Alternator 14v But Not Charging

[GeneM]

Is it possible for an alternator to show 14v up from 12.5v and not charge good batteries? When my batteries (bank of 2 4D's wet cells) get down to 12.0v my inverter shows 11.2v and cuts out. That's when I turn on the generator (70 amp charger) and see the amps jump from negative to about 10 amps positive. If I opt to run the stbd engine to charge with no generator, I get no needle movements. When I check the volts coming from the generator, it shows 14v - up from 12.5v before running. The engine starts well at 12.0v. Voltage at the battery and alternator are the same. My inverter is connected direct to the bank with 1/0 6ft cables across the whole bank just like the house load.

A few months ago my heat exchanger leaked salt water on the alternator. I didn't catch it for about two weeks, then flushed it with fresh water after fixing the leak.

Help!

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[a64pilot]

I see a few problems, first if your batteries are down to 12V or less and you turn on a 70 amp charger, it should initially max out, not only 10 amps, then no, its not possible I don't think for an alternator connected to a 12V battery to make 14V and not charge the battery.
My first thought is your ammeter is suspect, if it's good, then I suspect your bank or connections. Great batteries with a poor or loose connections will act like bad batteries

[boatbod]

With the engine running, measure the voltage at the back of the alternator and measure the voltage at the batteries. It should be roughly the same (within 0.5v or so). If you've got >14v your alternator is doing fine.

If the alternator is producing 14v and your batteries are at 12v or below, suspect a bad wire or failed isolator.

If the batteries were low and they immediately reached 14v with very little amperage, your batts are bad.

[GeneM]

Thanks for your help. I had the alternator tested and it's good. I also replaced the two house batteries and cleaned all the battery and alt connections. I still get no charging indication. I verified that the meter works, since I have two.

The shop that tested the alt said to be sure I'm getting 12v on the ignition line to the alt. It seems I'm only getting 10v, so that's what I'll focus on. Then I will look at the isolator.

Thanks again.

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[boatbod]

Originally Posted by GeneM

Thanks for your help. I had the alternator tested and it's good. I also replaced the two house batteries and cleaned all the battery and alt connections. I still get no charging indication. I verified that the meter works, since I have two.

The shop that tested the alt said to be sure I'm getting 12v on the ignition line to the alt. It seems I'm only getting 10v, so that's what I'll focus on. Then I will look at the isolator.

Thanks again.

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If you've got 14v on the B+ terminal at the back of the alternator your excite voltage is sufficient. Follow back through the wiring to find out where the 14v becomes significantly less and that is likely to be where the problem lies.

[roland stockham]

Have you checked whether it is 14vA/C or D/C. I may be that the leek bluw the alternator diodes so they are no longer rectifying the current. A/C will show a voltage and give some current flow but not charge the batteries. If you have a multi=meter set it for A/C and see if you get a higher voltage (about 16v)

[hamburking]

Do you have a battery switch?

[Lepke]

Any connection or wire can have enough resistance to stop a battery charging from a good alternator. Over the years when troubleshooting charging systems, I have sometimes found corrosion throughout heavy battery cables that looked fine on the outside and appeared to have good ends.

[rosco4271]

I concur disconnect all Power connections clean and reconnect do this with the sense connection as well usually the problems are corroded connections or as has been said check its true DC Volts. Also there are plenty of DC Tong style Ammeters on the market now so get one of them to ensure the charging amps are correct good luck

[Horus]

Is there a charging relais or diode bridge in your system? What about these?

[bill good]

Just had the same & it turned out to be where the neg battery was connected to the engine block. Connected to the bolt on the starter & all was good!!

[GeneM]

I found something wierd. The alt output is good. All connections are very clean and tight, especially the sense and exciter. There are no inline diodes. The wires look good, but I'll try to do a voltage drop test later.

I get 14v at the back of the alt, but only 12 v across the battery bank of 2 4D's. When I test the left one, I get 14v. When I test the right one, I get 12v. It seems that the right one is off the charging grid. I decided to change the way the batteries are connected, so - hopefully - both will charge.

If you want to comment on what I plan to do, please look at the new post I did. I think the title is "Changing Battery Wiring".

Thanks to all for your help.

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[smattie]

Originally Posted by Lepke

Any connection or wire can have enough resistance to stop a battery charging from a good alternator. Over the years when troubleshooting charging systems, I have sometimes found corrosion throughout heavy battery cables that looked fine on the outside and appeared to have good ends.

I concur with your wire analysis. If you had salt water leaking on the alternator, you may have corroded the wire to the battery. Several years ago I couldn't figure out why I wasn't getting ANY voltage at a termination only to find out that a very small pin hole caused by someone with a pin probe poked a hole in the wire. Salt water caused the copper wire to turn to green dust. You can easily get voltage drop over distance with undersized (or compromised) wiring

[boatbod]

What sort of battery switch do you have? Symptoms sound consistent with 1-ALL-2 switch.

[GeneM]

I'll look for bad wires when I get time. However, none of it is exposed to salt.

The battery switch is basically two separate switches for the batteries.

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