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Products => Test Equipment => Topic started by: jpetras on February 18, 2015, 05:59:34 pm

Title: E-Load instability with low input power
Post by: jpetras on February 18, 2015, 05:59:34 pm

Hi All, can I get your $0.02?

I have run into a problem with my use of a BK 8500 E-Load: At low input powers, the load is unable to stabilize.

The experiment works like this: attach power supply to e-load and set to 3V w/10mA limit. Set the e-load to 100 ohms.

Of course, this circuit should require 30mA. When given more than 30mA, the BK is just fine. But, when given less than the right ohms-law amount, the load gets pretty wild.

We also have a Chroma load and it does a good job with this... however, it is considerably more $$$. I was hoping for something a bit smaller (and with USB/RS232/GPIB/etc interface)

My questions are:

1. General thoughts?

2. Although I believe I have ruled this out, is there a supply to load interaction at play here? I am using a Rigol DP832A for the supply.

c. Does anyone have a load that can pass the above test? ... or can recommend a load that can?

4. Anyone have a BK 8600 who wouldn't mind trying this out?

Title: Re: E-Load instability with low input power
Post by: Christopher on February 18, 2015, 06:02:36 pm

Can you try a cap (1uf ceramic // 10/47uf electrolytic) directly across the input sockets on the load ? This has cured instabilities for me in the past before.

Title: Re: E-Load instability with low input power
Post by: jpetras on February 18, 2015, 06:54:52 pm

Quote from: Christopher on February 18, 2015, 06:02:36 pm

Can you try a cap (1uf ceramic // 10/47uf electrolytic) directly across the input sockets on the load ? This has cured instabilities for me in the past before.

Thanks Chris. I will give it a shot and let you know

Title: Re: E-Load instability with low input power
Post by: Christopher on February 18, 2015, 08:19:13 pm

I've found some loads can be problematic in constant resistance modes. Constant current is the more stable in some cases.

I doubt it's the power supply not liking a low current. To try this you could connect a high value resistor to the power supply and measure the output voltage.

Title: Re: E-Load instability with low input power
Post by: jpetras on February 18, 2015, 10:11:10 pm

Quote from: Christopher on February 18, 2015, 08:19:13 pm

I've found some loads can be problematic in constant resistance modes. Constant current is the more stable in some cases.

I doubt it's the power supply not liking a low current. To try this you could connect a high value resistor to the power supply and measure the output voltage.

This is part of what I did to prove to myself that its not the supply... unfortunately, I am stuck with CR... although I am tinkering with Constant Power

Thanks again