SciCan Bravo sterilizer poorly engineered, using underrated components. - Page 1
Forum section: electronics / general

author: inertg
author_rank: Contributor
timestamp: March 03, 2020, 12:00:04 am
content: We have 2 sterilizers in our office with the 120V Scican Bravo 21 blowing a fuse once in a whilehttps://www.scican.com/products/autoclaves/bravo/. A year ago, I noticed that the intake wire connected to the fuse has burnt insulation and part of the fuse housing was calcined so proceeded to replace that section of wire along with a new spade connector and fuse housing.After a few months, the glass fuse started blowing again. On inspection, the plastic sleeve covering the spade connector is melted and when I touched the wire at the entrance fuse, it was hot again, with the Infra Red thermometer showing 125.7C at the highest.Since it would be too much of a coincidence that resistance started to develop again at the wire/fuse connector junction, I checked the specifications label in the back of the machine and was surprised that its current consumption is 15A but it only has a 15 A fuse.Since we also have 230V Bravo 17, I also check its back label to observe that it draws 10A but has a fuse of 15A, giving it a 5A margin.So I wondered is there any reason why the manufacturer did not leave any operating margin for Bravo 21, or perhaps there is a typo and sterilizer does not consume 15A as indicated since there should be a margin between the overcurrent protective device and power consumed according tohttps://www.socfuse.com/technical-info-data/3509/.A digital clamp style ammeter was purchased and put to use as soon as it arrived: there is no mistake; inrush current is 14.98A leveling down to 11.3A during warm up.Since the meter does not provide a graph of current vs. time, a Hantek CC-65 oscilloscope current clamp was attached to the input wire so a graph of current consumption vs time could be recorded and the calculations showed max current of 15.83A during Bowie Dick test while the sterilization cycles hover around 15.25A. The power cord to the machine is 3X14AWG, which according tohttps://en.wikipedia.org/wiki/American_wire_gaugecan carry 15A if the insulation material can resist at 60C but according tohttps://www.electriciantalk.com/f5/14-awg-allowable-ampacity-1137/should not have a fuse higher than 15A. So the fuse keeps blowing occasionally and the copper wiring is hot because the machine once in a while has abnormal current higher than 15A and runs at or higher than its operational envelope. I do remember that dental supply companies recommend staying away from the any Bravo sterilizer using 110V like the plague but I assume never investigated why it failed so often.My question to those of you who are power engineers, did I miss something? If I didn't, how can such expensive equipment pass CSA inspection with underrated components installed?

author: inertg
author_rank: Contributor
timestamp: March 03, 2020, 12:45:30 am
content: Current draw during Bowie Dick cycle with Hantek CC-65 current clamp set at 1mv/100mACurrent draw during Wrapped sterilization cycle with Hantek CC-65 set at 1mv/100mANote that conversion from pk-pk volts to RMS Amps using sine wave assumption doesn't work because the wave is atypical.For calculations, I observed the momentary pk-pk volts and the corresponding amps in the ammeter to have 432mv=10.83A. From that, I calculated max amps in Bowie Dick cycle is 15.83A (yup, the fuse blows most often in this cycle) while max amps in wrapped sterilization cycle is according to the scope 11.7A although the ammeter shows that in some conditions the wrapped sterilization cycle does reach 15.25A.Note that the clamp ammeter has a max and min recording function but it goes into auto shutdown mode after a short time, too short to monitor a whole cycle.

author: Cyberdragon
author_rank: Super Contributor
timestamp: March 03, 2020, 02:27:01 am
content: My guess is they found some BS loophole in rating about how long it runs for, but does not seem like that would pass (not sure about Canadian code, assuming similar to the US). It should be a 20A plug and fuse with a min of 12AWG wiring and I recommend upgrading it to that otherwise DO NOT OPERATE.(Diodegonewild stamp)DODGEY

author: inertg
author_rank: Contributor
timestamp: March 03, 2020, 04:42:40 am
content: That is what I did: change the power intake wire to 12AWG, the fuse holder, and the fuse to 20A. The whole exercise was to check if there is something faulty in the sterilizer to make it consume more than the rated power or if there is anything abnormal since it would be the first excuse that the manufacturer would give.It has been working fine since.