Voltage Drop

[A216VCTi]

I have a 2003 24v VR6 GLi. I have a MTX 942 powering a 12" JL W7. I'm powering the sub through a 1/0 wire. I still have not done the big 3. I'm noticing a voltage drop down from 14.1 volts to 12 during heavy bass hits. Is this abnormal? I plan on doing the big 3 soon. What kind of difference will I be looking at after doing the big 3?

[NFrazier]

To drop 2v is kinda a large drop. Where's your ground? How is it attached? How long is it? Where's your power wire attached to?

[A216VCTi]

To drop 2v is kinda a large drop. Where's your ground? How is it attached? How long is it? Where's your power wire attached to?

Which ground are you referring to, battery or amp? If referring to the ground on the battery, it's attached to the factory location. For the amp, it's attached to a seat belt bolt.

When I was seeing the 2v drop, I was only measuring the battery with the car on across the battery terminals. I never checked the amp.

[A216VCTi]

Bump. I upgraded the wire going from the alt to battery to 1/0. Also upgraded battery ground to 1/0. The previous owner had a 8 AWG wire going from the block to a bolt on the fender, I moved that to the ground underneath the battery.

Still have a voltage drop. You guys think I should upgrade the battery?

[GTI-DNA]

Bump. I upgraded the wire going from the alt to battery to 1/0. Also upgraded battery ground to 1/0. The previous owner had a 8 AWG wire going from the block to a bolt on the fender, I moved that to the ground underneath the battery.

Still have a voltage drop. You guys think I should upgrade the battery?

Yep..and while you're at it, the alternator too.

Are you clipping the amp in any way? This will cause the amp to pull a **** ton of current. Where is the imput voltage set at? May try a line driver and turn the amp gains down a bit. MTX 945 isn't really a BIG amp, so I suspect battery and or clipping the amp. Also, check that your ground from the amp is SOLID.

Play your music at the volume you see the drop. Check the current draw at the amp. I bet you will **** when you see it.

I am running 3 amps on the stock alt with only an upgrade to battery and Big 3. No voltage drop for me.

[GTI-DNA]

Bump. I upgraded the wire going from the alt to battery to 1/0. Also upgraded battery ground to 1/0. The previous owner had a 8 AWG wire going from the block to a bolt on the fender, I moved that to the ground underneath the battery.

Still have a voltage drop. You guys think I should upgrade the battery?

Yep..and while you're at it, the alternator too. Just kidding

Are you clipping the amp in any way? This will cause the amp to pull a **** ton of current. Where is the imput voltage set at? May try a line driver and turn the amp gains down a bit. MTX 945 isn't really a BIG amp, so I suspect battery and or clipping the amp. Also, check that your ground from the amp is SOLID.

Play your music at the volume you see the drop. Check the current draw at the amp. I bet you will **** when you see it.

I am running 3 amps on the stock alt with only an upgrade to battery and Big 3. No voltage drop for me.

[BassNotes]

You have to find out where the voltage drop is occurring.

[A216VCTi]

How do I find out where is the voltage drop?

[A216VCTi]

Yep..and while you're at it, the alternator too. Just kidding

Are you clipping the amp in any way? This will cause the amp to pull a **** ton of current. Where is the imput voltage set at? May try a line driver and turn the amp gains down a bit. MTX 945 isn't really a BIG amp, so I suspect battery and or clipping the amp. Also, check that your ground from the amp is SOLID.

Play your music at the volume you see the drop. Check the current draw at the amp. I bet you will **** when you see it.

I am running 3 amps on the stock alt with only an upgrade to battery and Big 3. No voltage drop for me.

How do I check current draw at the amp?

[BassNotes]

How do I find out where is the voltage drop?

First measure the actual output of the alternator with the engine running and lots of load on the electrical system—headlights/high beams on, A/C on. Stick the point of the positive probe right through the insulation in the wire, close to where it's connected to the alternator. Put the other probe on the alternator body. You should read about 14 to 14.5 V. (If not, you probably have a problem with the alternator or voltage regulator.)

If the alternator output is good, next measure across all the points that are supposed to be the same voltage. They're not going to all be exactly the same but you want them really close, like 0.05 V or less.

Measure across all these points in each group:

• The alternator lead (where you measured the output voltage); the alternator terminal on the fuse box (on top of the battery); the + battery post.
• The alternator body; the engine block; the chassis; the - battery post.

All the test points in these groups should be within 0.05 V of each other. If you find any larger drop, especially about 0.2 V or more, you probably have a loose or corroded connection between the two points.

Some of the greatest hits for connections that need attention are :

• The ring terminal on the end of the alternator lead (one clue would be if your fuse box is melting in the vicinity of the threaded terminal post that the lead attaches to).
• Ground connection at the engine block/transmission bellhousing.
• Ground connection to the chassis under the battery.
• + and - connections on the battery posts (they sometimes have dirt and grease and contamination between the posts and the clamps, preventing a good, large contact area between them).