how long does utility power have to be off b/4 switching

[mike heckler]

When switching between the power supplied from utility supplied electricity to power supplied by an auxillary source ie. an inverter powered by a windmill, how long does one source have to be off before the other is turned on?

I made a switch using a relay and voltage sensor that switches a circuit between utility ac current, or to my windmill, battery, inverter. It turns on a relay when the battery is charged, and switches back to utility ac power when the battery becomes dis charged.

I know this sounds stupid but if the switching occurs when a load, like a pump is running can their be a problem with the switch being too fast,? Inductance???

Thanks ,,,,Mike

[alterfuels]

If you have the right inverter you can run your load through the inverter.  Put the relay on a charger so when the batteries get low the charger comes on from utility power and shuts of when it gets charged back up.  If your inverter has a charger you could just put the relay on the line in from utility then load runs of utility and charges battery at the same time.  I wish I had this problem.  I have to run a generator because there is no grid what so ever on our Island!

[Tom in NH]

Mike, This sounds very similar to the switch I made to turn on a grid powered charger when the batteries get low and the sun isn't shining on my solar panels.

( http://www.altenergyweb.com/gridcharger.htm ) It can be tricky, can't it. I noticed what may be something similar in my setup. The batteries could be in fairly good shape, but when the refrigerator turned on, the battery voltage dropped low enough to trigger the switch and turn on the grid power even though the batteries really were fine. The cause seems to be due to a drop in voltage caused by the surge of the motor starting.I implemented a fix in software (my circuit is controlled by a PIC microcontroller): whenever the battery voltage drops, I delay for a few seconds and retest the voltage. If it's still low, the relay turns on the grid power. Otherwise it's ignored. This takes care of about 95% of all the false readings I was getting.

I'm not sure how you could imlement something similar. Maybe you could cheat a little and lower the threshold voltage for your relay. Or maybe you could figure out some kind of capacitor timing circuit to slow down the response time. Good luck, --tom

[wpowokal]

Mike, there is no such thing as too fast, there MUST be a break before make though.

If there is a fast changeover most loads will only falter briefly and not stop, good for refrigeration.

But please ensure the two supplies can not be on at the same time, the mains will win and your inverter will loose.

regards Allan down under

[mike heckler]

Thanks for the response,,,

I was worried that the relay might make the transisitionfrom mains to inverter too fast. I have an aims 2500 inverter that stopped working for one reason or another shortly after installing this switch. I guess now that it would have failed any way..

My switch was made of a lm3914 voltage indicator, a 555 timer, an n channel fet, and a heavy duty relay.

I used the last voltage indicator pin, that is set to drive an led, to go to ground level at 12,72 volts, and ran this output to the trigger of a 555 timer, and the output of the 555 to an n channel fet, which drives the relays center contacts from the normally closed (grid power) to the inverter power. If the battery is 12.72 or above, the relay is activated to the inverter for 90 seconds, and then will turn back to the grid unless at this point the voltage of the battery is 12.72 or above, in which case it will stay on.

[DanG]

Seems my electric power provider intentionally drops power daily at 5am for enough time to activate the office UPS - just enough to bounce switch on-and-off. Make sure to accomodate nuisance dropouts with some safekeeper circuit testing...

[Bruce S]

Mike;

   According to the utility companies in MO the power should have a lag time of 4 seconds and most will not even allow a switch over box unless it been tested.

We have one for each of our buildings and both were tested to meet this timing.

This is to ensure there is no cross over feed from one to the other and to keep the outlets from trying to shove over voltages through the outlets.

We have a system wide UPS and generator as back ups.

Hope this helps,

Bruce S

[sahlein]

Mike,

See if you can find what is called a "Reversing Starter", a used one is O.K.

It is like a double relay that is interlocked both Electrically and Mechanically

to prevent both sides from pulling up at the same time.

Used usually for reversing a 3-phase motor... they can be used to prevent connecting

somethings at the same time... If one side is pulled up, the otherside is mechanically locked so it can't move.

Joe

[sahlein]

MIKE!!!... P.S...P.S...

You will have to reconfigure the wiring to make it work right..

You just cant hook it up out of the box!!!

Hope I added this in time!

Joe