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Amp clamp for battery drain? (Read 52,350 times)
MTech
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Amp clamp for battery drain?
Jan 19th, 2017 at 10:16am
 
I decided after recently having to diagnose a few battery drains I need an amp clamp that can measure low mA readings. With battery cable sizes getting bigger with modern EVs can anyone give me some advice on the T234 and T189? Im not looking to spend the most money possible but want something that will do an accurate job and that wont be needed to be upgraded in 12-24 months. Any help is most appreciated.
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richmunch
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Re: Amp clamp for battery drain?
Reply #1 - Jan 19th, 2017 at 3:06pm
 
I'm sure one of the Nerdz team will chime in. But the best option, in my opinion, is the 189. The 30 amp one. I use it often. For parasitic draw testing.

The first time I was nervous it wasn't accurate, so I tested it by using my old regular set up of breaking the battery connection and putting my DVOM in between to get the draw reading. I then compared it to the 30 amp clamp, set to 1 amp scale. I also created a draw by flipping open the visor vanity light and other small lights to see if it was reading properly. It does.  Smiley
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richmunch
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Re: Amp clamp for battery drain?
Reply #2 - Jan 19th, 2017 at 3:07pm
 
I forgot to add the larger jaws make it a natural choice for this type of testing.  Wink
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Tom Roberts
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Re: Amp clamp for battery drain?
Reply #3 - Jan 19th, 2017 at 4:27pm
 
Although no current probe is really well suited for parasitic draw testing the TA189 is the best we have seen.  During our tests we found this probe to be accurate to within 10ma so the 5ma spec is a bit hopeful.  Really nice probe though.

http://www.autonerdz.com/ampprobes.html
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Logic
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Re: Amp clamp for battery drain?
Reply #4 - Jan 20th, 2017 at 12:43am
 

Don't forget to press the zero button when you turn it on to prevent auto shut down
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rayray
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Re: Amp clamp for battery drain?
Reply #5 - Jan 20th, 2017 at 6:04am
 
Logic, good point and press the zero button when not connected to a wire.

Ray
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MTech
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Re: Amp clamp for battery drain?
Reply #6 - Jan 20th, 2017 at 6:11pm
 
Thanks for the great replies Nerdz!

So battery is most likely a 9v, is this capable of doing a drain test over night? (15hours).

I was aware the clamps were less accurate than a multimeter but don't like that they have no record function. Everyone that works in a shop knows that the bosses just want quick answers, at least with a recorded pattern you can 'prove' a vehicle is or isn't doing what it's supposed to!

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rayray
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Re: Amp clamp for battery drain?
Reply #7 - Jan 20th, 2017 at 7:37pm
 
I would not work with a 9v battery. Charge the battery to 12.8v then load test the battery by load testing it.
Minimum battery cranking voltage is 9.8v.

You should at least make sure the battery is good and the battery terminals are tight and clean before checking for battery drains.

I would ck the alternator voltage and amperage output.

I always do a battery negative terminal to the engine block ground voltage drop test

To test for battery drains, I usually leave the hood open, close the hood switch, remove the ignition key and lock the doors.
Move the key some distance away from the vehicle and let the vehicle sit for an hour before checking for the drain. Max battery drain is usually 50 ma

99.9% of the time, you do not have to record the battery drain overnight.

Ray
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Re: Amp clamp for battery drain?
Reply #8 - Jan 21st, 2017 at 5:23am
 
MTech wrote on Jan 20th, 2017 at 6:11pm:
Thanks for the great replies Nerdz!

So battery is most likely a 9v, is this capable of doing a drain test over night? (15hours).

I was aware the clamps were less accurate than a multimeter but don't like that they have no record function. Everyone that works in a shop knows that the bosses just want quick answers, at least with a recorded pattern you can 'prove' a vehicle is or isn't doing what it's supposed to!



Current shunt is the most accurate method for measuring current.
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rayray
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Re: Amp clamp for battery drain?
Reply #9 - Jan 21st, 2017 at 6:24am
 
If I suspected an intermittent battery drain, I left the hood open in the parking lot all day.

Then every hour or 2, I clamped my amp probe around a battery cable to measure the amp draw.

If you get Tom's TA189, I would connect one lead of a good multi meter in the 400 ma mode to a battery terminal.

Then connect the other lead of the multi meter in series with a test light connected to the other battery terminal.

Let's say the inline ammeter reads 150 ma. Connect the TA189 amp probe any where in that series circuit and the Pico scope should show near 150 ma.

Ray 

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Re: Amp clamp for battery drain?
Reply #10 - Jan 21st, 2017 at 6:36am
 
MTech wrote on Jan 20th, 2017 at 6:11pm:
So battery is most likely a 9v, is this capable of doing a drain test over night? (15hours).


Wink

rayray wrote on Jan 20th, 2017 at 7:37pm:
I would not work with a 9v battery.


Ray I took the MTech quote above as discussing the battery that is running the Amp clamp.

To answer his question as I took it, I would say if you are intending to capture this overnight drain watch then you should install a brand new battery which should last this amount of time.

Drift would have to be taken into consideration but large spikes that last periods of time is of course not drift.
Better said anything that rises over time and then falls square is a drain.


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Re: Amp clamp for battery drain?
Reply #11 - Jan 21st, 2017 at 6:47am
 
Logic wrote on Jan 21st, 2017 at 5:23am:
Current shunt is the most accurate method for measuring current.


You know when you go to a class and one person asks for a verification on a quote made by the instructor and half the class around him think to themselves they are so glad you asked, well maybe this is one of those times.

Could you go into detail on this above procedure, maybe with examples of scope findings and pictures of equiptment used?

Please and thank you  Cool
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 Mick
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Re: Amp clamp for battery drain?
Reply #12 - Jan 21st, 2017 at 6:52am
 
This is an example of using the scope to load test the battery cranking and what a battery negative terminal to the engine block voltage drop looks like while cranking.

CH A is the battery voltage and the spec for minimum battery cranking voltage is 9.8v

CH B shows the over 500 amp starter motor amp draw when the flywheel is not turning, to the average 236 amps when the flywheel is turning.

When the engine starts, you can measure the max amperage output of the alternator on most vehicles.

CH C is the cranking negative battery cable terminal to the engine engine block ground voltage drop of 284 mv.

For the ground voltage drop, the scope lead should be connected to the starter case because there may be a layer of corrosion between the starter nose to the transmission.

Ray
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Re: Amp clamp for battery drain?
Reply #13 - Jan 21st, 2017 at 7:04am
 
This one shows a good no load battery voltage of 12.8v on CH A, down to a bad, very low 4.8v cranking.

CH B shows a ground voltage drop of 200 mv

CH C shows the cranking amps and the maximum alternator output amperage of 93 amps on start

Ray
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MTech
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Re: Amp clamp for battery drain?
Reply #14 - Jan 21st, 2017 at 2:57pm
 
rayray wrote on Jan 20th, 2017 at 7:37pm:
I would not work with a 9v battery. Charge the battery to 12.8v then load test the battery by load testing it.
Minimum battery cranking voltage is 9.8v.

You should at least make sure the battery is good and the battery terminals are tight and clean before checking for battery drains.

I would ck the alternator voltage and amperage output.

I always do a battery negative terminal to the engine block ground voltage drop test

To test for battery drains, I usually leave the hood open, close the hood switch, remove the ignition key and lock the doors.
Move the key some distance away from the vehicle and let the vehicle sit for an hour before checking for the drain. Max battery drain is usually 50 ma

99.9% of the time, you do not have to record the battery drain overnight.

Ray
 

Cheers ray for this info always good to be reminded of the basics.


Yeah I meant the amp clamp sorry for not being more specific. Im new to the scope world but learning more everyday so eventually I may actually be able to say I know what I'm doing!  Smiley

Mick wrote on Jan 21st, 2017 at 6:47am:
Logic wrote on Jan 21st, 2017 at 5:23am:
Current shunt is the most accurate method for measuring current.


You know when you go to a class and one person asks for a verification on a quote made by the instructor and half the class around him think to themselves they are so glad you asked, well maybe this is one of those times.

Could you go into detail on this above procedure, maybe with examples of scope findings and pictures of equiptment used?

Please and thank you  Cool


+1 on this, Logic it would be most appreciated !
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