measured the current using a liinklite battery monitor. Since were also using these motors on sailboats, the prop tends to turn slower than would happen using the motor on for example a dingy (unless you change the prop) also reducing the output current.

Alternator coil for Mercury 8HP outboard to charge battery

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