Electrical Question involving Dual Batteries

[Appolyon]

I was recently trying to figure out how to wire my roof lights, and I was curious as to the feasibility of running a 12v and 24v system in the same vehicle, and tied together with a dual battery system. The reason is that I want to use a specific kind of cable and junctions to connect my lights to, and they are limited to 13amps per cable/connection.

I'm trying to run 4 lightforce driving lights on the roof, and they each draw 100 watts. With 400watts and a 12v system, i have to run one light per connection (8 amps a piece), which means 4 holes in the roof. If i use 24v, it means only 2 holes.

That's my problem. I've been looking at Odyssey batteries, and they've got a bunch of 12v small batteries, and i could tie 2 together to make a moderate sized 24v....

So again, is it possible to run a 12v and 24v system as part of a dual battery system in the same car? or is it more complicated than it's worth and i should just cut the holes in the roof?

I don't have a clue about this, and I didn't find anything on Google when i searched....

 

[Appolyon]

My roof rack plan....

(Just fyi, this is in an 80)
What I'm planning is to remove the stock roof rack, drop the headliner (not by myself), remove the nutserts, have the rear holes welded shut, dynamat the interior roof, and put in these clever little plugs (Female, straight 2 pin receptacles) in the front holes from the rack (i'm thinking of 4 of them, so drilling 2 more holes), and then running the cables down to an Aux fuse box. With the connections in the roof, I can cap them and seal them for when I want to take my rack off, but the lights plug right in with these plugs (Male, 90* 2 pin).

The reason I'm looking at 4 plugs is that I am looking to mount 4 Lightforce 170's on the roof, and they each will draw 8A, with the cable only able to support 13A.... hence my conundrum... I want the rack to be completely removable, but still allow me to put 4 Lightforce on the roof.... Is this a really novel idea, or have other people though of this and discarded it for a reason that I haven't figured out? I know I could run 2 cables to the roof if I used something like this (Heyco) but I want to be able to remove it.

That's what my choices are... I understand that if i use the Heyco plugs that the rack would not be removable, but that's a price i'm willing to pay to have lights on the roof....

 

[george_tlc]

12/24V would be an electrical charging nightmare. You would never have well balanced batteries when connected in series.

Spend more time solving your wiring gauge issues rather than trying for 24V in a 12V vehicle.

cheers,
george.

 

[mobi-arc]

How do you charge the 24v battery bank from the 12v alternator?

 

[george_tlc]

How do you charge the 24v battery bank from the 12v alternator?

That's the whole point (of the trouble...), I'm assuming the OP figures to use a dual battery setup to charge the 2 batteries (parallel) but then switch them to 24V for using the lights.... hence my point that it would be a charging nightmare situation....

WAY EASIER to just source decent gauge wires and a connector system versus some bizarre 12/24V Rube Goldberg machine

cheers,
george.

 

[Appolyon]

George, you hit it on the head.... that's exactly what i was thinking, but i wasn't sure if it could be done... I guess i just need to find better connectors... or just say forget it and make the whole darn thing permanent like most of you guys...

Rube Goldberg sounds fun and all, but they never seem to work right the first time.... or the hundredth....

Thanks George... and mobi-arc...

 

[TrickyT]

Are you sure about the 100A per light? That's 1,200W per lamp! Sounds extreme.

And how are you going to keep your battery from going dead? Have you got an alternator that puts out 400A (12v) or 200A (24v)? That's what would be needed just to power the lights, not the rest of the vehicle.

 

[george_tlc]

That was a typo by the OP - his second post talks about 8A per light, so 8 x 12 = 100W each. So, he's talking 100W per light, 400W for all 4.

Regardless I think he's figured out that a 12/24V rube goldberg machine is not what he wants on his hands

cheers,
george.

 

[Appolyon]

Are you sure about the 100A per light? That's 1,200W per lamp! Sounds extreme.

And how are you going to keep your battery from going dead? Have you got an alternator that puts out 400A (12v) or 200A (24v)? That's what would be needed just to power the lights, not the rest of the vehicle.

Yep..... that's what I get for writing things when I'm tired.... I switched amps and watts in that section....

The total amperage would be 32amps for all 4 lights with a 12v setup, with 8A per light...

George is still right....

 

[LeeGans]

Ok, heres the skinny. 1st, you really don't want to run a 12/24 VDC system. The voltage regulation will be a nightmare. 2ed, look at the way wiring specifications are actually done. The National Electrical Code has standards for the amount a guage wire can handle with several types of insulation. These guidelines (and all they are are guidelines) are written based on HEAT dissapation in a standard wireway.
American wire gauge - Wikipedia, the free encyclopedia

will get to one. Now, for a 100 Watt light at 12 VDC, you are correct, 8 Amp Draw. Remember though that as the bulb heats up, the current draw drops, so a nominal current might be in the area of say 6 Amps. Still you want enough oomph to light the lights without dropping current, because that will cause the lamps to burn out prematurlely.
So here it is. Go 12 VDC, make sure you have enough power to drive the lamps off the alternator. Wire them OFF THE POSITIVE AND NEGATIVE TERMANALS THROUGH A RELAY.
Use a relay of at least 25 amps per pair of lights. 8 AWG will handle all 4 lights with one hole, but the issue will be the relay, 50 Amp relays are closing in on starting soloinoid sizes. In addition, fusing becomes an issue. This Link VClassics Interactive - Archive has a ton of information. Dave Hueppchen is a leading authority on automotive lights and carries the heavy relays, and more importantly the heavy guage connectors you will need. I suggest using Scotch 33+ electrical tape and make all wire to wire connections as twisted wire, folded into 3eds.

Hope this helps. I have wired tons of vehicles, my 85 cruiser being the most complex.
I have a 180 A/H gel matte primary, through a hellroaring combiner and a 90 A/H wet cell secondary for starting(1MM wire.) I am running Cibie E beam mains with 130/100 W bulbs, 55 watt Cibie 95i fogs, 55 w PIAA projectors, 55W Cibie Super Oscars(switch controls just fogs, or fogs with low and PIAAs with hi beam-all 10 AWG per lamp), with a warn winch (9000 lb), inside I have a GPS, USB Quad radio with a 500 watt subwoofer, K40 CB, with a full light board for forward indications. Electric Toyota Locker on 4.11 gears from a 80 series, and in the rear I have a 750 Watt 120VAC inverter, with the Engles freezer.I figure I am drawing over 110 Amps when the system is running so I have a Mean Green Alternator with 220 amp output. All lights are wired in 10 AWG EACH, an * AWG wire goes to the rear through an 80 A fuse. Rule of thumb, above 9 Amps, 1.25 of max draw for fusing, below 9 Amps, 1.67 of max draw. Use high performance fuses or circuit breakers and make a board under the hood for them. Buy a GOOD crimp tool. My honest suggestion, and I will be doing the same thing you are is to run two wires up from a connector in under the hood on each side of the truck and connect these in parallel to a pair of lights on each side. I also use that stuff that covers the wires and protects them.
That will work well for you. Run 10 AWG wire for HOT and Ground. Don't trust the ground, it has to pass as much power as the HOT does. GL, and check out Dave at OJ Rallye OJ Rallye Automotive