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Overcharging Myth???

mill686

mill686

Regular Contributor
I've seen several talks of this in the past. I paid attention to them because my '84 50HP, with upper-range rpms, shows a reading just over 16 volts. I was concerned until I saw this illustration. I simply have a rectifier (no voltage regulator). What's your take?


Explanation_VG[1].jpg
 
My personal take is that you will probably get away with it if the reading stays just a tad over 16v...what you have is an rectifier only system and a newer battery that is not the one recommended in the owners manual...you would probably have a problem even finding the battery recommended....you have a choice of running it like it is or converting the engine from rectifier to a regulator...if you run it like it is watch your tach...if it starts giving erratic readings then the rectifier is starting to fail...do not run sealed or gel batteries with a rectifier only system...
 
As pappyson said use the correct battery...one that is serviceable w/distilled water only. Unregulated systems will cause the battery's electrolyte (water) to evaporate quickly therefore it is necessary to service the electrolyte level nearly every time you use the boat for a day. I use a battery service (green) bottle filled w/distilled water. It is designed to not overfill the battery w/out looking into each cell. Just insert the nipple and push down to seal the cell and it fills to the recommended level.

I had a 79 Evenrude that was unregulated and had to fill the battery daily...it would put out 18-19 vdc at WOT...6,000 RPM.
 
With my outboard at around 3000 rpm, the reading was 16.2 with a maintenance free battery. At the same rpms, it is 14.5 with an older deep-cycle serviceable battery. I bought this battery new in 2005.
 
I've always been told not to use maintenance free batteries w/an outboard due to the higher charge rates experienced.
 
That's why there are "Marine" batteries. Marine/Tractor batteries are "designed" (heavier plates or something) to be charged by a "rectifier" (and throwing upwards of 16.5 volts is NORMAL for a rectifier which sees the voltage increase above 12.5 volts as the rpms increase - amps increases too on a stator/rectifier set-up in a non-linear fashion, so you might get an amp at idle and 16 amps at WOT). Your car gets nice "regulated" power which rarely exceeds 14 volts (13.8 is more common).

So if you use a Marine battery on a Merc you won't fry it (a car battery will have a drastically reduced life, but will work in a pinch). Most OMC/BRP's and newer (higher horse) Merc's have regulated power, so it's best to know your motor and use the appropriate battery.
 
Thanks guys. Next is a higher pitch prop. The 13" seems like she cuts the water a little too much, and WOT RPMS at between 5500 and 6000 can be reached. Operating range is 5000-5500. Here's a video. I just don't let her run much above 5000 right now.

 
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Though crude, the charging system seems to work just fine. I get several years out of the lawn mower batteries I use.

Jeff
 
i would not rely upon a 2005 battery for ignition.....maybe for a trolling motor if a small one and not critical..
 
is a sealed battery ok to run on a regulated system?i had two batteries stolen about 18 months ago and had to buy 2 sealed batteries because they were the only marine batteries available in the location i was at...so far so good but i keep reading on here ''no sealed batteries in boats''...charging voltage never exceeds 15 volts...
 
On a regulated system you can use pretty much anything you want. Sealed marine batteries are still slightly superior to a regular car battery when used in a boat because the are designed to take a little more abuse/bumping around etc, and are always the superior choice..
 
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