12VDC to 110VAC

[t3clayton]

I want to build an inverter to allow me to run my furnace from a 12V battery. What parts do I need?
Thanks

[russlk]

Buy one from JC Whitney, $50. You cannot build one cheaper.

[myp71]

If you have a costco handy they have a 1000watt inverter for $70.00.Or maybe costco online?

[dacflyer]

make sure when you get the inverter...that you have enough battery power to make the power last a long while....large inverters 1,000 watts can draw very heavy loads off of a battery at full load... i have one here rated at 1,500 peak and it has a 200amp fuse rating on the input side...

[jollyrgr]

Question; are we talking about a natural gas (or propane) forced air furnace? If so than a simple inverter will do nicely. If you are taking about an oil burner furnace or even an electric furnace this will require a much different size inverter. Even a small space heater would tax a 1000 Watt inverter. <p>I'm not sure of the current draw an oil fired furnace. But a "Gas forced air" furnace has a blower as its biggest current draw. Some with pilotless ignitions have a sparker (low current draw) and others have a glow rod (slightly higher draw). Get an inverter that has a little more power than you require.<p>Just a thought. As a "cheap" alternative you might consider using an old Uninterruptible Power Supply or UPS. In some cases these become "throw away" items once the batteries and warranty expire. But you would need to install additional cooling fans on the UPS for continuous duty.<p>[ December 23, 2003: Message edited by: Jolly Roger ]</p>

[t3clayton]

The furnace is natural gas with a spark igniter. I'm not sure how much current is drawn yet (grandfathers furnace). <p>
What is the best way to wire it? Is it ok to pigtail off the furnace? <p>Thanks for all the feedback.

[dacflyer]

you could pig tail off the furnace...but besides the electric gas valve and igniter...you got to rember the blower...that draws at least 7-10amps it self and more at start up....<p>is the furnace 120v or 220v ?
just make sure the pigtail is heavy enough to carry the load...if its 220v.. i'd go with a clothes dryer cord..that will be fine...and if its 120v...go with a 10GA. cord,
both will be pleanty enough to handle the load

[jollyrgr]

Troy,<p>My suggestion of the UPS solves rewiring the furnace each time the power fails. My thought was to connect the power feed to the funace to the UPS instead. Then take the output of the UPS and feed it to the furnace. Then take the DC input of the UPS and connect the larger batteries. Here is a poor ASCII picture of what I thought to do:<p>
BEFORE:<p>AC MAINS------CUT OFF SWITCH------FURNACE LINE IN<p>
AFTER:
AC OUTLET---UPS(W/Bigger batteries)----FURNACE WITH PLUG---CUT OFF SWITCH (if desired)<p>
It might not meet building codes in certain areas but that is something you would need to check into for your area.<p>What I am expecting your furnace has is a hard wired branch circuit that is dedicated to the furnace. What you may want to consider doing is replacing the hard wire connection with a single AC outlet. Then plug the UPS into this outlet. Next connect a standard AC plug and power cable to the furnace; something like an appliance power cord. Thus you make your furnace a PLUG-IN device like a washer or dryer. In between the AC outlet and the furnace you insert the large UPS. You connect a large battery pack to the UPS. <p>Many UPS units are not cooled good enought to run continuously. So you might consider installing a few "muffin" fans and possibly extra cooling vents in the UPS. Should the UPS fail, you do not need to be an electrician to rewire the furnace. Simply unplug the UPS, unplug the furnace from the UPS and plug it into the AC outlet.<p>Hopefully I am presenting the idea a bit better in this post than in the previous.<p>[ December 30, 2003: Message edited by: Jolly Roger ]</p>

[upsmaster]

if u use a inverter or a ups .. which is a batery charger + inverter + a switch to connect the load to the inverter or to the main power lines.
the in rush will require at least 10 times load for the inverter to supply..inverters at low voltages on the dc side need lots of amps ( load = 20 amps total times 120 vac = 2400 va dc = 2400 va / 12vdc = 200 amps dc input and then times 10 for inrush...ups and inverters are soft as compared to mains power.