Hello and welcome to my online works. Beyond my full-time job as a professional engineer, I have created and participated in several podcasts most notably Pragmatic.

I’ve also created a few projects and I also write longer-form articles from time to time. In addition I’ve been playing with comic strips recently with Enginerd.

Thanks for stopping by.


9th May 2015

I’ve had my fair share of alcohol in my life. I’ve learned that I could drink most people under the table, though I never got the hang of beer or wine, only liqueurs and spirits. I’ve never had a hang-over. I like to think in my adult years I drank responsibly, mainly because I needed to drive a vehicle a lot. In Australia the drink driving limit is 0.05 grams of alcohol per 100mL of blood for those with an open drivers licence. (I referenced NSW but most states follow this AFAIK) and the guidelines that are often quoted for men are:

if no more than two standard drinks are consumed in the first hour and no more than one per hour after that…

…keeping in mind that a standard drink is any drink that contains 10g of alcohol; although the NSW Government site says of counting your drinks…

Trying to calculate your BAC is impossible…

Fast forward to about 12 months ago when I had Weight Loss Surgery I knew from my wife’s experience that the rate of absorption of alcohol is much faster and more intense as described here with the key point:

It is also harder to drink large amounts of alcohol after a sleeve and you will find that you will become twice as drunk, for twice as long on the same amount of alcohol! This is because the alcohol exits the stomach more rapidly and is very quickly absorbed.

I had been used to ‘pacing myself’ with alcohol intake such that I was able to drive if necessary and wasn’t impaired in my adult years. (Let’s exclude the teenage years from that though…)

That control is now impossible

The rules have changed far too much and try as I might, I can’t seem to get it right. It almost seems like any amount of alcohol has an adverse affect and I’m terrified to drive. There’s a school of thought that says if you’re going to drive you shouldn’t drink at all. Well I drive a car, every, single, day. So when is it okay/safe for me to drive a vehicle if I’ve had a drink if I can no longer trust the old guidelines?

And no, the answer isn’t to carry around my own personal breathalyser, I’m trying to figure out when a safe time is to actually drink and how much is safe ahead of swallowing?

What about the validity of 0.05 limit? Studies show that performance drops off sharply in areas of object recognition, reaction time and risk-judgement beyond 0.05 but this varies based on the individual. Safer still is 0.02 but then 0 is best. Of course a bad driver will always be a bad driver but a good driver plus any alcohol runs the risk of becoming a bad driver. The limit after which you are fined and disqualified from driving is legally fixed.

The problem I have is that I have four children and a wife that depend on me. At the moment even more so. So here we are. I think it’s time for me to say goodbye to alcohol.

It’s become something that is too difficult, dangerous and irresponsible to manage and should no longer play a part in my life. That said the most difficult part isn’t going to be giving it up, it’s going to be repeatedly explaining to others that no, I’m fine, I don’t want a drink thanks. What does that say about our society?

The Kids Are Alright and So Am I Thanks For Asking

5th May 2015

Circumstances have required that I once again play single parent to my four children for a month whilst their primary carer (my lovely wife Kirsten) is out of action (don’t worry - it’s all planned and she’s just fine). I really enjoy the chance to do it as I have done many times during her previous surgeries and once again I’ve been confronted by the same outsider commentary.

  • "You coping okay?"
  • "You handling the kids okay?"
  • "It’s hard work running after kids all the time isn’t it?"

It’s even nicer when another parent won’t ask me the question directly and goes straight to my older children instead:

  • "How’s your daddy coping?"
  • "Showing your daddy how it’s done?"

Like I’ve never cared for my own children before apparently. Of course people don’t always know what to say or do in certain situations and it’s probably not meant to be a mean-spirited comment and I have no doubt I’m being sensitive at some level but the litmus test in discrimination is: put the shoe on the other foot and ask, is it offensive?

Let’s say a women who was previously a primary caregiver to their children switched to working a full time job all week with commuting, late meetings, long hours, the works.

  • "You coping okay?"
  • "You handling work okay?"
  • "It’s hard working all the time isn’t it?"

Firstly, I would never even think of asking those questions to a stranger or even a close relation. Think of some people you know yourself and what do you think their reaction would be in that scenario?

Let’s not try to get all shirty about potential gender bias. Let’s look at this from an experience angle. Intuitively someone that does something twice as much as someone else is bound to be better at it. For certain repetitive tasks I’d agree but I think that parenting is more complicated and more subtle than that and it’s a broad brush to suggest all people are created with equal talents. Hence one person will be better an driving a car or painting a house than another and that’s because everyone is different. I prefer to think that so long as there is a minimum amount of experience and exposure to develop the skill set required, that individual should be competent enough to do a reasonable job at any task. Maybe not an expert, but passable at least. It got me wondering then; how big is the gap between the genders in terms of duration in the role of primary caregiver?

Clearly, historically speaking, women have bore the brunt of child rearing whilst the men have been off working/farming/killing animals/other non-parenting stuff and hence men didn’t have as much time taking care of children. Going back hundreds of years maybe, depending on the state of economic development of a country perhaps, the numbers were skewed away from men as primary caregivers. What about now and is it changing? According to the Australian Bureau of Statistics the figures haven’t changed much between 1997 and 2006 though the next figures are due early 2016(?) and will be interesting to revisit at that time. For the moment however the split of hours as primary caregiver is men at about half the amount of time as women, at least in my country. I have no doubt the time/split will vary from country to country. The truth is that if we run with the above numbers a significant proportion of men are in the role of primary caregiver regularly for a measurable and non-insignificant number of hours and that shouldn’t be ignored.

So if it’s not the raw hours is it something else? The preconceived notion that men are better at some things and women at other things is just the sort of gender bias western society is trying to stamp out (in some areas harder than others and we are far from truly balanced) but the problem is that the question of whether men or women are better parents is mostly about opinion and difficult to correlate with fact. Despite this, in 2007 PEW Research in America conducted a controversial survey that challenged whether men or women were better parents and suggested that men were doing a better job in recent years. I’m not sure if their results are valid but if nothing else it should at least make you stop and think about it if only for a moment.

I’m not taking sides. Honestly I’m not. I’m not saying men are better at parenting or women are better at parenting: All I want is for people to stop asking me those sorts of questions. I’m perfectly capable of taking care of my kids thank you very much. Not that you asked, but here’s how it unfolded in the Chidgey household in the last 24 hours:

Tonight I cooked Beef Nachos with salsa and although I used a sachet for the seasoning I tweaked the result by balancing out the salt and added a few other spices some tomato paste to add depth to the flavour of the dish. I made extra to reheat later in the week when time to prepare after kids sports training is scarce. I’ve done the washing, sorting, cleaning and the house is in order ready for my wife to return later in the week. I’ve successfully dropped and picked my kids up from school, sports, etc, paid bills, bought and wrapped a birthday present for one of my kids friends whose birthday party he will shortly be attending and blah blah blah are you bored yet? I’m not. I’m loving it…that is until I get comments like those above.

You know what though, it’s not all bad. There are people that do know what to say and that "get it" for the want of a better way of saying it. So instead as I close here’s a few more comments I also received though (disappointingly) they weren’t as plentiful. I’ll leave it you to determine which people made them.

  • "It’s great spending time with them when they’re that age."
  • "I’d swap with you in a heartbeat."
  • "You’ve got your hands full but you look like you’re having fun."

Yes I am having fun. The kids are alright and so am I, thanks for asking…but please stop asking.

The Democratisation of Energy

3rd May 2015

Two days ago Tesla announced the Powerwall which is essentially a Lithium Battery pack for the home that is wall mountable. That in and of itself is not revolutionary but it’s definitely interesting. (The presentation is only 18 minutes long and is worth a look before reading on if you haven’t already seen it). Elon had hinted at this back in February this year.

The presentation was a typical Elon Musk special. He has a nervous stage presence that comes across as honest and matter-of-fact that I find endearing and rare for a CEO. His suggestion midway through of fighting the urge to do a "billion dollars" little pinky finger against his mouth per an Austin Powers movie was a charming balance of awkward and hilarious that drew a smirk from me and I’m sure plenty of others.

The home model comes in a 10kWh pack and although not directly discussed in the presentation, also a 7kWh model for $3,500 and $3,000 USD respectively (given the relative cost/capacity ratios the 10kWh is the clear winner) of which a maximum of 9, 10kWh Power Walls can be chained together for a maximum of 90kWh of storage capacity.

Elon also announced the Power Pack, which is more like a 19" rack size equivalent for which each rack contains 100kWh, which no scalability limitations. Clearly the Power Packs aren’t meant for "easy" customer installation and hence cable sizing, distribution breakers etc would need to be customised per installation (hence no assumptions on maximum current and no need to limit at 90kWh). I have a few thoughts on the global scalability but let’s hold that thought for another post.

I saw many comments on Twitter along the lines of "but I still need solar panels" so yes, again Tesla aren’t supplying the complete solution (unless Solar City is available to you and it isn’t for everyone) but solving the battery problem is two-fold: Energy Density and Lifecycle-cost. As I discussed on Episode 2 of Pragmatic some time ago, the future of local electricity generation and the move away from centralised generation is the only sensible option as it solves so many issues, however the cost of doing so thus far has been excessive mostly due to the cost of energy storage.

Having done the sums myself a few times I can get about 7 Fusion 12V 40AH LiFePO4 deep cycle batteries for the same amount of money leaving some left over for some cabling and an enclosure: that’s only 3.4kWh of capacity (assuming parallel connection and you can source a 12V DC Inverter to do that job, but let’s just check the figures not practicalities). That makes the Power Wall about 3x more bang for your battery buck. That’s impressive. It’s actually cheaper than entrenched older wet-cell Lead-Acid batteries, which is a first for this application so far as I know.

As with all battery systems it comes with lifespan limitations based on how much you discharge it each cycle. Both models offer a 10 year warranty which I could probably believe on the assumption that it is correctly provisioned and the Power Walls aren’t driven to horrendously low DoDs (Depths of Discharge) so ensuring you get enough capacity to be comfortable matters to the lifetime of your battery pack. How much you provision is obviously a combination of how much you use, how much sunlight you get where you live and whether you’re grid connected or not. Your sums will vary.

Details on the Power Wall are still scarce but it’s unlikely to be a new battery technology but rather the advantage of building a Gigafactory for manufacturing Lithium Batteries means the economies of scale can be realised and drive the cost of the battery down. It does however provide an interesting potential insight into the pricing of the Tesla batteries in the Model S. (Another topic for another day?) Currently the Model S uses the Panasonic 18650 battery which has a good energy density of between 600 and 800 Wh/l but has less life expectancy than LiFePO4s do.

In terms of energy density LiFePO4 Batteries typically only have 220 Wh/l. Based on the dimensions of the Power Wall and assuming that only 1/4 or so of the volume is actual battery we get about 200Wh/l which suggests potentially a different battery to the Model S but without a teardown of a unit that’s pure speculation at this point, though it’s interesting to note.

Since the energy density problem isn’t a problem that they’ve solved here and we’re progressing on existing technology manufactured at scale then the only argument left is whether it’s worth the money. I looked into the cost-effectiveness of electric vehicles on Episode 52 of Pragmatic where we also discussed the price of electricity. I refer you to that episode for all the details but in short, according to this handy link in the USA it’s an average of 12c/kWh and 908 kWh/month (about 33kWh/day so let’s assume you have x2 10kW Power Walls and enough sunlight to handle 13kW of usage through the day and to fully charge your batteries too during that time) then $13k USD over 10 years for that grid-power is more than the double what the Power Wall would cost, but once you throw in the solar panels, installation costs plus the inverter unit it’s not going to save you money on the whole. On average. But electricity prices vary and so does usage so for some people it will be a cheaper option.

Based on my sums for my house here in sunny Queensland (yes it’s handy having all that sunlight) even with my Grid-connect inverter and 5.6kW of solar panels on my roof, I’m still shelling out $1200/yr on electricity. Using a local Fronius Symo Hybrid Inverter installers website and a straight dollar conversion, assuming 2, 10kWh Power Walls if I invested $15k AUD, and assuming the batteries lasted without fail for 10 years, I’d save $1k AUD. Of course, I’m cheating since I’ve already got the panels, but I’d be lying if I didn’t say I’m not extremely interested.

I’ve been looking at UPS systems for some time now and going off-grid is the ultimate dream - even if there’s a risk of household "range" anxiety on successive cloudy days. Another point: If I wanted to add an electric car someday and rely on home charging, I would be in trouble off the grid. I’d need more Power Walls and more solar panels to charge them as well. So I would be stuck on the grid. The math then isn’t quite so rosy but it’s damned close.

Tesla are trying to democratise energy. How long before Tesla release their own solar roofing tiles? Their own inverter units as well? If Musk is serious, you can bet it’s on the roadmap. And he’s serious. Opening up patents is an admission that he doesn’t need the money by protecting Teslas technology. He wants to change the world, to fix our dependence on fossil fuels. The numbers are beginning to stack up for many places around the world, including here for me. In coming months I’ll watch with great interest how the Power Wall unfolds in North America where it is admittedly a harder sell in most states, but I suspect it will be snapped up wherever electricity is not so cheap and I expect once the Gigafactory 1 is operational for a few years the prices will come down further still.

Tesla haven’t exactly "solved" the battery problem, but they have just made an appreciable dent in it.