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JDronesPermalink Reply by Jani Hirvinen on October 11, 2011 at 5:31am

Capasitor needs to as close as possible to the ESC or your ESC might start behaving badly.

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Permalink Reply by Hardcore on October 11, 2011 at 5:50am

Basically the ESC contains a micro controller and associated circuitry, when the ESC takes a large power hit, the supply rails dip.

This can be a problem since it can cause the micro controllers to see a voltage offset as the internal circuitry tries to catch up with the rest of the power supply, it can be a real big problem for ADC systems as the reference points move about relative to what you are trying to measure.

 

The Capacitor (cap.) is in a location that helps negate these issues,  just sticking a capacitor randomly on a power line, or moving one about can cause serious problems if you do not understand the circuit.

Also be aware that a capacitor is a short until it is charged, so if you just slap a really big capacitor in the wrong place, the initial inrush current can bust a semiconductor.

An example would be where you load a micro controller pin up with a large cap, then remove the battery power. The micro-controller pin is then potentially "reverse-biased" as the capacitor discharges into the rest of the circuit.

I once had to fix a design where the inrush current was 800A for half a cycle (in fact it was limited only by the resistance/inductance of the copper track.

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DeveloperPermalink Reply by Michael Oborne on October 11, 2011 at 5:54am

here is a comment from 2006 i just happen to have on file

“We just received a burnt up BCD 125 with standard sized Sermos (Anderson Powerpole) connectors on them. These are 35 amp connectors and are totally inappropriate for a 125 amp ESC. Let me explain.

The limiting factor in high current applications is the batteries. They really cannot put out anywhere close to 125 amps for any period of time. So their voltage drops and the current they can provide during the on part of the PWM plus drops even further. The capacitors on the end of the ESC make up for the voltage drop during the on part of the pulse. But if the caps get drained we get a condition called ripple current on the battery side which blow the caps (usually by burning the connector wire inside the cap) which then allows ripple through to the FETS which are taken out by the ripple. An inadequate connector on the batter side increases resistance which exacerbates ripple current. Bad batteries and poor plugs take out more high current controllers than any other problem.

How can you tell if the caps are blow? If you don’t get a spark when you plug in your battery the caps are gone, do not run the system. Send the ESC in and we will replace the caps. If this happens more than once go through the battery side of your system, good fresh batteries hot of the charger, large wires on the battery pack and good and not pitted plugs.

The only plugs we recommend on the battery side of these are 6mm bullet plugs, put the female on the battery positive lead the male on the negative so you can’t inadvertently reverse polarity.”

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Permalink Reply by Hardcore on October 11, 2011 at 3:53pm

Yep,

that would be about right. (not sure I like the bit about the spark though, it would infer a very high inrush current), and people......... do not maul your connector ends, they need to be as clean as possible.

Most people/ new electronics engineers  usually look at life in ther own time domain and tend to forget about sub milisecond/microsecond events.

 

The internal resistance of the battery+cabling would be the limiting factor, even if a battery is marked as 2A, you can still get a sub Mili-second pulse into the hundreds of amps, I once saw a car engine started (turned over, with 'D' cells), it is when this massive current starts bouncing about inside a system that you get problems. Electricity does not 'magically' disappear once the switch is off.

 

 

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Permalink Reply by Vincent Mees on October 11, 2011 at 6:49am

What about extending the leads to the cap with 4cm. Then I could put it in the boomarmitself solving my problem.

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Permalink Reply by Hardcore on October 11, 2011 at 3:53pm

You may be ok with this, use a multi strand wire to make the connection(resistors in parallel, ohms law).

and for god sake get the connections the right way round, the E. cap is polarized.

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Permalink Reply by Michael Pursifull on October 11, 2011 at 7:16am

@Michael Oborne and @Hardcore:

you guys say such lovely things. Say more sweet, sweet things in electronics-speak please!  

It's really kind of too bad we cannot "like" comments/replies, the most useful information is usually in a reply, not the original discussion post. Thank you both for sharing.

 

 

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