Road train lighting

[tamiya fan]

I have a question, if some one could help. I am building a 2nd flatbed to go with my 1st one. I would on occasion like to run the 2 together with a dolly in between.
So my question is, has any one run the 2 trailers, dolly, with lights for all 3 running off of MFC? This will be 4 tail/brake light, 4 turn signal lights each trailer and then dolly. I know the MFC has it's limits. Just wondering if some one has accomplished this, before I go through all the work to find out it won't work. I don't want to design a circuit if I don't have to. Any answers/Ideas?

[ricm]

If you are using MFU as power source it is a bit risky since the extra current drain can pop the MFU. I've known people run a second trailer light set in parallel from the MFU for a road train without trouble (initially, at least).....I've also known people break the MFU trying to add extra head lights which is kinda the same thing. But for 3 lights sets, safest option is to splice opto-couplers into your first trailer light set (one opto-coupler for each indicator, and a 3rd for the tail/ brake lamps). You can use the outputs to drive the mutiple trailer light sets in your subsequent trailers. The opto-coupler isolates the MFU from the extra current draw for the additional LEDs. If you search '4N25' or 'opto-coupler' on this forum you should find a few threads on how to do this. Not expensive to do, but you'll need a soldering iron, a bit of veroboard or stripboard, and a power supply on the trailer where you have the opto-couplers (which you could take from the truck itself).

[tamiya fan]

I read this earlier. Would this set up take 3 circuits? 1 for RH turn, 1 for LH turn, and 1 for tail/brake light, or can it be accomplished with 1 opti-coupler?

Thanks for response!

[mavrick0]

You would need one opto coupler for each function. So in total you'd need 3.

[tamiya fan]

Thanks for the info. I did some research and there is a quad unit.(LTV-847) I got some ordered and will experiment. Hope it works! I wanted to isolate the MFC any way to play it safe. Will be adding about 12 leds over the 3 circuits of the trailer lights and thought it would overload. I'll Feel safer this way, hope I get it to work.

Thanks for the help ricm and mavrick0.

[mavrick0]

Just keep in mind that it only has 50mA max output per channel. So a couple of LED's and you are at the max.

[tamiya fan]

Hey mavrick0 let me ask you this.(maybe I'm wrong) I can use the input of the opto splice into 1st trailer lights (as a trigger) and power the output of the opto from it's own power source off the 7.2v truck battery. (run set of wires back) Or are you saying that the opto coupler has a max of 50mA. And if so any ideas?

[mavrick0]

Each output of the opto coupler has the 50mA max. So the safest would be to splice it into the first trailer then run things back to the second trailer and dolly. Also you don't really need a 7.2v battery. Just the voltage to run the LED's. Using a big battery like 7.2v you'll need drop the voltage down a good amount.

To me 50mA isn't really enough which is why the opto couplers I use have a max of 600mA outputs. Even if I have to use multiples when it comes to the size on a circuit board it's still a small circuit.

[tamiya fan]

Thanks for your time! So I guess I picked the wrong Opto is what you are saying. The quad sounded right. I will have to do more research. You've been helpful and appreciate it!! Hope I figure this out, doesn't sound hard but ya know? Do you have any recommendation for the single Opto?

[ricm]

you've got the right approach - you'll need 3 opto-couplers as you've correctly identified, you can buy a single chip that has 4 of them all bundled together.

Each LED might only need 20mA so the unit you've got might be OK, but I would agree to buying a higher capacity unit to install. Maybe use the ones you've bought for R&D.

So you need to splice the 'input' side of each coupler into your trailer wiring loom...the coupler needs to be in series with the relevant LED circuit so it can 'grab' the signal. The 'output' side then also needs a power supply for subsequent LEDs.

You will need at least 5V supply because the tail/ brake lamp LEDs are connected in series with around 2.4V each. If using higher voltage supply, and when powering only 1 LED (eg. turn signal), make sure you have the right protection resistors where required. I use 7.2V supply because I find it easier to have same battery packs throughout my truck/ trailer combos. I have wireless control for my trailer lights so I've had to install a battery in each trailer. In your case if you plan to retain the standard hard wired system, I would suggest that you have a 'power supply' bus in each trailer (ie. a +ve and GND line) with the source being the truck. This way, you can avoid having to fit batteries everywhere.

Whilst technically you can put the optocouplers in the first trailer to switch LEDs in the other trailers, it will mean that you always have to couple your trailers together in the same sequence. I've put optocouplers in all my trailers so that ANY trailer can be hooked up to ANY of my prime movers, in ANY sequence. A bit more effort, but easier to work with once you're done...

[ricm]

for single opto, I used 4N25 everywhere.

[tamiya fan]

Thanks ricm, All that info. helps! I have been looking for more opto couplers and was getting no where fast for a higher output. The #4N25 will help, I'll look into it. I was almost going to ditch the idea but it's no good if the lights are just running lights, takes away from it all. Now to figure out how to hide all the wiring. I'll work it out.

Much thanks to both you guys!!

[ricm]

no problem.

Once last thing to be careful about - check the polarity of the signal coming out of the MFU. I -think- that the MFU provides a common +ve supply to all the LEDs, then switches them on the -ve side down to GND. Whichever way round it is, you need to make sure that your opto-coupler outputs work in the same way if you want all your trailers to be interchangeable between each other and the truck. The opto-couplers can equally switch a +ve supply to the LED, or they can switch the -ve side of the LED down to GND as long as you wire it up right for the operating mode you choose.

[mavrick0]

I use a AQV201 for my builds when I need one.

Another option if you don't mind paying a little more is looking at something like the OB1 system for the MFC. It plugs into where the trailer lights plug into on the MFC and uses Bluetooth to controller the trailer. It has lots of power to do what you are looking to do as I've used one on a friends truck and A train setup to do the same thing plus it has the bonus of having clearance lights and reverse lights if you want them.

[ricm]

Originally Posted by ricm

the tail/ brake lamp LEDs are connected in series

might have got that bit wrong - you'll figure it out if you look at the way they're hooked up....either way, I would suggest 5V minimum with protective resistors. I think the MFU actually provides 6V output if you measure it with a multimeter. The voltage that the LED sees is then dropped down through a protective resistor, once the LED lead is plugged in and the circuit is completed

[ricm]

Originally Posted by mavrick0

Another option if you don't mind paying a little more is looking at something like the OB1 system for the MFC. It plugs into where the trailer lights plug into on the MFC and uses Bluetooth to controller the trailer. It has lots of power to do what you are looking to do as I've used one on a friends truck and A train setup to do the same thing plus it has the bonus of having clearance lights and reverse lights if you want them.

Yep - if you can afford it go wireless, then everything works regardless of how its hooked up!

[tamiya fan]

Once again thanks for all the info. I am looking into all the options now and have to decide. The OB1 sounds great, wish I knew about this 2 years ago. Can't know everything even with the research. My dilemma is I have 4 trucks to pull trailers(+a couple other types), and this trailer would be the 6th, and they are all hard wired. I want everything to be compatible. I really don't want to back track all the builds and plenty of ways for things to go wrong while doing so. So like I said, decisions! I'll probably go hard wired, not sure. The OB1 would be the way to go!

Thanks to both of you for your help and advise!!

[tamiya fan]

I have another question. Can you hook up both hard wire and the OB1, say with a switch to toggle between the two? To operate at different option times? (IE: Road train and regular).........Once you think you know things.

Let me know.

[mavrick0]

You can get a stand alone OB1 that doesn't use the MFC to control it. It just gets wired between your RX and servo's. So with a couple of y-harnesses you should be able to hook everything up.

[tamiya fan]

I'm looking into everything know, Optocouplers, OB1, SS-Tronics (Which will be costly) I've got too many trucks to retro fit everything $$$. I did notice the stand alone OB1 but that just eliminates the MFC control. Probably go with the opto's but then hiding the wiring. One of the flatbed trailers is built with lights all ready (running, etc...) and was hoping to just tap into it. I'll mow it over for a few days to see which way to go.