mechanic shop trying to swindle me?

[SanDiegoSlapper]

so i have an 06 yukon denali, cab 1600.1 and a skar zvx 15 d1 wired down to .5 ohm. had a stock alternator (140amp? i think). Already have the big 3 and headlights were dimming really bad so i brought it to a mechanic shop to have them rebuild my alt to a 220 amp alternator. i got the car back yesterday and instantly i notice a decrease in voltage. I wasn't even at half tilt and my dash was dimming to the point lights weren't visible. I put on the multimeter and im dropping under 11v down to almost 10.0v when bass hits. i took it back this morning to have them look at it and they gave me a call about 20 mins ago talking about "well your car controls the alternator and when it sees ur battery is full it will cut it back to only 13v" and starts telling me i need a second battery if i want to hold 13+ volts solid at my amp.  i asked him "if this alternator cant even feed my amp 13v how is it supposed to feed a second battery fast enough so that my amp doesnt just kill it off, then kill off my main battery." he didnt really have an answer for me. i feel like the alt is not a 220, or they screwed something up on the rebuild, my stock one was better. has anyone heard of this ecu controlled thing cutting off the alternator, if so is there a way to bypass it?

[Broke_Audio_Addict]

Is this at idle?

[Jessica]

5 minutes ago, Broke_Audio_Addict said:

Is this at idle?

^ what he said

[SanDiegoSlapper]

3 hours ago, Broke_Audio_Addict said:

Is this at idle?

 

3 hours ago, strangeduck said:

^ what he said

yes

[Jessica]

modern vehicles frop alt voltage to save on fuel economy. Plus, when you upgrade an alt, the idle voltage tends to drop. Rev your shit up to about 3k rpm and see how your voltage does. maybe turn on your AC and headlights or some other accessory.  

[SnowDrifter]

Your alt is PCM controlled

Turn on your headlights, voltage should bump up over about 45 seconds

I was working with another dude on here. You may remember him. The carbon fiber box guy

He was having similar issues with his alt. DC power. Didn't seem to want to go full field. Never did figure that one out. I was ready to rip the damn thing open and hook an external reg to it

[SnowDrifter]

Also: Usually when you rebuild an alt in the stock case to a higher output, it comes at the expense of idle output. Especially if they didn't put a smaller pulley on it

[SanDiegoSlapper]

so what are my options here? getting a second battery? second alternator? smaller pulley?

[SanDiegoSlapper]

or is it ok that im reading low bursts of 11v at the amp? also will hooking the amp strait up to the alt output help/hurt anything?

[SnowDrifter]

First step: Rule out other factors

Measure your voltage at the alternator between the positive stud and casing, both at idle and 2k-2.5k RPM revved