At some point I will want a trailer. Before I get too advanced with construction, I want to do the trailer wiring. I figure a single power wire with relays tripped by the power at the rear light clusters. Given that the cable needs to carry enough power to light two reds, two ambers and possibly side lights too, what gauge of wire should I use?
12ga or 14ga to the trailer plug. 10ga from the batteries to supply the relays.
You should also consider that many buses have 4 circuits (tail, brake, left turn, right turn), whereas most trailers only have 3 (tail, left brake/turn, right brake/turn).
You probably want to build a system that combines your brake and turn signals.
http://www.gumpydog.com/Bus/MC9_WIP/Electrical/Tail_Light_Converter/tail_light_converter.htm (http://www.gumpydog.com/Bus/MC9_WIP/Electrical/Tail_Light_Converter/tail_light_converter.htm)
Gumpy, great post--well explained. Although I didn't have to deal with the 24/12 volt issue, I did have the same problem with the 4 circuit to 3 circuit conversion device weakly flashing the opposite turn signal particularly with several signal lamps in use. The actual cause of the problem is insufficient amperage being provided by the 4/3 converter to operate the several bright signal bulbs. I solved the problem by using the output of the conversion device to activate a pair of 4 terminal 12 volt relays, one for left and one for right. The output of the relay came from a fused link directly from the toad's battery which thereby lit the lamps. The tail lamp circuit seemed to provide enough amperage to work directly from the 4/3 converter so I left it alone. Since the stop and turn signals are in only intermittent use, the draw on the toad's battery is negligible. Jack
Commercial trailers use 14 gauge for the lights and 10 gauge for the brakes, 12 volt systems.
Brian
My bus is straight 12v. To pull my car or any other trailer, I made a 4 light magnetic lights with a long cable. As mentioned, I have running, brakes, left turn, right turn, ground-I use a 5 prong plug. I just run the wire down the side of the tow car and plastic tie wrap to the door handles. I tried wiring the car's lights, but wasn't bright enough. With running LED lights on the tail lights of the bus and LED's on the 4 magnetic lights, no relays were necessary. Just another thing to keep it simple. Course, if you have a 24v bus, that's a different story. Good Luck, TomC
With a 24 volt bus, you run 24 volt lights in the magnetic lights and lighter wiring.
I have a "Gumpy-made" 24 volt to 12 volt converter, it works flawlessly. I am very proud of it, I show it off to everyone who gets to see the passenger side of my engine compartment... :o
Brian
I don't know what kind of bus you have. I have an Eagle. 12V.
I burned out so many converters I finally just installed another pair of lights on the trailer.
That works perfectly. I've done all my trailers that way.
I have a schoolbus and it all seems to be 12v. Would it perhaps be better to have my own lighting board to tie over any pre existing board on a hired trailer?
Not sure I understand your question.
If you have split brake and blinker circuits, then I would recommend you install a relay system in the bus. That way, you can pull any trailer
that your bus can handle and won't have issues with the lighting, other than maybe needing a plug converter (6 prong, 4 prong, etc).
The relay system on my website will work for 12v, also. You just need to use 12v relays.
So... Relays coming off the rear lights with power to the trailer lights supplied by a single 10 gauge wire?
Quote from: Zephod on February 18, 2015, 04:32:36 PMSo... Relays coming off the rear lights with power to the trailer lights supplied by a single 10 gauge wire?
That's what I'm planning. I'm also going to use LED trailer lights to lessen the load.
Accidental double post ...
Quote from: Zephod on February 18, 2015, 04:32:36 PM
So... Relays coming off the rear lights with power to the trailer lights supplied by a single 10 gauge wire?
Yes, you can use the rear light signals to drive the relay coils. Switch the larger wire supply through the contacts and the outputs drive the trailer plug.
The schematic on my website does the combining of the separate brake and turn signals into a single brake/turn signal for each side.
There are some other schematics on the site for doing that combination, but they are basically the same. Most use less expensive relays
than I do. Mine uses the same relays already found in the MCI buses. Any decent DPDT relay will work.
Search for those other threads. This has been discussed a lot here.
Thanks. I'm praying 10g will be enough for sidelights indicators and brake lights. I like your idea of having two cables. From my reading, car lights use unusually high amps for low watts output.
Craig,
Is there a special reason to use the 1N4004 diode or can it be substituted with something else?
Reason is my local supplier does not usually carry that particular one.
Thankz,
Jim
These are the diodes I use http://www.ebay.com/itm/290641207911?_trksid=p2060778.m1438.l2648&ssPageName=STRK%3AMEBIDX%3AIT (http://www.ebay.com/itm/290641207911?_trksid=p2060778.m1438.l2648&ssPageName=STRK%3AMEBIDX%3AIT)
Easy to mount, high capacity, easy connecting and only about 90 cents each. Plus four diodes in each bridge.
Quote from: Lee Bradley on February 24, 2015, 02:05:35 PM
These are the diodes I use http://www.ebay.com/itm/290641207911?_trksid=p2060778.m1438.l2648&ssPageName=STRK%3AMEBIDX%3AIT (http://www.ebay.com/itm/290641207911?_trksid=p2060778.m1438.l2648&ssPageName=STRK%3AMEBIDX%3AIT)
Easy to mount, high capacity, easy connecting and only about 90 cents each. Plus four diodes in each bridge.
OK, now I'm confused by two things ....
1) Do you need a full bridge rectum fryer for this diode arrangement?
2) (To Gumpy) Why do you need diodes and the jumper across the coil terminals at all?????
Yeah, I'm easy to confuse .....
You don't need a full bridge but they are already potted and have nice spade connectors.
I believe the diode is to protect from a voltage spike back down the circuit when the relay closes. Don't know much about electronics thus my newbie question on the diode type.
"2) (To Gumpy) Why do you need diodes and the jumper across the coil terminals at all?Huh?"
Not gumpy, but I do know the answer to this question. You recall how in a gasoline engine you use a coil to generate the spark in the spark plug? The coil in the relay that switches the relay on and off also stores up energy, and the diode shunts off that energy to eliminate issues from that stored energy. It could cause issues with voltage spikes being fed back to whatever is switching the relay, or cause the relay to hang up and not switch properly.
Brian
Quote from: bevans6 on February 24, 2015, 06:03:49 PM
"2) (To Gumpy) Why do you need diodes and the jumper across the coil terminals at all?Huh?"
Not gumpy, but I do know the answer to this question. You recall how in a gasoline engine you use a coil to generate the spark in the spark plug? The coil in the relay that switches the relay on and off also stores up energy, and the diode shunts off that energy to eliminate issues from that stored energy. It could cause issues with voltage spikes being fed back to whatever is switching the relay, or cause the relay to hang up and not switch properly.
Brian
Thanks. I'm stupider about electrical stuff than I thought, I guess. I still don't see it but I'll take your word and Lee's and Gumpy's on it. Does "every" relay have a jumper and diode? If not, why not. Doesn't every relay have a ground on the coil and energy in the coil???? Isn't it the job of the ground to take away energy? If I read it right (and I guess I don't), that relay is set to direct energy back to the trigger wire. Is that what we want?
Some cube relays have them built in to them>>>Bruce
Gumpster, I really need to pay you to make one up for my MCI9..... Please?
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This has gotten a little far afield but coils can produce very high voltages with very little current. When the coil is energized a magnetic field is generated around the coil the rate that the field is generated depends on voltage and current available. When the coil is switched off, the switch opened, the magnetic field collapses much faster than it was generated, the magnetic field collapsing back across the coil winding generates a reverse voltage higher than the applied voltage but less current. This back voltage is not a problem on mechanical switches other than a little arcing when the switch is opened. When solid state switching was introduced, these high reverse voltage created problems as the solid state systems are very voltage sensitive. So a diode has added to drain the reverse voltage to ground and not back to the switch. Most relays are not polarity sensitive but if you have a diode protected relay and hook the coil up backwards it will toast the diode. Gasoline engine coils also create a magnetic field when the points/switch is closed and the field collapses when the points/switch opens but that would create a single high voltage spark at the spark plug not the best for lighting off the gasoline/air mixture. So they added a condenser/capacitor to the circuit (creating a tank circuit see Tesla). The condenser stores the current created by the collapsing field across the primary windings of the coil while current created in the secondary windings go to the spark plug but when the magnetic field has collapsed the current stored in the condenser flows back into the coil's primary windings creating magnetic field and another high voltage in the secondary and to the spark plug. The condenser/coil continues to charge/discharge until the energy in the system can no longer produce enough voltage to jump the spark plug gap. Shortly thereafter the points close and recharge the circuit for another go.
Quote from: Lee Bradley on February 25, 2015, 08:21:27 AM... back voltage is not a problem on mechanical switches other than a little arcing when the switch is opened. When solid state switching was introduced, these high reverse voltage created problems as the solid state systems are very voltage sensitive. So a diode has added to drain the reverse voltage to ground and not back to the switch. ...
OK, that's the "back story". Diodes probably not needed (but likely to be an advantage) for plain switches but probably needed to prevent damage for solid-state switching. Thanks for the help - I learned something today and I like that. BH
Quote from: Scott Bennett on February 25, 2015, 08:18:18 AM
Gumpster, I really need to pay you to make one up for my MCI9..... Please?
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I sent you an email...
Thanks Craig! I'll be in touch :)
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Thanks for the schematics Craig. I even put a copy of them inside my enclosure so that WHEN I'm old and senile I can figure out any electrical problem. I just have to remember where I mount the damn box!
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