External power for Fluke 87 - Page 1
Forum section: electronics / testgear

author: rx8pilot
author_rank: Super Contributor
timestamp: November 13, 2014, 10:04:02 pm
content: I have had a Fluke 87 for a long time - back when all my work was in the field. Now that all of my days are at the bench, it is in continuous use all day long. The problem is that if I lock it in the on position the battery does not last long as you would expect. I searched for similar projects on the forum but did not see anything.The question is, how to best power a DMM that is designed for 9V batteries with an AC source? I am guessing that their is little to no filtering since batteries would never need that. I am not sure how to ensure that an ext supply is not going to interfere with mV measurements which I do a lot of. I am expecting that I will need to build a filter if I end up using a 9V wall-wart type of adapter to make it clean enough.PS: I am planning to bite the bullet and get the Keysight 6.5 digit DMM, this is just a life extension for what I have already.If I simply missed this in the search as an already covered topic, I would be just as happy if someone pointed that out.Thank you all....

author: krivx
author_rank: Frequent Contributor
timestamp: November 13, 2014, 10:16:09 pm
content: You can just wire a DC jack to the battery clip (or use an adapterhttp://www.ebay.com/itm/MOEN-Battery-Clip-Convertor-For-9V-AC-adapters-/310224477107?pt=AU_Instrument_Accessories&hash=item483ad1dbb3) and plug in a 9V plug pack.I have a feeling that this is going to invalidate any safety ratings of the meter, as you now have a connection from inside the meter to outside without any protection circuit. This might be why external power isn't a standard feature any more.

author: rx8pilot
author_rank: Super Contributor
timestamp: November 13, 2014, 10:22:52 pm
content: My concern was that an arrangement like that would be too noisy and interfere with the accuracy of the meter. Maybe its not that sensitive, but I don't really know. If I designed the meter knowing that it would always be getting power from an on-board 9V battery, I would not bother with much front end filtering.If I am doing mV measurements and the DMM is also getting switching noise from some wall-wart, it would seem to be sketchy.

author: krivx
author_rank: Frequent Contributor
timestamp: November 13, 2014, 10:30:18 pm
content: Well a 9V linear wallwart should be cleaner... If you are concerned then get a 12V dc supply and use linear regulator?

author: retiredcaps
author_rank: Super Contributor
timestamp: November 13, 2014, 10:30:36 pm
content: Martin did a Fluke 287 video where he had an external adapter for a power source and it affected his readings. I think it is in this video?

author: retiredcaps
author_rank: Super Contributor
timestamp: November 13, 2014, 10:35:05 pm
content: You can always try a 9v rechargeable battery?https://www.eevblog.com/forum/reviews/tenergy-centura-9v-and-tn141-mini-review/

author: rx8pilot
author_rank: Super Contributor
timestamp: November 13, 2014, 11:47:51 pm
content: The rechargeable batts, unfortunately still require that I unscrew the case and replace the battery. Not that big a deal, but every few days is at least an annoyance. Ideal solution is that I get the bench arranged and never mess with it.I did not find the part of the video where he spoke of his external source although it seems to be in there somewhere. I can see the wire coming out of it.The linear supply with linear reg seems like an easy and clean solution. I can also put in some filtering to reduce any noise the wire picks up - small ceramic caps and a ferrite bead should attenuate well enough I hope.

author: PedroDaGr8
author_rank: Super Contributor
timestamp: November 13, 2014, 11:54:51 pm
content: Quote from: rx8pilot on November 13, 2014, 11:47:51 pmWhy not just use a bench meter?

author: retiredcaps
author_rank: Super Contributor
timestamp: November 14, 2014, 12:22:21 am
content: Quote from: rx8pilot on November 13, 2014, 10:04:02 pmBTW, the original Fluke 87 series I has a battery life of 500 hours on a fresh 9V alkaline.Sometime back, I measured the current consumption and most functions use 1mA. Assuming you used the Fluke 87 continuously and disabled the auto power off, that would imply roughly 20 days before needing a new batter. (500/24 = 20.83).How long does your battery last in your typical usage scenario?I ask because I have seen some reports/threads about poor battery in a Fluke 87.

author: rx8pilot
author_rank: Super Contributor
timestamp: November 14, 2014, 01:07:05 am
content: Quote from: PedroDaGr8 on November 13, 2014, 11:54:51 pmI am planning to get the Agilent (Keysight) 34461A along with a new scope, but it will be a few more months before I am able to afford them. At the moment, all of my money is going into a pick and place machine and I just want the Fluke 87 to be less of a pain.Quote from: retiredcaps on November 14, 2014, 12:22:21 amI have never really attempted to measure battery life, but I seriously doubt it is 500hrs. It seems to be a little over a week or so at 12hrs/day. This is clearly not a show stopper - but it seems that it always dies when I am really in the middle of something like min/max logging (especially overnight)

author: retiredcaps
author_rank: Super Contributor
timestamp: November 14, 2014, 07:19:52 am
content: Quote from: rx8pilot on November 14, 2014, 01:07:05 am7 days x 12 = 84 hours. Let's round up to 100 hours. Something is clearly not correct. That suggests the 87 is using 5mA for most of the time.If you can find time, I suggest you measure the current consumption of your 87.I will try to find some time this weekend to measure the current consumption while using min/max. I already know from past measurements that most functions consume 1mA. Perhaps min/max uses more?

author: retiredcaps
author_rank: Super Contributor
timestamp: November 14, 2014, 11:51:44 pm
content: For the following Fluke 87 series I ranges I get around 760uA (let's call it 800uA): ACV, DCV and mV. My readings are consistent with another post belowhttp://www.edaboard.co.uk/fluke-87-flat-batteries-t268153.htmlI get 1.4mA on ohms with open test leads. When measuring a 100k ohm resistor, I get 760uA.When using min/max on the DCV (measuring 9V battery) and ohms range (measuring a 100k ohm resistor), I get 760uA.So with a new 9V alkaline battery (assuming 565mAH*), it should get around 565mAH/0.8mA = 706.25 hours.With your 12 hour/day, you should get 58.85 days or close to two months.*565mAH from wiki.http://en.wikipedia.org/wiki/Nine-volt_battery

author: rx8pilot
author_rank: Super Contributor
timestamp: November 15, 2014, 02:28:13 am
content: Wow! Excellent info....I just put in a fresh battery that I just purchased and marking the calendar. Lets see how well it works.The meter works fine, but it is about 15 years old and been around the world a few times. Shouldn't have any impact on current consumption, but it owes me nothing. I am on bonus time with my 87. REALLY looking forward to purchasing the new 34461A 6.5 digit.

author: retiredcaps
author_rank: Super Contributor
timestamp: January 21, 2015, 08:10:25 am
content: Quote from: rx8pilot on November 15, 2014, 02:28:13 amWell, two months have gone by. Assuming you are still using it for 12 hours/day, the battery should be dying about now?

author: LaurentR
author_rank: Frequent Contributor
timestamp: January 22, 2015, 05:05:49 am
content: Quote from: rx8pilot on November 15, 2014, 02:28:13 amThe 34461A is awesome, but if your budget is tight, get a used 34401A from EBay instead. $300-400 will net you a good condition one and you'll get a lot of the same functionality for cheaper.And you can always connect it to a PC for trend and histogramming.

author: rx8pilot
author_rank: Super Contributor
timestamp: January 22, 2015, 05:31:17 am
content: Quote from: retiredcaps on January 21, 2015, 08:10:25 amImpressive memory you have.I replaced it late December, so it's a little over a month in rough numbers. This time I used fresh batteries instead of the ones that have been on the shelf for a long time. All said and done, its not enough to mod it for AC power. I think the last few batteries were fairly old when they were put in service so they had a shorter life. A month a constant use is not bad enough to make a fuss over.The 34461A is being bundled with a few other company purchases. Once my wish list of new test equipment got to the point that it needs to be financed, I decided to wait on the bench meter. I will get a whole bench worth of gear all in a single shot.