Seeking Honda alternator wiring advice

I use a 6 post switch, presumably that is what is posted above. The big posts on the switch are used to interrupt the connection from the battery to the starter. Power into the fuse box is removed from the battery terminal and attached to the to the post on the starter. Two of the small posts are used to interrupt the ignition wire, this wire is found under the engine bay fuse box and should be white with black stripe. The remaining two posts can be used for the resistor which must not be too important as I've never used it.
 
If you disconnect the battery while an alternator-equipped engine is running, the alternator could be damaged by a
voltage spike.
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Can anyone explain that? What causes this "voltage spike", and how does it damage the alternator? When the battery gets disconnected, the only source of current is the alternator itself, isn't it? When I turn off the ignition key, is there a similar voltage spike? Why not?
 
Mike, I'm gonna take a guess at this to get the ball rolling.

The battery is soaking up a considerable amount of the alternator output 'power'. If you turn off the battery "load" from of the alternator, the output will suddenly SPIKE well above normal and because the output is not protected by any kind of surge protecttion, it might be damaged. Notice in all of the discussions about this the operative word is "COULD" "MAY" "MIGHT" be damaged.

I think the bigger concern is, with an Alternator, turning off the battery power will NOT turn off the car.
 
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I think that Mr. Broadhead's last sentence addresses the crux of the matter.

The "kill switch" is required by the rules for the express purpose of "killing" all electrical power to the vehicle if a situation occurs such as a collision or roll over. The emergency response personnel need to have a single action that removes all electrical potential. With the engine running, an alternator can continue to provide electricity even if the battery is removed from the vehicle. It can, in fact, provide enough electrical energy to arc weld in a sort of Fred Flintstone fashion. Don't ask how I know...
 
Trout

I am not sure but back when meditation was all the rage everyone's mantra was ohm.....ohm......ohm

Just guessing this is the answer when the battery is removed.
 
Certainly, the point of the kill switch is to get the car shut off, and I understand that.

What I'm asking about is the warning that the failure to use the resistor causes "a surge" that might "burn out the alternator". I want to come to understand the mechanism by which the surge is generated and how it harms the alternator.

I expect the alternator to have a regulator that limits the output of the alternator to about 14.5 volts or so.

The alternator (itself) is a pretty beefy piece of equipment; heavy windings on a core that makes a three-phase generator. Large diodes rectify the current, a big regulator takes care of keeping the produced voltage under a sensible limit. While the semiconductors might susceptible to transient voltages, the alternator itself shouldn't be. And even so, the semiconductors are designed to perform in the harsh automotive environment so they're very beefy themselves.

The resistor provided is rated at 11 watts and has a resistance of 3 ohms. At 12 volts, 11 watts is just less than one amp (because Ohm tells us that P = E*I). 3 ohms load on 12 volts is 4 amps, though (because I = E/R). It would seem the resistor really isn't good enough to put enough load on the alternator to shut down the engine, either, as 12 watts is less than 1/50th of a horsepower, and even the smallest alternator is rated at more than 300 watts or so.

So why is this apparently-underrated resistor so important to avoid surges if it can't even withstand the power produced in the normal operating voltage of the circuit where it's employed?
 
I've never understood it either. I've had trucks, tractors, construction equipment and cars run on after the diesel engine was shut down and no damage done to the alternator. I think a generator system is more suseptable but even those situations had no damage. I have had systems run on after the battery kill switch was shut off because the alternator was not removed from the circuit at the same time so power was still being provided to the fuel shut off solenoid. So the battery kill switch should actually be referred to as a system kills switch and power output from the battery and the alternator needs to be shut off to both the charging and the main electrical curcuits.
 
Your battery does more than just yield electricity. It also shorts AC, spikes and transients to ground. Removing the battery from the circuit allows those spikes and transients to travel around, endangering every semiconductor circuit in your car. The ECU, the speed sensitive steering, the memory seat adjustments, the cruise control, and even the car's stereo. Even if your computers and stereo remain intact, in a great many cases removing the battery burns out the diodes in the alternator, necessitating a new alternator. If disconnecting the battery interferes with the voltage regulator's control voltage input, it's even possible for the alternator to put out hundreds of volts, frying everything

Actually, most alternators can sustain voltages approaching 30 volts. The diodes are generally rated at 200 volts. The key is the regulator (which is INSIDE the alternator). It doesn't really 'want" to see a voltage greater than 20 volts continously.

Keep in mind....."COULD" "MAY" "MIGHT" be damaged. You just don't know what's gonna happen so why take the chance?
 
Thanks for the explanation, Richard! I can buy that the battery acts as a giant filter capacitor to remove transients and low-frequency noise from the alternator's supply.
 
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