200amp Dual Voltage 28/14v Alternator with 12v Accessories Question

[HoveringHMMWV]

Electronics have always been kind of "smoke n mirrors" for me. So please tell me if my comprehension is functionally correct and safe.
I have the 200amp dual voltage 28/14v alternator in my 1097A2. I would eventually like to install one or more 12v accessories.
Am I able to connect the hot/power wire of the accessory directly to the lower battery's "+" terminal or to an installed gang/bus which is connected directly to the lower battery's "+" terminal?
The accessory can be grounded to the vehicle frame/structure/engine block barring any paint or rust, etc.?
A fuse, rated below the maximum amp of the accessory, should be wired between the lower battery's "+" terminal and the accessory itself.
And lastly, the dual voltage ability of the alternator should keep both batteries properly charged despite the draw on only one battery.
Thank you in advance,
- HoveringHMMWV

 

[Coug]

Yes, you would connect to the lower battery's positive terminal and then negative would just go to ground.
You always want a fuse to protect everything, if a wire were to run through and short out the fuse keeps the wire from turning into a heating element and catching everything on fire.

And yes, as long as you aren't drawing more power on the 14V lead from the generator (which is only rated to 50 amps, and remember it's there to power the transmission control module on 4 speed trucks) then it will work. Personally I don't like drawing at/near the possible max for an alternator/generator system, 80% or less is usually a good point. If you're expecting to draw more than 40 amps continuous/averaged of 12V power you should really get a large 24-12V converter to power everything.

The only part I think you might have wrong is the fuse amperage. The fuse needs to be sized for the maximum possible draw of whatever you are powering, or above it. If you size the fuse below the max amp of the accessory, then you'll blow the fuse whenever it's operating at full power.
The fuse is there more to prevent catastrophic damage to things.
Example, if you have an accessory that is rated for a max of 13 amps, then you will want to use a 15 amp fuse with it. You will also want to make sure the wiring you are using for that accessory is rated for the power draw as well. There are other factors like length and temperature that play a role as well.
So going back to the 13 amp accessory, and with a 15 amp fuse, if the entire circuit from fuse back to ground is 10 feet of wire, you'd want to use 14 gauge or larger wire. You can almost always safely use a larger wire, but never want to use a smaller wire.

The job of the fuse is mainly to prevent catastrophic failures resulting in fires and the like, most devices won't use more than their max rated power unless something else is going wrong.

A basic calculator for wire size/amps/length can be found here:

Wire Size Calculator

or basic chart here:

Automotive Wire Size Calculator – Wire Gauge Chart | MGI SpeedWare

Find the right automotive wire size using an interactive AWG chart that takes into account load current, temperature, wire length and voltage drop.

mgispeedware.com

 

[HoveringHMMWV]

Thank you for the response!
Was planning initially on a cell phone charger and later adding additional rear facing LED's. Therefore the amp draw on the alternator/generator shouldn't come close to max.
Thanks again,
- HoveringHMMWV

 

[Coug]

yeah, those are minimal loads.
If you look around though you can find 24V chargers and LEDs.


I've been using one of these, my only issue with it is the LED voltage readout is pretty bright.

https://www.amazon.com/gp/product/B07F84VVB4/ref=ppx_yo_dt_b_asin_title_o09_s00?ie=UTF8&psc=1

 

[JD4044M]

I am putting a Surface Mount Stereo in my M1078 that uses 12VDC and has a USB Port to charge Phones too. So I am going to install a 24VDC to 12VDC Solid State Chip that will handle 5 Amps at 12VDC. For now I will use the 24VDC till I tap in a Marine Rated Water Proof Sub Panel for 12 VDC Circuits all fused as needed. Here is a good site to learn about DC Fusing and Voltage Drops. I will link the Panel I will use may also work for you in the future. My truck is not here yet so install pictures and a tread on my changes will come later. Mark
DC Volt Drop and Wire Fusing.
This is how I will tap one time off the 12 VDC System and it is complete with pre/wired switch relays and fused circuits. Simple and real clean to install. They have smaller ones too.
Fuse Panel

 

[Coug]

I am putting a Surface Mount Stereo in my M1078 that uses 12VDC and has a USB Port to charge Phones too. So I am going to install a 24VDC to 12VDC Solid State Chip that will handle 5 Amps at 12VDC. For now I will use the 24VDC till I tap in a Marine Rated Water Proof Sub Panel for 12 VDC Circuits all fused as needed. Here is a good site to learn about DC Fusing and Voltage Drops. I will link the Panel I will use may also work for you in the future. My truck is not here yet so install pictures and a tread on my changes will come later. Mark
DC Volt Drop and Wire Fusing.
This is how I will tap one time off the 12 VDC System and it is complete with pre/wired switch relays and fused circuits. Simple and real clean to install. They have smaller ones too.
Fuse Panel
View attachment 810330

If you are going to be running a lot of 12V circuits then that isn't a bad way to go.
I do just want to double check, you're putting in a converter that only does 5 amps of 12V power? That isn't very much power (60 watts) so is that just for the phone charger and maybe an LED light or two or was that for something else?

 

[JD4044M]

No it is just for my stereo that is all. Later I will switch it over to the 12 volt panel. Nice to have music when working on it or driving at times. Everything is surface mount using existing screws to hold the stereo above the dash. It is this one. Has a Back Up Camera too. I may just tap the Trucks 12 VDC if the radio draw ie to much. I will measure the load before hooking it up when I test the system in my shop. One picture shows a 25 amp fuse another pic has a 10 amp fuse. It can be hooked up to motor raising antennas and other things. I will load check the radio cranked up and camera in use before putting it in the truck on the converter. The put the correct fuse in the radio. I used this panel when I wired my 48 Power Wagon I restored they work great for a whole vehicle too. I just don't want to keep adding wires to remote fuses or a bunch of taps later. I can save the rest for future lighting and control stuff.

 

[Milcommoguy]

The fuse and lead with the equipment maybe OK, if fuse is at the battery. Extended battery leads going to equipment, passing thru battery box, bulk heads, fire wall... then to equiment, will need a fuse.

Rule of thumb... Fuse is to protect the wire and is placed as close a possible to the source / battery. Check charts as to the wire size used / fusing.
Another at equipment, fuse sized per manufacture said equipment and less than sourcing wire above.

Ground returns in HumV's can be questionable. Best to go directly to ground of starter. Lazy way to negative of battery.

Keep in mind overall lead lengths when thinking of voltage drops. One 10 foot positive, also a 10 foot negative... 20 feet overall. Not that big of a deal for small loads, phones charger, CB, back up cams, led lighting. Something to think about.

Pulling more that alternator output "with a good set of batteries" is fine. Battery in the case of a 12 volt system (rear) can handle 150 Amp easy for peak / short periods of time, not continuous. Dual system alternator connected correctly will catch up and top off battery / s.

Important to follow good design and routing of cables. Proper grommets, cable covering / split loom, terminations - lugs, eye's, butt splices, tie raps, waterproofing, etc. if you want it to last.

Something else to ponder. Good idea to have a disconnect switch for the 12 volt equipment buss when not in use.

Fussing with electricity and fuses, CAMO

 

[Retiredwarhorses]

Not sure what this “Lower battery” is...it’s either a front or rear battery in reference to the truck.
pull direct from the “Rear battery, both pos and negative, never use body as a ground.
To make it easier, run a positive and negative to a good Marine grade fuse block, as high up as possible if you plan
on getting wet.
i strongly recommend having the ability to cut all power to your fuse block when not in use to prevent any draw from an
accessory.

 

[Milcommoguy]

Add to my post # 8 Fussing and fusing for 12 Volts in the HumV. After 8 hours of sleep, I have a couple more brain toots.

Will try and clear any con-fusing concepts. Many ways to make the 12 Volt connection. Pros and cons... you decide for your needs. (you will anyway)
I and others noted to have the ability to disconnect the 12 feed to accessories. This is a good idea to eliminate any chance that the rear battery is discharged, do to leaving 12 Volt circuits active. It comes with it's own set of issues.

Reasons vary. In my case, I want my truck to start in the morning and go home at the end of the day. (I have six radios) See WA6VVC on QRZ

One is going to need the full 24 Volts to do that. An unintentional/ extended discharge on the rear battery could be a call to AAA. (Ask about the trick to get out of dodge)

Many of the accessories described here are low Amps devices... your GPS, stereo, CB, LED lights. (discounting 400 watt boom boxes) Not a biggie until one leaves something on all day or thur the weekend.

Here's a warning >>> Should one not use a 12 Volt disconnect AND the rear battery as been discharged... good chance of fuses or equipment damage when doing a "blind" start. This is because the front battery (charged) is looking to supply current to start. Dead or weak rear battery and your positive 12 Volt lead receive a high current inrush condition and in a blink of an eye POOF goes your fuses... maybe the equipment

SO this is a ... BIG SO... Understand and PAY attention to direct connection to 12 Volts. Not so sure? Draw it out on paper and see for yourself.

Having the 24 / 12 volt alternator is a BIG plus to maintaining good battery charging / balance making for 12 Volt connection acceptable, if running rig regularly.

Many radios / stereo's have a need for a very low "memory" connection for clock and stations memory. For the most part this should not be an issues. With the switch, one gets to reprogram when disconnected. BiG PITB.

Having a fused distribution block is a good idea. Makes for simple circuit connections / management.

Another about me is I don't make direct connections to the 12 Volt rear battery. I use a 100 Amp Eaton / Cooper equalizer / power converter and have the 60 Amp alternator. (was cheaper and simpler with parts on hand)

This in my world eliminated any battery imbalance and provides 12 volts @100 Amps from the 24 volts. Allowed for simpler power management of radios. A simple 15 - 36 volt three terminal (LM7812) regulator to 12 Volt for any memory retention circuits. Basically convert and not mess with the rear battery.

While a bit over the top... It's goes right along with all the other WACK modifications HumV's have undergone.

Many options, with varying results based on needs.

Time for a nap, CAMO

 

[JD4044M]

Not a good idea to bring only one down and the others stay up when in series / parallel connection to get 24 VDC. Best to just convert the 24VDC to 12VDC and still have a equalize battery set up. Like in the post above.

 

[Retiredwarhorses]

Not a good idea to bring only one down and the others stay up when in series / parallel connection to get 24 VDC. Best to just convert the 24VDC to 12VDC and still have a equalize battery set up. Like in the post above.

so what your saying is AM General did it wrong and the internet experts way of doing it is the correct way?
yea, I don’t think so....OEM pulls all 12v from the rear battery, the job of the 14v tap off the regulator is to correct any imbalance, it’s clearly working in how many current hmmwv’s. As well as the entire fleet of all current US military Vehicles.

 

[JD4044M]

so what your saying is AM General did it wrong and the internet experts way of doing it is the correct way?
yea, I don’t think so....OEM pulls all 12v from the rear battery, the job of the 14v tap off the regulator is to correct any imbalance, it’s clearly working in how many current hmmwv’s. As well as the entire fleet of all current US military Vehicles.

That is different then what I am talking about. You have a 12VDC also charging the battery you getting voltage from. I was just talking about a strait 24VDC System not a split system with "12VDC/24VDC" charging ability.

 

[Milcommoguy]

WITH ALL DUE RESPECT to the hard core ones that have a hard time thinking outside the box... as to the HMMWV design.

IMO and I be no expert at anything... BUT pretty DAMM GOOD at figuring out, reading the TM's and follow along with the prints...

IMO, HMMWV was thrown together to meet the need in the late 70's, cabbaged together in the 80's to win a contract, got lucky with attention with big ass design and pushed that design to the MAX (20's), all along the way, add on, upgrades. Wasn't a vehicle per say, but a platform to push contract $$$ There... Said I had an opinion.

So, I work the same way. Work with what I got. At first, wasn't sure this PIG was much of a truck. Still not. If you look at HumV in a cartoon way... not much different than the "Filntstone Mobile". Two frame rails, simple top, tired motor, dusty, boxie, noisy pitter-patter going down the road with most owners having trouble starting up when cold.



YES SIR... BY the BOOK SGT. of the motor pool !

As a hobby rig. and I've had many too... OK kinda cool and gives an old retired guy an old tired truck to care for. It's MY platform chosen to build MY ideas on.

Well, like I said we are both retired... so some of the wacky crap gets reassigned and redesigned. It's 2020 not 1999.

So that's where I stand. Knuckleheaded and enjoying life along with most of you. (Tobash get back to work lol)

Now that the juices are a flowing, sparks a flying..............

Built the way I roll

Going with the converter made for a simpler design, after weighing in on form and function. There is NO chance to inadvertently kill the rear battery, but could kill them both. Not likely with low voltage disconnect feature. The one I have will equalize / balance the rear, capable 100 Amps double the military set up of 50, and power all radios with 100% over build. The 60 Amp alternator just hums right along.

Battery Equalizers

Sure Power, Shure, Buss, Bussmann, Cooper Bussmann, Bussman, power conversion, equalization, battery balance, converter, voltage, trail charger

www.cooperindustries.com

So if I broke rank with the command and control here, I am working on a motorized potatoes peeler... with converter for french fries.

Easy to spot on the road. Lipstick on the pig, CAMO

 

[HoveringHMMWV]

Looking at my battery compartment today and noticed two smaller wires already attached to the rear battery's "+" terminal. I'm assuming one must be power for the tranmission. But what about the other?
Also, didn't mean to start a stink amongst SS members. I'm just trying to keep from frying a piece of equipment or burning up my vehicle, or worse yet, stopping my heart.
- HoveringHHMWV

 

[86humv]

.

 

[Milcommoguy]

NO stink here. Just sharing knowldge, experience, different approach, what worked, what didn't... that kind of thing. Do what works in your world.

Kinda like music. You can play it right off the sheet or improvise and get funky. One way or another... Somebody going to like it.... somebody not. Same HumV tune.

Do your thing... and rock on. OK, two kinds of music country & western, CAMO

 

[Retiredwarhorses]

That is different then what I am talking about. You have a 12VDC also charging the battery you getting voltage from. I was just talking about a strait 24VDC System not a split system with "12VDC/24VDC" charging ability.

it’s not a split system, per sey....any hmmwv can add a 200amp gen and you have the capability.
the 200amp is the standard for ALL trucks...60amp is out of the system.
even than...most accessories don’t draw enough noticeable amps to make a difference anyway.

 

[Retiredwarhorses]

Looking at my battery compartment today and noticed two smaller wires already attached to the rear battery's "+" terminal. I'm assuming one must be power for the tranmission. But what about the other?
Also, didn't mean to start a stink amongst SS members. I'm just trying to keep from frying a piece of equipment or burning up my vehicle, or worse yet, stopping my heart.
- HoveringHHMWV

2 yellow leads on rear battery for 4L80e trucks..
one is TCM 12 v feed, the other is the 14v tap from the regulator to prevent battery imbalance.

 

[Usmcsteve]

Hello I am new to the HMMWV world on repairing. I have a 1993 m998 and while driving the lights dimmed out and after stopping would not restart. I tested the 2 main posts and only received 25volts and then it dropped slowly. How do I know if it is the voltage regulator or the actual alternator? Also how do the wires get hooked up to make sure they are in the right place?