My four year old batteries were not coming up to charge, I would see the
voltmeter reading 13 volts. I tested the alt. at idle, and at about 1500rpms. I
took out the batteries and had them loaded, the verdict was to replace them
(which I did). The problem is at idle everything seems to be great, but at
higher rpms the batteries discharge, I see a steady discharge on both the
voltmeter and the digital display on my sonar. How do I determine if its the
alt. or the regulator. The motor is a 1999 4.3 ltr mercruser and has the 55amp
mando alt. Thanks for listening.

John

"SaladinoJA" wrote in message
...
My four year old batteries were not coming up to charge, I would see the
voltmeter reading 13 volts. I tested the alt. at idle, and at about
1500rpms. I
took out the batteries and had them loaded, the verdict was to replace
them
(which I did). The problem is at idle everything seems to be great, but at
higher rpms the batteries discharge, I see a steady discharge on both the
voltmeter and the digital display on my sonar. How do I determine if its
the
alt. or the regulator. The motor is a 1999 4.3 ltr mercruser and has the
55amp
mando alt. Thanks for listening.

John

Newer Car alternator systems charge higher when cold than when hot.
Batterys require more voltage to charge cold than when hot. You can
overcharge and boil a battery if you charge at too high a voltage. PLUS
it's assumed that when cold the battery has just beeen massively discharged
(you just started the engine) and needs to be recharged quickly. If the
battery is discharged then charging at a higher rate won't hurt it.

My ALT system in my boat and car charge at 14.3V when cold and drops to 13.6
when hot. That may look like a discharge to you. Only way to tell is with
a GOOD voltmeter that's been checked (accurate).

On 08 Jun 2004 13:23:05 GMT, (SaladinoJA) wrote:
How do I determine if its the
alt. or the regulator. The motor is a 1999 4.3 ltr mercruser and has the 55amp
mando alt. Thanks for listening.

========================================

I'd be inclined to pull the alternator and take it to a shop for
testing. They should be able to tell you in minutes if its OK or not.

"SaladinoJA" wrote in message
...
My four year old batteries were not coming up to charge, I would see the
voltmeter reading 13 volts.

What condition did you measure this at? Engine off? Idle? 1500 RPM?

The problem is at idle everything seems to be great, but at
higher rpms the batteries discharge,

That seems a little backwards! Usually the charge rate at idle is very low
and comes up at higher RPMs.


I would take the alternator off and have it tested. Many auto part stores
have a setup for testing alternators and it only takes a couple of minutes.

If the alternator tests out OK then I would replace the regulator.

Rod

How do I determine if its
the
alt. or the regulator.

With a progressive test light or (better yet) a meter.

With the engine running, measure the voltage at the connections on the back of
the alternator. Should be well over 14 volts.
If it isn't, (and especially if its the same reading you're getting off your
battery terminals when the engine is not running or there is no charger
connected),
look at the alternator.

I had an alternator reading "12" (which was the discharged battery voltage,
in retrospect), but the problem was the regulator. My mechanic said he
diagnosed it by "just knowing."

(The following year, the alternator went - and I've learned a few things
about charging circuit management in the interim!)

====

Charles T. Low
- remove "UN"
www.boatdocking.com/BDPhoto.html - Photo Contest
www.boatdocking.com
www.ctlow.ca/Trojan26 - my boat

====

"Gould 0738" wrote in message
...
How do I determine if its the alt. or the regulator.

With a progressive test light or (better yet) a meter.

With the engine running, measure the voltage at the connections on the
back of
the alternator. Should be well over 14 volts.
If it isn't, (and especially if its the same reading you're getting off
your
battery terminals when the engine is not running or there is no charger
connected),
look at the alternator.

How do I determine if its
the
alt. or the regulator.

With a progressive test light or (better yet) a meter.

With the engine running, measure the voltage at the connections on the back
of
the alternator. Should be well over 14 volts.
If it isn't, (and especially if its the same reading you're getting off your
battery terminals when the engine is not running or there is no charger
connected),
look at the alternator.

Thanks to everyone who responded. I used a meter to check the battery voltage
with the engine off and noted 13v, I then checked each battery with the motor
running at idle, and got between 13.6 and 14v, I then checked the alternator
with the meter, and got a reading of 14.4v at idle and 13.8 at 2000rpms. I took
the boat out and ran it for about 20 minutes at 3000rpms. I watched the
voltmeter on the boat and on my sonar go from 13.8 down to almost 11.6 volts,
as soon as I would return to idle it would go back up. I was alone and didn't
think it was a good idea to leave the helm at speed to check the back of the
alternator with the meter, so I have only the two readings from the boat's
meters. At 3000rpms (or any rpms for that matter), are the meters on the boat
reading battery voltage or charging voltage? HELP!
John

The reason you're getting lower readings at higher rpm is that your ignition
system is
drawing down the battery to run the engine
and the juice isn't being replaced.


Assuming your alternator has an external regulator-
What's the cost of a new voltage regulator vs the "minimum diagnostic fee" in
your area? If you can get a voltage regulator for less, do so and put it in
place. That will either solve your problem, or almost certainly prove that it's
the alternator.
Worse case result if it is the alternator is that you now have a spare
regulator (the one you took off but that proved to be working).

If this is a "marinized" auto alternator NAPA and most other big auto parts
places will test it for free.
Don't just put a regular alternator back though, unless you are willing to
split the cases and swap over all of the marine hardware. (the "explosion
proof" screens are usually inside). That usually voids your warranty