View Full Version : anyone have that much faith in their engine mount bolts to carry 300A? hope not...
01-31-2002, 10:13 AM
hey- in doing my friend's electrical system upgrade, we never really considered the engine block to chassis electrical connection. i had asked some auto electrician if 300A would have any problems flowing back to the alt via the engine mounts. he said no problem at all (riiiight). anyways i never had a look at the braided ground wire that connects the chassis to the engine, but upon inspection i realized that it had been completely fried apart. this thing got toasted. not sure if it was from daily usage, but i think it was from the "incident" months back where the alt-battery wire got fried (didn't upgrade it, OOPS!).
anyways i was wondering if all of you are that confident in your engine mount bolts to carry the current back to your block. i don't hear much about people upgrading this wire.. i wonder why?
does anyone know "theoretically" what the resistance in this union is? how abou the current that is allowed to move through a bolt? just curious. we got 1/0 in there now...
01-31-2002, 12:51 PM
well its a bolt man, its ALOT, lol, it would take a **** load to get it hot enough to fry, anyway, i would go ahead and put some 1/0 in place of the ribbon, just my 2 cents
01-31-2002, 01:57 PM
well yeah.. it may take a lot to fry.. but is it sufficient to carry the current back? i mean, is it what you want handling all of your power? seriously-- why would car makers even put in that little ribbon if the bolts can do 50 times that? what would be its purpose?
i'm going by something i read from a source i trust quite well.
01-31-2002, 02:46 PM
The reason they use a strap is most cars dont come with 300 amp alts and they have rubber or liquid filled motor mounts so only thing holding engine to frame is the motor mounts and rubber is non conductive soooo thats why they use a strap from block to frame..
01-31-2002, 03:42 PM
You can also get a big ass aftermarket ribbon strap too. smile.gif
01-31-2002, 05:40 PM
no- actually there is rubber in there but the engine is physically bolted in also.. which is connected to your frame. i don't know what sort of union the bolt and frame make so i'm not sure how well this current would flow...
HOWEVER you don't need the strap because it was fried on my friend's car and he was running 2kW just fine all day long. the current went right back to the alt via the bolt.
ANYWAYS why would you reccomend a strap or an upgrade if the bolt can carry the current? is the bolt resistive or what? has anyone tried using an ohm meter from the chassis to the engine block while unstrapped compared to strapped? just curious.
The larger your return path the better,Screw the bolt question,Go from the back of your alt to the common grounding point on the body ,then from that point to the battery that your charging. This way you have eliminated the possibility of having a ground loop through your motor mounts.
01-31-2002, 08:50 PM
i just used the location of the stock ribbon/strap. it had a nice stud on the block so i figure-- what the hell-- might as well use it. the bolt question is simply to analyze the situation.. and perhaps to help others also.
02-01-2002, 04:17 AM
I leave the stock strap on but with another 1/0 gauge run of cable as well. You cannot overdo this ground connection so why not :D It's a short run & won't use much cable so add another one now smile.gif
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