Electrical Engineers: Need some help on a small project

[tangerine911S]

I see the irony in asking this but could use some help:

I have a very nice and very expensive Fluke 289 multimeter that I got for free from someone leaving my company. It's cool but I'll never use all of its features and it uses batteries extremely fast, especially with the backlit display. I considered replacing it with a more simple unit that won't eat batteries but seeing as how this will rarely leave a desk for small home projects, I thought that if I could convert it to use a DC wall adapter it would be great.

I keep old power adapters for things such as this but the 9V adapter I have (Fluke takes 6x AA's) is unregulated and shows 14V with no load. I found this article explaining why: http://www.robotshop.com/media/files/PDF/unregulated-power-supply-tutorial-prt-08619.pdf
So my question is, how do I determine if this is safe for the meter and if it isn't, how would I go about determining what is?

[carambola]

i can't see, can it tell rotation?

[tangerine911S]

Rotation? Sorry I don't understand.

Originally Posted by carambola

i can't see, can it tell rotation?

[MBAtarga]

Should you get a regulated 9V output - how are you going to connect to the meter? Rig something up to make contact with the battery compartment contacts?

In terms of battery life - how quick is it going through them?

$7 gets you this regulated supply:
https://www.adafruit.com/product/63

[tangerine911S]

Thanks for that link. I'm assuming that under load, batteries are also giving approx 9V?

I don't use it enough to have the batteries be a real issue but I do hate batteries and I always feel the need to turn it off as soon as I'm done taking a measurement.

I would take a connector and wire it to some dummy batteries so the leads make contact with the appropriate terminals inside. That way I can just take them out if needed.

[rick-l]

The list price on that meter is around $600

6 AA batteries are spec'd to last 100 hours.

EDIT: This might be a better choice to screw with. 7 Function Multimeter

[javadog]

Buy some rechargeable batteries.

JR

[aschen]

Originally Posted by rick-l

The list price on that meter is around $600

6 AA batteries are spec'd to last 100 hours.

EDIT: This might be a better choice to screw with. 7 Function Multimeter

Yeah thats a sweet arse DMM, which is why I would be nervous about leaving batteries in it as well. It seems like alkaline batteries only corrode in electronic devices I care about.

They seem to stay pristine in the 10$ walmart crap I dont care about.

[dad911]

They've been selling for over $300 on ebay....could buy a lot more useful (auto & home) related tools.....

I'm not familiar with that meter, but you are likely measuring 'peak' voltage, as it's a cheap, unregulated supply, and peak V is 1.414 times average. If you really want to hack the meter, add 2 capacitors and a 7809 voltage regulator. ($1.99 at Radio Shack, under a buck online)

[tangerine911S]

Ya the meter is way overkill but by the time I sold it and got a more suitable replacement, I may come out $100 ahead so may just keep it. By the way, it came in a larger kit with accessories so list price was something like $700. 😳 It was brand new in an unopened box when given to me.

I saw someone do something with capacitors but they were big and the back cover wouldn't go on so it was duct taped together with wires everywhere and had to break into the main body to do so. I think a regulated 9v adapter and some simple dummy batteries would work well and could be simply removed and replaced with real batteries.

Thanks for the help.

[rick-l]

The CAT IV rating goes away if you attach external wires to the internals so for safety reasons you are no better off with that meter than the free Harbor freight one.

Why not just use it as intended? It has an auto power off feature if you don't use it for 15 minutes. 15 minutes goes into 100 hours 400 times. How often are you going to use this thing?

[john70t]

6 x 1.5V AA batteries in series should equal 9V.
Alkaline batteries suck these days, but are mostly environmentally safe to throw away in the trash.

The charger should output 9V but it reads 14V?
Get rid of the charger.
Keep the Fluke.

[1990C4S]

The charger is unloaded and not regulated. 14v is likely right.

With a load it will probably be 9 v.

Still a terrible idea.

[Dan J]

I have no idea but you could ask this guy: https://www.facebook.com/172547052803759/videos/990120077713115/

[NICE 69 S]

Rechargeable batteries are rated @ 1.2V.......6X1.2=7.2V
Alkaline batteries are rated @ 1.5V...............6X1.5V=9V
Bob B

[LakeCleElum]

I paid $2.99 at Harbor Freight for my Multi-meter about 10 yrs ago........Replaced batteries once. My good one just sits in the tool chest....

[T77911S]

stop using the backlight. just get use to it that way.

I am an electronic tech and use a MM about everyday, don't ever use the backlight.

that's got a LOT of features on it.
I also use to do auto electric work for a little while. "we' very rarely used a MM when doing electric work on cars, MM's are too expensive and cumbersome when a test light will more than do the job.

for auto work save the MM for the charging system, about the only time you really need to know exact voltage.