Fluke 179 keeps blowing fues - Page 1
Forum section: electronics / testgear

author: Paul LGF
author_rank: Newbie
timestamp: May 19, 2024, 06:44:36 pm
content: Hi All,Hope someone can help?New here, but have read a lot of the different post on the 179 looking for answers. Very helpful information.I bought this Fluke on ebay about 3 years ago. everything apart from current/amp draw testing worked. (didn't find this out until i went to find a parasitic draw on a car a few months after buying). Both fuses were blown, so replaced them. Went to test for a draw again, with no luck. Tested fuse again, and both had blown.Have just put the smaller of the 2 fuses in, the milliamp one. Tested it with the Fluke itself and it reads 1.9 0hms. Acording to the manual this should be around <12 Ohms.Is this right or do i have a short on the boardHope to have the 10A fuse this week coming so will se what that reads when fittedAny help very much appreciated

author: Gyro
author_rank: Super Contributor
timestamp: May 19, 2024, 06:54:21 pm
content: Welcome.It's because, when you break the battery connection and re-make it (via the meter), many things draw surge currents and perform various high current consuming functions before the car shuts down to 'idle' / parasitic current.To stand a chance of measuring parasitic current, you need to work out a way of implementing a shorting wire to bypass the meter until the car has fully shut down and then cut it to take the reading. Note that any intermittent connection will cause the fuse to blow. The car could take anything up to 20 minutes or more to fully shut down. Also beware of things like bonnet switches which could affect the process while the bonnet is open.

author: Paul LGF
author_rank: Newbie
timestamp: May 19, 2024, 07:04:49 pm
content: Thank you for the quick reply Gyro,Should of said...I'm a mechanic/auto electrician, have been for over 30years now. Also for a hobby i repair pinball machines. Here in France they call them Flippers.Yes I am aware of the info but thank you again

author: Paul LGF
author_rank: Newbie
timestamp: May 19, 2024, 07:07:22 pm
content: Just thought that 1.9 Ohms was a bit to close to short for comfort

author: Fungus
author_rank: Super Contributor
timestamp: May 19, 2024, 07:22:09 pm
content: The only way to blow a fuse is to pass too many amps through it.Those fuses are expensive and designed to save your life in high power situations.People generally use current clamps for automotive work where there can be hundreds of amps and a high risk of blowing expensive fuses.Quote from: Paul LGF on May 19, 2024, 06:44:36 pmLess is better.Fuses should have as little resistance as possible to minimize the effect on the circuit.

author: Gyro
author_rank: Super Contributor
timestamp: May 19, 2024, 07:24:26 pm
content: Quote from: Paul LGF on May 19, 2024, 07:04:49 pmHaha, ok.If you are using the fuse test method shown in the manual (insert the volts probe into the current jack, with the meter set to resistance range), the meter is measuring the combination of the current sense resistor and the fuse. In an 'ideal' current meter, this value would be zero, but obviously both have resistance. No it doesn't indicate a short - the reason you are seeing 1.9R with the mA fuse in fitted in the Amps fuse position (which is what I think you meant*) is because the Amps current sense resistor is very low in value, so you are mostly just measuring the fuse resistance. The current sense resistor on the mA range is higher in value, hence the <12R indication in the manual.Nothing to worry about (aside from the cost of replacement fuses!).EDIT:*If this is not what you meant, then maybe thereisa problem.

author: Fungus
author_rank: Super Contributor
timestamp: May 19, 2024, 07:28:51 pm
content: Quote from: Gyro on May 19, 2024, 07:24:26 pmI don't see how any possible problem with the meter would blow fuses. The current range is a low impedance range by design.

author: Gyro
author_rank: Super Contributor
timestamp: May 19, 2024, 07:34:58 pm
content: I'm just working from the fuse test procedure and expected reading in the manual (assuming the OP did a fuse position swap)...Quote from: Paul LGF on May 19, 2024, 06:44:36 pm

author: Fungus
author_rank: Super Contributor
timestamp: May 19, 2024, 07:50:43 pm
content: Quote from: Gyro on May 19, 2024, 07:34:58 pm1.9isless than 12

author: Gyro
author_rank: Super Contributor
timestamp: May 19, 2024, 08:00:56 pm
content: Quote from: Fungus on May 19, 2024, 07:50:43 pmThat's helpful, did you work that out for yourself? What do you think the mA shunt resistor value is on a Fluke 179? My guess is 10R.

author: Fungus
author_rank: Super Contributor
timestamp: May 19, 2024, 08:52:00 pm
content: Quote from: Gyro on May 19, 2024, 08:00:56 pmNo need to guess, you can work it out from the spec.(nb. The spec willincludethe fuse ... which measured 1.9 Ohms)

author: bdunham7
author_rank: Super Contributor
timestamp: May 19, 2024, 09:02:52 pm
content: Quote from: Paul LGF on May 19, 2024, 07:07:22 pmI don't know where you see the "<12 ohms" in the manual, but I just tested a genuine Bussmann DMB-44/100 and it had a resistance of 0.733 ohms, which is pretty close to what I'd expect. The overall resistance of the meter in this range should be under 2 ohms AFAIK (I don't have a 179 on hand) and "being close to a short" is irrelevant--lower is better. The part of your question that has everyone puzzled is the notion that the meter is somehow at fault. There is no possible malfunction of the meter that would result in blowing that fuse inappropriately.

author: Gyro
author_rank: Super Contributor
timestamp: May 19, 2024, 09:30:27 pm
content: Page 14 of the 175/177/179 Users Manual (May 2003, Rev 3,4/23 from the Fluke site), "Test the Fuses". The procedure assumes fuse and shunt in series.(Don't ask me why it's so high)

author: bdunham7
author_rank: Super Contributor
timestamp: May 19, 2024, 09:40:21 pm
content: Quote from: Gyro on May 19, 2024, 09:30:27 pmHmm. Maybe a typo? To get the specified burden of <2mV/mA, the actual value should be less than 2 ohms and I don't see why there would be a signficant deviation measuring it that way unless they're adding in up to 10 ohm for crappy test leads. In any case, 1.9 is less than either 12 or 2.

author: Gyro
author_rank: Super Contributor
timestamp: May 19, 2024, 09:46:01 pm
content: Quote from: bdunham7 on May 19, 2024, 09:40:21 pmBeats me. 1.2R would be too low for the 2R shunt. 2R would still be too low if you include fuse and lead resistance.

author: AG6QR
author_rank: Frequent Contributor
timestamp: May 19, 2024, 10:24:23 pm
content: For what it's worth, I own a Fluke 179, and just tested the fuses using the method described in the manual. The 400mA range shows 1.8 Ohms, while the 10A range shows 0.1 Ohms. If I connect the same probe directly from the V socket to the COM socket (not going through either fuse or current sense resistor), the meter fluctuates between 0.0 and 0.1 Ohm.I also have spare fuses, the same Buss fuse part numbers as came with the meter. The 440mA fuse measures 0.8 Ohm, and the 11A fuse measures so close to the probe resistance that I can't distinguish it from shorting the probes together. I don't have a convenient four-wire Kelvin resistance setup, but it doesn't matter -- I'll just say that the resistance of that fuse is small compared to what the Fluke 179 can measure.I think that posted page from manual is correct, in that 1.8 is indeed less than 12. But I can't figure out why they placed such a high upper bound on the resistance.But as has already been pointed out, an ideal ammeter has negligible resistance. A fused ammeter must be used in a circuit such that theotheritems in the circuit will limit the current to something below the fuse rating. If it's blowing fuses, it's because you're passing too much current through it, so the fuse is doing exactly what it's designed to do, and your meter is not at fault.

author: Paul LGF
author_rank: Newbie
timestamp: May 19, 2024, 10:32:43 pm
content: Thank you for clearing this up, and thank you AG6QR for testing your 179.This has put my mind at restThank you all.

author: bdunham7
author_rank: Super Contributor
timestamp: May 19, 2024, 10:56:16 pm
content: Quote from: Gyro on May 19, 2024, 09:46:01 pmAFAIK it is a 1 ohm shunt, so that would all stack up correctly. The burden voltage includes everything other than the leads.

author: Paul LGF
author_rank: Newbie
timestamp: May 19, 2024, 11:19:01 pm
content: Its good to know that what they say in the manual might be some what off of reality, and to have all of you lot help to confirm what i was reading on my meter was about right.Also after reading on here about fake fuses. The ones that i bought were from Amazon and not as cheap as the chines copies.

author: Fungus
author_rank: Super Contributor
timestamp: May 20, 2024, 01:53:58 am
content: Quote from: Paul LGF on May 19, 2024, 11:19:01 pm"Reassuringly expensive" isn't a foolproof guide.(unless Bussman/Fluke have an Amazon store...)

author: AVGresponding
author_rank: Super Contributor
timestamp: May 20, 2024, 01:38:39 pm
content: Also bear in mind it can be problematic to get reliably accurate low-ohms measurements without a 4-wire setup.I prefer to use a shunt for measuring car battery drain currents; I have a home-made one that is good for 70 amps or so, and anything above that it's just easier to use a clamp.

author: Fungus
author_rank: Super Contributor
timestamp: May 20, 2024, 04:11:53 pm
content: A clamp is the answer and you can get a plenty-good-enough one for the price of two or three of those fancy Fluke fuses.eg. The Uni-T.

author: Paul LGF
author_rank: Newbie
timestamp: May 22, 2024, 05:40:51 pm
content: Clamps not to good when looking for a parasitic draw on the car battery, as most cars draw under 50ma. You have to be so careful not to touch the clamp and change its position while checking, and make sure there is no magnetic influence near by.

author: J-R
author_rank: Super Contributor
timestamp: May 22, 2024, 07:10:31 pm
content: In many cases you can use the mV range on the DMM and probe across the fuse.

author: AVGresponding
author_rank: Super Contributor
timestamp: May 23, 2024, 09:24:28 am
content: Quote from: J-R on May 22, 2024, 07:10:31 pmYou can, but you need an accurate measure of the resistance across the fuse and a bloody good microvolt meter or you're not getting an accurate picture of the current flow.For context, a 100A main battery fuse will have a resistance of something like 1mΩ, and 50mA through that is gonna be a volts drop of only 50uV, well down in the noise for your average handheld.My home-made shunt is 10mΩ, giving me a better chance of seeing the signal over the noise at lower currents.

author: BeBuLamar
author_rank: Super Contributor
timestamp: May 23, 2024, 10:32:26 am
content: I would use the clamp and see about how much current is flowing. There must be significantly more than 10A to blow the fuse before you can get the reading.

author: J-R
author_rank: Super Contributor
timestamp: May 23, 2024, 07:04:12 pm
content: Quote from: AVGresponding on May 23, 2024, 09:24:28 amYou don't need precise numbers for this method. The expected mV values are easy to find with an internet search. You're also be typically probing fuses under 10A, not the larger fuses.I've not found a clamp meter to be very useful on most vehicles when troubleshooting battery drain. The wires are very well wrapped/bundled in addition to being hidden. Resolution/accuracy isn't very good, especially when monitoring larger connections like the battery.

author: robert.rozee
author_rank: Frequent Contributor
timestamp: May 24, 2024, 03:03:21 pm
content: you can buy a couple ofreallybig schottky diode for just a few dollars, rated at 40A or more. connect these in parallel to a 1 ohm power resistor (also available for a few dollars) such that no matter the polarity one or other of the diodes will be forward biased. mount the whole lot on a moderate-sized heatsink with a 30A or so cheap automotive fuse in series.some big schottky diodes:https://nz.element14.com/vishay/vt4045bp-m3-4w/diode-schottky-45v-40a-to-220ac/dp/2115196?st=schottky+power+diodehttps://nz.element14.com/stmicroelectronics/stps60150ct/schottky-rect-dual-150v-to-220ab/dp/2806772?st=schottky+power+diodea big 1 ohm, 1% power resistor:https://nz.element14.com/arcol/hs25-1r-f/resistor-wirewound-1ohm-1-axial/dp/2478482?st=1%20ohm%20power%20resistorthe above assembly can then be connected in place of the earthing strap that runs from B- to the vehicle chassis. as long as you don't try cranking the engine, all will be well. if you do crank the engine, just the (cheap automotive) fuse will blow. the diodes will prevent the 1 ohm resistor ever seeing more than 1 volt across it, ie from ever dissipating more than 1 watt. and for currents less than half an amp or so, the diodes will have no effect on the measurements you will be making.now just measure the voltage dropacrossthe resistor, your meter will display 1mV per mA of parasitic current flow.cheers,rob :-)