View Full Version : PWM port power
02-17-2003, 07:31 PM
Does any one know how many amps can be safely pulled out of the PWM ports?
02-18-2003, 12:00 AM
Aren't they fused by one of the fuses around the rim ? Don't expect to use them for more than a few Gigawatts, tops.:D
The "Main" fuse, F1, passes 4.0 A, the Aux, F3, is 1.25 A, the other two are only 0.5 A
02-18-2003, 12:39 AM
I seem to recal that the PWM ports supply 25ma each. A speed controller draws 10, so you can saftely run two of of the same pwm port. A servo draws 20, so you can't run two together, or in combination with a victor.
02-18-2003, 07:25 AM
Ok thanks. We wanted 5 volts to run something on our robot but 25 ma is not enough. Are we allowed to drop the voltage in custom circutry to supply us with the 5 volts at like 10 amps?
02-18-2003, 09:00 AM
Yes, you may regulate 12v from the battery to 5v for your custom circuit board (as long as your regulator comes from digikey or FAI, etc, etc)
What do you need to draw 10 amps for, though? Remember that you are only allowed to have the custom circuit board send data back to the robot controller. It can not control a motor directly or anything like that.
02-18-2003, 03:02 PM
The 10 amps is for a custom circuit but I don't think I am allowed to go in to anymore detail then that.
02-18-2003, 08:33 PM
Let's see...5 volts @ 10 amps...50 watts! Can anything be that important in a custom circuit board? Your are not going to find something simple to get you from 12 volts to 5 volts @10 amps. The biggest three terminal voltage regulator is only capable of a three or four amps, the standard 7805 is only an amp and a half. To get 5 volts regulated from the 12 volt supply you have to dump something like 70 watts into heat just to make the conversion. You can use the 7805 to drive a couple of power transistors in parallel but you would get 5.6 volts output.
02-19-2003, 07:50 AM
That is a lot of power I know but it doesn't have to be a persice voltage either. Really any voltage between 5 an 10 is good but it does pull a lot or amps.
02-21-2003, 07:31 AM
In asking about PWM and Amps, you seem to indicate you want to vary a voltage for a HEAVY load.
The PWM outputs on the RC give little pulses every so often, NOT a continuous steady voltage. I haven't checked the timing since the 98 season, but they give an approx 1 ms pulse every, perhaps, 26 ms.
The way to achieve your end is to use a translator that will handle the current, and take the PWM signal and turn it into a voltage level. One such device is currently available to you : it comes from a company called Innovation First, in Texas. It is called a Victor 884. :D It gives square waves with a duty cycle from near zero to 100 % (not a square wave, just continuous 12 V). If your load can take 12 V with an average viltage of your choice (for instance a lamp, but not a portable radar-on-a-chip with a requirement for filtered 5 V dc)) then this is the way to do it. Current reportedly up to 40 amps.
Connect it, and in your program, limit the pwm signal to the maximum you want, and don't go to the other side of 127, if your load is polarity-sensitive.
02-21-2003, 07:44 AM
I forgot that a speed controller voltage probaly perfect to what I want but unfortunaly we have no more.
Really I care about voltage, between 5 and 10, constant at a voltage but other wise I don't care. My main problem is the amps. I have decided that I will not be able to get the power I need from the PWM ports so I am working on a alternate method of getting my power.
02-21-2003, 01:56 PM
If you wish, you can contact me through private message and I will respond. Always glad to help.
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