| Author | Message | ||
| Robert J. Wies (Ncbob)
Rating: |
Has anyone been able to come with a viable 24v to 12vdc convertor for trailers and toads? It just makes sense to me to be able to tie into tail, turn and stop lamps which are normally 24VDC and use that signal to operate trailer lights through a voltage reduction device. Otherwise it would take a raft of 24V relays and a 12v power supply to operate the trailer or toad lights. Any ideas? Thanks, Bob | ||
| Bryce Gaston (Busted_knuckle)
Rating: N/A |
Bob I know in the archives it's been talked about in several threads, and there are several commercially available units (some had issues). But what I think would be the ideal set up is a set of "tow lights" with 24V bulbs in them! Cheap, easy, use them on anything you tow with out it having to be wired the same or at all for that matter! We use them on the tow trucks everyday just secure the lights(magnet mount or other style), string the cord, plug in and yer ready to go! That's how I'd do it! Happy towing & congrats on that MC5A! Nice looking coach! | ||
| Gary Stadler (Boogiethecat)
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lots here, good stuff http://www.newenglandsolar.com/catalog_pages/catalog56.htm | ||
| Jon W. Rating: N/A |
I did that on my last coach and all I did was use the 24V coach light signal to power the coil of a relay. I ran the 12V power to the toad tailights through the relay contacts. I used a separate relay for each of the folowing functions: Stop, LH turn, RH turn, parking. It worked great on the turn signals because they flashed just like the coach lights did. | ||
| David Hartley (Drdave)
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I wired up some relays using the diagram that I think one of the guys here on the bbs drew up. I was going to use 24 volt relays but decided that since i had to run a 12 volt feed line for the trailer lights (interior) that I used 12 volt relays with 240 ohm 5-watt resistors in series with each of the relay gounds. Here is a link to the jpeg file. Looks wierd when veiwed but prints out the right size if you save a copy then print.... http://www.rvbus.net/24-12trl.jpg The reason I put it there is that I didn't remember where the original file was located. | ||
| Robert J. Wies (Ncbob)
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'Ask and ye shall receive' I think is the appropriate quotation to be used here. Thanks again guys...y'all have a way of simplifying even the most complex of problems. I think I can 'breadboard' the circuitry and come up with a applicable answer. Bob | ||
| John MC9 Rating: N/A |
Hah. And here I was going to suggest adding a 12v bulb in series with each 12v circuit you wanted to power from the 24v supply... oh well. | ||
| Leslie Robinson (Lesrmc9)
Rating: N/A |
try this http://www.gumpydog.com/bus/MC9_WIP/Electrical/Tail_Light_Converter/tail_light_converter.h tm | ||
| JR
Rating: N/A |
Have you consdidered installing 24V bulbs in the trailer? Won't solve the toad issue, but that would be an easy solution for the trailer if you don't also pull it with 12V vehicle. Additional set of lights installed on the trailer would also solve that problem to. I'm going to put a lightbar with 24V lighting into the trailer hitch on my Jeep. Just pull it out, or leave it, when not towing. I've heard of ECMs that monitor lighting failures can have their eggs scrambled by improperly wiring 12V into the lighting park and turn signal system. Don't know specifics. A light bar with 24V bulbs stuck into the toad hitch would allow no mods to the toad. A plug could be attached near where the regular plug is mounted and just plug up the lightbar at the hitch, and at the front on the bus. Leave the light lead on the toad permanently. That's my do centavos! JR Craig, are you offering the converters yet? How much? JR | ||
| Tim Strommen (Tim_strommen)
Rating: N/A |
About resistors in a series form with a Toad: (Note: The following current values are from http://mgaguru.com/mgtech/electric/et107.htm and have not been checked for absolute accuracy but should prove this point well enough). To correctly size a current limiting resistor (droping resistor) for this application, one needs to first identify the source voltage, the desired voltage after voltage dropping, and the current draw of the driven load. We use an equation: E --- I*R to caluclate the resistor. "E" stands for voltage, "I" stands for current, and "R" stands for resistance. Assuming that you want to drive two brake lights that have a standard 1157 dual-filament buld, the high-filament draws about 2.1 Amps - for a total of 4.2 amps on the brake circuit. Typical 12 volt systems run around 14.4 volt while the engine is running, so we'll assume that's the desired voltage for the load. Typical 24 volt systems run around 28.8 volts while the engine is running so again, we'll assume that's the supply voltage we'll design around. This is a difference of 14.4 volts - which is what the resistor should be dropping. By pluggin these numbers into the equation, 14.4V/4.2A = 3.43Ohms is your result. As anyone will tell you, this isn't really an easy value to find - especially at the power rating you'll need (14.4v * 4.2A = ~60 Watts!) Here's where the real trouble starts though - Once you have this resistor in the circuit and the "juice is flowing", it isn't hardened against component failures. If one bulb blows, the resistor's circuit changes: 3.43Ohms * 2.1Amps = 7.2Volt drop. This means your bulb will get 21.6 volts for a breif period before it blows (and could take out you ECM if it has an Airbag brake sensor or "Light Out" sensor). A fuse will not save the Toad in this case because the current draw will not go up enough to blow it before it does damage. Another brute force method that doesn't require too much attention to detail is using several silicon diodes in series. Each diode will "use" it's rated forward voltage value from the the total voltage. So, placing say 22 .7 volt diodes in a series string will "consume" 15.5 volts leaving about 12.5 volts for the lighting circuit at the plug (higher forward voltage diodes are available but are a little more expensive). Unlike resistors, diodes don't need to be recalculated by current draw if a bulb blows (therby providing a higher current spike to the toad). Further safety could be ensured by adding a 15volt Zener clamping diode to cover any spikes from load dumps on the alternator. The only caution is to pick diodes based on the circuit curent draw (i.e. 1N4001 is a 1Amp diode - most 1157/1156 type circuits are fused for 15 Amps). This diode from International Rectifier is rated at 10Amps and draws 1.1 volts per diode so you would only need about 13 of these per circuit. They go for about $1.5 each at Digikey. An added benifit of diode voltage regulation is polarity protection (this of course still requires planning when installing the harness in the toad) Cheers! -Tim | ||
| Robert J. Wies (Ncbob)
Rating: N/A |
Wow, Tim..that's a lot for this ol' mountain boy to digest but I see where y'all are going. What I've done is: I've ordered 5 Bosch type 24VDC relays (20A-no contacts) and 2 (6 pin) terminal strips from waytekwire.com in Minnesota. I've purchased from the for years and they offer quality stuff at fair prices. I will build the board by Dave's wiring diagram, and fuse each 12 leg @ 5A, and take it with me when I pick up the coach. It shouldn't be a big deal to wire it in the coach and take a flat wire, 4 or 5 pin connecter out to the rear bumper of the coach. By that time I will have harnessed the 'toad' with a matching harness which will be stored under the hood for connection when I'm ready to tow. Since the generator is 12V start, and there's already a 60A alternator belted to the coach engine I'll use that battery for the 12v power supply. Seemingly big problems can easily be solved when level heads get together. Thanks again guys! Bob | ||
| JW Smythe (Jwsmythe)
Rating: N/A |
This is applicable to your question http://rvbus.net/24-12trl.jpg He's suggesting doing it with relays. I would think you could use a small set of transformers from Radio Shack to drop your voltage from 24v to 12v. It's your call on if you want to do it yourself. Tail lights are kinda important, so if you're not 100% sure of your work, you could put yourself at risk. | ||
| David Hartley (Drdave)
Rating: N/A |
Jw, Uh.. Transformers are for A.C. not D.C. Maybe you were thinking Transistors? Could be done but 4 30-amp auto/marine relays are cheaper and easier to maintain. The same relays are used on lawn tractors, mowers and many cars and boats too.. easy to get while on the road.. The hardest part was locating the lamp feeds in the rear junction box of my MC9 but the diagrams made that easy. I also found some spare wires from the front junction box to the rear to get the 12 volts back to the relays and to send the brake light 12 volt signal back up to an LED under the dash so I can tell if I lose a relay or power to the trailer plug. Also handy to use that for tripping off the cruise control later. | ||
| ChuckMC9 (Chucks)
Rating: N/A |
"I also found some spare wires from the front junction box to the rear to get the 12 volts back to the relays and to send the brake light 12 volt signal back up to an LED under the dash so I can tell if I lose a relay or power to the trailer plug." Now that's a neat idea. | ||
| JW Smythe (Jwsmythe)
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David, Thanks.  I don't make a lot of my own electronics, so I usually draw out what I'm doing, and then show it to a friend who does know 'em, so he can tell me how I'm an idiot. It's just little stuff like, "Hey, a transformer is just for AC". I found the right part for him though. This one is in England for 7.99 pounds. http://www.maplin.co.uk/Module.aspx?ModuleNo=37730&TabID=1&C=SEO&U=SEOsearchPages&doy=sear ch I found a whole bunch of them, if you search Google for dc-dc converter. Just make sure it'll handle the power you require. I don't know how much car lights draw off hand. I *BELIEVE* you can put a connection on the front of your towed vehicle, to feed back into the front turn signals, and it may light the rest of the lights on the circuit also. Be careful, I take no responsibility for you blowing out fuses. He can always do it the good ol' fashion way (i.e., U-Haul hooks up your trailer and usually screws up your wiring). Hook it up by the bulbs with those no-cut splices. You know, the original wire goes through one side, and the new wire goes in the other, and you squeeze with plyers and tape it up real good (hopefully). | ||
| Bruce Henderson (Oonrahnjay)
Rating: N/A |
__. JW, that's a helpful link. 1.1 Amp is a little low, though. Most (car) taillights are 5 to 7 watt; a pair of these lamps on a circuit is about 1.1 amp at 12 volt right there. Tail and turn bulbs are 21 watt each, so you'd overload one of these converters with only one bulb. __. On the other hand, if you're doing a center-tap and have 12 volt available, you could put one of these converters on tail, stop, and turn signal circuits (that's four but it's less than $50 at the price quoted) and use them to trigger ordinary $4.98 12v relays, which would then feed your toad lights. __. Not cheap, and getting away from the KISS principle, but it should work well. ' |
