12 volt series headlights?

ttomas · July 15, 2007, 08:38:38 PM

Going over Craig's (grumpydogs) web site, I saw where he wired his 12 volt clearance lights in series so they would work on 24 volts. Can this be done with the headlights? Thanks Tomas

TomC · July 15, 2007, 08:43:50 PM

Can be, should not. Every effort has to be made to make the headlights as reliable as possible. If they are wired in series and one burns out, the other would follow rather quickly. And you know that would be exactly the time your in the mountains on a narrow, windy road with no lights around. Need I say more? Good Luck, TomC

Jeremy · July 16, 2007, 02:02:25 AM

In fact, if one burnt out the other would stop working instantly because there would be no power to it. Having said that, haven't I read that some MCI headlights are 12v wired in series? If for some reason you have to use 12v lights then you could use a step-down transformer (commonly available so truckers can use 12v stereos and other 'car' gadgets), or you could take a central 12v tap off your battery, and wire the 24v from the headlight switch so it operated a relay on a 12v circuit.

Jeremy

Jerry32 · July 16, 2007, 04:09:01 AM

MCI's are wired so as to have a 12V backup to keep the other lite working if one fails. Jerry

Stan · July 16, 2007, 06:03:54 AM

Search the BB for the MCI 12 volt wiring diagram, Another choice is to run the headlights (or all the exterior lights) of the 12 volt battery terminal with a Vanner equalizer maintaining equal voltage on the batteries

gomer · July 16, 2007, 06:08:58 AM

on my 4905 they are wired series/parall el and on my mci they are 24 volts. They use a relay that will let 24v work in series with the low beams and them series/parallel on high beams. as stated when one burns out u r n the dark. If you tap the 12 v from the 24v and run a lot with lights on you will not have proper charging to the battery and will burn one of them up since you will pull a bigger load off one instead of two. You can get a step transformer to help that tho and that is what I would recommend
on my mci-8 they are 24 volts

Gomer

Stan · July 16, 2007, 06:21:47 AM

We now have two posters who know where to get transformers that work on DC. There are DC to DC converters, dropping resistors and package regulators, but DC transformers are impossible.

gomer: The Vanner equalizer is used by bus manufacturers and most converters who have 24 volt systems to eliminate the problems that you describe. If you have have a headlight system wired so that if one burns out, you are in the dark, it should be changed to one that works properly.

gomer · July 16, 2007, 06:50:56 AM

that is what I was trying to think of VANNER thanks again for that info gomer

DavidInWilmNC · July 16, 2007, 08:34:57 AM

It's my understanding that MCI has had a bulletin out since way back... some time in the '80's about this. My '78 MC-8 has its headlights wired in series with diodes and the center tap (12V) to keep 'em working if one burns out. My headlight bezel even has '12V' stamped on it to prevent confusion.

David

ceieio · July 16, 2007, 09:24:13 AM

Tomas - my bus has a DC to DC converter to run the headlights. It was part of the R&M headlight upgrade kit. My bus has the VR24-1220 (Info here: http://www.transpo.de/cgi-win/product.exe?VR241220)

For more information on other choices go to: http://www.transpo.de/Catalog/Browse.htm

On the left side, scroll through the product categories and choose the DC/DC Equipment category (last in the list). This action will cause another box to appear under the categories box.

In the new box, select VARIOUS. This will bring up a product list.

Scroll down until you find the part numbers VR24-1220 and VR24-1224. Looking at the device specs, I gather that VR24-1220 translates to "Voltage Reducer" 24 to 12 volts, 20 amps continuous. The VR24-1224 is 24A continuous. My bus has the VR24-1220 and works fine with my 4 rectangular headlights. The 24A might give more insurance.

Mine is wired with switched 24v from the headlight switch powering the converter. The converter feeds the low beams, and the high beams via the dimmer switch.
This unit was part of the R&M conversion kit at the time; can't say if it is still that way.

Craig - MC7 Oregon

Buffalo SpaceShip · July 16, 2007, 09:30:14 AM

Ask Dex nuthin'. Ask Chuck instead!

:

http://busbuilding.com/bus-conversion/mci-headlight-wiring-12-volt-lights-on-a-24-volt-system/

gumpy · July 16, 2007, 11:32:33 AM

MC9 headlights are 12v bulbs wired in series on 24v system. There is a 12v backup wired in between the two bulbs. This system works great, if someone who knows more than MCI hasn't mucked with them. Absolutely, it is a good way to put 12v bulbs on a
24v system, without the expense of transformers, converters, heavy duty switches, breakers, etc.

As for the clearance lights, I'm not recommending that any longer with LED lights. Nearly all of mine have burned out, and until I can figure out if they were just plain cheap junk, or it was a result of series wiring, I'm not recommending it. I'll be changing them out this fall and running them off 12v. Will then see if I have as many die as I did before.

craig

Stan · July 16, 2007, 12:21:10 PM

gumpy: Series wiring will only work with identical bulbs. Otherwise, one bulb gets high voltage and one get low voltage.

If you have a heavy wire (#4 or even #6) from a Vanner equalizer to the front junction box, it is easy to put in a 12 volt bus bar and connect all the exterior light breakers to 12 volts. None of the switching needs to be changed but you need to change to a 12 volt signal flasher. If you have current relays to sense brake or signal bulb failure, you have to adjust the relay for the higher current at 12 volts. They cannot be adjusted low enough for LED lights.

Jerry32 · July 16, 2007, 07:28:30 PM

Most here don't understand MCI's system . They actually us the center of the 12 V batteries in series to stabilize the voltage for the series headlites so even if the bulbs are mismatched they still get the proper voltage. Jerry

gumpy · July 16, 2007, 09:38:14 PM

Quote from: Jerry32 on July 16, 2007, 07:28:30 PM
Most here don't understand MCI's system .

Boy, there's the understatement of the decade.

If they did, you wouldn't get people telling you it can't be done, and won't work.

My headlights had been mucked with prior to my purchasing the bus. Left me in the dark on a deer infested highway one night at 0-dark-thirty. I wired them back to the original schematic. Haven't had a bit of problems with them since, except when I hit those two deer last December. Shattered one low beam bulb, but gosh, the other side continued to shine as if nothing had happened. Someone must have forgot to tell that bulb it couldn't continue working without it's partner.

I didn't have to change any breakers, readjust any relays (whatever the heck that means), or increase the size of the wires. All I did was move the diodes and breakers up out of the moisture of the steering compartment.

Why anyone would want to change from a tried and proven system is beyond me, but it happens all the time, and there are several on this board who seem to think they know more about MCI engineering than the engineers at MCI who designed the system.

I just don't get it.