Fluke 117 current shunt burnt - Page 1
Forum section: electronics / testgear

author: danno_cj
author_rank: Contributor
timestamp: March 03, 2019, 09:09:54 pm
content: I got a Fluke 117 to repair. She/he has decided to improve Fluke design and changed the 11A fast fuse with a "better" one, 32A. Now the current shunt R3 is burnt and split in two parts. 32A fuse is fine. Current function fail but the others appear to be fine. Has somebody idea what value is R3?Thanks for any tipshttps://flic.kr/p/9JUe3P

author: killcode
author_rank: Contributor
timestamp: March 04, 2019, 01:19:17 am
content: You could feed a small known voltage (Id start with a few mV) across the shunt location and use that to figure out what the shunt should be based off what the meter reads.Assuming the nothing past the shunt is damaged.

author: retiredcaps
author_rank: Super Contributor
timestamp: March 04, 2019, 05:57:14 am
content: The Fluke 17B, a different meter obviously, schematic shows its current shunt as 0.01 ohm.As a guess, it is likely in the 0.01 ohm ballpark area.

author: Gyro
author_rank: Super Contributor
timestamp: March 04, 2019, 10:40:32 am
content: With the shunt gone, you ought to be able to see a reading with a voltage source in the order of mV to 100mV across the 10A terminals - if not then I would suspect other damage to the meter. It wasn't expecting to see full voltage of whatever high current source was being measured, you can protect the lower current ranges with inverse parallel diodes and the small fuse but I doubt they would be present or effective on the 10A range.If you can get some sort of reading on the 10A range, then you ought to be able to calculate the shunt value. Eg. It it displays 10A for a 100mV input then the shunt resistor would be 0.01R.

author: Fungus
author_rank: Super Contributor
timestamp: March 04, 2019, 11:17:15 am
content: Look in the manual for "burden voltage". It's basically the shunt resistance disguised by Ohm's law.Quote from: retiredcaps on March 04, 2019, 05:57:14 amYep.

author: mzacharias
author_rank: Frequent Contributor
timestamp: March 04, 2019, 12:20:16 pm
content: Are you sure it didn't burn out a foil run instead? The high-current shunt would be pretty hard to make fail in that way.

author: ModemHead
author_rank: Frequent Contributor
timestamp: March 04, 2019, 12:53:44 pm
content: Quote from: mzacharias on March 04, 2019, 12:20:16 pmYes... would love to see a picture of this failure.

author: 0xdeadbeef
author_rank: Super Contributor
timestamp: March 04, 2019, 12:59:41 pm
content: Also there's usually a bridge rectifier (and some diodes) to protect the shunt (and ADC) which vaporizes before the shunt dies.

author: danno_cj
author_rank: Contributor
timestamp: March 04, 2019, 04:31:21 pm
content: Connecting my power supply to Com and 10A I got reading. At 10mV is around 1A and at 100mV is around 10A. At 10mV (the lowest voltage of my power supply) is not stable at all but at 100mV it is stay better. It jump up and down because I think my power supply is not stable at low voltage and/or is noisy. So, the R3 value is 0.01R. No other damage appear to be on this PCB side. I don`t know what the owner has done but is safe to say that his load was under 32A.Here is the picture:

author: MarkF
author_rank: Super Contributor
timestamp: March 04, 2019, 05:12:40 pm
content: Quote from: danno_cj on March 03, 2019, 09:09:54 pmThat is not a "design improvement".That is "removing the input protection"!Hence, the burnt front end.Replace the shunt and replace the fuse with thecorrectvalue!!!

author: ModemHead
author_rank: Frequent Contributor
timestamp: March 04, 2019, 05:19:24 pm
content: Quote from: danno_cj on March 04, 2019, 04:31:21 pmHoly crap!BTW, I measured an (intact) shunt, and it is indeed 0.01Ω.

author: floobydust
author_rank: Super Contributor
timestamp: March 04, 2019, 05:45:30 pm
content: Fluke 83, 85, 87 (R6), Fluke 8810 milliohm 1W 0.1% 100ppm Fluke P/N 807305 (old) Mfgr. P/N R-3269010Fluke 78 (R11), Fluke 29/79 (R6)10 milliohm 1W 0.25% 100ppm Fluke P/N 877076Fluke 775 milliohm 0.5W 1% Fluke P/N 720415Fluke 27 (R23)5 milliohm 0.5W 0.5% Fluke P/N 655423Fluke 45, 867B, 86310 milliohm 1W 5% 100ppm 4-wire Fluke P/N 820845

author: floobydust
author_rank: Super Contributor
timestamp: March 04, 2019, 06:12:36 pm
content: Quote from: danno_cj on March 04, 2019, 04:31:21 pmIt looks like somebody connected it to a car battery, low voltage so no arcing or burns on the pcb. The test leads must have smoked too.

author: retiredcaps
author_rank: Super Contributor
timestamp: March 05, 2019, 04:10:48 am
content: The solder leg to RV1 looks like it has a solder crack.

author: Electro Detective
author_rank: Super Contributor
timestamp: March 05, 2019, 08:40:54 am
content: Luckily it wasn't oops-graded to a 100 amp T-FuseIf the 117 can be fixed, the owner hack/reverse engineer needs to seriously consider a decent cheap AC-DC clamp meterto keep the 117 company and out of harms way...and yeah, how did thebarbequedleads fare?

author: Cnoob
author_rank: Regular Contributor
timestamp: March 05, 2019, 09:57:07 am
content: If I want to measure any high current above 8 Amps or so I use an external shunt. I brought a 30 Amp one from Ebay[urlhttps://www.ebay.co.uk/itm/10A-50A-75mV-Shunt-Resistor-for-DC-Current-Meter-Amp-Analog-Panel-Ammeter/352365629434?hash=item520aa0cffa:m:mylcWBpG3S8CTHdJm5diT6Q:rk:79:pf:0]I don't like when manufactures state you can measure up to 20 Amps for X amount of seconds it encourages misuse and even at 10 Ampsthey state let the meter cool down.

author: Electro Detective
author_rank: Super Contributor
timestamp: March 05, 2019, 09:31:59 pm
content: Quote from: Cnoob on March 05, 2019, 09:57:07 amlol especially when the internal fuse is 11 or 15 amps (and EXPENSIVE)and no mention of ambient temperature vs 'X seconds' derating stuff,or lead length, wire gauge, contact/connector resistance etcor how to tell when it's cooled down enough for another shotI wonder (not) what would happen to some of the meters out there with UNFUSED 10 and 20 amp socketsIf a clamp won't do the job and I need to break into a circuit, I use fused leads (or a knockup bodge job with croc clips) with any value below the meter's internal fuse