I need to test some battery packs. We predict the load of the target product will cycle from high power (80 W for 10 ms) to low power (5 W for 240 ms) during operation. I would like to simulate that load including the dynamics in the battery test. I have found a few loads for rent at Electrorent, but before I commit, does anyone have some suggestions? Precautions?
I liquid cool ordinary tube type power resistors. Cost: $5.00 from electrical surplus..
Light bulbs are ok if you account for the dynamic resistance.
Perhaps get some nichrome wire and wind your own test load.
22AWG is about 1ohm/ft Stabilize it's temperature to control R drift.D from BC British Columbia Canada.
We have used both Elgar and HP at work. They can do up to 5kw and can switch dynamically.
When I needed something like that for similar loads I just built my own using a power transistor on a heat sink. I was only testing for constant power, you'd need to switch the transistor with the output from an MCU for the appropriate time.
Leon
You can make a nice load by placing a power N-FET on a heat sink. Wire the source to ground through a resistor with a small ohms value. Drive the gate of the N-FET with an opamp and the inputs from a voltage source (IN+) and the other input (IN-) from the feedback at the resistor source connection. This makes a nice voltage controlled current sink that sinks from the drain of the N-FET. If the opamp is a dual it is easy to use the other half to make a voltage scaler such that control voltage can be a larger range than the actual voltage applied to the IN+ of the first opamp. For higher power applications put a heat sink fan over the N-FET.
ciscodsl
What criterion will you use to judge battery capacity? I'd like to know about those rented "loads." Can you show us a link to them? You didn't say what kind of battery pack your product uses.
The test is to compare different packs in our simulated application.
Electrorent page:
The most promising technology appears to be lithium ion stacked to provide 12-14 volts.
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Yeah, I was wondering why you need to rent a load. That thing weighs almost 50 pounds. I'm not going to offer advice about the rent-a-load, because I wouldn't go that way. I'd build the load. If you're developing a product, surely someone there is competent to build a load that cycles at 4 Hz between 80 watts and 5 watts, with a 4% duty cycle on the higher power. A hobbyist could do it with a 555 timer, a couple of power resistors and mosfets, and spend no more than a few dollars doing it. Actually, you only need one mosfet. Keep the 5 watt load on constantly, and cycle a 75 watt load at 4% duty cycle and 4 Hz, using power resistors calculated to dissipate 5 and 75 watts according to the battery voltage. Or if you want constant current loading, that's easy enough, with only a slightly more complicated circuit. Then you'll have some criterion, such as voltage, by which to measure the battery life. So which would you prefer, a fixed resistance, or constant current load?
page:
I suppose for battery testing it isn't an issue, but for LDO testing, the homebrew load is the way to go. I've seen some really crappy loads, i.e. hardly looking like a resistor. For the homebrew loads, I've gone to a local store with "free resistors" and just paralleled them using scrap PCB. It makes a very low inductance resistor.
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Wads
mfr=3DAgilent&mf...
Two constant power modes, switching between them as described.
I have an old PIC development kit that could be lashed up with resistors and DC/DC converters to do what I need, but I don't have the time or budget to pay someone to build something I can rent.
:I need to test some battery packs. We predict the load of the target :product will cycle from high power (80 W for 10 ms) to low power (5 W :for 240 ms) during operation. I would like to simulate that load :including the dynamics in the battery test. I have found a few loads :for rent at Electrorent, but before I commit, does anyone have some :suggestions? Precautions?
I have a Kikusui PLZ152W electronic load
(read the operations manual for load switching to see how it operates.)
This electronic load can handle 2 loads A and B, with potentiometer adjustable switching times such that the total load cycle period (Load A + load B) is 200mS (not quite what you want but I am sure it would be close enough for practical purposes). The load can be set to CC or CR depending on what you want. It also has a BNC connector so you can monitor the load current duty cycle on an oscilloscope.
Other loads may require connection to a PC for load programming but the PLZ152W is totally manual in standard form and is a nice little performer.
You can buy one for not too much:
As an old test engineer myself i would just build one.
The nearest similar thing that i have done is a current pulse test set. i could produce accurate repeatable pulses from sub millisecond to sub microsecond with fast edges. The most difficult pulse was
300 A at 300 ns and 10 ns edges. All done with discretes and a few one shot chips. First transistor provided voltage and current gain from logic to 12 V the second drove the big FET output. That was about 25 years ago. I had to contend with 12 foot lead lengths to get in and out of the vacuum chamber.Do all your wiring with shielded twisted pairs. It will prevent a lot of pain. It worked for me.
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