Author Topic: AC ONLY products  (Read 307 times)
F96T12 DD VHO
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AC ONLY products « on: February 12, 2018, 06:26:41 PM » Author: F96T12 DD VHO
Why does it matter weather you use AC or DC?
For example:
15 AMPS
1875W
120VAC AC ONLY
This is on one of my vacuums
Like what would happen if I used DC, would it blow up?
« Last Edit: February 12, 2018, 06:29:10 PM by F96T12 DD VHO » Logged

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Re: AC ONLY products « Reply #1 on: February 12, 2018, 06:39:25 PM » Author: Lodge
I don't think it would blow up, but it might catch on fire and burn your house down, so the net effect would be almost the same, AC motors really don't like being fed DC power, and things like switches don't do well unless they are designed for DC power and fuses and breakers have the same issue with arcing in DC, really DC is different monster the current doesn't ever stop like it does on AC allowing the arc to extinguish ( there is no 0 Volt point ), but you can get DC stuff without to much effort just make sure it's DC or AC/DC rated before playing with DC power..
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Re: AC ONLY products « Reply #2 on: February 12, 2018, 07:58:05 PM » Author: Lumex120
Why does it matter weather you use AC or DC?
For example:
15 AMPS
1875W
120VAC AC ONLY
This is on one of my vacuums
Like what would happen if I used DC, would it blow up?
Wow, 1875 watts? That's crazy.
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Re: AC ONLY products « Reply #3 on: February 12, 2018, 08:26:56 PM » Author: Lodge
Wow, 1875 watts? That's crazy.

Most likely Locked Rotor amps to get that value, so it's only right at start up and only last a few cycles if your lucky,  Vacuum cleaner companies like showing the maximum values, like shop vacs with a 5 Peak HP motor on them, but some how they only use only 10 amps at 110, where the extra 2528.5 watts need to hit 5 hp comes from is most likely the tiny black hole they included in the unit that is powered by dust bunnies that the house hippo didn't eat....
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Medved
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Re: AC ONLY products « Reply #4 on: February 13, 2018, 12:40:00 AM » Author: Medved
Wow, 1875 watts? That's crazy.

Why? Quite common power rating, if you want something to function in few passes and does not need to sweep the carpet 10x.

For the AC vs DC: The vac's motor itself wont likely care at all (the commutation inside is already way fastervthan the mains frequency, so it happensfar outside the zero crosses), but what will have problems are really the switches and control (the soft starts are triac based,so work only on AC). So turning it ONo  DC would just cause a bit jerkier start, turning it off would mean a fire starting from the switch mechanism.
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F96T12 DD VHO
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Re: AC ONLY products « Reply #5 on: February 13, 2018, 05:58:02 AM » Author: F96T12 DD VHO
Wow, 1875 watts? That's crazy.

I can't use it continuously for more than 20 mins or a trip to the breaker switch
So every time I plug it into the wall its plugged into a power strip so that breaker trips instead of the mains
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Re: AC ONLY products « Reply #6 on: February 13, 2018, 07:11:03 AM » Author: funkybulb
Most vacuume cleaners  use Universial motors
Cause it only motor u can get such high rpm
Yet it Ac /DC  type of motor due to commentstor and
Brushes.  Same with most power tools except for
Air compressors as it use inducttion motor
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Re: AC ONLY products « Reply #7 on: February 13, 2018, 03:34:18 PM » Author: Ash
I can't use it continuously for more than 20 mins or a trip to the breaker switch
So every time I plug it into the wall its plugged into a power strip so that breaker trips instead of the mains
Vacuuming for 20 min straight with a residential grade vacuum is pushing the thermal design limits of the motor, even if it wouldn't trip any breakers....

 
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Re: AC ONLY products « Reply #8 on: February 13, 2018, 05:09:58 PM » Author: F96T12 DD VHO
Vacuuming for 20 min straight with a residential grade vacuum is pushing the thermal design limits of the motor, even if it wouldn't trip any breakers....

 
I’ve mentioned in the thread “Things which annoy you”  that my breakers are sensitive thus preventing me from vacuuming longer than 20 mins
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Re: AC ONLY products « Reply #9 on: February 14, 2018, 01:56:03 AM » Author: tolivac
Appliances with universal motors for AC only-the big problem is the power switch--The most common power switch for these are single pole switches.These work fine for AC power--BUT NOT for DC.The single pole switch arcs over due to reactance of the motor to DC.The motor runs fine from DC.I have an older Skilsaw that can run from AC or DC.It has a DOUBLE pole snap action switch so there would be no arcs on DC.It also works fine on AC power.Also if the appliance has an electronic controller or speed control-those won't work from DC power.
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Re: AC ONLY products « Reply #10 on: February 14, 2018, 08:45:52 AM » Author: Medved
It has a DOUBLE pole snap action switch so there would be no arcs on DC.

With any voltage greater than about 15V per contact in series, you will always have an arc to deal with, so you need some means to extinguish it.
With AC and not that high currents (not much above 20A) it is straight simple: The inherent zero crossing uses to be just enough.
For higher currents (e.g. fault currents to be interrupted by a circuit breaker) and/or DC you need really designed in arc quenching mechanism. The lower the voltage and lower the current, the easier it becomes.
E.g. for an automotive environment up to 24V battery you suffice with single contacts, they just need some heat hardening. Higher battery voltages (up to 60V or so) need double contacts (two contacts in series - e.g. two fixed contact terminals, with a moving bridge in a relay), which is obviously more expensive.
That is the main reason, why larger road vehicles, as well as e.g. aircrafts use 24V (28V when charging) battery systems and why higher voltage levels (e.g. PowerNet42V system proposed for cars in early 2000's, today the proposed system is 48V) are long time not that much spread around.
Larger voltages up to e.g. 120V you may get away with just larger distances between contacts (that means higher operating forces, higher consumption of the control electromagnets in relais,...).
Higher voltages than about 120V need really dedicated arc quenching structures (arc blowing magnets, quenching traps,...). These may be incorporated into seemingly plain switch and be very easy to overlook (if you dont know, what features to look for; for 120V just a bit prolonged pieces of metal behind the main contact will quite efficiently suck the arc from the contacts and prolong it so it is not able to hold on), but they must be there.
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Re: AC ONLY products « Reply #11 on: February 14, 2018, 01:56:11 PM » Author: MissRiaElaine

Like what would happen if I used DC, would it blow up?
Are you likely to..?
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