headlight current source. battery or alternator ?

Hi,
I recently replaced my headlight bults with a halogen 100/130 Watts bulbs. This means that my total headlight bulb watt load would be 200Watts or 260Watts at high beam.

I have connected these new bulbs to 2 bran new Relay contacts with separate thick high current wirings via extra external fuses. This is to ensure that I dont overheat or burn the original car wiring and also extra fuse for protection.

I have connected one of the contacts of relay to the +ve terminal of battery and other contact to the right side bulbs. The same wiring repeated for the other relay to left side bulb.

My question, when the engine is running at full speed, who would be providing current to the bulbs , is it the battery or the alternator ?


I have a Honda City 1.3 liter India version car. I assume ( i dont know how to find it out) that my alternator capacity is 60 Amps. At 260Watts, my bulbs would need just over 20 Amps. Since I dont have any other load ( A/C off, no audio system), the 20 Amps should be ok for the alternator.....

But with my connections, will the alternator be able to provide current to my bulbs ? I have this doubt because I have connected my bulbs to the +ve terminal of battery.
I feel that the alternator will provide just enough charging current to the battery and may not be able to sense that there is extra bulb load... I dont know how much maximum current the regulator of the alternator would provide to the battery for charging.. I would guess it would not be 20Amps ( as the battery itself is a 40Ah capacity)....

So if I am not getting 20Amps from my alternator, this means my battery is being drained at a higher rate than the current supplied to charge the battery and eventually my battery would be discharged... correct ???

If the above is true, what connection changes do I have to do ? Is there a way I connect my bulbs directly to the alternator at the bridge rectified output point ( i.e before the charging regulator circuit) ???

My headbulbs light up when the engine is off or on.... so this verifies that there are no obvious connection problems... but I have realised that the headlights are a bit dimm on highway driving.... they are not too dim but somehow I dont get a feel of a 130Watts high beam.... the light output does not give a enough visibilty feel...



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Stop worrying. Since all alternators are equipped with a voltage regulator, they will provide the proper voltage to charge or maintain a battery as long as the alternator's current output capabilities are not exceeded.

At low RPM, the current capability of an alternator declines, much less than 60 amps. However, I would suspect 20 amps plus whatever's used to run the computer, radio, radiator fan, and fuel injection pump is probably just within the alternator's capability at idle. Maybe close to break-even. A clip-on DC ammeter can determine if it's charging or discharging. Actually a voltmeter on the batt will also tell you. If your batt starts fully charged and is over 13.8V or so that's probably charging the batt.

Oznog
Thanks for reply.

However, I need more help. Isn't the voltage regulator/battery charger unit designed to just send enough charging current to the battery ?

Or is it that the entire load of the car is connected after the voltage regulator/charger circuitry ?

The reason I am in doubts becuase typically a battery charger is designed such that it provides just the amount of the charging current as per the battery capacity and then the trickle charge current.

If the same applies to the regulator/charger circuit then most of this current would be diverted to the bulb...atleast partially...

This , as a result , even if does not hamper the battery charge, will definitely not have enough current given to the bulbs and due to inherent bulb nature, even if the current supplied is 25% less than rated, it has increased adverse effect on the light out ..

Your alternator will put out 13.5 -14.5 volts (for a 12 volt system) and whatever current it needs to ( up to its rated output) to keep up with the load ( battery and whatever else is drawing current) lights ect.

sam

Sam
Thanks for the reply.

Assume I connect a totally discharged battery to this alternator, will it pump current to its fullest capacity i.e 60Amps into the battery ?

I would be surprised...wont this kill the battery.... With all modern day cars equipped with computers and advanced sensors, I think there would be a charger circuit that would sense the battery voltage or whatever and limit the current to the battery rated charging current. I think its a common practice to have 1/10th or 1/5th the Amp-Hour rating of the battery as charging current.

hi,
As sam2 said in his last post.
The vehicle regulator will control the current from the alternator to ensure that it stays with the design limits of the alternator.

A fully discharged 12v lead acid battery should be around 10.8volts.
The 1/10, 1/5 rates you refer to are usually for 'off car' battery chargers.

You should have a fuse in the +V terminal of the battery to the lead connected to your headlights. The way you have described it, suggests there is no fuse???

Any connection to the lights should be made from the fuse box.

What was the rating of the 'old' headlight lamps.

Yes, I do have a fuse put in for each of the relay.

My earlier bulbs were 60 watts/70 watts rating.

So, if I understand this well,
If my bulbs need 20A and my needs lets say 3Amp charging current, at highway driving, the alternator will send out 23 Amps. right ???

The reason I am in doubts becuase typically a battery charger is designed such that it provides just the amount of the charging current as per the battery capacity and then the trickle charge current.

Click to expand...

No it doesn't. The battery automaticall takes as much as it needs which is somewhere between quite a lot for a discharged battery and not much at all once it is charged. Thats the beauty of lead-acid car batteries - they don't need sophisticated charging techniques and can handle massive currents.

The battery is in effect connected in parallel with the alternator and the load so will be continuously charging and discharging to comensate for when the engine is idling. So when you are driving normally, the alternator is easily able to provide all the current for your lights and charge the battery as well.

At the traffic lights the alternator probably cannot supply all the cuurent so the battery makes up the difference. When you get moving again the alternator replaces what was taken from the battery.

Your high current lights are overloading your little alternator. When the alternator fails soon then replace it and the battery with more powerful ones.