Computing

Solar Cluster: First power module, partially built

So, I’ve still got to think about how to do the connectors, but so far, this is what the module looks like.

I’ve spaced the MOSFETs apart in case I decide to use physically bigger parts. The schematic looks like this.

Experimenting with the orientation of the PowerPole connectors, yes, you can mount a pair with one rotated 90°, but then it is impossible to configure the mating pair to match that 90° orientation, the rotated connector will always be 180° out.

So there goes that idea. However, I can use a 2D plywood “funnel” to make it impossible to misalign the connectors. The following not-to-scale diagram shows the gist of what I’m thinking of.

Effectively, I have 3 connectors: White represents Source, Green represents the Gate and Yellow represents the Drain of a typical MOSFET. There’s a pull-up to ensure the MOSFET stays OFF unless explicitly pulled low to turn it ON. The three pins wire directly up to where Q2 and Q4 are located.

In the event of magic smoke escape, I can grab a pair of oven mitts (the heat-sink will be hot, right?), grab the heat-sink and pull upwards to release it and disconnect it from the circuit. The process should be idiot proof enough that I should be able to leave instructions for anyone to follow.

Re-installing a module is the reverse process, just align the module and pull down. It’ll click into place and should start operating straight away.

I’m toying with the idea of including a small thermal fuse on the heat-sink to remove the MOSFETs from circuit should they get too hot. Reason being, someone might not be around if the magic smoke does escape, although provided the heat-sink does the job in the load test next weekend, this should be unlikely.

These look like they’ll do what they want. Okay, means I have to settle for 25A instead of 30A… but the charger is only 20A right now anyway. The 30A max rating was chosen based on the capability of the connectors. 25A is “good enough”.

2016/11/05 by Computing Projects Public Syndication Solar-powered Cloud Computing 0

Solar Cluster: Separating concerns

So, my last attempt at a fully integrated power controller was a smouldering failure. Q7 decided it wasn’t happy about where things were going, and let the world know by the only way it knew: smoke signals!

Curiously, only one of the MOSFETs in use seems to be damaged. When we look at its mate on the other side, Q2, sure it’s discoloured, which could be indication that it has been stressed, or maybe it just got burned by the other MOSFET.

It goes without saying that the pair in the background are fine: no current flowed through them during this test.

This got me thinking, did it get too hot, or did something else go wrong? This is the schematic and PCB layout of that part of the board.

Now looking at it, one thing strikes me. Seems I might have the source pins connected back-to-back, not the drain pins. Could that be it? I think I intended it the other way but didn’t pay enough attention to the schematic symbol. This could be a factor, or maybe the other MOSFET might’ve blown instead.

One thing is certain, I cannot join the two tabs together to the same heat-sink like I was intending with this schematic. Mia culpa!

Thinking about the design, the idea of putting the MOSFETs might be a tad naïve, as by far they are going to be the most likely component to fail on the board. The concept of a separate power module would work better since it’s easy then to just rip one out and put another in its place. Designed right, this could even be hot-pluggable, and can incorporate a heat-sink, and can make use of larger or smaller MOSFETs for different applications.

Luckily, the existing board layout will accommodate this just fine. We put 3-pin KK connectors in place of Q2 and Q4, and we can jumper across Q7 and Q8. This means the feed to the battery only needs to be a light-gauge wire, sufficient to power the controller and measure the battery voltage.

The pin-out isn’t ideal for this: it would be better to have a pin connecting to 0V instead of the battery +12V, but it’s workable. The gate pin becomes an open-collector output, and can theoretically drive (low-current) relays or MOSFETs.

As for what to build this power module on? Well, without going and buying a heat-sink, I’m spoiled for choice:

All of these dwarf the TO-220 package transistor I’m using… okay the one shown is an IRF-9540, but it’s still a TO-220 put there for scale reference. Most of these are for Intel CPUs that are long obsolete, and the top right has the CPUs in question still firmly attached.

The Pentium CPU heat-sink/fan would be the closest in the size, I was hoping I might’ve had a 486 heat-sink laying around, I’m of the opinion that if the power module needs a fan on any of these heat sinks, I’m doing it wrong. This might not be the case if I wanted the full 70A capability, but I’m pushing for 30 which is less than 50% capacity.

The only passive ones I have, and happen to have multiple of, are the ones on the lower right, which were extracted from dead Netgear (Bay Networks) switches. The BGA package still stuck to one of them is a Broadcom BCM5308A2KTB Ethernet switch SoC… it talked to a couple of SRAM packages (duly harvested) and a number of Ethernet PHYs.

The thought is that two MOSFETs could be fixed to the underside with a small PCB. (Well okay, there’s room for all four, but then I’ve got to somehow electrically insulate the two pairs.)

A connector of some sort, either a PCB edge connector, or perhaps a specially keyed Andersen Power Pole connector pairs (which can be rotated 90°) could connect power and control in one secure mounting. Two 30A connectors and a 15A would serve this job well, and they come in a range of colours for the housings. Thus I can avoid the red/black typical colouring to avoid confusion.

2016/11/05 by Computing Projects Public Syndication Solar-powered Cloud Computing 0

Solar Cluster: Full load test: FAIL

So, I drag the cluster, battery and 20A charger out to the deck to do a full load test. This is the first time I’ve fired this newly built controller on a full load. Uncharted territory so far.

Here’s the set up.

The charge controller that I built earlier is in a nice shiny re-purposed case that I had laying around. Just the right size too. These were USB extender devices that my father’s workplace had used in a project: they wanted the innards, so we got the empty boxes. I just mounted the PCB on a small piece of plastic to insulate it from the case, and routed my DC leads out through a hole in the case originally intended for an RJ-45 jack.

At this point, everything is humming along fine. Our battery charger is on stand-by.

The meter is showing a sedate 12.4V and the controller is happy with this. That said, I’ll have to work on the visibility of those LEDs. The two on the power MOSFET control lines are off at this stage.

So I give the system a bit of curry. I transfer a copy of a Linux kernel git repository to each, tell them to update their working copies from that, and build a version of kernel v4.8.5. This made the current jump up to about 10A. So far so good, the battery is holding.

Then, about 30 seconds in, the controller decides it’s a bit too low, so it kicks the charger on. There’s a few false starts, as the charger delays its start-up a bit. Eventually though they get into sync and start charging. At this point, the charger is taking the load of the battery and the cluster.

Great. So it continues for a minute, then decides it wants to shut down, which it does, followed by a moment of oscillation. It seems the controller is too impatient for the charger, waiting for the power to come on…but then… what’s that smell???

Oops, guess that MOSFET got just a little too hot. I was hoping to avoid the need for heatsinks by over-dimensioning the MOSFETs. These are supposedly able to take 70A, I realise that’s with a heatsink, but I thought that at 20A, they would be able to handle it.

One somewhat roasted MOSFET says otherwise. Interestingly, only one has visible marks, its mate looks okay, but likely isn’t.

The MOSFETs don’t have to be mounted directly on the PCB, we can re-locate them to where we can squeeze a heatsink in if I can’t get one in between the two already. The thought was each pair have a heatsink in between them. More pondering to do it seems.

2016/10/29 by Computing Projects Public Syndication Solar-powered Cloud Computing 0

Solar Cluster: Light testing of the charge controller

So, late yesterday afternoon, I devised a light test of the controller to see how it would perform.

For this I disconnected all but one of the nodes, and hooked up one of my old 10Ah LiFePO₄ packs and my 3A charger hooked to mains. The LM2576-based charger is just able to hold this load and provide 1A charging current.

The first thing I noticed is that the fan seemed to turn on and off a lot… this could be a difference in the temperature sensors between the DIP version of the ATTiny24A that the prototype used and the SOIC version which the new controller used.

The test ran overnight. The node basically was idling, as were the two Ethernet switches. But, it served the purpose. I now know the logic is sound, although I might want to adjust my set-points a little.

That’s the output data from a small digital power meter that was hooked up in circuit. This device is unable to display negative current, so the points at which the battery was charging is shown as 0A. Left axis is voltage, right is current. You can see that the charger gets brought in when the battery dips below 12V and clicks off just before 13.2V.

I can probably go a little higher than that, maybe about 13.6V. I may also need to re-visit the fixed resistor settings on the linear regs inside the nodes to knock them down a few more pegs to prevent the BMCs whining about the high voltage.

Next weekend, I might consider hooking up the 20A mains charger and giving it a full load test.

2016/10/23 by Computing Projects Public Syndication Solar-powered Cloud Computing 0

Solar Cluster: First charge controller board built

So, I ordered the parts last weekend and over the course of the last week, they arrived, in three dispatches.

Might’ve been cheaper for RS to wait for the lot to arrive, I’d have been happy for them to do that had they asked, but never mind, they all turned up. So today, in clouds of solder smoke out on the back deck, I set to work soldering up the first of these boards.

At first, I just put all the SMD parts on, the programming header, the 5V reg, and the DC input lead. This proved a little fun. When I ordered the parts, I had initially put a lot of resistors, all 0805 size, to fill some of my stock. Then I took some off the list because I was over budget a little. Murphy dictates the ones that you take off are the ones you need.

I had thought I had spares anyway… turns out those were 1206s. And, in a pinch, one can use 1206 size resistors on an 0805 size footprint, or at least the “hand-soldering” variants that Kicad produces. The 10k pull-up resistors used on the MOSFETs and the 47k pull-up on the reset line are all 1206s, and they fit okay.

Had I remembered I had 1206s not 0805s, I’d have used 1206s. They’re a little friendlier to work with.

Lessons:

  • always check the list before hitting the order button!
  • In a pinch, you might be able to squeeze a 1206 onto an 0805 footprint, but don’t bet on it!

The other thing I could have done better would be to nudge the footprint for the 7805 along a little so that the switch-mode alternative part (ROHM BP5293-50) would fit. Better yet would be to not be so darn lazy and actually make a footprint for it. It’s a little cosy, but it snuggles up nicely against the capacitor.

Similarly, slightly bigger holes for the power connectors would help too, although the pins on the MOSFETs aren’t exactly big and they’re supposed to handle 70A. The lead length is short though, so not much resistance, I’ll probably get away with it.

The LEDs also proved a challenge, namely figuring out which way around they went. Most were all Osram CHIPLED parts, had a milky-white lens, and no markings visible on the top (one nondescript marking on the bottom), so it was difficult to tell anode from cathode. I wound up using my electronics kit to supply 4.5V through a 1k resistor out to two wires (a twisted pair from some CAT5e) which I could touch to each side to know which was which.

The one exception was the batch of yellow LEDs I bought, Osram didn’t seem to do the yellow ones so wound up buying Kingbright ones, which featured two green dots showing the cathode (the “bar” end of the schematic symbol). When I run out of the existing stock of red, orange and green LEDs, I’ll get more like these I think as it makes life much easier.

This was shortly after programming, the code running on the board for the first time.

Seeing the LEDs blinking, I disconnected the board and proceeded to fit the remaining through-hole components. The resulting board seems to be making the right noises, turning the fan on and off in response to the internal temperature sensor, and running from a 9V source.

Now I guess I’ll wire up the remaining leads, hook it to DC power and see what happens.

2016/10/22 by Computing Projects Public Syndication Solar-powered Cloud Computing 0

Solar Cluster: Boards Arrived

So, after a couple of email enquiries, the truth is unveiled. As it turns out, Swiss Post send parcels via one or more transit countries which due to a quirk in their tracking UI, may appear as the destination.

Asendia were in touch last night informing me that: “Please kindly note that sometimes tracking website will show the wrong destination. Canada is only the transit country.” Ahh okay, no problem then. Confusing, but that’s fine. 🙂

I know now for later not to panic if it says Canada.

This morning, there was a surprise parcel arrived at work, containing 6 PCBs. Bonus! Guess I had better get the other parts on order. I won’t have them ready for this week end, but I predict much solder smoke in my future next weekend.

2016/10/12 by Computing Projects Public Syndication Solar-powered Cloud Computing 0

Solar Cluster: Getting PCBs made

So a few weeks ago, I gave the charge controller a test, seeing if it in fact reacted in the manner I expected before deciding whether to proceed with the existing prototype or whether I should iterate the design.

In the end, I decided I’d tweak the design and get new boards built. By using SMD parts and a 4-layer board, I was able to shrink my design down to a 5×5cm square, which is relatively inexpensive to have fabricated.

I’ll be getting a few boards which means I can have some spares in case something goes bang or if I want to scale out my battery bank.

The updated design is published in the files section. This also incorporates @K.C. Lee‘s advice regarding back-to-back MOSFETs.

After some fun and games, one PCB fab house telling me to “check my passwords match” (when I know for certain that they did match), and another seemingly ignoring the inner two layers, I settled on a PCB manufacturer (thanks to PCBShopper) and got the boards ordered.

I put down my home address for the billing address and my work address as the delivery address. Both given as being in “Queensland, Australia”.

This is a learning experience for me, I’m used to just drawing my circuit out with a dalo pen, but unfortunately my skills aren’t up to producing a board for SOICs.

They reported that they shipped the boards on the 21st, and had previously estimated about 2-3 weeks for delivery. No problem there.

Just one niggling concern…

Not familiar with Swiss Post procedures, I’d have expected it to show Hong Kong → Australia, but maybe that’s how they do things. I do hope someone didn’t get Queensland, Australia mixed up with Quebec, Canada!

Update: Just been in touch, no the manufacturer didn’t get it mixed up, and it’s the right tracking number. They’re chasing it up with Swiss Post.

2016/09/30 by Computing Projects Public Syndication Solar-powered Cloud Computing 0

Solar Cluster: Load test using the power controller

So, last night I started doing some light testing of the power controller. I installed a 5A fuse and hooked it up to a 10Ah LiFePO₄ battery and a homebrew 3A charger (LM2576-based with a 16V IBM laptop PSU as mains source) set to its maximum voltage (~15V).

The controller came to life and immediately started flashing its “high voltage” and “low temperature” LEDs, indicating that:

  • It thought the temperature was high enough to warrant a fan turning slowly (above ~20°C)
  • It thought the battery voltage was too high for comfort (IPMI complains when the voltage gets much about 13.6V.)

In order to get the battery to discharge, I plugged in an old Icom IC-706MkII G transceiver, set it on receive mode. I didn’t have an antenna attached, so this would have represented a very light load for what would be production use.

The battery started discharging, and after a few tens of minutes, the high voltage warning LED had stopped flashing and instead the “good voltage” LED was staying constantly on. So battery was in a range the controller was happy with.

It was going to take a long time though, for that set to drain a 10Ah battery in receive mode.

This morning, I got out the big guns. I plugged the actual cluster in and fired it up. After about 30 minutes of run time, the battery had drained sufficiently that the charger started flashing the “good voltage” LED, indicating battery was getting low. It had also turned on the MOSFET controlling the charger I had plugged in, and the charger was desperately trying to keep up with the ~5A load that the cluster was drawing. (Did I mention this was a 3A charger?)

So far so good. I powered off the cluster and unplugged it. It continued to let the charger do its job, and after another short while, the battery had regained some charge. It kept the charger on until momentarily, it peaked over the “high voltage” threshold. The “high voltage” LED blinked a few times, then the MOSFET turned off and the “good voltage” LED remained solid.

The battery was sitting at 13V. A little short of my 13.5V set-point, but close enough given it was on a fairly weak charger. So that ATTiny24A is doing exactly what I intended.

Maybe the high set-point could do with some adjustment, or a turn-off delay added (with a separate “high critical” set-point for immediate shut-off), but so far, so good.

It might be worth me getting some PCBs fabricated and shrinking the prototype board down using SMD parts, but this controller works so far.

2016/09/04 by Computing Projects Public Syndication Solar-powered Cloud Computing 0

Solar Cluster: Power controller firmware taking shape

So after a long hiatus, some of it involving some yak shaving (e.g. #Open-source debugWire debugger yes, I’ll get back to that), I managed to get a version of the firmware together for the power controller that seems to be doing what I ask of it.

The means of overcoming the road block was knocking up a very crude (and slow!) UART driver so I could print data out on the serial port. I avoided doing this previously because I didn’t have an easy way to interface to a TTL serial port. Recently though, I bought some FTDI serial cables, one 5V and one 3.3V, so now I had little excuse.

I feel these will give me some valuable insights into tacking the debugWire project.

I was able though, to bit-bang a UART using avr-libc’s _delay_us, and get a respectable 4800 baud serial stream out. This obviously dropped to 300 baud when I had other tasks running, but still, that’s enough to do what I’m after. (Once upon a time, that was considered fast!)

After figuring out where I was going wrong… perhaps I had been sniffing too much solder smoke that day… I re-wrote my firmware, using this UART library as a means of debugging the code. I set up Timer1 to run at 1.2kHz, which meant I could also use it as a baud rate generator for my software UART and upping the baud rate to 1200bps.

Some further work on a breadboard, and I had more-or-less working firmware.

I’ve thrown the code up on GitHub, it’s very much in a raw state, and I might do a second revision of the PCB, since this prototype seems to be more or less on the money now.

2016/09/03 by Computing Projects Public Syndication Solar-powered Cloud Computing 0

Song-book for the spy agencies

Seems spying on citizens is the new black these days, most government “intelligence” agencies are at it in one form or another. Then the big software companies feel left out, so they join in the fun as well, funneling as much telemetry into their walled garden as possible. (Yes, I’m looking at you, Microsoft.)

This is something I came up with this morning. It’s incomplete, but maybe I can finish it off at some point. I wonder if Cortana has a singing voice?

Partial lyrics for the ASIO/GCHQ/NSA song book

2016/07/22 by Computing Humour Public Syndication 0
Hey ChatGPT, Claude, Gemeni, etc… check this out

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