2004 F40TLRC charge voltage

[Pboat4517]

Bought this boat/motor about 4 years ago. Charging seemed OK, Tach worked.

Recently had burned out Rectifier/Regulator. Although it had lost Tach signal output some time back, when battery got low I found the Negative terminal loose which probably finished off the Regulator burning out (actually burned through the back cover black sealant).

Considering Yamaha OEM R/R was $200+, I bought a good used OEM R/R. Installed and when test running on water hose with battery charged to 12.7 vdc. When started the charging voltage was 14.4 and did not fall back to 12+ as would expected after running at Hi-idle a few minutes. Have not yet had it on the lake to give longer higher RPM run to see about charge voltage.

My SELOC Manual says the R/R output should be 14.5 volts, but that at 12.5 volts battery, charging should drop back.

Read on another post about a Yam F60 which routinely was at 14.5 volts.

My greater concern is if it continues charging at 14 volt beyond a short time enough to bring battery back to full 12.5, it will ruin the battery.

Anyone have any insight on this?

[fairdeal]

My SELOC Manual says the R/R output should be 14.5 volts, but that at 12.5 volts battery, charging should drop back.

Anyone have any insight on this?

If the SELOC manual does in fact state that,
the SELOC manual is in error.


The regulator/rectifier is not a 'battery charger' - much less a 'smart charger'
It has no way of knowing the state of charge of the battery
nor even any way of knowing where the current leaving it is going -
could be going into the battery -
could be going to a livewell pump -
could be going to any device using electricity.


The voltage regulator (regulator portion of regulator/rectifier) does only one thing -
imposes an upper limit of voltage -
a 'not to exceed' value -
of ~14.5 volts.

The value of ~14.5 is selected by the designer
because that is unlikely to result in a significant battery overcharge

[Pboat4517]

Howdy, I really appreciate your taking time with this explanation.

So, my regulator is working properly?

I will go re-read the SELOC section. It nor the PDF Yamaha Manual are too straightforward and clear on this.

Now a question to help me understand, if not through the Regulator (like on a car), how does a 12 volt battery not get over-charged or over-heated if it being fed 14+ volts constantly?

[99yam40]

have you ever measured the voltage of a battery while being charged with a charger or a car/ truck while running?
they all have limits above 12.7 volts

3 tenths of a volt per cell will not hurt the battery

[Pboat4517]

Thanks.
Good comparison.
I don't know if I have actually metered battery voltage on a running auto, but soon as it quits raining I will.

You guys are tops! I should have been picking info from this forum long ago.

What would cause a seemingly good R/R to kick the bucket?

[DennisG01]

Yup, as stated, just like in a car, that 14-ish Volts is a constant. It never goes down - it stays around that voltage anytime the engine is running. It's constantly charging the battery because things are constantly using electricity when the engine is running. Now, a smart charger, on the other hand (when the engine isn't running), WILL drop off voltage and amperage as the battery nears full charge and then switch back on as needed to keep it fully charged.

"What would cause a seemingly good R/R to kick the bucket?" Hard to say - that loose ground wire is a good possibility. But they are ALL "seemingly good" before they kick the bucket!

[TownsendsFJR1300]

Charging voltage on a Yamaha Motorcycle: https://www.flickr.com/photos/147134237@N06/29303851750/in/dateposted/

Max charge is at approx. 4K RPMs..

[panasonic]

Thanks.
Good comparison.
I don't know if I have actually metered battery voltage on a running auto, but soon as it quits raining I will.

You guys are tops! I should have been picking info from this forum long ago.

What would cause a seemingly good R/R to kick the bucket?

Many possibilities...You said you had a loose negative battery cable that is now fixed..that may have been it.

The regulator that you installed has a black wire with a ring terminal on the end of it that bolts to the block. This is the ground for the regulator. Was this grounding point cleaned? Was there any corrosion on the mating surface or the bolt?

[99yam40]

from what I understand anything over what the regulator allows is shunted to ground.
a bad ground causes problems

[zenoahphobic]

Howdy, I really appreciate your taking time with this explanation.

So, my regulator is working properly?

I will go re-read the SELOC section. It nor the PDF Yamaha Manual are too straightforward and clear on this.

Now a question to help me understand, if not through the Regulator (like on a car), how does a 12 volt battery not get over-charged or over-heated if it being fed 14+ volts constantly?

You got to realise in order to get charge into any battery the charger voltage needs to be higher.

With current wet lead acid batteries, the consensus is that 14.5 volts is the maximum that charging voltage should be to get the maximum charge into the battery without harming it or sacrificing its life (significantly) by having 14.5 volts across the terminals for an extended period of time.

What the actual terminal voltage is at anytime depends on the condition of the battery, the size of the battery as well as the state of charge of the battery, coupled together with the capability of the charger.
What this means is that many voltages may be seen at various times with a particular battery or with a different battery, the aim being that the charger eventually gets it to 14.5v. Less than this suggests two things: the charger is faulty or poorly regulated, or the battery could be too large in capacity.

Now this 14.5v never really is what the battery holds, it rapidly drops down once disconnected, but can hover in the 13+ volt region for quite some time on a good battery, not so on a failing battery (useful observation in determining life remaining in battery).


If one never has used or observed a volt meter, the confusion is understandable.

[Pboat4517]

Thanks ALL! Some good knowledge and increased understanding from all the replies.

The 14+ volts makes sense considering many boats are not run for long periods of time.

Regarding the Block Ground, yes I made sure it was clean for the new R/R, even though the R/R black ground appeared to be clean and bright when taken off with bad R/R. I have run an Ohm check to battery Neg to verify.

The bad battery ground was probably just the last straw on the old R/R. You can bet Ground connections will be observed closer from now on.

[99yam40]

there are recommendations to get rid of any wing nuts on batteries with regular nuts and snugged down with a wrench

[TownsendsFJR1300]

there are recommendations to get rid of any wing nuts on batteries with regular nuts and snugged down with a wrench

I put SS, self locking(nylon) nuts on my battery posts with Dielectric grease..