Alternator Output

[vscorsa Member Find all posts View Profile Close vscorsa]

Hi Guys,

When you are talking 80 amps is that 80 amps per hour? Also, is that the same on the 150 model and does the dioide I have installed make any difference to amps/hr or just max volt outpout?

Thanks

[Guest Close Guest]

Amps is a unit of current. Amp hours is a unit of energy. Not sure about amps per hour. Haven't come across that one before.

The alternator is rated in amps. The amount of energy stored in a battery is amp hours.

[Matty80 Avid PP Poster! Find all posts View Profile Close Matty80]

80A is the Australian standard for both petrol and diesel models for the 120 series.

standard voltage outputs range from around 13.6v to 14.0v.

the petrol sees a higher voltage output at the battery than the diesel because the alternator is next to the battery not on the other side of the engine as found in the diesel. Yet despite the increased distance, likely more than double the length of cable, Toyota has used the same size charge cable.

we've all heard of voltage drop?

Try measuring the difference in voltage between the terminal on the actual alternator an comparing that to the voltage at the battery. Will show you (for diesel owners) just how badly rated the cable is.


The alternator itself:

an alternator has a set VA rating, that being VA (or Watts) = voltage x amps

80A x 13.6 = 1088VA (1088 Watts) the VA rating can never change.

increase the voltage to say 14.5v?

1088 / 14.5 = 75.6A this is a reduction in maximum current output.

increase the size of the cable from the alternator and reduce the voltage drop? Reduced voltage drop!


The load (or cars electrical system):

every time you switch something on, you increase the load, every time you switch it off, the load reduces.

when you add loads (resistances) together they equal the inverse of the sum of each load inversed. Confused?

Total load = 1 / ( ( 1 / load ) + ( 1 / load ) + ... )

that being with each additional load added the total resistance reduces on the circuit.

if the following is true: voltage = current x resistance ( v = I x r ) and voltage is fixed at which ever value your car operates at an increase in voltage will reduce the current drawn and a reduction in voltage will increase the current drawn for the same load.

or for a constant voltage turning your spotties on increases current draw or switching them off reduces it.

simply adding a larger alternator with a larger maximum output will not mean that you will ever actually use that additional power available.

the math does not allow for what is available, only what is required.

increasing the size of your alternator will not benefit anyone in any way unless you have added a large number of large power consumers. And with that, I would mean a few fridges, heaps of spotties and a constantly operating air compressor.

[Matty80 Avid PP Poster! Find all posts View Profile Close Matty80]

Now for ampere-hours... What I be wrong that we have all heard the following?

"watts a joule per second" as a response to a child's question of "What?"

well the ampere hour (Ah) is similar in that it is a measure of electric charge, being the following:

Ah = time (hours) x Amperes

Ah = (3600s) x (C / s) = 3600C where C is coulombs

its a lot easier to work out than you think...

taking it back to basics, you can work out how long your battery will last without charge when applying a load, for example:

120Ah = 1 hour @ 120A rate

or

120Ah = 10 hours @ 12A rate

or

120Ah = 120 hours @ 1A rate

it is important to note though that a battery voltage will vary during the discharge cycle and that the Ah can be used as a guide only. But it should give you a good idea of where you are at.

[D4D Addicted PP Member Find all posts View Profile Close D4D]

Has anybody had their alternator rebuilt/replaced to run higher A? I upgraded to a later Nissan alternator in my GQ however I think the Prado is a little more complex.

[vscorsa Member Find all posts View Profile Close vscorsa]

Great reply's thanks for the info.

The reason for my amps/hr question is around how long the car needs to run for after I have drawn my 105A/hr battery flat. My understanding was that the alternator could only charge at a maximum rate which may be 30 amps/hr and therefore the motor would need to run for 3.5hrs to charge the flat batter?

I might be looking at it a little to simply.

[Guest Close Guest]

Apologies in advance but I think we should get the units right first. Sorry for being pedantic
105A/hr should be 105Ah
30 amps/hr should be 30A

So now that this is straightened out...

Great reply's thanks for the info.

The reason for my amps/hr question is around how long the car needs to run for after I have drawn my 105Ah battery flat. My understanding was that the alternator could only charge at a maximum rate which may be 30A and therefore the motor would need to run for 3.5hrs to charge the flat batter?

I might be looking at it a little to simply.

The equation is 105Ah / 30A = 3.5h (Ah / A = h)
So simplistically, you are correct. How fast the alternator can charge the battery will be determined by what else is drawing from the alternator and the output voltage.

[AJ120 Out of control poster! Find all posts View Profile Close AJ120]

Ive read a lot about charging batteries and to be honest once the formulas and the tables and the Soc figures start flying I tend to glaze over a bit, so please correct me if I am wrong here.

My understanding is that even if you have 100Ah battery whilst it seems logical that you should get 100 hours if drawing 1A that is not actually the case, I think because voltage gets too low before the battery is "fully" discharged.

Likewise when charging a battery, if it is in low Soc (state of charge) then it can and will suck up a lot of Amps from the alternator, however the closer it gets to fully charged the less it is able to take in, even though the Alternator has plenty to spare.

so without getting too detailed I understand that the alternator will pump its maximum (or close to it) into the battery for a relatively short period giving it a big boost in charge, then it will slowly give less and less the closer it gets to being fully charged and some will say that its impossible to "fully" charge a battery from an alternator.

So the moral of the story is, a larger alternator might give that initial bulk charge in a shorter period, but once the battery is unable to take whats on offer a larger alternator is not any use at all. A larger alternator is really only useful if you have ongoing high demand for power, and I have run 1 x fridge, 1 x freezer, external lights, invertor etc etc over extended trips without any issue.

If you have long stays camping with relatively short drives in between to charge the batteries I would look at solar rather than a larger alternator.

Cheers Andrew

[fridayman Senior Member Find all posts View Profile Close fridayman]

If you have a winch, a higher output (amps) alternator is useful.

[vscorsa Member Find all posts View Profile Close vscorsa]

Hi amts,

Thanks for clarifying the units.

I am used the 30A as an example for the alternator output, is the above 80A for the D4D the correct number to use for how long it will take to charge up a 105Ah battery?

Also, as mentioned it would be interesting to see how much of the 105Ah is actually useable. At 9.6v's my Waeco will stop working yet the Engel will continue to operate.

Cheers

Apologies in advance but I think we should get the units right first. Sorry for being pedantic
105A/hr should be 105Ah
30 amps/hr should be 30A

So now that this is straightened out...


The equation is 105Ah / 30A = 3.5h (Ah / A = h)
So simplistically, you are correct. How fast the alternator can charge the battery will be determined by what else is drawing from the alternator and the output voltage.

[mjrandom Out of control poster! Find all posts View Profile Close mjrandom]

At 9.5V you have done permanent damage to your battery, that is reduced its life. Depending on the type of battery (wet cell or AGM etc) there will be a minimum pull down that the manufacturer will state, go lower than that and the life of the battery becomes affected. So based on the max and min voltages you can work out the useful capacity of a battery. Sometimes this is depressing reading. Google the manufacturer and model of the battery quite often there are details which will clarify that for you.

[Guest Close Guest]

I am used the 30A as an example for the alternator output, is the above 80A for the D4D the correct number to use for how long it will take to charge up a 105Ah battery?

Also, as mentioned it would be interesting to see how much of the 105Ah is actually useable. At 9.6v's my Waeco will stop working yet the Engel will continue to operate.

Cheers

Have a read of this
http://www.engineersedge.com/battery...ry_ratings.htm
and you will probably realise that battery ratings and real life applications can be quite complex. For example, the battery capacity is dependent on what the manufacturer tested it at (i.e. discharge rate (amps) and time (hours)). Your use of the battery is different to the manufacturer's test parameters so your 105Ah can be anything because a lower discharge rate results in higher capacity.

When I first got my 130Ah battery, the fridge couldn't run continuously for a day. I took it back to the retailer and he performed a discharge test using the manufacturer's discharge rates. From there he determined that the battery was at 35% capacity using the 20A discharge rate.

[gumboot Avid PP Poster! Find all posts View Profile Close gumboot]

80A is the Australian standard for both petrol and diesel models for the 120 series.

standard voltage outputs range from around 13.6v to 14.0v.

the petrol sees a higher voltage output at the battery than the diesel because the alternator is next to the battery not on the other side of the engine as found in the diesel. Yet despite the increased distance, likely more than double the length of cable, Toyota has used the same size charge cable.

Try measuring the difference in voltage between the terminal on the actual alternator an comparing that to the voltage at the battery. Will show you (for diesel owners) just how badly rated the cable is.

Thats a very interesting fact.
So are you saying an easy way to increase voltage to the battery is as simple and replacing the current cable with a larger one?
What's the Voltage diference at the alternator terminal verses the other end of the cabledl you have measured?
Have you tried any diferent sizes?

Cheers

[vscorsa Member Find all posts View Profile Close vscorsa]

Interesting info, it looks like I might have to do some research!! My assumption which appears to be wrong is that a deep cycle battery can be pulled down to significantly low voltages and will return back to full capacity from charging.

Cheers amts I'll have a look at that page.

At 9.5V you have done permanent damage to your battery, that is reduced its life. Depending on the type of battery (wet cell or AGM etc) there will be a minimum pull down that the manufacturer will state, go lower than that and the life of the battery becomes affected. So based on the max and min voltages you can work out the useful capacity of a battery. Sometimes this is depressing reading. Google the manufacturer and model of the battery quite often there are details which will clarify that for you.

[gxl_d4d Advanced Member Find all posts View Profile Close gxl_d4d]

My 40L Engel runs until the battery is flat i.e. 8.8V no load. I found this out the hard way. Battery bounced back after a 9 hour charge however after 2 years with light use it only runs the fridge for 14 hours until flat. Would be less with a low voltage cut off. Pitty they don't include a low voltage cut off from the factory. The battery cranks the engine fine even when I lift the battery terminal from the factory starting battery i.e cranking from deep cycle only.

Hi amts,

Thanks for clarifying the units.

I am used the 30A as an example for the alternator output, is the above 80A for the D4D the correct number to use for how long it will take to charge up a 105Ah battery?

Also, as mentioned it would be interesting to see how much of the 105Ah is actually useable. At 9.6v's my Waeco will stop working yet the Engel will continue to operate.

Cheers