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Discussion Starter #1 (Edited)
Hi,

Has anyone upgraded the alternator wire from the alternator to the battery? It looks like 20 - 25 feet of dual 8-gauge wire. I upgraded my alternator to a 200 amp and think the 2 8 gauge wires need to be swapped out for better ones. I think overall this would be much better for the car on many levels since I have power everything, direct wires to my fuel pump, extra spal fans, all my other electronics and my main objective is to be safe for the 200 amps. I just want to make sure my battery and cap are being charged well because of the additional load caused by my sound system and that I?m not going to melt my 20 year old dual 8 gauge wires in the process.

I?m thinking of doing something like this:









I also want to run a dual fuse.. one close to the alternator and one up front by the battery. I know the factory one just has a fuse up front but I want to make sure I?m protected just in case..

Your thoughts??

Thanks,
Eazy
 

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I ran a new wire from the alternator to the fuse box, have not gone all the way to the battery yet. I ran a single 4g wire off the alternator into a splitter where it went to (2) 8g wires. The fuse box has 2 posts so it made sense to do it this way. I did a wire tuck so I wanted to tuck this cable and I ran it all through the trunk.
 

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Where is the factory fuse ? from positive battery post to the rear fuse box ?
I must say that i have never seen alternator fusing, to low a rating at it will blow , too high and it will do nothing.
 

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Discussion Starter #5 (Edited)
If I remember.. It?s a 120amp fuse in the front box.. Nowhere else. The stock alt is 100 amps. With that said, I think its only there to protect against a full short on the line. The only reason I want to put one in the back is because I feel that this alternator will keep juicing if shorted. So I?m thinking for a 200 amp alternator I should run something like a 220-240amp fuse in the front and back.
 

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I am thinking on alternator upgrade also. Can you tell me where to buy a 2-300 amp alternator? Is alternators fairly standard and fit several cars? If so, anyone know wich car's altenators that would fit in a MR2 mk2?
 

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How big is your audio system? Whats the amperage draw? If you aren't sure at least what fuses are in the amps? I have 110 total fused and I'll tell you I run a stock alternator (from a 93 with P/S), I don't run a cap casue they are useless and I have ZEZO issues. Upgraded the grounds to the battery as this is usually a weak link, but other than that nothing much. I have no power issues under and load condition.
 

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I have about 3kw rms total. One amplifier is fused with 250 amp and the other 150 amp

Ground wire is upgraded both at the battery and engine. I also have an Apollo a1750 battery.
 

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Dont fuse the alternator.
In my car audio word i read this 25 years ago.
Google Richard Clarke , David Navone Fuse an alternator ?
 

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Trustnoone said:
I have about 3kw rms total. One amplifier is fused with 250 amp and the other 150 amp

Ground wire is upgraded both at the battery and engine. I also have an Apollo a1750 battery.
Those are some interesting numbers. I'd challange you to run your system and actually check for amperage draw. Your power to amperage numbers are out of wack. See what the system is actually drawing. Even maybe try with HVAC stuff on, then with and without lights, get an average and then a max and go from there.
 

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Discussion Starter #11 (Edited)
Nighthawk26 said:
How big is your audio system? Whats the amperage draw? If you aren't sure at least what fuses are in the amps? I have 110 total fused and I'll tell you I run a stock alternator (from a 93 with P/S), I don't run a cap casue they are useless and I have ZEZO issues. Upgraded the grounds to the battery as this is usually a weak link, but other than that nothing much. I have no power issues under and load condition.
If you know when to use a cap its definitely not useless. I have upgraded my grounds already and using a yellow top battery with a cap.

Trustnoone said:
I have about 3kw rms total. One amplifier is fused with 250 amp and the other 150 amp

Ground wire is upgraded both at the battery and engine. I also have an Apollo a1750 battery.
no way in the world are you running at optimum performance on the stock alternator with 3000 watt RMS which is aprox 6000 max..

just so you know.. 12 watts/12 volts = 1 amp so 6000/12 volts = 500 amps for just the amplifier alone. now with your car running lets say you charge at 13.8 volts as an average. 6000 watt / 13.8 volts = 435 amps for just the amplifier alone. your car requires 100 amps with everything running.. With that said you need about another 50 amps to your amperage supply to the system to keep it running efficient. so lets say you need 100 for the car and 485 for the system. Your looking at a total of 485 amps needed to run a 6000 watt system. now you run into the problem of your amp not getting juice fast enough for heave usage/load. by adding a 6-6.5 farad capacitor (1 fared per 1000 watt max power) your music will play much smoother and not load the alternator. keeping it running healthy and it will last longer.

now comes the problem of the MR2 alternator only being able to push aprox 2-250 amps fully tweaked out.. you will need to run one up top and one below to hit 500amps and then your good to go. i plan on doing this.

i am running a 2000 max watt amp, 2000/13.8=144 amps, add another 50 amps for efficiency, I?m looking at 194 amps, now add 100 for the car accessories and I?m looking at a 300 amp alternator plus a 2 farad cap. so I?m looking to add another stock alternator on the bottom with a MR2 crank pulley to give me another 100 amps of power putting me at 300 amps exactly.

If you follow my suggestion you will enjoy the sound coming from your sound system 10 fold.. Hope that helps.

MANDALAY said:
Dont fuse the alternator.
In my car audio word i read this 25 years ago.
Google Richard Clarke , David Navone Fuse an alternator ?
the stock alternator has a 120 AMP fuse.. i see no problem with putting 2 in my system. its safe and as long as the AMP is slightly above the alternators amperage you will be fine.
 

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Discussion Starter #12
actually i found 130 amp alternators on ebay for 100 bucks shipped. i may just get one of them and be sitting on aprox 320.. should be fun..
 

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ad nighthawk said, it is my rated amplifier power. I am very aware that I dont use anywhere near 3kw at normal levels, and atleast not 6kw as you say.

But I have done some measurings of voltage, and when I crank it up, it goes below 12v, even with the car running. So a 2-300amp alternator would be nice, but 5-600 is just overkill. There is no use for that unless you are going to compete in dbDrag or something.

But I have no issues at normal play volumes, I just want a bit more juice avaiable from the alternator if I decide I'm in a "loud-mood" :)
 

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Discussion Starter #14
going below 12 is a bad thing and ur alt wont last.. 485 is what you would need.. plut another 100 for the car.. its not overkill.. its a requirement.. now can you get away with it yes.. if you dont turn it up all the way.. i picked up all i need today and will install it tomorrow. i got 17 foot of 0 gauge and a nice fuse holder for up front. i got a 250amp fuse and i know i only needed a 220 but its all they had. ill change it later if i can find a 220. ill take pics and post them when i have time.

it would have been nice to have got a single 300 amp alt but it was not an option.. cause i really dont want to put in a second alt. but ill figure out something..
 

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Discussion Starter #15 (Edited)
so i was doing some research about voltage drop.. seems that toyota didnt do such a bad job on the 2 8 gauge wires. it seems that when you run two of the same size wires it drops the gauge by 3. so two 8 gauge wires = 5 gauge.

now for the drop.. i estimate 20 feet of wire from the alt to the bat. 20 feet @ 100 amps is aprox .65 drop which is not so bad at all from 14.5.

now if you were to just replace that with a 0 gauge wire on the stock alt and run it in the exact same path with a total of 20 feet. the voltage drop would be .20.

now in my case...

200 amps across 20 feet of 5 gauge (8+8-3) is a 1.3 volt drop. there is a big difference.. :(
at 0 gauge im looking at .4 drop which is much closer to the factory .2 drop.

i am going to try and use 16-17 feet and at 17 feet with 0 gauge wire on 200 amps im looking at a drop of .34 which is even better. so it seems that these upgraded alt's cause more bad than good if you dont look at everything that needs to be done to use the extra amps. now i know why i have such a hard time getting good voltage on a overnight start with the new alt. it takes aprox a minute or so before the load drops on the alt then its fine. the stock alt didnt have that problem and now i can see why. so this will be a fun and much needed upgrade..

the crazy thing is that with the way my car is now.. factory wires and 4 gauge to the trunk which is about a 20 foot run.. i drop 1.3 to the batt from the alt putting me at aprox 13.2 then another 1.2 or so to the amp. so the amp only gets like 12 volts.. damn.. good thing i got a cap.. but the problem was after i used up all the power in the cap the amp would draw from the alt and i could drop down to about 12 volts.

with the 0 gauge.. i should drop .34 to the bat from the alt then .65 from the bat to the amp and i will end up with like a 1 volt drop giving me a whole volt and a half more power at the amp. well really to my cap.. so this should be ten times better for the music and 30 times better for the car.. :)
 

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Discussion Starter #16
ok.. all is done and i see aprox a .3 drop from the alt to the batt.. so everything worked out perfect.. i have pics on my phone and will post them tomorrow sometime. it took me aprox 2 hours to run the wire, wire the external fuse box, brace and cover the wire, change the pos batt terminal and button everything back up.

i still see the car sit at aprox 12 volt or so when measured at the batt then it makes its way up to about 13.65 or so. my system is not connected and prob wont be till next week cause its just way too hot outside right now to do any more to this car..
 

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Pics?

Keen to see what you guys are using in the fuse box at the rear of the car to connect the upgraded cable (from the alt) to the two post terminal.
 

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Discussion Starter #18 (Edited)
sorry.. here are the pics.. and i only used one fuse up front.. just like factory.. i am on a 200amp alt.
 

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If it were me.....and I somehow needed all that amperage......

Since I care about total weight and handling. I'd of run 2 8sq wire fused at 120amp from the starter to the alternator. and left all the stock stuff alone.

You realize there is a huge wire running the shortest path possible to the battery from the engine bay and that is the starter wire.

Don't crank the stereo, high beams, heater, deffoger, horn, hazzards and brake lights when you start the car and you'd be fine.

Or if I was really in need of power I'd add a 2nd battery in the trunk and from there to the load.

Ishii
 
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