Using multimeter on car battery


If the red port is a low amp (200 mA) but it has a 10 a port why does it cause damage to the multimeter to use the 10 A port?

In: Technology

Your question doesn’t make sense to me. Can you try rephrasing if?

A multimeter needs at least two different red ports. One to measure voltage as it does not allow any current to go from the red port to the black port and one to measure the current as this port have a direct short to the black port. The reason you need a direct short is to allow the current to go through the multimeter to measure how much power something uses. For example a fuse have current going through it. You can replace the fuse with the two leads of the multimeter and set this in amps mode to measure how much current goes thorugh that circuit. You can also measure how much power draw your car have when not in use by disconnecting one of the battery leads and connect the multimeter between the unconnected battery terminal and the unconnected battery lead so all the current goes through the multimeter. But I guess what you are worried about here is what happens if you connect the multimeter directly to the two ports of the battery when using one of the amperage ports of your multimeter. With this port you are allowing the current to pass through your multimeter so you can measure it. But without any other restrictions like light bulbs, electronics and motors all the current from the battery will pass through the multimeter to the other connector of the battery as fast as it can. That is too much power for your multimeter to handle. Instead what I suggest you do is to connect the wire to the voltage port and set your multimeter to measure voltage. This blocks the current from going through your multimeter so you can measure the voltage instead of the amperage.

In some multimeters the voltage port and one of the ameperage ports are shared and it will have an internal switch depending on your settings. This is a sleaker design as there is one less port and you do not have to move your probe to the other port as often but it is often considered a bad design because you may accedintally switch your multimeter over to amperage mode while measuring voltage which will create a short circuit and blow your multimeter. If you are lucky you have only blown the internal fuse of the multimeter and you can replace this.

The 10A means it can measure amperage *up to* 10A. But the meter will allow more than 10A to flow through it: so, hooking it up straight to the battery allows the battery to send *all* of it’s amperage through the meter. Hopefully this just blows the fuse, but the meter might also melt/burn before the fuse can blow.

This doesn’t happen in voltage mode because then the meter allows only a tiny trickle of amperage to flow through it.

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