Dual atlernators

Hi guys has anybody done or got pics of the finished project of fitting twin alternators to a 4 litre '95 sport with air and steer?
I have seen one advertised on ebay with twins fitted but I didn't get to see how it was done.
Cheers, Junglejuice

junglejuice said:

Hi guys has anybody done or got pics of the finished project of fitting twin alternators to a 4 litre '95 sport with air and steer?
I have seen one advertised on ebay with twins fitted but I didn't get to see how it was done.
Cheers, Junglejuice

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It would probably have been done with the second alternator mounted in place of the aircon compressor, which therefore means that the aircon would have been deleted.

It's also possible to fabricate a bracket to mount it underheath the aircon (on LHD models anyhow - I'm not sure about RHD) in a similar fashion to mounting a York for OBA. However, this would require the addition of at least one idler pully (to get enough wrap around the alternator pully) and you'd have to measure for a new belt.

You can simplify wiring for the second alternator by using a "self-exciting" Delco unit, since it's a one-wire hookup. The regulator is internal to the alternator, and both units will simply use a common ground.

Might I ask why for do you want the second alternator? Only because it may not be the best approach to the problem you are trying to solve, or an incompleat approach, and I'd like to help you out if I can.

Thanks for the response, I have an issue with the charging voltage for my second battery which is an AGM 120a/h unit mounted in the rear when we go touring and it requires a higher charge voltage than a standard battery (14.4-15v), so there in lies the problem, how to get the voltage up for the second battery and allow for voltage drop to the rear of the car without frying the computer or boiling the standard battery.
I have two options that I am looking into, firstly a second alternator set to a higher voltage and as you stated using a common ground.
Or secondly fabricate a dc-dc power supply that will be installed inline with the second battery and be of the switchmode regulated variety set to 15v with the feedback circuit connected to the second battery directly to achieve correct regulation taking into account the voltage drop of the circuit....
I am exploring both options at the moment to see which is the best for my needs....

option #3
new battery which doesn't require the higher voltage to charge properly.
seems the AGM may serve a particular purpose for you, but if it doesn't and is just your 2nd battery, why not replace it as opposed to building a system around it?

AGM batteries are the best for running fridges, plus they are sealed so they give off no fumes which is important when the battery is fitted in the rear of the cabin, they require no charging when not in use even for a year.
So there is plenty of good reasons but the other one is that I have one and here they are worth $$$$ and I got it for less than a good quality standard car battery.....

junglejuice said:

AGM batteries are the best for running fridges, plus they are sealed so they give off no fumes which is important when the battery is fitted in the rear of the cabin, they require no charging when not in use even for a year.
So there is plenty of good reasons but the other one is that I have one and here they are worth $$$$ and I got it for less than a good quality standard car battery.....

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Not quite true. ANY lead acid battery will give off Hydrogen when being charged and can give off Sulfer Dioxide if it becomes Sulfated.

Don't beleive? spray some soapy water on the little gray "vent filter" thingies on an Optima while its charging. Bubble, bubble bubble.

Make sure you vent any battery in the cabin to the outside of the car.

Dc to dc is the only way your going to get 15 volts to the rear of the XJ.
Even with 2 alt the run to the back will drop your voltage some and that at best isw 13.75 at the alt. You could use an externally regulated type secondary alt and custom make a regulator set to 15.75 volts or so.
If you have a big load on the factory alt now. The higher voltage secondary alt would be the way to go becouse dc to dc suck amps big time.

Switchmode dc-dc converters are pretty efficient (typically around 90%) and with this AGM battery requiring a maximum charge current of 32A so some quick maths would suggest that 32a @ 15v = 480w so at a supply of say 12v would equate to 40a and allowing for losses in the supply would give us around 44a, of course the higher the voltage on the supply side the lower the current draw...
I will have to test my twin Waeco's to see how they will go on 15v....