With A/C on and fans at maximum and engine on it drains the battery
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Joined: Mar 2016
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From: Bologna
With A/C on and fans at maximum and engine on it drains the battery
I have a problem
I restored the A/C system of my FC. Tested the system and it works well.
But it emerged another problem. With A/C on, fans at Maximum speed and car at idle if i left the car turned on it drains the battery in 35/40minutes (Can't start the car anymore).
I thnk the current that alternator send to the battery it s lower than the current adsorbed by the system.
I tested the alternator and it gives out more than 14volts.
I think that this problem is even more clear with car idling, because at normal cruising speed it seems the draining is slower. That always with fans at maximum speed, A/C on and stereo also on.
What can it be the problem?
Weak battery or weak alternator?
Can it just be the battery to be damaged (cell in short) so it doesn't keep the load? It's AGM battery.
Thank you very much.
I restored the A/C system of my FC. Tested the system and it works well.
But it emerged another problem. With A/C on, fans at Maximum speed and car at idle if i left the car turned on it drains the battery in 35/40minutes (Can't start the car anymore).
I thnk the current that alternator send to the battery it s lower than the current adsorbed by the system.
I tested the alternator and it gives out more than 14volts.
I think that this problem is even more clear with car idling, because at normal cruising speed it seems the draining is slower. That always with fans at maximum speed, A/C on and stereo also on.
What can it be the problem?
Weak battery or weak alternator?
Can it just be the battery to be damaged (cell in short) so it doesn't keep the load? It's AGM battery.
Thank you very much.
Last edited by Venturer; Jun 25, 2018 at 04:35 AM.
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Joined: Mar 2016
Posts: 184
Likes: 17
From: Bologna
Another detail: i noticed that sometimes even with a full charged battery the car fails to start if the battery clamps are not so heavily tightened.
Can my problem be caused by dirt and oxidated contacts? I'm not really an expert of this stuff but i noticed that the battery poles are covered like a dark grey coating.
Can it be just a weak contact that prevent the alternator to full charging the battery?
Can my problem be caused by dirt and oxidated contacts? I'm not really an expert of this stuff but i noticed that the battery poles are covered like a dark grey coating.
Can it be just a weak contact that prevent the alternator to full charging the battery?
Joined: Jun 2006
Posts: 4,815
Likes: 24
From: Columbia, Tennessee
It is common for a charging system to fall below battery voltage of 12.6 volts with high load and low idle speed for an extended period of time. At that time the alternator is flying solo as the battery is simply a storage device. The alternator will actually start to pull reserve power from the battery itself when below 12.6 volts and eventually cause a full drain. The alternator actually powers the vehicle while running and helps maintain proper and consistent power.
At idle with with heavy load what is Voltage at the battery? Turn ac on high, fans, radio, headlights, flashers, wipers,defrost etc on.
Cooling fans pull close to 20 amps give or take. Consider that the FC charging system is good at 80-90 amps and you add another 20 amps to the equation... it will effect how the car performs.
If it was me, I would slow charge the battery a couple times and take it along with the alternator to a shop that can load test them and give you a CCA # for the battery and amp output from the alternator.
At idle with with heavy load what is Voltage at the battery? Turn ac on high, fans, radio, headlights, flashers, wipers,defrost etc on.
Cooling fans pull close to 20 amps give or take. Consider that the FC charging system is good at 80-90 amps and you add another 20 amps to the equation... it will effect how the car performs.
If it was me, I would slow charge the battery a couple times and take it along with the alternator to a shop that can load test them and give you a CCA # for the battery and amp output from the alternator.
Last edited by NCross; Jun 25, 2018 at 04:31 PM.
Our cars have weak alternators. S4 is 70A, S5 is 80A and they are BARELY capable of handling a stock car in perfect order. What I noticed early on (2007-08) with my FC is that a common aftermarket radio from Walmart would overstress the alternator. The car received a FD Alternator (100A) and all was well untill I wanted to switch to a Taurus Fan. So I upgraded the alternator again to one from a 92-95 Ford Taurus (3.8L engine), putting out 130A.
Simply put, a Taurus Alternator puts out 130 amps on a bad day and somewhere over 150 amps with the regulator failing. But with any upgrade, 4awg cables at minimum are necessary. Also, I strongly suggest Marine Battery Terminals. Aaron Cake taught me this trick and I swear by it because it makes connections nearly foolproof. It was one of the first modifications to my daily driver and it made life much easier thanks to not needing tools to remove the battery.
Simply put, a Taurus Alternator puts out 130 amps on a bad day and somewhere over 150 amps with the regulator failing. But with any upgrade, 4awg cables at minimum are necessary. Also, I strongly suggest Marine Battery Terminals. Aaron Cake taught me this trick and I swear by it because it makes connections nearly foolproof. It was one of the first modifications to my daily driver and it made life much easier thanks to not needing tools to remove the battery.
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