I'm trying to replicate something I've used on a prior vacuum pump system for composite bagging (I no longer have) but I cant seem to land on the correct electrical do-dad. The vacuum pump draws through the cylinder tank/reservoir. The square black thingy on top senses vacuum pressure. The pump is plugged in all the time & turns on from atmospheric until a certain set point vacuum level is reached, then it shuts the motor off. It is able to automatically cycle like this. You can see the sticky label saying switch is preset at 7" Hg but it is adjustable within limits. If I recall it was wired directly into the motor leads which leads me to think some kind of relay is integrated within the black thingy itself - I don't recall any other electrical stuff. I have a larger (cfm, vacuum level, wattage) pump that I want to use in a similar cycling manner. Appreciate any input.
-
Scam Alert. Members are reminded to NOT send money to buy anything. Don't buy things remote and have it shipped - go get it yourself, pay in person, and take your equipment with you. Scammers have burned people on this forum. Urgency, secrecy, excuses, selling for friend, newish members, FUD, are RED FLAGS. A video conference call is not adequate assurance. Face to face interactions are required. Please report suspicions to the forum admins. Stay Safe - anyone can get scammed.
vacuum switch/relay help
- Thread starter PeterT
- Start date
That's kind of my issue/confusion. I see various flavors of vacuum switches but if they operate at 12V, how can that on/off interrupt the line in of the pump itself operating at 120VAC & say 1-3 amps? That's why I used the word 'relay' to do the physical switching, but that's just an uninformed guess. The unit I referenced does not look like it has any kind of 12V transformer. Just (white) wires lines running from the black module to the pumps wiring.
Switches don't normally care about voltage. They only care about amps - up to a point. Just get one rated for your current and a maximum voltage higher than you expect.
The voltage rating indicates the quality of the insulation - how high the voltage can go before it starts arcing
The amperage rating indicates the size of the conductors - how high the current can go before it starts melting
For AC switches, there is another factor. The switch mechanism must be physically powerful enough to break the circuit. How much force is needed depends on the power. For most manual switches (circuit breakers etc.) you preload a spring with enough force to do that when you turn them on. It's fail safe that way. But for a switch like this, there is probably no source of power to pre-load anything, and the power provided from the pressure difference is all there is. That will bias the actual disconnect from the selected pressure by some amount. Probably it will be fine. If you need a very accurate pressure, or you are worried about it, run the pressure switch on a simple DC circuit and use a relay to control the AC circuit
The amperage rating indicates the size of the conductors - how high the current can go before it starts melting
For AC switches, there is another factor. The switch mechanism must be physically powerful enough to break the circuit. How much force is needed depends on the power. For most manual switches (circuit breakers etc.) you preload a spring with enough force to do that when you turn them on. It's fail safe that way. But for a switch like this, there is probably no source of power to pre-load anything, and the power provided from the pressure difference is all there is. That will bias the actual disconnect from the selected pressure by some amount. Probably it will be fine. If you need a very accurate pressure, or you are worried about it, run the pressure switch on a simple DC circuit and use a relay to control the AC circuit
The new pump I have is something like this (standard 110 VAC in). So spitball math: 250 watts/110v = 2.5 amps. So is there such a thing that measures vacuum, operates on same wall 110vAC but can switch off this level of motor current? Because to my simple mind, anything that runs off low voltage and/or DC low voltage additionally requires some kind of transformer/rectifier no? Drawing your attention to the unit in my post#1 as a reference. To the best of my recollection there was only the single vacuum sensor black box thingy on the tank. The output wires went directly to the motor wires (the white lamp wires). Now maybe that was a but iffy but some of these units have been going on 30 years. Now maybe there was a relay inside of it?
Last edited:
This looks like it 'controls' but needs DC power supply & I'm confused about its output. Would it be signaling a relay & the relay is what is switching pump motor on & off?
Isn't my requirement kind of the inverse of shop compressor that says 'turn motor on' when pressure falls below a certain low level pressure pre-set & 'turn motor off' at a different high pressure preset?
Isn't my requirement kind of the inverse of shop compressor that says 'turn motor on' when pressure falls below a certain low level pressure pre-set & 'turn motor off' at a different high pressure preset?
A quick search on Amazon shows a whole bunch with different pressure ratings. This one needs power because it has a circuit of some kind. This kind is purely passive, but you can't adjust the pressure.
It should be noted that all of these operate on a pressure difference using the ambient air pressure as a reference. So if you are going to use it at high altitude or something, the triggering pressure will be different
It should be noted that all of these operate on a pressure difference using the ambient air pressure as a reference. So if you are going to use it at high altitude or something, the triggering pressure will be different
Pressure Switch 120-150 PSI Air Compressor Pressure Switch 1/4"-18 NPT Air Pessure Switch 24V 12V Pressure Switch Air Tank High 150PSI Pressure Switch 120PSI Pressure Controller
I'm after a vacuum switch. Assuming atmospheric pressure is nominally 101 kPaA (Absolute), I might want to operate at anything (settable) between say 50-80% (50-80 kPaa = 7 - 11 psia) ). In composites, depending on what you are doing, too much vacuum can be a bad thing. You can distort the substrate or resin starve the cloth. The hobby unit in post #1 is preset to 7" Hg about 23 kPa, but from memory I think it would draw up to 50 kPa by dialing in the screw
If money was no object I would just buy my way out of the issue. I suspect there is a pump like mine inside the box, but they have the controls figured out. 1750 lb/ft2 = 12.15 psi = 83% of atmospheric
www.vacupress.com
spendy buggers
www.vacupress.com
Compact 150 Vacupress® Pump | Vacuum Pressing Systems
Compact 150 Vacupress® Pump perfect for the home woodworking shop. Explore veneering and laminating wood projects without the expense of larger systems!
www.vacupress.com
spendy buggers
VacuPress® Pumps Archives - Vacuum Pressing Systems
www.vacupress.com
Might this work? 15A, 250VAC rating.
www.evcreate.com
Here is schematic diagram for DC operation.
Vacuum pump for power brakes - EVcreate
In a car converted to electric there is no motor vacuum available. Most straightforward solution is to use an electric vacuum pump. Unfortunately these are noisy. I have looked at a few and tested a Mes-Dea and Hella. Spoiler: I prefer electric power brakes.
www.evcreate.com
Here is schematic diagram for DC operation.