Comment by KennyBlanken | Hacker News Reader

Comment by KennyBlanken | Hacker News Reader

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"I doubled up the relays feeding the main motor and the heating coil, which gives a lot more headroom on the amperage"

...That's not how that works. One of the relays is going to close first, and those set of contacts will take all the load. Similarly, one set is going to bear all the drama from breaking the connection (and with the motor, there's inductive kickback.)

The correct way to do this is to look up the motor rating for your relay and then size accordingly, not to do dumb shit like "oh I'll just double up these two relays."

Of course he fucks up and uses a resistor from mains to logic, too. Mains and logic should never, ever, ever come anywhere near each other. They're supposed to be physically isolated on a PCB, cutouts in the board, even.

Don't fuck with mains / appliances / HVAC / household water supply if you don't know what you're doing. This guy has no fucking idea what he's doing, and some winter day he's going to come home to a house that's 100 degrees inside and a flooded first floor (notice he didn't connect the water leak sensor?)

Home insurance is scummy, annoying, difficult and weasely in the best of circumstances. The second they figure out you had some chewing gum and duct tape hodgepodge running your dishwasher and that's what caused the flood, they will not only refuse to pay, they'll cancel your coverage on the spot.

Then you find out the joys of not having home insurance coverage on a house with a mortgage.

Edit: Holy christ I missed this part: "It seemed to be due to the push-on jumper cables either becoming too loose after years of jiggling or perhaps oxidizing and self-insulating a bit."

That is how you start a fire, people.

Looks to me like he maintained proper mains separation except for the one assembly mistake he admitted to (which wasn't catastrophic, obviously -- his wiring color choices look good for avoiding catastrophic errors). The relay board he's using (I recognize it) is rated for mains voltages, and power-wise is ok-ish for the task (I wouldn't choose it for a commercial product, but for his exact scenario--see below--it's probably ok). Doubling up the relays works fine for the main concern, which is overheating via sustained high amperage, which is how fires start. Surge risk is usually just welding the relay, not starting a fire (unless you're way over spec, which he is not), and it almost always welds shut, not open, so less likely to fail silently into the scenario where it's running on one relay and the sustained amperage becomes a risk, and instead into behaving obviously badly as is typical when motherboards go out (at which point you turn it off and rectify, just like a commercial one). He mentions the whole unit is isolated from mains when not in use, so in that respect it's safer than a commercial one as long as he doesn't run it when away from home/asleep.

Again, not a viable commercial design, but not insane with proper supervision either.

I was curious how you knew about the leak sensor so I did a quick search, and see you're just making things up to complain about -- that model has a turbidity sensor (which I suspect are the NC wires you noticed), but no leak sensor. Oh no! His water might be too turbid! Also the fill valve is wired inline with the float switch (in the machine itself), so it's double-covered for overflow prevention. Flooding seems highly unlikely.

The flaky connections he mentions are the 3 volt ones -- again, not a fire risk. Common for low-voltage contacts like that to get flaky in commercial devices too (e.g., face-plate contacts for thermostats, etc) and without disastrous outcomes. The high-voltage/amperage connections he uses are plugged into the OEM harness, so the same connectors as the OEM motherboard. So, again, seems like you're just making up things to complain about.

I don't want to encourage people to mess with mains power if they're not adequately informed, but it's also not a magical domain you can't learn about with a little research and caution (easier in the US than the UK...). And his gadget worked for years, by the sounds of it, which is better than any commercial appliance I've bought in the last decade...

But I agree he's probably gambling on the home insurance issue, even if his device(s) isn't at fault...

> Don't fuck with mains / appliances / HVAC / household water supply if you don't know what you're doing. This guy has no fucking idea what he's doing

A little OTT. How do people learn to maintain their house or learn to hack improvements? Should we all have your expertise? Perhaps you think paying a qualified installer would be better?

Any work on your home or car or whatever runs risks. Making mistakes is often an important part of learning (and can be expensive). Being a Swiss watch isn't a good compromise.

It is great that you share your knowledge: good feedback is difficult to get.

For building mains devices, you should start by learning about creepage, clearance, double-insulation, the role of earth connections, the requirements for isolation between low voltage and high voltage, etc. Basically a good bit of electrical engineering.

This is different from what you need to know to do house wiring. That's done by following electrical code, which is basically a distillation of the engineering above into a set of relatively easy-to-follow rules.

>How do people learn to maintain their house or learn to hack improvements?

You don't when it comes to mains electric. You hire an electrician who learned through study, training and certification rather than just proding things until it either works or kills you.

Play around with low voltage power all you want but leave mains voltage alone.

> You don't when it comes to mains electric

You definitely can. Any residential home in the US was probably built by those who had no formal training on "mains electric" and was inspected by a building inspector who also knows nothing really about electricity, but can follow guidelines.

It isn't difficult to buy devices that are built and rated to interface low voltage with "mains electric".

The issue is when you arrogantly assume you know things you don't, and that can harm you regardless of the application. Yet, that is often a path for some to learn and become experts or cautionary tales.

IMO, the gatekeeping risk-averse shouldn't stand on soap boxes attempting to dictate the lives of the curious.

I live in a 240 Volt country with reasonably strong regulations.

Yet I'm regularly having to identify and resolve electrical safety issues because other people create risks. Sometimes issues are historical, or have developed over time.

Some of those risks are created by qualified and licensed people.

The most recent: a licensed electrician putting a female supply plug on a friend's bus (I think because he knows houses have female sockets) and then suggesting taking the power supply lead and replacing the female connector with a male one (male to male leads are rather unsafe and illegal for good reason and the friends were skeptical).

I see people that have done the study, training and certification create serious risks. So I don't blindly trust study, training and certification for my safety or safety of those I care for. I do use professionals but I'm very careful when choosing who to trust (for more than just electricity, water and gas).

We learn how to do things correctly because of our own interest in risks. I appreciated the comment because they didn't just say "don't", they also explained the engineering reasons for saying "don't".

However I am a risk-taker, and I take risks that would likely shock you. I am somewhat careful to avoid creating risks for others (when there is a floor level of risk, you can't go below the floor).

It's a balance. The logical conclusion of your world-view is that we shouldn't do anything for ourselves!

Don't fix that leaky tap without training! Too risky. Good example since I lent my pipe wrenches to a friend and told her to have a go at replacing her tap. Very successful. It was outdoors so low risk?

> just proding things until it either works or kills you

I am not suggesting that strawman.

"A little OTT. How do people learn to maintain their house or learn to hack improvements? Should we all have your expertise? Perhaps you think paying a qualified installer would be better?"

Start with low voltage instead of high voltage. Learn how it works. When you know enough that you want to move to high volt, don't start with improv -start with repairing outlets, replacing lights, etc. Things that have good directions, are not made up by you, and you can read and study. Read the relevant electrical code portions when you do it, understand why you have to do things the way it tells you to.

As you get better at it, and understand more and more, sure, branch out into your own stuff. But not until you understand it and can be safe.

Messing with mains when you have no idea what you are doing isn't just dangerous to you. It's dangerous to people around you, to future homeowners, to houses around you, etc.

Mistakes in the field are not meant to be part of the learning process, anymore than they would be in any other hazardous-to-life situation. Sure, they happen, and risks exist, but working on mains and high volt panels in any sane place is learned while you have you have someone overseeing your work and stopping you before the mistake is dangerous. People stop and ask whether what they are about to do is the right thing before they do it, not try it and see if it works.

Otherwise, it's not just money, it's your life, or someone else's life.

As for learning having risks and mistakes sometimes being expensive - sure. But having never dove in a pool, would you think it's a good plan to try to do a triple backflip off a ten meter high dive?

After all, any way you learn to dive runs risks, and making mistakes is often an important part of learning (and can be expensive).

You would instead hopefully start small, work your way up, understand things, and be appropriately fearful of things you should be fearful of.

Beyond that - I don't know why people are so tolerant of this kind of thinking with high voltage stuff.

People seem totally intolerant of it when it comes to natural gas lines, for example. Nobody is out there saying "well you know i just started fucking around with my gas line, added some tees and some relays to control some valves. Sometimes it smells funny but who knows. I wrapped some more tape around it and it seems fine most of the time".

Messing with mains is much more dangerous. Electrical codes are written in blood, the same as all others.

If you want to learn to do home fixing, you learn to be safe first, you start small, and you don't improvise until you can be safe.

Like safety everywhere, it's about understanding, discipline, and process. You can't shortcut it.

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