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2380 Display

Series 2380 DC Electronic Loads
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alanhawse
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Joined: January 26th, 2020, 8:46 am
Country: United States

2380 Display

Post by alanhawse » January 26th, 2020, 8:51 am

I have a 1.2v buck regulator (that can do 3A)

It is attached to a Keithey 2380 dc Electric load (the manual is ummmm... not that great)

I have the 2380 in "Constant Current" mode.

The display of the 2380 says 1.2v at 0A (this makes sense)

When I turn up the constant current to 1A the display says 1V 1A 1W... which I assumed meant that the output of the buck regulator was drooping...

The problem is that when I measure the output of the buck with a volt meter it is still 1.2v

Where did the 0.2V go?

The more I turn up the current the lower the voltage goes.

Obviously it is displaying some other voltage than the input to the 2380... but what it it?

Then things get even more confusing. When I put another meter in the current path I get exactly the same current measurement as the 2380 (that's good)... it reads 1A as well... BUT... the voltage displayed on the 2380 goes even lower.... 0.31v but still 1A

What is the display really telling me?

Thanks,
Alan Hawse
www.iotexpert.com

Andrea C
Keithley Applications
Keithley Applications
Posts: 1576
Joined: October 15th, 2010, 10:35 am
Country: United States
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Re: 2380 Display

Post by Andrea C » January 28th, 2020, 10:55 am

Are you connecting and enabling use of the remote sense lines on the 2380?

alanhawse
Posts: 20
Joined: January 26th, 2020, 8:46 am
Country: United States

Re: 2380 Display

Post by alanhawse » January 28th, 2020, 1:36 pm

No. I am using the lugs on the front of the device.

I am pretty sure that the impedance of the path is something like 0.1ohm... and that is where the voltage is going.

What I don't understand is:
#1 why not measure the voltage at the inputs?

#2 why bother to show the voltage and power if it is not the real power and voltage? (for me when I set the 2380 at CC=1A and the voltage at the terminals is 1.2v ... then the display should show 1.2W and 1.2V .... not whatever the lower voltage (and power) is.

Alan

Andrea C
Keithley Applications
Keithley Applications
Posts: 1576
Joined: October 15th, 2010, 10:35 am
Country: United States
Contact:

Re: 2380 Display

Post by Andrea C » January 28th, 2020, 5:50 pm

When not using the remote (voltage) sensing leads, the voltage measured by the 2380 will be at the front terminals. Your buck converter is not drooping. Instead at 1 Amp, the 1.2v from it is spread across the I*R of the lead wires and only what is left over drops across the load.
When you inserted the amp meter, the load reports even lower voltage, because now the amp meter voltage burden drops part of the 1.2v too.

Sketch:
2380_CC_Mode.PNG
Local Sense - Voltage measured at terminals
2380_CC_Mode.PNG (50.71 KiB) Viewed 838 times
By connecting and enabling use of the remote sense, the voltage measurement will be taken where you connect them. Similar to when you connected in and measured the buck converter voltage with a dmm volt meter.

alanhawse
Posts: 20
Joined: January 26th, 2020, 8:46 am
Country: United States

Re: 2380 Display

Post by alanhawse » January 29th, 2020, 7:18 am

Thank you very much.

It really didn't occur to me that the IR in the lead wire would be that much. (I suppose that is what I get for being a software guy).

Your response was awesome.

Now I just need to figure out how to hook up remote sensing :-)

Alan
www.iotexpert.com

alanhawse
Posts: 20
Joined: January 26th, 2020, 8:46 am
Country: United States

Re: 2380 Display

Post by alanhawse » February 18th, 2020, 12:05 pm

Here is an article I wrote about the back panel and using remote sensing

https://iotexpert.com/2020/02/18/keithl ... e-sensing/

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