Battery operated robot design is being sabotaged?...deliberate noise issues - Page 1
Forum section: electronics / general

author: zenerbjt
author_rank: Regular Contributor
timestamp: September 20, 2020, 09:50:28 pm
content: Dear Engineers,We think our contractor is trying to sabotage our 48V Battery operated robot design.We have a little 3W SMPS LED driver board with LEDs on it. Its three MIC2287 Boost LED drivers. He has put no inductance at all in the input filter to this…....just capacitance.The LED driver board has a 15cm twisted pair cable feeding it as attached.We feel that this cable will radiate and interfere with other operation on the robot. Would you agree?

author: Daixiwen
author_rank: Frequent Contributor
timestamp: September 22, 2020, 07:12:18 am
content: A badly tuned inductor can do more harm than good by resonating with the capacitor. In most cases a capacitor is enough, and if the drivers are well bypassed they won't inject so much noise on the cable.A twister pair cable radiates less than a non twisted one.Does your contractor perform the EMC testing or takes responsibility in case of failure? Which EMC requirements did you give them?

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: September 22, 2020, 08:50:52 am
content: no

author: dmills
author_rank: Super Contributor
timestamp: September 22, 2020, 11:38:33 am
content: Treez, nobody working as a contractor deliberately sabotages products.It is a good way to get a bad rep (And no contractor needs that).What spec for RFI did you give the contractor? And does what they came up with meet that spec?This is the nice thing about using contractors, with decent ones you give them a spec, check they met it and can otherwise treat the results as a black box, if there is a problem it is because either your spec was inadequate or the contractor screwed up (Not that uncommon actually).Now there ARE some very poor contractors out there, I have had shocking (literally) work from one or two, but that is incompetence rather then malice (For all that sufficient incompetence can make you wonder sometimes).

author: Doctorandus_P
author_rank: Super Contributor
timestamp: September 22, 2020, 02:36:01 pm
content: Suggesting malice, based on your "feelings" alone, with apparently no fault seen yet, nor anomalies measured.The only solution is to do everything yourself.Start by digging a hole in the ground (with your bare hands of course) to get to the resources to make your electronics. Chips are made of sillicon, which is just ordinary sand so it should be easy.Also, in addition to Daixiwen's post:For any decent review, the whole system must be taken into consideration. Not just some cable and whether there is an inductor somewhere on the PCB. It just don't mean much.A little deeper, still simplified:If your led driver has an inductor, then (at high frequencies) the current through the inductor is sort of constant.Some part of the time the inductor is connected to the power supply (and current increases a bit), at other times the inductor is connected to the LED, where it dumps that current (and energy)When the inductor is connected to the filter capacitor, then the capacitor deliveres most of the current to the inductor. When the inductor is connected to the LED, then the input filter capacitor recharges from the current from the main supply. Total result is that the current through your cable to the LED driver already is near DC. More filtering probably is not needed. If you really want / need to add an extra RLC filter, then make sure it's Q is low enough to prevent oscillations.I am of opinion that any uC should have some kind of inductor or ferrite core in it's power supply. I've had too many problems with a simple wallwart to a breadboard or matrix board with a uC in the past to ever skip this step for non trivial applications.

author: tom66
author_rank: Super Contributor
timestamp: September 22, 2020, 09:09:23 pm
content: Is zenerbjt the new treez?

author: Gyro
author_rank: Super Contributor
timestamp: September 22, 2020, 09:31:02 pm
content: No, he's the old one.

author: janoc
author_rank: Super Contributor
timestamp: September 22, 2020, 09:42:15 pm
content: Quote from: zenerbjt on September 20, 2020, 09:50:28 pmHanlon's razor:"Never attribute to malice that which is adequately explained by stupidity."I will only add the latter part may not apply only to that contractor in this case. Why don't you effin' measure whether it actually interferes or not and whether the extra choke is actually needed before accusing someone of sabotage? Do you really want to get sued for libel so badly? If your contractor is serious and sees this thread I am sure they will be totally amused and won't send you packing, along with your entire project.Seriously, you have to be a real pleasure to work with.