[Rhodes22-list] Wiring Q. with the electric O/B lift

[david.walker5 at comcast.net]

Michael,

Its not the operation of the alternator or magneto without a load that is damaging, its the sudden change in current through the coils at the moment of disconnect that causes a voltage spike that can blow the diodes. Low current magneto coils may not create a large spike to cause a problem but I would be very cautious about diconnecting a load from a running engine. 

I'm away right now but when I get home I'll look up a couple of references. 

Dave W
Sent from my Verizon Wireless BlackBerry

-----Original Message-----
From: "Michael D. Weisner" <mweisner at ebsmed.com>

Date: Sun, 30 Aug 2009 10:44:38 
To: The Rhodes 22 Email List<rhodes22-list at rhodes22.org>
Subject: Re: [Rhodes22-list] Wiring Q. with the electric O/B lift


David,

I do not understand how a diode rectifier configured as a half-wave, 
full-wave or bridge would be damaged if operated without a load.  These 
outboards typically utilize a magneto design and should be perfectly happy 
to operate in any condition, wired or not.  I think that Rummy was referring 
to damage of the excitation winding of an alternator design if battery 
voltage is continuously applied without the cooling provided by engine 
operation.

Mike
s/v Shanghaid'd Summer ('81)
       Nissequogue River, NY

From: <david.walker5 at comcast.net> Friday, August 28, 2009 9:13 PM
> On inboard engines and possibly bigger outboards with alternators, the 
> rectifying diodes can be blown if the load is removed.  This is why 
> battery switches for selecting battery banks (the off- 1-2-both switch) 
> will usually be a make before break design and have warnings not to switch 
> to off with the engine running.
>
> Our small outboards don't have alternators and the currents are much lower 
> so switching the battery off may not hurt it. Any way, its the diode that 
> would blow, not the coil and they are relatively easy to replace.
>
> Dave Walker
> Sent from my Verizon Wireless BlackBerry
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