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Cheap digital voltmeters


ditchcrawler

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            Some time I bought a couple of cheap panel mounted voltmeters off Ebay, I mounted one in the lounge so I could keep an eye to the battery voltage. Since I installed it about 9 months ago it has always read 0.2 volts lower than my Sterling Battery Management panel right through its working range.

            Last night I glanced up and thought, my word those batteries are doing well, we have used the kettle a couple of times also the coffee maker and even watched TV all evening. I went through to the engine room and the voltage there was much lower at a value I would have expected, so I think the volt meter is on the way out.

            Just before I go to bed I turn the lounge lights out and the voltage drops by 0.8 volts, back to 0.2 volts below the Sterling. Switch the lounge lights on and up it jumps again.               

            The light in the lounge are all LED's but if this had happened before last night I am sure I would have noticed it.

 

Since then I have changed the volt meter, this one reads the same as the Stirling unit but it still jumps by about 0.8 volts when I turn the lights on.

There are six LED's in the lounge switched in 2 banks, only the bank nearest the meter effects it. Now the very strange bit. If I remove "ether" of the LEDs closest to the meter it performs fine.

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I have a similar meter and one of my LED lights does actually make it read .1 higher when I switch it on, switch it off and it goes back down again, don't know why.  Reading charge voltage correctly otherwise, checked it against my old garage Crypton voltmeter which says its leading collectly.

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8 minutes ago, bizzard said:

I have a similar meter and one of my LED lights does actually make it read .1 higher when I switch it on, switch it off and it goes back down again, don't know why.  Reading charge voltage correctly otherwise, checked it against my old garage Crypton voltmeter which says its leading collectly.

Well the digital meter's Chinese so it would say that.

One LED in the truck upsets a cheap digital meter but the Avo mk8 sees no change.  I wonder if the regulator in the led (10 to30V) is getting among the scan rate of the digital meter.

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3 minutes ago, Taslim said:

Well the digital meter's Chinese so it would say that.

One LED in the truck upsets a cheap digital meter but the Avo mk8 sees no change.  I wonder if the regulator in the led (10 to30V) is getting among the scan rate of the digital meter.

Could be I suppose. I thought perhaps the two wires on it might be around the other way to the others but swapping them over made no difference.

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Similar problem for me as well.  I think it is to do with the little switch mode supply that some of the wide volt range leds use.  Probably very cheap and therefore very (electrically) noisy. 

Added - one of my LED's also upsets my radio.

Edited by Chewbacka
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