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I have an old Nimex NI2100 multimeter that is working fine with 9V batteries.

Btw i'd like to power it with 6x AA batteries instead so i've bought a battery holder and wired like this: enter image description here

I've checked with another multimeter the voltage beetween the +BAT and -BAT pins on the PCB is 8.4v. However it does not turn on!

Is it possible it has some kind of protection for using with different kind of power sources?

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    \$\begingroup\$ When you use a 9v battery snap to feed another, the polarity is reversed. The internal construction of an alkaline 9v battery is 6 small cells, so apart from dodgy designs that rely on source impedance there would be no difference but longer run time. In addition to fixing the polarity issue make sure you do not have a loose connection somewhere. Also keep in mind that exposing the internals violates any safety measures for use above low voltage applications. \$\endgroup\$
    – Chris Stratton
    Mar 29, 2019 at 15:37
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    \$\begingroup\$ You should reverse the wires in the screw terminals so you get the + applied to the correct terminal on the meter connector... Then make sure you don't use it to power something else... ALWAYS check polarity before final connection... \$\endgroup\$
    – Solar Mike
    Mar 29, 2019 at 15:48
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    \$\begingroup\$ Chris is correct. DMM Socket(F) connection expects V+ and and you are using this adapter in reverse of normal use. with Bat ext on screw terminal end. \$\endgroup\$
    – Tony Stewart EE75
    Mar 29, 2019 at 15:49
  • \$\begingroup\$ A 9V battery is in fact a battery pack built of 6 standard 1.5V cells. \$\endgroup\$
    – JRE
    Mar 29, 2019 at 16:02
  • \$\begingroup\$ @JRE so how do you get 6 AA celks into a PP3 battery? \$\endgroup\$
    – Solar Mike
    Mar 29, 2019 at 16:50

3 Answers 3

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The AA cells will power the meter if your polarity is correct.

schematic

simulate this circuit – Schematic created using CircuitLab

Figure 1. Standard 9 V battery and clip arrangement.

You are using a clip as a battery so the terminals are reversed and you must reverse the wires so that the terminals are the correct polarity.

enter image description here

Figure 2. A close-up of your clip by the guys in the forensics lab indicates that you forgot to reverse the polarity.

Quick check. Disconnect from the meter and measure the voltage on the clip. The bump terminal should be positive.

Why this is a bad idea

The meter is designed so that the user is fully isolated from all conductive parts. Sockets are recessed, battery is totally enclosed and the case is, most definitely non-conductive. By using an external battery you risk electric shock should the meter leads come in contact with mains voltage.

Buy the correct battery. They last for months or years of normal use.

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  • \$\begingroup\$ I've tried reversing the polarity as suggested and indeed it worked! Btw I've found a way to close the case and fix the battery holder in a safe position on the back. Besides, i will be using this multimeter only with low DC voltages... (<=5V) \$\endgroup\$
    – eadmaster
    Mar 30, 2019 at 16:35
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As others have said, you've undoubtedly got the polarity wrong (hopefully not fatally, but it's possible), but also note that you have a bit of a dangerous setup there. The batteries are tied to the unknown voltage being measured so the battery is normally contained completely within an insulated box. For example, a cheap B&K meter I have in front of me carries this warning:

WARNING: To avoid electrical shock remove test leads before opening case.

Your case, as shown, is effectively open all the time. As well as shock, you could damage something electrically if the battery connections shorted to something.

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8.4V should be enough since a typical 9V alkaline battery runs closer to 8V in use.

enter image description here

From: LINK

Make sure you have the polarity correct.

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    \$\begingroup\$ Come to think of it though, while 8.4v should work, it suggests cells that are not new, or perhaps one that is quite weak. Either that, or a flaw causing excessive load. \$\endgroup\$
    – Chris Stratton
    Mar 29, 2019 at 15:52
  • \$\begingroup\$ the cells are not new \$\endgroup\$
    – eadmaster
    Mar 30, 2019 at 16:28

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