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Discussion Starter #1
I'm going to install a HID kit - The existing head light power will be connected to a relay . Now I need to find a good source of 50W power for each side of the head light.... The battery is in the rear trunk... Is running wire from the trunk to the front the only way to go ?
The fuse box in the front access compartment doesn't seem to have a "main" fuse.

I'll post a write up when I do the actual install.
 

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I thought the HID kits used less power than the stock lights, not more. If that's the case, can't you use the existing headlight power instead of a relay?

I've always seen the "more light less current" feature hailed as a benefit to HIDs. Is it untrue?
 

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Discussion Starter #3
You're right on HID power consumption . Hid bulbs are 35W to run , which is less than the stock headlight.
But when it starts, the ballasts could draw as much as 2X the power to ignite the bulbs . Over time it may burn the stock headlight relay.

That's why HID kits have a relay, driven by the stock head light power , to avoid stock system seeing the 70W load.
 

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Inside the dashboard at the driver's side you'll find a main battery cable terminal that's directly connected to the battery at the back and has at least 50A spare capacity according to Lotus.

You will need to remove the dash top to access it and run a cable to the front of the car though.

Bye, Arno.
 

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svllotus said:
You're right on HID power consumption . Hid bulbs are 35W to run , which is less than the stock headlight.
But when it starts, the ballasts could draw as much as 2X the power to ignite the bulbs . Over time it may burn the stock headlight relay.

That's why HID kits have a relay, driven by the stock head light power , to avoid stock system seeing the 70W load.
A simpler solution might be to get a higher rated relay in place of the standard headlight relay. The burst current won't damage the wiring unless it lasts a long time. Are we talking just a half second or so of higher current? Does anyone know? Does anyone have a HID that they can measure the burst current time?

The only way to damage the relay with high current is if it overheats the relay, and it takes a good bit of time of high current to heat up the internal contacts and wiring to the point damage occurs. Since the normal bulbs draw 50W, and the 2x load of the HIDs is 70 W, I doubt the stock headlight relays will have a problem. Of course, that is just an opinion not based on measured evidence or specifications. You could do us all a big favor and just use the headlight circuit then let us know how long the relay lasts. :)
 

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Discussion Starter #6
The peak draw only lasts less than 1 second ...

About the positive terminal under the dash ... Can I access it by removing the plastic steering column cover ? Or do I have to remove the dash that faces the sky?
 

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svllotus said:
The peak draw only lasts less than 1 second ...
If that's the case, I'm wondering if it's even a concern. You're not going to melt wires or connectors by drawing 1.4x the current for just one second. Is there a dedicated fuse for the headlights? What rating?

I'm just thinking that a 70W spike on a 50W headlight harness/relay/wires isn't risky. Am I nuts?
 

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svllotus said:
About the positive terminal under the dash ... Can I access it by removing the plastic steering column cover ? Or do I have to remove the dash that faces the sky?
Entire dash top needs to be removed as the connection box is mounted forward quite a bit.

Not sure how much problems this will give on the Fed-Elise with the airbags though.. No such issues on the Euro-Elises of course..

Bye, Arno.
 

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Ground Loop said:
If that's the case, I'm wondering if it's even a concern. You're not going to melt wires or connectors by drawing 1.4x the current for just one second. Is there a dedicated fuse for the headlights? What rating?

I'm just thinking that a 70W spike on a 50W headlight harness/relay/wires isn't risky. Am I nuts?
Auto fuses are slow-blow so that they can handle current surges. To blow, the current has to be high for enough time to heat the fuse to the melting point. Incadescent and halogen lights have an inrush (start-up) current that is 10 to 25 times that of the steady-state current (once the filament is warmed up). This transient time is on the order of 20 to 50 milliseconds. The fuse and the relay are already dealing with this level of inrush current with the current headlights. It seems like the HID's total inrush energy (voltage x current x time) is comparable to the current lights, and hence the excess temporary heating in the fuse, relay, wires and connectors would be about the same.

Still, comparison measurements would be needed to be sure.

Too bad there isn't a precharge circuit in the ballast to keep the capacitors charged up and ready to go when the lights turn on.
 

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I think my left side HID blew the stock relay; the right side is still good. I checked the fuses and they are good. If I draw the power direct from the battery then it works. Is it the stock relay? Where is it? Thanks.
 

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HID starters/ballasts are a switching supply. Switching supplies draw more current than a standard bulb for about half a second. The steady state current (once the HID bulb is lit) is less. Most people just put a slightly larger fuse in the front right fuse box to compensate for the higher inrush current at start-up. Keep in mind the standard fuse is 10 amps. Ten amps times twelve volts equals 120 watts, obviously more power than the steady state current of a standard bulb or an HID bulb. I am going to be installing a relay-less HID kit in a couple weeks and see how it works for me.
 
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