6-71TI alternator testing advice.

[hcalmar]

1979 37C with 6-71TI Covington( I think) Belt driven alternators. 12V system.
Not sure where to start. Been chasing gremlins all spring. On a cruise yesterday to check the starboard engine which was running hot ( but much better, though not perfect, after using Genesis’ phosphoric acid process) I noticed the port volt meter was right at 12V, starboard was showing 14V. (Engine off battery tests at 12.8V) With my engine & generator running and the Xantrex charger on it was showing 14V and the starboard 16V. I think I had this problem at the very end of last year but attributed it to a pretty dead port battery after the boat was on the mooring for a while. I am pretty sure the port battery is not charging when the engine is running. I always be have to tap the voltmeter at start up to get it to jump off of 0.

Of course access to the port alternator is difficult unless you're a thin guy. But I can see it. It is belt driven and there is an electronic package about the size of a pack of cards hanging off the back. I've read all the related posts going back to 2009. But I am still not sure how to test it before I hire a thin guy to take it out.

I should note that my hour meters stopped working a couple of years ago because of a pair of bad oil pressure sensors. They were not connected to my ignition switches. I do not have fuel pressure sensors as far as I know. I am not sure where the alternator gets the 12V excite if it does at all.

I have a voltmeter. What testing can I do in place before I am compelled to pull it out of the boat?

Thanks in advance.

 

[Genesis]

Some are internally excited and some are not; depends on what you have installed. The flange-driven ones typically found on 92-series are internally-excited.

If yours are externally-excited then the usual source is a pressure switch on the secondary fuel filter canister, the same location (and could be the same circuit) used to energize the hobbs meter.

 

[hcalmar]

Thanks Genesis. Pretty sure my Hobbs meter lead goes to the oil pressure switch. There are two piggybacked with one wire going to the helm.

 

[hcalmar]

Re: 6-71TI alternator testing advice. Now I am really confused.

Barely moved the boat last year. Lots of Generator time. Maybe both alternators are off? But my gauges were both reading @14v running last year.
Alternator has three wires. Two heavy gauge and one that runs from ground on the bracket to a cylinder like a roll of quarters to the alternator. Has a red square plug that says " pull to set voltage". The thin wire is connected at the same spot as the heavy gauge black wire. The third spot on the alternator to attach a wire is empty.

Note house is on the port batt/ Genset on the starboard batty
Readings:

12.38/12.78 Cold
12.34/12.68 Running - Helm reads 12/14
12.70/13.68 Genset running charger off
13.80/13.85 Genset and charger on
12.30/13.60 Cold generator off
Thanks Hal

 

[dsharp]

That pack of cigarette thing hanging off the back is probably the regulator. There should be a delco wiring diagram on the net. A lot of them use a fuel pressure or oil pressure switch to energize the alternator.

 

[Nick]

Hal,

I think you and I have the same setup of engines/alternators. The alternator on mine is not connected to a fuel or oil pressure switch. It is excited internally.

Check the belt and make sure it is tight.

With the battery charger off, and the inverter off, check the voltage at the battery. Start the engine and run it fast idle for a few minutes. Measure the voltage at the battery and it should be 14V +-.

I had the port alternator rebuilt a few years ago by a local shop and yes it is tough to get at. It is a 2 man job because it is heavy and in a tight spot. One person in the bilge and one up top to set it in place.

 

[hcalmar]

I have Delco-Remy alternators. Neither work. Pulled the easy one to get it tested. Two heavy gauge wires Pos/Neg to two different posts. Then a small wire from Pos to the round cylinder thing to ground on the alternator. Could it be a capacitor that stores a charge to excite?

Funny thing. 12.68 at the battery but nothing at Pos on the alternator. I assumed it would be a straight run from the battery. Where does pos from the alternator go? Is there a fuse?
Hal

 

[seasalt]

I had a pair of Covington 6-71 TIBs and one engine intermittently showed 12 volts. What I found was a corroded spade connector on the alternator or regulator (can't remember).

Grab each one see if any fall off in your hand like mine did.

 

[Jim saco]

There are fuses. There inside the main fuse panel in the engine room. Remove the large panel under your battery switches. Mine are fused at 70 amps with anl fuses.

 

[Genesis]

Yep -- my boat had ANL 80 Amp fuses in the alternator feed lines to the main DC bus.