DIY auto trailer wiring circuit

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I am looking for a circuit that will allow one to hook a trailer to a modern car. Something similar to this unit from eTrailer. I would like to set this up on 2 or more cars so for $65 each I am willing to take a look at it.


I do not think I have PWM or multiplexed wiring. I expect the heart of this is 3 mosfets but am unsure of the short circuit protection. Maybe a resetable fuse for each of turn signal and running lights.
 
What I have done is to just tie into the lines going to the brakes, blinkers, and running lights bulbs and use those for the trailer lighting power sources. If you are only running a few lights on the trailer for each function their shouldn't be any problems with the stock system being able to handle the added load.

If you have other concerns or need more power I would suggest tying into the stock bulb power lines and running relays instead and a dedicated 12 volt fused power lead from the battery or an ignition source to drive the trailer lighting loads.
 
If you have other concerns or need more power I would suggest tying into the stock bulb power lines and running relays instead and a dedicated 12 volt fused power lead from the battery or an ignition source to drive the trailer lighting loads.
Click to expand...

That is the plan but instead of relays I will be using solid state devices designed for such a purpose as mentioned earlier in the thread. Just need to get my butt in gear and order the parts.
 
I doubt you will find a common circuit for all trailers. Each hookup is specific to a particular vehicle.
 
If you use LED light assemblys on the trailer you probably dont need any thing, as they draw verry little current.
 
#debe Strangely enough the trailer does use LEDs but I want to protect the car from short circuits in the trailer wiring.

@shokjok I intend to make one of these units for each vehicle. Regardless of what is in the car the connector will work with the standard flat 4 plug I have on all my trailers.

@KeepItSimpleStupid Yup including the one that had the part number for the Linear brand chip I wanted to use.

LTC1156 - Quad High Side Micropower MOSFET Driver with Internal Charge Pump
or
LTC1155 - Dual High Side Micropower MOSFET Driver
 
A polyswitch fuse on the negative return would protect against a bulb short, or a polyswitch on every line to protect everything.

The commercial units esp the ones that multiplex will probably use a microcontroller and a current sense resistor to measure the current, and shut down in the event of over current.

How complex do you want to go?
 
Originally I was going to use a microcontroller and I still may if I have the need.

I have the LTC1156 which does a lot of neat things including over current protection on order. AN53 has a lamp drive circuit, shown below, but uses 2 old hard to find fets. Need to check a cross ref.


I also need to grab a car tail ligh bulb and check the current.
 
I have used that series of high-side drivers and don't believe the mosfets are critical to the operation of the controller. The mosfets are both normal gate voltage. The main current carrier is the MTP3055 which is just a 12A/60V mosfet. I suspect anything similar or greater current will work. The VN7002 is just to provide a delay in voltage sensing (1M X 0.1uf on its gate). I couldn't find it quickly, but considering its role, any small mosfet with a 60V rating or so should work. A 2N7002 or 2N7000 might be a good replacement.

BTW, I need to wire up a small trailer this Summer too, so will follow your progress closely.

John
 
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Yes the mtp3055 shouldnt be hard to replace, if its 1 or 2 amps then maybe an irf540 would be a good replacement, the fet will be on or off rather than operating in its linear region so dissipation shouldnt be an issue.

Stop lights usually pull a couple amps, and side lights 1/2 an amp.

That circuit looks overkill if your going to use a pic as well as the ltc chip, if you can stand a little more volts drop, like maybe 0.5v you could stick that straight into a pic's atod channel.

Edit: I just wired a 12v 5w auto bulb to my power supply, at 12v it pulls 450mA, and at 13.8 as on a vehicle with the engine running it pulls 490mA.
 
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Thanks guys this is great. I am taking my time on this so don't be surprised if there are weeks between posts.
 
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