A Fluke 87 (1st model) eats up battery in 3 months - normal ? - Page 1
Forum section: electronics / testgear

author: roli_bark
author_rank: Regular Contributor
timestamp: June 02, 2013, 12:44:04 pm
content: Is it "normal" for a Fluke 87 (1st version) to consume a 9v fresh (with a 3 years expiration date ...) Alkaline battery after 3 month ? No heavy usage, and when not in use in the OFF position at all times.

author: Dave
author_rank: Super Contributor
timestamp: June 02, 2013, 01:25:44 pm
content: It does seem kinda fishy. I have the series 5 model and after almost two years, it's still chewing on it's first battery (I do use it pretty lightly though).Have you tried powering the multimeter from a bench power supply and measuring the current when you have the switch in the off position? Do you have the equipment necessary to measure such low currents (something like the uCurrent or a picoammeter)?

author: roli_bark
author_rank: Regular Contributor
timestamp: June 02, 2013, 01:41:26 pm
content: Thanks - I'll definitely measure current at OFF.What should be the reading at OFF - absolute 0 A, or some minute uA s ?

author: ModemHead
author_rank: Frequent Contributor
timestamp: June 02, 2013, 02:53:25 pm
content: Quote from: roli_bark on June 02, 2013, 01:41:26 pmIt should be about 9uA or thereabouts.Check the code select switch and rotor mechanism on the back of the circuit board. If the black PTF material has been damaged it can create a low-impedance path from Vbat+ to Vbat-, regardless of whether the meter is on or off.

author: Rick Law
author_rank: Super Contributor
timestamp: June 04, 2013, 03:42:01 am
content: Quote from: Dave on June 02, 2013, 01:25:44 pmActually, to chew down a battery in 3 months, it would be a lot more than picoamp.For easy math, say the battery is about 3/5 full putting it at 300mAH.Chew down in 3 months puts it at 100mAH per month.Say 33 days a month puts it at 100mAH in 33 days = 3mAH per daySay 30 hours a day puts it at 3mAH/30 = 0.1mAH per hourOf course it doesn't drain to 0mAH. Say merely draining just half (150mAH) would kill it puts it at 0.1mAH/2 = 0.05mAH per hour. It drains at 0.05mA every hour. 0.05mA is not so small. Something that even the low cost UT61E should easily measure.That is 30 hours a day (33% too high an estimate) at 33 days a month (another 10% too high an estimate) draining only half the power to kill it which likely is too high an estimate too which kind of balanced the other two. Even with that, the current is stillat least 0.05mAto kill a pretty new battery in 3 months.My 9V rechargeable starts at 200mAH. A 150mAH would almost be a fresh battery in my UT61E far from dead. So it would be a good bit higher than 0.05mA constant drain -or-perhaps the battery was not as fresh as thought.RickEDIT: adding this:Measuring uA leakage is fine, we should not need to measure picoAmp.Say the new battery is spec tohold charge for 5 years. (I know it is not constant but percent lost, but this is a range estimate)At 500mAH, it looses 100mAH a year.At say 500 days a year that is 100/500 = 1/5 mAH = 0.2mAH per day (low by 500/365 times).At say 50 hours every 2 days so 2*0.2mAH/50 = 0.4/50 = 0.8/100 = 0.008mAH per hourSo, the self discharge would be 8uAH. If it is a 10 year battery, the self discharge is still 4uA per hour. If the meter is discharging at picoAmp range, that is 1000 times smaller and is not noticeable. Only when leakage is in the uA range would it have a noticeable effect on battery life.So any thing that measures uA/0.1uA range leakage is good enough. Below that is noise.Agree?

author: Dave
author_rank: Super Contributor
timestamp: June 04, 2013, 09:06:06 am
content: Obviously it's going to draw more than picoamperes if it drains a 9V battery in 3 months. I said picoammeter, because I was thinking of low current meters like the Keithley 480 or similar.

author: saturation
author_rank: Super Contributor
timestamp: June 04, 2013, 01:18:40 pm
content: A sickness in 1st general Fluke 80s is with age, the rotary switch get dirty and does not fully power the DMM off. If you wiggle it in the off position and it turns on briefly, it needs to be cleaned. This is a very common reason for premature battery wear.

author: roli_bark
author_rank: Regular Contributor
timestamp: June 04, 2013, 01:58:33 pm
content: Wow thanks, that helped !