Author Topic: Fluke 85-3  (Read 26951 times)

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Offline Spawn

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Re: Fluke 85-3
« Reply #50 on: January 15, 2013, 04:19:37 am »
Hi there Laplace, if I am reading this part correct:

...my problems are exactly as stated 8xxuA powered on and approx 8uA constant drain when powered off

You are telling us that your Fluke 85 (the original one) drains 8uA when it is turned off? If so, I don’t want to rain in your parade but that’s normal consumption of the meter when it is turned off, 8uA is not that much to be honest, I would not worry about that.

I got 4 original 85’s here and just cracked one open for you and measure the current in OFF and it was 9uA so it is even more than yours ;)
« Last Edit: January 15, 2013, 04:31:53 am by Spawn »
 

Offline Laplace

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Re: Fluke 85-3
« Reply #51 on: January 15, 2013, 05:48:36 am »
Hi there Laplace, if I am reading this part correct:

...my problems are exactly as stated 8xxuA powered on and approx 8uA constant drain when powered off

You are telling us that your Fluke 85 (the original one) drains 8uA when it is turned off? If so, I don’t want to rain in your parade but that’s normal consumption of the meter when it is turned off, 8uA is not that much to be honest, I would not worry about that.

I got 4 original 85’s here and just cracked one open for you and measure the current in OFF and it was 9uA so it is even more than yours ;)

Cheers Spawn,

Many thanks for the reply, testing and the confirmation that you also see the same numbers or there abouts give or take a uA!

Just a bit of background I used both these 85's as a bench engineer in the early to mid 90's when the company decided to relocate they sold off alot of the workshop equipment to the engineers. I mainly used another DMM from memory I can't quite remember the model. So these 2 meters weren't used daily but for sure weekly or bi-monthly. I would say I replaced the batteries perhaps once every 3-6 months as an estimate.

After I dug these out and not wanting to spend money I don't have on a nice new Fluke, I decided to use them replacing the batteries with fresh ones.

The problem I have is this, if I leave the battery connected and the meters OFF and not use them for lets say for a few days, the batteries are completely drained when I come to use them this is a real pain as you know the original 85 has no battery cover (as I expect fluke did not expect the battery to replaced frequently) unlike the later 85's. And has 3 screws to remove the back cover not to mention if they sit in the rubber holsters you have to remove that then the screws then wrestle the back cover off and replace the battery.

Given the 8-9uA drain it would take some time to drain a 200mAh battery.

I could just retro fit a switch to solve the problem but the problem has only occurred in the past 5 years or so?

How long do your batteries last? And do you see this kind of problem?

Many thanks once again for the reply and testing much appreciated.
« Last Edit: January 15, 2013, 06:07:26 am by Laplace »
 

Offline Spawn

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Re: Fluke 85-3
« Reply #52 on: January 15, 2013, 06:32:16 am »
Given the 8-9uA drain how long given the maths will it take to drain a 200mAh 9v battery?

How long do your batteries last? And do you see this kind of problem?

No problem at all Laplace :)

I think I replace my batteries around 2 years or close to that.

If we have to calculate for a 200mAh battery, there are several calculation methods like taking 75% average of it because battery being dead after discharge to certain point, some use even more or less.

9uA = 0.009mA so if the battery capacity is 200mAh/0.009mA = 22222 hours * 75% = 16666 / 24h = 694 days = 1 year and 329 days.

Well when I wrote two years above I didn’t do the calculation yet and it seems pretty close :D

I am sure someone else will calculate it differently but this is how I do.
 

Offline retiredcaps

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Re: Fluke 85-3
« Reply #53 on: January 15, 2013, 06:43:05 am »
And do you see this kind of problem?
I haven't seen this personally myself, but someone over at badcaps.net has the same problem with the battery draining in an original 87.  See

http://www.badcaps.net/forum/showthread.php?t=18947

He hasn't reported back unfortunately to see if any of our suggestions, particularly cleaning the range switch, has worked or not.

ModemHead's blog on fixing a Fluke 83 might also give you some insight?

http://mrmodemhead.com/blog/fluke-83-dmm-repair/
 

Offline Laplace

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Re: Fluke 85-3
« Reply #54 on: January 15, 2013, 06:49:29 am »
Given the 8-9uA drain how long given the maths will it take to drain a 200mAh 9v battery?

How long do your batteries last? And do you see this kind of problem?

No problem at all Laplace :)

I think I replace my batteries around 2 years or close to that.

If we have to calculate for a 200mAh battery, there are several calculation methods like taking 75% average of it because battery being dead after discharge to certain point, some use even more or less.

9uA = 0.009mA so if the battery capacity is 200mAh/0.009mA = 22222 hours * 75% = 16666 / 24h = 694 days = 1 year and 329 days.

Well when I wrote two years above I didn’t do the calculation yet and it seems pretty close :D

I am sure someone else will calculate it differently but this is how I do.

I would say you were pretty spot on there with your guesstimation and calculation  ;)

Odd fault I seem to have hit a wall as to why they both have the same fault, see what Fluke says but I predict I will be modifying them so they aren't consigned to the dustbin.

Many thanks  :)   
« Last Edit: January 15, 2013, 07:12:19 am by Laplace »
 

Offline Spawn

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Re: Fluke 85-3
« Reply #55 on: January 15, 2013, 07:01:54 am »
I am also curious what they have to say, I don’t have rubber holsters unfortunately for my 85’s since I got them second hand, a battery door would be nice like on III models but to be honest I like them a lot even they are almost 25 years old :)

But about the calculation I forgot to add up the usage  :-[ , most 9v alkaline batteries are around 600mAh so it’s hard to calculate if you don’t know how many hours you use, but I am pretty sure I replace them around 2 years.

Offline EEVblog

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Re: Fluke 85-3
« Reply #56 on: January 15, 2013, 10:30:14 am »
If we have to calculate for a 200mAh battery, there are several calculation methods like taking 75% average of it because battery being dead after discharge to certain point, some use even more or less.

9uA = 0.009mA so if the battery capacity is 200mAh/0.009mA = 22222 hours * 75% = 16666 / 24h = 694 days = 1 year and 329 days.

An Alkaline 9V will be well over 600mAh. But all of that may not be usable depending upon the low batt voltage.

Dave.
 

Offline Spawn

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Re: Fluke 85-3
« Reply #57 on: January 15, 2013, 01:53:07 pm »
Indeed, I was calculating with 200mAh because Laplace was asking for that  ^-^

Offline ModemHead

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Re: Fluke 85-3
« Reply #58 on: January 15, 2013, 03:47:36 pm »
ModemHead's blog on fixing a Fluke 83 might also give you some insight?
To summarize that long story, there is a CD4069 hex inverter package powered directly from the battery terminals. And more importantly, a 1Meg pull-up resistor (R54) straight across the battery when the switch is in the off position.
 

Offline Laplace

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Re: Fluke 85-3
« Reply #59 on: January 16, 2013, 03:30:13 am »
Many thanks to everyone that has replied to my post all information and comments have been most helpful.

Spawn, I used 200 mAh as example because I got fed up and a little lazy replacing the battery every time I used the meter(s) buying Duracells even in bulk can get pretty expensive so as a work around I used some Uniross Ni-MH 9v batteries and cycled them when I forgot to take them out and were drained. Problem solved <smiles> and far greener and healthier for my bank balance.

The Uniross are marked as 200 mAh hence why I mentioned that.

Apologies for the idiocy regarding the question in powered off state current drain given uA=10-6 and mA=10-3
Obviously 1000uA = 1mA so as you replied the current drain in the powered off position is negligible.

My excuse it was very late 5am and my brain had long since gone to count electric sheep.  I have also found which my memory had completely omitted the 85 does have auto power off approx 30 mins or so.

I haven't tested yet to see if the drain increases over time after auto shut off but given what has been said about the series 80's and the known auto shut off current drain fault. I suspect they both have.

I have had a look at one of the boards and it appears it is date stamped 29 Mar 89 the board revision is H. I have managed to get a 83 85 87 service manual from around 89 component placement and silk screen idents all seemed to match up.

I expect Fluke will laugh at my complete lack of sense in my email and given as Spawn has pointed out these meters are approaching almost 25 years I expect they won't get fixed or replaced.

I will revisit the problem when I have time (seems a little rare these days) it may be a good little project given I have 2 and as previously stated I like the meters selling them off would be unfair to a buyer and I would only use the money to buy a 87 series or something similar given test equipment is a little like your beloved 1st guitar you get used to all the nuances.

Many thanks to everyone ModemHead, EEVblog, Spawn, retiredcaps & saturation (apologies if I have missed anyone) who have posted info, links and suggestions they have been very helpful and also the OP who started the thread way back.

Thanks to Excavatoree for his excellent fluke ebay guide(s) although some of the picture links now appear as place holders.

I will post back when I can. 
« Last Edit: January 16, 2013, 03:37:04 am by Laplace »
 

Offline Spawn

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Re: Fluke 85-3
« Reply #60 on: January 16, 2013, 07:19:21 am »
No problem at all Laplace, I am glad to see a fellow 85 user trying to keep them alive, even for it's age it is still a great multimeter :)


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