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Forum Index : Microcontroller and PC projects : High-Beam lights for your computer-controlled car....
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Grogster Admin Group  Joined: 31/12/2012 Location: New ZealandPosts: 9308 |
Hi all.  Many modern cars now have LED headlights, and more then that, those LED headlights are controlled and monitored by the car's computer unit. Any excessive current flow in the headlight circuit will cause the computer to go into an error state, as will ZERO current in those circuits - the computer will conclude the lights have failed, and will indicate as such. So, the days of just paralleling extra lights onto the high-beam circuit are gone with modern cars and car computers, and also modern cars use much thinner wire for the headlights, as LED's are much more efficient then old halogen or globe-type bulbs that were used for headlights in the past. A chum of mine needed to interface a pair of 50W halogens to the standard HB circuit, but could not directly connect, and could not even put a relay on the HB circuit, as the car computer decided that the relay current was a fault condition!  So, this circuit was born. 5mA load to the computer-controlled HB light circuit, but switches the big-boys on via the battery, a protection fuse, and a 10A relay. The relay and load current are totally isolated from the car-computer HB circuit. PC123 opto-coupler to the HB circuit, paired with a standard BC337 in a Darlington arrangement, to drive a 12v relay coil. Let me know if anyone thinks this is useful enough, and I can post a constructor pack.  Smoke makes things work. When the smoke gets out, it stops! |
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| robert.rozee Guru  Joined: 31/12/2012 Location: New ZealandPosts: 2350 |
what is the relay's coil resistance? when turned on, the BC337 will see 0.6v across collector to emitter and so will at the least get warm. google says that a headlight relay's coil typically draws 150-200mA. i would suggest either: 1. cut the track running to pin 4 of the optocoupler and connect pin 4 to B+ via a resistor of perhaps 1k5. this will ensure that the BC337 is fully saturated when on. or: 2. leave out the optocoupler completely and bridge between pins 1 and 3 of the optocoupler's footprint - this would mean HBI is connected via the existing 2k2 resistor to the base of the BC337. btw, did you intend that the LED be permanently illuminated? as shown it will permanently draw a few mA from the battery and create a (red) glow from wherever the PCB is mounted. the current draw is likely far less than existing parasitic losses within the car, but the glowing LED may be an annoyance. cheers, rob :-) |
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Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 6798 |
Why would the BC337 stay warm? Not unless the opto is conducting. There's no other base current. Not sure what the opto is, but I assume it's the usual collector and emitter output and it shouldn't conduct normally. It would have been nice to see a pull down resistor from the base of the BC337 to reduce leakage though. Agreed, the opto is perhaps a little bit of overkill. I like to put a zener in series with the input resistor (e.g. 1-3 of the opto position), say 8V, so that the transistor turns on when the control input is Vz+0.6V and drops out cleanly when the input falls. Of course, the opto will be needed if the input circuit needs isolation from ground. Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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Quazee137 Guru Joined: 07/08/2016 Location: United StatesPosts: 571 |
Have a look RT9193 I started using these to drive the 5VDC relays using the EN pin. Quazee137 |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 6798 |
Not for a 12V car electrics system with a big, meaty relay, I don't think. :) Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| Quazee137 Guru Joined: 07/08/2016 Location: United StatesPosts: 571 |
I have a 48VCD E-Trike using a MM170 to control and monitor the system. The relays I use are good up to 10Amps on the contacts. Led headlamp, turn signals, back and side IR lights for nite use with camera. Each has a breaker don't want to be out have have a fuse blow. Things have been working no problems. Quazee137 |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 6798 |
But the RT9193 data sheet says supply input voltage 6V. Great for switching a 5V relay from a 5V or 6V supply and would interface nicely to a PicoMite. Perhaps your relays come after a regulator? Grogster is using a 12V relay from a 12V supply. Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| Quazee137 Guru Joined: 07/08/2016 Location: United StatesPosts: 571 |
I have a 48VDC to 12VDC buss and 12VDC to 5.5VDC needed for the MM170 display. Here is the relay SLA-05VDC-SL-C it also comes as SLA-12VDC-Sl-C both good to 30amps but using 10amp breaker. The 5.5VDC feeding breaker then RT9193-50PB feeding the SLA-05VDC-SL-C and EN from the MM170. I guess my thought was that a lower voltage would be available like the HIB is. Quazee137 Edited 2023-06-17 05:04 by Quazee137 |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 6798 |
I suspect that the HB wire will simply be connected to the high beam headlight, but via a current monitor in the computer. It'll be 12V. The B+ will be 12V via a heavier wire from the fuse box (I hope! The wire needs protecting). There is no bus connection so this would work with any version of any bus :). Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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