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

[Michael D. Weisner]

Dave,

While I would not disconnect a heavy load while supplying power if avoidable 
just to reduce arcing or sparking, the action of removal of the load will 
not damage the diodes.  The diodes may be damaged through the application of 
a "reverse voltage" in excess of the PIV (peak inverse voltage) rating of 
the diode.  The most common way to do this in a power generation system is 
by removing the SOURCE of energy to a coil and allowing the magnetic field 
to collapse, inducing a reverse voltage to the devices attached to the coil. 
This requires a complete circuit to expose the diode to the inverse voltage. 
If the load is removed, this would not be the case.

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

From: <david.walker5 at comcast.net> Sunday, August 30, 2009 12:05 PM
> 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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