Cummins diesel engine alternator overcharging

[Evidence]

I am wanting help to solve, what I understand is a very unusual problem, with a 24V Delco 22S1 alternator on a youngish Cummins 6CTA 8.3 mechanical diesel engine. It has suddenly begun to continually pump out highly fluctuating / high current into a bank of 2 x 12V, fully charged, (electrolyte SG > 1.24) lead acid / deep cycle batteries – connected in series.
The Amps range is about 15-70 Amps at the idle RPM of 600.
The duration of each period at approx 15 amps at 27V and 70 amps at approx 22v, is about 3-4 seconds – as measured at the battery – with a clamp meter and multimeter. I’ve found no current leakage elsewhere ( no loads attached) – its all going to the battery. My initial reaction was to replace the alternator – which I did – with no improvement.
I’ve doubled the ground and positive cables to their respective connections – to rule out impact of poor connections.
This engine is one of an identical matched pair in my boat.
The sister, Port, engine alt. is connected to the same battery bank. It performs normally – putting out a rock steady of around 2 amps immediately after start up – at same idle RPM.
The Delco has an internal regulator. The only connections to it is the ground wire, positive cable and a sensor wire.
I’ve established the cause of the problem is in the engine room – both the instrument cluster and harness are good.
Further testing showed: (done with battery charger turned off, and a 24VDC/24V AC inverter ground cable removed from the starter motor)
1. A diode test on both port and S Alt. – with my multimeter – with batt+ cable and sensor wire removed, gave 880 and 870 (mv?) – which may indicate that rectifier diodes are OK. However, opinions sought on significance of that result.
2. However, the AC content of the alternator’s ~24V DC output was a massive ~ 1.5V – and fluctuated wildly – compared to – what I understand is the max acceptable level – 100mv.
3. Similarly, the diode in the engine harness labelled “Alt diode” read 0.589 – which I understand indicates it is functioning properly – same as on the P eng. However I do not knw if that diode controls the Alt warning light on the dashboard.
4. The dashboard warning light comes on – but only briefly (1/2 sec), after the engine starts – same as Port engine.
5. I’ve verified that all engine harness wires are not grounding on the engine and, also, are “open circuit” with respect to the alternator sensor wire – except for the red wire which shows <0.1 ohms – all those results agree with those on the good engine.
6. All resistance checks on the Aux magnetic switch and associated connections agree with the good engine
7. Because the alternator heats up quickly when delivering these high currents – and at idle, I cannot risk running the engine for more than about 3 minutes at a time
8. Removing the sensor wire from terminal No. 2 of the Delco made no difference to the output.
9. Both the alternator Batt + terminal – No. 2 and No. 1 terminal is shorted to the Batt + terminal – which is not the case with the port engine.
Ive yet to connect the sensor terminal on the alt directly to the battery’s + terminal and check impact on output.
The shorting of the No. 1&2 wires certainly looks to be a fault- but hard to reconcile with fact its a new alternator. Nevertheless it displayed the prob on first test run – so unlikely repeated test runs damaged the circuitry.
All suggestions, hints, comments greatly appreciated.
Thanks, E

[nctnico]

Sounds like the regulator inside the alternator is broken. Or the alternator is wired wrong. Try and lookup the wiring diagram for the alternator and the boat itself to see what is what. Maybe shorting both terminals on the alternator overrides the internal regulator. But you shouldn't rule out the new alternator has a problem.

[Xena E]

...The sister, Port, engine alt. is connected to the same battery bank...

Can you clarify the context here please: are you saying that you are charging the same batteries  from both engines?

[johansen]

Clean, strip and re crimp every connector.. use vineagar if needed to clean the wire, then solder the crimp.

Seen this stuff many times. Crimp appears solid but the corrosion products have insulated every strand from themselves.

A friends truck had a lead acid battery post insulated from the lead battery connector by a thin film of lead oxide. I noticed this when i stabbed the joint with a volt meter and noticed a spark.

Same goes for the aluminum body of the alternator bolted to the engine ..dont think that cant go open circuit .

[nctnico]

Clean, strip and re crimp every connector.. use vineagar if needed to clean the wire, then solder the crimp.

F*** no, don't solder a crimp!      A good crimp is way better compared to soldering. Especially in vibrating environments you don't want to have solder joints in power connections unless you like your boat or car to catch fire at the least inconvenient moment. Leave crimps alone unless the strands of the wire going in are broken OR somebody did a shoddy job. In both cases get the right tools and A-brand crimps in there otherwise the situation will be worse instead of better.

Same goes for the aluminum body of the alternator bolted to the engine ..dont think that cant go open circuit .

The OP's problem is that too much current is going into the batteries. By definition that can't be an open circuit problem. The internal regulator of an alternator should shut down or default to a safe voltage level in case a control wire becomes open.

[johansen]

Clean, strip and re crimp every connector.. use vineagar if needed to clean the wire, then solder the crimp.

F*** no, don't solder a crimp!      A good crimp is way better compared to soldering. Especially in vibrating environments you don't want to have solder joints in power connections unless you like your boat or car to catch fire at the least inconvenient moment. Leave crimps alone unless the strands of the wire going in are broken OR somebody did a shoddy job. In both cases get the right tools and A-brand crimps in there otherwise the situation will be worse instead of better.

Same goes for the aluminum body of the alternator bolted to the engine ..dont think that cant go open circuit .

The OP's problem is that too much current is going into the batteries. By definition that can't be an open circuit problem. The internal regulator of an alternator should shut down or default to a safe voltage level in case a control wire becomes open.

Im reminded of a song.. you think you know... Everything...

Very few situations will fatigue a soldered stranded wire crimp connection, and like it just breaks off. If that happens, your wire was not secured properly prior to the crimp. What happens usually is the solder between the strands splits, and the solder remains as a corrosion inhibitor. As it splits due to fatigue it acts as a fatigue/vibration dampener that soaks up a lot of energy. If you let the wire soak up the solder 3 inches up the wire because you overheated the joint with shitty flux.....yeah it might break off, 20 years later.

Pure copper not crimped hard enough (which is most of the time) corrodes internally over time depending on the environment. You get intermittent failures. Including fire...when say, a 10th of the outer strands take all the current and light the insulation on fire...Now if you get the copper hot enough that you embrittle it due to the copper tin inter metallic while soldering. why? Why did you do that?

Those outer strands in a typical crimp connection usually stay outer strands and they can fatigue and break further down the cable. Intermittent variable resistant connections paradise.

[floobydust]

It's a puzzle.  batteries test OK, doubled up wiring. I'll take a stab at it, considering there's no boats out, snow on the ground here lol.

22SI alternator terminals #1 and #2 are not supposed to be connected together. Whose idea was that.

For a simple 1-wire setup terminal #2 (SENSE) is connected to BATT(+). But Terminal #1 still needs to go to IGN via the alt diode+CHARGE lamp or a resistor substitute. This might be wrecking things i.e. the voltage regulator's diode-trio. It's only good for a few amps, you are not supposed to pull any power out of that terminal, ever.
The only way I can see the alternator over-voltaging the output is if the SENSE line is grounded or dragged down.
Left floating or not connected, some alternator's SENSE has an internal resistor so it still works as a fail-safe (output does not go to Mars like you are experiencing). Not sure about newer 22SI behaviour.
I expect both alternators have their SENSE terminal connected to the same place on the battery bank. Nothing else in the way, no switches etc.
Is there an AUX battery? What is this "Aux magnetic switch"? {edit: it's a starter relay} No diode-isolator diode thingy? Any TACH terminal used?


Soldered crimp-connections do not flex well and the strands are more susceptible to breaking. Ask the aviation industry.
This assumes a proper crimp connection, the right tool/die etc. which is rare out in the wild, but superior to soldered crimps.