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Old 30-11-2008, 15:58   #1
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Alternator Field Disconnect?

Excuse my ignorance.
Can anyone tell me when and/or why I would use an Alternator Field Disconnect?
I'm sure there are reasons, I just don't know them yet.

Thanks,
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Old 30-11-2008, 16:16   #2
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I have one on my boat. I installed a large case generator, 210 Amps, and I wanted the option to disconnect it if I needed the extra horsepower in adverse conditions. My engine is 56 hp, which is good for most situations, but you never know...
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Old 30-11-2008, 16:47   #3
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Quote:
Originally Posted by Hud3 View Post
I have one on my boat. I installed a large case generator, 210 Amps, and I wanted the option to disconnect it if I needed the extra horsepower in adverse conditions. My engine is 56 hp, which is good for most situations, but you never know...
That makes sense to me.
Is it a problem if you disconnect the alternator when it is putting out maximum charge?
Is there other reasons to have a Alternator Field Disconnect?
I like your first answer.

Thanks,
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Old 30-11-2008, 16:58   #4
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If you disconnect the alternator while it's putting out current, you will fry the diodes. Some battery switches will disconnect the field before disconnecting the load, thus preventing this mishap. This also allows you to direct maximum engine power to propulsion by turning off the alternator while the engine is running.
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Old 30-11-2008, 17:32   #5
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AFD doesn't work with some alternators, like the Prestolite that used to be on our engine. Even though it is described as being field excite, the thing actually is self excite once it's making power. Turning off the field through the AFD does nothing, it just keeps on making power and would blow the diodes if disconnected from loads.
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Old 30-11-2008, 17:40   #6
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Any safe workarounds to achieve the alternator being disconnected safely?
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Old 30-11-2008, 17:45   #7
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Why do you want to do this?
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Old 30-11-2008, 18:52   #8
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Why do you want to do this?
Don't know if I do.
I am redoing ALL of my electrical (AC&DC) (never had an AC system before) and I don't know what I don't know. When I was looking for my battery switches, I did see Blue Sea makes one with an AFD. Wondering if I need it for something.
Hud's reply made sense.

So far I have purchased:
- Balmar ALT-120A 12V-SR-IG, 3.15 Inch.
- BALMAR Max Charge Digital Regulator MC-612-H
- BALMAR Alternator Temp. Sensor - Digital
- BALMAR Battery Temp. Sensor - Digital
- Zap-Stop Alternator Protector
- BALMAR Digital Duo Charge Controller c/w Battery Temp. Sensor - Digital
- PROFESSIONAL MARINER ProSafe Galvanic System & Isolator 22086
- MAGNUM ENERGY INC MS-Series Pure Sine Wave Inverter/Charger MS2012-U
- MAGNUM ENERGY INC Sensor kit-Batt- Inv/ChrgrME/MS ME-BMK
- MAGNUM ENERGY INC ME-RC25 Remote Control ME-RC50
- Blue Sea Panel 120VAC 7 Pos 2xCB/3CB/RP
- Blue Sea Panel 120VAC 3 Circuit Breaker
- And some other stuff....

Now I'm looking at a Wind Generator and see I may need a Load Diverter.
Without a doubt, my electrical system has become far more complicated then I thought it was going to be.

Any comments?

Regards,
Extemp.
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Old 30-11-2008, 18:55   #9
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Quote:
Originally Posted by Ziggy View Post
If you disconnect the alternator while it's putting out current, you will fry the diodes. Some battery switches will disconnect the field before disconnecting the load, thus preventing this mishap. This also allows you to direct maximum engine power to propulsion by turning off the alternator while the engine is running.
Do you know which switches do this?

Thanks.
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Old 30-11-2008, 18:59   #10
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Extemp: You mention you have the Balmar Max Charge Regulator. Read the instructions. Find the lug (terminal 13 - and +)that goes to an installed toggle switch in the cockpit, which you can label "Small Engine Mode". Connect it as directed and you will have what Hud is talking about.
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Old 30-11-2008, 19:51   #11
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Originally Posted by Roy M View Post
Extemp: You mention you have the Balmar Max Charge Regulator. Read the instructions. Find the lug (terminal 13 - and +)that goes to an installed toggle switch in the cockpit, which you can label "Small Engine Mode". Connect it as directed and you will have what Hud is talking about.
Thanks Roy.
Any reason why one would want to take the alternator from the 50% output to 0% output? Even when the batteries are asking for a charge.
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Old 30-11-2008, 20:50   #12
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Quote:
Originally Posted by Extemporaneous View Post
Do you know which switches do this?
Perko Heavy Duty and Marinco/Guest 2100 series (Cruiser Series Battery Selector Switch With AFD | Marinco) switches have alternator field disconnect.
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Old 30-11-2008, 20:59   #13
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Quote:
Originally Posted by Ziggy View Post
Perko Heavy Duty and Marinco/Guest 2100 series (Cruiser Series Battery Selector Switch With AFD | Marinco) switches have alternator field disconnect.
Thanks,
With what Roy was good enough to point out, still trying figure out if I could use one.

Thanks again.

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Old 01-12-2008, 04:03   #14
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For more on AFD, Goto: Alternator Field Disconnect - Resources - Blue Sea Systems
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Old 01-12-2008, 04:50   #15
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Quote:
Originally Posted by Extemporaneous View Post
Don't know if I do.
I am redoing ALL of my electrical (AC&DC) (never had an AC system before) and I don't know what I don't know. When I was looking for my battery switches, I did see Blue Sea makes one with an AFD. Wondering if I need it for something.
Hud's reply made sense.

So far I have purchased:
- Balmar ALT-120A 12V-SR-IG, 3.15 Inch.
- BALMAR Max Charge Digital Regulator MC-612-H
- BALMAR Alternator Temp. Sensor - Digital
- BALMAR Battery Temp. Sensor - Digital
- Zap-Stop Alternator Protector
- BALMAR Digital Duo Charge Controller c/w Battery Temp. Sensor - Digital
- PROFESSIONAL MARINER ProSafe Galvanic System & Isolator 22086
- MAGNUM ENERGY INC MS-Series Pure Sine Wave Inverter/Charger MS2012-U
- MAGNUM ENERGY INC Sensor kit-Batt- Inv/ChrgrME/MS ME-BMK
- MAGNUM ENERGY INC ME-RC25 Remote Control ME-RC50
- Blue Sea Panel 120VAC 7 Pos 2xCB/3CB/RP
- Blue Sea Panel 120VAC 3 Circuit Breaker
- And some other stuff....

Now I'm looking at a Wind Generator and see I may need a Load Diverter.
Without a doubt, my electrical system has become far more complicated then I thought it was going to be.

Any comments?

Regards,
Extemp.
Ain't it amazing how much stuff on a sailboat has nothing to do with the act of actually sailing?!
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