110V AC to 12V DC suggestion

[Gdeaver]

If one looks back at the problems the tan jag had. One of them was that running them on a stiff bench power supply would kill them fast. While the BLDC24 is more rugged all motor controllers can be damaged by running them on a ac to dc switching power supply. The problem is the switching transients and back EMF can cause the switching regulator to output some high short term voltages that can go above the voltage rating of the controller components. Motor controllers and big motor currents and ac switching power supplies are a bad idea.

[Ether]

FWIW, per the data sheets:

40amp breaker less than 1 second at CIM stall current of 133 amps.

120amp breaker less than 6 seconds at 4x133 amps.



Has anyone ever actually used a scope to measure the inrush current spike on a CIM (both unloaded on the bench and loaded on a drivetrain)?

[Al Skierkiewicz]

I have checked the currents but did not record the data. As I remember, the current spiked as expected and loaded currents were not far from predicted. I used a four motor chassis with one motor on each side providing dynamic loads to the other motor. We connected various values of resistance across the driven motor including a dead short to simulate loading on the driving motors.
From observation, few teams will actually trip any breakers. Several teams appeared to trip the 40 amp breakers this season and a few also reported tripping the main breaker this season. Making some assumptions on wiring designs, the "must hold" data for 250% would likely be the most accurate for general use. From the linked spec sheet that would be 1.8 seconds max.
I would agree with Gary and add that motor start currents would likely trip this supply on over current even with just a single motor.

[ChuckDickerson]

A few years ago when Circuit City was going out of business I snapped up a couple of these power supplies for real cheap:

http://www.audioauthority.com/product_details/978-100

They are 100A 12VDC power supplies and are what places like Circuit City use to run their big car stereo demo boards. Two of these units can be synced together with a simple patch cable to generate 200A of 12VDC.

We have a test station setup in our programmers cave with a CRIO, PD board, digital side car, speed controllers, spikes, motors, and a test pneumatics system, etc. We have one of these Audio Authority 100A power supplies setup to power the test board. It is way overkill but it is what I had handy and works well. We have never needed to connect 2 together for the 200A but have everything to do so if the need arises. It is much more convenient to just flip the power switch on and not need to go get a battery out of the rack (but we can use that option as well if needed).

Given that Circuit City went under, there are a bunch of these things floating around out there in the second hand market. I have seen them on Ebay and Craig’s List.

[Andy A.]

A battery usually is the best answer. If you're willing to invest a little money you can buy a smaller battery that's a little easier to move around. Take a look around on McMaster for lead-acid batteries- there are a variety of options that use the same sort of non-spillable design that the official battery uses, but in smaller capacities/sizes.

The official battery has a 18amp/hr rating. Around 6 amp/hr would probably run a tethered control system and a few small motors for quite some time while being considerably smaller/lighter. Expect to spend somewhere around 30-50 dollars.

You can charge the small batteries using the same chargers you use for the big batteries as long as you can limit the charge rate- 1amp would be the safe limit for most cases. Smaller batteries also have lower safe discharge rates, so trying to run a full size robot could overheat and damage it- so don't do that!

[Ether]

Just a note of clarification so as not to confuse students:

Batteries are rated in ampere-hours, not amperes per hour.

[Richard Wallace]

Originally Posted by Ether

Has anyone ever actually used a scope to measure the inrush current spike on a CIM (both unloaded on the bench and loaded on a drivetrain)?

Come back to the motor lab one afternoon and we can do that. The duration of the spike will naturally depend on the load and the load inertia -- probably just a few milliseconds when the shaft is free.

[Ether]

Originally Posted by Richard

Come back to the motor lab one afternoon and we can do that.

Invitation accepted. I'll contact you to work out the date/time details :-)

[chris.boyle]

We had a similar situation last year. We borrowed a Tripp-Lite PR-60 power supply from my company. We connected it directly to the robot in place of the battery when we were trying to dial in the shooter. I just looked up the PR60 and it costs new for about $282 from Tripp-Lite (http://www.tripplite.com/en/products...txtModelID=244). If you do not need 60 amps, they have smaller power supplies.

[chris.boyle]

Our team did something like this to tune our shooter motors. We used a Tripp-Lite PR-60 power supply I borrowed from work. We connected it directly to the robot in place of the regular battery. We were only running the shooter motors (had the robot up on blocks to prevent any moving) and it worked great.

A new from the manufacturer PR-60 is about $280.
PR-60 Power Supply

If you do not need a 60 amp supply they have a 10 amp for about $80.
PR-10 Power Supply

[Daniel_LaFleur]

Originally Posted by Mk.32

If a CIM is pulling 132amps wouldn't PD 40amp breakers throw? And there is a 120amp breaker, so the robot should never pull more then 120 amps, and if it tires to wouldn't the breaker just kill power?

Those power supplies look like the deal of the decade for high power applications, I might get one to run my battery charging array...

The 40 amp snap action breakers are a thermal device. When the current is high the device heats up, when it gets to s specific temperature it breaks contact. Since it's an automatic resetting breaker, when the temperature cools down it will reengage the contact. The 40 Amp specification is a requirement that it will NOT break contact below that current. Above 40 Amps it WILL break contact, but only after a specified time (at 132 Amps it's just under 1 second).

Do not use the above power supplies to charge batteries. They do not have a current control and do not have an automatic shutoff.