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Old 10th June 2011, 10:59   #31
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Default Re: Car Battery/alternator capacity query

1. Modern alternators are designed to run fast enough to supply all the standard accessories at just above idling - all lights, wiper and AC (yes the clutch consumes power).

2. Most of the power of an Amp (barring a few cases) is delivered at low frequencies, upto 90% of it. So unless you are using heavy base and a subwoofer, you may assume that the Amp is using max 30% of its rated power. My son's have blown woofer by pumping deep base at high volume after installing a new amp.

3. The voltage measured is moderated by the battery which acts as a sink. If voltage from alternator is less than the battery, no current will flow (the rectifiers prevent it). So the only method of finding whether the alternator is supplying the requisite current is to connect an old style -50 0 +50 ammeter at the battery end. Then you will see either negative reading (means the battery is supplying) or positive reading (means the alternator is charging the batter after satisfying all the current requirement).

4. Aftermarket alternators come in two garbs. One those which are designed to run at high speeds so that they can supply higher currents at lower speed and at the same time not spoilt at high speeds. Two those which run at the same speed as the OEM, but supply more current. As at 12V nominal 1 HP ~ 65A, you will loose 1 HP of power for every 65A you add to the alternator capacity.

Note :

As petrol engines have a higher RPM range compared to Diesels engines, alternators for petrol engines have better bearing to withstand higher RPM.

While choosing a high capacity alternator always go for one which has ball/roller bearings at both the ends. Most of the "cheap" ones have sleeve bearings which will give way very soon.

The best installation I have come across was the one which had an extra battery and a second alternator to cater to all the extra loads - ICE, Winch, Refrigerator etc. The controls were such that you could isolate the secondary battery and the alternator from the primary one. In case you needed extra power from the vehicle, the second alternator could also be taken out of the circuit.
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Old 12th June 2011, 22:02   #32
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Default Re: Car Battery/alternator capacity query

@Aroy,
Have you ever come across dual output alternators? I hear that such a system is available in tourist buses wherein one battery powers ignition,headlights and driver cabin lights,other one powers passenger cabin lights,ICE,DVD etc. I'd like to know whether such a setup is possible in Jeeps (Looking esp to power up a winch)

Warm Regards
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Old 12th June 2011, 22:05   #33
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Default Re: Car Battery/alternator capacity query

newbie question- the discussion about the point where the ICE peaks the power demand, isnt that the point where Farad Capacitors come in use to supply a constant level of current. to rectify the depreciation in current from the battery/alternator, in turn reducing load on the alternator/battery?
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Old 13th June 2011, 09:38   #34
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Default Re: Car Battery/alternator capacity query

Quote:
Originally Posted by Grace View Post
@Aroy,
Have you ever come across dual output alternators? I hear that such a system is available in tourist buses wherein one battery powers ignition,headlights and driver cabin lights,other one powers passenger cabin lights,ICE,DVD etc. I'd like to know whether such a setup is possible in Jeeps (Looking esp to power up a winch)

Warm Regards
I have never come across a dual output alternator. What I have read about is TWO alternators and/or TWO batteries used mainly in Expedition Vehicles. Of course Military Vehicles are different and may have what you are saying. The normal configuration for two alternators and two batteries are

1. One alternator to one battery
2. Both alternators to both batteries. The control circuits isolate the alternators and batteries.
3. One alternator to two batteries the second comes up if extra current is needed
4. One heavy duty alternator to two batteries.

Normally if there are two batteries, they are isolated to prevent both discharging and stranding the vehicle. One battery is for normal vehicle functions and the second for "auxiliary" loads - winch, refrigerator, high power ICE and any other electrical device fitted.

Here are links to some articles on the net

Vehicle Dual Battery Systems
ARB Dual Battery Systems | Products | ARB 4x4 Accessories
How do I Install a Dual Battery System in a Vehicle? | eHow.com
Dual Battery Systems
http://www.landroverweb.com/Pdf-file...arge-relay.pdf
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Old 29th March 2012, 08:15   #35
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Default Re: Car Battery/alternator capacity query

What is the alternator rating of modern cars, say a Ford Fiesta, Ikon etc.

I recollect Premier Padmini, M 800 used to have 35 A.
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Old 26th January 2013, 08:28   #36
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Default Electrical Load and ICE

Please merge this thread if its repeated.

Many of us install aftermarket HU, amplifiers (multi-channel and/monoblock), screens etc., to have a better ICE experience in our vehicles.

I have been lately thinking about the load they place on our electrical systems; for example, the DLS CA 41 which I have takes 60A and DLS CAD 15 consumes about 160A on full load. This totals to 220Amperes.

Assuming they operate at about 25% most of the time, the current consumption becomes about 55A. Our car batteries are rated between 40-60Ah.

So dont you think this places a huge load on the car batteries. Even with the car running, I feel with the alternator, the load would still be high and at times the car electricals/electronics may not get sufficient power.

Please suggest.
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Old 26th January 2013, 09:32   #37
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Default Re: Electrical Load and ICE

You may want to go through this
http://www.team-bhp.com/forum/techni...uti-800-a.html (Am I Electrically overloading My Maruti 800 ?)
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Old 28th January 2013, 13:55   #38
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Default Re: Electrical Load and ICE

Quote:
Originally Posted by nitinbose View Post
I have been lately thinking about the load they place on our electrical systems; for example, the DLS CA 41 which I have takes 60A and DLS CAD 15 consumes about 160A on full load. This totals to 220Amperes.

Assuming they operate at about 25% most of the time, the current consumption becomes about 55A. Our car batteries are rated between 40-60Ah.

So dont you think this places a huge load on the car batteries. Even with the car running, I feel with the alternator, the load would still be high and at times the car electricals/electronics may not get sufficient power.

Please suggest.
There are a few things here. Your audio amps consume 220 A at full load driving into the rated load with a constant sine wave of 1 kHz. In reality when you listen to 'normal' music - your amplifiers don't belt out full output and they don't work with a single constant sine wave. As a result they rarely consume anything more than 10-20 % of their normal consumption. Bass frequencies tend to consume more than others - as you can see from their speaker sizes and ratings.

Your car batteries are rated at 40 - 80 AH. Automobile Lead Acid batteries can supply hundreds of Amperes for a fraction of a minute. Or else they can't run starter motors. For an example, Tata Safari has an alternator rated at 135 A and has a battery of 80 AH capacity. It has a starter motor rated at 2.25 KW which means it draws about 187.5 A when it starts. The starting current can easily be 5 times or more of the normal current.

So your car electrical system is not going to be overwhelmed by your audio system within reason. Other things being equal, on a long drive when the engine is running at reasonable speed during the day time, you will have enough output from the alternator to supply your audios.

But in a city drive - crawling traffic condition, with the AC running and the headlights on - you should turn down the volume.
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Old 28th January 2013, 16:20   #39
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Default Re: Car Battery / Alternator Capacity Query

You can always replace your alternator with a more powerful one, and in some cases add a second one, but remember that alternator consumes power which in your case is the fuel. A 1KW alternator will require more than 1KW of power from the engine. So if your engine is producing 10 KW or less (a reasonable number in city driving), your alternator will be consuming 10% of it. Both the response and FE will be affected to at least this proportion.

A large alternator will behave same as an AC as far as FE and Power goes.
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Old 29th January 2013, 09:24   #40
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Default Re: Car Battery / Alternator Capacity Query

Quote:
Originally Posted by Prowler View Post
There are a few things here. Your audio amps consume 220 A at full load driving into the rated load with a constant sine wave of 1 kHz. In reality when you listen to 'normal' music - your amplifiers don't belt out full output and they don't work with a single constant sine wave. As a result they rarely consume anything more than 10-20 % of their normal consumption. Bass frequencies tend to consume more than others - as you can see from their speaker sizes and ratings.

Your car batteries are rated at 40 - 80 AH.

So your car electrical system is not going to be overwhelmed by your audio system within reason.

But in a city drive - crawling traffic condition, with the AC running and the headlights on - you should turn down the volume.
Quote:
Originally Posted by Aroy View Post
You can always replace your alternator with a more powerful one, and in some cases add a second one, but remember that alternator consumes power which in your case is the fuel.
I have been hearing several cases of cars catching fire due to accessories, hence thought of asking as such audio systems consume huge power. I am also concerned if the ECU ever gets starved of power.
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Old 29th January 2013, 12:15   #41
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Default Re: Car Battery / Alternator Capacity Query

Quote:
Originally Posted by nitinbose View Post
I have been hearing several cases of cars catching fire due to accessories, hence thought of asking as such audio systems consume huge power. I am also concerned if the ECU ever gets starved of power.
It is usually because of shoddy workmanship when they fit the accessories. Generally they take the power directly off the battery terminals for high power amps. Many don't bother to fit in-line fuse at the minimum. The wires are not routed through rubber grommet through metal bulkheads. Over a period of time the wire gets chaffed and rubs against the metal causing a short. As there is no fuse to protect the car from a fire hazard, the wire goes up in flame.

The ECU controls the power supply to accessories with OEM. It sets priority to vital circuits of the car. Your radio is not a top priority in a moment of crisis - like when your alternator gives up the ghost. BTW, ECUs generally don't hog power. Most ECU are permanently hooked to the battery. They are well shielded with metal boxes and live in a dust free chamber of their own. Most will outlive the cars in which they are fitted.
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Old 29th January 2013, 13:37   #42
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Default Re: Car Battery / Alternator Capacity Query

Quote:
Originally Posted by Prowler View Post
It is usually because of shoddy workmanship when they fit the accessories. Generally they take the power directly off the battery terminals for high power amps. Many don't bother to fit in-line fuse at the minimum. The wires are not routed through rubber grommet through metal bulkheads. Over a period of time the wire gets chaffed and rubs against the metal causing a short. As there is no fuse to protect the car from a fire hazard, the wire goes up in flame.

The ECU controls the power supply to accessories with OEM. It sets priority to vital circuits of the car. Your radio is not a top priority in a moment of crisis - like when your alternator gives up the ghost. BTW, ECUs generally don't hog power. Most ECU are permanently hooked to the battery. They are well shielded with metal boxes and live in a dust free chamber of their own. Most will outlive the cars in which they are fitted.
So its only Skoda who creates fuss then aftermarket audio accessories are installed! Wonder if there would be problems such as "return current" causing the modules to blow off!
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