Big 2?

[av83 10+ year member]

Is there any reason to do a engine block/batt negative to chassis if you aren't grounded to it? I grounded my front batt negative to the block, ran my alt to batt +(of course), and ran +/- runs from the front to rear batts. All with monster cable 1/0, soldered to ring terminals. I have 14.6-14.7 volts, at idle, at the rear batt....

Click to read more...

 

[kramer_212 10+ year member]

the engine block is already grounded to the chassis.

 

[shizzzon 10+ year member]

I will take the time to say this-

When doing the Big whatever, you should know WHY you are doing it rather than just doing it.

So i will explain-

Alt + to Batt +

This gives the current output from the alt more than 1 channel to flow through. This will allow higher voltage to all of it's destinations and is primarily recommended for aftermarket alternators and for stock alternators, minor upgrade in AWG size is recommended. 4awg, for example, is plenty for an addition for this cable.

Batt - to frame\chassis

This is referring to your starting battery.

The reason why this is recommended is because if the + cable coming from your alternator actually did benefit and increased the voltage to the battery slightly, then you will only ever really notice it if you complete the cycle by upgrading the ground as well.

I will say that stock grounds are actually quite sufficient in terms of AWG size, it's just the location sometimes that isn't the best.

But in any event, adding 8-4 AWG wire for ground is plenty of overkill to get this job done for stock alternators. Aftermarket, only 1/0 or larger recommended.

And the last one, pay special attention to how i word this last subject.

ALT Ground to Batt Ground

Notice how i didn't say engine block to frame...

The point of doing this step is as follows-

You increase your ground at your starting battery to benefit when upgrading the + charging cable to the battery.

Well, the alternator needs a perfect cycle too so it's ground should be upgraded as well, not just it's +.

By default, the casing of an alt is ground. Typically, the casing is attached to a Steel bracket using Grade 8 Bolts.

This is attached to the Engine block. The Engine block pretty much barely makes conductive contact with the frame which is where the battery is grounded too.

So, the stock grounding technique for an alternator is terrible and for an aftermarket, dangerously terrible!

So, you do not want to ground your engine block, you want to ground the SOURCE, the alternator itself.

The best way to do this is to ground at the casing itself(without removing any vital bolts), or the bracket that surrounds the alternator or the CLOSEST thing to the alternator and run this ground either directly to the Batt - terminal, the Batt - ground location or straight to chassis with a sanded, clean contact.

 

[BrownVanMan 10+ year member]

I will take the time to say this-
When doing the Big whatever, you should know WHY you are doing it rather than just doing it.

So i will explain-

Alt + to Batt +

This gives the current output from the alt more than 1 channel to flow through. This will allow higher voltage to all of it's destinations and is primarily recommended for aftermarket alternators and for stock alternators, minor upgrade in AWG size is recommended. 4awg, for example, is plenty for an addition for this cable.

Batt - to frame\chassis

This is referring to your starting battery.

The reason why this is recommended is because if the + cable coming from your alternator actually did benefit and increased the voltage to the battery slightly, then you will only ever really notice it if you complete the cycle by upgrading the ground as well.

I will say that stock grounds are actually quite sufficient in terms of AWG size, it's just the location sometimes that isn't the best.

But in any event, adding 8-4 AWG wire for ground is plenty of overkill to get this job done for stock alternators. Aftermarket, only 1/0 or larger recommended.

And the last one, pay special attention to how i word this last subject.

ALT Ground to Batt Ground

Notice how i didn't say engine block to frame...

The point of doing this step is as follows-

You increase your ground at your starting battery to benefit when upgrading the + charging cable to the battery.

Well, the alternator needs a perfect cycle too so it's ground should be upgraded as well, not just it's +.

By default, the casing of an alt is ground. Typically, the casing is attached to a Steel bracket using Grade 8 Bolts.

This is attached to the Engine block. The Engine block pretty much barely makes conductive contact with the frame which is where the battery is grounded too.

So, the stock grounding technique for an alternator is terrible and for an aftermarket, dangerously terrible!

So, you do not want to ground your engine block, you want to ground the SOURCE, the alternator itself.

The best way to do this is to ground at the casing itself(without removing any vital bolts), or the bracket that surrounds the alternator or the CLOSEST thing to the alternator and run this ground either directly to the Batt - terminal, the Batt - ground location or straight to chassis with a sanded, clean contact.

perfect advise. On my 77 buick i was running 700 watts and getting slight dimming. all i did was alt + to batt + because the stock wiring was BIG OFC 4 G from the factoy, which is more than enough.

 

[gckless 5,000+ posts]

I will take the time to say this-
When doing the Big whatever, you should know WHY you are doing it rather than just doing it.

So i will explain-

Alt + to Batt +

This gives the current output from the alt more than 1 channel to flow through. This will allow higher voltage to all of it's destinations and is primarily recommended for aftermarket alternators and for stock alternators, minor upgrade in AWG size is recommended. 4awg, for example, is plenty for an addition for this cable.

Batt - to frame\chassis

This is referring to your starting battery.

The reason why this is recommended is because if the + cable coming from your alternator actually did benefit and increased the voltage to the battery slightly, then you will only ever really notice it if you complete the cycle by upgrading the ground as well.

I will say that stock grounds are actually quite sufficient in terms of AWG size, it's just the location sometimes that isn't the best.

But in any event, adding 8-4 AWG wire for ground is plenty of overkill to get this job done for stock alternators. Aftermarket, only 1/0 or larger recommended.

And the last one, pay special attention to how i word this last subject.

ALT Ground to Batt Ground

Notice how i didn't say engine block to frame...

The point of doing this step is as follows-

You increase your ground at your starting battery to benefit when upgrading the + charging cable to the battery.

Well, the alternator needs a perfect cycle too so it's ground should be upgraded as well, not just it's +.

By default, the casing of an alt is ground. Typically, the casing is attached to a Steel bracket using Grade 8 Bolts.

This is attached to the Engine block. The Engine block pretty much barely makes conductive contact with the frame which is where the battery is grounded too.

So, the stock grounding technique for an alternator is terrible and for an aftermarket, dangerously terrible!

So, you do not want to ground your engine block, you want to ground the SOURCE, the alternator itself.

The best way to do this is to ground at the casing itself(without removing any vital bolts), or the bracket that surrounds the alternator or the CLOSEST thing to the alternator and run this ground either directly to the Batt - terminal, the Batt - ground location or straight to chassis with a sanded, clean contact.

This is a great explanation, in the case that amps are grounded to chassis. In OP's case, amps are grounded straight to battery. Therefore, OP you are correct in assuming that those 2 should be all you need. You upgrade the alt positive to battery positive, and the alt negative (or engine block. As stated above, it is better to do directly from alt, but IMO you aren't going to notice much of a difference if you have good contact between your alt and engine block.) to battery negative, which completes the circuit where you are drawing big power. Battery ngative to chassis is still needed for stock electrical, but you shouldn't need to upgrade it. IMO you might as well go ahead and do battery negative to chassis though.

 

[av83 10+ year member]

This is a great explanation, in the case that amps are grounded to chassis. In OP's case, amps are grounded straight to battery. Therefore, OP you are correct in assuming that those 2 should be all you need. You upgrade the alt positive to battery positive, and the alt negative (or engine block. As stated above, it is better to do directly from alt, but IMO you aren't going to notice much of a difference if you have good contact between your alt and engine block.) to battery negative, which completes the circuit where you are drawing big power. Battery ngative to chassis is still needed for stock electrical, but you shouldn't need to upgrade it. IMO you might as well go ahead and do battery negative to chassis though.

Thank you for confirming what my thoughts were on the situation. I will do the last of the big three, just to strengthen the cars electrical as whole. Just have had this question in my mind for a little while now.

 

[JoeK 10+ year member]

Why would i ground my ALT to BATT if my Batt is in the backseat? Point is, that step is redundant for me. Yes, my engine battery is in the backseat

 

[shizzzon 10+ year member]

Why would i ground my ALT to BATT if my Batt is in the backseat? Point is, that step is redundant for me. Yes, my engine battery is in the backseat

Nobody told you to.... You assumed it.

Now, for your situation, if your vehicle is a unibody and they did not provide a dedicated ground cable, then i would assume charging voltage in the rear under MAXIMUM load would create lots of resistance.

IE - people who have sustainable current draw between 200-300A i've tested using a 250A alternator with NO extra ground cable from front to rear typically has 0.6-0.9v voltage drop under maximum load from front to rear.

You will not see this drop at idle because there is no resistance.

 

[av83 10+ year member]

Why would i ground my ALT to BATT if my Batt is in the backseat? Point is, that step is redundant for me. Yes, my engine battery is in the backseat

I would do it if I were you.... a negative run from the block/alt case to the batt in the rear is a great idea. Chassis grounds in newer unibody cars can be iffy....