Question about measuring Amps on UNI-T UT61E

[clintonelston]

Hi All

Total newbie question, why am I only able to get amp readings with my Uni-T UT61E meter if I have the cable plugged into the 10A Max, and not the mAuA. Surely the load is tiny (0.005mA) or (0.022mA) with a fresh battery?

Very small setup of a 9V battery powering a 4W LED bulb?

Picture attached.

TIA/Dankie
Clinton

[retiredcaps]

While I don't have an UT61E, almost all multimeters work in the same way.

The normal "convention" is to put your black probe in the COM and leave it there.  Red goes into V/Ohms, mA/uA, A as needed.

If you want to measure mA/uA, put your red probe in the mA/uA jack.  Switch the rotary dial to either uA or mA.

[retiredcaps]

If you are doing everything right and you still don't get a reading, check the lower Amp fuse.  You could have blown it easily by leaving the red probe in the mA/uA jack and then switching the rotary dial to DC or ACV to measure voltage.

[clintonelston]

Many thanks for the advice, I think yes you're right and its a fuse, Ive removed it and tested and yes its dead. I see its a ceramic type fuse, would a glass fuse be suitable to replace?

Thanks for the advice on the leads, i had them crossed over for polarity (I didn't want to change on the breadboard)

[retiredcaps]

I see its a ceramic type fuse, would a glass fuse be suitable to replace?

Almost every multimeter says to replace the bad fuse with an identical (in every respect) good one.

If you are going to work on just low powered breadboard circuits, you could probably get away with a glass one.  Just be aware the glass one could shatter dramatically if you make a mistake later on.

If you want to see what is inside a HRC fuse, see

http://mrmodemhead.com/blog/inside-a-multimeter-fuse/

[retiredcaps]

BTW, there is a huge debate (putting it mildly) regarding the fuses in the UT61E. 

Details over at the http://www.eevblog.com/forum/.  Use search and you find that the UT61E is a much discussed topic.

[clintonelston]

Thanks I didn't realise the difference, the link you posted was a helpful visualisation of why to use the correct type fuse. I see the UT61e is a much discussed meter. Looks like it has it fans and detractors!

I like it because of the price and 22000 count and for my use its a nice meter to learn with, before maybe one day investing in a higher quality meter.

[jamesp15]

Unless I am looking at you picture wrong..  it appears you have it hooked up incorrectly. (Or am I  just way too tired and not seeing it clearly?)

When measuring Current the meter should be in series with the load.  It appears you have it hooked up in parallel? (which would be correct for any other measurement.)

[SeanB]

No, it is wired right, just the leads are reversed. If running a LED there should be some current limiting resistor there, relying on battery and other wiring to give current limiting is very bad. LED's are a current driven device, they essentially are going to need a defined current through them, as the forward voltage is variable, rather than giving a constant voltage. Also, the 4W led does need a heatsink on it for any current above 20mA, otherwise it will overheat and fail in short order.

[clintonelston]

The LED "Lamp" used was the type designed for 12V house lightning circuits, so I assumed using a 9v battery would be fine? Am i mistaken by this thinking?

[SeanB]

Unless they are the type with an integrated current limiting circuit almost all LED's need a series resistor to limit the current through them. Unfortunately you cannot tell the difference between them, so it is best to use a resistor in all cases. 1K to 2k2 works for most cases running from 5-12V.

[bitwelder]

Many thanks for the advice, I think yes you're right and its a fuse, Ive removed it and tested and yes its dead.

Now, do you have some idea in which occasion the fuse may have blown? (which means also, if you understand where you have used your meter wrongly)

[jamesp15]

No, it is wired right, just the leads are reversed. If running a LED there should be some current limiting resistor there, relying on battery and other wiring to give current limiting is very bad. LED's are a current driven device, they essentially are going to need a defined current through them, as the forward voltage is variable, rather than giving a constant voltage. Also, the 4W led does need a heatsink on it for any current above 20mA, otherwise it will overheat and fail in short order.

I should never post after working 3 18 hour days in a row