HID Start up current draw

Found an interesting study about HID ballast start up current draw.

After reading this it should conclude if an aftermarket relay is needed or not for aftermarket HID kit installation on our NSX.

http://theeshadow.com/files/volvo/hidcomp.html

Excellent post! Thanks for sharing! I've always wondered (& worried) what the current draw at startup was.

The biggest take away for me was this quote:

From a cold start, both 50/55 watt HID kits draw significant current, over 10 amps for almost 250ms. This is not long enough to blow a 7.5 amp fuse.

Click to expand...

I don't know what the stock wiring is rated at, but I purchased a HID wiring harness for all my cars running the 55W kits for that cold start amp draw.

Question is what is the fuse amp limit for our headlight?

And he also talked about noise made by the HID ballast and will need to use a filter to cut out the noise.

I have the ddm 35w on my low beams and the 55w on the high beams, all installed on the factory wiring. I am considering installing a relay for the 55w lights. When I turn on the brights from a cold start, the left light cuts on for a fraction of a second but then dies. The right light works normally every time. If I cut the brights off and then back on, the left light warms up and stays on. I am taking this to mean that the required power is too great for both to do a cold start up at the same time.

Any thoughts?

I had so many issues before a I got a relay harness that pulls power straight from the battery..

I got this but it came from China..like everything else. Works fine. Only note is that you need ONE per set, e.g. 1 / low, 1 / high. I assume it was 1 per headlight... and bought 2 too many. I may sell the other two if someone is interested...
http://www.ddmtuning.com/Products/HID-Kit-Wiring-Harness

swimmingpie said:

I have the ddm 35w on my low beams and the 55w on the high beams, all installed on the factory wiring.

Click to expand...

Personally, I would swap the ballasts so that the 55w ballast powers the low beam and the 35w powers the high beam. You'll notice much more usable light when driving normally with your low beams.
If you have DDM Tuning bulbs, they all are rated to 60watts, its the ballast that determines the wattage.

nsxotic911 said:

I had so many issues before a I got a relay harness that pulls power straight from the battery..

I got this but it came from China..like everything else. Works fine. Only note is that you need ONE per set, e.g. 1 / low, 1 / high. I assume it was 1 per headlight... and bought 2 too many. I may sell the other two if someone is interested...
http://www.ddmtuning.com/Products/HID-Kit-Wiring-Harness

Click to expand...

This is exactly what I have on mine. No issues so far and I highly recommend it.

One thing that you must remember is that a standard incandescent bulb has a 10 to 15 times surge current during startup until the filament reaches thermal equilibrium. The peak current is usually higher than an HID system.
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analogdesigner said:

One thing that you must remember is that a standard incandescent bulb has a 10 to 15 times surge current during startup until the filament reaches thermal equilibrium. The peak current is usually higher than an HID system.
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Jay<o></o>

Click to expand...

According to the test, the surge current of the halogen incandescent is only about 3 times the equilibrium current (15amp cold start & 4.52 amp average).
The DDM shows a 13.64amp start & a 4.36 amp average which is about 3 times as well.

What I'm concerned about is the duration of the cold start current. I believe there's a typo because the graphs are labeled as <20ms and the text/analysis says ~250ms...

This is the Halogen cold startup:


This is the 55W DDM cold startup (I don't quite understand this either because it looks like it hits the 13.63amp peak, then drops, then "feathers" between 10 and 13amps for 10-15 seconds...):


Does anyone know what the difference is between the red lines and the white/yellow lines?

Hello Hapa88,<O</O
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There are many things going on here. First, the incandescent bulb being measured has much lower peak surge current than in theory due to all of the resistance in the wiring of car. Ohm's law will prove that.
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HID ballasts designed for automotive use have high initial current draw because the law says (at least it used to be) that the brightness of the headlamps must exceed 50% within 2 seconds after turn on. When the HID lamp is initially "struck", meaning it arcs between the electrodes when it is turned on, the arc voltage is extremely low, 8 to 12 volts (usually) when the lamp is cold. At this time the lamp current is very high because it is overdriven (by design) in an attempt to heat it up ASAP (in order to make it bright)! This is needed to meet the 2 second-50% minimum brightness turn on spec mentioned above. If your HID bulb is 35 watts, the ballast may actually deliver roughly 70 watts for many seconds! Multiply this by two, for both lamps, we now have about 140 watts. Now the ballast has an efficiency of about 80 to 85%, so now the input (12 volts) wattage could reach 170 watts. There are many more things going on in its actual operation, however I wanted to mention some of the basics.
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In regards to scope traces, the upper red trace looks like it's the input current draw, the lower trace is the system (battery) voltage (5 volts/ DIV).
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I hope this helps, Jay<O</O