A simple DC motor has torque proportional to current. If somehow you can create a constant torque load it should draw constant current. I think you could put a pump on the shaft of the motor and let the pump circulate with a closed loop and a pressure regulator it would be a constant torque. The fluid will get hot and will have to have some way to get rid of the heat. No way around getting rid of the heat no matter what you do.
Electronic only methods are simple in concept but if you want to burn the power with an active device that will take some serious heat sinking and some serious devices. If you want to PWM into a resistive load, that will take more of complicated circuit. An MCU could easily be programmed to control the PWM but that takes work. I can’t think of anything simpler than a motor and pump. Not totally sure how tight it would regulate itself. From: Chuck McCown via Af Sent: Wednesday, December 31, 2014 7:05 PM To: af Subject: Re: [AFMUG] Dc electric load ? Chuck ? 2 kW is some heat, no matter how you do it. Not sure if there are any common power transistors that can dissipate that much in a single device. If you parallel them then you have to ballast resistor them. Be nice to do full on and full off into a resistive load with input filtering. Then you could use smaller devices and heat sinks. PWM with input current feedback. From: Forrest Christian (List Account) via Af Sent: Wednesday, December 31, 2014 3:59 PM To: af Subject: Re: [AFMUG] Dc electric load ? Chuck ? The electronic way is a constant current source shunted to ground or through a resistor bank. One hefty npn power transistor and a few smallish components. Or a jfet with source tied to gate, with a current adjustment resistor in the source lead. Or any of a hundred circuits. For more wattage you can parallel several, each adjusted to take their fraction of the total amps. I seem to be slowly turning into a power electronics engineer over here. On Dec 31, 2014 3:42 PM, "chuck--- via Af" <[email protected]> wrote: I am thinking a DC-DC converter that will take a wide input and constant voltage output into a nice temperature compensated resistive load. What voltage range do you want? Doh!, that would be a constant power load. You want constant current load. Have to continue thinking... From: [email protected] Sent: Wednesday, December 31, 2014 3:39 PM To: [email protected] Subject: Re: [AFMUG] Dc electric load ? Chuck ? I know how to do it really cheap and easy under 2 amps. Have to think on this a bit. I have used hot water heating elements and coils of wire (in a bucket of water) for high wattage resistors but obviously not constant current. From: TJ Trout via Af Sent: Wednesday, December 31, 2014 12:11 PM To: [email protected] Subject: [AFMUG] Dc electric load ? Chuck ? Anyone know of a inexpensive do it yourself way to make a dc constant current electric load for testing power supplies, lithium batteries , etc ? Looking for something maybe 2kw+ and the cheapest premade thing I can find is $3500. Maybe I'll just use a carbon pile load but that will be much less accurate.
