I do know how electricity works since i'm an electrician, and thats my error for swapping the two numbers. brain fart or something. I don't need a lecture on how things work. but thanks. I never said you upgraded anything but wiring nor did i know your had moved your battery without already uprating the wire size for the hot bus. Since you elongated the positive side for the starter, i guess you kept the fusebox in its original place? Yeah i see what you mean as to the starter being out of the picture. I'd thought the hot bus had something to do with a tap in for the solenoid drive power.
Hi ... just a bit of clarification about switch load ratings.
One of the things I've noticed over the years, is that switches are being sold through auto outlets that don't have a DC load rating on them, only AC. This is where the problems start, people see a switch that says something like 125 V AC 15 A (for example) and assume that, if it is rated at 125 volts .. then it is good for the same (or better) at 12 volts DC.
The trouble is, DC (direct current) is a lot harder to switch than AC (alternating current) ... to be safe (and reliable) ... rule of thumb is to halve (use 50% of) the AC current rating for use on 12 V DC ... ie for a 125VAC 15A switch ... treat it as a 7.5A switch.
Lot's of simplified science stuff ..you have been warned
Here's why ... strange as it may seem ... current flowing through a conductor has the equivalent of inertia in a mechanical system, ie when a current is flowing .... it wants to keep flowing. (it's all about the energy stored in the magnetic field, generated around the conductor when the current is flowing having to go somewhere when the circuit is interrupted).
So when you open the switch, an electric arc forms between the switch contacts as they open (that's the current trying to keep flowing). In an AC circuit, the voltage and current reverse direction during each cycle so for a brief moment the current is zero as the waveform goes from +ve to -ve ... at this point in a low voltage AC circuit, the arc self-extinguishes.
In a DC circuit, the current is flowing in one direction only, so when the switch contacts open, a large arc is draw between the contacts until they are far enough apart and the arc collapses. During this period of arcing each time the switch opens; the contact faces suffer spark erosion which leads to an increase in the contact resistance when the switch is closed. This in turn leads to heating of the contacts. The more eroded the contacts become, the more they heat up during operation. I've actually seen cases of switch contacts getting hot enough to weld themselves together so they couldn't be turned off!
D.C. rated switches are usually a bit physically larger than A.C. switches to allow the contacts to open further to stretch and break the arc.
Now as to what 320i78/82 was talking about ..... (ignoring the fuse analogies and hoping they will go away ) ... copper wiring is not a perfect conductor and wiring has a certain amount of internal resistance/unit length .... the smaller the cross sectional area of the conductor the higher the resistance. Under some circumstances, the internal resistance of the wiring could limit, to certain extent, the current flow through a circuit with an overheating switch. If the wiring was replaced by a larger gauge having less resistance .. then that would allow more current to flow through the circuit increasing the heating effect across the switch contacts and cause more problems. This is a possible scenario, but ... not something that can generally be predicted ... so much is dependent but the configuration and actual loading on the circuit.
So the moral off the story .... don't get the load capacity of your switches wrong.
Oh .... and no fuses were hurt in the writing of this post
Cheers
Last edited by GDAus; 03-22-2017 at 09:39 PM.
hmm .. Wonder what happens if I do this ...
Thanks for the post, GDaus. I always appreciate well informed input. I'm certainly no electrical engineer and I'm sure my explanations seem silly to one.
Is this the point that 320i78/82 was trying make, or did I miss something? It seemed to me he's telling me I should have stayed with 10 guage instead of going to 8 guage. This would be the only logical reason why that would make sense, but i don't think that's an issue here.
I didn't feel I needed advice either which is probably why I got defensive. I tend to disagree too strongly when people offer advice I feel is wrong or not needed. I apologize. I still disagree with the need to fuse the circuit in question. The problem was an underrated made-in-china switch, problem solved.
The starter is getting voltage directly from the battery via a 2 guage cable with soldered terminals. The fuse box gets voltage directly from the positive post on the starter via 8 gage wire with soldered terminals. The fuse box is in the stock location. I'm not sure why that's relevant to the ignition switch that failed. Once I ran 8 gage wire to the fuse box and ignition switch and replaced the bad switch, cranking is faster & stronger, the car starts quicker and my fuel pump sounds stronger and doesn't slow down when other accessories turn on. I also don't get any headlight dim with other accessories like I did before.
thanks. Yes I am, not in a good way.
To the first part, yes thats a bit of what i was going after, not so much the arcing but just the current draw. I didn't know that dc switches suffered from this phenomenon, though it makes sense with the way electricity behaves.
Last part, the reason i had questioned your fusebox location was under the same principle for you uprating the battery cable when you moved it. I wasn't sure whether you had done so with the fusebox as well. Just because increased length stresses the current carry in the wire. So since you hadn't moved the box i wasn't sure why you changed the wire size. The poorly made switch identified itself (though i'm not sure why it took 4 years). I got done with the wiring setup on mine today. I put a 30 amp auto-reset CB in line with the 35 amp main(kill) switch i put in, from there it links power to the other three switches. I separated the ACC(Violet) and ON (Green) wires to keep the loads evened out. The push-button is still awaiting a mounting location just trying out some different ideas.
JR- on not liking to be critisized i understand where you're coming from, in fact i think you and I are pretty much alike. I rebuilt my first motor when i was 15 but i did have a manual. I do enjoy embarking on my own projects and don't want to hear criticism on my "new idea." Though i've learned alot about listening to what everyone has to say and have developed a pretty good filter for bs...seemingly what i was throwing at you the other day. happy trails, i'll put pics up when time allows.
Now that it's cooled off abit outside, I gotta get out there and trim some more plywood for my "supercahrger brainstorm" before my wife drives the car tomorrow.
Nope, Nope, don't say nothin yet, just be patient, Robert .
Tbd
dude seirously like wtf does that have to do with anything being spoken in this thread? your failure of a supercharger has already created an epic failure of a thread. Go talk about your failing experiment in that and stop clogging other threads with it, hearing or reading about your "supercharger" infuriates me, atleast if you keep it in your thread i can stay away dude, seriously man.
My ignition switch is totally destroyed and I don't have key anyways. So I want to bypass the switch completely. Would it be possible to do this with 1 toggle and 1 starter switch rather than 2 toggles? Could you just splice the ignition and acc wires together? From doing some research the brown wires are just for door buzzers and whatnot, but what about the black wire?
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