I'm having trouble with new alternator.

[jlp0217]

I've been a long time reader, but this is my first post. I'm having trouble getting new alternators to work. Both my old alternators died last week, and I was able to get replacements (not exact replacements) in Prince Rupert, Canada. The new ones are "self exciting" Prestallite 8MR2069TA also known as 110-602. The salesman said just hook up the Positive, and the Tack to one of the AC lugs and we were good to go.
I did that, but got no output from the Alts. Thought maybe its because the other end of the Positive lead is a diode pack with 2 inputs and 3 outputs, start, house, and NoConnect, so we conntected the leads from the idiot lites to the positive terminal. I'm not sure now, perhaps it was late, or too many beers, but I thought it was working.
We departed Port Hardy heading for Ketchikan and after a few hours realized the start battery was well below 12 volts, and the House battery down to 12.4. We checked the alts and neither was producing any voltage.
Here in Ketchikan, I figured out that the alts are not case grounded, and learned to excite them by touching a hot lead to an AC post while the engine is running, and how to connect the idiot lights to via a relay to the AC post.
But they still do not self excite. If, after starting the engine, I touch a hot lead to an AC input, it outputs 14.3 volts, but otherwise nothing. I'm wondering if I need 12V on the Positive lead, like either routing around the diode pack, or connecting 12 Volts to the Pos terminal through a resister.

Jim

 

[Stu Jackson]

Jim,

Have you tried this?

http://www.downors.org/file/12-volt-dr-039s-alternator-handbook-free

Google 12V alternator handbook, too.

Good luck.

 

[jlp0217]

Thanks Stu,
I've read it, and now understand all the connections on my old alternator, but it wasn't much help with the new ones.

They have 4 terminals, labeled POS, NEG and 2 ACs. They're supposed to be self exciting, but no voltage is produced until I spark an AC terminal with 12 volts.

I found a diagram for connecting the idiot light on Prestolite's web site (cant find it again) using a relay with the coil connected from an AC terminal to ground, and the Normally Closed contacts connected to the light and ground.

Because the POS terminal is connected to a battery isolation diode pack, there is not 12V on the POS terminal until the alts are spinning and then excited.

Jim,

Have you tried this?

http://www.downors.org/file/12-volt-dr-039s-alternator-handbook-free

Google 12V alternator handbook, too.

Good luck.

 

[Maine Sail]

Thanks Stu,
I've read it, and now understand all the connections on my old alternator, but it wasn't much help with the new ones.

They have 4 terminals, labeled POS, NEG and 2 ACs. They're supposed to be self exciting, but no voltage is produced until I spark an AC terminal with 12 volts.

I found a diagram for connecting the idiot light on Prestolite's web site (cant find it again) using a relay with the coil connected from an AC terminal to ground, and the Normally Closed contacts connected to the light and ground.

Because the POS terminal is connected to a battery isolation diode pack, there is not 12V on the POS terminal until the alts are spinning and then excited.

Isolation diodes do no one or any battery any good.. Best to get rid of them as there are much more efficient & reliable answers for charging more than one bank today, compared to back when people used buggy whips & diode isolators of course...

 

[jlp0217]

I disconnected one battery lead and one alternator lead from the diode pack and connected them together, and started the engine. That alternator produced power.

The question remains, how should I provide 12Volts to the alternator outputs and still get the isolation from the diode pack?

 

[Charles Erwin]

Why do you want to keep diode isolation?

 

[mitiempo]

Replace the isolator with either a Xantrex Echo Charge or a Blue Seas ACR. The isolator has a voltage drop that will increase your charging time to full by a large margin - very large. The above items have no voltage drop.

 

[Charles Erwin]

Does this help? The picture is all I can come up with however self excites may use a separate jumper wire from the S to +.

Anyway since the alternator energized when you bypassed the isolation unit - maybe your isolation unit defeats the alternator self excitement logic?

 

[jlp0217]

I don't really want to keep the diode pack, but can't locate an ACR or Echo Charge or similar device here in Ketchikan. I could connect each Alternator directly to one battery, but I'd rather not. I do have an ACR for the batteries up front for the windlass and bow thruster.

 

[scallywag2]

On my westerbeke there is a fuel switch. The alternator does not generate anything until the fuel.switch senses fue
l. I took the.alternator to be Checked because my new tool did.not sense current..

 

[heart of gold]

I had a similar issue with a brand new self exciting alternator this spring with an isolating diode. It would not charge until I ran a number across the diode pack for a few seconds with then engine running and off it went charging at 26.5 volts(24V system)like it was supposed to. You can leave the diode pack in if you want after the initial excitation occurs. I read that if these alternators sit on a shelf for extended periods of time that they will lose the residual magnetism that provides the field and jumping out the diode reinstalls it. You only have to do this once.

 

[heart of gold]

Sorry that should have been "jumper across the diode pack"

 

[Maine Sail]

I had a similar issue with a brand new self exciting alternator this spring with an isolating diode. It would not charge until I ran a number across the diode pack for a few seconds with then engine running and off it went charging at 26.5 volts(24V system)like it was supposed to. You can leave the diode pack in if you want after the initial excitation occurs. I read that if these alternators sit on a shelf for extended periods of time that they will lose the residual magnetism that provides the field and jumping out the diode reinstalls it. You only have to do this once.

This is but just one of the inherent issues with diode isolators. Any charging device that needs to see a voltage to turn on, modern battery chargers, solar controllers, wind regulators and self excite/self sensed alts, don't play well with isolators because there is no voltage to "sense" on the input stud...