I use an automatic charger to charge my lead acid battery. After the battery is fully charged, it shifts to maintain mode where the charging current reduces to as low as 13 mA. I noticed that even after I unplugged the charger, while still connected to the battery, the charging current didn't fall to zero but stayed at 13 mA.

  1. Is this normal?
  2. If eventually there is still a “non-zero reading“ for the current, would it cause a spark when I'm removing the charger clips?
  3. If such spark happens to occur, would it favor a bigger problem as exploding the battery due to ignition of hydrogen generated if the battery has been overcharged?

The battery is 12 V and is being charged by a Motomaster charger on its automatic 2 A setting. Current before turning it on is 0.001 A.

This is a photo of the charging setup:

Before Charging - check DMM for Voltage and Clamp-DMM for Current: Current 0.001A

After charging, with same measuring setup as previous photo: Current 0.013A

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    \$\begingroup\$ well need a schematic (we'll close it without a schematic, no use discussing). Where do you measure that current? How are you measuring that current? \$\endgroup\$ – Marcus Müller Apr 24 at 21:03
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    \$\begingroup\$ 13 mA is most likely the offset in your meter. \$\endgroup\$ – winny Apr 24 at 21:11
  • \$\begingroup\$ If you are measuring at the input of the charger and its a kinda shitty one, this might be the chargers quiescent current. \$\endgroup\$ – user158029 Apr 24 at 22:18
  • \$\begingroup\$ Current measured by a clamp meter at 2A DC setting, shows 0.013A in the picture. \$\endgroup\$ – Harshvir Singh Apr 27 at 14:31
  • \$\begingroup\$ Assuming you've zero'd the DC clamp on, it may be supplying a small current. 13mA is okay. See the manual: Maintain Mode: When the FULL CHARGE (green) LED is lit, the charger has started maintain mode. In this mode, the charger keeps the battery fully charged by delivering a small current, when necessary. If the battery voltage drops below a preset level, the charger will go back into charge mode until the battery voltage returns to the full charge level, at which point the charger will return to maintain mode. The voltage is maintained at a level determined by the battery type selected. \$\endgroup\$ – Spehro Pefhany Aug 31 at 15:46

It is offset and/or noise if it reads when your meter's jaws are closed and not around any wires.

I can't zero my meters lower than 13mA RMS either. Mine is a different type of probe but cannot be zeroed below 13mA RMS at the 10A range. At 100A range it cannot be zeroed below 130mA RMS.

I can zero it so the average is zero, but not the RMS, due to noise (RMS counts anything that strays from zero, whether positive or negative with no cancellation). If you hook it to a scope you can see how much is offset and how much is noise. You can center the middle of the fuzzy line right on the zero of the x-axis and average will read zero but RMS will not due to the fuzziness of the noise.

If it reads only when your meter is clamped around the wire then it is real (or there is a stray magnetic field local to that area so at least the magnetic field is real).

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This is most likely a measurement (offset) error by the meter and no real current is flowing. Especially when using a clamp current meter like showed in your picture.

Do not expect any large sparks or dangers when disconnecting the charger.

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