My voltage says 17 as well

muskyjim

Seaman Apprentice
Joined
Mar 12, 2007
Messages
43
I posted this earlier, and it seems that I'm getting conflicting answers. I have a 1979 70hp Johnson. My voltage while running is charging at 17 volts while running. I'm changing the rectifier. That seems to be the common suggestion from this forum and my Clymers manual. My battery is a 3 year old marine starting battery, 500ccl, water is good and I had it load tested and it tested at 500ccl plus. The guys at the battery store say there is nothing wrong this battery. I've talked to 2 locale OB mechanics and got 2 different opinions on changing the rectifier. One said that it would make no difference and the other agreed that was probably the problem. Is this battery too small to handle the charge being sent to it from the charging system?
As I stated earlier, I'm changing the rectifier regardless. I'm getting rid of my old speedometer and installing a tachometer. Based on info from members of this forum and other sources. I've been told that if the rectifier is bad the tach won't work. So what the heck, the rectifier is a fairly inexpensive and easy fix. I'll also feel more confident that my new tach will work as well.
Thanks for the help with my other posts. I'm interested in your suggestions and thoughts on this.
I'll let you know how the the upgrades go to the boat and motor.
Jim
 

jtexas

Fleet Admiral
Joined
Oct 13, 2003
Messages
8,646
Re: My voltage says 17 as well

You mean 17 volts at idle, or at WOT? Bad recitifier, your voltage while running would be equal to battery open circuit voltage or less. Your motor has a 6-amp alternator and no voltage regulator. I don't think 17V would hurt the battery.
 

F_R

Supreme Mariner
Joined
Jul 7, 2006
Messages
28,195
Re: My voltage says 17 as well

A bad rectifier won't charge the battery. Therefor, with a bad rectifier the voltage won't go up to 17 volts. It isn't the rectifier. 16+ volts is normal with a long run on an unregulated system. You need a high capacity battery to take all that output.
 

Kevin W

Petty Officer 1st Class
Joined
Apr 18, 2006
Messages
256
Re: My voltage says 17 as well

Let us know your outcome.

There are alot of posts about high voltage on unregulated outboards.
even though it is very possible the rectifier is the answer alot of answers i have heard where the battery.
basically an unregulated outboard needs a non-maintenance free, non-automotive group 24 or bigger marine starting/deep cycle battery.

there is no doubt the other batteries will test ok and crank ok but the internal resistance of the batteries is too high and the voltage will float too high with these batteries.
 

ezeke

Supreme Mariner
Joined
Sep 19, 2003
Messages
12,532
Re: My voltage says 17 as well

Those choices are up to the owner and his checkbook. If you want to have an up-to-date charging system, it has to be regulated in which case you can use more types of batteries.

If you run most types of batteries on an unregulated charger, eventually you ruin the battery.

If you run a large, deep cycle, marine battery, the battery acts as a regulator unless it is already overcharged, and will tolerate the unregulated rectifier fairly well.

For the voltage output of most engines that were originally fitted with unregulated chargers, the CDI water-cooled regulated charger 193-4204 sold here at Iboats should be adequate.

http://www.iboats.com/193_4204_Regu...7626582--**********.948973638--view_id.335911
 

Kevin W

Petty Officer 1st Class
Joined
Apr 18, 2006
Messages
256
Re: My voltage says 17 as well

I agree, most batteries can't handle unregulated.
A voltage regulator is the best solution if you really want the voltage lower.
The battery will last longer too.
High voltage can be (not saying all the time) a sign that the batteries internal resistance is getting higher and it may be time to start pricing new.
also if its a cheap battery, maint. free or automotive it will read higher sooner.
They have thiner plates and cannot handle the stress of being unregulated.
 

muskyjim

Seaman Apprentice
Joined
Mar 12, 2007
Messages
43
Re: My voltage says 17 as well

I just want to get this straight before I purchase a new battery. Because my battery is on the smaller side it could be one the reasons I'm charging 17 volts at WOT. My current battery was purchased at one of those farm stores that sells everything from saddles to batteries. The battery does require maintenance and is a marine starting battery. It is about 3-4 years old, and as stated earlier, it load tested fine. I am willing to go out and spend some $$ on a bigger marine starting battery. Can I still use the same type and make of battery, or do I need to go for a brand name? I thought they were all pretty much made by the same companies, and just have different brand names slapped on them. I'm looking at a flyer from the same business I've bought most of my batteries from and they show a 27M and a 29HMDC. Whats the difference and which do you guys recommend? One other bit of info, I have a 6 amp. unregulated system. If this is done that should lower the charging rate some at WOT, correct?
Like I stated in the earlier post, I am still replacing the rectifier. I already bought the part. I may be making a mountain out of a mole hill, but I just don't want any weak links in the electrical chain. I've been towed in a couple of times, and found it very embarrasing. So if I can avoid it by thinking ahead, it's time and money well spent.
Jim
 
Last edited:

BoatBuoy

Rear Admiral
Joined
May 29, 2004
Messages
4,856
Re: My voltage says 17 as well

If your battery is 3-4 years old, obviously the situation is not immediately terminal. Just run it til it drops. You might run with the running lights on at WOT to reduce the voltage just a bit.
 

jtexas

Fleet Admiral
Joined
Oct 13, 2003
Messages
8,646
Re: My voltage says 17 as well

It's been running like that for 3 or 4 years & still tests good, then I'd say it's handling the charging voltage pretty darn well. Get a hydrometer, use it to monitor your battery's condition as it ages, so you can make a good decision on when to replace it without actually waiting for it to fail. Unless you have another battery on board (like for a trolling motor) to use as a backup. I use an interstate marine deep cycle battery to crank my '79 70hp, also run the accessories (lights, bilge, livewell), they last 5 or 6 years.
 

Kevin W

Petty Officer 1st Class
Joined
Apr 18, 2006
Messages
256
Re: My voltage says 17 as well

If you already have the rectifier you can change it.
I realy doubt it will be the fix but they are pretty easy to change.

Newer engines do not have this problem because alot have voltage regulators.

I may be reaching a bit here but i would guess the marine batteries built in the vintage if yours and my outboard may have been built having a lower internal resistance and the electronics and running lights in that era didn't care about 16V.

CDI makes a Voltage regulator for around 60$
That will most definately solve high voltage issues.

its most likely cheaper to buy the regulator and a less expensive battery than to buy a expensive battery that will solve the problem.

Thats most likely what i am going to do once i need to replace mine in a year or so.
 
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