Adding fuse to cheap Chinese multimeter: DT830X - Page 1
Forum section: electronics / testgear

author: beavernuggetz
author_rank: Newbie
timestamp: May 11, 2023, 10:48:20 pm
content: Hello everyone,Let me start by saying I'm a long time lurker and joined today because I have a specific question.I've seen some videos where folks add a fuse to the DT830 series multimeters which have the pads for the physical fuse but don't come with one pre-installed.Here is one such video:In each one, they cut a trace which connects (continuity) the pads for the fuse but on mine I cannot see such trace.So my questions are:Can anyone see where I would cut to do the same?Does it matter if the pads are continuous?If I do this, will it provide better protection?I'm not a complete n00b and own other meters such as Fluke 25, 87 III, etc. and simply bought this cheapo as a backup and novelty item.Any constructive feedback will he greatly appreciated.Thanks!

author: tunk
author_rank: Super Contributor
timestamp: May 11, 2023, 11:37:05 pm
content: Look for the current shunts, the copper wire is for the 10Arange, and R13 and R15 could be for the lower ranges.Edit: The two large unpopulated pads near R15 could befor a fuse. Trace them to the other side and see if there'sa zero ohm "resistor" somewhere.

author: beavernuggetz
author_rank: Newbie
timestamp: May 12, 2023, 12:40:08 am
content: Yes, the 2 unpopulated pads are indeed intended for a fuse. Not sure if I can solder the fuse directly to those pads or if additional tweaking is needed such as in the video.

author: Fungus
author_rank: Super Contributor
timestamp: May 12, 2023, 06:27:56 am
content: These holes are called "vias" and they're places where traces go to the other side of the PCB.Look on the back of the PCB, I bet you'll find a cuttable trace between these vias.

author: Fungus
author_rank: Super Contributor
timestamp: May 12, 2023, 06:34:00 am
content: Quote from: beavernuggetz on May 11, 2023, 10:48:20 pmNot really.Fuses are only connected in the Amps range, they don't make any difference when you're measuring volts/ohms, and you shouldn't really be using this meter on anything where you need more "protection".

author: Kleinstein
author_rank: Super Contributor
timestamp: May 12, 2023, 12:59:20 pm
content: Without a fuse the current ranges are a possible liability and likely the least protected / safe part. Even just some 5 V could burn a shunt resistor possibly doing additional smoke damage.In case mains is connected even a cheap 20x5 mm fuse is usually better than a 0805 size SMD resistor in breaking the current path.To also protect the shunt resistors (at least the 9 ohm) one would need additional clamping diodes, that as not visible in the PCB pictures. It can be anoying to damage to current ranges and not knowing that it is broken.The voltage ranges are usually still a little bit protected and should be OK to usually survive mains votlage, though maybe not the transisents needed for a proper class 2 rating.

author: beavernuggetz
author_rank: Newbie
timestamp: May 12, 2023, 01:42:52 pm
content: Thank you all for the intuitive replies.Here is a picture of the underside of the PCB; there is no SMD resistor there.The pads are marked in red as well as the trace that apparently joins them according to continuity tests.Can I safely cut it to add the fuse on the top side? Don't want to negatively affect the rotary switch functions by doing so.

author: tunk
author_rank: Super Contributor
timestamp: May 12, 2023, 01:51:15 pm
content: Try to cut the small (almost horisontal) trace above your red line.Solder in a fuse holder and see if it works.

author: beavernuggetz
author_rank: Newbie
timestamp: May 12, 2023, 02:17:52 pm
content: Just realized that the small track you mentioned is what joins these.Will cut it and solder the fuse; will report back.Thank you very much to every one of you who have been very helpful and kind.

author: NoisyBoy
author_rank: Frequent Contributor
timestamp: May 12, 2023, 07:04:46 pm
content: I agree with Fungus. As you have a couple other Fluke to use and you are only using this meter as a novelty and backup, I hope you won't use it for high voltage and relying on this fuse to give you the protection.I have the fuse in my free Harbor Freight meters, but I only use it on my car and tractors when things are dirty and greasy, and perhaps for checking batteries. As there is really nothing novel or interesting about the DT830 other than it is free in my case.

author: BillyO
author_rank: Super Contributor
timestamp: May 12, 2023, 10:21:24 pm
content: This is a perfect example of the old phrase "polishing a turd". Great fun. I do it all the time.

author: coromonadalix
author_rank: Super Contributor
timestamp: May 13, 2023, 12:18:43 am
content: man toss it in a trash bin and find yourself a better meter, what a way to do dangerous things ......... plain stupidthats no excuses ... and you say im not a complete noob sorry contradictory ?sorry may sound rude but ... wow loll my fuse as blown loll

author: Fungus
author_rank: Super Contributor
timestamp: May 13, 2023, 12:22:32 am
content: Quote from: coromonadalix on May 13, 2023, 12:18:43 amHow is measuring the current of a USB powered LED strip dangerous?Quote from: coromonadalix on May 13, 2023, 12:18:43 amNo, itisrude.

author: NoisyBoy
author_rank: Frequent Contributor
timestamp: May 13, 2023, 05:43:22 am
content: Looking at the input sockets, I don’t know what is on the bottom half of the case to keep it in place. I tend to think each insertion and removal would stress the single solder point. If it ever comes loose, it won’t have far to rotate to short circuit the probes.I would leave the probe in permanently. It is amazing how they manage to further decontent the design. I would only use this meter for low voltage and low current circuits when all my others DMMs are unavailable.

author: BradC
author_rank: Super Contributor
timestamp: May 13, 2023, 06:46:06 am
content: Quote from: BillyO on May 12, 2023, 10:21:24 pmYou can't polish a turd, but you can roll it in glitter.

author: Fungus
author_rank: Super Contributor
timestamp: May 13, 2023, 08:09:02 am
content: Quote from: NoisyBoy on May 13, 2023, 05:43:22 amYeah, those are really crappy connectors.(also zero strain relief on the battery cables - I garantee they'll break off if you open the meter up a few more times to play with it...)Compare with the $4 "Big Clive" version:

author: Fungus
author_rank: Super Contributor
timestamp: May 13, 2023, 08:19:40 am
content: Gotta hand it to them though, they managed to make the PCB smaller than the diameter of the selector switch - the dial sticks out on both sides: