auto power using relay

System · September 2010

I'm a master electricain experimenting with solar. Have done a few small set ups. What I want to do is have a relay set to turn off at 10.5V and on at 13V. OR on at 10.5V and off at 13V. This way when the batteries get down to 10.5V it shuts down and using more relays I can have the circuit switch back to Utility Power. Then when the batteries are charged it will automaticly switch to solor power.

Any suggestions on how to do this?

BB. · September 2010

Re: auto power using relay

Part of this depends on the amount of power you wish to control... There are some charge controllers that have Low Voltage Disconnects (LVD) that do exactly this (search this page for some "LVD" enabled charge controllers)--But for the most part, they are only rated around 8 amps DC.

Normally, AC Inverters have their own LVD protection circuitry built in... You would use the LVD circuits to control radios/lighting/etc. from "killing" the battery bank and/or damaging the devices with low voltage DC.

NOTE: 10.5 volts DC is typically a dead battery... Draining a battery to 100% dead can permanently damage a battery bank. And LVD setups are approximate... Battery voltage varies with load, temperature, and state of charge--Making it very difficult to "accurately" use an LVD to protect a battery bank from misuse.

If you need to cut off a battery bank before it is damaged--You might look at a programmable Battery Monitor... A couple (like the Xantrex Units, and the Victron Energy monitors have a programmable output that can be used as an LVD control).

Or you can get separate programmable controllers too.

Using simple high current relays can cost you a fair amount of power on a small system (~1 amp of 12 volts).

And there are latching relays that only use power to switch state...

For switching the AC side, there are some simple Transfer Switches that you can wire up for different options.

There are lots of options out there--And probably none of them are cheap.

Some inverters have a separate AC Inhibit line (no large DC relays required)--For a "small" 12 volt PV system--the MorningStar Sureshine 300 watt TSW 120 VAC inverter would be a nice unit to experiment with. And for small solar, it is "appropriately sized" (you can get big/cheap MSW inverters that are kWatt sized units--but for small solar, they can drain the entire battery bank in tens of minutes or an hour or so).

-Bill

czyhorse · September 2010

Re: auto power using relay

I remember reading an article from Solar John about this topic on his web site (http://solarjohn.blogspot.com/)...coincidentally, this is also a project I was considering with my setup as well.

Has anyone here used an Outback FM60's AUX port for a LVD? I'm thinking of setting mine up to switch my Exeltech XP1100 inverter off when the bank voltage drops below roughly 75% SOC, then transfer over to the grid.
Only problem is the Outback AUX function can only be programmed for one task at a time. If I wanted to power a small vent fan, could I use something like the Morningstar Relay Driver in conjunction with the FM60's AUX settings?

Here are some examples of John's setup:

vcallaway · September 2010

Re: auto power using relay

The IOTA switches rock. I'm using those for the battery backup system in my house. Oddly enough it got used last night.

Intellitec makes a honkin big 200A latching relay for battery disconnect. The way latching relays work is power is supplied to a set of poles that "latches" the connection one way. The polarity is reversed (only takes a couple of milliseconds) and then it is latched the other way.

The beauty of latching relays is they draw no current except during the split second it takes to switch them. They are used a lot in motor homes to switch battery banks in/out for that reason.

Building a circuit to switch them at a desired voltage level would not be hard.

System2 · September 2010

Re: auto power using relay

I am trying to plan for my future home I am planning on building in a few years. Was going to put my lighting on seperate circuits so those could be run off the solar power. CFL's would keep the wattage down for the time being until LED bulbs come down in price.

If I could get the battery bank to shut down at low voltage then I could hook up a basic 15 amp 120V contactor for the lighting circuit so that Utility would be restored. Thats what I was hoping. If I could figure out how to do this I may try it in my current home.

This would give me back up power considering I loose power often where I live. Usually not for more then a few hours when it does happen. Course I have a gen for back up power.

Thanks for all the post so far. Getting some great idea's!!!

vcallaway · September 2010

Re: auto power using relay

Sound similar to what I have setup.

This is my setup:

Power comes in from the mains to the top left box via 2 x 30 Amp breakers.

Down at the bottom you see the box with the black tail. That is the genny cord.

The way it works is switch (1) is set so that the relay is engaged when we have main power. When power is lost it is fed by one leg of the genny cable.

Switch (2) is set the same way but feeds into switch (3) before going to the panel. Switch (3) is set so that when there is no input the inverter is connected to the panel.

When my power goes off the inverter immediately takes over. The relays are fast enough that the Tivo and computers don't miss a beat.

The outlet under the panel has one plug wired to the inverter side and the other to the generator side. Just in case I need to plug something in out in the garage.

This system is overkill for most people. We have outages that last for days sometimes. If I was going to set this up for someone else I would probably not do a generator connection and just use one switch.

The inverter is the second one I put up. The first was a Vector 2k and it blew up. I also toasted an AIMS automatic 3-way switch. I am pretty sure the switch took out the inverter. This inverter is a Chinese made that works surprisingly well. I've loaded it to the max and it has performed. I chose it because when not under load it draws almost no power. You are also supposed to be able to stack them for more power but I have not tried it. Don't need to.

The inverter at 10.5 volts will start beeping and shut off. Since this is a rare occurrence I don't think it is an issue as far as the batteries are concerned.

XRinger · December 2010

Re: auto power using relay

VCallaway, How has that inverter been working out for you?

I've been thinking about getting the Ebay "2500/5000W Stackable Power Inverter 48V DC TO 120V AC" version,
for the little backup system I'm building.

I was wondering if you ever got to look at the "semi-pure" waveform on an O-scope,
while the inverter was under a 50 to 100 percent load??

Those IOTA switches look like some nice hardware! A couple of those are on my shopping list.

Cheers,
Rich

vcallaway · December 2010

Re: auto power using relay

Surprisingly the inverter is working pretty good. Standby draw is almost non-existent which is why I chose it. None of the electronics it powers seem to have an issue with the output. In fact the one time I fired up the generator I found that the output from it was not as clean.

I have my lights which are CFL's, 2 TV's, 2 Tivo's, surround sound, internet hardware and two laptops are connected to the inverter. We have had a whole slew of outages in the last few months and it works great. The transfer is quick enough that we don't notice the power going off when watching TV. At least until the cable goes out

Right now I have a single 8D (200Ah) battery connected. A power outage in the evening means I need to charge the battery around noon the next day. That is when it hits about 60%.

When I bought the inverter I figured it would be temporary until I could afford a good one. It is 3 yrs old now and I don't think it is going to go anywhere. I was tempted to to buy another one for the RV but a local vendor had a Xantrex Sinewave inverter on sale and I went with it instead.

niel · December 2010

Re: auto power using relay

that's a very interesting arrangement and i too was looking at those iotas. if it works don't fix it right.:-):cool:

dagr51 · December 2010

Re: auto power using relay

I have 2 Iota-30's and an Iota-50 transfer switches to transfer various things. I love them except when I stop my generator, the switch from the genny back to my inverter isn't fast enough or clean enough on the Iota-50 for my audio receiver or my DirecTV satellite receiver and they both have to be restarted, which I found annoying. I wired a separate, dedicated inverter circuit for just the electronics to avoid the problem.

niel · December 2010

Re: auto power using relay

unfortunately when using more than one, the relay delay times can be additive at some points of operation.

XRinger · December 2010

Re: auto power using relay

Okay VCallaway,
Thanks for your input.
I would use the 2.5kW stackable for general small load use,(200 to 400w)
but really need it to power three sump pumps (300w each), during grid failures.
Since the Semi-sine-wave turns on under load, I'm betting it will work good enough.
And my batteries should last long enough for me to roll the 5kW gas gen out
of the garage and connect up some extension cords.

I don't think that many people have ever heard of a Semi-sine-wave inverter.

Semi-sine-wave? Sounds like Almost a virgin.. haha.

Thanks,
Rich

RCinFLA · December 2010

Re: auto power using relay

I did a quick check on one of the IOTA transfer switches and it seemed to have a 20-30 second transfer delay. Not sure about other models.

This is good, and is a requirement if you are running anything with a motor, like a refrig, on the inverter.

Since the inverter is asyncronous to the grid you do not want a quick transfer since the inverter may just happen to be out of phase with previous grid connection.

To a motor, if the A.C. phase changes suddenly by 180 degrees it is sort of like hitting the breaks.

niel · December 2010

Re: auto power using relay

RCinFLA wrote: »

I did a quick check on one of the IOTA transfer switches and it seemed to have a 20-30 second transfer delay. Not sure about other models.

This is good, and is a requirement if you are running anything with a motor, like a refrig, on the inverter.

Since the inverter is asyncronous to the grid you do not want a quick transfer since the inverter may just happen to be out of phase with previous grid connection.

To a motor, if the A.C. phase changes suddenly by 180 degrees it is sort of like hitting the breaks.

wow, with a delay like that one can expect to need to reset pcs, modems, cable or satellite boxes, and clocks lacking battery backup. i guess that would be the brakes.:roll:

RCinFLA · December 2010

Re: auto power using relay

The only way to get faster transfer is to use a grid syncronizing hybrid grid-tie like XW. Old Trace DR series modified sinewave inverters did syncronize the modified sinewave to the grid so it could do a quick transfer. Most small PC UPS units do this.

If all you are using is lights, TV's and PC's you don't have to worry about abrupt phase reversal. But don't use a syncronous motor on it. I personally would not run a refrig on a modified sinewave inverter as it is rough on the compressor.

It is just bad practice to do an immediate transfer with async inverter.

Looking at inverter in picture, the 'semi-sinewave' inverter looks like a modified sinewave, or a more appropriate name, 'modified squarewave' inverter.

A modified sinewave inverter has an output that chops between three voltages. +155v, 0v, and -155 volts. It works out to an RMS voltage of 120 vac, but waveform is nothing like a sinewave.

MSW have lowest no-load current drain, but still several watts. A true sinewave inverter has a higher no-load current drain as it is chopping the output MOSFET's very fast. It also has some extra losses due to output filter. But you get a true sinewave output.

Generally, the higher power the inverter, the higher the no-load current drain. Some units do have automatic standby modes that shuts down the inverter when load drops to very low level.

vcallaway · December 2010

Re: auto power using relay

The IOTA transfer delay is set to either on or off by a switch on the circuit board.

I have mine set so the relay is energized when on grid power. I have the delay on so that it stays on the inverter while the grid does its usual cough and sputter when coming back online.

I emailed IOTA about the duty cycle of the relay and having it energized 99.9% of the time. They told me it was not an issue and that many others are doing it the same way.

I'm fairly confident the "semi-sinewave" claim by the guy who sells those inverters is marketing B.S. Mine does not run an inductive load any better than my Vector did.

XRinger · December 2010

Re: auto power using relay

RCinFLA wrote: »

I did a quick check on one of the IOTA transfer switches and it seemed to have a 20-30 second transfer delay. Not sure about other models.

This is good, and is a requirement if you are running anything with a motor, like a refrig, on the inverter.

Since the inverter is asyncronous to the grid you do not want a quick transfer since the inverter may just happen to be out of phase with previous grid connection.

To a motor, if the A.C. phase changes suddenly by 180 degrees it is sort of like hitting the breaks.

Maybe I misunderstood what I read. I was thinking the 30 sec delay was to allow the generator to stabilize for a while, before taking over the line feeding your loads.

When the generator first came on and sent AC to the IOTA, it would start the timer, and after 30 sec, the relay would be pulled in, disconnecting the source A (the grid?) and connecting the generator (Source B?) to the loads.

That's the 'Use Backup when available' mode and I believe it can also be wired to use the grid (or other source) until that source fails..
The relay drops out (blackout occurs) and the NC contacts connect the backup power to the loads.
You can still watch TV, if there was actually any backup power available..

If that's not the way it works, sorry to have distracting you all..

I think the power source switch is pretty fast, since some loads (laptops TVs etc) don't reset.

As for AC motors, I would think the inertial would overcome any braking action, and the motor would easily re-sync to the 60Hz. Like when the grid drops off line for 1/8 to 1/2 of a second.

Cheers,
Rich

BB. · December 2010

Re: auto power using relay

The Iota transfer switches are configurable to use the delay or not... Normally the delay is used to allow the gensets to get up to speed and stabilized before hitting with a load.

-Bill

niel · December 2010

Re: auto power using relay

BB. wrote: »

The Iota transfer switches are configurable to use the delay or not... Normally the delay is used to allow the gensets to get up to speed and stabilized before hitting with a load.

-Bill

and that delay will cause things to be reset as i stated. it just won't be a near instant on transfer to allow pcs and such to stay on without a reset. even when not set for delay, going through 3 relays will cause a 3x larger response time over using 1 of them and although this is still fast it may be enough for a reset to occur on some things.

mike95490 · December 2010

Re: auto power using relay

Switching a fridge or other compressor - 30 seconds off does nothing - you still have high output line pressure, and the compressor motor will stall trying to start, till the overload trips. You want a 5-10 minute delay before restarting to let the pressure drop.

dagr51 · December 2010

Re: auto power using relay

The delay (if set) on the Iotas is 17 seconds after "alternate source power" is detected (in my case, the alternate source is one of my generators). But when the generator power is REMOVED, the transfer back to the default setting is supposed to be instantaneous, but my receivers still notice it (only when the load is removed). I do not have all 3 switches hooked up in series. They each do different things. The 50 amp switch (17 seconds after generator start) switches from inverter power on one leg to generator power, and on the other leg sends generator power to a 30 amp switch, which waits 17 more seconds before sending the genny power to my Iota-75 battery charger (didn't want all loads coming on line at once). The second 30 amp switch is used when I want to switch from my 300 watt TSW inverter to my 1000 watt MSW inverter and is a separate issue.

XRinger · December 2010

Re: auto power using relay

dagr51 wrote: »

The delay (if set) on the Iotas is 17 seconds after "alternate source power" is detected (in my case, the alternate source is one of my generators). But when the generator power is REMOVED, the transfer back to the default setting is supposed to be instantaneous, but my receivers still notice it (only when the load is removed).

I wonder if the receiver drop out (when gen is removed) is caused by
the difference relay arm speed? Since, when the gen voltage (after delay)
pulls in the relay, it's doing the job with gen AC power to the coil.. Motor action.

But, when the gen goes off-line, the relay is returned to the NC posistion,
(the grid) by mechanical spring action. Which could be a good deal slower.?.

Listen to the relay, does it really snap when energized? And just click when it drops out?

Cheers,
Rich

dagr51 · December 2010

Re: auto power using relay

Yup. That's exactly the sound. Anyway, as mentioned, I have since wired a dedicated inverter only circuit just for the electronics that doesn't include the transfer switch and have had no problems since. Thanks.

ggunn · January 2011

Re: auto power using relay

dmmcallister26 wrote: »

I'm a master electricain experimenting with solar. Have done a few small set ups. What I want to do is have a relay set to turn off at 10.5V and on at 13V. OR on at 10.5V and off at 13V. This way when the batteries get down to 10.5V it shuts down and using more relays I can have the circuit switch back to Utility Power. Then when the batteries are charged it will automaticly switch to solor power.

Any suggestions on how to do this?

A SMA Sunny Island will do this, though the programmable relay switch points are triggered by the state of charge of the battery, not the voltage.

ggunn · January 2011

Re: auto power using relay

niel wrote: »

wow, with a delay like that one can expect to need to reset pcs, modems, cable or satellite boxes, and clocks lacking battery backup. i guess that would be the brakes.:roll:

You could get a small uninterruptible power supply to bridge the gap for those pieces.

auto power using relay

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