Alternator working, but battery not being charged

[rebars1]

Restoring a 1984 Chris Craft Scorpion 230 with orginally a Merc260 set up, now a GM5.7 engine from a VolvoPenta set up. The guy before me installed, but did not finish the engine. A transition wire harness coupler was used between the engine harness and the boat harness, so, many of the wires change colors. The engine starts and runs fine. I pulled and had the alternator bench-tested at a shop and the guy said it was working fine. However, when installed back in the boat, it does not seem to charge the battery.

The output terminal has 16.3v at 1500 rpm but the voltage at the battery does not change from the engine-off static reading. The guage in the dash reads only about 10v. The output wire is connected to the starter at the same terminal as the heavy red cable from the slave solinoid. Should there be another wire? Is there a diode in the "1-2-both" switch that would block the flow of electricity?

 

[wire2]

Re: Alternator working, but battery not being charged

>>The output wire is connected to the starter at the same terminal as the heavy red cable from the slave solenoid.<<

The "heavy red cable" should be the main battery cable. If the alt output wire is connected to it there should be the same voltage on the battery.

Do you read any voltage between the output post and the slave solenoid? Or between the solenoid post and the + battery post?

How about from the alternator body to the neg battery post?

 

[Don S]

Re: Alternator working, but battery not being charged

The output terminal has 16.3v at 1500 rpm but the voltage at the batterdoes not change from the engine-off static reading. The guage in he dash reads only about 10v.

Don't go by what that dash gauge reads, they are wrong all the time, use a DVM and check the voltage at the battery itself. You also have a problem with the alternator. Should NEVER go over 14.8 Volts (using a test meter, not dash gauge)

 

[rebars1]

Re: Alternator working, but battery not being charged

Thanks Wire2 and DonS. I have been using a digital voltmeter to check the voltage at various points. I thought the output was high also. I don't know if the voltage regulator is adjustable on this alternator.

 

[wire2]

Re: Alternator working, but battery not being charged

Can also check for voltage across the switch. On "Both" there should be almost 0 from any terminal to another. A few millivolts is normal when alternator is charging. If you read 1 volt or more, the switch is defective.

 

[rebars1]

Re: Alternator working, but battery not being charged

Update: I had the alternator bench tested again and it is working correctly (about 14.5v at the bench). Back on the engine, I am getting 14.3v at the starter at the cable/wire connection from the alternator. At the slave solinoid, at have 14.3v at the cable from the starter, but only about 12.3v at the cable from the battery (which matches the battery voltage with the engine off). So, I do not seem to getting voltage flow across the slave solinoid from the alternator to the battery.

The slave solinoid is new and cranks the engine. Is there a diode or something inside the slave solinoid that would limit the voltage flow or only let it flow one way? Could I have the cables reversed at the slave solinoid and still have it crank the engine properly?

I replaced the wire from the key to the voltmeter at the dash so it now reads pretty close to the battery voltage.

 

[Don S]

Re: Alternator working, but battery not being charged

The slave solenoid has nothing do do with the charging system to the battery.
If you have 14.3V at the main battery terminal on the starter, then the only thing between the starter and the battery is the wiring and battery switch.
Do you have an AMPmeter at the helm? Not a Voltmeter, an Ampmeter. Big difference.

 

[rebars1]

Re: Alternator working, but battery not being charged

Thanks DonS. I don't have an ampmeter at the panel, just a volt meter. I think I will install one though. I do have a battery monitor/battery switch which has LED lights for battery static, starting voltages and alternator status.

The red cable starts at the battery, then to the battery switch, then to one side of the slave solinoid (on the transom). Then a red cable runs from the other side of the slace solinoid to the starter.

The output wire from the alternator connects to the same post on the starter as the red cable from the slave solinoid.

As I wrote before, at the slave solinoid, the cable from the battery side reads 12.3(same as battery) and the cable from the starter side reade 14.3(same as alternator)

 

[Don S]

Re: Alternator working, but battery not being charged

The red cable starts at the battery, then to the battery switch, then to one side of the slave solinoid (on the transom). Then a red cable runs from the other side of the slace solinoid to the starter.
The output wire from the alternator connects to the same post on the starter as the red cable from the slave solinoid.

From your discription, here is how your wiring is setup. The slave solenoid should not be where it is.

Here is how your wiring should be. The only thing missing is the battery switch which is between the battery and the starter.

The alternator is not shown in the bottom picture, but hooks to the starter just like in the first picture.

 

[Boatist]

Re: Alternator working, but battery not being charged

Your alternator wire should connect to the common post on your battery switch.

 

[rebars1]

Re: Alternator working, but battery not being charged

Thank you, DonS: The upper diagram is correct for the existing wiring, and I can see the difference in the lower one. I have two questions, partly because I cant quite see what is happening with the wires at the main post at the starter:

1. Does the red/purple wire from the slave solinoid (after passing through a circuit breaker) attach to the same post as the red cable from the battery (and the alternator)?
2. What is the recommended wire guage for the red/purple wire?
3. Does the red/yellow wire attach to the other post at the starter?


Thanks Boatist. I think that would be at other end of the cable from the switch to the starter, right?

 

[Don S]

Re: Alternator working, but battery not being charged

1. Does the red/purple wire from the slave solinoid (after passing through a circuit breaker) attach to the same post as the red cable from the battery (and the alternator)?

The red/purple wire hooks to terminal A, (See pic below)

2. What is the recommended wire guage for the red/purple wire?

8 ga.

3. Does the red/yellow wire attach to the other post at the starter?

It hooks to terminal B

 

[rebars1]

Re: Alternator working, but battery not being charged

That picture helps a lot DonS.

I now have the red/purple wire, the alternator wire, and the Battery red cable installed to the to the large post on the starter.

The existing red/yellow wire looks like it is only a 16ga (and does not look original). Right now it runs to one of the small posts on the slave solinoid. The wire on the other small post runs to the ignition switch. The two small posts are labled "S" and "I". My questions are:

1. Should the red/yellow wire between the slave solinoid and starter be a heavier guage (it will attach to the other large post at the solinoid and the small post at the starter)?

2. The wiring diagragm shows one small post with a red/yellow and the other small post with a black wire to ground, but the solinoid has the "S" and "I" designation. Which should get the black wire to ground? The existing ground is attached to the solinoid base.

Sorry for all the questions.

 

[Don S]

Re: Alternator working, but battery not being charged

Basically, you have the wrong type solenoid. The one you have is for an old Ford starter (like an 888) that put power to the coil with a points type distributor when the engine was cranking. But it can still be used.
Hook the big terminals up like in the Merc drawing above, but on the small terminals you will only use the "S" terminal. NOTHING goes on the "I" Terminal.

The 16ga (normal size) yellow/red will go to the S terminal, ground will be thru the base of the solenoid, NOT the other small I terminal.

 

[rebars1]

Re: Alternator working, but battery not being charged

Update:
I attached the exisiting yellow/red wire to the large post on the solinoid. When I turned the key the starter cranked the engine, but would not stop cranking (yikes!) until I pulled off the battery cable (which was now quite warm).

I checked the battery voltage, which was low, and charged it back up. In checking the existing yellow/red wire I noticed it was spliced into another wire to ??? So, I removed the existing wire and installed a new one between the solinoid and the starter. This time the starter cranked and stopped properly each time.

I started up the engine and now the alternator is charging properly and all the LED's on the monitor are green. Happy day!

Thanks for all of your help! This charging thing had been haunting me for a very long time.


By the way, I could not find a yellow/red wire at West Marine, so I bought a yellow one and put a red stripe on it with a red sharpie pen. Just a detail. Not required, but I like to keep the wire color coding intact where possible.