schematic proofread

Hey everyone, hope all is well. I have a request, I have made up a schematic and I don't see any problems with it, however would like someone to proofread it for me, before we go spending the money to buy the supplies and spend the time putting it in, just to find out if it will work.

Back story, I drive a tow truck for a large local company, one of my coworkers has recently bought his own flat deck tow truck, down the side of the deck are 8 or so lights, containing 2 less each, they are wired to the driving light, and come on with the headlights, when they come on, they are on solid. He would like to make them flash when he turns on his light bar.

What is not included in the schematic is the wiring to each light, as it is now, each light has a local ground, and the positives are hooked in parallel to a single line that runs the length of the deck, with splices coming off as it passes the light, the plan is run a second wire along side, and change the positive lead in the light to this new wire, so all the lights will come back to be in 1 of 2 groups, and will be brought back at one of two wires to the cab.

The other thing to note is anything grey on the schematic is what must be added, and the rest is what exists



Thanks in advance for your help!

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the second I hit submit, I realized that schematic was missing the uber important relay, that will allow these lights to flash while the headlights are on!



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So the strobe is flashing whenever the lightbar is on, and it has a grounding output - not +ve. (?)


Are all 4 triangles LEDs, or are the left two controllers/circuits?
If the latter, do they have their own power, or only the +12V from the headlight switch (in which case LEDs are off when headlights are off unless it's a +12V strobe)?

hey old spark, as normal, you've talked in words a little more technical than I know.

as for the controller, I am not sure just yet what it's leads are, the one I have (but not the one we will be using) just has a positive and negative, then the outputs have positive and negative each, however I believe most of the better quality ones (mine is a cheap ebay chinese deal) are designed for self grounding lights, as most of the lights ARE.

the two left diodes (triangles) are just to prevent the back flow of current from one group to the other, while it is strobing, the one with arrows are the LEDs. I pulled the symbols mostly from memory, except the relay, which I googled

I will know more about the controllers, hopefully next week, I will be going to talk to my stepdad, who is the manager of a commercial truck outfitters, and they have a parts section I will talk to, and check out some of the modules. For the time being, I am going to assume they are all switched positive, if not, that makes everything much more difficult!

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this is very similar to what we are most likely going to be using, it's wires are positive, negative, bank 1, bank 2, and mode (which I believe is a momentary pos switch)

https://www.strobesnmore.com/Able-2-Universal-LED-Flasher.html

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That linked strobe is for common ground LEDs/lights which is the normal aftermarket offering (since GNDs can often not be intercepted) - ie, it's +ve or +12V switching.
It handles 3A per side.


Include diodes in the strobe's L & R (or 1 & 2) output as per the diodes from headlight +12V. That's to ensure the headlight +12V does not (feed into &) ruin the strobe's outputs.

So the LEDs flash when the light bar is on irrespective of the headlight switch.

With the lightbar off, the LEDs are only on with the headlights.


And sorry - I should have realised they were diodes to prevent backfeed.   

those extra diodes are a great idea, i hadn't thought of that, I will add them in, it makes sense... I can't see the headlight circuit causing damage to the flasher module, but at a cost of $2 each for diodes, I think we can add them in...

yes, that is exactly the plan, if the light bar is active, everything should be flashing. The leds down the side of the deck of the truck are there to make the truck a little more visible when driving at night, and aren't required by law or anything, so there's no reason we wouldn't want them to flash with the other lights, when the truck is in "high visibility mode" lol.

other than that though, it seems like it should work with no issues?

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True - normally headlight should not be present to get to strobe, but if the relay is slow to open (yes - it may take a few mSecs to disconnect), or if the relay fails or loses its headlight connection. Hence it may be safest to add the diodes (at the expense of a ~0.7V drop (or lower - say ~0.3V - if Schottky diodes).


PS - yes, it should work assuming the LEDs are less than 3A and the diodes handle the LED current.

Cool!

That manufacture makes a heavy duty version, that is 6a per side, (12a total) and worst case scenario, I can just make one side of the deck run off of 1 controller, and the other side off of a second controller... I'll have to figure out what the current draw is on them first.

The resistance of wire doesn't need to be taken into account on the amp draw does it? And if say all those little lights add up to exactly the max, there would be a margin of error built into the max rating, right? (Not going to be a situation where if you're over by 5% it's a guaranteed failure)

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Well, resistance versus Amperage is always important.
Whilst the Amperage cannot exceed cable etc ratings for safety reasons, if that limit is approached for long runs it's usually pretty disastrous simply because of the voltage drop - ie, the end load or loads with not have sufficient voltage.

In your case - a long truck - the furthest LEDs could be dimmer.

However, if LEDs have replaced traditional incandescent bulbs, Amperage is unlikely to be a problem - ie, a 20mA LED string verses a 250mA 3W 12V bulb or 125mA 3W 24V bulb.


From the safety POV, heat can melt insulation which could lead to an arc which might NOT be protected by a fuse, and hence a fire starts. That's probably the cause of most (old) house electrical fires tho fusing is more likely to protect in 12V & 24V DC vehicles.


IMO a 5% overcurrent is not much more likely to cause an issue, but I could paraphrase and say it might be more likely than running at 95% of rating and having a problem.
Ratings are often worst case or allow for 95% or 99.995% of samples etc. Ratings may have an added safety margin or they may be at a certain (lower) temperature or not take vibration or separation from chassis/frames into account.

The main problem is that if ratings are exceeded and something happens, insurance may not hold etc. (The same same thing happening with non-exceeded ratings may be totally acceptable... LOL.)

IMO one of the best checks is cable warmth (ie, when not flashing, and before the first LED).

The voltage across the last LED could also be checked if a visual dimness test is difficult. (Then again, brighter LEDs closer to the cab....)

cool, that answers most of the questions I had. the lights are LED right now, and likely were LED when they were installed by the outfitters...   I think it's highly unlikely that the LED's will be over the current limit for the modules...

I think this has been put on hold anyways, I was away from work for a couple months due to a motorcycle accident, and the guy who owns this truck just bought a motorcycle, and wants me to help him build that first, so you know...

As always, thanks for the help oldspark!

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