Prop 2 getting hot

[GOT]

I was suprised at how hot my prop 2 got with just a few minutes of use (specifically, the JC79RC chip at the top.  I had it connected to 2 servos through pin 3, 5 LEDs on pin 4 and 20 LEDs through OUT 5.  I was using the standard 12V 1000 amp wall wart to power it and the ON switch was in position 2.  No other power sources were connected.  Within 2-3 minutes, it got hot enough that I could not keep my finger on it.  Is that normal?  Should I put a heat sink on the chip?

[johnb]

Hi there,
Short answer: something is wrong.   Unplug the power and start over.  This time, measure the current of the individual loads (or calculate them) and sum for a total.  Measuring the current on each load should help you identify the problem.   Start with the Prop-2: disconnect all loads, connect power, and monitor it alone to see if it gets warm unloaded.

The voltage regulator on board is good for about 1000 mA.   Depending on the servos and the mechanical load thereon, you may be approaching that limit already.  With the LEDs, you can re-arrange the series-parallel arrangement such  that the current limit resistor is small and there is only one path of 25mA or so.

If the load on the servos is the cause, let me know off line (jbarrowman@efx-tek.com).  We are working on a new little board that would fix your problem and, in that case, you would serve well as the first Guinea Pig.

John B

[randyaz]

John...your teasing us again...

What have you guys got coming up?

edit:  Ok...Im blind... DC16 update..

[JonnyMac]

If you're powering you LEDs from the TTL connections you can move them to the OUTx terminals to reduce the strain on the regulator.

[GOT]

I did a little experimentation.  It's not the LEDs, it's the servos.  I have two Hitec HS-425BB servos attached to one pin with a Y-connector.  If I have only those connected, the chip gets hot.  I wouldn't think two servos would be a problem.

[JonnyMac]

Yeah, that's a problem.  As JB pointed out we're working on a little something a alleviate the load that servos can put on the DC regulator.  Lots of folks getting creative with servos, so we're getting a little create with an power add-on.  We've measured run-of-the-mill servos at up to almost half an amp each so two on the 5v supply could really warm things up.

[GOT]

Would there be a difference between a servo operating with a load vs. one with no load.  I hooked up two different servos (without a load) and they work fine without any heating up.

[JonnyMac]

It does make a difference, and the position is a factor.  In tests that Parallax ran a long time ago it seem like the closer the servo was to the center value (without being dead on center) the higher the current load.  The results were not intuitive which is why a test fixture was built and the test conducted in the first place.

[GOT]

Ya, I just did a test and the load does matter.  I need these servos for just about one minute then they can rest for about five.  Any suggestions?  Will heat-sinking work or do I run the possibility of burining out my prop 2?

[JonnyMac]

You know, in the heat of Halloween I wouldn't take a chance.  We are working on a solution and will let you beta test it for us.  Please send message to our normal e-mail so that we can send that solution to you (and others that we had previously identified).

[GOT]

Which e-mail is that?  Would it help to split them to two pins?  The thing is I want them to operate simultaneously. (This sucks because the decending elevator effect I am working on looks great, until it catches fire).

[JonnyMac]

teamefx at efx dash tek dot com

Like you, we don't want your Prop-2 going up in flames.