# voltage controlled switch

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I recently purchased a Voltage Controlled Switch 10 to 60 volts DC input, 30 Amp relay from northern arizona wind and sun and have a question about hooking it up to my 1500 watt aims dc to ac inverter. I have 8 12volt batteries hooked up in parallel. My goal is to have the voltage controlled switch turn on the inverter when the batteries are fully charged. So the question is, the voltage controlled switch input terminals are sized to recieve a 6 qauge wire. Is this big enough to handle the power needed to run a 1500 watt inverter? The distance from my inverter to my batteries is very close only 2' away. Thanks for your help!

Here is a link to the switch http://store.solar-electric.com/volconswit.html

Here is a link to the switch http://store.solar-electric.com/volconswit.html

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## Comments

814✭✭✭cable size not the problem

12v x 30 a = 360 watts:grr

#6 is way too small for a 1500w inverter. # 4 absolute minimum or 3 runs of #6

3,017✭✭✭✭As john p noted, The larger problem is that the relay is far too small to handle the current demanded by the inverter. You will need another approach. The maximum current could be well over 100 Amps at 12 Volt nominal input. At 12.00 Volts, 1000 watts is 83.3 Amps, so 1500 watts, with some surge could be about twice that amount.

You could possibly use a large contactor, paralleling multiple contacts. or perhaps a LARGE solid-state switch -- essentially, a number of transistors in parallel.

Perhaps there is a more direct approach. Many inverters have fairly low stand-by power, but this does become a lot of power in 24 hours.

This is my 2 c worth for now. Good Luck, Vic

30,737adminTwo possible solutions...

- Some inverters have a "DC Remote Switch" option--connect that to your voltage controlled switch.
- Some inverters have "search mode" which cuts back their standby usage from 6-8 watts or so, to less than 1 watt average (the inverter stays off and turns on for a few cycles looking for >8 watt loads). So, they only "turn off" if you turn on one or more AC loads.

-Bill6,290adminThanks for all of your quick responses. It seems to me that I either need a bigger switch or a smaller inverter. I should explain more about my goal. I have a coal stove that runs 24 hours a day heating my hot water and hot tub and my house. It uses 310 watts and 4.76 amps when running. So my 1500 watt inverter is oversized for running the stove. I have tried using a xantrex c40 in Load Control Mode but it would not work. I called there tech help number and they said that the inrush of the inverter was to high. I then tried to find another way to switch on the inverter and the only thing i could find was the 30 amp relay. I also have to add that i have an Iota ITS-30R automatic transfer switch that i will be using to keep the stove going when my batteries are not charged.

It looks like a 750 watt inverter would be big enough to handle the stove but would 6 gauge wires be big enough to feed a 750 watt inverter? or does anyone know of a specific voltage controlled swith that would work with my 1500 watt inverter?

Thanks again for your help!

814✭✭✭You could use that voltage controlled switch but only if you connect another relay/contactor across its output. the best place to find such a contactor would be at a marine or 4wheel drive accessory store as they are used on power winches are most are rated at 200 to 400 amps8)

30,737adminActually, there is a possibility that the 1,500 watt inverter is not really that over-sized...

Basically, for AC power you have the power equation that we all know and love:

- Power= Volts * Amps
- V=P/A=310 watts/4.76 amps = 65 volts

Note, for the numbers you gave, the results do not make sense. I am guessing that you have a 117 volt or so AC inverter, not a 65 volt inverter...It turns out that the above power equation is not really correct for AC (or non-steady state DC power either). The missing part is the phase angle between the voltage and current since waves (if you remember your math, Volts and Amps are vectors and you use trig and Pythagorean Theorem to do the math). This missing term is the Cosine (angle) or Power Factor:

- Power = Voltage * Current * Cosine (phase angle)
- Power = Voltage * Current * Power Factor
- Cosine (phase angle) = Power Factor

So, in real terms, a Power Factor that is less than 1.0 increases the current flow through the wire and inverter electronics. And is typically found to be less than 1.0 for motors and many electronic power supplies (battery chargers, wall transformers, etc.).Many inverters, transformers, and generators will have their output defined in both maximum Watts and VA (Volt*Amps or VA). For smaller Inverters and generators, many will have their Watt rating = VA rating. For some units (and larger devices) they may assume PF = 0.6 or so and show

- Watts=VA*PF=VA*0.6

UPS manufacturers will typically advertise VA ratings because it makes the UPS "look bigger" than it really is. It makes the battery capacity look larger (battery energy consumed only uses Watts, not PF or VA).Note, non-sine wave current (such as electronic power supply input current) which is more of a series of peaks than a sine wave) can also be represented by the Power Factor number.

And MSW inverters with their Modified Square Wave also make PF worse for motors/inductors/transformers/some power supplies.

If you have a Kill-a-Watt meter there is a PF and V*A (VA) setting too. Using your numbers:

- Power = Volts * Current * PF
- PF = P/(V*A) = 310 watts / (117v * 4.76a) = 0.56

And the VA rating (sometimes called VAR for utility power for Volt Amp Reactive) of your load is:- VA = Volts * Amps = 117v * 4.76a = 557 VA

Also, an MSW inverter will make the PF worse for motors and such...Plus, you need a larger inverter because the current into an AC motor goes way up during starting (typically 4x or more). How the inverter and loads react the starting current is different--so there is a bit of hit and miss trying to guess which units will work together.

So a 750 Watt inverter may be a bit small for your application.

If you can find an inverter that meets your needs and has a remote control on/off input would be the best way to handle the problem... Most likely though, it will be the more expensive MSW and TSW inverters that will have the remote switch option.

I don't know your situation, but if you have a lot of solar panels (say around 2-3kW or more) and your utility supports Net Metering--You are approaching the point where a Xantrex XW Hybrid (GT and off-grid capable) Inverter woudl makes sense.

Regarding the load control outputs on typical solar charge controllers--they are only rated for 8 amps or so DC--not the hundred or so you need.

Wire size for a 750 Watt inverter, you can use a Voltage Drop calculator to figure out wire gauge. You should also follow the NEC tables for minimum wire gauge ratings too.

For the Voltage Drop Calculator. Say you need:

- 750 watts * 1/10.5 min input votlage * 1/0.80 eff at max power * 1.25 NEC safety factor = 112 amp rated circuit minimum
- 750 watts * 1/10.5 min input votlage * 1/0.80 eff at max power = 89 amps maximum

Say your battery goes down to 11.5 volts under full load--and the inverter cutoff is 10.5 volts, the maximum drop allowed would be 1.0 volts in the wiring. Assume you have the inverter 4' from the battery bus/bank connection. Using the Voltage Drop Calculator we find:- 4' run (8' round trip) of 10 awg wire will drop 0.9 volts

From one of the NEC tables for general wiring, we see that a minimum size for 112 amps would be around 2-1/0 depending on insulation type...So, in this case, you are limited by NEC minimum current support. If you had a longer wire run, you would be limited by voltage drop.

-Bill

814✭✭✭Bill while all your maths appears to be correct. To me it does not really answer his question which was how does he get a voltage controlled switch to turn on and off the inverter.Or did I miss something?

I personally think my solution was a simple solution to his problem at least effort and expense?? As even a small 200a contactor would be more than adequate for a 1500w inverter and for not much more money a 400a ones are available.They are very reliable for this type of heavy duty use.

Please dont think I am saying your post was not useful for him or others to learn from.

30,737adminI did not address the contactor--because you guys have done a nice job of that already already... I was addressing the sizing of the inverter and the wiring which he also typed about.

Also, mechanical contactors can take 6-12 watts (or more?) to operate their relays--for smaller systems, those loads cannot be ignored.

The alternative was to find an Inverter that has a remote inhibit switch (typically 0v/Vbatt) which is pretty easy to turn on and off with the small voltage controlled switch. But all of that adds money to the overall costs too...

-Bill

5,400✭✭✭✭Why not use a DC pump and avoid the inverter loses?

Tony

6,290adminI think i found what you are talking about on this link http://www.curtisinst.com/index.cfm?fuseaction=cProducts.dspDcContactors

Here is another i found

http://www.dc-contactor.com/Product-show.asp?id=846

Would this be the correct thing and if so i would assume that the proper way that this would be installed would to have it hooked up inline in the positive cable of my inverter feed. Having the inverter cable hooked up to the large posts on top of the contactor and then the voltage controlled switch hooked up to the small connectors on the side of the contactor?

814✭✭✭Would this be the correct thing and if so i would assume that the proper way that this would be installed would to have it hooked up inline in the positive cable of my inverter feed. Having the inverter cable hooked up to the large posts on top of the contactor and then the voltage controlled switch hooked up to the small connectors on the side of the contactor? YES YOUY HAVE IT ALL CORRECT and the bolts on the contactor can handle very large lugs. As for cable use either 2ft of #4 or 3 runs of #6 ,Then very little loss

TRY MARINE SHOP OR 4WD STORE FOR THE CONTACTORS. They are used in Warn winches one of the well known brands

Attached is very rough circuit diagram

6,290adminThanks very much for your help!

7✭✭I am interested in getting one of these voltage controlled switches to control my 120 volt AC Sunfrost refrigerator.

What I would like to do is have the voltage controlled switch power on when my 12 volt battery bank reaches 13.2 volts or so (whenever the sun is shining) and it would control a 120 volt circuit which powers the fridge/freezer. I would buy an active high switch, correct?

Would this work? Can the voltage controlled switch activate a 120 volt circuit?

Thanks

17,615✭✭One of these http://store.solar-electric.com/volconswit.html is only good for 60 Volts.

Something like this might be better: http://store.solar-electric.com/moredr.html

Remember: relays are your friend!

7✭✭I wrote to the manufacturer and this is what they said about controlling a 120 volt AC load with the voltage controlled switch controlled by a 12 volt DC system.

Question:

Can this unit above be used to control a 120 volt load. For instance when the 12 volt system is over 13.2 volts during charging can this unit turn on a refrigerator?

Thanks

Response:

Hi,

Yes, the relay on this unit can control a 120VAC load. In order for it to work properly the instructions in the manual dictate that the varistors on the board must be removed if you are going to use the VCS with 120VAC. Once the varistors are removed your application will work.

Dave

Im talking about this switch here: http://store.solar-electric.com/volconswit.html

Just thought you all would want to know.