Products > Test Equipment
ARRAY electronic loads
rx8pilot:
Definitely crude, but I needed it in one day and had to build it from parts on hand. Serves the purpose while being the ugliest piece of gear on the bench by a long shot.
Yours looks like its nearly ready for a production run. Nice.
Sent from my SAMSUNG-SM-G890A using Tapatalk
forrestc:
--- Quote from: dolomike on September 14, 2015, 03:38:54 pm ---Well, we normally run DC motors in automotive and heavy duty applications so this isn't a lightweight system. I think we would normally run CC or CR mode for most tests but some could be upwards of 800W. I believe this can be achieved by paralleling the devices in CC or CR mode. Some re-brands state they can be paralleled but I didn't recall seeing anything in the Array manual about it.
......
Filtering: What type of filtering are you asking about?
--- End quote ---
In relation to the filtering: I guess I should have asked "are you using PWM to derive DC, or are you using it to drive a motor".
My experience is that a DC load doesn't really like a dynamic power source. For instance, to illustrate I hooked my Array load up to my Rigol Power Supply, and set the load to constant resistance mode, and set the rigol to deliver at most 1A at 24V. See the video below to see what happens..... in short the load can't adjust correctly with this type of power source - it keeps trying but it doesn't succeed.
(Sorry about the shaky handheld Cell-phone video).
dolomike:
We are using PWM to drive a motor - we're not generating
forrestc - Thanks for posting the video as I think it answers my question. It appears that the DC load cannot adjust quickly enough to handle a switching source. Looks like I might have to go for some of the more advanced and thus more expensive models out there.... or I can look at creating a resistive load bank with some smarts like what nctnico has done.
I may also play around with an DIY electronic DC load circuit and see what kind of response I can get with it with some high speed component. I wonder what sort of speeds I could get?
Mike
MarkL:
--- Quote from: forrestc on September 15, 2015, 12:40:12 am ---My experience is that a DC load doesn't really like a dynamic power source. For instance, to illustrate I hooked my Array load up to my Rigol Power Supply, and set the load to constant resistance mode, and set the rigol to deliver at most 1A at 24V. See the video below to see what happens..... in short the load can't adjust correctly with this type of power source - it keeps trying but it doesn't succeed.
--- End quote ---
It depends on the design of the control loops in both the power supply and load.
I tried the same experiment on an ITT MX100TP set for 24V @ 1A, and an Array 3723A load set for 20 ohms. It worked with no instability.
While I agree it's hard to beat the simplicity of a real resistor, I wouldn't rule out an electronic load just yet.
dolomike: What range of duty cycle for 5kHz-20kHz is needed?
In a quick test the above Array settles in about 40us to a 10A target setting. It settles in about 10us to a 1 ohm target setting (@ approx 16A). These numbers are from a simple switch closure, and they're too long for 20kHz, but it might do better with a MOSFET-driven steady state PWM.
Edit: Fixed model number.
MarkL:
Here's a little more about applying PWM to an Array 3723A load.
A 10kHz square wave was generated by a beefy LIPO 4S battery pack (approx. 16V) put through a MOSFET switch.
Here is the load in 10A mode. Blue is current, red is voltage across the load. Until it settles at 10A, it's unreasonably high at almost 65A.
Here is the load in 1R mode. For whatever reason, it settles much faster and with much less of a current spike. There's an odd spike in voltage above the idle battery voltage indicating some inductance inside the load.
Just for comparison, here is the same plot but with the load disabled. The PWM generator was manually triggered. There's some current being drawn in the beginning due to a capacitor inside the load on the input and likewise, the voltage does not return to 0V because the capacitor is holding it up.
So, I think in resistance mode, this load could be usable at 20kHz as long as you know what to expect out of it. Because it overshoots, it's certainly going to stress your circuit for testing.
You'll have to be the judge. Maybe it's worth a try. No idea on the parallel requirement, though. I only have one.
Edit: Fixed model number.
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