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Old 20-07-2015, 06:34   #1
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Connect exciter/field wire while running the alternator

Hi,

I plan to put in a switch for exciter/field wire. The wire runs from the ALT to the starter panel and via a 100 ohm resistor and a LED diode.

As far as I know its not a problem to:
a) disconnect exciter wire before starting the engine
b) disconnect exciter wire while running (since the ALT is selfexciting at this point)

So, to my question.
If I accidently connects the exciter cable while running, what will happen and is it problem? Will it start to charge?

The make of the ALT is Paris Rohne 50 AMP (A13N2M)

GO!
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Old 20-07-2015, 06:43   #2
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Re: Connect exciter/field wire while running the alternator

If you disconnect the field wire while the alternator is running, it will cease to charge (ie no output voltage).

If you reconnect it while running, the alternator will begin charging again.
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Old 20-07-2015, 07:19   #3
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Re: Connect exciter/field wire while running the alternator

Assuming the existing Excite circuit goes from the engine ignition switch to the AUX terminal on the Alternator (via the LED "idiot" light and a resister) and nothing else is connected to this circuit, you should be able to manually control the circuit with no ill effects on the alternator. Some Excite circuits are activated by the oil pressure switch or other automatic means. I'm not sure what would happen with some of these different configurations.
The obvious question is why do you want to manually control this circuit? If the reason is the "idiot" light does not extinguish when the alternator is outputting, this can usually corrected by increasing the wattage of the light or the resistance of the resistor.
Without knowing what problem you are trying solve, it seems this is just making a simple operation unnecessarily complex.

John
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Old 20-07-2015, 07:32   #4
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Re: Connect exciter/field wire while running the alternator

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Originally Posted by jstevens View Post
Assuming the existing Excite circuit goes from the engine ignition switch to the AUX terminal on the Alternator (via the LED "idiot" light and a resister) and nothing else is connected to this circuit, you should be able to manually control the circuit with no ill effects on the alternator. Some Excite circuits are activated by the oil pressure switch or other automatic means. I'm not sure what would happen with some of these different configurations.
The obvious question is why do you want to manually control this circuit? If the reason is the "idiot" light does not extinguish when the alternator is outputting, this can usually corrected by increasing the wattage of the light or the resistance of the resistor.
Without knowing what problem you are trying solve, it seems this is just making a simple operation unnecessarily complex.

John
The exciter wire is not connected to anything else. The idiot light does extinguish when charging. No problem.

I gues im worried overcharging. And I thinks its a knee-jerk reaction. But I guess I have to trust the internal regulator to take care of my precious AGM batteries.
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Old 20-07-2015, 07:52   #5
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Re: Connect exciter/field wire while running the alternator

"I gues im worried overcharging."
In that case disconnecting the Excite circuit while the alternator is outputting should have no effect on the charging, as that is controlled by the regulator via the field circuit. With alternator outputting there is no current in the Excite circuit as the voltage at each end of the circuit is the same. That's why the "idiot" light goes out.

If the internal regulator on the alternator cannot be set to properly charge AGM batteries you do have a potential problem. I killed a set of AGMs that way.

Usually there is a way to bypass the internal regulator and connect an external one that will protect your batteries.

John

Edited to Add: Even if you start the engine with the Excite circuit disconnected, the alternator will likely start to charge once you bring the engine up to cruising RPMs.
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Old 20-07-2015, 12:54   #6
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Re: Connect exciter/field wire while running the alternator

All that assumes that it IS an exciter circuit. If it is remote sense, disconnecting it could boil your batteries dry.
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Old 20-07-2015, 13:28   #7
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Re: Connect exciter/field wire while running the alternator

So since your question is answered you can do it the hard way if you want to. Probably something the next owner of the boat or a surveyor will find fishy... Or spend a few dollars and do the best thing for your batteries and install a regulator. Something like a Balmar ARS-5 has a program to limit the amps going in to your battery and limit the voltage so your batteries don't get overcharged.
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Old 20-07-2015, 14:13   #8
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Re: Connect exciter/field wire while running the alternator

Quote:
Originally Posted by Golden Orchid View Post
Hi,

I plan to put in a switch for exciter/field wire. The wire runs from the ALT to the starter panel and via a 100 ohm resistor and a LED diode.

As far as I know its not a problem to:
a) disconnect exciter wire before starting the engine
b) disconnect exciter wire while running (since the ALT is selfexciting at this point)

So, to my question.
If I accidently connects the exciter cable while running, what will happen and is it problem? Will it start to charge?

The make of the ALT is Paris Rohne 50 AMP (A13N2M)

GO!
It was/is common practice on local fishing boats to do this with Delco Remy 10SI series. The switch was usually a relay contact & relay was turned "on" thru an oil pressure switch. Powering the field wire directly by the contacts of oil pressure switch resulted in early burn out of o/p swx contacts,but it worked.

I don't see why it wouldn't work fine with a Paris Rohne or similar alt.

But take note of jstevens comments re-charging AGM's. No personal experience with AGM's but I am led to believe by many posters that AGM's require a 3 stage regulator to charge properly & last.
Your Paris Rohne has a replaceable internal regulator assy,readily available,& it probably can be "bypassed/adapted" so that your alt. is regulated by an ext.reg.-no personal exp. on this.

Cheers / Len
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Old 20-07-2015, 14:25   #9
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Re: Connect exciter/field wire while running the alternator

Had an off/on switch on many of my boats with no ill effects. Had regulators though, no other resistor!
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Old 20-07-2015, 14:33   #10
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Re: Connect exciter/field wire while running the alternator

Quote:
Originally Posted by Golden Orchid View Post
The exciter wire is not connected to anything else. The idiot light does extinguish when charging. No problem.

I gues im worried overcharging. And I thinks its a knee-jerk reaction. But I guess I have to trust the internal regulator to take care of my precious AGM batteries.
Seems like a band aid approach to a problem that probably doesn't even exist. If that is your worry why don't get the proper regulator?
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Old 20-07-2015, 15:05   #11
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Re: Connect exciter/field wire while running the alternator

I guess I didn't understand the OP. You are trying to charge without a regulator? Rather than just switch the regulator off and on?
My guess you will burn up the alternator or a battery soon. One distraction and you're done....
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Old 22-07-2015, 14:16   #12
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Re: Connect exciter/field wire while running the alternator

Why don't you install a Smart Regulator. I use Next Step and my precious AGM batteries are over 12 years old. You can Google them and other makes.
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