24-12v conversion diagram any help?

[NormB]

AM General feeds ALL 12v components from the rear battery...TCM primarily, the 14v tap from the gen takes care of the imbalance. If it’s so bad, why does the mfg do it?

I missed something in translation there, RTW.

You mentioned this earlier, about the rear battery.

Not having owned a 24/12V system before, I had no way of knowing how to wire it and used the rear, spare, battery I’d mentioned.

IF you tie the 14V output to the REAR battery from which you’re pulling current to operate the TCM, the regulator charges THAT block as if it’s a 12V cell; when the TCM (or whatever) circuit is idle, the 28V side treats the series 24V battery as a single unit charging all cells.

Same principles apply. If you’re taking from a portion of the cells in series, you have to put power back INTO them.

I’m a little rusty on this, but not far off the mark.

NB

 

[Milcommoguy]

It is not so much of a problem with the 200 Amp dual voltage configuration. With this set up and using the 14 volt output to the rear battery you get the best of both worlds, A stable 12 volt circuit for your 12 volt goodies (reasonable, see my thread above) and both batteries are charged and equalized (this is important) for maximum output and life. This system allows for a bit of a mix-match of battery conditions

Where it becomes a headache is with the 60 Amp systems. (pay close attention cuz it's this simple) With the two batteries in series... two 12 volt batteries in series just like any 24 volt system... it would seem that one could just tap into the 12 volt battery and pull 12 volts. Yes, you can to a point. When you pull down that rear battery, you now might ?? have say 10.9 volts while running the 12 volt goodies. The front has say 11.9. So you had your fun playing the 12 volt radio listening to the ball game. Total system voltage both batteries 22.8. Games over and time to hit the road. That voltage should get you started and your on your way.

Here's where it get messy... (60 Amp system) The internal resistance and terminal voltage (10.9 & 11.9) of these two batteries above are different and will require (no two are alike, matched maybe from same batch?) So started truck, good. Voltmeter shows in the green GOOD more or less 28.5. Remember, it is a voltmeter. MEANS nothing to charging batteries in this condition, but at least the alternator is working.

Trying to charge this 60 Amp set-up of unequal batteries from a common 28.5 volt charging alternator due to the UNequal condition created above. The likelihood of the front battery having 15 to 16 volts across it and due the the lower internal resistance of the back battery... it will never see a complete charge. Note: front battery will boil out, smells like a fart... rear battery sits dead and never recovers and this thread starts all over again... can's start truck.

With the 60 Amp older system (many out there) are fine and will charge as designed with two EQUAL and MATCHED batteries FROM the SAME LOT and MAY work well with one type or another as in Los Vegas lucky.

Another OVERLOOKED headache is with the rear battery trying to charge and your now 12 /14 volt load in play, unequal voltages maybe flowing thru that equipment and keeping it simple... POOF!!! especially when on and trying to start. Undesired HIGH sneak currents with reverse voltage.

SO that the story from this FREE to you, how it works, no magic, no voodoo. Been there, seen it, done it.

There are ways around 60 Amp charging systems. Don't be fooled by the 60 Amp numbers. Running the truck and a small 24 volt military radio is fine and even better with the engine running.

Solid state 24 to 12 volt equalizer products are available that are acceptable, cost a bit of money and FULL understanding pro & con's to use.

Front and rear battery refers to NORMAL placement per TM of batteries.

Lead acid wet cells in series are a fine balancing act, to long life and few headaches, CAMO

 

[Coug]

Without offending anyone, can someone explain why half the planet suggests taking 12v from the main batts and the other half says never to do it as eventually it will create problems? I understand electronics fine but I’m not an engineer to be able to weigh the facts and create a basis either way. To me they both make sense. I just want to get this right and wire it 1 time.

The early M998s had a 24v 60 amp generator, no tap in the middle for 12v. If you used the 12v from the rear battery, the front battery would get over charged, and the rear battery would never get back to being fully charged. A good way to kill batteries if you were drawing more than a very minute amount of power.

With the newer system, the 12v tap in the middle keeps the rear battery charged up even if you have a small load on it, and keeps the batteries balanced. it's only 50 amps of 12v, so not very much power compared to 100 amps or more of 24v, but more than enough for most lower draw accessories. still can be overloaded with things like a big stereo or a winch though.

(12v systems are actually around to 14 volts when running and charging, so that's why you hear 12/14v and 24/28v used interchangeably on here)

 

[Milcommoguy]

I wish I could type as fast as some of you guys.

Not to be left out. Just bringing up the rear?? CAMO

 

[Milcommoguy]

AND... at some point the 24 volt converter input (the way drawn) and maybe the output needs to be disconnected. Some converters outputs are isolated / floating. It is possible the negative may not be tied together.

It's all do-able. Just have to figure what time and money it's going to take. Check with the war dept first.

Has a side note. I run a Cooper / Surepower 100 Amp battery equalizer. It does the job providing three commercial public safety radios and a 100 watt HF radio, light bar, PA/siren, GPS with clean regulated power with battery equalization. Does the job and will require control circuits on the input and outputs. For me it was the easier and the cheaper way to go.

The only failure point IS > NO matter what system using TWO batteries (standard HUMMWV config) one MUST pay attention to the drain on the rear battery. You discharge it below reason...get out the slave cables. I have a low voltage disconnect, so this is not going to be an issue.

So the third battery solution could be the fix?

To much Rube Goldberg for me, CAMO

 

[Retiredwarhorses]

First of all, I NEVER mentioned using a 60 amp, go back and read my post. 60 amp has no 14v tap.
Secondly, TCM equipped trucks would have 200amp gens.
Ive been doing hmmwv crap for a few minutes “20 plus years” never had any issues on ANY truck I’ve owned just taking
12v off the rear battery. But the most important caveat here is what are you connecting to that battery, that’s the key.
Cell phone charger, USB, don’t give it a 2nd thought, 10 trillion watts of lighting, stereos with mega Watt subs? Totally different story....but AGAIN, the thought process has to be, are you dealing with a 60amp or a 200amp with 14v tap.

 

[pipeandwire]

The exact load is a wetsounds 200 watt sound bar and 300 watt sub + a small phone charger and backup cam. About 50amps. And where I do agree a light load would be acceptable I feel a full 50 amps may be too much from a center tap. While the 14v tap would probably serve its purpose while its running, with the vehicle off ide have to have it connected to the 12v midpoint of the batts. If I read correctly, everyone may agree at that amperage it’s too much to tap ? The positive side of adding a nice converter is using a portion of the available 200a alternator which there’s plenty power left for grabbing. 2nd option would be a 55 or 75 ah batt tapped off the alt. Is that a fair assessment of my options?

 

[pipeandwire]

First of all, I NEVER mentioned using a 60 amp, go back and read my post. 60 amp has no 14v tap.
Secondly, TCM equipped trucks would have 200amp gens.
Ive been doing hmmwv crap for a few minutes “20 plus years” never had any issues on ANY truck I’ve owned just taking
12v off the rear battery. But the most important caveat here is what are you connecting to that battery, that’s the key.
Cell phone charger, USB, don’t give it a 2nd thought, 10 trillion watts of lighting, stereos with mega Watt subs? Totally different story....but AGAIN, the thought process has to be, are you dealing with a 60amp or a 200amp with 14v tap.

I’ve been doing HMMWV stuff for a few minutes plus or minus a few weeks so I sincerely appreciate all the knowledge helping me out with this.

 

[pipeandwire]

AM General feeds ALL 12v components from the rear battery...TCM primarily, the 14v tap from the gen takes care of the imbalance. If it’s so bad, why does the mfg do it?

My m998 has no 12v devices that I know of. There is nothing tapped off the 14v alt or anything from the 12v at the batts.

 

[Milcommoguy]

Not sure that's the exact load? pipeandwire. Looking up those products... they are fused at 15 Amps each. Not a big deal as it is not a continuous load (music /audio with varying demands) peaking at less than the 15 Amp fuse rating. Can't tell for sure as the specification are not well described.

You never said or I missed it as to what alternator you have.

Sounds like... pun intended, money shouldn't be an issue as these speakers are a bit pricey. Build out a 200 amp 28/14 system and no problems.

Good luck and wear ear protection, CAMO

 

[springer1981]

You never said or I missed it as to what alternator you have.

Very first line in the original post

200a dual voltage alt.

 

[pipeandwire]

Not sure that's the exact load? pipeandwire. Looking up those products... they are fused at 15 Amps each. Not a big deal as it is not a continuous load (music /audio with varying demands) peaking at less than the 15 Amp fuse rating. Can't tell for sure as the specification are not well described.

You never said or I missed it as to what alternator you have.

Sounds like... pun intended, money shouldn't be an issue as these speakers are a bit pricey. Build out a 200 amp 28/14 system and no problems.

Good luck and wear ear protection, CAMO

I’ve actually spoken with the manufacturer and they said it was drawn incorrectly in the manual and 20 and 30 were the correct requirements. The speaker setup I got from the guy who sold me the humvee as he was going to install it with a Orion 2412 70a comnverter. I have the 200a dual alt. While I certainly don’t expect to running at full blast I definitely don’t want to be undersized. The nice thing about the Orion is it has a separate on input in lieu of always converting.

 

[pipeandwire]

I have a plasma table that I will be making some custom brackets for the sound bar to be able to mount on main pillar A and have the bracket extend out far enough to clear the windshield wiper motor. Will post some pics when it’s gets warmer here and I start putting everything together.