Any problems with tapping one battery for 12v accessories?

[ida34]

I used to do it in the Army all the time. I would just tap the first battery in the series to get 12 volts for lights etc. Anyone have any experience with this type of setup? When uncle sam paid for the repairs it was not a problem but now I have to pay. I did not have any problems when doing this in the army but I did not use it alot. Now I want to put in a terminal strip for a 12 volt powerpoint and to power an interior light or two. Input on the subject would be greatly appreciated.

Thanks
Chuck

 

[cranetruck]

It's ok to do,but you should recharge the batteries individually when truck isn't used.
Charging two batteries in series (normail operation) works good as long as the battries are identical in state of charge. If one battery is pulled down more than the other, the charging voltages will no be correct.
So, it's ok as long as you restore the batteries on an individual basis.

I do, by using the 120 vac Chargetek 500, which maintains the batteries at all times after a trip. (Note, after two years it blew in a lightning storm, but that's another story).

For 12 volts, I now have a 24 to 12 volt regulator. I will post the schematic diagram when I get it redrawn.

Bjorn

 

[Brad900]

I would get a DC to DC converter to run the accessories. I have heard that you will shorten the life of your batteries if you run 12 volts off 1 battery.

 

[Djfreema]

Im running 12v off 1 battery for boost guage and interior lights. Had that set up for about 8 months with out any problems. I plan on putting in a stereo soon and a cigarette lighter socket for my cell phone charger.

 

[Recovry4x4]

For small current draw I don't think you will notice ill effects for quite some time. Gotta have 12V for the cell charger and such but on the dome lights, why not swith to 24V bulbs? I have a dome light out of armor and it has a blue lense for blackout and a regular white one as well. It puts out tons of light in the white mode. No reason one can't use 24V bulbs in conventional universal tail lights.

 

[Crazyguyla]

for a few bucks.. ok, more than a few buck, you could convert to a dual voltage generator. the new humvees have them because they come with electronic transmissions and some other 12v accessories.

 

[ajg6989]

I have a fan, instrument panel light, that i run out of a 3 way cigarette thing and a set of lights under the bumper to see things better up close all off the 12vdc line from one battery the only problem I ever had was when the connector on the battery got loose it rusted and fried the batteries.

 

[ida34]

The light I was talking about is a map light from my old patrol car. I will have to check and see if the bulb is available in 24 volt. It is unique in that it is mounted on a flexible metal shaft and it gives of a red light to fit with the tactical theme of the vehicle. I have to have a 12volt to 9volt converter for an aircraft intercom system. I then need to have a 12v plug for a MP3 player or cell phone charger. I would also like to have a car stereo wired into the intercom. I figure the max draw would be around 10 amps or so. I may check into a 24 v converter. Thanks for the input.

 

[TheSHAD0W]

I'm planning on adding an under-the-hood arc welder, which uses a special alternator; I'll use this for a secondary 12V electrical system which will be used to run accessories, power an inverter and I hear 12V bulbs are an order of magnitude cheaper than the 24V ones so I'll switch the lighting systems over too.

 

[rmgill]

The place I look first for odd Bulbs is Newark.com. They'll ship mail order from online and have LOTS of electronics and such. I found some 24 volt bulbs for some basic armored marker lights for my 2 axle trailer that I bought at Advance Auto Parts. They have a LOT of bulbs listed, you have to search carefully. If you have an equivalent bulb in 12 volt, search for that to get the type of base and such and then search for that base in 24 or 28 volt.

I'd like to add some driving lights of some sort under the bumper (or perhaps in fairing on the fenders like the M35A3s).

 

[M543A2]

I agree with the comments that the tapping of one battery eventually gets the two out of balance and can cause problems. I did this on an M135, and had problems if I used too much power. I had taillights, turn signals, cab lights, and a tach on it. I recommend investing in a voltage dropping box. I know Cat dealers have good ones, and others sell them as well. Might check NAPA.
Regards Marti

 

[RR-CirKits]

Hi,
We have an M35 fire truck that has a lot of 12 volt loads. Here is what I did to solve the dual voltage problem. I originally just tapped the midpoint between batterries for the 12V, but to keep the low side battery from getting out of balance I mounted a standard 12V automotive alternator that is only connected to the low side battery. The 12V unit keeps the low side battery up to snuff, and the original 24V alternator takes care of the 24V load. Since the original installation I had to replace the batteries, and instead of putting in two new MIL batteries I put in three heavy duty automotive units. Two are wired in series for the 24V system, and the third is for the 12V stuff. I just moved my tap over to the new third battery, and the automotive generator takes care of it.
http://www.waxhawvfd.com/station27/picvfd06.jpg This truck just got damaged and has been retired from the fire service. I think it will get repaired by me.

Dick

 

[Recovry4x4]

Wow, thats a nice 530B class pumper. Nice to get ahold of one of those, and with a winch! The CUCV uses a similar system but more complicated. One alt sends 12V to one battery and also is wired in series with the second alt which provides 24 to both.

 

[mangus580]

This is what my original plan was for running a 12v system. I just never got around to it. Some pictures fo the mounting of the extra alternator would be nice though!

 

[Boatcarpenter]

With a $30 marine battery selector switch and an ammeter in the loop you can charge one battery at a time or both. You can tell how much charge each battery is taking and charge accordingly. It would also in the off position kill the whole electrical system and prevent any bleed off due to faulty wiring etc. It would also prevent accidental starts, sort of a crude anti-theft device. The only part I don't quite know how to overcome is how to reduce the voltage going to an individual battery when charging one at a time. CT can probably figure something but it might be too much wiring etc.
Just thinking about how my boats are wired with the 2 batt. setup. But that's 2 12 volt batts in a 12 volt system. Oh well, just some thoughts!

 

[RR-CirKits]

OK, here are the pictures if I can figure out how to include them. I was not present when the drum got wrapped.

We made a bracket for the alternator and bolted it to the nearest locations available. The alternator is fixed, and one of the original alternator belts was replaced with a longer one. The idler style belt tightener lets it be adjusted. If I remember right we also had to put a longer pipe nipple on the heater connections to give some clearance to the alternator. There is a relay to slave off the ignition for the 12V system.

Dick [/img]

 

[mangus580]

Actually, the hook will fit through Go ahead, ask me how I know

I got really lucky!

 

[Armada]

Nice truck RR!