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Hi All

I'd like to set a Ram up to pull a trailer and I'd like to put a BIG alternator - 160 amps or better - in and wire it to recharge the trailer's house batteries when I drive down the road.

I've done my research and I understand - I think I understand - the different ways to isolate the two batteries, huge marine battery switches, Diodes, Constant Duty Solenoids and so on.

The sticking point right now is understanding how the alternator's output is controlled.

If I understand it correctly,the alternator output is controlled by the vehicles' computer, which monitors only the vehicle battery. So if I've been parked out in the boondocks for several days and run the trailer's house battery way down, I can start the truck with the engine battery, but as soon as the charging sytem senses that the truck's battery is fully charged, it will cut the alternator output way back instead of letting it put out a lot of amps for the trailer's house battery. Right?

Or am I missing something? Does the computer also sense the house batteries too in a dual battery set up?

And if it does and it keeps the alternator output high, how do you keep the truck battery from getting overcharged by it?

I'd love to hear from someone who's actually running such a set up successfully. Or somebody who just understands this stuff better than I do. Thanks.

Regards
John
 

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Great queston - I don't have a good answer but here is where my travels have led on this issue:

For my camping trailer and boat, both which have marine batteries, I have asked the essentially the same question you have posted to many electrical experts: can you charge your marine batts with your truck/boat alts. The answer I have always heard is that it is not a good idea (if even possible) since your alt will charge the marines too fast (even with a resister mechanism) and will lead to shorter batt lifes. I am not sure you will be able to regulate the outflow of you truck alt to keep your marines batts getting a slow, deep charge. I was never able to find a way to do this so I charge my marines with trickle charges overnight. I think part of the issue is you need a 2 (preferrably a 3) stage charger for marine batts that is not how a truck alt works.

One other thought: They now make solar marine chargers that work well - my boat has one and when it is sunny and boat sitting in its slip, they charge pretty well. Still use a plug in charger when not in the slip. I am thinking of getting someting for my trailer when it is on the road being towed.

If you do find a way to use your truck alt, please share as my guess is many would like to hear how it can be done without damaging your marines.

I hope you find something that works for you better than charging marines the old fashioned way.
 

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I've run two batteries since 98 on my 98, 2500 V10 4x4.
I bought the diesel battery tray, relocated the AIR canister (turned it),
ditched the coolant overflow and installed a V8 coolant overflow on the radiator shroud. Looks factory. I use the factory HD alternator that came on the truck, a constant-on solenoid that switches off with the key, an inline fusible link for the wire going to the alternator, and a circuit breaker on the output side of the deep cycle battery. I have a 1000cc marine starting/deep cycle for the camper battery and the factory battery for starting.
Both batteries get charged equally with no overcharging. The batteries lasted about 6 years each. Only issue I've ever had was the solenoid failed closed one time after about 8 years. Buy a good American made solenoid from NAPA. M.A.D.sells the quality wire and fusible link you will want to use to do the installation right. Good luck. This is a great mod with no drawbacks.
 
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