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Old 04-28-2010, 12:36 PM   #1
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Wiring a separate alternator for charging trailer batteries

I would like to get some feedback on a project that I have just finished. This project was a take-off from information that I found through other threads like the one started by Jammer(thanks for the idea)

i just finished an installation and wiring for a second isolated alternator for charging only the batteries within the RV. i had two goals in mind.... to not only improve the ability to fully charge the RV batteries but, to do it efficiently during a short trip to a new camping site...a couple of hour drive, and then to later add an inverter which could be used for running a large appliance (15A, 120V) while on the move. I have not purchased the inverter yet, the costs for a new one are pretty high, but have completed this portion of the installation for less than a couple of hundred dollars...minus the cost of the alternator(it was free.)

In the attached file I have a sketch of the wiring diagram that I modified which represents the wiring,connectors, fuses, etc., that I used. I guess my biggest concern was getting too much juice to the batteries and/or ruining the alternator if it accidentally became unplugged or was plugged in while the engine of the truck was running. Any thoughts on how it is wired?? BTW, the length of 2/0 cable one-way is about 25'. Ground cables, also 2/0, are very short and are run to the frames.
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File Type: pdf RV Alternator Wiring Diagram.pdf (472.1 KB, 235 views)
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Old 04-28-2010, 12:54 PM   #2
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wow, I am impressed, and would like to

see the photos of how you mounted the alternator to the engine of the tv. the 2nd alt could have been completely "isolated" from the tv wiring using only a switched 12v source to excite the field-how did you trip onto the idea of running a connection to the ECM? that's pretty cool, and something my pea brain cannot fathom...good job.
ol' bill
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Old 04-28-2010, 01:10 PM   #3
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Don't know exactly what you need to protect from an accidental unpluggage while the truck is running.
Do a goggle search on 'alternator load dump' for ideas.
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Old 04-28-2010, 01:40 PM   #4
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WMARSHA

Attached is a labeled picture of the engine compartment...cant figure out how to put pictures in these messages yet. I had not quite completed the install at this point and had a smaller 8 gauge charge wire attached to the fuse block to test out the system.
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Old 04-28-2010, 01:44 PM   #5
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Markdoane,

Would the way I have the system wired help. I have the alternator "turn-on" wired through the relay which in theory...and we all know how theory goes... would turn off the alternator at the same time the main umbilical charge wire was disconnected at the Anderson plug or if the 130A fuse or relay were blown. At least that was my thought process in wiring it up.
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Old 04-28-2010, 01:55 PM   #6
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If you put a resistor between the output lead and the sense line, and a capacitor between the sense line and ground, you can eliminate any tendency for the output to reach unacceptably high levels when the sense line to the trailer is unplugged. I'd start with a 470 ohm resistor and, say, a 100 uF electrolytic capacitor with a 35 volt (or higher) rating. The resistor will bring up the voltage on the sense line any time there's output and the sense line on the trailer isn't connected, and the capacitor should remove any tendency for the voltage to bounce up and down while this is happening. The values aren't critical and could be doubled or halved without changing the way the circuit works.

If you want to provide some protection for the output line being disconnected a largish capacitor (1000 uF, 35 volt) should do the trick. It isn't necessary to dump the load, just provide enough of an output sink to allow the sense circuit to get the field shut off.

If it were me I don't think I'd breaker the individual batteries quite that tightly. The 110 amp breaker should be the one that trips first, and the way you have it drawn it will usually be one of the 55a ones that will go, unless there's always a load on in the trailer, since the current won't be quite the same into each battery even though we want it to be. I'd go up to 75 amps or so unless there is a cost penalty that dictates a lower rating.
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Old 04-28-2010, 02:04 PM   #7
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Thanks Jammer for input on how to save the alternator in case of disconnect.

And here are some pics of the tv and trailer connections along with a jpeg of the wiring diagram
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Old 04-28-2010, 02:06 PM   #8
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Nice. I edited in some more stuff after your post, sorry.

Very cool installation. How did the bracket/belt/idler end of things work out?
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Old 04-28-2010, 02:08 PM   #9
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I see your engine compartment photo now. Are the brackets etc stock?
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Old 04-28-2010, 02:17 PM   #10
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Pretty slick how the alternator install went. In all it took about 45 minutes for that part. The setup uses a "stock" belt for a two alternator setup on the duramax. Mine was old and I needed the preventative maintenance anyway. Saved the old belt as it will still fit the old system even with the new parts added. the belt is fairly simple to put on if you use a 1/2" breaker bar in the adjustable idler arm. The second idler pulley is fixed and simple to get to also.

funny you mentioned doing away with the smaller breakers. Those were a part of the factory installation and I hesitate to do away with them. the reason for the 110 amp breaker is to protect the line going out of the RV to the tongue...just in case a dead short happens.
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Old 04-28-2010, 02:22 PM   #11
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Got the bracket from a 105A dual alternator "install" Kit, $25. The 4 pin connector i got from a local alternator repair shop, $8. Idler about $35. did not include the cost of the belt as I need a new one even if I did not do this job.

the "original" GM parts cost a lot more--for example the 4-pin connector was costed out at $45.....They really like theirs.
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Old 04-28-2010, 02:36 PM   #12
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As far as treating the batteries right goes, for the marine world Baldor makes alternators which accept specialty external voltage regulators that perform multiple phase charging (as in bulk charge, finish charge and float charge) which will treat your batteries right. Big bucks though.

For insurance, you can build a lock box to enclose the mated battery connectors so that only the person with the key to the box can disconnect the connectors.
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Old 01-04-2012, 09:24 PM   #13
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Quote:
Originally Posted by Crusty View Post
As far as treating the batteries right goes, for the marine world Baldor makes alternators which accept specialty external voltage regulators that perform multiple phase charging (as in bulk charge, finish charge and float charge) which will treat your batteries right. Big bucks though.

For insurance, you can build a lock box to enclose the mated battery connectors so that only the person with the key to the box can disconnect the connectors.
It appears that BALDOR makes backup generators, commercial to home sized.

BALMAR seems to be the source suggested.

Excellent thread. I got back onto this idea of faster battery charge by having re-read ETN550's Silver Streak Project recently. And the need to review what works best.
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