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[VT-VX] How To Increase Alternator Output Voltage

shane_3800

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Not how electricity works. If you increase the voltsge it will draw less current. The power (watts) is constant.

P=VI - at 14.4V the power consumed is 14.4V x 40A = 576W

If you add the diode and take it to 15V output the current will reduce as the load has not changed - it will still require 576W to power it

I=P/V so 576W/15V = 38.4A - less current is required as more voltage has been applied.

This 15V is now overcharging your battery - it won't kill it today but you won't be getting 4 years out of it either. It is a slow and painful death for the poor old thing.

The draw on the alternator's power has not changed - theoretically. In practive you need to provide additional power to the field windings in order to increase the magnetic field to produce the additional voltage so the motor has to work harder to drive the armature to cut the field so the additioanl power requred to do this comes from the engine (motive power) not the alternator Nothing is free.

The resistance is constant regardless of the voltage - resistance from the cables and components does not change (theoretically) however, heat and other variables come into effect in real life situations.
You are some watt correct. But amps will not flow without volts. If a load only has half it's rated volts not all the current will flow.
 

Deuce

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Slightly off topic, but where did you get that little gauge from? I want one...

edit: Amazon? I think I found it.

I think all cars should have a volt gauge as it's a sure fire way to see if something is going amiss before total failure of the electrical system.
My high end (10years ago) head unit has voltage read out and it is very VERY useful. Saw it high one day and everything got brighter, turns out brushes in alt were worn, voltage spiked and had blown both fog lamp bulbs.


On another note. I am at this stage opposed to this mod. But may be swayed if:
Will this mod lift my idle voltage (as it currently runs super low on a cold winters wet evening stuck in traffic) but the voltage reg will still cap charging voltage at the same point while driving (approx 14.8v).
If so, then it is a simple win and worth doing.
If not, I will pass thank you.
 

Jolls

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In my case, I'm getting to the upper end of what the factory pump can supply, I'm pushing the ignition system much harder than ever intended. I could compromise and run a smaller plug gap due to higher boost but that compromises other engine tuning characteristics that I'm not will to sacrifice so I could invest a lot of coin into another ignition system, I could spend a lot of coin on a bigger fuel pump or as I have done, I spent about NZ$4 on this little mod and can get just a little more from what I already have which gives me a safety margin.

Your major concern seems to be with cooking batteries, I don't think this will be a major issue with a small bump in system voltage but I guess only time will tell.
@immortality thanks I got it - in your case you have reached the limitations of the system and need a safety margin. Fair cop - easy and cheap mod for you needs. I am not overly concerned with cooking batteries - it is something you have to be aware of. If you bump the system up to 15+V you should be thinking about the benefit. If you are under 15 i'm sure the battery will survive.

There's no shortage of amps. What I'm losing is voltage. I'm losing tension because I'm adding more current (there's the laws). Now add a bunch more systems and I'll eventually drop to an unhealthy level to keep my battery charged. I only need a couple amps but what I really need is voltage.
@Pollushon I get where you are coming from. I have not said there isn't enough power - amps or volts to go around - although I did use an example to try and illustrate a point about what would happen if you exceeded the capacity of an alternator. I am also not saying the mod doesn't work.

As for overcharging a car specific SLA that's ridiculous. I don't think you understand the type of battery it is. The higher end of the power spectrum will prolong its life. If you've ever used a battery recovery charger after calcification has corrupted it you'd understand what I'm talking about
I assume you are referring to reversing sulphation by providing a prolonged charge aI 15-16V. This is to reverse the effects of a battery that has been undercharged by a poor charging system or numerous short runs without fully charing the battery.. If the vehicle is being run for more than half an hour the best charge method is to apply a constant voltage of 2.40–2.45/cell (14.4 -14.7V). If you are keen and then want to put it on trickle charge overnight to prolong battery life it should then float at 2.25–2.30V/cell (13.3-13.8V). If your system is operating within 14.4 -14,8V, and there is no other specific reason you need a boost, there is no need for any electrickery.

I did provide an example of how adding tjhis mod to a system that is healthy could have detrimental effect on the battery. On short runs you are right 15v may be beneficia; however, if you do prolonged runs during daylight hours you can provide too much. I simply showed how adding a diode to a healthy system could exceed this limit. I am not focussed on it - just trying to show real world examples of how it could go wrong

I have tried to steer away from terms like ergs, and sag etc by focussing on the electrical principles. It appears that tying to use well defined terms in context has confused some.

So

The question I asked was simple - why would you do it. After all of this discussion I only have a few valid answers.

1. Your charging system is not great be this due to age or failing components. The mod will prolong the life a little longer but eventually you will need to fix the underlying problem, that could be realated to an earth side voltage drop, a poor regulator, failed/failed windings etc.
2. You are at the high end of the performance scale (be it spped or loudness haha) and the voltage drop due to load affects performace - eg pumps, ignition systems ect. This will only be an issue for a select few.
3. Dual battery system to overcome the VD caused by the isolation diode.

On the down side - if you already have a healthy system this mod may be detrimental to the overall health of the battery.through overcharging.

My conclusion is that this mod may be worthwhile for some but unless you are pushing the system to its limits it is not something required by the majority. If your system is in good shape it may even be detrimental. I will leave it to you to make up your own mind.
 

Skylarking

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It’s a simple mod and regardless of whether it’s a good mod or less good mod, it doesn’t really matter. Confirmation bias will reinforces that warm fuzzy feeling that one has done the correct thing.

It’s almost like religion where there is no conversion.

 

Pollushon

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I think we wrote seven pages to agree it's a good mod if you need it. Like when you add two more fuel pumps, a high flow water pump, two gauges and a 4 channel amp
 

Skylarking

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Yes pages of discussion to conclude that fiddling with sence wire isn’t really needed unless you’re trying to cheaply overcome some other defect as a quick fix at the potential expense of your battery.

If anyone wants an easily digestible primer on alternators, their current and voltage regulation, look at the following, especially the warning at the bottom of the page re the sense wire :p

http://www.tb-training.co.uk/MarineE08.html

That‘s my bit of conformation bias done :rolleyes:
 

immortality

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Yes pages of discussion to conclude that fiddling with sence wire isn’t really needed unless you’re trying to cheaply overcome some other defect as a quick fix at the potential expense of your battery.

If anyone wants an easily digestible primer on alternators, their current and voltage regulation, look at the following, especially the warning at the bottom of the page re the sense wire :p

http://www.tb-training.co.uk/MarineE08.html

That‘s my bit of conformation bias done :rolleyes:
Yes, if the sense wire is damaged and has a larger resistance across it the alternator voltage will increase a lot and cook your battery. This mod will not do this unless you damage something in the process.

The thing is, whether or not you do this mod, if that wire is damaged the end result will be the same. It really is a shame manufacturers removed volt meters from the dash as that alone will show what is happening long before catastrophic failure unless some sort of mechanical damage occurs.

Ever seen a 6 pole alternator?
 

Pollushon

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Yes pages of discussion to conclude that fiddling with sence wire isn’t really needed unless you’re trying to cheaply overcome some other defect as a quick fix at the potential expense of your battery.

If anyone wants an easily digestible primer on alternators, their current and voltage regulation, look at the following, especially the warning at the bottom of the page re the sense wire :p

http://www.tb-training.co.uk/MarineE08.html

That‘s my bit of conformation bias done :rolleyes:
How many times have you performed this mod @Skylarking? You read some opinions to gather your confirmation bias, as you're totally entitled to do but it doesn't make any of your assumptions correct. Practical experience does. If you really believe that a <1v increase in source output will create catastrophe with your electrical system all I can suggest is more practical and less theory ;)
 

Skylarking

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@Pollushon, everyone suffers conformation bias as it’s more natural behaviour than being cold and clinical. It’s just human nature. But that conformational bias line was more a joke which you seem missed :p

As for alternators, I’ve rebuilt a few. Many years ago I also had a 4x4 where I added dual batteries with a diode isolator, voltage and current meters. I did have a problem in the middle of nowhere when the isolator‘s diodes died in the heat. Their death was due to driving in 45C temps at 120kph through long stretches of outback with aircon on full bore and music playing. So I bypassed the isolator and kept going until I got to a bigger town where it was an easy fix (better rated diodes and a bigger heat sink). I was not surprised the diodes overheated and died as cheap stuff does that. It was then I tried the sense wire mod and didn’t see any problems as it simply compensated for the diode isolator’s voltage drop so there was no boiling of the battery even on a long long 10 hour drive across the Nullarbor (loved that long range diesel tank and the 1100km range).

These days diode isolators include compensation diodes which do the same job as this mod in question, see here but also note the comments...

I’ve never used such a mod In a single battery situation and don’t see the point really. There are better solutions to service high load equipment if one wants reliability. Police use a dual battery setup with separate fuse box for the accessories and presumably a higher power alternator though I haven’t heard if isolators are in the mix. Oddly, supposedly the police cars are still put on charge between shifts. But if people feel a $0.20 diode and a single battery is a good solution for their high power needs, all the strength to them, practice and theory and all that :p
 
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The original claim was that the battery voltage went from 14.1 to 14.7 volts with this mod.
The power dissipated in things is equivalent to the square of the voltage.
So, the headlights for example, will now glow at 14.7^2 / 14.1^2 = 1.0869 times the power - approx 9% higher.
How long the headlights last is bound to be a square (or square root, depending on how you look at it) ratio to the power
so my guess is that you will lose about 20% of the lifespan of your headlights.
If anyone wishes to do this mod then it might better to also install a switch across the diode so that you can switch it back to lower voltage
in summer, as the battery wont like the combination of heat + higher charging voltage.
 
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