do i need to...............

[jcvhsle]

gents, do i need to replace the main loom wire if i plan to fit an 85 amp alternator to a vh sle. im just curious will the extra amps cause issues going back to the loom terminal and then ultimately back to the ignition.
cheers jon

 

[drewVHSS]

Quick lesson in electrical theory:
The alternator cannot force more current through the system than what it draws/requires, so no it wont hurt the existing harness, as the car wont now be pulling more current before, just because more is available now doesn't mean the car will pull it unless you've added in a stereo system and thermo fans which increases the cars electrical needs beyond the original design.

Therefore if you want to provide more current to the car, i'd be adding in a 2nd or extra cable from the alternator to the battery and leave the original cable as is.
The battery's first job is to start the car, it's 2nd job is to soak up any excess current from the alternator, so the 2nd cable is mean't exactly for that.

Reasoning behind this is: if you have installed a decent stereo system, the amplifiers main power feed cable is connected directly to the battery, so the extra load on the car's electrical system begins at the battery so the extra juice from the bigger alternator needs to go directly to the battery before being sent to the rest of the car anyway.

If you've got thermo fans etc the relay power feed should be connected as close to the battery anyways (to feed it from under the dash defeats the purpose of using relays to get better power feed to new/extra circuits in the first place)

When a high current load device in the car's system starts up/turns on, the alternator's regulator allows more current to flow.
When that device switches off (say thermo fan for example) the extra juice coming out of the alternator now has nowhere to goto except to the battery to be soaked up.

This is why in fuel injected cars with ecu's... they can get fried if you run the car and disconnect the battery while the engine is running. As soon as a high draw device turns off... the current forces it's way back to common/earth wherever it can, usually burning stuff out along the way.

The original cable splits near the battery, one direction goes into feed the rest of the car the other goes to the battery via a fuseable link.
Electricity follows the easiest path exactly like water does, so if you hook a 2nd cable 8 or 4 gauge from the alternator to the battery, the charge from the alternator will as above follow the easiest path which will be the new cable to the battery, the car then will pull that charge like normal from the old wire via the battery ignoring the section coming from the alternator.

Leave the original cable in place for 2 reasons: 1 to share a load balance of current and 2 if in the event of a wiring issue, at least you have a backup source from the alternator.
I usually have 2 fuses on the 2nd extra/new/upgraded cable from the alternator. 1 close to the alternator end and the other near the battery. You dont want to have a short on a 8 or 4 gauge cable and end up with unwanted "arc welding"

Is the alternator a aftermarked 1 wire replacement or a VN-VS (not series 3 vs...) 5.0L alternator?
If it's a VN type, lookup the bosch website for info on it... it's not much better than a 55amp VK alternator as the VN one is only 14 amps at idle but ramps up to 85 amps above 1200rpm.
VS series 3 and VT series 1 (vt 5.0L) are 60 amps idle and 120 amps above 1200 rpm.
So if you're looking to solve a lack of power when idleing for extended periods with alot of load, the vn alternator isn't much good if you're stuck at the lights for a long time at night with headlights on, big stereo running and having ac/fans and thermo's running.

I'm not drunk yet tonight... can anyone on here tell?

 

[bcw61]

I'm not drunk yet tonight... can anyone on here tell?

Yep.

Your first paragraph was spot on.

Pity you then destroyed it with the utter tripe that followed.

 

[drewVHSS]

Ouch, keyboard warrior much?

 

[jcvhsle]

thanx drew, thats the most i ve read of anything in along time. that was gold. dont have stereos or thermos yet but for the little driving the old girl does the draw is more than i can replace. the other nite i was only getting 8 volts on idle at the lights. will read it again to confirm your recommendations if any are there as to which unit to run. thanks heaps, very easy to understand.
cheers jc

 

[DAKSTER]

Drew..

Firstly, a very comprehensive explanation, detailed and easy to understand. Well done, if people bothered to explain things well more often, a lot of threads would be a lot more useful.

I do however have some questions, perhaps you have mistyped, got mixed up or something or I just dont understand. I dont make any claims of expertise here, and you may be completely correct, but perhaps you could clarify for me.. this is in no way an attack, you sound very informed, but its a bit different to the way I understand it and I do like to learn..

Quick lesson in electrical theory:
The alternator cannot force more current through the system than what it draws/requires, so no it wont hurt the existing harness, as the car wont now be pulling more current before, just because more is available now doesn't mean the car will pull it unless you've added in a stereo system and thermo fans which increases the cars electrical needs beyond the original design.

Makes sense to me.

Therefore if you want to provide more current to the car, i'd be adding in a 2nd or extra cable from the alternator to the battery and leave the original cable as is.
The battery's first job is to start the car, it's 2nd job is to soak up any excess current from the alternator, so the 2nd cable is mean't exactly for that.

How can you provide extra current to the car if it cant use more than it needs? The batterys purpose, of course to start the car, and to provide storage for power. Of course, the amount of storage it provides depends on the battery, but all it does is store power.

I dont actually see the point in the second cable, a single heavier cable would be neater but not provide the probably unnecessary backup, thats all. A single heavier cable will also provide less resistance, giving a net gain over two smaller cables.

Reasoning behind this is: if you have installed a decent stereo system, the amplifiers main power feed cable is connected directly to the battery, so the extra load on the car's electrical system begins at the battery so the extra juice from the bigger alternator needs to go directly to the battery before being sent to the rest of the car anyway.

As I understand it, it needs to go to the battery, but it doesnt need to go through it. The battery post is effectively a connector, via which you connect all of your power cables to your alternator, and to which the battery is also connected.

As you have mentioned further down, electricity follows the path of least resistance, and this does not include detours through the battery. The current will travel down the alternator cable, and if a demand exists further down the line, it will continue via the connections at the battery to where it is required, not into the battery and then back out.

Obviously the battery, being the path of least resistance, will get first priority, but once it is fully charged it is not drawing any current at all, therefore the current continues to somewhere else.

If you've got thermo fans etc the relay power feed should be connected as close to the battery anyways (to feed it from under the dash defeats the purpose of using relays to get better power feed to new/extra circuits in the first place)

When a high current load device in the car's system starts up/turns on, the alternator's regulator allows more current to flow.
When that device switches off (say thermo fan for example) the extra juice coming out of the alternator now has nowhere to goto except to the battery to be soaked up.

Isnt that contradictory? 'When the load increases, the regulator allows more current to flow'
'When the load decreases, the extra juice has nowhere to go but to the battery to be soaked up'

Doesnt the regulator then reduce the extra juice if this is the case? And just how much excess power can the battery soak up.. what happens when the power has nowhere left to go and the battery can soak up no more?

I think the basic problem with most of this post is 'the regulator allows more current to flow'. I believe this to be incorrect as I explain below.

This is why in fuel injected cars with ecu's... they can get fried if you run the car and disconnect the battery while the engine is running. As soon as a high draw device turns off... the current forces it's way back to common/earth wherever it can, usually burning stuff out along the way.

Again, isnt that what the regulator is for in your explanation? Remember I am not the one with knowledge here, I am simply hoping you can clarify. I'm having difficulty understanding what the regulator has to do with current draw at all.

I always thought a voltage regulator regulated volts, not amps. Amps are simply how much current is being drawn, and current draw is controlled directly by demand, and available total current obviously is controlled by the output abilities of the alternator.

The original cable splits near the battery, one direction goes into feed the rest of the car the other goes to the battery via a fuseable link.
Electricity follows the easiest path exactly like water does, so if you hook a 2nd cable 8 or 4 gauge from the alternator to the battery, the charge from the alternator will as above follow the easiest path which will be the new cable to the battery, the car then will pull that charge like normal from the old wire via the battery ignoring the section coming from the alternator.

Leave the original cable in place for 2 reasons: 1 to share a load balance of current and 2 if in the event of a wiring issue, at least you have a backup source from the alternator.
I usually have 2 fuses on the 2nd extra/new/upgraded cable from the alternator. 1 close to the alternator end and the other near the battery. You dont want to have a short on a 8 or 4 gauge cable and end up with unwanted "arc welding"

If you leave the original cable in place, or upgrade it, or add a second one, if it goes to the battery it will not ignore anything? It will simply provide power via the shortest available route as required, again, not detouring through the battery. The redundant cable may be useful one day I guess, but how often do you burn out an alternator cable anyway?

Is the alternator a aftermarked 1 wire replacement or a VN-VS (not series 3 vs...) 5.0L alternator?
If it's a VN type, lookup the bosch website for info on it... it's not much better than a 55amp VK alternator as the VN one is only 14 amps at idle but ramps up to 85 amps above 1200rpm.
VS series 3 and VT series 1 (vt 5.0L) are 60 amps idle and 120 amps above 1200 rpm.
So if you're looking to solve a lack of power when idleing for extended periods with alot of load, the vn alternator isn't much good if you're stuck at the lights for a long time at night with headlights on, big stereo running and having ac/fans and thermo's running.

This makes sense if the numbers are correct.

 

[drewVHSS]

Dakster, from what i learn't in tech getting my apprenticeship is the battery soaks up excess.
There is always a delay from when load is no longer required and the regulator switches off as quick as it can but usually there is a spike when a high draw device shut's off just before the reg has a change to drop supply (this is how ecu's get fried if you run an efi car with no battery, an early girl like a VH has an electronic dizzy with a mosfet type ignition module in it which can get fried in the same manner but nowhere as delicate as newer cars)
That's why the battery needs to be connected at all times to soak up the excess.

The second cable to the battery is only for when he add's in things like a stereo amp and maybe thermo fans in the future.
The current always prefers to draw from the battery vs the alternator so having in that circumstance a thicker cable parallel to the original straight to battery helps make sure you have enough current flowing to the battery and to reduce load on the original cable which might not be able to flow as well as it should due to age.
When i added in a 2nd cable onto my VH SS, it made a difference mostly due to the old cable being old and having more resistance. So it wouldn't hurt for the OP to install one anyway.


With the alternators, yes the VN one has less than ideal output at idle. If he has problems with lack of power having to idle at lights at nighttime, the VN 5.0L alternator wont be much better than what he's using now.
I have a VN 5.0L alternator on my lap as i type this, it reads:
BXU1285 14v (14 volts max) 14/85A. The 14/85A means 14 amps at idle and 85amps at above idle.
Earlier alternators like the 55 amp on in my VH currently is 20amps at idle and 55 above idle.
VT series 1 (5.0L only) and VS series 3 5.0L alternators are the better choice for needing more grunt at idle.
VT series 1 alternators BXH1253 (14V 60/120A) are 120amp above idle and 60 amps at idle.
So for sitting at traffic lights at night time with headlights on, having the cooling fan kick in and also having things like blinkers running, the VT alternator is going to do a much better job of keeping the juice flowing than VN alternators will.

 

[jcvhsle]

wow, this is one of the best threads i have read and im glad i asked the question. thanx for the input guys. it would be grate if posts like this could be put into there own folder for common questions asked. i have found on many occassions that the same questions are asked with varying levels of answers and patience provided by the repsonders for the same question. responses like this one should go straight to its own page, as should other common questions like vt brake upgrades. that is another very common question of which i have been frustrated by in the past cause you need to read 20 different threads to receive all and i mean all the relevant answers. the administrators need to filter all threads and compile all the best information into its own category as a quick link. it would save alot of time and frustration for all. but im no guru with computers and websites so it would probably be a massive challenge. i acknowledge there are folders at the start of each forum section but rarely does relevant and new information like this make it to theses folders, with a label like common upgrade questions for vb-vk. anyway thanks gents and i look forward to further chats with the many and varied brains on this site. cheers

 

[DAKSTER]

Dakster, from what i learn't in tech getting my apprenticeship is the battery soaks up excess.
There is always a delay from when load is no longer required and the regulator switches off as quick as it can but usually there is a spike when a high draw device shut's off just before the reg has a change to drop supply (this is how ecu's get fried if you run an efi car with no battery, an early girl like a VH has an electronic dizzy with a mosfet type ignition module in it which can get fried in the same manner but nowhere as delicate as newer cars)
That's why the battery needs to be connected at all times to soak up the excess.

The second cable to the battery is only for when he add's in things like a stereo amp and maybe thermo fans in the future.
The current always prefers to draw from the battery vs the alternator so having in that circumstance a thicker cable parallel to the original straight to battery helps make sure you have enough current flowing to the battery and to reduce load on the original cable which might not be able to flow as well as it should due to age.
When i added in a 2nd cable onto my VH SS, it made a difference mostly due to the old cable being old and having more resistance. So it wouldn't hurt for the OP to install one anyway.


With the alternators, yes the VN one has less than ideal output at idle. If he has problems with lack of power having to idle at lights at nighttime, the VN 5.0L alternator wont be much better than what he's using now.
I have a VN 5.0L alternator on my lap as i type this, it reads:
BXU1285 14v (14 volts max) 14/85A. The 14/85A means 14 amps at idle and 85amps at above idle.
Earlier alternators like the 55 amp on in my VH currently is 20amps at idle and 55 above idle.
VT series 1 (5.0L only) and VS series 3 5.0L alternators are the better choice for needing more grunt at idle.
VT series 1 alternators BXH1253 (14V 60/120A) are 120amp above idle and 60 amps at idle.
So for sitting at traffic lights at night time with headlights on, having the cooling fan kick in and also having things like blinkers running, the VT alternator is going to do a much better job of keeping the juice flowing than VN alternators will.

Thanks mate but I still dont understand what the voltage regulator has to do with current draw.

I also still dont understand 'The current always prefers to draw straight from the battery vs the alternator'.

The battery may absorb a spike in current up to a point, but in normal situations with the battery fully charged, current will go where it is required, and via the shortest possible route. This means it isnt going to go through the battery at all, but simply follow the wires which happen to have a connection at the battery post. Just because the power is going via the battery post doesnt mean its preferring to draw from the battery? The battery post is a connection point in this circumstance, nothing more.

A possible analogy would be a hole in the road (the battery) with a bunch of storm water (the current) going across and around it. Initially, when the hole is empty, it will retain the water that crosses it, impeding or stopping the flow past that point. Of course, other water is also able to go around it too (via the connection at the battery post).

If the hole is like a cave entrance, then it will eventually fill the cave (battery), but the size of the entrance and the size of any air vents in the cave will limit just how fast it fills, the remainder of the water flow will still carry straight over it.

Once its full, the water will just run straight over the top of the already full hole. Once it reaches that point, the hole no longer plays a major part in the exercise, although it may have some effect by creating turbulence. Maybe a battery will have other effects too, instead of the turbulence in the water analogy... I have no clue, but it certainly isnt going to remain the primary source of power?

Then, when the storm stops (engine is turned off), you are removing any further water flow (current), so the surrounding area becomes dry and the hole (battery) remains the only part left with any water. Until you remove the water flow (current), once full the battery is effectively playing no further part in the process.

If there is a spike in power, the battery may help to absorb this I guess, but surely that is actually the function of fusable links and fuses to deal with?

 

[bcw61]

Thanks mate but I still dont understand what the voltage regulator has to do with current draw.

Quite simply, the voltage regulator basically has little to do with the current draw. The current draw is dependent upon the load that is placed upon the electrical system. If a steady load is applied to the alternator output, and the regulated voltage changes, then the current draw may vary slightly (Ohms Law), however modern voltage regulators are quite accurate & responsive, so the effects due to a varying alternator voltage output would be minimal at the most.

Remember - the voltage output from the alternator is effectively constant due to the regulator, and the output current is dependent upon the load applied to it. The current rating of an alternator is the maximum current that can be drawn from the alternator, before the alternator goes effectively into a 'current limit mode' - at which point the voltage output of the alternator will simply start to decay with any increase in the load applied to it. This alternator 'current limit mode' is a design feature of the alternator (unlike a DC generator) involving the type of construction, magnetic saturation of the stator, etc, that is probably outside the scope of this forum.

To recap:

1. The alternator output voltage is set by the voltage regulator.

2. The current draw from the alternator is virtually entirely dependent upon the load applied to it.

3. With an applied load, the alternator will simply supply the required current - up to it's maximum current limit rating.

BTW, the reason why you should not run an alternator furnished vehicle without a battery connected, is that the voltage regulator only senses the average of the alternator three phase output, and a VOLTAGE spike can possibly be generated (within any of the phases) - which can do damage to electronic equipment. The battery acts as a buffer to prevent these voltage spikes.

I hope this helps a little.