| Electronics > Beginners |
| DMM amp fuse question |
| (1/3) > >> |
| haizaar:
Good day again guys, My BM235 DMM prints "MAX 10A HBC FUSED" in a ammeter port. I'm probably missing obvious, but does it mean I can't measure more than 10 amps even on 3.3 voltage? |
| TimFox:
Yes. If you need to measure higher current in a low-voltage circuit, you need an appropriate 4-terminal “shunt” resistor that typically produces 100 mV across the voltage terminals with a specified high current through the current terminals. These are specialty items. “Ammeter shunts” used with analog panel meters usually produced 50 mV at full-scale current, for use with 1 mA meters with 50 ohm resistance. |
| Kleinstein:
The fuse limits the maximum current independent from the voltage in the circuit (unless way to high) . The fuse can blow at more than 10 A, though it may take quite some time if only a little more. Still it's not a good idea, as the proper HRC (HBC) fuses are relatively expensive (e.g. $5-$15). Anyway it is difficult to measure a high current directly with the DMM in a low voltage system, as there can be quite some drop: some 50 mV for the shunt, some 500 mV or so for the fuse, some 200 mV possible for the leads and contacts. This drop can upset a low voltage system. A separate external shunt or clamp on meter may be the better choice in such a case. The external shunt may very well get away without a fuse if the system is known to be safe without it. |
| malagas_on_fire:
As discussed in many threads, the UT210E looks like a good clamp meter for such measurements or search on ebay for "current shunt" as mentioned from Kleinstein, both of choices. |
| haizaar:
Thank you everyone for elaborate responses. It's very helpful. |
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