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[VT-VX] How To Increase Alternator Output Voltage

Jolls

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The example shows the detriment of voltage drop in a standard 12 volt system.
Not as I read it. (see below.) He purchased the 16V alternator and battery but did not run the alternator n the testing. Baseline was a standard alternator at 14V. 6hp drop with fully charged 12V battery no alternator so it is operating at 12V and below from the start. Then other 6hp loss with a 12V battery at 3/4 charge and no alternator then a 16V battery with no alternator.added 6hp over baseline.

What the OP indicated is that with a standard 12V system in a race car at the end of the race the battery is not fully charged and the VD is detrimental to performance. If the alternator is not producing enough charge to maintain the battery in race conditions it is not sized correctly for the task - power demand exceeds output. If he increases the alternator size to combat this it will come at the cost of reduced hp to drive it. (no free power). Interesting 3/4 of 16V is 12V - the magic number to drive the components.

In race applications there are other electrcial systems that can be used - total loss systems , magnetos etc. It is not really a comparable scenario to a six banger commodore or an LS1 on a skid pan.

I'm not saying increasing the voltage can't be benficial - especially in a race/performance situation. I am simply trying to ascertain what benefit this provides to joe average and if it is worth investing the time and effort.


Thanks everyone, I have purchased a powermaster race 16v alternator so all good. Smitty, I did a thorough dyno session with a super sedan engine a while back, baseline was with the dyno battery and alternator around 14v. Then tested with a fully charged 12v battery and no alternator, lost about 5-6 hp. Then a 3/4 charged 12v battery no alternator, lost another 5-6 hp, this test simulated what the output would be at the end of a race. Then a fully charged 16v race battery, no alternator, picked up 6 hp over the 12v with alternator combo.
This was with MSD ignition and simulated race set up how it is raced with no alternator. I am going this way for my own drag car and 6 hp is 6 hp, I am picky with things like that.
 
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shane_3800

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The higher the volts more current will flow.
If you're using 40 amps of your 65 amp alternator there will be VD in the system as there is resistance from the 40 amp worth of load. If you increase the voltage the load will have the same VD but will appear like it has less VD and will be flowing more current.
This means you will use more watts so you gain more power at the load and the alternator is still within it's limits.
 

shane_3800

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Get your multi meter put it on your battery. Take some readings as you add loads and keep adding more load and record the results.
 

Jolls

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The higher the volts more current will flow.
If you're using 40 amps of your 65 amp alternator there will be VD in the system as there is resistance from the 40 amp worth of load. If you increase the voltage the load will have the same VD but will appear like it has less VD and will be flowing more current.
This means you will use more watts so you gain more power at the load and the alternator is still within it's limits.
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.
 

immortality

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Not as I read it. (see below.) He purchased the 16V alternator and battery but did not run the alternator n the testing. Baseline was a standard alternator at 14V. 6hp drop with fully charged 12V battery no alternator so it is operating at 12V and below from the start. Then other 6hp loss with a 12V battery at 3/4 charge and no alternator then a 16V battery with no alternator.added 6hp over baseline.

What the OP indicated is that with a standard 12V system in a race car at the end of the race the battery is not fully charged and the VD is detrimental to performance. If the alternator is not producing enough charge to maintain the battery in race conditions it is not sized correctly for the task - power demand exceeds output. If he increases the alternator size to combat this it will come at the cost of reduced hp to drive it. (no free power). Interesting 3/4 of 16V is 12V - the magic number to drive the components.

In race applications there are other electrcial systems that can be used - total loss systems , magnetos etc. It is not really a comparable scenario to a six banger commodore or an LS1 on a skid pan.

I'm not saying increasing the voltage can't be benficial - especially in a race/performance situation. I am simply trying to ascertain what benefit this provides to joe average and if it is worth investing the time and effort.
Some drag racers run without the alternator connected because they argue the parasitic loss of the alternator on the engine is greater than the performance loss of the reduced power from the battery alone. The example above also shows that at 12volts (battery only and should be about 12.8 volts on a fully charged battery) you are already loosing power over the conventional standard 14 volt alternator.

I watched a video recently of a drag car that lost the drive belt at about 1/2 track but the driver didn't realise. On the following run they realised as they staged the car but elected to still run the race. By 3/4 track the voltage had dropped enough that the electric fuel pump lost enough flow to lean out the motor and cause a decent pop through the exhaust. The chart I posted earlier shows a 100lb/hr loss for 13.5 volts down to 12 volts (The A1000 is a big pump), that sort of loss of flow on EFI would screw up your tune. On old school motors running carburettors and low pressure pumps the loss of flow would be considerably less.

With EFI systems fuel pressure is critical, high volume, high pressure pumps consume a lot of power.

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.
 

Skylarking

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... I have not ever said it doesn't work I asked "to whar end". Apart from the fuel pump example - to which I believe upgrading the pump is a better solution - there has been no other valid reason provided for doing so provided...
Useful in a dual battery setup where diode isolators are used; post #36 ;)
 

Pollushon

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Here's my magna. Uses the same 130amp alternator as my VY SS. Jolls your fixation on the laws is holding you back. Let's be clear, there is more than enough amps to go round and then some so forget laws, focus on the use case. Mine runs 90a idle and hits peak after 2500rpm.

Idle
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Add lights and radio
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Add aircon
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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.

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
 
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immortality

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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.
 
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Pollushon

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It was eBay or Amazon. I went through a couple til I found this which I tested is proper accurate. I agree, it's how I identified my rectifier was dodgy long before it left my battery flat
 

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Interesting mod. I haven’t read though all the posts in detail but I saw a few posts asking ‘why?‘ or what the is the benefit of this modification.

The car’s charging system should regulate the voltage to the battery but there are a couple of compromises in some systems.

To charge a battery properly (to maximise it’s life) the charge voltage voltage (often called the ToC Voltage - top of charge voltage) needs to adjusted according to the temperature of the battery. This is called ‘temperature compensation’. The typical temperature compensation is about -3mV/degree C per cell. So about -18mV/C for a 12 V battery. i.e. the charging voltage should be reduced as the temperature increases.

Unfortunately, many charging systems take a shortcut with the temperature compensation. Instead of placing a temperature sensor on the actual battery, they place the temperature sensor within the alternator. The alternator will typically run much hotter than the battery, so the temperature compensation circuit drops the voltage to the battery as it is assuming that the temperature of the battery is the same as the temperature of the alternator.

The diode-in-the-voltage-sense-wire modification is a simple way of bumping the voltage up a bit to compensate for the compromised temperature-compensation. It’s not ideal as it isn’t addressing the cause of the problem, but it’s probably better than a soggy charging system.
 
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