power flickering from small 12vdc -> 120vac inverter attached to EV

[RustyShackleford]

A fleshed-out schematic ...

The SPST switch would be used to switch between normal and grid-outage mode. Turning off the DPDT switch when changing modes is probably not strictly necessary, but would be good practice - if the pump pressure switch were "on" when switching to grid-outage mode, it'd be a good to energize the transformer before loading it.

I'm bewildered and clueless about the varieties of fuses. K5 seems like a good general-purpose one. I think fast-acting is ok since the pump has no startup surge.

 

[gthomas785]

I'm bewildered and clueless about the varieties of fuses. K5 seems like a good general-purpose one. I think fast-acting is ok since the pump has no startup surge.

If all you're looking for is short circuit protection on the secondary side, I think you could use a circuit breaker.

 

[RustyShackleford]

If all you're looking for is short circuit protection on the secondary side, I think you could use a circuit breaker.

Have to figure out how to mount it.

 

[RustyShackleford]

Seems like this thing has gotten awfully complicated, when some people might just say keep the transformer always in the circuit, and then the only other component would be the fusing on the transformer output.

In particular it seems like overkill to have TWO switches. So I'm thinking to omit the DPST switch on the output and just use a delay-on-make timer between the 120vac going into the transformer and the relay coil. Let's the transformer saturate before it's loaded.

 

[gthomas785]

Have to figure out how to mount it.

Get a short piece of DIN rail?

If you use a circuit breaker on the secondary, you can just turn that off before switching on the transformer.

 

[Whitenuckler]

A fleshed-out schematic ...

View attachment 347119

The SPST switch would be used to switch between normal and grid-outage mode. Turning off the DPDT switch when changing modes is probably not strictly necessary, but would be good practice - if the pump pressure switch were "on" when switching to grid-outage mode, it'd be a good to energize the transformer before loading it.

I'm bewildered and clueless about the varieties of fuses. K5 seems like a good general-purpose one. I think fast-acting is ok since the pump has no startup surge.

Leviton​

Model # 37921-741 TD CRN - I never had to fuse small pumps, but a TD seems correct. Fast Acting is only for electronics SCR's ect.
I would have a small toggle switch for the relay coil, so that energizing the transformer and coil are not happening at the same time.
The transformer could have a fuse too, on the 120V, if you buy a 3 pole fuse holder. I am missing my meter

 

[RustyShackleford]

If you use a circuit breaker on the secondary, you can just turn that off before switching on the transformer.

I'd have to open the enclosure, unless I mount it into the side of the box somehow - but I guess i'm not going to be doing it often.

I just don't see why a circuit breaker would be better than the cartridge fuses - I'm not planning to blow a bunch of 'em.

Model # 37921-741 TD CRN - I never had to fuse small pumps, but a TD seems correct. Fast Acting is only for electronics SCR's ect

Thanks. So just go for a Type D of the right amperage ? (The place I usually buy from doesn't carry the Leviton).

I would have a small toggle switch for the relay coil, so that energizing the transformer and coil are not happening at the same time

I'm really liking the idea of a delay-on-make timer, so the output isn't connected until some time after the transformer is energized. Then just one action required, flipping that toggle switch.

Here's a new schematic. Thank you guys for playing along with my obsessing ...

 

[Whitenuckler]

I'd have to open the enclosure, unless I mount it into the side of the box somehow - but I guess i'm not going to be doing it often.

I just don't see why a circuit breaker would be better than the cartridge fuses - I'm not planning to blow a bunch of 'em.


Thanks. So just go for a Type D of the right amperage ? (The place I usually buy from doesn't carry the Leviton).


I'm really liking the idea of a delay-on-make timer, so the output isn't connected until some time after the transformer is energized. Then just one action required, flipping that toggle switch.

Here's a new schematic. Thank you guys for playing along with my obsessing ...

View attachment 347129

I go to bed dreaming of this crap. I hope it ends soon. Watching utube seems to help. I think you have it nailed down.

 

[RustyShackleford]

I might have to go back to the DPDT toggle switch. I'm having trouble sourcing a DPDT relay with high enough contact rating. Everything seems to be the White-Rodgers 90-341 (and clones from other manufacturers). Here's its label:

At 240vac, the FLA rating is only 6 amps. Now FLA is a motor thing, and this pump doesn't look like a motor: power factor is 1.00 and there's no startup surge. So maybe it's ok.

Otherwise, there's the much more expensive class such as: https://www.zoro.com/schneider-elec...iU_QQnnlheK1IGOLTCZnN2Ro6c338eSBoCWK4QAvD_BwE.

 

[Whitenuckler]

I might have to go back to the DPDT toggle switch. I'm having trouble sourcing a DPDT relay with high enough contact rating. Everything seems to be the White-Rodgers 90-341 (and clones from other manufacturers). Here's its label:

View attachment 347131

At 240vac, the FLA rating is only 6 amps. Now FLA is a motor thing, and this pump doesn't look like a motor: power factor is 1.00 and there's no startup surge. So maybe it's ok.

Otherwise, there's the much more expensive class such as: https://www.zoro.com/schneider-elec...iU_QQnnlheK1IGOLTCZnN2Ro6c338eSBoCWK4QAvD_BwE.

https://www.automationdirect.com/adc/shopping/catalog/relays_-z-_timers/electro-mechanical_relays/ad-pr40-2c-120a

This is the one you posted. It seemed to be beefy enough.

 

[RustyShackleford]

https://www.automationdirect.com/adc/shopping/catalog/relays_-z-_timers/electro-mechanical_relays/ad-pr40-2c-120a

This is the one you posted. It seemed to be beefy enough.

Yep, backordered except for the one with a 12vdc coil, so I need a whole 'nother component for that. Or at extorntionate place that was double the price plus $22 shipping. Or the much more expensive clones, like the Zoro one. But one pro tip about Zoro: if you just stick something in your shopping cart, they will inevitably send you an email saying "will 20%-off help ?". So I guess I'll just grin and bear it; that DPDT switch is $35, so the cost isn't that much more.

 

[Whitenuckler]

Yep, backordered except for the one with a 12vdc coil, so I need a whole 'nother component for that. Or at extorntionate place that was double the price plus $22 shipping. Or the much more expensive clones, like the Zoro one. But one pro tip about Zoro: if you just stick something in your shopping cart, they will inevitably send you an email saying "will 20%-off help ?". So I guess I'll just grin and bear it; that DPDT switch is $35, so the cost isn't that much more.

Weasch High Power Relay JQX-62F-2Z, Coil Voltage AC 110V 80A, DPDT 2NO 2NC, Electronmagnetic Relay, 35mm Rail Mount (AC 110V) : Amazon.ca: Automotive

Weasch High Power Relay JQX-62F-2Z, Coil Voltage AC 110V 80A, DPDT 2NO 2NC, Electronmagnetic Relay, 35mm Rail Mount (AC 110V) : Amazon.ca: Automotive

www.amazon.ca

Search "power relay DPDT relay 30A 600V"

 

[RustyShackleford]

FWIW, I posted this as a stackexchange "question" and just posted my own "answer" ...

wiring transformer to drive 240vac well pump from 120vac circuit

This is a followup question from: running 200-240v well pump from 120vac using step-up transformer I am planning to provide backup power (for grid outages) to my home using a 120vac power station. ...

diy.stackexchange.com

 

[RustyShackleford]

One more thing: thinking the fuses should be on the transformer output (before the DPDT relay) instead of on the overall output.

 

[Whitenuckler]

One more thing: thinking the fuses should be on the transformer output (before the DPDT relay) instead of on the overall output.

Yes, that would be standard design. We always had a "primary" fuse too, but that was for industrial panel boards/ switchgear ect.

 

[RustyShackleford]

Arghh, I've realized another potentially-serious problem: The transformer outputs are floating with respect to ground, so they represent a "separately-derived system". So I should probably tie one transformer output to ground, making it effectively a neutral. Which means the DPDT will suddenly be switching the well pump from a 240vac pair with common-mode voltage zero to one with common-mode voltage 120v. I worry the pump won't like that.

 

[Whitenuckler]

Arghh, I've realized another potentially-serious problem: The transformer outputs are floating with respect to ground, so they represent a "separately-derived system". So I should probably tie one transformer output to ground, making it effectively a neutral. Which means the DPDT will suddenly be switching the well pump from a 240vac pair with common-mode voltage zero to one with common-mode voltage 120v. I worry the pump won't like that.

Does the pump have any sort of ground fault detection now? This is just for emergency anyway, so not it's normal feed.
You could have two 120V stove light bulbs and have the center grounded. Then you would have a ground on the 240 and ground detection lights.

 

[RustyShackleford]

Does the pump have any sort of ground fault detection now? This is just for emergency anyway, so not it's normal feed.

Yeah, but it's damage to the pump on the switchover that concerns me. I'm gonna feel like a real dope if I eff-up my pump with this. I don't know if the pump has ground-fault detection; I know I ran it successfully in preliminary testing with the transformer (and no grounding on the transformer outputs).

You could have two 120V stove light bulbs and have the center grounded. Then you would have a ground on the 240 and ground detection lights.

So sort of fake a center-tapped transformer. Could just do it with resistors too I guess. It's also possible the transfomer outputs are 180 degrees out of phase with the inputs (or in-phase, depending upon how the windings are done); if I can determine that (without a scope) I can just reverse the outputs to get them sync'd.

 

[gthomas785]

I think you'll be fine to leave it floating. The ground detection lights are not a bad idea but not really necessary either imo. For one thing, the pump motor is fully isolated and does not care about the ground. The capacitive coupling of your long cable to the earth makes it likely that each leg will have an approximately equal voltage to earth ground.

The only feature lacking is the ability to clear a line-to-ground fault, which is not intrinsically hazardous on an ungrounded system. It would be taken care of during normal times by your circuit breaker, and if it happened while on backup then the ground fault would just make one leg grounded for a while until you switch back to regular power and discover it.

 

[RustyShackleford]

I think you'll be fine to leave it floating. The ground detection lights are not a bad idea but not really necessary either imo. For one thing, the pump motor is fully isolated and does not care about the ground
The capacitive coupling of your long cable to the earth makes it likely that each leg will have an approximately equal voltage to earth ground.

Yes, but when the switchover occurs and it's seeing a very different common mode voltage. Except it's actually not, I think you're right. I checked the DC voltage to ground on each (unloaded) transformer output and got about 4 volts on one and 100mV on the other. Then I put a 10K resistor between each transformer output and ground and got 1/2v on each (the resistors aren't balanced, 10.3K and 10.5K, maybe that explains it ?). I guess smaller resistances would be better but I need to get some high-wattage ones.

I'd still like to be able to have the two inputs to the DPDT be in phase; I guess I can just measure the AC voltage between one of the inputs and each of the outputs and it'll be lower for the in-phase one.

I definitely need to add NTC thermistor(s) to the inputs to the transformers: the breaker has flipped about every 1/4th time I've powered up the transformer while I do these experiments.

 

[gthomas785]

There's no way to make them in phase if one side is coming from the inverter. Don't you have to shut your whole panel down to switch over anyway? That'll give the pump some time to stop and it won't care about phasing the next time it starts.

 

[RustyShackleford]

There's no way to make them in phase if one side is coming from the inverter.

Can you hear me slapping my forehead up there ? I might be switching during testing, of course, but I can simply turn off the breaker.

Don't you have to shut your whole panel down to switch over anyway? That'll give the pump some time to stop and it won't care about phasing the next time it starts.

True. Need to switch my adapter (whatever I call this thing) over before I power the panel back up with the inverter.

 

[Whitenuckler]

Yeah, but it's damage to the pump on the switchover that concerns me. I'm gonna feel like a real dope if I eff-up my pump with this. I don't know if the pump has ground-fault detection; I know I ran it successfully in preliminary testing with the transformer (and no grounding on the transformer outputs).

This is why we have the output switch. That is off during any switching. That should be the first thing to be shut off, and the last thing to be turned on. The pump itself will have no ground detection, but it would be a good thing to have(add). If you start to get a ground, it's time to order another pump.

 

[RustyShackleford]

This is why we have the output switch. That is off during any switching.

Well, my latest iteration has no switch on the output. But, I realized the input (to my enclosure) will be powered down when I'm doing this, because I'm switching the panel over to grid-outage mode (main breaker off, interlocked generator breaker on). So that's just as good I think. So when that happens the pump has been off ahwile. And if I'm testing, I'll just turn the breaker off, to simulate a grid outage.

I'm still going to add resistors (like the bulbs you recommended) to keep the transformer outputs referenced to ground. And an NTC thermistor on the transformer input for sure, which probably elminates the need for the delay-on-make to the DPDT coil.

 

[RustyShackleford]

Argh, this is driving me crazy (and you too, no doubt). Thinking I should bag the relay and go back to the DPDT switch (with center "off" position). I just liked the idea of only having one switch. Instead of two switches and having to remember to operate them in a certain sequence; but with the NTC thermistor, don't need to worry about transformer inrush so much, so probably doesn't matter if I turn the SPST switch on after I've switched the DPDT switch to grid-outage mode.