Jumpre cables :-) Actually it takes a second or two to get the
alternator up to full current. The main thing is that once the
regulator starts putting out a significant current and the circuit is
broken, the regulator can't drop the field current fast enough to
protect the diodes.

With a starter battery, the alternator is usually only topping off the
battery for what was needed to start the engine which only takes a few
minutes. After that the load is just the other devices on the system
and disconnecting the battery makes little difference. An alternator
recharging a house battery bank could be putting out many amps for an
hour or more. This is one of the major differences between a normal
automotive alternator and a true "marine" (read EMT, utility or
industrial) alternator. In comparison an automotive alternator has it
real easy.

Also, the voltage is directly related to the number of flux lines broken
by the coil wires. When the field current stops the magnetic field
collapses and then the number of flux lines broken is the combination of
the coil rotation and the collapsing field. The result can be a spike.

johnh wrote:
If he's "running the engine while the battery is disconnected," but he
didn't disconnect while it was running, I'm wondering how he got it started.

"Glenn Ashmore" wrote in message
...


SAIL LOCO wrote:

What does fry diodes is breaking the
output circuit WHILE the alternator is producing current

I think that's what the poster said:

I didn't read it that way.

HE said "running the engine while the battery is disconnected."

I am talking about disconecting the battery while the engine is running.

BIG difference.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com







--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com