# power transfer relay



## Explorer (Dec 2, 2003)

I finally received my Watts up? device and have measured the power usage of my new pellet stove. My intention is to build a backup power unit.

The total start up draw is about 280 watts. 250 or so for the start fan & glow device and 25 for the pellet auger motor. Run wattage is 90 to 115.

I have a gel cell battery, almost new, and a automatic battery charger. The charger will trickle charge and auto switch to full charge, up to 10 amps, and then to standby. I also have an 200 watt 5 year old Tripp lite inverter that is good for surge up to 300 watts. It is a heavy unit, about 6 lbs, and worked well when it was installed in my traveling van.

I would like to get some kind of power transfer relay that would automatically switch between inverter and line voltage and not spend to many $$. I will use a manual switch if necessary. Any ideas where I can buy the relay?


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## Jim-mi (May 15, 2002)

Backwoods (among others) sells that sort of thing.

You could also use a regular relay-with a 120vac coil- wired such that the 'grid' energizes the relay and powers the what ever. fans etc. If the grid drops and de-energizes the coil then the other contacts let you go to 'plan B'

That Triplite wont last long running that much load through it.

You might want to time how long that the "glow bar" is on.

That glow bar load could easily change that Triplite into a can of smoke.


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## idahodave (Jan 20, 2005)

If you go the relay route, think about adding a second one to switch 12v to the inverter so it doesn't have to run all the time.

Before doing anything with a switch or relay, power up the stove with the inverter and see if it works. Sounds like the inverter is a bit small to run the stove. The "surge" rating might be for a fraction of a second...


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## Explorer (Dec 2, 2003)

Thx for the replies. This is my first attempt at 'alternative' power for my house. I figured I would start small and learn. This is also a sandbox project as a house heater is nice, but not necessary as it rarely gets below 10 degrees here and 45 is the lowest I have seen inside my house after several days of no heat.

The reason I wanted to have an automatic transfer relay is if power fails when the stove is running and I have a backup: then I can run on low feed without doing a start-up. The start-up cycle is normally 10 minutes, but just playing with it I have it down to about six and maybe I can lower that.

The first thing I will try is hooking up the inverter. I will go to town later this week and I can get some heavy stranded wire then to hook to the battery.

I do have another question about inverters. The one I have is about 5 years old. It measures 4" x 4" x 6" deep and weighs maybe 5 or 6 lbs. It is in a slotted steel case and has a fairly large transformer inside (rated 200 whats). Are those little one inch thick 400 - 500 what inverter I see at the auto parts store superior for my needs?


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## Runners (Nov 6, 2003)

Most of those auto inverters put out a frequency unregulated SQUARE wave. Beware of using them on brushless motors (syncronus motors - SP!). A cheap computer UPS usually has a modified sine wave and some frequency control, which would help keep those little syncronus motors running quiet and cooler. If you can, change out the motor to a brushless DC motor and skip the inverter all together! 

Did you know... those little box fans on computer power supplies are 12vdc brushless, draw very little current and make great camping fans or cooling fans for rabbits on hot summer days?

Here's the problem with making an automatic transfer switch out of a RELAY.
The contacts ARC under load, and could weld into one position or the other, either locking your equipment in an ON or OFF position. The worse case would be the arcing and pitting builds up so it conducts both LINE and INVERTER power. Hence, these are _illegal_ . 

Early transfer switches had 2 contactors/relays with a mechanical link to lock one or the other out and prevent energizing your back up source with line power. Square D useto make 'em. Today, transfer switches are constructed so that it's nearly impossible to energize two sources (unless it gets crushed together). I saw the results of a generator that was fed line power, they said it went BANG! and was _relocated off the cement pad - it was anchored to with 4 5/8" studs!_ Kinda looked like dynamite!

You're on the right track with the heavy wire, the bigger the better - but do yourself a favor and add a quick means of disconnect (a coupler) and a 20-30 amp fuse between the battery & inverter (size for your inverter draw and wire requirements)! and a 2-3amp between your inverter and ??? I'm assuming your taking 12vdc and inverting to 120vac.


Lest anyone begin to think _I have all the answers_ - forget it, someone's probably got another idea, probably better and cheaper... and probably meets or exceeds NEC code requirements. This forum looked a little dead, and shouldn't be!


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## Explorer (Dec 2, 2003)

Runners said:


> Most of those auto inverters put out a frequency unregulated SQUARE wave. Beware of using them on brushless motors (syncronus motors - SP!). A cheap computer UPS usually has a modified sine wave and some frequency control, which would help keep those little syncronus motors running quiet and cooler. If you can, change out the motor to a brushless DC motor and skip the inverter all together!
> 
> 
> You're on the right track with the heavy wire, the bigger the better - but do yourself a favor and add a quick means of disconnect (a coupler) and a 20-30 amp fuse between the battery & inverter (size for your inverter draw and wire requirements)! and a 2-3amp between your inverter and ??? I'm assuming your taking 12vdc and inverting to 120vac. *YES*


I have been thinking along this line also. Locally I can only buy a 200 watt backup power unit. I will go to a larger town next month hand would like to get a 600 watt unit. I have been unsuccessful in finding out if I can also hook up a larger battery to these units. I am guessing I can. I like the idea of fusing and did plan a battery disconnect switch on the + side.

There are two AC motors involved that are a speciality item as far a fit is concerned so they can not easily be replaced. Also, 95% of the time AC is fine.

I am going to go slow and understand exactly what I am doing before I do it.


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## Runners (Nov 6, 2003)

Explorer,
Here's a consideration, now that WIRE costs have gone through the roof.

Do you have access to FREE wire in large conductor sizes? I'm thinking about the nice stranded stuff that you'll be using to hook up batteries together. Heavier the better! My 12vdc battery strings are using #2 cables between 8 batteries (totaling about 780ah @ 12vdc). 

Consider higher battery voltage strings.
a. It will save you money in wire, higher voltages = less voltage drop.
b. It will save you batteries & trying to equalize a bunch of unruly batteries (like I got in the above string!)
c. It will interface easier with the larger Inverters & charge controllers commonly used in Alternative Energy applications. My choice is 48vdc, second choice is 36vdc.
d. Higher voltages are _not_ less safe than lower voltages when the wattage is the same. Lower voltages might sound easier to manage, but _anything under 50 nominal volts is still considered "low voltage"._ 
e. Relays and switching devices last longer with higher voltage/lower amperage than lower voltage/higher amperage. (I have plenty of fused relay contacts to back this up, from one of my incubators)
f. Lest it someone isn't obvious, WATTAGE - it's the final product measurement, pick the lowest amperage & highest voltage you can safely/comfortably deal with.

Volts x amps = watts. Example for a 600 watt load:

12 volts x 50 amps = 600 watts. (higher voltage drop over cables, more heat on the cables and 6 awg wire to boot!)

48 volts x 12.5 amps = 600 watts. (lower voltage drop over cables, less current & heat on the cables, and really easy to find/work with 14 awg wire)

In the L-O-N-G run, and believe me, your batteries will eventually be located AWAY from your living quarters, some safe distance... we all start thinking about _resistive losses & voltage drops due to cabling._ 

I grab big cables ANYTIME I can find them, espically the ones with lots of fine strands (like a welding type cable). Same with big connectors, which I'll either soldier on or crimp, depending on the type.


One thing about INVERTERS... and I mean the REAL thing, Grid tie, charge controller, sine wave and a few $$ more. Why spend the money on a cheap automotive, unregulated square wave, frequency shifting (according to input voltage and/or load) - and risk your precious house hold appliances?

I got 3 of these old Micronta 300watt, 12vdc inverters Radio Shack useto sell. I'd give them away, but I think I can get $5 for the aluminum heat sinks! This is really cheap stuff and yields basically unusable power in the range of 50-75 hz and 90-135volts ac! It was cost engineered down to the level of a _neat little toy - and useless!_ They are so _inefficient_ coverting power, I'm better off buying 12vdc RV light bulbs for lighting - at least the radio would stop buzzing!


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## mightybooboo (Feb 10, 2004)

Im thinking a UPS with an external battery(s) would be the way to go.Fully automatic all the way around (charging and switching) relatively cheap,and fully engineered,sounds like a winner.

BooBoo :gromit:<----"It'll never Work"


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## Explorer (Dec 2, 2003)

mightybooboo said:


> Im thinking a UPS with an external battery(s) would be the way to go.Fully automatic all the way around (charging and switching) relatively cheap,and fully engineered,sounds like a winner.
> 
> BooBoo :gromit:<----"It'll never Work"


What is 'relatively cheap'? Any brand name? Keep in mind, at this point, I am only looking at a 300 watt load, max.


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## Runners (Nov 6, 2003)

Is this too expensive?
http://www.apcc.com/products/family/index.cfm?id=21#anchor1
This link actually has some SPECs...
http://www.advizia.com/v41/Comparison.asp?User=TrippLiteUPS

Sure, they only come rated for a handful of minutes ('cause the batteries are SMALL - and they probably lack a little cooling fan).

Get a little one, add a little cooling fan, like one off a computer's power supply, add some real battery capacity and you'll have converted a cheapie to something that can run a couple of lights or a small 120vac appliance for hours.

If you get lucky and find someone that's junking one, grab it and yank the batteries. If those batteries are your basic 12v 7ah sealed lead acid type - which MOST of the little UPSes have - you can EASILY replace them, or wire in some big honking Gell or AGM and you're home free!

BTW... the same batteries are used in those 10,000,000 candle power flashlights Northern Tool sells... (as a reference). We got a bunch of them, I mean a BUNCH of those 12v 7ah batteries.


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## mightybooboo (Feb 10, 2004)

Good post Runners,thats just what he needs.Doesnt matter if it takes a month to charge that large cell,its only going to be rarely used.Small charge,honkin' battery,yep,wtg.

Must be sure to match battery type to the unit though,agms/gels have different charging needs than lead acid.A couple deep cycle marine 12 volts would work fine Im thinking,2- 6 volt trojans deep cycle better still (last many many years r/t low cycling).Just place the batts in some cheapo plastic batt holders from any auto supply place.

Think 300 dollars would do it well.Or even 150 or so with a cheap UPS and 1- 12 volt marine batt.79.00 dollars will usually get you an 1100 watt inverter,thats what I paid for mine at costco.And its a good modified sine wave,Xantrex,hard to beat.

Folks with rarely used cabins will put up a very small solar array,and lots of batteries for capacity.Slow charge,large storage for rare weekend usage.Fine way to go .

BooBoo :gromit: <----"It'll never Work"


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## mightybooboo (Feb 10, 2004)

If absolute cheap and dependable is the goal,just charge the batteries every month.Have the 1100 watt inverter next to batts with clamps on inverter wires,or even hardwire inverter to batts.

Power goes out,turn on inverter and plug in stove.Not auto,but so what?

At home,I dont have auto switch over,though my inverter/charger has the capability.When power goes out,I bring in extension cords.No biggie,and the price is right,and its safe and sure.

BooBoo :gromit: "It'll never Work"


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## Runners (Nov 6, 2003)

BooBoo just mentioned the a real PLUS for Gell cells. They LIKE to be charged slowly, and they're SAFE to leave inside a cabin or unattended for extended periods of time.

Some websites have an aversion to gell cells, Curiously, they push/sell AGM (Absorbed Glass Matt or starved electrolite). Just my opinions here... The safer the battery, the slower the charge/discharge rate. More safe generally means shorter usable life & more difficult to recover from sulfation.


I got 2 UPSs that got nailed when lightning hit the power company's transformer outside our house. Both are the APC SmartUPS 1400va rack mounts. One is an old metal type, the other about 5 years and plastic. Anyone know how/where to fix them or have you worked on them before? I could troubleshoot it, but without a schematic - I'd be pretty much wasting time.


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## Explorer (Dec 2, 2003)

Thx everyone for the information and guidance. After much consideration my plans have been finalized (as much as possible as I usually make changes midstream in any project).

I have ordered a surge protector, a battery cutoff switch, an additional gel cell battery and a Xantrex 1000 watt inverter. I already have a battery charger, automatic regular and trickle.

The main reason I wanted an automatic transfer switch is due to the limitation of a currently owned inverter. After deciding the inverter was to small, the design was simplified. I will use a manual switch over (power cord). Power fails here on a regular basis and while heat is probably not essential, it certainly is pleasant. The pellet stove I have can be run continuously on low and thereby avoiding extra start cycles (a large power user). The two batteries should give me about six days of continuous heat without outside power. More than I will need based on this areas history.

I plan to mount this equipment in the living room next to my pellet stove. All the stuff is scheduled to arrive before the end of the month and then I can put it together.


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## mightybooboo (Feb 10, 2004)

Beautiful setup,think you made great choices for a great entry level back-up system,very good.And if you want to really get into it later,just add more batts and run all kinds of things.Running 1 or 2 13 watt CF bulbs is also a very very nice thing,may want to have a lamp setup for just that need.

Oh,BTW,throw in a genny somewhere along the line and dont worry about a 2 week power outage either.Run batts til low,toss on a nice recharge,you are set to go.

Thats pretty much my home backup system.I'd rather listen to the batteries 24/7 than a genny,LOL.  

BooBoo :gromit:


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## mightybooboo (Feb 10, 2004)

Explorer said:


> I plan to mount this equipment in the living room next to my pellet stove. All the stuff is scheduled to arrive before the end of the month and then I can put it together.


Maybe a bit of a ways from the stove,hydrogen gas doncha know......Better safer away.Really no practical need for being by the stove.

BooBoo :gromit:


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## Explorer (Dec 2, 2003)

I didn't think gel cell batteries off gassed. In any event, there are no openings as it is completely sealed.


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## Runners (Nov 6, 2003)

Explorer said:


> I didn't think gel cell batteries off gassed. In any event, there are no openings as it is completely sealed.


They do NOT off gas. Should the event ever happen, they'll be bulged really bad, be very hot to the touch & ready to explode! (usually from overcharging, rapid charging or shorted cells)

Gell cells are designed to be shipped by any carrier, stored practically anywhere and are the safest rechargeable battery to have in a house. They are so safe, they are the battery of choice for residential, computer data rooms / UPS type applications.

DON'T ever put a gell cell on a high rate automotive type battery charger, they charge s-l-o-w-l-y... check w/manufacturer for charging voltages & amps!


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## mightybooboo (Feb 10, 2004)

Explorer said:


> I didn't think gel cell batteries off gassed. In any event, there are no openings as it is completely sealed.


I understand that,Im just a stickler for safety,I way over design my systems for that reason.

Think putting batteries by a heat source,especially when it doesnt need to be,is bad planning .Cant see taking any chances in event of a component failure.Or possibly helping to create a bad outcome.Just seems like a poor design that can be done better.

Batteries and electric can be dangerous,I treat them with a huge respect.

Thats just me though.

Ditto on checking that charging too.Gels have specific needs.

BooBoo :gromit:


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## Runners (Nov 6, 2003)

mightybooboo said:


> I understand that,Im just a stickler for safety,I way over design my systems for that reason.
> 
> Think putting batteries by a heat source,especially when it doesnt need to be,is bad planning .Cant see taking any chances in event of a component failure.


*Good advice.* 

Last winter, I visited a guy who was warming up cans of spray paint INSIDE a $50k piece of telcom transport gear. The cans were so hot he had to grab a rag to pull them out! Talk about a potential "career altering" decision! (..yea, he USETO work for us...)


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