DC Volt and Current Panel Meters - some things to look out for
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- Опубліковано 15 сер 2024
- My current project uses panel meters and is taking longer than expected. So I decided to put up a video on my experience with these cheap eBay panel meters, in particular how to power them safely and how to use them to measure voltage and current in power supply that has a positive and negative rail.
00:00 eBay panel meters
00:50 2 and 3-wire meters
01:42 Regulator limits
03:19 3-wire test
04:14 2-wire test
04:37 construction
05:56 simplified schematics
07:04 wiring scheme
07:37 getting a safe supply voltage
10:31 use with pos & neg rails
11:29 current accuracy
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Dude, that was beautiful I almost peed myself when you addressed the negative voltage as I am working on the Elenco XP-720K kit. thank you for being thorough.
Another great video; thank you! This reminds me of your PeaceFair Meter investigations. When you said a solution was needed for the hot voltage regulator, I, as you, thought of a Zener. Later in the video, you suggest that solution. Great minds;-)
Very nice explaination! Good work 👍
Nice video thanks ! So replacing the wire shunt with a 4 wire shunt should cancel the nonlinearity much more right ? I know the shunt is probably twice the price of the module but the wire also have some temperature coefficent that 4 wire shunts are minimal with.
Thanks for the nice words. In principle your are right but I have some doubts whether this module is worth the effort and money converting to an external current shunt. The cheap opamp may be responsible for some of the non-linearity. Maybe getting a panel meter that already comes with an external shunt may be a better option. To be honest, I never look into that because for my project a reasonably accurate readout 0..5A was good enough and I don't have the space for external shunts. If you do modify this panel meter, please let me know the results.
Why not using CC source for the zener for such wide Voltage range?
Good point. I was in a hurry and used what I had in the spare parts bin. Also, the aim here is not to have a stable voltage for the panel meter. That has its own regulator that can deal with a lot of variation. All that is needed is to prevent the voltage from rising too high.
I wonder how these compare to the "RD 4 Wire Variable Precision DC 0-33 V" from RIDEN. I got a few to build a milliohm meter as they are 5 digit meters.
Generally their electronics are quite good unless its a clone. For sure have a look at the voltage regulator. Also power it with say 25V and touch the regulator to see how hot it gets.
M3430 version?
Did anyone use the version of those panelmeters that say "M3430." on the PCB (in stead of DSN-VC288)? They look identical but they use different chips. I have two of those and both are totally wrong on the Current measurement (they show only about half of the real current,as compared with 2 multimeters). I played with configuration in different scenarios (incl. omitting the thin black wire) but the faulty Amperage indication remained. I also replaced the I-adj trimpot from 5K to 300K. Then I could make it show the right current (at about a 1A measurement), but when removing the load, they still showed 300mA... not good.
Thank you for creating this video with a great level of detail
ChrisV
I looked at a M3430 on an eBay picture, and it looks very similiar to DSN-VC288., so I suppose it should work the same way. If your meter is reading only half the current it should then the shunt resistor is too low. One method that may work is to carefully notch the metal bar with a saw, because shrinking the diameter will increase the resistance. Just a few strokes and then test the readings. Then repeat until the value at mid-position of I-ADJ trimpot is what you want. Be careful though because if you go too far, its very difficult to go back (filling the crack with solder may(!) work to get you back if you cut too deep but solder behaves different at higher currents, so best avoided). If you dare to try it, could you please report your results. I have never done it myself and am curious about the success rate
@@TheHWcave Just an update:
I have just put 2 shunt wire/resistors in series (from another M3430) and then, using the "I-adj" mini potmeter, I was able to get a current-reading close to the one on my Digital voltmeter.
This, more or less, fixed the problem of too low Amperage indication, but it introduced another problem: a too high shunt resistance is now causing an unacceptable voltage drop at high current.
Or maybe not... I'm planning to use this in old ATX (computer) power supply that I want to render adjustable. I guess I can put the voltage-sense for the voltage-control loopback circuit _after_ the shunts, so it should adjust/correct the voltage regardless of differences in current/shunt.
To be continued ...
@@anonymoususer6448 Thanks, keep us updated please
Sorry, but I don't see a link to your Patreon in the description. You might consider making a template or footnote that contains general channel information the applies to all videos and then add specific stuff before posting.
Oops, I missed that. The link has been added in the description...
www.patreon.com/user?u=45604138
Those sell on ali for $13 for 5 meters including shipping.
I feed them with a 60V HV-buck converter set to 10V.
why so extreme? I would just use an aux supply for the meters. Plenty of wall-warts in the world to recycle.
That's a good option . Better than converting 50V into heat
@@TheHWcave true, till the el-cheapo buck-converter hiccups and you have a popcorn party with the 60V on some parts of your circuit
True, maybe one should not go for the bargain basement converter if a lot of expensive kit hangs one the other end....
@@msana4420 I trust my $2 HV buck on 50V way more than your $2 wall-wart on 240V.