12 volt wiring issues, need help!

Hi guys,

Our M813A fire/brush truck project is coming along and I have some questions about adding 12 volt equipment to the truck.

If I understand all this correctly I have 3 choices for adding a 12 volt system to the truck.

1. pull 12 volts from the first battery on the 24 volt system, this seems undesirable to me as this can lead to issues with uneven charging in the 24 volt set-up.

2. I can make a bunch of modifications and add a 12 volt alternator to the engine, this seems like a pain but will give me a system that should work well for the long haul.

3. I can add a 24 to 12 volt converter which was the choice I was going to use until I ran into a few snags.

When looking for a 24 to 12 converter I found locally a reasonably priced 20 amp unit. Then I started looking at my amp draw for the equipment I was putting on and got the impression that this isn't going to work.

The radio will pull 37 amps when you transmit, this doesn't count the strobe light-bar on the roof that pulls about 10 amps when all strobes are going, the take-down and alley lights I did not check yet. Long story short I am adding much more amp draw than a 20 amp unit can put out. Most of the items will be somewhat intermittent but when first responding to a call all the emergency lights and the radio will need to work.

Ok, so adding to my plan, I thought maybe this would be a solution. If I put two 12 volt batteries on the truck, wire all the 12 volt equipment with dedicated grounds back to these batteries they should be able to take the shock load of radio and the converter would work like an alternator charging them back up when I draw them down. If this will work can I put two or more 20 amp converters and end up with 40 or more amps of charging power to handle the amp draw.

Keep in mind that most GM alternators for cars were around 60amps or so and on a piece of fire apparatus is usually above 130 amp alternator.

Looking for thoughts on this as I would like to have this truck ready for service in the next two weeks, Fall brush fire season is coming up quick and I hate walking up the mountain to the fire.

Thanks in advance for any thoughts or ideas

Chris K.
President
Clover Fire Co.
Heckscherville

PS. If I can get it ready in time for the rally at Rausch Creek, we will be there, We are located 3 exits north of the Tremont exit on I 81.

PSS. I am looking for a winch for the front of this truck, If anybody might have one sitting around, all donations accepted otherwise tell me how much you want for it.

My BAD!! just noticed the wiring part of the forum, if A mod will please slap me and move this to the right forum I would appreciate it!!

Chris

I'm no expert by any means, but have you considered to converters? Try www.OKoffroad.com because they offer the converters and apparently have experience with emergency vehicle wiring. Good luck.

RE my last, that should be TWO converters not to. Sorry.

I thought about using two converters, was hoping that somebody more knowledgeable with electricity than me would confirm that this would work.

Adding up all the load I am putting on the 12 volt system I am unsure that two 20 amp converters would be enough, I did find up to a 80 amp one on the Internet but they are misleading in the way they represent them, it is 80 amps momentarily 40 amps continuous load.

Chris

please list the watts, amps draw of all the 12v accessories that you need to power. it will help determine your actual needs.

Ok, I know that the radio will pull 37amps when you key the mic, milliamps when in standby.

The rest of the stuff I have to get power to and check with a amp meter as I am not finding the information in either the manual or on the internet.

Soooo at this point I am saying I am trying to pull a whole lot more amps than a normal person would be trying to put onto thier hobby MV.

I will work towards getting full list of amp draw for tomorrow night,

Chris

Advice from one who is less than an expert: Charging batteries from a converter won't work because lead-acid batteries need 14.7 volts to charge.

An opinion from the same: Something like fire equipment should be over-designed if anything. All the business of uneven charging, converters, etc is likely to be problematic. The reliability of the converters is probably not up to par and might fail you at just the wrong time, about an hour into service.

Of all the options you listed the only one that I’d bet my ass on is getting a serious heavy duty alternator that you know will do the job and mounting it on the engine. We added a 12 volt system to an old 6 volt truck and it worked for years. The interesting thing about that one was the 6 volt system was a positive ground and you could go across the 2 batteries and get 18 volts.

I think I saw a thread on this site that talked about some equipment, I think an armored car, that ran two 12 volt alternators to charge up the 24 volts. That type of system would allow for uneven discharge. The ground on the high side alternator would have to be isolated.

There must be other fire departments that have solved this problem because a lot of military equipment has gone to use that way. Is there some organization or web site that works specifically with fire departments?

I would install all the new lights/horns/flashers using 24 volt units/bulbs. Most heavy truck shops have these available. Memphis Equipment shows converters in their ads. There is a fire truck shop on Long Island, NY that did have a web site, just can't remember the name.

having serious computer/keyboard problems at the moment, joy!

12/24 i dont think matters for strobe bulbs, but the power supply/capacitors are a 12 volt set-up, this is a $1300 lightbar, dont wanna make modifications that mjght screw it up.

All of this has me leaning towards adding an alternator

Chris

The dual voltage alternators a couple of us have installed seem to work good. Don't know if it will fit the M813.

Joe Trapp

here ya go, found this on a hmmwv site

"I use a super power 800 24v/13.8v DC_DC converter very simple install unit has it's own cooling fan I have had very good luck in my HMMWV. up to 80 amp draw constant! web page to powerstream is http://www.powerstream.com
To get 12v reliably without wrecking batteries in a Humvee I use a REDARC charge equalizer. It has been fitted for two years now with zero problems. I run 12v HF, frig, CB, stereo, air compressor, nicad battery charger, etc etc. the website is www.redarc.com.au look for charge equalizers."

Redneck approach - return the 1300 light bar and put money back in fire company treasury. Install twin-beacon convoy light kit. Replace amber globes with color of your choice (the convoy beacons are a standard product). This will remove that portion of the load from the system, and save a grand or so and use part of it to buy a dual voltage alternator (mentioned above) and use rest for new turnout gear etc.

My .02,
David Doyle - with some degree of experience with miiitary fire trucks

Dave $1300 light bar was salvaged from a previous truck, didn't want to spend money to buy another so we are using the one we have, We certainly are not a rich fire company and most everything we have has been salvaged from somewhere. We procure much equipment through the unofficial "one fire co.'s junk is another fire co.'s fortune" program. I am just trying to make what we have work, would not be a problem as the last brush truck we had was 12 volt, but now I have this neat 24v system to work with.

As of the moment I think I have spent a total of about $30 to put this truck together, keep in mind I am using everything from the last truck we had to fit onto this one.

I am looking to see if I can salvage a 150amp 12v alternator off of a piece of apparatus that is being taken out of service at another fire co. If I can get this I am going the route of adding an alternator. End of problem, I hope.

Chris

Battery equalizer works for me. They should be disconected when the power is off to avoid a slight but annoying battery drain.