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Re: Headlight conversion to LED? Posted by eric in vermont [Email]  (#2058) [Profile/Gallery]
(more from eric in vermont) on Sat, 17 Feb 2024 05:24:23
In Reply to: Re: Headlight conversion to LED?, BradW  [Profile/Gallery]
, Fri, 16 Feb 2024 16:28:50
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Ashcraft's electrical book is great!
You can search the internet to find tables of wire gauge vs current capacity. Here's an example:
https://www.powerstream.com/Wire_Size.htm
From that table, it says that 22 AWG can carry a max of 7 amps. For a 12V system, that means it can support a maximum load of 12V x 7A = 84 Watts. I'd probably derate it by 20% to be on the safe side, so that would be on the order of 70 Watts or a little less.
But then you have to make sure that the new wire is fused properly so it doesn't blow. That means looking at the current draw of the LED lights over temp including the inrush current when they first turn on so you don't get irritating fuse blowing.
And as to wire size, I personally wouldn't go smaller than 22 AWG, as the wire simply gets too fragile and then you're introducing the possibility of breakage.
Finally, you talked about reducing complexity and failure modes. Two comments: once you deviate from the original Saab wiring, it can get a bit messy and future issues (if there are any) may actually be harder to troubleshoot unless you clearly document what you've done and completely understand it. Second, in all my years of VSaabs (since 1978) I've RARELY had a rely fail. And if it does, 3 of the 4 in the headlight circuit are standard relays that can be bought anywhere and simply replaced. ONCE I can remember, the headlight relay went in one of my VSaabs and opened it up, cleaned the contacts, and away I went.
So in sum, I don't want to discourage you from LED headlights, but I'm not sure the work involved to eliminate the relays is truly solving much. I think it might introduce more problems. The fundamental engineering idea behind automotive electrical systems is that low current sources (switch) control the relay, which is used to switch the high current source (headlight). And of course both circuits need to have the appropriate fusing to protect the wiring from melting and causing a fire. IE, fusing is designed and sized to protect the wiring of the vehicle.
Just my 2 cents...
eric in vermont
, Tue, 13 Feb 2024 21:04:24, Mon, 26 Feb 2024 19:50:09, Fri, 16 Feb 2024 08:09:39, Fri, 16 Feb 2024 16:28:50, Sat, 17 Feb 2024 05:24:23 <-- Viewing This Message, Sun, 18 Feb 2024 14:15:01, Sun, 18 Feb 2024 18:57:40
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