YB27VA Dual Digital voltmeter/Ammeter in Dual Rail PSU?

Hi Forum,

I have a similar dual rail PSU query to the chap asking about metering his negative voltage rail. I had posted to AllAboutCircuits also.

I bought a pair of YB27VA volt/amp meters, hoping to use one for the +ve rail & the other for the -ve rail, but I'm beginning to see that I maybe cannot use it on the -ve.

My PSU is very similar to the Visio-Jameco unit:
( http://www.jameco.com/Jameco/Products/ProdDS/20626 Manual Revision 3.pdf ).

Does anyone have any suggestions? Maybe I could get the -ve voltmeter working, but not the -ve ammeter? These meters seem to monitor the current flowing in the return connection rather than the supply wire.

I've pasted my original post below for info.

Many thanks & sorry for any duplication.

Simon B.

--------------------------------------

Ive made myself a nice adjustable voltage dual rail lab style Power Supply Unit (PSU); just a standard design using adjustable Linear Voltage Regulators (LM317 & LM 337 for the positive (+ve) & negative (-ve) voltage rails).

These regulators are rated at up to about an amp & will give me about +1.4v to +30v for the +ve rail, & -1.4v to -30v for the -ve. No adjustable current limit control, apart from the built in short circuit & over temperature protection.

Obviously it's not as good as something I could buy, but will be adequate for my circuits. Maybe a few extra decoupling capacitors would improve it further.

My question is about fitting volt meters & ammeters to it. It's easy to fit an analogue voltmeter & an ammeter to the +ve & -ve supply rails, but these 4 meters will take a lot of space.
I found these twin-colour digital modules (YB27VA seems to be the part), each showing voltage in red & current in blue.

I can see how easy it would be to put one in my +ve supply rail, but am not sure if I can ever put one in the -ve supply rail, as wouldn't I need to connect it 'backwards' to work? But would it work or get damaged?

Does anyone have any experience in these modules? It took a while to work out what to do with the red, black & yellow wires & the badly translated specification & weird trio of connection diagrams!!!. It seems the module derives its power form the test voltage, but only if its between 4.5v & 30v, & who knows how the one in the -ve rail derives its power from!

If anyone has any advice or suggestions, please let me know.

If I get it working properly, I shall put it in the Projects Section of the website.

Many thanks,

Simon Bond.



-----------------------------------------------------------------
Sent from my iPad2:-
Simon.D.Bond MEng, BSc(Hons), IEng, MRAeS.
-----------------------------------------------------------------.

 

Thanks for your help.

That's a shame, as I bought a pair of +ve ones, rather than a matched pair.

Maybe I can use the +ve module as planned & the voltmeter part of the 2nd one for the -ve rail? Or back to analogue ammeters?

Thanks again,

Simon B.

 

Hi again,

As suggested, I have abandoned using the ammeter for my negative rail.

I was trying to get the positive side working, & the voltmeter was straight forward, but I could not get a reading on the ammeter. I was using a decade resistance box as a load, & used the yellow wire which is the ammeter supply labelled IN+.

But according to the spec, these modules have a resolution of 0.1A or 100mA, so neither is suitable for use in my lab PSU as current drawn will me minimal.

So definitely back to analogue ammeters!

Thanks again for your help.

Simon B.

 

Thanks Steve,

That's a concept I didn't think of. I assume the better the precision of the 0.1Ohm current sense resistor the better.

The circuit I am basing my lab PSU on is:

http://orca.st.usm.edu/~jmneal/dual_psu/
http://orca.st.usm.edu/~jmneal/dual_psu/psu2.pdf

Mine has extra diodes between the Vout & Adj pins of the LM317 & LM337 Voltage Regulators.

It would be very useful if I could see your circuit diagram, so I can work out where to place the current sense resistor. That would be very kind of you & I would be very grateful.

I found an old analogue ammeter in my spare parts/junk drawer. I can easily shunt it to read f.s.d at 1000mA, which is the max I would ever drawer form these small regulators. Somebody suggested that I could build this meter into a nice gray box with standard 4mm banana sockets, & use it in series with my PSU when I want to monitor current. Most of my work is with dual-rail op amps, & other analogue electronics, & I rarely ever monitor the current drawn.

However I'm building some high-power laser diode circuits, & will need to carefully monitor things more closely! So I will be going for the complete dual ammeter solution. Ultimately I'd like to build a more capable PSU over the next year or so; with maybe 5A capacity, with current limit & 5v & 3.3v rails for my MicroControllers/logic etc.

Thank you very much (from a rather cold & damp UK) for your help, & look forward to maybe seeing your circuit diagram.

Many thanks,

Simon B.