Omron scales battery drain. Where do I start?

[david74]

Hi, I have these Omron BF511 scales which notoriously develop a battery drain problem. Normally they are supposed to last a year but suddenly they start draining a set of 4 AA batteries within a day.

I took it apart to see if it has suffered from water damage. And indeed it had. The water itself dries off but there is a metallic ceiling above the board which has dripped a rust water on it and I suspected was the culprit.

After few accidentally ripped and resoldered (with a nail heated on gas ring) wires and rust cleaned off, I am reluctant to test next set of batteries to see if they quickly die.

I just received analog ammeter I ordered on Aliexpress. My idea was to measure the resistance and see if disconnecting some elements would clear it but I am confused now.

It shows -20 with needles disconnected and somewhat around 0 when connected. Does it mean there is no resistance?

I have been solving the problem up until now by putting an insulator in between batteries as on photo.

 

[david74]

With a nerve to continue this imbecility I tried amperage with the scales on. The needles are located around break in chain so are indeed part of the draw. And the scales go off if ammeter disconnected or switched to voltage. Why is draw nothing? The draw is the same nothing with scales ON and OFF.

 

[david74]

Ah, I get it, when I put it to 0.5 instead of 500mA, it maxes out instantly even with the scales off. And at 50 it averages at 10.

 

[DPG]

You haven't started using batteries from the pound shop have you?

 

[newfutile]

Using the meter on amps and ohms is never going to work out , only DC volts should be used to measure battery voltage, current draw would require the meter in series with the batteries

 

[david74]

Thanks. Especially about the comment about the pound shop. As they have worked for a year before.

Amps, volts, watts.

I wish somebody could shed a light.

I have concluded that the scales draw certain amperage while idle.

 

[brianmoooore]

You need to get the meter in SERIES with the batteries to check.
Why did you buy an analogue meter? They have there uses, and I have one, but the digitals get used 1000 times to every time that is used.

 

[david74]

Because I use meter so rarely that by the time I do use it, its 9v £2 battery is dead. This one uses just one AA battery and in my opinion does all the digital one does except it has needle instead of digits no?

BTW I think the cleaning the board from dried rust water has sorted it out. I forgot the batteries in and they have not drained.

I noticed there is a flat screw head on the center of the meter. I suspect that it is zeroing screw. I will try to turn it to see if I can get it to 0 when it shows -20.

Ah, no it is fine, the read reading is dB. The mA is black and that is on zero.

And yes, I understand I need to connect the black to the plus and red to minus between batteries for current to flow in tested direction.

But when it comes to resistance, it does not matter which direction, no? If there is resistance there is or if there is not there is not or does it depend on direction too? E.g. if there is a diode....

Actually no, it moves the needle clockwise only if i connect black to - and red to +. The resistance maxes out at any setting and the mA shows 50 with the scales off. So assuming the batteries have 1000 mAh, they run out in 20h.

 

[brianmoooore]

That gets 10 out of 10 for an original reason not to go digital! There is a +/- tolerance on the readings on a digital meter, but even a very cheap one allows much more accurate readings than an analogue meter, even one with a mirror on the scale to help you avoid parallax errors.
The screw on your meter is to set the needle to zero.
Congrats on sorting the problem.

 

[Marvo]

I'd suggest you maybe watch a YouTube beginners tutorial on how to use a tester. Measuring pure resistance doesn't matter which way around you use the leads but if there's a diode in circuit it gets complicated with the forward voltage and the resistance reading you might see a different reading depending on the polarity of your test leads.

 

[david74]

Sure, sure, but I do not like waste. The AA batteries I can use everywhere else like in clocks and remotes but the 9v batteries nowhere so I basically would pay £2 and throw one away after each test.

And the meter was cheaper too, only £4 something from China.

I like the vintage look and feel of analog. And I am getting used to it. And it seems precise.

***

I watched couple of youtube videos but they are packed with annoying music and spelling mistakes and none of them answer the questions.

• how to check if the device draws power when idle (the above advice to use voltage only for everything seems daft)
• the ohmmeter shows 2, 5 and 8 on x1k, x100 and x1 scale which does not seem consistent, how much should there be for batteries to last a year? The power on button is a trigger so clearly it needs some power to monitor it
• amperage shows 10mA with scales off and 18mA with the scales on

What is normal resistance of an idle, turned off device which has a tigger power on (a one which turns the device by being shorted out briefly and is turned off similarly). I do not have any devices around to compare but a 10/18 ratio between idle and powered on states seems to big.

EDIT:

I just checked my amplifier which has similar trigger on power button for power off resistance and it consistently shows 5 at x1K scale, between 50 and 60 on x100 scale and between 1K and ∞ on x1 scale.

 

[DPG]

Not sure I understand the bit about throwing the 9V battery away after each test.

Worth pointing out that a £4 analogue multimeter will not be very accurate at low mA levels.

 

[newfutile]

If it accurate 10ma standby is quite a lot for small batteries, isopropyl alcohol is best for cleaning circuits board , i would but a cheap £5 digital meter , i have several of these and the batteries last for months or even years

 

[david74]

Not sure I understand the bit about throwing the 9V battery away after each test.

I normally use multimeter once in a year or two

Yes, I do have a little 10ml isopropyl alcohol spray.

Thanks for the 10mA tip. Ha, I just realised, I have two more scales at home, micro scales and normal kitchen scales.

The micro scales are too awkward to series connect the probes. But the kitchen scale which in fact has a 9V battery with 6V left in it also shows about 20mA when on but it shows a very minute needle movement when idle even at 0.5mA scale. So the conclusion is, the idle should be indistinguishable from zero.