Checking F150TXRD charging output

[pstephens46]

I can't get my #1 starting battery to charge properly. It is 6 months old. I have two batteries and a typical 1-2-both switch. I also have hooked up isolater run from engine to #2 battery and that seems to do the job for that battery. All battery cables replaced last fall. I want to check the charging output without interference from the battery being under-charged. I am assuming I could start and run motor with battery switch set to "2". Then disconnect red and black from #1 battery and check with meter. That should give me the true output from motor to battery, correct?

[DennisG01]

So... you have the charging lead from the engine going to the battery switch, then individual cables from the #1 and #2 switch positions to each battery, right? With the switch on a specific battery, you're getting full charging at that battery - no need to disconnect anything. And, with switch on #2, you're seeing about 13.5V at battery #2, but with the switch on #1 you're only seeing battery voltage? What is that battery voltage at each battery with switch OFF? If both batteries are good (load tested?)... Either swap the batteries or the cables and see if the problem follows the cables or stays at the battery.

Are the grounds good?

[99yam40]

seems to me the #1 battery should be the starting battery, and #2 would be the house battery with all of the electronics on it.
the main red lead from motor to switch should keep that battery charged as long as the switch is set to #1.
the motor should have an auxiliary charging lead for the house battery to keep #2 charged.
only time you should switch to #2 would be if #1 was dead and you want to start the motor on #2 battery

[fairdeal]

The 'main charging output" gets TO the battery
through the same big black cable
that the battery uses to send current to the starter motor;
and that big black cable
is on the "Common" lug of the switch

when you have the switch on 1,
it connects the Common to battery 1
so charging output goes to battery 1

when you have the switch on 2,
it connects Common to battery 2
charging output goes to battery 2

when the switch is on 2,
Battery 1 isn't connected to anything,
so a voltmeter on "red and black from #1 battery"
will just tell you what the battery voltage is -
nothing about the engine's charging output

[pstephens46]

The 'main charging output" gets TO the battery
through the same big black cable
that the battery uses to send current to the starter motor;
and that big black cable
is on the "Common" lug of the switch

when you have the switch on 1,
it connects the Common to battery 1
so charging output goes to battery 1

when you have the switch on 2,
it connects Common to battery 2
charging output goes to battery 2

when the switch is on 2,
Battery 1 isn't connected to anything,
so a voltmeter on "red and black from #1 battery"
will just tell you what the battery voltage is -
nothing about the engine's charging output

Regarding last paragraph, yes, I realized that later. I should have typed "setting switch to Both". I was considering disconnecting the red and black on #1 to battery and putting meter on those leads to take the weakest battery out of loop. I am not sure if that would interrupt power to motor? Before connecting the isolator lead years ago, I put the meter on that wire while running motor and got a solid 14.4 volts. I would assume I should be getting charging voltage in a similar fashion to #1 battery, correct? #2 battery is six years old and is still strong, #1 is six months old and choking like a dog.......

Thanks for everyone's input.

What is the science by con*****ing so many functions with ground/common?

[99yam40]

I guess it is just what the Yamaha engineers decided to do.
I have seen 120VAC circuits also where they make and break the neutral, it is what some decide to do.



as far as flipping the switch while the motor is running is concerned, I would not do that.
I am not sure if it is a bad thing to do, but they say a bad battery connection can cause RR failures.
So opening that switch while running could act like a bad connection unless it is a make before break switch

Have you put #1 battery on a charger to make sure it is fuly charged up before starting and testing battery voltages?

[pstephens46]

I guess it is just what the Yamaha engineers decided to do.
I have seen 120VAC circuits also where they make and break the neutral, it is what some decide to do.



as far as flipping the switch while the motor is running is concerned, I would not do that.
I am not sure if it is a bad thing to do, but they say a bad battery connection can cause RR failures.
So opening that switch while running could act like a bad connection unless it is a make before break switch

Have you put #1 battery on a charger to make sure it is fuly charged up before starting and testing battery voltages?

I am not planning to change switch setting while running. I want to check the charging output of the cables to #1 without the battery interfering. Can I disconnect the #1 battery cables while running when battery switch is set to both?

[99yam40]

are you using the auxiliary charging cable for the house battery, or are you charging both batteries with just the one output of the RR?

Seems to me as long as one battery is tied to the output of the RR you are using, it should be OK

[pstephens46]

are you using the auxiliary charging cable for the house battery, or are you charging both batteries with just the one output of the RR?

Seems to me as long as one battery is tied to the output of the RR you are using, it should be OK

I use the aux cable to charge the house/#2 battery.

[99yam40]

I use the aux cable to charge the house/#2 battery.

then disconnecting the out put of the normal one from its battery may not be a good idea.

But since you are talking about hooking #2 to the RR that #1 was attached to also, I have no idea what that would affect everything

[Keithbaja]

A battery isolater is not a switch per say. Sounds like your talking about a battery switch. Most folks call a "Perko" you don't need/want to disconnect while motor is running. A good DVM will tell you the output that the battery cable end see's. Also a ohm or voltage drop test never Hurts. Min. Charge voltage is 13.8 and float charge is 13.2. A good batt at rest will be 12.6 or higher. If you have a shorted cell and don't know how to test or spot it you can drive yourself Nuts. Marine batts have more room under the plates at the bottom of the battery to help prevent cells short's. Deep cycle should NOT be used on Outboards. And mix matching batts open a host of issues. Typical isolaters are not recommended as u loose 1V across the Zenor diode. Battery boxes SUCK ! Hold down trays are the TICKET. Out

[pstephens46]

A battery isolater is not a switch per say. Sounds like your talking about a battery switch. Most folks call a "Perko" you don't need/want to disconnect while motor is running. A good DVM will tell you the output that the battery cable end see's. Also a ohm or voltage drop test never Hurts. Min. Charge voltage is 13.8 and float charge is 13.2. A good batt at rest will be 12.6 or higher. If you have a shorted cell and don't know how to test or spot it you can drive yourself Nuts. Marine batts have more room under the plates at the bottom of the battery to help prevent cells short's. Deep cycle should NOT be used on Outboards. And mix matching batts open a host of issues. Typical isolaters are not recommended as u loose 1V across the Zenor diode. Battery boxes SUCK ! Hold down trays are the TICKET. Out

Charge voltage should be 13.8 volts with battery included in the loop? Measured at battery I assume? Attempting to put a full charge on suspect battery now. I think I have a crappy 6 month old battery.

[pstephens46]

Looked up purchase date of battery. 9/26/21. I charged it to 12.75 and it’s not connected to anything. Dropped to 12.55 in two hours. I would assume it’s toast. Thoughts? Measured with meter, not the Yamaha guage.

[99yam40]

what are you charging it with?
was it only putting out 12.75?
and how many amps where you putting into it and for how long?
what was the battery voltage before you started charging it?

[Keithbaja]

Sounds like ur doing it correctly. If it reads 12.6 or more that's fully charged. But dropping as fast as it did sounds like shorted plates (cell) and possible major sulfated. You can take it to a auto place and have it charged on a known good charger then tested with whatever test they have. I prefer the load drawdown type. Floaded batteries don't like to sit around partly charged. Sulfates them quix..