Author Topic: Power Boards  (Read 1438 times)

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Offline lucTopic starter

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Power Boards
« on: April 17, 2014, 09:03:26 PM »
Hey guys,

Would any of you have suggestions / resources that would help me build a power board for a robot Im trying to build?
It'll need to power the following:

Raspberry Pi
Dual Channel Serial Motor Controllers (2)
Servos (4)

Also, a problem in the past when trying to implement this bot was that the servos were immediately going to stall when a signal was sent to them.  The stall current is 1.5A, I believe.  What could I do to perhaps 'disconnect them' if they start to pull this much current?

Offline waltr

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Re: Power Boards
« Reply #1 on: April 18, 2014, 07:25:31 AM »
What will be the power source?
AC Mains?

For servo power use a separate PS that has enough current capacity for all the servos.
For protection a self resettable fuze does work but it will take some time to reset.

The R-Pi and Arduino could use linear regulator chips (7805 type) or switching regulators (Pololu and other haves these). Again ensure that the regulator has enough current capacity plus some for the devices being powered. And if you use a linear regulator ensure to have enough heat sinking.

Offline jwatte

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Re: Power Boards
« Reply #2 on: April 18, 2014, 10:40:13 AM »
If your servos are stalling, then they are not sufficiently specified to do the work they're intended to do. If you cut them off, they will not be able to hold the load.
If that is what you want to do, then you can try:
1) A 1.5A slow-blow fuse.
2) A 1.5A trip-point resettable PTC fuse.
3) A current sensor and a switch/relay of some sort.

The problem with 1) and 2) is that they are not particularly precise, and they are ambient temperature and duty cycle sensitive. Pololu has some nice current sensors for 3) based on the ACS line of Hall effect sensors. Like this one:
Read it with a microcontroller, and use a relay or power MOSFET to cut the power.


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