Recommend me a good automotive DVM multimeter that will measure up to 30 amps - Page 1
Forum section: electronics / beginners

author: Chris Wilson
author_rank: Super Contributor
timestamp: January 11, 2012, 05:30:22 pm
content: Looking for a good quality hand held DVM multimeter for mainly automotive diagnostics that will allow current measurements of up to 30 amps without add ons. Does such a thing exist? A lot of automotive circuits are over 16 amps, and I just blew two fuses in my cheap meter when I guessed a circuit was sub 15 amps and it wasn't. Two new replacement Bussman fast blow 600V fuses here in the UK come to as much as the meter is worthThanks!

author: IanB
author_rank: Super Contributor
timestamp: January 11, 2012, 06:17:05 pm
content: I doubt you'll find one, but you could rig something up with one of these:http://www.allelectronics.com/make-a-store/item/SNT-50/50-AMP-SHUNT-50MV-50A/1.htmlObviously taking care to provide proper insulation and guard against short circuits. Putting it inside a plastic box a bit like the uCurrent would be a good plan. Accidental shorts under a car hood are not pretty.

author: BravoV
author_rank: Super Contributor
timestamp: January 11, 2012, 06:33:11 pm
content: Agilent U1213A Handheld Clamp Meter, capable of measuring AC andDC currentup to 1000 Amps->http://www.home.agilent.com/agilent/product.jspx?id=1769939&pageMode=OV&pid=1769939&lc=eng&ct=PRODUCT&cc=ID&pselect=SR.PM-Search%20Results.Overview

author: Chris Wilson
author_rank: Super Contributor
timestamp: January 11, 2012, 07:33:44 pm
content: I have a current clamp for up to 60 amperes, but they are of limited use when access is limited, although I do use them on a fuse adaptor with a wire loop to clamp around when checking all the circuits on a given fuse. The shunt looks better if multimeters stop at around a 10 ampere limit. I'll have a look on some of the UK electrical parts web sites for something similar. Thanks for the ideas guys.

author: Unknown
author_rank: Unknown
timestamp: January 12, 2012, 07:05:21 am
content: You could thread a piece of test lead wire with two probes through the current clamp if breaking the circuit is not an issue. Typically clamps are used for these kinds of currents. There are some smaller clamps. If you break the circuit, either with a shunt or a loop of wire, don't forget about fusing. Connecting a short across the battery terminals could result in some serious fireworks. You'll need to use a heavier wire gauge, typical test leads are not designed for 30A.

author: Psi
author_rank: Super Contributor
timestamp: January 12, 2012, 07:33:10 am
content: Could put an external resistor in parallel with the dmm when needed.If its the same value as the DMM internal shunt it will half the current reading.So a 20A meter will say 20A when 40A is flowing, since half the current will bypass the meter.It's not ideal as you have to half the reading and i'm not sure what it will do for safety but it should work if you occasionally need to measure 30A.

author: Unknown
author_rank: Unknown
timestamp: January 12, 2012, 10:27:39 am
content: This will introduce extra uncertainty due to differences in heating and tempco of the internal and external shunt resistors. It will also require a fairly constant contact resistance. Something that does not matter for normal current measurements (since the voltage is only measured across the shunt resistor), but will change the ratio of currents between the two parallel 'resistors'. It would need a separate fuse. Especially since it will get the full current if the fuse in the meter blows.