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Old 01-15-2016, 01:13 PM
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Adam Gardiner Adam Gardiner is offline
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2nd alternator wiring on off road truck

I'm helping a friend fit a suzuki grand vitara 2.5v6 into his off road truck. He wants a 2nd alternator for charging the batteries as a single one is not big enough for his winches etc. So I've drawn a quick sketch of how I think it should be done. Obviously we have the red fia style battery master switch fitted which kills all power when turned off and then earth's the engine alternator through a resistor. He said that the 2nd alternator he used to have on the old engine ran straight to the battery and not through the kill switch. This said I think it should be wired as the sketch below.

My thinking is if I wire the 2nd alternator back to the battery direct and run the charge light through a relay which is switched by the ignition this will be ok

Any thoughts on this

Regards

Adam
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Old 01-15-2016, 01:58 PM
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You might consider that in many if not most situations you 'may' only need the original alternator. If the second is triggered with a switch in the cab then the second Alt can idle and not use any of the engine power when not needed...

E
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Old 01-15-2016, 02:11 PM
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I don't understand your diagram for the master switch. Also I'm not sure what the circle with "X" represents on what I assume are the field wires for the two alternators?

I'm definitely no electrical engineer or expert on alterantors, but assuming each alternator has it's own voltage regulator, what I think is going to happen with this system is one alternator, likely whichever has the higher voltage regulation setpoint, is going to kick in and supply pretty much all the current it can before the voltage starts to drop with a high enough load. At that point, the second alternator will start to kick in supplying whatever current is needed on top of what the first alternator supplies in order to maintain voltage. I don't think they will equally share the current load - one will max out first then the other will start adding.

What I would like to know is if you have an external voltage regulator, if you could have it control the field for both alternators at the same time so they equally share the load. This would prevent one alternator from being maxed out any time you load heavily.

All speculation on my part.
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Old 01-15-2016, 02:14 PM
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Digging around just a bit, it appears they make specialized voltage regulators for this situation: http://www.downwindmarine.com/Balmar...-90892605.html
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Old 01-15-2016, 04:32 PM
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The x in a circle is the symbol for the warning lamp. And the master switch is using a normally open switch to turn battery voltage on to the car and a normally closed switch to break the (switched voltage) to earth connection. If you don't have the normally closed switch the engine will continue to run with the voltage supplied from the alternator if you disconnect the battery.
When you turn the switch off it closes the normally closed switch which puts the voltage to ground through the resistor
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Old 01-15-2016, 04:45 PM
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How is the field power supplied to the alternator? That normally closed circuit through the resistor will not stop the alternator from powering its own field from what I see in this diagram. I'd expect it to keep running.
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Old 01-15-2016, 05:08 PM
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The alternator he has only has 2 connections. I will get the terminal numbers sunday when I get to the truck
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Old 01-15-2016, 05:51 PM
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Here are some disconnect switch options I outlined in this post.

Quote:
Originally Posted by TheBandit
Master disconnect wiring was a topic of interest for me. There are three conventional ways of accomplishing this:
Method 1: Run a STSP (single throw, single pole) disconnect switch and run on dedicated, heavy gauge charge wire from battery positive terminal to the alternator and a separate heavy gauge wire from the disconnect switch to the rest of the vehicle. When the switch is opened, the alternator can charge the battery, but can't keep the engine running so everything shuts down. There are two disadvantages to this method: (1) the heavy gauge alternator cable is kept hot by the battery even with the switch is open and (2) it requires two heavy gauge wires to the back of the car.
Method 2: Run a STDP (single throw, double pole) disconnect switch. For one pole, run a heavy gauge wire to the starter and rest of the vehicle. For the other pole, run a heavy gauge wire to the alternator charge wire. Compared to method 1, this has the advantage of eliminating a hot wire to the front of the vehicle, but still requires two heavy gauge wires and violates the current limitations for most STDP disconnect switches where the second pole is typically only rated to around 20amps.
Method 3: My favorite of the conventional wiring methods is this method. You run a STDP disconnect switch. For one pole, you run heavy gauge wire to the starter, alternator charge line and the rest of the vehicle. You run the other pole in series with the alternator field wire. This allow use of a light gauge wire because the field line for the alternator is relatively low current. When the switch is open, no wires are hot forward of the battery/disconnect area.
Method 3 can't be used for an internally regulated alternator, so you may be left with method 1 or 2. Or you can do something like what I plan to do and cut power to the ignition.
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Old 01-26-2016, 09:14 AM
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Thankyou for the replies. I actually had the information wrong he is running 2 alternators but to 2 different batteries so they are not attached together. I have a feed from the battery to alternator and switched the 2nd warning light/exciter wire through a relay.

Thanks again for the replys

Adam
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