Think like an engineer before modifying your vehicle (or caravan)

Nut psychology versus engineering: it’s a fair fight. This is one of the best nut questions ever, highlighting the nuance of the modern automotive nutbag…

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There are two kinds of nut: the dogshit-dumb, rabid kind, who infests the comments feed and reaches out from time to time. A walking advertisement for the Dunning-Kruger effect.

And then there’s kind whom I actually love, albeit in a deeply non-fag way. Pants on, every time. This is the nut with an enquiring, but somewhat adrift, mind - which is exactly what it takes to become the creme de la creme of nut de la nut.

Galileo, Copernicus, Kepler, Newton, Einstein, Da Vinci, Pascal, Bernoulli, Darwin, Pythagoras, D’Lamert, and of course Marie Curie (#inclusivity) - the list goes on. Enquiring minds, all. But where these scientific luminaries failed, the modern backyard automotive nut succeeds.

You don’t get to achieve ‘hero nut’ status when you possess high-level technical competency, and (I think you’d agree) this is ultimately what held these science types back. Newton was almost a nut, though, because he believed in alchemy. He was so close, as geniuses often are. And Einstein, with the socks; come on.

Today’s correspondent is refreshingly unburdened by the millstone of technical competency, which will shortly become clear.

I would like to know if you think it a viable proposition to use the air passing under or over a caravan to drive a 12v alternator for battery charging.

I am aware that standard practice atm is to use the towing vehicle to supply 12v whilst travelling.

I have a 2017 Tucson 2.0 CRD and have concerns about the smart charging alternator and other electrical systems in the car. 

I was thinking some sort of ducting leading to a pelton wheel type turbine, only for air, not water. I have the workshop (lathe/mill) and fabrication equipment. The construction would be easy, however, l am at a loss on the physics, airflow strength voodoo etc. 

Is the fact that l have never seen or heard anyone else doing it telling me its all pointless trying to build something to do what l have been thinking about. 

Many thanks for your time JC…keep roasting the nuts mate.

- Rob Benge

What an epic (nee long) question, but this is what it takes. And this is exactly why you - the normal, middle-of-the-road viewers at home not seriously considering putting a big, ducted windmill under their caravan - will never be a nut. Authentic nutbaggery like this simply cannot be faked, no matter how much you really want to.

To Rob here I say, thank you for your enthusiasm about the show. Will do on the ongoing nut roasting; you’d better brace for impact there, mate… You just put yourself in the crosshairs. 

Short answer: Yes, yours is totally pointless speculation, of the export-grade nut variety. Well done.

But rather than roast Rob gratuitously, how about we use his question to illustrate the difference between the way, I dunno, civilians think, and the way engineers think? 

Bear in mind, I’m a fairly shit engineer (on balance), which is why I became a journalist. But even a shit engineer is a Jedi at applied physics, compared with your average civilian, or virtually all journalists for that matter.

I’d suggest it is a uniquely male mental preoccupation to place a beer on one’s gut and muse as to the solution of a modern automotive problem, which does not exist, and for which there’s no evidence, beyond merely a feeling (or even a random lightbulb-moment of curiosity which refuses to be switched off). This random musing process wastes valuable time, which of course could be better devoted to thinking about (among any number of things) like boobies.

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If it ain’t broke…

What, I wonder, exactly is the unspecified, imagined, deficiency with the Tucson’s smart charging alternator and sundry electrical doo-hickeys, which begs for the supplementation of a home grown, aerodynamic ducted turbine charging system on one’s caravan?

A smart charging alternator merely adjusts its output in response to load and operating conditions. Mainly for fuel efficiency, but also to improve things like idle quality. Because drawing the full current at idle is going to feel unrefined, for example. It’s sucking 2.4 kilowatts from the engine at idle, at full load - undignified.

A caravan with a refrigerator running, is merely a bit of additional electrical load. It’s hard to see how that could punt the Tucson’s smart alternator into an Apollo 13-style main bus B undervolt.

And let’s bear in mind: the car runs off the battery. The alternator just keeps the battery topped up. That’s how this works. The charger in the caravan, therefore, simply taps into the car’s battery - like everything else. It’s just additional electrical load. 

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Charged particulars

So let’s think about the electrical demand from the caravan.

I found a 130-litre, 12-volt fridge online. Nominal power consumption: 40 watts. I can’t imagine what else you would need to power in the van, en route, but let’s say you also have - I dunno - a vital cigar humidor, a filter for the moat around your bed, and an emergency inflation system for your inflatable let’s call them ‘travelling companions’...

...whom, admittedly, you really don’t want going down on you, especially en route. So to speak. So let us allow a hugely conservative total of 100 watts of electrical demand from the van, in transit. Call it eight amps at 12 volts.

The alternator in the Tucson is probably 110 amps. (And I say that based on finding a 110-amp replacement Tucson alternator online.) So the van is gunna pull about seven per cent of the Tucson’s maximum alternator capacity - absolute max. But more like three per cent assuming no humidor and all the Bendy Wendys maintaining … let’s call it ‘hull integrity’.

It’s nothing. Three and a bit amps. I don’t even know why you would bother charging in transit. One deep-cycle battery with 120 amp-hour capacity would run just the fridge for about 40 hours. Just plug the van into the mains and recharge the batteries when you get where you’re going.

But let’s say, just for shits and giggles, that charging in transit was essential, and the existing vehicle electrical system could not cope. And bear in mind, we’re already in the domain of the anti-vaxxing, flat-earth, creationist here - but let’s see where this goes.

I don’t know why a wind turbine is the primary solution to this non-problem. Especially a DIY one from scratch. I mean...

You certainly can get yourself a wind turbine off the rack. I found a 400-watt AWS marine grade turbine generator with carbon-composite blades, max airstream speed 176 kays an hour. And it comes with a battery charge controller. For under a grand. That’s nice.

Granted: It's not one that you made yourself in the shed with your own lathe and mill, so it would probably work, out of the box. You really can’t do this kind of thing yourself, without a wind tunnel and $20 grand. (Pro tip.)

The off-the-shelf one is comfortably over-engineered to meet the caravan’s demands - not that there aren’t practical impediments to using it on the move.

For example, it’s 1.2 metres in diameter. Fair to say, therefore, you’re not putting it under the van any time soon. And you’d want to stick it on a fairly substantial mast, I’d suggest, so that it operates in clean air.

Rob plans to blend right into the elitist elite caravan mob.

The turbulent wake close to the van - just not efficient. Ask any UH-1 Iroquois pilot, taking off on a hot day, fully loaded, in the mountains. So there’s that.

I think you’d probably want to stick it on, say, a 1.4-metre mast, just to be safe. It would thus project ‘only’ two metres above the roof of the van. Which of course would not be a hazard, or look fucking ridiculous, as you drive from A to B.

You could probably make the impeller smaller by putting it in a duct - which is why the propeller on a modern turbofan engine on a jet airliner sits inside that cowl / duct thingo. But then you’d really need that wind tunnel and $20k budget to get it right.

Non-problem solved, Rob. Move on, mate.

And, of course, for the $1000 you’d be spending on the off-the-shelf one, you could spend it differently, and get change from (say) procuring four additional deep-cycle batteries. If you just bought those instead, they’d run the van on location and in transit, until the heat death of the friggin’ universe. Just saying.

Alternatively, you could spend $1200 and fit a 740-watt solar kit to the roof of the van. No mast required there. If you add an inverter and batteries (another couple of grand there, I suppose) … that’s kind of a low-profile solution. And you can tap 240 volts out of that.

Granted, it’s not gunna be a carbon-fibre propeller five metres off the deck, on a stick. So you won’t be able to advertise your ‘elite nut’ status to passers-by quite so easily. Something to factor in, I suppose.

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Simpler minds

In short, nuts are fascinating. I could play with mine all day long, but from time to time it’s also good to get things done.

If you are an elite nut, as Rob appears to be, don’t lose your enquiring mind, but do try to develop some technical skill and education before cracking on with these interesting projects in the shed at home.

The technical thing is hard, of course, and if it’s too much for you, just remember instead not to solve any problems that do not actually exist.

Instead, just think about boobies. It’s great for one’s mental health.

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Are all caravaners cognitively impaired, or just the ones who commented after the first video report?  I think I know who’s been buying all that toilet paper recently...

Captain’s log: March 18, 2020.

The zombie apocalypse has become abruptly worse. Yesterday, I answered Rob Benge’s apparently straight-faced (but nutbag) question as to the viability of DIY-ing your own wind turbine in the shed, for the caravan, to cure the non-problem of the vehicle not being adequately able to recharge the caravan’s battery.

Pro tip: the vehicle will do it just fine.

So we’re all clear on this, the ‘solution’ here is: Do nothing, because the vehicle’s electrical system will cope. 

A DIY wind turbine is unworkably absurd. Simply plug in and recharge off the mains, at home, and again when you get where you’re going.

If that doesn’t work, add an additional battery or two, and possibly some modest rooftop solar. Seems reasonable.

Here's hoping you were tongue-in-cheek about that fellow's question. Or are you under the misguided impression that anyone without 'a degree' is a drooling, brainless mook?

I've seen quite a few projects made up by 'idiot morons in their home shops' that match anything made by much larger production shops and their engineers. And they work just fine, thank you. But I suppose that would discredit your degree.

-Troy

To me, there’s someone who is overly touchy about not having a degree, and probably a toilet paper hoarder. Although I do not know this for sure. Where, exactly, did I say - ever - that anyone without a degree is a ‘drooling, brainless mook’? I think you’re making that bit up, Troy, possibly because you are a drooling, brainless mook. When did I categorise people with their own shops as 'idiot morons'? Never.

I have the utmost respect for competent tradies. I’ve met some amazingly capable tradies, and I know enough about what they do to know they’re a lot better than me on the tools. The chap whose question I answered yesterday, was hell-bent on solving a problem that did not exist with a proposed solution that was - literally - nuts.

I’ll also freely admit there are plenty of engineers who are totally impractical. I just don’t happen to be one of them. But for balance I’ll admit there are plenty of dumb shits who could never understand engineering no matter how hard they tried, and who appear to think that less education is better than more. I’m looking at you, Troy.

If you’re planning to tow heavy, whether you’re one of these nutter caravaners or just the normal kind, here’s an engineer’s guide to heavy towing >>

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A turbine would increase fuel consumption due to the drag

- Gazza2

Yeah - aside from being huge, and impractical, it certainly would increase fuel consumption. A lot of people pointed this out. Yet, this is not a reason not to do it.

Everything you employ the powertrain to do, such as drag the vehicle and the caravan’s sorry arse all over the country, drive the alternator and the HVAC system, drive a windmill - it all uses fuel. Otherwise you have just invented a perpetual motion machine, and you can therefore expect a warrant for your arrest to be issued by the thermodynamics police.

Now this, from Weldon Thompson, who also suggested removing all the van’s external cladding to save weight, and replacing it entirely with laser cut photovoltaic panels, with excess power, even in moonlight, being devoted to an ion thruster to prevent the death wobbles. I’m not making this up.

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Mr Thompson added:

Comment on the technical specs in video. 2.4 KW  = 165 amps @ 14.5 volts. some vehicles may produce this but a 2 litre. In the military we used a 24 volt 200 amp generator in some vehicles and these were the size of a 10 litre drum.

- Weldon Thompson

I’m always happy to debate anything technical with a visitor from the military, so allow me to retort: 

What I actually said yesterday, was that a 110-amp alternator delivering 110 amps (ie full load) at a nominal 12 volts imposes about 2.4 kilowatts of drag on the engine.

This is because the alternator is producing 110 amps times (let’s say) 12 volts, equals about 1320 watts (of electrical output) but the alternator is obviously not 100 per cent efficient, and neither is the serpentine belt driving it. 

The system is about 55 per cent efficient, and 1320 divided by 55 per cent equals 2.4 kilowatts. In other words, the engine needs to deliver 2.4 kilowatts to the alternator, for the alternator to pump out 1320 watts of electricity at its peak capacity.

And one of the things smart alternators do, is not do that maximum pumping out at idle because it would severely impact idle quality.

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Many vans also have a TV, outdoor lights, low power microwave, laptops, etc. We aren't living in the dark ages. People have tech. That means the deep cycles are likely to be half or more drained by the morning on any given stop.

- Milamber319

Yeah, agreed.

So, let’s say your 120 amp-hour battery is half drained overnight and the charging circuit demands 10 amps from the vehicle. That's a pretty conservative load. So, you need to pump 60 amp-hours in to recharge the battery fully. That’s six hours running on the highway, or a modest rooftop solar panel.

Although I generally like your channel, I fail to understand why do you belittle people asking questions of you in quite a polite manner, regardless how bad the questions are? Do you get off on that behavior?

- Tabaks

Yeah, I do. Probably because it’s actually not okay to be a dickhead, if you’re a grown man. Australia is already overstocked on grown-up dickheads, you might have noticed. Scientific illiteracy is in plague proportions - which is evidenced by all the zombie apocalypse preppers buying all the toilet tissue right now. What’s the benefit?

Johnny should be encouraging scientific experimentation and not mucking it.

100 watts you say. Maybe you forgot about the rice cooker and don't forget the oven is on because they're cooking a roast, sure they can use gas but maybe they wanted to use electricity, because gas requires taking the bottle out and refilling it and all that good jazz.

With their driving down the road they want to take advantage of electrical energy and I think that is quite fair logically.

-Darren Munsell

Speaking of dickheads, coincidentally: Scientific experimentation is fine. I’m all for it. Only, fucking about aimlessly in your shed making a fan that won’t work is not actually ‘scientific research’. It’s time-wasting.

Also, are you seriously suggesting cooking a roast, in an oven - gas or electric - in the van while driving to your destination? You don’t think that might be, like, a fire hazard?

Having the oven on at 100 kays an hour? You hit a bump, fat goes everywhere; the element in an oven is well over the auto-ignition temperature of dripping.

And not to mention, who has a roast with rice?

Compared to emptying a container full of shit that’s been percolating for days in the heat, swapping a gas bottle at the servo occasionally doesn't really seem that inconvenient. 

Plus, the energy density of gas murders electricity and makes it a far superior solution for energy dense processes like cooking.

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Unfortunately, Darren went on.

Maybe it's cold outside and they have a 1200 watt heater keeping their van nice and warm for the opposite there running the air conditioning so when they jump out they can go to their van and feel oh so cool.

I think you've been a little hard on these people John especially when they're trying to understand more science.

-Darren Munsell

A 1200-watt heater. That’s fairly impractical, electrically, unless you’re plugged into the mains. That’s 12 volts at 100 amps. That’s about one hour run time from a substantial deep-cycle battery - if you can control the temperature at that discharge rate, and if you’re not also running lights, your oven, your tech and your fucking rice cooker at the same time.

But let’s just say, to highlight your spectacular scientific imbecility, Darren, that your van has 1200 watts of heating or cooling capacity - the physics doesn’t give a shit. Heating or cooling - flipsides of the same energy exchange. Plus of course let’s assume you have miracle batteries that never run flat, and don’t blow up when you discharge them at 100 amps.

A 15-foot van contains about 25 cubic metres of air. That’s about 30 kilos of air. It takes one kilojoule of energy to change the temperature of one kilo of air by one degree C, so if it’s 50 degrees C in the van when you stop (or minus 10) and you want the van at 20 degrees C, you have to change the temperature of the air by 30 degrees.

And that’s gonna take about 13 minutes, using a 1200-watt heat exchanger. So, driving down the highway endlessly with the air on (or the heater) in the van, just so you can be comfy on arrival, is beyond stupid. It’s Scott Morrison stupid. It’s gonna take 13 minutes.

Why wouldn't you just drive an alternator off one of the caravan wheels.  If you really needed to charge your caravan battery while you drive.

- Bryan North

Jesus, Bryan. Bolt some solar panels to the roof. Easier, more reliable, and it’ll recharge even when you’re not moving, including for months on end when your caravan is making your home look like a third-world slum, in the front yard.

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Last comment in this report goes to, as John Paul Young would categorise him, yesterday’s hero. Who apparently has changed from windmill drive to axle-driven alternator. In the shed. Who knew?

I will probably build my alternator drive regardless of what John says. It costs me nothing to be in the shed and if the idea works bonus for me. If it doesn't l might learn something from trying.

- Rob Benge

Bad idea, Rob. Stop trying to be Professor Pat Pending - you’re going to kill someone, or yourself.

Fit solar panels and a second battery mate. It’s that simple - if you really need a project, do that. But let’s detain ourselves briefly with the practicality of Rob’s in-shed ‘axle warp drive’ proposal.

It’s certainly possible, just stupid. Gotta remember the whole axle doesn’t spin. There’s just a hub on bearings, plus brakes. So, physical space for access to the spinny bits is kinda limited.

The alternator in the car is run off the crank by a belt. And if the engine’s doing 2000 revs at highway speeds, the caravan’s wheels are doing only about 800 rpm. 

And that means the drive pulley on the axle is going to have to be 2.5 times bigger than the one on the crank, to achieve the same gearing, and I doubt there’s an elegant solution for that, in the available space. Because the space is quite constrained.

And a catastrophic failure, on the move - is potentially very dangerous. Because it could damage the braking system or blow out a tyre. Prototype systems are prone to unexpected failures, which is one of the curses of DIY anything. It’s great fun until it kills you.

Also, you might have noticed the alternator is always up high in the engine bay to give it some degree of weather protection. How, exactly, are you going to protect it from the water, dust and general filth that goes hand-in-hand with operating down near the caravan wheels? How are you going to keep it even reasonably dry?

They say there are no problems; only opportunities - but to me that’s always been a bit of management double-talk bullshit, and this one certainly looks like an insurmountable opportunity to me - especially as it’s a proposed fix for a problem that does not actually exist.

Or better yet, it’s a solution to a problem that has already been solved  - using fucking solar panels and secondary deep cycle batteries. Much safer. less Wacky Races.

Are all caravaners this fundamentally impaired? Are today’s correspondents representative of the breed? Is it a product of living for months at a time in an aluminium box that allows you to take your own shit on an epic sightseeing tour of this great nation, and in which the dunny doubles as the fifth seat at the dining table? I’m just not seeing the attraction.

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