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Honda civic 2011 with 98k kms. My alternator just went out. I drove the car with the battery reading 12v. After turning it off the car wont start anymore. I changed my alternator, I measured the Battery immediately while the ewngine is running. 13.8 Volts, then I opened the ac headlights on then dropped to 13.1-13.4 is it normal. Note I immediately checked it after installing without waiting for the battery to be fully charged

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It's a little low under load, typically you want to see 13.5 to 14.5 volts, except maybe on newer cars with "smart" on-demand charging. Charge the battery up and recheck.

Still the same. But when reved up to 1500 rpm it reaches 13.8 volts

It sounds to me like the replacement alternator is a bit weak. I have not worked on one of those cars though, you may want to double-check on a Honda forum for what is considered "normal" for that vehicle if no one here knows for sure.


https://www.hondacivicforum.com/forum/

I have checked it again. The Volts remain at 14 Volts when all accessories including headlights and Ac are on. BUT i noticed that when the Auxilliary Fan beside the Radiator fan kicks in, it momentarily drops to 13volts then climbs back up to 14 after. Note this is at idle speed of 800 rpm

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Sounds like weak alternator but check the battery. Hook up volt meter to battery and crank car over. Watch the voltage as you crank it's possible your battery is screwed up. Also check your connections make sure everything is clean and tight as well

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Topic starter

Honda civic 2011 98k kms. I have checked my alternator at idle. The Volts remain at 14 Volts when all accessories including headlights and Ac are on. BUT i noticed that when the Auxilliary Fan beside the Radiator fan kicks in, it momentarily drops to 13volts to 13.1 Volts  then climbs back up to 14 after the fan kicks off . Note this is at idle speed of 800 rpm

What is your question please? Does the vehicle exhibit any drive-ability issues or symptoms?

Is it normal?

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Posted by: @donrub

when the Auxilliary Fan ... kicks in, it momentarily drops to 13volts

A stationary motor is basically a short circuit.

https://en.wikipedia.org/wiki/Inrush_current#Motors

 

 
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Posted by: @donrub

Is it normal?

#1 - It's normal as explained in the motor wiki article link I posted above.

#2 - Please try to keep all your related questions together in one topic. Thanks.

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Posted by: @donrub

After turning it off the car wont start anymore

Are you still having this problem?

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You normally do not check your voltage when idling. It is not really indicative, since cars, their alternators, and battery charging systems are not designed to support much load at idle. Cars are made for driving 😉

You can only tell whether or not your voltage situation is normal after you have checked your voltage in line with your specific car manufacturer´s voltage checking guidelines. Those are normally contained in the technical documentation for your car one can normally find in the Internet.

On most cars I know voltage is checked at 2000 RPM, and there are also specific conditions to be observed when doing this check (e.g. some electrical systems and devices have to be turned on, and some - off). Even temperature matters, since charging systems normally have temp compensation in them.

That the voltage drops when powerful devices (like headlamps) get turned on, is absolutely normal.

P.S. At first glance, the voltage figures you mentioned sound ok to me.

This post was modified 1 month ago by DontKnowler
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With the battery fully charged and the engine idling with all accessories off, the voltage at the battery should be very close to 14.5 volts.

When the battery is fully charged, the computer will reduce alternator output to prevent overcharging the battery. Same thing when accessories are turned off. I've mentioned this to you numerous times.

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