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Old 05-30-2013, 08:34 AM   #226
craftycoder OP
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Originally Posted by genka View Post
I'm watching this thread with amazement and excitement. I've never seen a product development shared in such detail!
I don't think that inclusion of constant current LED driver will have much practical use- it would be interesting only for someone building lights at home, as all commercially available ones come a with built-in driver.
It would be more interesting to have a high current USB charging ports compatible with Apple and Android. I think Android needs 200 Ohm between data pins to switch to high current mode, and Apple uses something else.
I do not dispute your suggestions. I too think the constant current drivers are of limited value but the overall cost to add a pair is rather small and for some it will hugely valuable. I also agree that USB changing would be handy. The issue with USB ports is that they are NOT rugged and I want this device to submersible and mud and dust friendly. So, you will be relegated to wiring a automobile style 5V charger directly to this device. The good news is that when Apple and Samsung change their high current resistor dividers to new values, the PDU won't be broken.
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Old 06-03-2013, 08:40 AM   #227
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36A
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Old 06-03-2013, 10:22 AM   #228
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I've worked on my transient generator some. It can now generate a 240V swing in 20 nano seconds (the green trace below). The yellow trace is the output protected by a clamping diode. It was able to tame it down to 26V. That is not quite good enough (I'd prefer that be below 20V) but I've got new Transzorbs coming in the mail which will hopefully take a bit more of the edge off that peak. Assuming that peak is generated by an inductive kick because of a low side disconnection (which it was in this case), that 26V represents a only a 13V spike across the MOSFET which is actually just fine and well within spec. In other words, while I am not satisfied the current protection does appear adequate.

I'd like to get a some better test gear but until I do, my home made stuff will have to do.

Transient trace

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Old 06-03-2013, 09:22 PM   #229
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Originally Posted by craftycoder View Post
Next prototype PCB order is going in tonight. These should be fully protected and ready for use in a vehicle. They should be here in a few weeks and will be built up within a month. These ones will be epoxy potted to confirm the radios work when the devices are rendered waterproof.
Yup, I'll get in line for one! Screw adding an ordinary fuse block when Spock has beamed us this gem from Nebulon 4... :)

You're a rockstar, crafty! I'd throw my underwear at you, but I suspect cash might be more appropriate...
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Old 06-05-2013, 10:05 AM   #230
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I added a system temperature sensor to the gizmo last night (notice the 34C below system voltage). It will tell us the current temperature of the PDU. This is useful (for testing purposes at least) as it will let us know if we are cooking the electronics by running too much power through the device. I do not expect any issues, but I really want to make sure the device is robust and these sorts of details help ensure we get many years of reliable service.
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Old 06-07-2013, 10:50 AM   #231
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Temperature testing

With the new access to temperature sensor data from the PDU, I embarked on a study of the PDU's temperature characteristics. This is important to understand because the temperature of the silicon affects how the circuits behave. It is especially critical for the ADCs (analog to digital converters) which are used to measure current flow. Essentially all the bits and bobs placed on the PCB (printed circuit board) will behave differently based on their temperature though. Characterizing the temperature movements therefore will help inform the maximum currents we can work with and how the final enclosure will have to be designed to handle the expected temperatures.

The PDU was designed to keep the heat creating parts away from the logic circuitry. You may recall that the design is two PCBs stacked together but separated by about 17mm (.65").


The power FETs (field effect transistors) are on the bottom board and all the logic is on the top board. The FETs are what directly control the current flow and are where the majority of the heat is expected to be "created". The FETs are sensitive to temperature as well but I selected rather expensive FETs that can each handle up to 100A continuous current and 1400A peak current and I am limiting them to 15A each (some 85A below their maximum continuous figure). In this configuration they are dropping a maximum of ~225mW of power @ 15A. If all the FETs were dropping this amount of power (not possible because I've set the total current to 100A and 8*15A = 120A) it still represents only 1.8W. You should all be relatively well familiar with that it feels like to hold something burning ~2W in your hand as that is about the same as the amount of power used to transmit voice over with a cell phone. It gets a little warm but that's about it. There is another source of heat on the power PCB, the resistance of the copper on the board to the currents flowing. The current goes in on one side and flows across the board to the get to the farthest FETs. This is not necessarily a small amount of heat and must be managed. I solve this problem by using thick copper on the PCB as well as busbar (a big chuck of copper) to further reduce the resistance across the board. The thickness of the PCB is equal to 9 AWG wire and the busbar is equal to another 4 AWG wire. Combined they are just over 26mm of copper conductor moving current across the board which is roughly equal to 3 AWG wire. The power conversion there is (0.06465mΩ/meter * 2") * 100A and equals ~320mW. That adds to the 1.8W above and still places us comfortably with cell phones in the 2W realm. By the numbers, things are looking fine but nothing replaces a good lab test so lets see how that went.

I performed a "controlled" test so I could get a measure of the heat transferred from the power PCB to the MCU (micro controller unit) where the temp sensor resides and the heat generated on the logic board itself where the MCU is. The first test I performed was to run 30A (about the most I can do with my current lab power supply) through the board until we achieved homeostasis of temperature. It took about 30 minutes for the temp stop climbing but I let it sit for an hour to confirm it was done warming. It raised 10C above room temp (the starting point). That figure is affected by the test conditions somewhat. A relatively significant issue is that the loads are within 10" the PDU and they are radiating a lot of heat, ~375W. The power supply is also blowing all of its heat in the general direction of the PDU via it's cooling fan. I used two sheets of copier paper folded over the PDU to protect it from directly radiating heat of the bulbs (I made shade ) but that does little to ameliorate the heat moving around the PDU from the two cooling fans blowing heat around from the power supply and the giant .6Ω load and it's cooling fan. Taking all that into account, the numbers are still quite encouraging. Of course, a test cannot be "controlled" without a control test so lets discuss that one. The control test was running the PDU with no load until we achieved homeostasis of temperature. I again let is sit running for an hour but turned all the outputs off. The power supply was still blowing it's warm air but as it was doing less it would have been running cooler than the previous test, there was no radiant heat coming from the bulbs though as they were not on. In this test the it raised 5C above room temp. To me, this means that the 30A from the previous test accounted for only 5C of the 10C shift. So, what is responsible for the other 5C? Well, I suspect most of that is the switch mode power supply which is converting the 12V DC to 3.3V DC to run the electronics. All the logic electronics do consumer power too so they all contribute a little to that total as well. I logic board is burning about 330mW when on but not driving any loads and 375mW when driving the 30A so that by itself contributes about .66C of the 5C. The heat contribution of the power PCB while sourcing 30A therefore is responsible for 4.33C. Assuming this is a linear function (a huge assumption that SHOULD NOT BE MADE) at 100A the power PCB will contribute 14.5C to the system at 100A while the logic board will contribute about 6.5C to the mix for a total of 21C at 100A (with the poor assumption that the power board's contribution is linear). These numbers are all relative to the board sitting on my bench in relatively still air and not encapsulated. The epoxy used for encapsulation can actually improve the thermal characteristics. The actual numbers at 100A will require further testing which is waiting on the new boards and a new power supply (a Jeep in this case).
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Old 06-07-2013, 12:41 PM   #232
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Does this schematic make sense to y'all?...
Yes, it does
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Old 06-08-2013, 12:18 PM   #233
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just burned another $1000

Another big order of parts and tools has gone in. This time I've put just over $1000 on the AMEX. We will be building 5 new prototype units for testing on various types of vehicles. I'm cautiously optimistic that we will have something darn near ready to manufacture.

In the mean time Lonestrom is busy working on the Kickstarter resources so we can get that going on. We are running a bit behind schedule at this point. He and I have other businesses that we run and they are unfortunately intruding on our ability to get this project up on Kickstarter. I assure you I am burning the midnight oil on the engineering side of this project though and as soon as we get the video and website finished up we will be ready to open this up for 200 lucky people to be the first to try out our PDU for themselves.

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Old 06-09-2013, 06:35 AM   #234
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What's going to be the process for those lucky 200? This forum? Kick starter?

So excited about this!

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Old 06-09-2013, 10:28 AM   #235
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Originally Posted by craftycoder View Post
Another big order of parts and tools has gone in. This time I've put just over $1000 on the AMEX. We will be building 5 new prototype units for testing on various types of vehicles. I'm cautiously optimistic that we will have something darn near ready to manufacture.

In the mean time Lonestrom is busy working on the Kickstarter resources so we can get that going on. We are running a bit behind schedule at this point. He and I have other businesses that we run and they are unfortunately intruding on our ability to get this project up on Kickstarter. I assure you I am burning the midnight oil on the engineering side of this project though and as soon as we get the video and website finished up we will be ready to open this up for 200 lucky people to be the first to try out our PDU for themselves.

I have been lurking for quite a while on this thread. I will be buying in when the kickstarter kicks off. Can't wait. Just wish it was before I left on my TAT adventure on the 19th... Got a fuze box in there now... Can't wait to swap it out...
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Old 06-09-2013, 10:33 AM   #236
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I have been lurking for quite a while on this thread. I will be buying in when the kickstarter kicks off. Can't wait. Just wish it was before I left on my TAT adventure on the 19th... Got a fuze box in there now... Can't wait to swap it out...
Have fun on the TAT. Sounds awesome!
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Old 06-12-2013, 08:26 AM   #237
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PWM Modulation

I've added PWM modulation to each output channel. You might use this for daytime running lights as vehicles are more visible when their headlight is oscillating in brightness during the day. I'm sure there are tons of other uses as well, that is just one idea.

The process to use this function is to go to the output setup screen for a given channel and turn on the modulation by selecting the "Slow" or "Fast" button and then adjusting the lower bound of the PWM modulation. The upper bound is the main PWM slider at the top of the setup screen.



Output Setup Screen
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Old 06-12-2013, 08:29 AM   #238
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I am really excited to see this on Kickstarter
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Old 06-12-2013, 02:16 PM   #239
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The new power supply has arrived that I will use for testing. It is a 60A 13.8V current source. I've added a bunch of 100A diodes in series with it so that I can fake an ignition signal. The diodes should drop about 1.4V when the current goes through them so that it appears the device is on a battery and when I turn that red key I short the diodes out and it delivers the full 13.8V simulating the voltage delivered form the alternator.
This is helpful because the PDU can trigger actions based on this transition from 12V to 13.8V and back.

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Old 06-12-2013, 02:24 PM   #240
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You've done a lot of temp testing in open air- isn't the device going to be sealed into a container (if not potted)? I wouldn't expect disastrous results, but I'd expect some change from open air testing.
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