Automatic line voltage switch?

d a

That was roughly the original configuration, problem being that the pump's starting surge exceeded the not-to-be-named-here chain of devices' capacity by a factor of 2x. The pump, therefore, wouldn't always start; the unit was unreliable.

A single-to-single phase AC motor controller has all the needed stuff in a COTS black-box. Very attractive, if I can find a suitable one.

I still prefer a switch--it's a lot tougher and more reliable than inserting all these converters, inverters, VFDs, etc in the power stream, to save flipping a single switch, once.

-- Cheers, James Arthur

And I'd include a real fuse. The self-resetting poly fuses are prone to self destruction.

Spehro's observation about the interrupting voltage capability of PTCs pretty well rules them out in this application.

I'm not sure I see the advantage of a thermal cutout in each primary leg--that just seems like more parts to fail compared to a single cutout in the common feed.

A fuse or other current-limiter per primary, OTOH, means the protection limit could be halved.

I don't think the VFD thing is viable here--wrong motor type. Too bad.

-- Cheers, James Arthur

The latter has been my goal, but you make a good point--I'll have to make sure that limitation is understood.

How does it know? (Or is it one of those glorified triac lamp dimmers?)

-- Cheers, James Arthur

ormer and a

automatic

rmer,

avy.

lease

=A0I

ute

it

t.

l-

A carefully characterized, optimized mechanical relay might do, I just can't afford the effort. It has to work, it has to be safe, I have little control over the end product, and low confidence that, for example, another (unsuitable) relay might not be substituted ex post facto.

Artificial constraints to be sure, but I've got to work within them.

Low qty., maybe 100.

-- Cheers, James Arthur

Autotransformer and relay - nice. :-)

He could also use a 240 VAC coil relay and wouldn't need a driver, assuming he doesn't need the precision your circuit offers. At 120, a 240V relay won't energize; at 240 it does. A possible down side is that in a brownout it will stay energized down to roughly 30% nominal.

If that - too much hysteresis - isn't a problem, he could use most any common AC coil relay with a suitable series dropping resistance. Those relays generally have a "must transfer" rating of ~80% nominal, and must drop out rationg of ~ 30%.

Ed

=A0 |

=A0 |

=A0|

=A0| =A0

=A0|

=A0|

=A0|

No workie--I'm using Google. Can you give a date, title or other clue so I can search for it?

Thanks, James

=A0 =A0 |

=A0 |

=A0|

=A0| =A0

=A0|

=A0|

=A0|

..

I can't see John's driver, but a brute-force approach with a more predictable threshold could just use a diode bridge, a power zener, and a lower voltage DC relay.

Too much hysteresis--I think that's okay as long as the pulled-in condition is "no step up" mode.

-- Cheers, James Arthur

I see two problems with that..

1. For the time it would take for the replay to respond, you'd had 240V

into a 120 volt config thus, generating a double voltage on the other side before it latched in.. Maybe short but still there.

1. Many replays will maintain at 50% voltage, a little mechanical shock and that relay may pull in.. This would result in only half the voltage. Also, depending on the type of relay you're using, it can make it operate hot to the point of destroying the coil at %50 level if the contacts are not pulled in..

We've seen many AC contactor coils burned and collapsed to the point where they will no longer mechanically push all the way in or get stuck half way, due to lack of voltage for too long!. (Lack of L)

I guess one could use a DC coil via a diode to correct for this..

jamie

That's essentially what John drew in Ltspice.

The pulled in condition is "no step up mode". But examine the "too much hysteresis" with some care before deciding it is ok:

With a 240VAC relay, the typical "guaranteed to drop out" voltage is around 30% of nominal, so a power dip from 240 down to around 72 volts might leave the relay energized, meaning the pump could burn out if the power stayed at that level long enough. It may be extremely unlikely, it might be valid to say you'd have worse troubles in other equipment in that situation, and maybe a whole bunch of other "yada yada yada" but the hysteresis is a factor to be considered. John's 240V circuit has a lot smaller hysteresis, as I recall. His 120 volt version may have too little, but is easily modifiable with one part change, as I recall.

Ed

Maybe add some "smarts" to it: Delay applying any power to the pump while voltage level is decided. And hold up all the controls during a brown-out? ...Jim Thompson

=A0 |

=A0 |

=A0|

=A0 =A0|

=A0 =A0| =A0

=A0 =A0|

=A0 =A0|

=A0 =A0|

John was kind enough to e-mail it to me (that was super nice).

The relay being pulled in selects "no step up." If the initial voltage is 220VAC, the relay pulls in and the AC line voltage x1 is applied to the pump. That's fine. If there's a brown out after the unit is turned on, the pump sees the brown-out. That's fine.

If the unit is turned on during a mega brownout where 220VAC drops below 130VAC, well, the pump sees 2x the line voltage. When the line voltage recovers (in this highly improbable situation), there's a brief transient, then the relay engages and switches to 1x mode.

True. The use of zeners plus a lower voltage relay means the relay hysteresis is far less significant.

Thanks for all the ideas guys.

-- Cheers, James Arthur