660 Watt (55A) Running light

For my Chevrolet Van I’m going to make a 12 lights running light. There are six lights on the roof, and each light has 2 halogen light bulbs in it.

I’m going go use the Arduino Mega and use 12 PWM outputs. I want to be able to dim the lights also. I’m also going to use 3 boards with 4 mosfets on each board.

See video:

Now my question: Can the Mega drive the mosfets directly, or will the current for driving the 12 mosfets be too high?


The Arduino is only driving the gates of the MOSFETs, not the 55A. So you're okay, the gate current for the 12 MOSFETs isn't a problem for an Arduino.

Thank you very much Septillion.
I saw in a video that driving for example 8 relay's will be a problem, but ofcourse a relay needs higher current...

Actually there is a minor problem with driving the gates - they have substantial capacitance, so draw current as you try to switch them on.

You need 220 ohm resistors between the Arduino outputs and the FET gates, also 47k pull-down resistors on the Arduino outputs so that the FETs do not randomly turn on when the Arduino is in reset.

And you need to use "logic level" FETs that turn on fully at 5V, and they have to go in the ground wire of the lamps, so the lamps have to have both power wires fully isolated from the chassis. This is a problem with automotive halogen bulbs as one terminal is usually the mounting flange.

12 light at 55A each? Are you running a spare alternator/generator in the back to power these things?

Because it’s automotive I think he’s using 12 55W bulbs zo 55A total.

And yeay, you need the tings Paul mentions but I guessed (maybe wrong) he’s using of the self Arduino MOSFET boards…

And indeed, you drive the low side of the bulb, this needs to be free from the chassis. Also, the common 12V+ rail to the lights needs to be huge… Like 8,5mm2. not even talking about the fuse. I think it’s better to split them into 3 chunks with a 20amp fuse and 2,5mm2 cable at least.

If you've got the budget, I'd at least consider LEDs. You can probably get by with 20% of the energy consumption. I don't know if you'll get the same projection/focus, so it's something you'd have to try. I mean, just try one first and compare it to the halogen.

You'll need a power supply for LEDs, and you can get dimmable LED power supplies that are controlled by 0-10VDC (low current). But, I don't know how common 12V high-power LED power supplies are.

Somewhere, I've seen an automotive LED light bar. [u]Here's one[/u]. (It's rated for 9 to 32V, so this one is not dimmable.)

LEDs are finally getting to the point where they are practical & useful... My girlfriend added an outdoor LED floodlight to her townhouse and it's better than the 90W halogen flood she has in the back. It was installed by a contractor, so I don't know the wattage of the LED. (I did the inside wiring but her homeowner's association required the "installation" to be done by a licensed contractor.) I'm going to replace the Halogen in teh back with an LED fixture... We don't need the homeowner's association's permission for that, since we are not drilling a new hole in the structure... Plus, I'm not asking first...

Also in our area, they are starting to replace the streetlights with LEDs. They are a LOT better than the lousy old orange sodium lights. (Of course, I don't know the wattage of those either.)

If you go for LEDs you can dim with PWM

You may be better off using a proper MOSFET driver for this
high power application, or otherwise the slow switching through the
150 ohm gate resistors will lead to excessive switching losses with
PWM. You can with halogen bulbs make things more managable by
using a low PWM frequency, 100 or 200Hz perhaps.

Remember halogen bulbs take about 8 times their running current
from cold, so you definitely want to always ramp up the PWM to help
limit this, and derate components appropriately. Arranging that lights
come up in sequence rather than simultaneously will help reduce peak
currents too.

The large currents involved mean that you'll have to pay careful attention
to RFI, each MOSFET should probably be mounted right on or next to the lamp(s)
with copious decoupling (several 4700uF high ripple current caps perhaps)
to confine the switching currents to a small area.


I think you'll need mosfet drivers for that. Otherwise the gate capacitance will lead to relatively slow turn-on, and the mostfets will overheat (possibly exploding, at 55A!) during the transients. Especially if you're doing PWM.

Well, it works now. :slight_smile:

Nice finish, although the forum software provides better ways to post the code , like the CODE TAGS [</>] toolbutton (first one on the left). Also, if you use Microsoft Paint to resize your photos so the total does not exceed the maximum for all your attachments, you can post the photos using the “Attachements and other options” link below and then once you have posted them you can “copy the link address” using the right mouse click button and then click Modify to re-edit the post and select the “insert image” toolbutton (computer monitor icon) and paste the copied link. You will have to click SAVE and then repeat this process for each photo, or copy all the link addresses into Notepad.

Glad to hear its working - you might want to document the MOSFET boards and other hardware
you actually used for the benefit of future visitors to this thread?

At the request of the OP I have split the other posts about powered wheel-chairs into another thread. Please confine this thread to being about running lights.

Two items come to mind here - 1) make sure what you have is legal - different areas have different views on extra lights on vehicles and 2) if I remember the halogen cycle correctly, it only works when they are full on where the tungsten boils off the filament and then is re-deposited back again. At lower voltages where they are not as bright/hot, it does not work as expected and I'm not sure how it affects the life of the bulb.