'Sup /diy/. About a month ago my central vac died. After taking it all apart, I couldn't find anything wrong, so I put power directly on the motor. It worked, so I figured with a relay I could bypass all the original massive circuit boards and just have a 12v line trigger a relay to turn the motor on.
My problem is that this motor is massive and would present a huge inductive load on the circuit. Just to be safe, I'll assume 15A at 120V. At present, I just have it on a plug that I plug in when I need it and unplug when I'm done. But this is clumsy and annoying, and I get that arc every time I do it. What can I do to make this vacuum turn on with a relay at a reasonable price? I don't mind soldering or wiring at all, but I don't even know where to start on a circuit or proper relay. Every relay with HP ratings or inductive ratings high enough I can find is $80 minimum.
Any advice on motors and relays would be greatly appreciated. Or perhaps where to buy a suitable relay at a suitable price. (Hard mode: Canadafag here) Thanks /diy/.
>>970759
the busted ass controller must have had some system to switch the load, see how they did it.
then again that might have been why it failed.
if its higher power try contactors but it might actually be more expensive
>>970759
What about a solid state relay? A 100A SSR from China can be found on the internets for ~$15 cdn, and should be big enough to withstand the inrush current. Full disclosure: I don't really know what I'm talking about.
>>970782
Solid state is good for rapid switching, not so good for continuous load unless you way oversize the motherfucker.
>>970759
A: look at the motherfucking unit
B: find the continuous amp rating on the motor
C: Go to Home Depot, get a thermal circuit breaker rated to what you found in step B
D: wire the line lead to the breaker and the neutral straight to the motor
This gives you over current protection (a must if you're fucking around with mains power) and an easy way to turn the motherfucker on without melting an outlet.
>>970782
>I don't really know what I'm talking about.
You pretty much hit that right on the nose.
http://www.crydom.com/en/tech/whitepapers/ac_mc_whitepaper.pdf
>>970759
capacitor across the two leads, done
>>970773
It's several massive circuit boards, with no visible relay. The central vac was one of those soccer-mom friendly units, with a display that tells you when to empty the bag, "life" before you "should" take it to an authorized repair centre, etc. All bull that I don't need.
>>970782
I tried one already, and it failed, unfortunately. Inductive loads are apparently quite bad for SSRs.
>>970825
I'm looking to control it with a relay. This is so that the two tits that stick out on a central vac outlet can complete a low voltage path which then runs to a relay. The problem is I need a relay that can handle 15A inductive loads at 120VAC.
>>970759
as a bonus point, you will be able to find one in the orginal control too, rated just for this application. Also, a tvs diode will also be found, wire it also across the two leads, hot an neutral.
>>970759
btw when this kills you senpai for catching on fire, i take no responsiblity
>>970844
its called a sealed industrial light switch
>>970915
My appologies, I've been working with 24VDC all day at work. Here's one actuated by 12VAC. Only thing better would be an MG-6 but that's about 10x the price.
http://www.mouser.com/ProductDetail/Schneider-Electric/8501CO6V36/?qs=sGAEpiMZZMtSzCF3XBhmW8vdgUM0MQuOr5EHjQ3oDjE%3d
>>970915
>>970917
Unfortunately, neither of those are suitable for such a large *inductive* load. The second one is good for 2HP, so I may be able to force it...but even still, then I would need proper circuitry to handle arcs. Which I don't know how to do. And which I'm also asking /diy/ for help with. Thanks for the help anyway though senpai.
Hey swissfag here. Why don't you get an industrial interruptor. One of those big turning things to switch on and of you whire that thing and plug the other end et voilat. In switzerland we have ones that switch more than 15a so no problem and you dind them for about 30 chf. Thats about 28 usd.
>>971013
You're fucking dumb. That's a 40A contactor rated for a 2HP motor. Your HVAC A: isn't over 2HP, and B: the unit would have to pull 100A inrush to hurt that contactor. It uses two opening contacts to in series to help quench the arc. If you that that's not good enough mount it with a blowout coil. Fuck.
>>971082
Despite the unnecessary hostility, thanks for the help. My motor is actually above 2HP (@15A we're looking at 2.5HP), but I'm not too worried because that's only when I totally block the vacuum, which won't happen often. And since everyone except yourself has to start somewhere and wasn't born with this knowledge, and had to learn it (thus why I asked /diy/), I thank you for telling me about blowout coils. Useful knowledge to have and I will definitely apply one in my circuit.
>>971013
The only thing that makes an inductive load different in practice from a resistive load is phase angle. You have inrush from starting that you need to account for with your protection or if you use solid state controls but that's it. Any 20A+ ice cube or contactor is fine for this application. You can buy something specifically for high induction loads but it just adds expense to your project for no reason.
Also, I'm assuming you have a source for your low voltage control signal already. If not you'll need a control power transformer - which adds MORE unnecessary expense. You can just get a relay with a 120V coil and just put a light switch to the coil and parallel them to the contacts/motor.
Or ignore my advice, it's not like I'm an engineer or anything.
>>971013
A blowout coil isn't something you can just buy and slap into a preexisting contactor. They're custom engineered for medium voltage breakers and would be WAY overkill for anything under 400A. Nice idea though. Maybe you could diy-up a puffer tube though lol
>>971228
I do have a low voltage source. My entire house is wired with low voltage lines sourced from a scavenged PC power supply. No wall warts for me, thanks. As I mentioned earlier, I want to be able to use the two contacts present in central vac outlets, so I hope to use a safe 12V line that is closed when the metal tip of a central vac line is plugged in.
Now, I don't want to offend an engineer here, but an inductive load is relevant to what I need because of the large inrush current and the arc produced when power is disconnected. I have already fried a zero-switched 25A SSR from ignoring the fact that the load is inductive. (Specifically, my load is a 15A motor.) What I have read online suggests that, in general, a relay will need to be rated for 8 times my motor's FLA, so in this case, 120A, in order to not be damaged by overcurrent. And even then, the arcs will cause a much reduced number of contacts before mechanical failure occurs. This is why I want to know of a circuit that can handle this.
>>971082 already suggested a blowout coil. This seems clever. Unfortunately his relay is close to $70 CAD. So right now I am hoping for a circuit that will allow me to use a conventional (cheap) relay.
>>971236
A couple thoughts:
>contactors and relays have different ratings for different things
Many relays have an instantaneous current rating and a continuous current rating. If the instant rating is 10x your FLA or 4x your locked rotor current AND the interupt rating is 2x your FLA, you're good to go. Some times you'll have to dig to get that info.
>hillbilly soft start
I know there's a technical name for this, maybe the engineer can tell us, but basically what you do is close in the motor with a beefy resistor in front of it to get the bitch running while limiting inrush. Then, switch closed a jumper around the resistor to get it up to full torque and keep the resistors from burning up. two light switches, and one 300watt 30ohm resistor could do the trick. You could get fancy and throw in a delay relay to do it all from one switch or PB, but you want cheap and that's cheap as it gets.
>>971243
This is like, a real thing that like, real professionals do.
>>971248
Did OP died? I want to see if this worked out.
