Feel the POWER!

November 19, 2013 in 8 Channel PDU by Joshua Oster-Morris

I ordered this absolutely incredible Electronic DC load from eBay a few days ago. It arrived an hour ago. The purpose of this device is to consume power fed to it by the Motobrain. It will eat 2500W of power with any mix of 80V and 500A while staying under 2500W. Motobrain is speced at 100A and 14V (aka 1400W) so this is perfect. I test drove it a few minutes ago with great affect. After spending the last year suffering inadequate load testing tools it is absolutely outstanding to have some professional tools to do this task. I need a better power supply now. That unfortunately requires a new electric service in my office so I am working on finding a better lab space with 3 phase power available.

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Thermal Tests (with images)

November 14, 2013 in 8 Channel PDU by Joshua Oster-Morris

I received the thermal imaging camera yesterday and went about doing my first thermal survey of the Motobrain this morning. In this test, I let the Motobrain draw about 40A for an hour and then took some thermal photos of it. What I found surprised me. I assumed the warmest part of the circuit would be the switching transistors that all the current is flowing through. This is not the case however. It turns out the hottest part of the circuit are the MOSFET drivers which use a charge pump to create 20V+ and are used to turn the MOSFETs on and off. After an hour the drivers are running at about 37C as you can tell from the top photo below (the cross hair is on the driver chip). The second photo shows the bottom of the power board which is the board that has all the current flowing through it. The warmest part of it is <32C after an hour (this board is thermally coupled on both sides so the top and bottom should be roughly the same temp). That is not very exciting at all. That is hardly even warm. Great news for Motobrain! The third photo shows Motobrain against the backdrop of the test jig. It is the coolest thing in the frame essentially. I promise, all the 40A of current driving those loads in the background are running through the Motobrain but its impedance is so darn low it doesn’t break a sweat.

FLIR0011

FLIR0013

FLIR0010

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iOS 7 Interface for Analog Inputs

November 13, 2013 in 8 Channel PDU, Tutorial by Joshua Oster-Morris

I wrapped up the important parts of the analog input software last night. I am pleased with everything. It’s always tough to design a UI that can provide good situational awareness at a glance and adding analog inputs made that an even harder proposition. I think the little faux knobs I am rendering do the business.

Analog Inputs

November 10, 2013 in 8 Channel PDU by Joshua Oster-Morris

I’ve completed most of the firmware for the analog inputs. They work great. All the digital input functions remain and more can be implemented. The new analog input functions are as follows.

  • Standard Analog Input
    • User selects 1 or more outputs
    • User sets a low voltage threshold and PWM duty cycle for an input below that level
    • User sets a high voltage threshold and PWM duty cycle for an input above that level
    • User sets a PWM duty cycle for an input between the two thresholds
  • Linear Potentiometer
    • User selects 1 or more outputs
    • User sets a low voltage threshold and PWM duty cycle for an input below that level
    • User sets a high voltage threshold and PWM duty cycle for an input above that level
    • The PWM duty cycle for the selected outputs scale linearly between the low PWM value and high PWM value with respect to the low and high voltage threshold
  • Logarithmic Potentiometer
    • User selects 1 or more outputs
    • User sets a low voltage threshold and PWM duty cycle for an input below that level
    • User sets a high voltage threshold and PWM duty cycle for an input above that level
    • The PWM duty cycle for the selected outputs scale logarithmicly between the low PWM value and high PWM value with respect to the low and high voltage threshold


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Analog Input Testing

November 6, 2013 in 8 Channel PDU by Joshua Oster-Morris

The analog inputs work perfectly and are currently able to completely replace the digital inputs I was using before. They also will allow much more complex features I have not yet implemented but can imagine. Things like knobs for dimming lights and controlling loads with temperature or light sensors among many other cool ideas.

So far, this new board has worked exactly according to plan. I am stoked!

The next step is to create all the new analog functions and update the iOS software to support those functions. Once I am happy with that, I’ll redesign the boards one more time adding 4 more analog inputs and completely removing the digital input circuitry which is officially deprecated now. I’ll take that opportunity to reconsider the physical layout as well. I am considering a waterproof plug for all the low current IO. It should make the product quite a bit better looking.

new IO interface

New board testing

November 5, 2013 in 8 Channel PDU by Joshua Oster-Morris

I’ve been out of town on business for a couple weeks. I got back home yesterday and this evening was finally able to program the new board. I always like to start slow with my testing because with the current this device can push a fire is always a possibility if something is not right. An hour into the testing is telling me that it is time to get testing it in earnest. Clearly the new high efficiency power supply is working well (otherwise we’d be dead in the water). I was also able to successfully test the high capacity short circuit without damage to the output devices. Furthermore, the new higher measurable current limit and new output devices are working great too. The next task is to write the analog input software and see how that goes. I’m very excited about the future though! So excited in fact that I just purchased a new thermal imaging camera today to start observing the thermal characteristics of the Motobrain as well. Worst case scenario, the thermal imaging camera is going to provide us with some awesome photos!