quote] What I would go with: Two deep cycles batteries (starting capable) in parallel with no fancy isolation switch. An issue with letting one drain without the other is charging them. OT me it makes more sense to let them both run the load and dischage to the same voltage level. A good practice is to make sure they are both in good condition and similar chemistry. [/quote]
You will be taxing two batteries instead of one. Why not tax one? The only thing you will gain is Amp Hours so why not run the engine like you suggested to pick up the slack?
As far as spikes and surges go: The winch motor can draw a lot of current. When you turn it off the load side of the motor ( connected to the windings) will see a large inductive voltage spike. The good thing is the relay contaces isolate the rest of the sytem from the motors windings as the relay opens. A good desing practice is some sype of filter across the relay contacts. Your relay should have this built in.
Are you talking about a relay provided by the winch company?
On the battery side you will also see an inductive spike. This is caused by the power cables since they are carrying current and will generate field.
Once the current is shut off this field collapses generating a voltage. The greater the current and the more inductance your cabling has the greater the level of a spike you get.
This says your winch power relay should have short cables to the battery to it to reduce the inductance.
The batteries will absorb some of this spike but their resistance goes up with the voltage. A good way to shunt this voltage is with some type of protection diode and or a capacitor that has a low ESR.
I do agree short cables are best, but where would you put a protection diode and what type of diode would you use? Also where would you place the capacitor? It would have to be quite large to handle the current, right?
The alternator has protection diodes built in to it as do almost all vehicle electronics. Remember your starter motor is connected to the battery and will do the same thing. The size of the pulse again depends on the current draw and the inductance of the cables.
I thought the diodes job was protecting the battery and converting AC to DC, not to protect the alternator. I will do some research.
The starter motor is isolated form the vehicles sensitive electronics when you start the vehicle.
