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high output alternator upgrade voltage fluctuation


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I figured I would post this on here if anyone has installed a larger high output alternator on their 2014+ silverado/sierra. I noticed that after switching from the factory alternator to a 370A mechman alternator that my voltage fluctuates between 15.2v to 14v. This fluctuation in voltage occurs only after the truck runs longer than 1 minute and will continue until the truck is shut down and does not change if I have the lights turned on or am in tow/haul mode. I followed the instructions on wiring through the factory hall effect sensor and tested voltage drop on the wires and have 0.0v of voltage drop on all power and grounds. The only thing I can possibly think of is that since the upgraded alternator is far higher in output than the factory unit that it is able to charge the truck faster and as a result the truck is regulating the voltage to bounce up and down as fast as it is now.

 

Has anyone ran into this problem with an upgraded alternator? At the current moment I do not have anything other than the factory electronics installed. I do have a second battery under the hood and there is 0 gauge running between the alternator and 2 batteries. Any help would be greatly appreciated! I do not feel the alternator is bad at all since the areas where I noticed voltage drop on the factory alternator are gone now and the voltage drop was present when switching 4 wheel drive modes or if I was sitting at idle and had the turn signal on, it would bounce up and down like this in those scenarios.

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can you post the instruction manual?

ive seen a fellow upgrade to both stock and duramax alt,  the Dmax runs off a clutch like an ac condensor. so maybe high output alts are not meant for full duty, just activate when needed using the switch to the clutch.  otherwise you'll cook the electrolyte off...  

 

now 15 volts is the correct charge voltage if your running Dry cell or AGM batteries, while lead acid cells is designed to be closer to 13.8 or 14vlts.

 

also you can bump your voltage up by hitting tow haul if the battery is in the 12.5 vlt zone this will charge the batteries to 14vlts. usually take about 2-5 minute to top up using this method

Edited by flyingfool
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1 hour ago, kickass audio said:

I figured I would post this on here if anyone has installed a larger high output alternator on their 2014+ silverado/sierra. I noticed that after switching from the factory alternator to a 370A mechman alternator that my voltage fluctuates between 15.2v to 14v. This fluctuation in voltage occurs only after the truck runs longer than 1 minute and will continue until the truck is shut down and does not change if I have the lights turned on or am in tow/haul mode. I followed the instructions on wiring through the factory hall effect sensor and tested voltage drop on the wires and have 0.0v of voltage drop on all power and grounds. The only thing I can possibly think of is that since the upgraded alternator is far higher in output than the factory unit that it is able to charge the truck faster and as a result the truck is regulating the voltage to bounce up and down as fast as it is now.

 

Has anyone ran into this problem with an upgraded alternator? At the current moment I do not have anything other than the factory electronics installed. I do have a second battery under the hood and there is 0 gauge running between the alternator and 2 batteries. Any help would be greatly appreciated! I do not feel the alternator is bad at all since the areas where I noticed voltage drop on the factory alternator are gone now and the voltage drop was present when switching 4 wheel drive modes or if I was sitting at idle and had the turn signal on, it would bounce up and down like this in those scenarios.

On my 2014 1500 I upgraded from the 150amp to the 170amp when it started showing signs of failure.  370amp seems like way too much.

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15 hours ago, btj_z71 said:

On my 2014 1500 I upgraded from the 150amp to the 170amp when it started showing signs of failure.  370amp seems like way too much.

it isn't too much when you have an amplifier drawing at peak 250A of current on it's own.

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15 hours ago, flyingfool said:

can you post the instruction manual?

ive seen a fellow upgrade to both stock and duramax alt,  the Dmax runs off a clutch like an ac condensor. so maybe high output alts are not meant for full duty, just activate when needed using the switch to the clutch.  otherwise you'll cook the electrolyte off...  

 

now 15 volts is the correct charge voltage if your running Dry cell or AGM batteries, while lead acid cells is designed to be closer to 13.8 or 14vlts.

 

also you can bump your voltage up by hitting tow haul if the battery is in the 12.5 vlt zone this will charge the batteries to 14vlts. usually take about 2-5 minute to top up using this method

I have the actual sheet boxed up with the OEM alternator so I can't get to it easily. The instructions were to remove the factory ground cable (both of them) and use a single ground of 1/0 gauge to the case of the alternator and have it fed through the load sensor next to the battery and then connect to the negative battery terminal. The positive just gets connected directly to the positive terminal of the battery.

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it isn't too much when you have an amplifier drawing at peak 250A of current on it's own.
Ahh, gotcha. Makes sense now!

Sent from my SM-G960U using Tapatalk

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  • 10 months later...
On 5/29/2020 at 11:10 AM, kickass audio said:

I have the actual sheet boxed up with the OEM alternator so I can't get to it easily. The instructions were to remove the factory ground cable (both of them) and use a single ground of 1/0 gauge to the case of the alternator and have it fed through the load sensor next to the battery and then connect to the negative battery terminal. The positive just gets connected directly to the positive terminal of the battery.

Hey brother, did you ever find a solution to this? Im having the same issue with the same setup as yours. 

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20 hours ago, Zori Marfazelian said:

Hey brother, did you ever find a solution to this? Im having the same issue with the same setup as yours. 

A buddy of mine had fixed the issue by bypassing the OEM control wire on the alternator and using an external voltage regulator for the alternator. He shorted out the two pins on the OEM alternator harness which will stop the battery light from the dash lighting up and he also used a Mechman adjustable voltage regulator to control the charge voltage himself. What I don't know is if the voltage reading on the dash will be accurate or if it just relays what the PCM wants to get out of the alternator when you short the control wires on the alternator.

 

This is the external regulator he used: https://www.mechman.com/accessories/voltage-control-modules/adjustable-external-regulator-w-2-pin-alt-harness/

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