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Old 05-18-2019, 07:24 AM   #1
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Dual alternator charging?

Has anyone added a second alternator? I am considering adding a second 300 amp alternator to my new tow vehicle for charging the house batteries. Looking at the cost of solar it seems like an economical way to charge the house batteries without adding the weight of a generator to the 5th wheel. My new truck already has the high idle installed, but it's mainly just to keep the batteries charged when traveling. If it works well I may use it a couple of months a year for boondocking.
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Old 05-18-2019, 07:45 AM   #2
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No. I do not belive they would provide any value to an rv battery. The length of run from hood to bumper, thru a plug in connector and the length to your rv battery, all on a ( usually) 14 guage wire. The resistance of that would keep your charge rate down to 10 amps or less.
Go solar or rely on your rv charger.
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Old 05-18-2019, 08:00 AM   #3
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I'm not sure you could utilize the capacity of a 2nd alternator. You didn't say what the capacity of the house batteries were, but nominal charge current is 10% of capacity so for bank of 4 GC2's that's about 50A. Getting that current from the front to the back will take either a heavy cable or remote sensing. Boondocking is another consideration, it's not the most practical thing to idle a tow vehicle for hours on end for a few hundred watts of power. A small inverter genset would check a lot of boxes there. Solar is a whole 'nother kettle of fish and I wouldn't go down that road unless you knew you really wanted it.

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Old 05-18-2019, 08:14 AM   #4
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Mark has it nailed. Batteries (in this case lead/acid) limit charge current to a fraction of the 300 amps. Wire from alternator to TT connector would have to be huge. 7 Pin plug could not handle it. TT wiring could not handle it.
A more reasonable alternator size should be between 30 and 60 amps. Even 60 amps would require unusual tow vehicle wiring and a special electronics to control the charge voltage at the battery terminals.
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Old 05-18-2019, 08:20 AM   #5
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I have 400 amp hours now of flooded cell batteries now. I am thinking of replacing with a minimum of 4- 100 amp Battle Born lithium batteries.
I really am not sure how many amps I could run through 20' of 1 AWG welding lead cable from the second alternator. I may only be able to utilize a second 150 amp alternator. I definitely am going to need a professional to design the system. Because I am thinking lithium batteries I would think a second alternator set up to charge at the correct voltage would be best.
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Old 05-18-2019, 09:03 AM   #6
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No affiliation, but this kit is what got me interested in the idea.

https://www.nationsstarteralternator...mddk-300xp.htm

I don't see a available kit for a 2019, but I am sure somthing could be fabricated.
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Old 05-19-2019, 01:25 PM   #7
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No affiliation, but this kit is what got me interested in the idea.

https://www.nationsstarteralternator...mddk-300xp.htm

I don't see a available kit for a 2019, but I am sure somthing could be fabricated.
The Battle Born batteries you mention have their own battery management system. I think they require 13.6 to 14.4 volts to work properly. Automotive alternators usually supply that voltage.
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Old 05-19-2019, 01:30 PM   #8
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Quote:
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I have 400 amp hours now of flooded cell batteries now. I am thinking of replacing with a minimum of 4- 100 amp Battle Born lithium batteries.
I really am not sure how many amps I could run through 20' of 1 AWG welding lead cable from the second alternator. I may only be able to utilize a second 150 amp alternator. I definitely am going to need a professional to design the system. Because I am thinking lithium batteries I would think a second alternator set up to charge at the correct voltage would be best.
400 Ah of BB batteries sounds like my dreams. I don't know how much they will draw when charging, but 1 AWG should work very well. They are an excellent match for tow vehicle charging.
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Old 05-19-2019, 05:22 PM   #9
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My truck came with the high idle option. I didn't even realize there is a second 220 amp alternator option from the factory. I already have alot on my plate for the next couple of months, but I really would like utililize the truck instead of a generator or solar to charge the house batteries. Right now only the fridge and lightning are running off the batteries, but I could see running one of the air conditioning with a second 3000 watt inverter and some more batteries.
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Old 05-19-2019, 06:29 PM   #10
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4 BB's can theoretically take 1C or 400 amps when charging. Of course your 1 AWG charging wire will not support that rate, especially when you consider the length of the cable between the alternator and batteries.
https://www.wirebarn.com/Wire-Calculator-_ep_41.html
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Old 05-19-2019, 08:18 PM   #11
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It looks like by that chart, I should use 00 gauge if I want to utilize the charging of more then 150 amps at 20 feet.
That's a little disappointing, because I would of liked to just use the welding lead connectors for connecting at the bed of the truck.
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Old 05-19-2019, 08:54 PM   #12
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It looks like by that chart, I should use 00 gauge if I want to utilize the charging of more then 150 amps at 20 feet.
That's a little disappointing, because I would of liked to just use the welding lead connectors for connecting at the bed of the truck.
Here's a better chart. Bear in mind you have to figure it for round trip, meaning if your batteries are 20 ft away, you will need to figure for 40 ft.
Another way is a Honda 2200 inverter generator, weighs less than 50 lbs, and if you have the proper charger or inverter/charger, it can supply a 140 amp charge to your battery bank.
If you need to recharge 200 amp hours, should be able to do it in less than 2 hours on less than a gallon of gas.
You can leave the generator in your truck and just plug the trailer power cord into it.
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Old 05-19-2019, 09:31 PM   #13
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That may make the most sense. I have 3500 watt Champion inverter generator that runs off lp, or gas. I was just looking for a way to do it without the weight or Inconvenience. I can't justify solar unless I was going to boondock alot in a sunny location. The residential fridge is 7.5 amps and that would require a lot of solar.
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Old 05-19-2019, 09:45 PM   #14
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That may make the most sense. I have 3500 watt Champion inverter generator that runs off lp, or gas. I was just looking for a way to do it without the weight or Inconvenience. I can't justify solar unless I was going to boondock alot in a sunny location. The residential fridge is 7.5 amps and that would require a lot of solar.
Yes agree, probably need over a 1000 watts on the roof, but the Battle Born's make a lot of sense, you can charge them up in an hour or two instead of 4 or 5 with lead acid, and never worry about bringing them up to 100%
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