{"id":118,"date":"2010-01-25T12:48:43","date_gmt":"2010-01-25T17:48:43","guid":{"rendered":"http:\/\/ammonsengineering.com\/blog\/2010\/01\/current-spikes-with-resistor\/"},"modified":"2010-01-26T12:09:03","modified_gmt":"2010-01-26T17:09:03","slug":"current-spikes-with-resistor","status":"publish","type":"post","link":"https:\/\/ammonsengineering.com\/blog\/2010\/01\/current-spikes-with-resistor\/","title":{"rendered":"Current spikes with resistors"},"content":{"rendered":"

I decided to try another experiment.\u00a0 I removed the motor from the 9505 controller and replaced it with a 1000 ohm resistor.\u00a0 I still get a spike whenever the voltage switches, and it has the classical RC circuit decay.\u00a0 The initial value is about 60 counts (6.2 mA per count) and it decays to a steady state value of 4 counts (24 mA), which is the expected current with the resistor.\u00a0 I can’t explain why the second peak is positive instead of negative.<\/p>\n

\n
\n
\"Current<\/a>

Current waveform, 25% duty cycle, 1000 ohm resistor<\/p><\/div>\n<\/div>\n<\/div>\n

Next I removed the resistor and tried it with nothing connected as a load.\u00a0 The curve looked almost identical to the previous curve, but it goes to a steady state value of zero, which is no surprise.<\/p>\n

\"Current<\/a>

Current waveform, 25% duty cycle, open circuit<\/p><\/div>\n

My final test for the day was to use a 150 ohm resistor to get a larger steady state current.\u00a0 In this case, I noticed the peak still starts at 60 counts but decays to the expected steady state value.\u00a0 It does weird things when it switches back to zero volts that I can’t explain.<\/p>\n

\"Current<\/a>

Current waveform, 25% duty cycle, 150 ohm resistor<\/p><\/div>\n

It appears for resistive loads the current always starts at 60 counts and decays to the expected steady state value.\u00a0 I do wonder what would happen if the steady state value was greater than 60 counts.\u00a0 From the decay curves, I figured out that the time constant for the decay is about 1000 ns or 1 us.\u00a0 I also noticed a third small spike just before 2000 counts.\u00a0 It looks to me like the circuit disconnects from one source about 30 counts before connecting to the other source.<\/p>\n

I noticed in the 9505 manual that the minimum inductance is 500 uH.\u00a0 I assume my motor’s inductance is much lower than this.\u00a0 My current plan is to buy a 500 uH inductor and put it in series with the motor.\u00a0 It will smooth out the current to a triangular waveform that can be measured predictably.\u00a0 The only negative effect I foresee is that it will also filter changes in voltage and delay the response of the motor.\u00a0 The delay may not be large enough to worry about, though.\u00a0 I might also get a smaller inductor, about 250 uH, to try out as an intermediate step – less smoothing but less delay.<\/p>\n","protected":false},"excerpt":{"rendered":"

I decided to try another experiment.\u00a0 I removed the motor from the 9505 controller and replaced it with a 1000 ohm resistor.\u00a0 I still get a spike whenever the voltage switches, and it has the classical RC circuit decay.\u00a0 The initial value is about 60 counts (6.2 mA per count) and it decays to a […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[4],"tags":[],"class_list":["post-118","post","type-post","status-publish","format-standard","hentry","category-software"],"_links":{"self":[{"href":"https:\/\/ammonsengineering.com\/blog\/wp-json\/wp\/v2\/posts\/118","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/ammonsengineering.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/ammonsengineering.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/ammonsengineering.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/ammonsengineering.com\/blog\/wp-json\/wp\/v2\/comments?post=118"}],"version-history":[{"count":8,"href":"https:\/\/ammonsengineering.com\/blog\/wp-json\/wp\/v2\/posts\/118\/revisions"}],"predecessor-version":[{"id":119,"href":"https:\/\/ammonsengineering.com\/blog\/wp-json\/wp\/v2\/posts\/118\/revisions\/119"}],"wp:attachment":[{"href":"https:\/\/ammonsengineering.com\/blog\/wp-json\/wp\/v2\/media?parent=118"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/ammonsengineering.com\/blog\/wp-json\/wp\/v2\/categories?post=118"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/ammonsengineering.com\/blog\/wp-json\/wp\/v2\/tags?post=118"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}