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Harbor Freight Battery/Alternator Tester

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CamJam View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote CamJam Quote  Post ReplyReply Direct Link To This Post Topic: Harbor Freight Battery/Alternator Tester
    Posted: Mar/02/2016 at 9:23pm
This little gizmo solves a big problem for me. 

I recently ruined a nearly-new $300 reproduction "Clear Power" battery because my alternator was overcharging.  I had tested voltage with a meter just hours before, but on a 40 mile drive something failed and ruined the battery before I knew it.  (Yes it actually WAS the alternator and not the regulator in this case.)  The AMX's alternator light apparently does not provide an overcharging indication... the first clue I got was the smell of hot battery acid, and by then it was too late.

A voltmeter is the obvious solution, but I am entering shows in the stock class and want to keep everything showroom correct. 

I happened to stumble upon this device at Harbor Freight the other day.  Plugs into the cigarette lighter. and if the red "alternator" LED lights while I'm driving, then I know I'm over-charging.  When I get to a show, I unplug it, put it in my pocket and plug the cigarette lighter back in.  Also gives a very basic indication of the battery voltage when the motor isn't running.

With a 20% coupon they'd mailed me it cost only $5.59!

http://www.harborfreight.com/12-volt-battery-alternator-tester-66842.html

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Wrambler Quote  Post ReplyReply Direct Link To This Post Posted: Mar/04/2016 at 8:49am
I got my son one that reads actual voltage on an LED panel so he could see the voltage and know he had played his stereo with sub long enough he needed to start the car.

Worked great, never killed the battery.

Even though the port on the Altima was hot all the time the LED panel drew so little voltage it could be left plugged in. In some cases over week and the voltage was still good.

I've seen a guy dive for cover when he was load testing a battery in a wagoneer years ago. He saw smoke curling out of the battery and turned to duck and bang, no more battery. We literally hosed the guy down after he pulled his wallet. Had to call his wife to bring him in a change of clothes and the uniform he wore disintegrated at the cleaners.  He was way lucky, could have been very bad. Acid really cleans a concrete floor! It was sparkling white for quite some time!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 73hornut Quote  Post ReplyReply Direct Link To This Post Posted: Mar/20/2016 at 11:00am
How does the alternator overcharge, if the regulator is still good?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote CamJam Quote  Post ReplyReply Direct Link To This Post Posted: Mar/20/2016 at 11:38am
Originally posted by 73hornut 73hornut wrote:

How does the alternator overcharge, if the regulator is still good?


I'll leave that to someone smarter than me to explain (BillD perhaps?) but I changed the regulator first and the voltage with the engine running was still close to 17V. Replacing the alternator fixed it. I suspect that the regulator doesn't actually limit the voltage, but rather controls the alternator's output, so if there is something wrong with the alternator's sensing circuit you can have an overcharging situation, same as if you had a bad regulator.

In any case, this HF device will show you if you're overcharging, no matter what the cause.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bigbad69 Quote  Post ReplyReply Direct Link To This Post Posted: Mar/21/2016 at 6:51am
Originally posted by 73hornut 73hornut wrote:

How does the alternator overcharge, if the regulator is still good?
Originally posted by CamJam CamJam wrote:

  I suspect that the regulator doesn't actually limit the voltage, but rather controls the alternator's output...
That's correct. The VR senses battery voltage and supplies the appropriate current to the alternator field terminal to control the alternator output current.

In your case, the alternator fault probably put the regulator outside of its capture range. i.e. the regulator was at its minimum and the alternator was still overcharging the battery.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote partsguy Quote  Post ReplyReply Direct Link To This Post Posted: Apr/07/2016 at 9:34pm
im lost,doesnt the vr control charging the battery? if it doesn't, there would be no need for a vr.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote CamJam Quote  Post ReplyReply Direct Link To This Post Posted: Apr/10/2016 at 1:40pm
Originally posted by partsguy partsguy wrote:

im lost,doesnt the vr control charging the battery? if it doesn't, there would be no need for a vr.


Seem like bigbad69 described it pretty well:

"The VR senses battery voltage and supplies the appropriate current to the alternator field terminal to control the alternator output current."

So rather than limiting the voltage after the fact, the VR actually adjusts the output of the alternator. I can see why an overcharging situation could be caused by a faulty regulator-- my guess is that's probably more common-- or by the alternator itself.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote onree Quote  Post ReplyReply Direct Link To This Post Posted: Jun/20/2016 at 9:32pm
I've got a couple of these, from Amazon. that show the battery voltage and also the temperatureinside the car. If you were ever curious how hot it got inside your car...

https://www.amazon.com/gp/product/B00SXZERW6/ref=pd_luc_rh_sbs_01_03_t_img_lh?ie=UTF8&psc=1
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Post Options Post Options   Thanks (0) Thanks(0)   Quote pit crew Quote  Post ReplyReply Direct Link To This Post Posted: Jun/21/2016 at 7:06am
Good catch onree. I was just going to suggest the same thing.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote purple72Gremlin Quote  Post ReplyReply Direct Link To This Post Posted: Jun/21/2016 at 3:38pm
My 74 Gremlin has an old SW voltage meter in it. The original owner put it in. It's very useful. The alternator has a bad diode. It charges, but if I have the headlights on, it can't keep up.   So I know what it's doing.
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