Alternator overcharging

[Robert Denis Taylor]

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

Topic

[Clark Leighs]

Tony is an expert, I am not but I agree with him.   Take it to a good repair shop and if need be is get a good marine electrician down to have a go over.

 

Just because it is a new alternator does not mean it cannot have a problem.    The problem of course could lie elsewhere.

[Tony Athens]

Why so complicated?

 

Take the alternator to a good repair shop and have it TESTED   and be sure YOU UNDERSTAND how it supposed to wired, and how the output is properly sensed

 

If the problem still persists, it’s your vessel’s boat wiring or DC power distribution system

[Author]

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