Low cost programmable high power "resistor emulator" ? - Page 1
Forum section: electronics / beginners

author: e100
author_rank: Frequent Contributor
timestamp: March 20, 2021, 04:59:37 am
content: I see plenty of low cost 100+ watt 'constant current' programmable loads typically used as battery testers, however I haven't seen anything that emulates the behavior of a high power resistor where the current is proportional to applied voltage.My particular application is simulating an electrolytic salt water chlorinator cell on the bench without actually generating chlorine (not good indoors). The cell resistance varies from about 0.3 to 0.6 Ohms depending on the salinity and lime scale build up on the electrodes. The power supply is just rectified AC from an 8v transformer. The peak current is about 25 amps.

author: Vovk_Z
author_rank: Super Contributor
timestamp: March 20, 2021, 10:17:29 am
content: So, you needCR mode.It is more rarely used than CC mode (CC is the most common), that's why it is so much rare. Butit can be implemented almost as easyas CC mode.Here in attachments is a picture of an circuit design idea (from Keysight Electronic_Load_Fundamentals.pdf):

author: calzap
author_rank: Frequent Contributor
timestamp: March 21, 2021, 02:03:30 am
content: Not sure if OP wants to build a load with CR or buy one. Most commercially available loads (BK Precision, Gossen, Array, Rigol, TTi and Instek) have a CR mode. Would have to look carefully at specs on CR programmability.Mike in California

author: e100
author_rank: Frequent Contributor
timestamp: March 21, 2021, 09:05:24 am
content: Quote from: calzap on March 21, 2021, 02:03:30 amLooking to buy. Vovk_Z helpfully pointed out that the key word was "CR" which made my search much easier.Unfortunately the prices on the cheapest usable CR loads are about 6 times that of the cheapest CC modules on Aliexpress/ebay.I did find one low cost CR module but the documentation and accompanying Windows program were in Chinese.

author: Siwastaja
author_rank: Super Contributor
timestamp: March 21, 2021, 01:42:21 pm
content: But AFAIK the electrolysis process is far from being a constant resistance load, it's more like a diode (i.e., exponential current per voltage) with some series resistance. In order to simulate it, you'd need a freeform curve.If you can live with less accurate model, I'm sure the more usual CC-CV is not any worse than CR.

author: calzap
author_rank: Frequent Contributor
timestamp: March 21, 2021, 03:16:12 pm
content: A rheostat turned by the shaft of a timer or microcontroller-driven stepping motor might work. Old tech, but simple to put together. Would need a frame and shaft coupler too. Inexpensive parts available on eBay and elsewhere.If you’ve got the funds though, a name-brand electronic load is a valuable addition to any electronics bench.Mike in California

author: e100
author_rank: Frequent Contributor
timestamp: March 22, 2021, 02:38:23 am
content: Quote from: Siwastaja on March 21, 2021, 01:42:21 pmI've done the VI measurements and the curve is dominated by series resistance. Chlorinators of this type are run straight from rectified AC. For the majority of the cycle the voltage is way above the conduction threshold. Mine typically peaks at 12v.