Rear LED car indicators with 60V supply going on and off as the indicator flashes?

[Flyback]

Hello,
We have 30 rear car indicator LEDs which are running from BJT based linear regulators (three LEDs in each string, and a pass BJT in each string, running from the 12V car battery).

However, the indicator current has just been increased to 120mA, and now the SOT89 BJTs are running hot (443mW total in each SOT89 BJT). Therefore we wish to change to a SMPS LED driver solution.

Would there be any problems with us having a 12V to 60V boost converter on the remote rear lamp control PCB, and then bussing this 60V to the rear LED indicator PCB, and then having two ZXLD1366 buck LED drivers on the indicator PCB to drive the 30 LEDs?

I mean, is there a problem since its 60V that would be going on and off as the indicator relay switches to give the indication.....? That is, the 60V would be going on and off in the connector to the LED indicator PCB, and this may cause too much sparking in the connector contacts?.....obviously before it was just going on and off with 12V....but would a move to 60V cause sparking problems in the connector contacts as the indicators flash ON and OFF?

ZXLD1366 LED driver
https://www.diodes.com/datasheets/ZXLD1366.pdf

 

[ChrisP58]

Sparking in a connector is usually only a problem if the connector is plugged or unplugged while power is applied. Unless the connector pins are very loose so that vibration causes connect/disconnect events, you shouldn't have a problem.

Of course, increasing the voltage beyond what the insulation is rated for is another issue you need to look at. And that applies to the wiring as well. I expect that the insulation is capable of standing up to 60 Volts, but what is it rated to handle. Because, there only expected to carry 12V, many automotive electrical components have relatively low voltage ratings.

 

[ronsimpson]

Having done auto design:
I would never run 60 volts around in a car. For auto repair it is typical to test to see if a wire is live by connecting a 12V bulb. (or a meter) No one will be prepared for 60Volts! Also there are roles about no voltage above 48 volts. (shock a person)

I would run 12V to the bulb. What happens inside the bulb is no ones concern.

 

[Flyback]

I thank you kindly for your advice, but its not good news, .....we need to get rid of these linear regulators as they are running well hot.....theres no room inside the lamp enclosure for the smps.....we have to put it in the rear lamp control unit, and run the 60v to the lamp from there.
Surely in this day and age, running 60v to a lamp is manageable?

60 volts is within SELV limits...the 48V refers to AC I thought?

The rear lamp control PCB will be in an enclosure... and the wires with 60V , which run to the lamps, will be within shrouded connectors...
The 60V is the output of a power limited (12W) SMPS....its nothing dangerous surely?
I must say I've zapped myself on voltages from 80VDC, to 230VAC, even touched the drain of a flyback that was going up to 1000V......also used to test 10W, 500V SMPS's whilst working at a scanning microscope place...used to shock myself on it every day because it was impossible to do the test without shocking oneself.

I must confess I wasn't shocking with one hand connected to the circuits ground return.

At one company, who were developing a mains lighting product, I was the company's "shock dummy"...they would get me to touch conductors to test the shockability just in case installers might touch it......I only grabbed the conductors between thumb and forefinger...but some of them left me with strange numb feelings inside the finger for several days after ward.

However, surely no one can touch inside a shrouded connector?

 

[4pyros]

Well lets put it this way 60 volts at 120ma can kill you!!!!!

 

[Flyback]

in that case we would have to run the 12v into the lamp enclosure and boost up in there.....that's not too good as its hot in their with all the leds on etc

 

[alec_t]

I must confess I wasn't shocking with one hand connected to the circuits ground return.

Maybe you weren't, but vehicle mechanic Joe might be standing in a puddle in some muddy farmyard trying to fix a faulty lighting circuit .

Edit: I'm all for modern technology, but wouldn't it be a lot simpler to replace all the LEDs etc with a filament bulb?

 

[Flyback]

thanks, so anything up to 48VDC is ok though?
Anyhow, These are LED lights, on a PCB etc, nobody can open them up, its a garage job. So I doubt anyone unqualified will try and fix them....the Rear Lamp Control Board will have a warning on it stating....do not fix it yourself.

 

[alec_t]

the Rear Lamp Control Board will have a warning on it stating....do not fix it yourself.

That may give some comfort to the manufacturer, but will act as an open invitation to tinkerers .

 

[Flyback]

I see, SELV rating is to 42VDC I believe, so anything up to to 42V is absolutely fine?.....I mean , a few years ago, every car in the world was going to be with a 42V bus?

 

[JimB]

I'm all for modern technology, but wouldn't it be a lot simpler to replace all the LEDs etc with a filament bulb?

Strange isn't it how the old technology which is no longer "cool" is often the overall best solution?

JimB

 

[Misterbenn]

I might be wrong but I'm fairly sure lorry's use 24V. And of course with electric cars these days there can be very high voltages present. Any garage that just assumes everything is a 12V system would be stupid if you ask me.

However amateur mechanics would be quite likely to fall foul of this, but if its listed clearly in the wiring manual then i'd say its fine. In any case it sounds like your developing this commercially so you should read up on the relevant industry standards.

You can have quite a lot of stored energy in your SMPS so arcing might be possible, certainty your LEDs wont turn off immediately. A better approach may be to supply 60V and separately supply a square wave control signal to the SMPS. Why would you ever have modern LEDs with SMPS and then use an old school relay!

You mention putting two buck regulators on the Lamp PCB to drive your LEDs. well instead of boosting and then bucking why don't you just put two boost regulators on the Lamp PCB to drive the LEDS then you could just use the standard 12V.

 

[4pyros]

so anything up to 48VDC is ok though?

I don't think anyone said that!
Why would you use such a high voltage for car LEDs anyway??????????

 

[Flyback]

48v is a nice high voltage with which lots of leds can be driven from a cheap, low component count, zxld1366 led driver.

 

[4pyros]

48v is a nice high voltage with which lots of leds can be driven from a cheap, low component count, zxld1366 led driver.

Why is it nice?
Most automotive applications would not put all the LEDs in series anyway.
How much power are you wasting by stepping up to 48 volts and then back down to what the LEDs really need.
What happens when your car gets rear ended and the high voltage blows up the leaking gas???
Why do you want to kill people???
If it was a good idea then the car companies would already be doing it.
I think you need to rethink this hole thing, its not just about if the LEDs light up!

 

[Misterbenn]

wow that's some serious paranoia

48V is still considered Extra Low Voltage. Plenty of cars have higher voltages that 48V, think of spark plugs to name but one!
As for igniting the leaking petrol, I'd be more concerned about the hot engine and sparks from the shorted battery terminals.

Aircraft routinely use 28Vdc and 115Vac, they carry some seriously explosive fuel and don't seem to consider these 'high voltages' a risk. Again hot components are far more likely to be the cause of the fire.

I'm not saying this person should use 48V, I'm just saying I don't believe its as absurd an idea as people here are making out.

DO check the relevant standards, cars are some of the most standardised machines in the modern world, you will find a section telling you what voltages you can use and what markings / safety precautions to use for unusual voltages.

 

[4pyros]

Plenty of cars have higher voltages that 48V, think of spark plugs to name but one!

Yes and they have been properly designed, routed and secured and crash tested to minimise the dangers. Can the OP do that?

 

[Misterbenn]

Can the OP do that?

We don't know but this is the same for almost every other thing on this forum. We show people how to build RF transmitters, HV & grid tie inverters, battery chargers and a whole host of other things. We assume a lot of regulation compliance from the forum members here.

In this case the repeated use of 'we' and 'us' by the OP makes me think this is a commercial application (tut tut coming on a DIY forum if that's the case). However it could just be a group of boy racers looking to do up their car...though I doubt it. In any case if the OP is looking to sell this then it is down to 'them' to ensure this satisfies relevant regulations and safety requirements.

 

[Flyback]

there are plenty of automotive led drivers out there for rear lamps which boost up to more than 48V for long led strings. -nobody complains about this.
We currently use linear led drivers and multiple led strings for the rear indicators...however, they have increased the current to 120mA...and the SOT89 BJT regulators are running hot.
Therefore, we wish to use smps instead.
We don't wish to use a boost led driver as the led current must be routed between multiple led pcbs...and when someone disconnects them, the led driver will see output open circuit....it will then drive its output cap up to the overvoltage limit.....then when the leds subsequently get reconnected, a spike of current will surge through the leds...this is bad, and therefore we don't want it that way...instead we will route a constant voltage 42v bus between the led pcbs, and just run local buck converter led drivers from that.
The buck led drivers are great because the hysteretic ones have no feedback compensation, and thus they can be quickly changed to drive more leds as the led light pattern shapes are constantly changing on these rear pcbs.....have you seen the rear led lights which look like eyeball/eyebrow/eyelashes?

Regarding high voltage in car lights...HID headlights have high voltage in them, and no one complains...also, front led headlights are multi-led and the led string is at least 50V+, but again, no one complains.