12 volt Wiring help

[humvenube]

Hey everyone, trying to get my new to me HHMWV ready as a hunting truck.
I am ok with turning a wrench but electrical is not my forte.
I am installing a 24/12 volt converter, cutoff switch and large fuse in the battery compartment. And mounting light bars & cubes, installing a interior light and made me a switch panel/ arm rest / cup holder.
I have seen several wiring combinations on here.
So my question to the experts is do I have my connections correct on my batteries?

 

[Milcommoguy]

Schematic would be helpful. Looking at the pictures ?? and trying to follow it thru, it looks like you have the 24 volt connections thru the CONVERTER disconnect switch right. Going to be a pain in the butt to have to pull the seat every time you want to turn off 12 volt equipment. Unless you have some SMART converter that knows to turn on... on demand? Most of the LED lighting?? will run 10 to 30 volts (check yours first) so the converters not really needed & easier to manage / install for most LED's. Any 12 volt need (in most cases) should be minimal (Ipod, CB, cell phone charger, unless you running super boom box, ham radio gear so converter is one way around the 12 volt requirement. OEM / upgraded 28/14 volt alternator package even better for larger demands. As seen here a 12 volt winch? Duh, wrong application for both.

Picture worth 1000 words, Schematic says it all.

What alternator is under your hood??

CAM

 

[humvenube]

Thanks for the reply Cam. I have a60 amp alt. And I didn’t use a schematic just wired it as I went. I am happy with the way I have wired it. But my concern is that I hooked the negative from the converter to the negative on the rear battery and I have seen some people wire this to the positive of the rear battery as it is the ground in the 24 volt system as I understand. I just want to make sure my batteries will still charge correctly.

 

[Milcommoguy]

Whoa WHOA ! I'am not sure where your going with this & Mr. Edison is spinning in his grave. The set-up will work. Note the the real ground is thru the shunt (the thingie mounted on the side of battery box) which is then terminated to the starter then to the frame. While the voltage drop in very small (milli-volts per large Amps) it is there for diagnostics and true system ground is on the starter.

This is why there's talk of checking grounds, cleaning, bonding and kits.

I am always confused... so I think your trying to say is, at the back battery you have seen a wire connected to the positive. This should be at a 12 potential and could / can ?? be used for light 12 volt loads. (not light but little)

I have seen GI Joes connect there for I-pods, cell phones, small CB radio, etc. Problems can result with uneven discharge & charging of both batteries in a 24 volt system. 0+12+12=24 (its late I hope I got that right)

Not in your case with the fancy regulated electronic (not a resistor) 24 to 12 volt converter you take your power from the systems 24 volt supply and all is good up to its Amp rating for your 12 volt needs. (12 volts is relative for discussion, could be 12 - 14 Volts output)

Not sure if your converter has a floating ground or chassis ground. Might want to connect converter negative to the negative at starter ground or you could end up with a ground loop back thru the converter to ground if some other ground/s lets go.

Still not clear why switch (fuse a good thing) is not easily accessible to energize you 12 Volt buss. Does this magic box sense load and turns on. If not, could be an on going load to the rear battery and that's going to be a problem in the morning.

You have the better of the options with the 60 Amp alternator for 12 Volt equipment up to your converters rated output amps. Note wire gauge in and out.

Watch out (remember) it is there when splashing through deep water as it didn't lookie water proof or poof.

CAM and Sparky the bear.

 

[spoonsc1]

Milcommoguy has some good info in there for you. just to add to it, the decision has to be made about the 12v convertor, whether you run it isolate or not. this meaning if the ground will be sharing the chassis of the truck or separate all together.

the shunt (like previously stated) has a resistance. as we have all heard before one time or another "the path of least resistance". this is where I have seen problems. all vehicles (cars, trucks, aircraft) use chassis grounds, aircraft use many voltages ac and dc with a common ground. touch on this in a minute.

some have used the first battery for a 12v source, (taps off of the jumper cable between the batteries whether the positive of the first battery or the negative of the second) which ends up draining that battery faster than the other, then the alternator senses the (24v) battery(both batteries in series) needs charging which it over charges the second battery, every few months you will have to change the one battery. so this set up is a bad choice. I prefer a battery equalizer, to maintain the batteries equally, the alternator puts out the 25+ volts and the equalizer makes sure both 12v battery stay equal and neither gets overcharged

(I use a cooper bussman 100A unit used in MRAPs)​

. this also allows a 12v tap for accessories which is essentially using the first battery 12v (+) terminal without depleting this battery lower than the other.

Now back to the problem set ups with the "path of least resistance". when you use a convertor or choose to use the equalizer, I recommend the shared chassis ground(not isolated). all 12v accessories SHALL be grounded to chassis and NOT directly to the battery negative terminal. if 12v devices are grounded straight to the negative terminal, as bad as the corroded ground/chassis problems on these trucks, and the shunt being a resistor, this allows all components, 12v and 24v, to find the current path through the devices back to the battery ground terminal as they may be the "path of least resistance". when 24v devices find the path back to the batteries through a 12v device, bad things happen. this is definitely the case when a 12v CB or radio is used since the antennas require a ground plane of the vehicle through the coax to the device, which finds it way back straight to the ground terminal of the battery when connected directly (usually connected with a smaller gauge wire unable to support the current in the first place) . (I have heard of times when the minute the antenna is connected to the 12v device the ground wire of that device burns up immediately).

without going into it the sequence to disconnecting the batteries will be critical as well.

my set up has been very reliable, running stereos, CB, rough country lights and FLIR camera without issues, not to mention my battery health is great.

 

[humvenube]

Great info guys and much thanks. I have a much better understanding of what needs to be done now.
searching equalizers now.

 

[Milcommoguy]

Equalizer not really needed if your batteries are in good "balanced" shape with your converter build. Basic 60 amp alternator should handle it just fine. Since you already have the converter wired in... run with that.

Equalizer is other option and usually expensive $$ to provide 12 volt outputs, while managing the batteries. Up side no converter need.

The other with more nuts / bolts & belts is the dual output 24 / 12 volt alternator.

AND neat job on the fat wires, lugs and colored shrink sleeve. AAA+++ to the front of the class.

QUESTION? How does your converter turn on / sense the need to supply the 12 volts?

Signed, Curious under the hood. Now where's that sticky black tape?

CAM

 

[humvenube]

Thanks for letting me know that Cam.
my converter turns on when it senses power, that’s why I went with a cutoff switch. This thing will sit long periods at the ranch without being run so I wanted the ability to shut that leg off. I don’t mind the location I won’t be turning on and off regularly.

 

[lgscott3]

Resurrecting this thread a little, because it seemed like a good place to ask. I'm planning on installing my converter where the radio rack would be in a homemade center console. Where should I ground my convertor on the chassis? Looking for the shortest path, but a good place to connect to.
Thanks.

 

[Milcommoguy]

IMO, to the big fat ground wire / stud on the starter.

Not all grounds are equal, CAMO

 

[lgscott3]

Thanks! That sounds good. I'm planning on doing the improved ground modification too, so maybe I'll do it all at the same time.

IMO, to the big fat ground wire / stud on the starter.

Not all grounds are equal, CAMO