Author Topic: Problem with panel meter  (Read 747 times)

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Offline jeet55

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Problem with panel meter
« on: October 14, 2017, 02:57:12 pm »
Currently iam working on a simple power supply project,
It consist of a 12v 2A smps and a dc-dc convert , i used a panel meter to display the voltage and current but the problem with panel meter is it needs a isolated supply like from a battery , if i used a 9v regulator powered by smps the panel wont work and it just displays 1(overloading). But i dont wont to use a battery so what are my options?
 

Offline Signal32

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Re: Problem with panel meter
« Reply #1 on: October 14, 2017, 05:02:05 pm »
 Link to power meter ? Very strange that it would require an isolated supply. I think you may be doing something wrong, also perhaps post your schematic.
1. You can use a different power meter that doesn't want isolated power supply
2. You can get a DC-DC isolated converter http://www.ebay.com/itm/-/282666465349 / https://www.digikey.com/product-detail/en/cui-inc/PEM1-S12-S12-S/102-2762-ND/4009686 (similar to this, based on your requirements)
« Last Edit: October 14, 2017, 05:04:49 pm by Signal32 »
 
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Offline jeet55

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Re: Problem with panel meter
« Reply #2 on: October 14, 2017, 06:20:54 pm »
Here is a very curde block diagram / schematic , sorry iam just a beginner.
 

Offline Signal32

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Re: Problem with panel meter
« Reply #3 on: October 14, 2017, 06:57:15 pm »
What model is the power meter ? Can you post pics of the setup ?
If you don't use the battery, is the error happening when you try to measure current, voltage, or both ?
 
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Offline Vtile

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Re: Problem with panel meter
« Reply #4 on: October 15, 2017, 07:36:50 pm »
Yep, there is some of the "better range" digital meters that need a separate power to allow them to float. Only option I can think of is to make a small separate (floating) transformer circuit to power the meters.

ie. http://www.peaktech.de/productdetail/kategorie/id-3-12-stellen-voltmeter-module/produkt/ldp-340.html
« Last Edit: October 15, 2017, 07:40:36 pm by Vtile »
 
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Offline Brumby

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Re: Problem with panel meter
« Reply #5 on: October 16, 2017, 05:00:53 am »
Having a link to the actual meter module might be helpful in looking for ideas.  Sometimes you can play some games with sense connections to work off the same supply - but if you are doing current measurement as well, then that's pretty much off the books.

Also, two things -
1. Your voltage divider for the volts range is wrong.  It will divide by 101 not 100.  To divide by 100, the ratio of the sum of the upper and lower resistors must be 100 times the value of the lower resistor.  For example, with the lower resistor being 100 ohms, the upper resistor needs to be 9900 ohms, not 10K.

2. As wired, the current display will be negative.  With current flowing, the meter's "negative" input will be at a higher potential than it's "positive" input.  If you want it to show as positive (and still keep your voltage sense correct) you will need a DPDT switch and switch both sides of the meter input.
 
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