Question about the capability of car battery

[bigfatmonkey]

car Battery question.

Hi I have a question that I hope some one would be able to help me with.

I want to attach an item to my car that with draw 100amp. My car battery is 70ah and my alternator is rated at 70 amp.

I understand that a 70 ah batter will provide around 50amp for 1 hour or 100amp for say 30 minutes.

My question is. Because the alternator is in parallel with the battery will the available current double?

Also the battery will provide around 12.5v were as the alternator will provide up to 14v. Will this make a difference?

If I had the engine running when I draw the 100amp where will it come from?
I.e. 50amp from the battery and 50 amp from the alternator or 100 amp form the alternator.

i hope some one can help.

thanks

 

[Borber]

Re: car Battery question.

Alternator has circuitry to hold it's voltage at 14V and it overtakes all loads. If you want to draw such current, I think you will destroy alternator.

 

[Moof]

Re: car Battery question.

I desagry with border, your alternator is not going to be destroyed, because the nucleus ( i dont know if that is the correct name) is going to be satureted, and your alternator is not going to be able to give you more tan 70 Amps. So the battery is going to give the rest. If you have insted of alternator, a dinamo, thats is diferent, only in that case, your "dinamo" will be destroyed. What i wrote, is ONLY in car alternator, not in other type (i used to work in a car factory, and my job was testing alternators) so i tell you that you shouldnt have problems. But, check the temperature of your alternator when you make the test.

 

[bigfatmonkey]

Re: car Battery question.

i don't want to burn out the alternator when i try it out.

 

[platonas]

Re: car Battery question.

I am curious about the kind of load you are going to connect, is it a high power amplifier of a heater or ... what?

In order to have a better and more accurate answer we need to know the type of load.

Definetly u need an alternaton rated at 120A or more. The 70A aulternator will run full load and will overheat and finally destroyed. The battery also with such a load will not last long. You must consider also the rest of the loads in the car.
The alternator is sized at 70A because it should be able to supply the lights, a normat car saudio system and any loads considered by the manufacturer. Appart from that it must spare some power in order to be able to charge the battery. All these are simultaneous loads for the alternator, worsed case senario.

Also, a car battery is not designed for such high currents at continous use. It can supply more than 100A for short time in order to start the engine but cannot supply currents of such a magnitute (50A) and expext it to last for a year or more. It is heavily loaded and will die very soon.

Further the alternator cannot supply the 70A whenn the engine is idle, it needs some more RPMs, hence you need to be moving with u r car or the battery will be loaded more than expected.

 

[flatulent]

Re: car Battery question.

One standard method is to have another set of batteries that power your equipment and are sized for the load current. There is a relay that connects these batteries to the alternator for charging when the equipment they power is not being used. The relay is opened when the equipment is used.

 

[bigfatmonkey]

Re: car Battery question.

i am connecting a 1000w inverter to power a microwave that draws 1000w.it wont be on continually just for a few minutes at a time. it would only be used a small number of times as well.

I was going to use 2 80amp leisure battery in parallel and that would do it fine of my use but was considering the existing system in the car.

 

[kukitron]

Re: car Battery question.

It is quite a challenge to get such kind of power from a car battery,

If you really need it, install a few cells in the back of the car, otherwise there is no way you can do it,

Your alternator would not explode, or get damage, but most likely you will end up pushing your car on the side of the road,

 

[andreas1982]

Re: car Battery question.

You must always remenber that :

1 Ah is 1ampere×hour so your battery can delivery 70 ampers for hour!

Regards.

 

[prinsloo]

car Battery question.

Why do you want to connect micro wave to battery? Your feul consumtion and running cost /litre of feul will be high.You can cheaply heat your food on fire/hot-cold cooler combo's.

 

[lsrama]

car Battery question.

your thinking is wrong.because the basic requrement
for an parallel operation is the voltage levels must be same.

 

[Diksi]

Re: car Battery question.

Added after 1 minutes:

1. Alternator have a regulator to keep 14.4 or 13.6V to charge akk. and get ENOUGH current to supply all electrical devices in a car..
2. probably your alternator have overload protection so ... it will be realy funny that havent ... its many reasons for that... one reason its posibility to short circuit ... only question its what kind of overload protection it have, fuse or some smart electronic ...
3. I think that you have answer on problem with existing equipment, especialy because its not so long working time .. only my suggestion its that you buy or make one fuse .... 70A=12-14 standard litz wire; and connect between alternator and akk. ...

bye!

 

[yeechyan]

car Battery question.

I think the so called "nucleus" mentioned above is the magnetic core/coil.

If you want 100A output using a 70A alternator with a 70Ah battery, the alternator can only provide up to 70A (rated). So the rest 30A will be drained from the battery. When the battery runs flat, what's going to happen?

 

[echo47]

Re: car Battery question.

You must always remenber that :

1 Ah is 1ampere×hour so your battery can delivery 70 ampers for hour!

Regards.

That's not quite correct. Under heavy load, a typical lead-acid battery provides significantly less than it's rated ampere-hour capacity. For example, see page 3 of PowerSonic's handbook:
**broken link removed**

 

[e_eja]

Re: car Battery question.

do not attach high amp alternator with lower amp battery cause it could damage your battery

 

[komi]

Re: car Battery question.

do not attach high amp alternator with lower amp battery cause it could damage your battery

In a global its not correct! Because most of alternator have 13.6-14.4V output voltage ... because this voltage its meassure of "how strong will be charge current" its clear that most of alternator will be compatibile with most of akk. i know only one case(it doesnt mean that exist only one exception) ... one company developing special akk. charger for strictly defined akk. maybe most company develop something similar but i thing that classic way to charge akk. its always safe...


bye!

 

[yeechyan]

car Battery question.

The charging current from alternator to the car battery also depends on the voltage of the battery, it's discharged state, it's internal resistance. High amp alternator is able to provide more output current but the output voltage is more or less the same with lower amp alternators. It may not be damaging to a low amp battery unless you plug a 6 volt battery to the alternator.

 

[platonas]

Re: car Battery question.

The car alternator provides such current as to keep the battery at a specified level.
That means, an alternator of 100000A can safely charge a battery of 1Ah and a battery of 100Ah or a battery of 10000Ah.
The only difference is that when the voltage drops due to loading, the alternator will have enough spare capacity to supply the load.
In a car system, the alternator is rated such as to be able to charge the battery and simultaniously supply the rest of the loads, Lights, heaters, radio etc. So, when more load is introduced in a car, common practice is to increase the size of the alternator.
It is also advisable to increase the size of the battery but it is not a must.
In the case of a load of 1KW inverter where it is used occasionally and when the cars engine is running, there might not be a need to oversize the alternator or the batery. Although it is suggested to use a larger alternator in order to avoid discharging of the battery. An alternator cabable to supply at least 120A in order to cover the 1KW load and spare some power for battery charging and/or some other loads.