Help with electrical question (UPS)

[farmerscotty]

I am wanting to build an uninterupable power supply to run my blower on my furnace when we have intermitant power outages. I want to use 2 marine batteries with a floating charger to keep them up and I need parts go from the 12 volt to 110 volt. The blower on the furnace requires 2.9 amp running and 3.7 amps to start at 110 volt.

I don't know where to look or read on doing this. We have outages lasting 4-6 hours at a time

ANY help would be great. If you know where I need to post this for an answer on another board by all means let me know where to go do that.

I thank you for your time!

Scott

[Darren]

You'll need a battery charger plus an inverter to convert 12V to 110 AC plus a way to transfer the power when the electricity to the house is interrupted. You could probably rig a relay to do that.

Another suggestion is a used Clary (brand name). A Clary UPS will have a built in charger and inverter plus you don't need a transfer switch if you power the furnace blower straight from the UPS. The internal batteries may be more expensive.

Best source for a Clary is eBay. I've seen some capable of running a room full of servers up for auction. Usually they don't sell because, no one knows what they are. A Clary reconstitutes a pure sine wave from the batteries. They're used for critical applications where the equipment is sensitive to variations in the power.

In the past Zenith sold Clary units under their name. Clary now longer sells to the civilian market. A lot of their units go for military or medical support.

On ebay look in the categories "Business & Industrial" and "Computers & Networking". There are three on eBay now. One is listed for $1500 which is probably extreme over kill. You'd need a forklift to pick it up. One is setup for 208V. The other pictured below you need to check the specs. Plan on replacing the batteries on any unit you buy. They use the rechargeable gel batteries. If you're not in a hurry you can find what you need on eBay.

[artificer]

Check over in the Alternative Energy forum. Hmmm... can't seem to find the thread I was thinking about...

If you're using about 400watts of power, thats 2400 watt-hrs. 200 amp-hrs at 12 volts, or 100amp-hrs at 24volt. The UPS/inverter needs to be at least 500 watts continous, but better 750 or 1000 watts.

If you don't care that you'll only get several dozen cycles out the batteries, you can take them down to totally discharged. If you were going to draw them down over 20 hours, you could get several hundred cycles. Since the discharge rate would be 4 times that, the number of cycles is greatly reduced.

The other option is to go with the only 50% depth of discharge. That means you'll need 400Amp-hrs of 12v batteries, or two batteries with at least 200amp-hr. Typical Walmart special marine batteries are only going to have about 80amp-hrs capacity.

Next, you'll have to decide what you want for an inverter. If you get an inverter/charger, the power transfer, inverter power, resume AC operation, and charging are all built into the system. You should be able to get a modified sine wave one for under $500.

Some people say that motors don't run correctly on modified sine wave power. You would have to determine if its a problem with your blower. If it has problems, you need a sine wave inverter.

One thing to do is to see if anyone locally has a larger computer UPS that has bad batteries. You can replace the battery(s) with larger ones for longer run time. It all comes down to how reliable you want the system to be, how much money you have to spend, and what level of technical know how you have. The other option is to get separate charger, inverter, voltage sensing relay, switches/contactors, and wire it all up yourself.

Michael

[Oldcountryboy]

Wouldn't a Generator be more simple. Fix a pigtail on your blower to plug into power. When electricity goes out simply unplug blower motor from house current and into extension cord coming from the Generator.

[Sawmill Jim]

Originally Posted by Oldcountryboy

Wouldn't a Generator be more simple. Fix a pigtail on your blower to plug into power. When electricity goes out simply unplug blower motor from house current and into extension cord coming from the Generator.

Could do the same with an inverter too.

[artificer]

I read the want of a UPS to mean unattended operation, not just backup power.

Michael

[Sawmill Jim]

Originally Posted by artificer

I read the want of a UPS to mean unattended operation, not just backup power.

Michael

I see said the blind man

[deb]

My company uses a UPS for the network equipment at each of the regional offices We use APC brand UPS. You will need to know the power requirements for the equipment you want to support and the length of time you want it to supply power. We get a UPS model that takes a network card. It allows us to check on the UPS remotely and get messages from the UPS when power goes out.

deb
in wi

[Gary in ohio]

You DONT want A UPS, Most consumer grade UPS's are designed for VERY short period usage, just enough time to get the computer turned off..

How often and how long does your blower motor run? Our kicks on only once or twice and hour unless its really really cold out and only runs for a few minutes.

[farmerscotty]

I just had hoped we had an electrian in here.........I need to know what switches or whatever to turn on the power inverter maybe when the AC power died.....something to do it automatic.....it cannot be hard to do if I just knew the correct names for the parts I need for the automatic switching part.........have batteries, power inverter.......anymore ideas How about where to search for this .......forums somewhere? am at a loss........Scotty

[Michael Kawalek]

Scotty
Here is one more thing you have to take into consideration. The blower of your furnace is not the single consumer of electricity. Most likely you also have a "glow lamp" heating element that gets red hot before the furnace can light.

When the furnace gets the signal to turn on, it will first sends electricity to the glow lamp to get red hot. It is the igniter that sets the fuel on fire. Once the furnace detects heat, it automatically turns the lamp off. If the lamp can't light the fuel, the fuel gets automaticly cut off. In addition to the blower motor, you must also add in the watts consumed by the lamp, which most likely is higher, maybe 500 watts or so. You won't have a glow lamp though if your furnace has a pilot light.
Good luck,
Michael

[artificer]

If you really want to do this yourself, and already have most of the parts, heres a few hints. I'm not an electrician, but I wire up our equipment in our prototyping shop.

There are going to be three modes of operation in your system. Standby, inverter, resume AC/charging.

For standby, you need to have a trickle charger connected to the batteries.

For inverter mode, you need to sense when the power goes out, and then activate the inverter. An elegant solution would be to use a voltage sensing relay to control a power relay that feeds the blower. These devices will sense brownout conditions, and switch over. The easiest alternative way is to wire a relay that is powered by the grid AC. When grid power is in use, the relay is activated, and the blower power comes from the grid, goes through the relay, and to the blower using the NO connections. Blower is connected to the common connection. When grid power goes down, the relay drops, and a second set of NC and common connectors on the relay pass DC from the batteries to a control coil on a second relay/contactor that powers the inverter. The AC from the inverter can be wired to the first relays NC connection. A 3 pole relay would be better, so you can switch both hot and neutral wires.

If you have a manual three stage charger, NOT one of the pushbutton type, you can leave it connected to the batteries, and plugged into the grid AC. When power goes out, it has a small drain, but not bad for a couple of hours. When power comes back on, it resumes charging the battery. You need a charger that will resume charging when plugged in, and not wait for you to press buttons to select the correct mode, battery type, etc.

************************
Relay 1: 120V at least 10 amps, better 20 amp capacity. Double throw, triple pole.

Coil: Grid AC hot and neutral
NO1: Grid hot
common1: blower hot
NC1: Inverter hot

NO2: nothing
Common2: battery+
NC2: to relay 2's coil

NO3: Grid neutral
common3: blower neutral
NC3: Inverter neutral
*************************
Relay 2: 12Volt, single pole, single throw, at least 75 amps, 100 is better

Coil: from relay1:NC2 and ground/battery-
NC: battery+
common: inverter + in
**************************
Probably confusing, and this doesn't cover anything about being up to code, but drop me a line if you need more help.

[Harry Chickpea]

I think you want a locking or lock-out relay (contactor). A small connection from the mains keeps the relay energized in one position, with mains power going through the contacts. When the power goes out, spring action in the relay closes the alternate set of contacts. An electrical supply house or Granger should have the part.

[Darren]

"You DONT want A UPS, Most consumer grade UPS's are designed for VERY short period usage, just enough time to get the computer turned off.."

Gary, the Zenith/Clary UPS I have, easily runs a desktop computer for 4+ hours after the power goes off. It was the smallest unit they sold back then. It's as big as a rural mailbox. Weighs about 40 lbs.

The Clary's are not consumer grade equipment. I was sold on the brand after reading a review by a writer whose house had been struck by lightening. Every thing in the house connected to an outlet was fried. The exception was all of the computers connected to the Clary UPS. Lightening fried the Clary, but it did not get through to the computers. That was Clary's state of the art 20 years ago

Scotty can cobble something together. With the right commercial/military grade UPS, it will be a lot simpler. Especially the wiring. All he has to do is use the Clary to power the furnace blower and controls all the time. He won't have to be concerned with shock hazards. He won't need to transfer power. It's the closest thing to a plug in solution. The battery charger and inverter are built in and you have perfect sine wave electricity from either a voltage or frequency aspect.

Most folks couldn't justify buying a high end piece of equipment like a Clary UPS. Ebay solves that. As I said, when I checked, I've never seen one sell on ebay because most people don't know what they're looking at.