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The starter is isolated when you turn the key to start unlike the winch. Have you notice the electronics, gauges, radio ect., are off while starting the vehicle?

Batteries will not eliminate spikes.



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Here is another way using a combiner You might want to do a search on combining batteries. Some good reading out there.

I would rather use a battery combiner than the relay mention in Kris's post, but they are a few bucks more. On the other hand, by using the relay, you have a quick way to jump start your vehicle without using jumper cables as would be the case using the combiner.

Here some food for thought, if you would like to run the engine while winching, I would suggest that you move the charging wire, from the alternator, to your second battery. Isolate the two batteries while winching using the switch I recommended. This will protect the electronics.

Lots of possible approaches...

Why I would isolate: If I wanted to run a load that drained a battery significantly but wanted to be sure I still had sufficient power to crank the engine.

Why not? The engine should be running when winching.. If not its dead (the engine) and cranking it over is not a big issue.

The other would be that your primary battery is not a deep cycle and a long winching cycle would reduce its life.

Decent reason if you winch a lot. A better solution being two deep cycle batteries.

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.

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.

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.

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.

So far starting my vehicle has not caused any problems... There are a number of other tricks and tips to putting together a robust system, at some point its overkill.

A good way to find out how far you need to go is to put a acope across the battery terminals. Many people ignore these details and never have a problem. If it were my vehicle I would verify.


Kevin

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?



Are you talking about a relay provided by the winch company?



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?



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.

Just to further clarify (or muddy the waters), how about looking at what Mitsu does from the factory? On the diesels that have two batteries, Mitsu simply put them in parallel, so that the truck would see one big battery, but with large cranking amps, for firing the glowplug system. When replacing a battery system like this, you replace both at the same time, so that one doesn't draw down the other.

I went with two yellow tops, so I'd have lots of amp-hours, in addition to good CCAs.

But this doesn't really solve the problem if you want to run a battery for extended periods with no charge going to it. I wanted an aux batt too, so I used a separator from SurePower, which has a priority start function. Here's the unit: http://www.ase-supply.com/product_p/sp-1314.htm . I ran a 1/0 cable from the main battery bank (since the optimas are parallelled, it didn't matter which one connected to the separator) back to my rear battery. I also grounded the rear battery. This separator compares the signal from the main battery and the aux after startup, and when the main has reached sufficient voltage (~13.7v I think?), it then parallels the two batteries (or in my case three), and all are charged. When the ignition is turned off, the batteries are separated again, allowing you to run your aux down if you want to, and still start your vehicle on the main bank. Another cool feature is if, when it compares voltages, it finds your aux higher than your main (say you left your lights on), it will parallel the two banks on startup, essentially enabling you to give yourself a boost, if need be.



Food for thought anyway. All depends on how you want to use your aux battery.

Yes




The alternator has two types of diodes. One is for current rectification the other is to shunt excess voltages to ground in the case of a load dump.

A winch can draw a lot more current than the alternator can supply. In the case of a long pull having the batteries in parallel doubles your capacity and maintains a higher voltage to the winch. It also reduces the level that the batteries are cycled to.

As far as sizing a capacitor I have not gone through the numbers. My experience is in designing much smaller circuits, but the theories are the same as are the failure modes. Typically the capacitor is not a very large value.

Large value capacitors in theory could do the job but have a high ESR so they are not effective as absorbing a fast changing transient voltage.

In my Raider there is nothing isolating the starter from the rest of the vehicle. I have never seen a vehicle that had a different setup.

I know theory but IÆm not an automotive EEà However I have worked on similar issues on industrial equipment.

http://en.wikipedia.org/wiki/Load_dump

Have you ever notice when you turn the key to the start position that anything that is ignition activated inside the vehicle shuts off, dash instrument lights, radio, cigarette lighter socket ,etc? That's isolation.

How about the ECU for fuel injection? <img src="/forums/images/graemlins/smile.gif" alt="" />

For that matter the alternator, brake lights, ignition and the gauges (meter circuit) on my Raider are all live during cranking.

Your right some accessories do disconnect from the battery during cranking. My understanding was that itÆs to allow max power to be available for starting and not for isolation. Turn off the headlights more powr to cranks... Good to have the radio off so you can hear the engine start.

Critical systems you needed to make the vehicle function are all live with no special isolation when the vehicle is being cranked over.

Kevin

ECU power path is somewhat different in ign ST vs. ign ON positions, since the ecu control relay bypasses the ecu control of the fuel pump in cranking. My gauges work in start, too. I always crank the motor with the coil grounded after oil changes until I see good pressure on the gauge to avoid start up scuffing.

Otherwise, I agree with Kevin, as usual.

1)How big of a circuit breakers should i use?

2)How big should the Amp Value of the isolator be?
The same as alternator output?
Or much more to handle additional electronics?



Please....just some straight forward answers.