CIM Motor Capacitors

[theprgramerdude]

Originally Posted by ProgramLuke

We are indeed having issues with communications. We are using all 4 CIMS on our drivetrain but if we don't have a battery that idles around 13V We lose comms if we try to accelerate quickly. What happens is that the Dlink drops out and we have to wait for it to restart to get communications. Are other teams having issues like this and do you have any solutions?

Yes, the solution is to not accelerate so quickly. Motor noise isn't causing the problems you are experiencing, it's safe to say. What's happening is that while trying to accelerate quickly, your send out far too much current to your motors, which results in a massive voltage drop on the system. This voltage drop will cause things like the radio, and possibly Crio, to shut down. You probably either need to instead tell your drivers to be easier on the throttle, implement a software safeguard against reckless behavior, or some combination of the two.

Additionally, partially charged and old batteries just like to exacerbate the problem described above. While a new one may be capable of putting out enough current to keep the voltage sufficiently high, a bad one will surrender.

[Al Skierkiewicz]

Originally Posted by Munter2081

We did the same thing two years ago! We were at the BMR, when a mentor from WildStang help us out.

Me?!?

[DarrinMunter]

Originally Posted by Al Skierkiewicz

Me?!?

It was Raul,
He said that he seen a couple of teams make the same mistake.
Blew us away, because everything was working on the test frame. When we moved everything over to Lunacy robot some how that got changed.

Lesson 1: Move over stuff one thing at a time.
Lesson 2: Take picutes before hand. Use them as a reference.
Lesson 3: Labels! What to where.


You can learn a lot from making mistakes - even more from fixing them.

[Ether]

Originally Posted by theprgramerdude

a new one may be capable of putting out enough current to keep the voltage sufficiently high

A healthy battery can put out enough current to trip the main breaker without browning out the cRIO.

[Al Skierkiewicz]

Originally Posted by Ether

A healthy battery can put out enough current to trip the main breaker without browning out the cRIO.

Not exactly, the Crio power supply on the PD will continue to output 24 volts until the battery voltage falls below ~4.5 volts. The analog jumper in module 1 monitors the battery voltage and when it falls below 5.5 volts, the Crio output is inhibited to allow the battery voltage to rise with no load. Sort of a no-battery backup battery.

[Ether]

Originally Posted by Al Skierkiewicz

Not exactly, the Crio power supply on the PD will continue to output 24 volts until the battery voltage falls below ~4.5 volts. The analog jumper in module 1 monitors the battery voltage and when it falls below 5.5 volts, the Crio output is inhibited to allow the battery voltage to rise with no load. Sort of a no-battery backup battery.

How much current does it take to trip the main breaker.

[theprgramerdude]

Originally Posted by Ether

How much current does it take to trip the main breaker.

A lot. It can withstand 600 amps for a second, if I recall. I'll try to find the curve.

[Al Skierkiewicz]

In a few seconds the main breaker would take ~720 amps to trip. The NP18-12 battery is only speced at 500 amps out into a short circuit at which point (at full charge), it is dropping 5.5 volts just across the internal resistance of the battery ignoring any other losses internal to the battery. 500 amps will drop another volt across the #6 wiring ignoring the resistance of the main breaker, Anderson connector, crimps and terminals.

[Ether]

Originally Posted by Al Skierkiewicz

In a few seconds the main breaker would take ~720 amps to trip.

If you have a link to the spec for that could you post it please.

The NP18-12 battery is only speced at 500 amps out into a short circuit

So it is. Interesting. The 2009 battery spec says 720 amps for 5 seconds.

[bobosalad]

What are you running besides your four cims? Did this problem show up during Duluth? If it did, you guys managed it pretty well. After the communication dropped, were you ever able to get it back?

[ProgramLuke]

We are also using 2 of the smallest banebot's, a window motor, and the compressor.

[Al Skierkiewicz]

The main breaker sheet is on CD already. You just have to search to find it. The actual spec is 600% over current for a few seconds and several minutes at 200%.

[Tristan Lall]

Originally Posted by Ether

If you have a link to the spec for that could you post it please.

The main circuit breaker is Terminal Supply's CB3-SM-120, which is actually a Cooper Bussmann 18X series breaker (probably a 185120F). Their characteristics are here (from the manufacturer, see page 32 printed/34 PDF), or here (directly) or here (for an older spec sheet from FIRST).

According to that diagram, some breakers may last for up to 3 seconds before tripping at 720 A.

[Ether]

Originally Posted by Al Skierkiewicz

The main breaker sheet is on CD already. You just have to search to find it. The actual spec is 600% over current for a few seconds and several minutes at 200%.

The Terminal Supply P/N CB3-SM-120 that AndyMark markets as their P/N am-0282 is spec'd by the manufacturer Cooper Bussman at 440 amps nominal for 5 seconds.



[edit] I see Tristan beat me to it. Nominal 440amps, range 352..528 amps for 5 seconds.[/edit]

[kamocat]

Originally Posted by Ether

The Terminal Supply P/N CB3-SM-120 that AndyMark markets as their P/N am-0282 is spec'd by the manufacturer Cooper Bussman at 440 amps nominal for 5 seconds.



[edit] I see Tristan beat me to it. Nominal 440amps, range 352..528 amps for 5 seconds.[/edit]

Does this alarm anyone?

We're using this thing as a switch, not a breaker.