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Old Jun 01, 2003, 05:17 PM
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East Sussex UK
Joined Jul 2002
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400 Amps From SCR's and 500 size motors !!!!

I was in my LHS today and one of my sons was looking at the RC Car controllers, he asks the man behind the counter which is the cheapest. He points to one and says that one adding it will only do down to a 17 turn motor. How many amps is that, says I.

70 comes the reply. When I can speak coherently again I ask how many amps do they go up to then.

That one will do 400 comes the reply as he points to one on the end of the shelf. From SCR's I enquire. Yes comes the reply. How long do they last I ask.

About 15 minutes comes the reply. That explained it I thought 1 charge and 1 run! and Bang!. But you can recharge them a thousand times or more he added.

Surley they can't be drawing that kind of current from SCR's and what are those buggy motors made of?

Can anyone out there explain
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Old Jun 01, 2003, 06:14 PM
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San Diego, CA, USA
Joined Mar 2001
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It's marketing baloney.

If they were drawing 70A from 2400mAh cells, the'd only run for a maximum of about 2 minutes, assuming 100% efficiency and assuming that you really get the rated capacity at that current. Neither one of which is going to happen.

400A, if nothing else melted, would drain the same cells in about 20 seconds. Of course, this is impossible because the cells just won't deliver any significant voltage under that kind of load. Oh, and they'd vent and start leaking their guts.

The FETs are what the car ESC ratings are based on... and even there it's a joke. They ignore the rest of the controller. The best RC car controllers for brushed motors are only good for about 40-70A continuous.

-David
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Old Jun 01, 2003, 06:14 PM
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Bundaberg, Qld, Australia
Joined Jun 2002
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Methinks he knows not of what he speaks.
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Old Jun 01, 2003, 08:48 PM
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Joined Aug 1999
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F5B's pull 100 amps for 2-3 seconds, for just a few bursts to climb.

They maybe stating up the startup amps that only last a few miliseconds.
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Old Jun 01, 2003, 09:25 PM
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United States, MA, Cambridge
Joined Jul 2002
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Startup amps mean nothing....
Startup amps on a plane are just as insignificant.

George
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Old Jun 02, 2003, 03:50 AM
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N. Staffs, UK
Joined Jan 1997
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As davidfee says, car controllers are typically rated at a theoretical current based on what the output devices WOULD stand if you had them on an infinite heatshink and the current lasted no more than 1/1000th of a second. Don't ask me why.

If you divide by somewhere around 5 to 8 you'll get the real constant current rating which is used for aircraft controllers. I'd guess the "70A" controller at around 15A and the "400A" at around 50-60A.

Steve
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Old Jun 02, 2003, 04:06 AM
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Mostly in Norman, OK
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Just about everything in R/C cars is over-hyped and over-prices fwiw ...
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Old Jun 02, 2003, 02:42 PM
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East Sussex UK
Joined Jul 2002
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Ah Ha!

This all makes sense now. I always thought those R/C car guys talked out their exhaust pipes.

Thanks for the replys
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