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Discussion Starter · #1 ·
I have a problem with my battery holding charge for more than 2 days, so with my limited knowledge, have pinned it down to a tired battery (3 years old with 4 year guarantee) or a rather large current draw.

I'm charging it as I type, and hope to get the battery tested at Halfords where it was bought. In the meantime though, can anyone tell me if this multimeter is capable of measuring current draw in Amps? Which jack plug do I use and which setting?

Posted Image


I have read Imagewerx excellent guide (here), but my multimeter has different numbers on it and I'm easily confused!!

Cheers
 

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NooNoo
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Move the red lead into the left hand 4mm socket and initially use the meter with the s elector straight down (10A DC).

Depending on the reading you may then want to click the s elector one or two clicks clockwise (200mA and 20mA ranges).

DO NOT connect the red and black leads directly across the battery in this mode, the meter is unfused at 10A and you will have a meltdown.

The meter needs to be connected in series with the positive battery connection. Remove your keys from the car (have them in your pocket) and remove the + positive battery terminal. Connect the red meter lead to the battery and the black meter lead to the cars positive battery lead. Do not let the any leads touch the bodywork. Cover the battery area with a towel or rug to help stop this occuring.

If you are at all unsure about this procedure don't do it! Ask an auto electrician, a direct short across a battery is not a pretty sight.

Hope this helps.

[:)]

Edit: Do not switch on too many car electrical items, the meter is rated to 10A for 10 seconds. Otherwise you will damage the shunt resistor in the meter (a tiny value, high power resistor).
 

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Discussion Starter · #4 ·
Thanks for a rapid response (only just done the dishes!!).

I'll give that a go soon as my battery is charged already. I'll leave everything switched off when I do it like when the car is left. Only thing then is the alarm won't be on.

A friend mentioned similar problems was down to a worn alternator that was earthing from inside (or something!!). Assuming I see a large draw from doing the above, would I then have to re-connect the battery lead, then remove the alternator fuse and bridge them to see if it is the alternator?
 

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NooNoo
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Yes elimination is the key to this one, methodical removal of fuses and observe the meter. Alternator is a fusable link IIRC.

I'd leave a window down just in case during testing, I've seen cars central locking lock inadvertantly!!!

[:)]
 

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Discussion Starter · #6 ·
Ok, just done the first test as you suggested. I forgot to switch settings, but from the 10A DC setting, I had average readings of 0.55 (sometimes it jumped around from 0.2 to 0.7 when first connected, but I guess thats normal until it settles).

This seems to be on the "don't get paranoid" scale as mentioned in Imageworks guide. So, I think I will get the battery checked now before worrying about the alternator - which does charge the battery and the car runs fine and starts fine as long as she is used every day or not left for more than 1 day.

Thanks NooNoo, you're a true gent !
 

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NooNoo
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Hmmm, 0.55A (550mA) seems a little high to me. 12 hours loses you 6Ah.

You will definitely have trouble starting in this weather if left for a few days.

Perhaps worth waiting for the better weather for more thorough testing (when your hands can actually tolerate the cold).

In the meantime, use your car everyday as you said!

[:)]
 

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Discussion Starter · #8 ·
Ah ok, it needs an MOT early in the year so could have it looked at by someone who knows what they're doing at the same time. However, the good news is that I just had my battery declared 'unserviceable' and swapped for free. Who says Halfords are bad?! I can't help thinking this isn't the end though... time will tell.

...and yep, it is ruddy cold.
 
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