Bought new 250amp alt but same voltage drop?

[1-12-t1 10+ year member]

Just installed my new alt, before I was dropping to low 12's full tilt on a stock 130 amp alt. Installed my new 250 amp alt, which was tested at 279amps at 1800 rmp, but still same voltage drop? Still low 12's. Im running a SQ3500, which is around 4krms at 1 ohm and I have around 320ah to back it up. Does this voltage drop sound reasonable? Why not even a little better voltage?

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[los33]

From what you have said.. you either dont have the big 3 done or have a bad ground.

Where did you buy your altrrnator?

 

[1-12-t1 10+ year member]

Just got from mechman, have big 3 done with 1/0. I only have one ground on the back bank of batteries to the chassis, all wires of course are 1/0. BTW, love your amp.

 

[CerwinVega_Fan 10+ year member]

Are u using cca wire?

 

[1-12-t1 10+ year member]

yes its CCA, its the cadence 0 gauge. Im running 2 runs of pos back to my bank with 1 neg. And is it normal that my stock only changed to 14.0 volts and my new alt does too? Not 14.4?

 

[Jeffdachef 5,000+ posts]

yes its CCA, its the cadence 0 gauge. Im running 2 runs of pos back to my bank with 1 neg. And is it normal that my stock only changed to 14.0 volts and my new alt does too? Not 14.4?

most likely your ECU, same shiet with my high output alt.

 

[bgowdy 5,000+ posts]

hm... kinda odd. My last build was using a 220a dc power alt, with a Crescendo Bc3500 @ 1 ohm, with 315ah batt bank. i had 4 runs of CHEAP CCA 1/0(install bay //content.invisioncic.com/y282845/emoticons/suave.gif.858fc102f7646e678ee8af7e1fbc41d1.gif) 2 pos & 2 neg front to back. I could run full tilt at idle rpms and would only drop to about 13.3-.4v from 14.3, and at 2k rpms i would only drop to 13.8-14v from 14.3. Sounds like a ground issue some were or maybe try adding another run of 1/0?

 

[bgowdy 5,000+ posts]

yes its CCA, its the cadence 0 gauge. Im running 2 runs of pos back to my bank with 1 neg. And is it normal that my stock only changed to 14.0 volts and my new alt does too? Not 14.4?

run another negitive. you should try to have 1 dedicated neg to every positive, it helps the circut

 

[yogegoy]

Did you hook up a ground directly from alt to your negative post? My 370a Mech does 14.6vdc @ a 1k rpm and 13.3vdc @ 6-700 rpm.

 

[ylpkm]

My mechman alt didnt come with a neg post. OP does your mechman alt have a dedicated negative post?

 

[yogegoy]

My mechman alt didnt come with a neg post. OP does your mechman alt have a dedicated negative post?

To the negative post of your battery from your alternator mounting bolts, as long as it's from the alt body. 1/0 is what I used and Mechman even suggests it with a note that comes with the alt.

 

[ylpkm]

hmm, could that actually be the cause of OP voltage drops and mine? I thought that the engine ground was strong enough by itself. gonna have do that.

 

[yogegoy]

It makes sense to do that because there is more resistance through the engine block than simply grounding it directly from the mounting bolt to the negative post of the battery. Mechman strongly suggests to use a 1/0 with copper terminals as part of before you install preparations procedure. As always keep everything bare and clean, I used some of that batt red paste on all my contact surfaces just to satisfy my self I guess.

 

[Papermaker85 5,000+ posts]

Bad connections mean higher resistance. Depending on the situation it can lower effiency. If its st the amp your going to get a lack of output. If its at the alt your going to get lack of output. Usually a bad amp ground won't cause major voltage drop cuz the resistance is high so it naturally don't pull as much current. Where as the alternators ground will limit the alternators output causing the voltage drop. Make sure u have the alt battery and amp ground to the frame. Not the body. Chances are they might be isolated causing problems.

 

[yogegoy]

Beside all1/0 grounding cables to original points, I also used 1/0 from neg post of front batt to the batteries I have in the back seat which terminates to seatbelt bolt.