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ContinuousWave: Small Boat Electrical
17-Volt Output From Outboard Charging Circuit
|Author||Topic: 17-Volt Output From Outboard Charging Circuit|
posted 04-10-2009 10:24 PM ET (US)
I have a Johnson 70 that has an output voltage of up to 17-volts at about 5,000-RPM. It drops down to 13-volts at idle. Does this sound like I need a new voltage regulator? If not, what else could cause this?
posted 04-11-2009 02:16 AM ET (US)
What year Johnson 70?
posted 04-11-2009 09:27 AM ET (US)
If you have a late model 70hp with a voltage regulator, likely the regulator is bad.
If you have an earlier 70hp without a regulator, just a rectifier, then use a larger battery such as a group 27 or group 31. The battery acts as a regulator in these types of charging systems. Do not use a maintenance free or sealed battery.
The very first thing to do is to connect a digital voltmeter directly to the battery terminals to determine the actual charging voltage. Dash mounted voltmeters are not the most accurate.
posted 04-11-2009 10:24 AM ET (US)
This may save you some time and money- went through the same thing with my 15 years ago. Read it to the very end, if your outboard is an 80's model-k
posted 04-11-2009 11:23 AM ET (US)
This is a 1984 Johnson 70. I have an Optima D34m. I went through 2 batteries last season so I think something is not right.
posted 04-11-2009 11:27 AM ET (US)
Also, my Lowrance LMS-527 also displays voltage consistent with the dash multimeter. I don't want to buy a new battery because I just got this Optima.
posted 04-11-2009 12:41 PM ET (US)
Yuu have an unregulated charging system and those require a large capacity acid battery with removable caps for the addition of distilled water. Later model motors with voltage regulators can use maintenance free style batteries.
That is probably the reason you have had battery problems. Any trained technician knows how the system works and do not recommend sealed batteries for unregulated systems.
You can also contact Optima and ask their thoughts on unregulated charging systems.
Using a large capacity flooded-cell battery will keep your charging voltage down. Also running with lights on helps absorb the excess charging voltage to keep things in limit.
posted 04-11-2009 04:14 PM ET (US)
I would be concerned about my other electronics receiving this high voltage (17v), I wonder if there is an aftermarket inline voltage regulator that would control the voltage so that you only recieve 14.5v max. That would probably save the battery and your other electrical components.
posted 04-11-2009 10:05 PM ET (US)
Humminbird used to make a inline voltage regulator called the
Surevolt. Put in anything from about 6V to 18V and 13.8V
comes out. It can handle about 1A, so it can handle your
fishfinder and GPS, but not your VHF.
posted 04-11-2009 11:58 PM ET (US)
Here is one on ebay http:/ / cgi. ebay. com/ ebaymotors/ Humminbird-SureVolt-Marine-Power-St abilizer-NEW-NIP_W0QQcmdZViewItemQQhashZitem200262681245QQitemZ200262681 245QQptZBoatQ5fPartsQ5fAccessoriesQ5fGear
posted 04-12-2009 05:47 AM ET (US)
Again, read the link to the thread I posted. When I had my 15 footer, with a 1987 Johnson 70 hp, I went through the same thing, and discovered this:
Just click on the link I posted above for more details-k
posted 04-12-2009 09:24 AM ET (US)
It is unfortunate that your older outboard with an unregulated battery charging circuit has caused the failure of two quite expensive Optima-brand sealed valve-regulated lead-acid batteries using absorbent glass mat construction. There is an enormous amount of hype for SVRLA AGM batteries in many boating discussion groups, to the point where a casual reader would think that the availability of the SVRLA AGM battery has been something of a godsend for boaters, but, as your experience demonstrates, the SVRLA AGM battery requires very careful regulation of the charging voltage applied to it. The SVRLA AGM battery is not a good choice for applications like yours where the charging current source will provide an unregulated voltage.
With an SVRLA battery the charging voltage should be carefully regulated to be no more than 14.35-volts. Higher voltages cause the electrolyte in the battery to bubble out hydrogen gas. While sealed batteries contain a recombinant to return the hydrogen gas back to the electrolyte, if excessive pressure develops in the sealed battery, a release valve actuates and allows the gas to escape. This leads to loss of electrolyte and eventual loss of capacity in the battery. Your Optima battery probably failed in this way.
posted 04-12-2009 10:48 AM ET (US)
You could spend just over $200 for the full wave regulator/rectifier that is air-cooled and used on later model 70hp motors, pn 0585001.
The V-4,V-6 regulator/rectifier mentioned in a previous post will not fit your motor and requires water cooling as it mounts on top of a V-block engine.
Of course, selling the Optima and buying a quality $100-$150 high-capacity battery is your best and most cost effective bet.
posted 04-12-2009 11:21 AM ET (US)
seahorse- The part I mentioned:
"...the description of the part simply says REG KIT V-4 V-6 part number 173640. It cost $123.00 plus installation for a total of around $200."
Fit and worked perfectly, fit the 1987-88 70hp Johnson, and was not water cooled that I know of. The motor continued to perform well with no further overcharging problems for at least 3 years of continuous use until I sold my 15 foot center console in the summer of 2008. -k
posted 04-12-2009 12:15 PM ET (US)
I think I'm just going to get a high capacity battery and use the Optima as a spare on board or in my car if it fits. It looks like the voltage regulator costs more than a new battery.
posted 04-12-2009 08:52 PM ET (US)
Sometimes ya just can't win.
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