Alternator good, not charging battery

[ramblinrod]

Originally Posted by mrybas

I took the battery to an alternator shop that bench tested the alternator and said it was good.
When I reinstalled the alternator, the battery voltage is 12.40 and does not rise when the engine is running (at idle or higher rpm). Any ideas?

Ok, first of all, your post is confusing. Did you take your battery to an alternator shop or your alternator to a battery shop?

Next, at least the first few responses you received far from folks who don't know jack about batteries. I stopped reading at about 3 x nonsense and had no patience to read moe crap.

Sorry, I just spent all day becoming intimate with a customers mechanical fuel pump and have little patience for BS.

If your FLA battery is discharged to about 50% SOC, it will have a resting voltage (no charge, no load for several hours) around 12.2 Vdc. If your start the engine, the battery voltage may go up to about 12.4 Vdc, initially, as your battery bank sucks all the Amps from the alternator it can. As your battery bank becomes fed (charged) the voltage will increase until it reaches 14.something Vdc. What happens after that will depend on how good (read Smart and expensive) your alternator and regulator are.

Regardless what you have, if your bank is fully charged, after the alternator (engine) is turned off, with some loads on (e.g.Fridge and lights) the voltage should drop fairly quickly to 12.7 - 12.8 Vdc, and then the voltage reduction should slow way down.

If this is what is happening, all is well.

If for voltage with the alternator on starts at 12.4 Vdc and never increases after 2 orm3 hours, them and only then, may you have an alternator issue.

How rapidly the voltage rises will be directly proportional with the alternator output and inversely proportional to your bank size. Ie. The bigger the alternator the faster it will rise, the bigger the bank, the slower if will rise.

Rod Brandon
Sheen Marine
(Design, install, and fix this stuff for a living.)

[redbeard1]

Originally Posted by mrybas

Attachment 155948
Could it have something with this diode? The red/yellow wire becomes hot when the key is turned on.

That looks like the parallel circuit I mentioned in post 29. If it is, it would be wired something like the attached diagram. It is strange that both circuits fail to excite the alternator. That suggests to me the problem might be internal to the alternator. Or that the problem could be before the two circuits split (did you confirm 12v at the red/orange wire?)

Here is more than you want to know about debugging this problem. I found the section “Test 2. Verify voltage at harness plug” very useful.
Charging System Tests

[ramblinrod]

PS, to all of the responses you have received about using an ohmmeter to measure things, STOP! You must disconnect
The device or cable from the voltage source (battery or alternator) before using an ohmeter.

Lastly, if you are not as intimately familiar with marine electrical systems, (as I became with a customers 1987 Mercruiser 230 today) just stop before you hurt someone, and hire a "sparky"'to look at it. Check their qualifications AND commercial liability insurance limit, before you let them on your boat. They will tell you in less than 15 minutes whether your alternator is working properly. If
They have a min 1 hour charge, get your monies worth. And have them do a quick electrical inspection (even if it costs you 2 billable
Hours). 9 times out of 10, they will find something serious that will save you a ton of grief and possibly your life, or your loved ones.

[bateaubonsai1]

Have you look at your ( boat ) indicating instruments , it could be " boat indicating error "

[jimbunyard]

To troubleshoot things like this, it's best to provide as much information as possible...at least the complete model number of the engine, even better would be the engine manufacturer's part number for the alternator, even better than that, the OEM part number.

Since we have none of those, we can make some assumptions. From the color, it's on a Perkins, from the connections on the back it's a Iskra/Lektrika-made alternator.

I couldn't find the proper schematic for the illustrated alternator, though I didn't look very hard, not knowing for sure which it was. If you can provide some numbers from the case of the alternator we may be able to research it, though if you ask the people who tested it for you they can tell you what each individual terminal's function is , and you can make sure it's hooked up correctly from that, by tracing where the individual wires go.

Until we hear back from you, you can try a couple of things.

1. Advise where both the yellow and red wires feeding the 'mystery component/diode come from.

2. Disconnect that component, preferably from both ends, but at least from one end, and check it with the engine ignition off, first from the disconnected side to ground for current, then continuity.

There should be no power with the ignition off, but there might be continuity, depending on the circuit and the direction of what appears to be a diode.

Then, with the ignition still off, check the mystery component itself for continuity, that is select 'ohms' on the meter and read directly between the two end leads (between the 'diode' and the other component) of the gray cylinder.

I'll make a WAG and say that there's no continuity there.

If you want to take a chance, remove the purple wire from the alternator connection, and make a jumper wire to connect the main output (leave the main battery cable connected! on both ends!) to the where the purple wire is normally (which is, I'm speculating, the field connection.) If the alternator begins charging, you've isolated the problem to the red/yellow/purple/mystery component circuit.


Safest though to work backwards from an informed position.

[mrybas]

Originally Posted by jimbunyard

To troubleshoot things like this, it's best to provide as much information as possible...at least the complete model number of the engine, even better would be the engine manufacturer's part number for the alternator, even better than that, the OEM part number.

Since we have none of those, we can make some assumptions. From the color, it's on a Perkins, from the connections on the back it's a Iskra/Lektrika-made alternator.

I couldn't find the proper schematic for the illustrated alternator, though I didn't look very hard, not knowing for sure which it was. If you can provide some numbers from the case of the alternator we may be able to research it, though if you ask the people who tested it for you they can tell you what each individual terminal's function is , and you can make sure it's hooked up correctly from that, by tracing where the individual wires go.

Until we hear back from you, you can try a couple of things.

1. Advise where both the yellow and red wires feeding the 'mystery component/diode come from.

2. Disconnect that component, preferably from both ends, but at least from one end, and check it with the engine ignition off, first from the disconnected side to ground for current, then continuity.

There should be no power with the ignition off, but there might be continuity, depending on the circuit and the direction of what appears to be a diode.

Then, with the ignition still off, check the mystery component itself for continuity, that is select 'ohms' on the meter and read directly between the two end leads (between the 'diode' and the other component) of the gray cylinder.

I'll make a WAG and say that there's no continuity there.

If you want to take a chance, remove the purple wire from the alternator connection, and make a jumper wire to connect the main output to the where the purple wire is normally (which is, I'm speculating, the field connection.) If the alternator begins charging, you've isolated the problem to the red/yellow/purple/mystery component circuit.


Safest though to work backwards from an informed position.

It's a Nanni 3.21. Not much info on these engines as it's a French company.

[mrybas]

Originally Posted by bateaubonsai1

Have you look at your ( boat ) indicating instruments , it could be " boat indicating error "

The light on the panel comes on when battery voltage is low as it's supposed to. When the engine is running and I put 12v to D+ at the alternator (purple wire), the alternator kicks on and the light on the instrument panel goes off as it should.

[jimbunyard]

Originally Posted by mrybas

The light on the panel comes on when battery voltage is low as it's supposed to. When the engine is running and I put 12v to D+ at the alternator (purple wire), the alternator kicks on and the light on the instrument panel goes off as it should.Attachment 156003

Well, since it seems you're willing to take chances, remove or bypass the 'diode' and gray cylinder (either a capacitor, resistor or fusible link) (a short piece of wire will do the trick), and see if everything words correctly (most importantly that the engine shuts down when you want it to).

What the results are determine your next action...

[fwilmeth]

One thing to check for is the presence of a external diode in one of the cables attached to the alternator. These diodes can (and do) separate. If they do, or partially separate, you will not get a full, or in your case, any charge to the battery. I couldn't tell from the photo if there was one present or not.

[mrybas]

Originally Posted by jimbunyard

Well, since it seems you're willing to take chances, remove or bypass the 'diode' and gray cylinder (either a capacitor, resistor or fusible link) (a short piece of wire will do the trick), and see if everything words correctly (most importantly that the engine shuts down when you want it to).

What the results are determine your next action...

It's a catamaran so I checked the other engine for comparison purposes.
Working engine/alternator has 1.7 volts at D+/purple wire with key on.

So on the not working engine I cut the purple wire before the diode. It has 1.7V with the key on. When I splice a piece of wire to 1.7V purple and run it to the back of the alternator, it now reads .2V.
As soon as the connection is made to D+ on the alternator, voltage of the purple wire drops from 1.7V to .2V

[Cheechako]

Originally Posted by mrybas

It's a catamaran so I checked the other engine for comparison purposes.
Working engine/alternator has 1.7 volts at D+/purple wire with key on.

So on the not working engine I cut the purple wire before the diode. It has 1.7V with the key on. When I spice a piece of wire to 1.7V purple and ran it to the back of the alternator, it now reads .2V.
As soon as the connection is made, Voltage of the purple wire drops from 1.7V to .2V

Whoa! new info, it's a cat. The engines aren't tied to the same battery bank are they?

[mrybas]

Originally Posted by Cheechako

Whoa! new info, it's a cat. The engines aren't tied to the same battery bank are they?

no, both are only tied to the start battery (each has its own start battery)

[mrybas]

Originally Posted by fwilmeth

One thing to check for is the presence of a external diode in one of the cables attached to the alternator. These diodes can (and do) separate. If they do, or partially separate, you will not get a full, or in your case, any charge to the battery. I couldn't tell from the photo if there was one present or not.

Winner winner chicken dinner! When I make the broken connection with the diode, the alternator starts charging.

Any better way to rewire this?

[mrybas]

Here is how it's wired:


Here's a close up of the diode and resistor (assuming that's what they are)

[Entheos251242]

Originally Posted by mrybas

Here is how it's wired:
Attachment 156009

Here's a close up of the diode and resistor (assuming that's what they are)
Attachment 156010

Hi, this post helped me so much, after spending $175-00 for a apparent repair. Could you please indicate where you found the diode in the harness?, Was it close to the alternator? Did you have to cut the harness cover to locate it?