adding third battery to HMMWV with dual volt alternator for 12 volt accessories

[Outfitters]

I have searched google and here with no definite answer....so thanks in advance for your input.
I have a 1986 M998 and just finished installing a dual voltage 210 Amp Niehoff 1387 alternator (it has the 3225 Regulator).
I currently just have the 14v tap on the alternator grounded to the regulator mounting bolt since I am not using that tap currently.
I want to install a separate 12 volt auto battery under the rear seat and charge it from the 14v tap on the alternator so I can run a large power inverter for 110v, a 12v winch, jump start other vehicles, and run 12v accessories without jepardizing the 24 volt batteries and main vehicle electrical system.
My questions are:
1. Is this alternator designed to do this? (charge two separate systems...one 28v one 14v at the same time)
2. Can I use the same grounding point on the engine block? (is there a conflict with sharing the ground between both the 28v and 14v systems?)
3. Do I need to add any fuse protection or other safety items on this new 14v system?


I have read where others just tap into the series cable on the batteries and then connect the 14v output from the alternator to there, but I like the idea of two separate systems if this will work.

 

[Outfitters]

so I believe the answer is here:

http://www.ceniehoff.com/Documents/Ctrl_Hyperlink/TG0019A_uid12172009217332.pdf

But deciphering that terminology and those schematics is beyond me....

 

[mechanicjim]

N1387 is a dual voltage alternator which will charge both 28v and 14v at the same time.
it uses the Regulator to Rectify one of its two stators down to 14v 50amp max.
what that means is that total system Amperage will be the combined load 28v and 14v.(so if you have 100amp on 28V and 50amp on 14V you have 150amp total)
so when you hook up the 14V system if it draws its max Amperage then the most you will get out of the 28V side will be 150amps.

you could do the tap method for the 14V side or put a separate battery the ground can be shared.
for fuse protection remember its 50amp max so your fuse should be something that can handle that at least.

 

[happycamper]

so did you do it? i want to do the same thing for a 12v winch. I was planning to go to the 24v ground and run a 6 gauge wire to the 14v post of the dual regulator. Hoping that will keep it all charged and good to go. Thanks!

 

[Augi]

You don't need to install a third battery. The 14v tap will maintain the lower battery for you and you can draw 12v from there.


Augi

 

[happycamper]

I considered that, but read from a "random internet expert" that it would be a bad idea to run a winch off of one battery. Too much pull and imbalance they suggested. Thoughts? I appreciate your help

 

[LiveFreeOrDieTryn2B]

I have a dual voltage alternator on my deuce and have 3rd battery. I would IMO do it with the winch your ground will not interfere with the separate voltage.

 

[Dock Rocker]

A good winch pulls 300 amps while winching. The cheaper winches can pull up to 500 amps. After about 40 seconds of pulling a deep cycle battery is using everything the alternator can give it because the battery has been depleted.

With only a max of 50 amps being put back in by the 12v side of the alternator it wouldn’t take long to burn up a winch due to low voltage.

The moral of the story is just get a 24 volt winch.

 

[Outfitters]

I decided not to add a third battery exactly because of what Dock Rocker said...50 amps is not enough.

 

[papakb]

Dockrocker, do you understand battery ratings? A battery rated at 700 Amp hours should be able to supply that current for that time period. Lower the current and you lengthen the hours. ie 350 amps for 2 hours etc. This is all from the batteries and has nothing to do with the alternators contribution. Along the same line you never want to jump start another vehicle with the alternator running. If the starter is drawing more current than the alternator/battery can provide the alternator usually moves to the "needs changing" list.

 

[Dock Rocker]

Dockrocker, do you understand battery ratings? A battery rated at 700 Amp hours should be able to supply that current for that time period. Lower the current and you lengthen the hours. ie 350 amps for 2 hours etc. This is all from the batteries and has nothing to do with the alternators contribution. Along the same line you never want to jump start another vehicle with the alternator running. If the starter is drawing more current than the alternator/battery can provide the alternator usually moves to the "needs changing" list.

Turn your motor of and run the winch hard. Get back to us and tell me how long it lasts. That in itself lets you know that it depends on the alternator resupplying power.
Several of the larger (10-12 K) warns pull 480 amps. That will suck a battery dry in a matter of minutes.

Also do it a couple of times and see how long your winch lasts while running at low voltages.

Lastly read up on the duty cycle of a winch and overheating. This is also exacerbated by low voltage.

I have rebuilt dozens of winches and have probably spent more time pulling people out of holes than anyone else on this site other than the wrecker drivers. I can assure you that if you have a dead Motor you will be very lucky to pull yourself out of a small situation before you run out of juice.

 

[AVGuy]

I know I'm late to the game on this subject, but wanted to get some opinions...

I have a '91 M998. The previous owner had a pair of Red Top Optima batteries put in. That being said, I will be adding the following...

• (2) 24V Viair Air Compressor
• Winch (I have not yet decided on what I'm getting, but having difficulty finding something in 24V)
• Stereo system with the following fuse sizes
  • (3) 15A fuses for speakers
  • (2) 30A fuses for subwoofers

The air compressors shouldn't be an issue as they are 24V, but I'm concerned about the winch and stereo causing an issue. I initially thought about adding a 3rd battery, but wasn't sure of the proper way to do that or if it was the best option.

Thanks in advance for any thoughts...

 

[rolling18]

You don't need to install a third battery. The 14v tap will maintain the lower battery for you and you can draw 12v from there.


Augi

what battery is the "lower" battery? or "primary"? whats the difference??

 

[mechanicjim]

what battery is the "lower" battery? or "primary"? whats the difference??

In a dual series battery setup like most 24v systems the lower battery is the one closer to the chaisis ground and the higher is the one you pull 24v power from. so to find the lower battery look at where the ground post cables go. On one battery it will go to chassis ground, the other will go to the positive of the other battery. so when you make the prayer to the elecrical gremlins in the battery just say "Higher power, Lower ground this is how the current goes around.".

 

[rossbart]

In a dual series battery setup like most 24v systems the lower battery is the one closer to the chaisis ground and the higher is the one you pull 24v power from. so to find the lower battery look at where the ground post cables go. On one battery it will go to chassis ground, the other will go to the positive of the other battery. so when you make the prayer to the elecrical gremlins in the battery just say "Higher power, Lower ground this is how the current goes around.".

Are you saying that the 200 amp dual voltage alternator setup (as factory setup) will maintain the “lower” battery as is - or is there some wiring setup that needs to be done? I have an M1123 that I’m wanting to run my 12v cattle feeder off of. Would it be correct to just wire it to the “lower” battery positive and negative terminals?
Thanks for the clarification