Back up battery?

[fields_mj]

Does anyone have any idea what size of 12v battery would I need in order to run a furnace blower for about an hour? The blower is for a Clayton wood furnace from US Stove. I think it's 1400 CFM. We had a power outage for about an hour today, and now the wife is all nervous. We have a lift station back behind the house, so when the power goes out, we are one of the first ones to get back on line. Having the power out for an hour happens 4 or 5 times a year. I don't ever remember it being out for more than 2. I've drawn up a simple wiring diagram that should allow me to use one 120V 8 pole relay, a trickle charger, and a small transformer, and one or more 12v deep cycle batterys to do what I would like. I'm just not sure how to size my need for the batteries. Personally, this is just a good reason for me to get another deep cycle battery or two for the boat

Thanks,
Mark

 

[blackdogon57]

With the low prices on generators I think it makes sense to own one. I have a cheap 6500 watt diesel that is hard wired to all the necessary
circuits in the house. We usually only get short outages but have been out for as long as 5 days. Not something I want to do again. Since i no longer burn oil, my tank is full of #2 heating oil (225 gallons). I am sure it would keep the generator going for about a month in a pinch.

 

[zogger]

You'll have to read the specs on your blower motor, and go from there. There should be a plate attached to it, or maybe look it up at your dealers website.

 

[stumpy75]

Here's one of the best sites I have found for figuring out what battery power is needed for a given pull through an inverter. Easy calculations. It's set up for musicians to calculate what kind of battery power they would need to run sound equipement, but it applies to all inverter applications...

Battery Calculations – Battery Life Span – Current Draw & Amp Hour Rating

 

[Somesawguy]

You'll need an inverter that can handle the startup current for the motor.

I'll have to second the generator, but it would be a good start for a solar/ alt energy setup.

 

[freemind]

From my experience with a power inverter, run off two deep cycle batteries, you don't want to do that. They don't provide power very long to something like that. This set up I speak of, is on the farm's service tuck.

You are better off with a generator. Don't forget the switch box. Your linemen will appreciate it.

 

[reaperman]

Another vote for a generator. A small generator unit to handle under 1000 watts can be had cheaper than a deep cell battery. How ever your furnace is hard wired wouldnt matter. In a power outage you could strip the end from a extension cord, and wire that cord to your furnace. And of course un-wire the electric wire running to your breaker box for the duration of the outage. Run that cord outside where it is convenient to the generator.

Harbor freight has a 2 cycle generator that has great reviews and it capable of 800 watts of continuous power ( 900 peak) with a 5 hour run time per one gallon of gas at 50% load. If you watch for deals this unit is on sale quite often. Last week I bought it for $72.00 on sale. I really didnt need it since I have a 6500 watt plus a transfer box installed to my home. But I will definitely use it for my wood furnace during a outage the same way I described above. Instead of running the larger generator if the wood furnace is the only thing I need to run during a outage.

800 Rated Watts/900 Max Watts Portable Generator

 

[ancy]

One of these is your best bet!

Amazon.com: Honda EU2000I 2000-Watt Inverter Equipped Portable Generator: Home & Garden
You will go through more batteries than these cost to do it this way. Wire it right and show your family how to run it.

 

[Whitespider]

I've drawn up a simple wiring diagram that should allow me to use one 120V 8 pole relay, a trickle charger, and a small transformer…

Rather than tell you to buy a generator I’ll answer your question.

First-of-all you can’t use a “transformer” with DC voltage, the battery supplied 12v DC must first be inverted to AC voltage. The inversion of 12v DC will yield around 9v AC (approximately 80%), which will need to be stepped up to 120v by a “transformer”. Whenever you increase AC voltage through a “transformer” you decrease amperage, wattage remains the same. So, for example, if you start with 50 amp/120v AC and “transform” it to 240v you will only 25 amps; both will supply 6000 watts of power (amps x volts = watts). Possibly you meant one of those boxes (called inverters) you can plug into the cigar lighter of your vehicle that supply 120v AC, which are actually an “inverter” and a “transformer” built into the same box.

OK, you need to determine two things…
1 – What size inverter/transformer to use.
2 – What size deep-cycle battery will run it for 1 hour.

To determine the inverter size you’ll have to read the label on the blower motor. If for example the motor is rated at 10 amps (10 amps x 120v = 1200 watts). Now, that 1200 watts would be maximum, the only time the motor would probably pull that much would at start-up. But at the same time you don’t want to be short on power when you need it, causing the internal breaker on the inverter/transformer to kick out. In practice, 80% is a good number to use, so a 1500 watt inverter would be a good choice (1500 x .80 = 1200).

To determine the size of the deep-cycle battery (in amp-hour rating) you’ll need to read the label on the inverter/transformer. An amp-hour (Ah) is 1 amp at 1 volt for 1 hour. A 100Ah 12v deep-cycle battery can supply 12v at 1 amp for only 8 hours (100Ah / 12v / 1 amp = 8.3 hours). So, if the inverter/transformer uses 10 amps your battery run time becomes greatly reduced (100Ah / 12v / 10 amps = o.8 hours). Again, the 10 amps would be maximum, the inverter/transformer would only be drawing the full 10 amps when producing the full 1500 watts of power. So once again, using the 80%, a 100Ah deep-cycle battery would probably run the blower for a full hour, maybe more (1 hour x .80 = o.8). Using two 100Ah batteries would provide 2 hours of run time.

Something to keep in mind is that an inverter/transformer also has a start-up time when both voltage and amps start low and build to rate; they do not instantaneously produce full wattage. IF the blower was in start-up phase at the exact same time the inverter/transformer starts-up there is the potential for damage to both, especially if it happens time-and-time-again. The chances of that are almost nil though… more likely the blower would be running, and momentum would keep the cage turning as the inverter/transformer starts-up… greatly reducing, or eliminating any chance for damage.

Hope this helps.

 

[brisawyer]

Whats the specs on the blower motor? I would be surprised if that lil HF gen will start much of an electric motor. It says 20 amp in the specs but in reality 800 watts is only 6.6 amps.

 

[v8titan]

Rather than tell you to buy a generator I’ll answer your question.

First-of-all you can’t use a “transformer” with DC voltage, the battery supplied 12v DC must first be inverted to AC voltage. The inversion of 12v DC will yield around 9v AC (approximately 80%), which will need to be stepped up to 120v by a “transformer”. Whenever you increase AC voltage through a “transformer” you decrease amperage, wattage remains the same. So, for example, if you start with 50 amp/120v AC and “transform” it to 240v you will only 25 amps; both will supply 6000 watts of power (amps x volts = watts). Possibly you meant one of those boxes (called inverters) you can plug into the cigar lighter of your vehicle that supply 120v AC, which are actually an “inverter” and a “transformer” built into the same box.

OK, you need to determine two things…
1 – What size inverter/transformer to use.
2 – What size deep-cycle battery will run it for 1 hour.

To determine the inverter size you’ll have to read the label on the blower motor. If for example the motor is rated at 10 amps (10 amps x 120v = 1200 watts). Now, that 1200 watts would be maximum, the only time the motor would probably pull that much would at start-up. But at the same time you don’t want to be short on power when you need it, causing the internal breaker on the inverter/transformer to kick out. In practice, 80% is a good number to use, so a 1500 watt inverter would be a good choice (1500 x .80 = 1200).

To determine the size of the deep-cycle battery (in amp-hour rating) you’ll need to read the label on the inverter/transformer. An amp-hour (Ah) is 1 amp at 1 volt for 1 hour. A 100Ah 12v deep-cycle battery can supply 12v at 1 amp for only 8 hours (100Ah / 12v / 1 amp = 8.3 hours). So, if the inverter/transformer uses 10 amps your battery run time becomes greatly reduced (100Ah / 12v / 10 amps = o.8 hours). Again, the 10 amps would be maximum, the inverter/transformer would only be drawing the full 10 amps when producing the full 1500 watts of power. So once again, using the 80%, a 100Ah deep-cycle battery would probably run the blower for a full hour, maybe more (1 hour x .80 = o.8). Using two 100Ah batteries would provide 2 hours of run time.

Something to keep in mind is that an inverter/transformer also has a start-up time when both voltage and amps start low and build to rate; they do not instantaneously produce full wattage. IF the blower was in start-up phase at the exact same time the inverter/transformer starts-up there is the potential for damage to both, especially if it happens time-and-time-again. The chances of that are almost nil though… more likely the blower would be running, and momentum would keep the cage turning as the inverter/transformer starts-up… greatly reducing, or eliminating any chance for damage.

Hope this helps.

Not exactly correct here on your assessment of the 12V Amp-Hour rating of a deep cycle battery. First of all the amp hour rating of a battery is completely independent of the cell voltage. So for example, the 100 amp hour12 volt deep cycle battery you described will be able to deliver 1 amp for 100 hours @ 12 volts. If you want to include voltage into the equation you now will be talking about Watt hours. In the case of your 12 volt 100AH battery example you have a battery capable of delivering 1200 watt hours.

Another note to consider. As you increase the discharge rate of a lead acid battery the capacity of the battery decreases. So if you take that same 12 volt 100 AH battery and discharge it at a 5 hour rate (20 Amps), the overall capacity will decrease and you will not be able to realize the full 100 AH capacity. This is in part due to the losses associated with the internal resistance of the cells.
Many manufacturers of large deep cycle batteries specify capacity at 3 discharge rates so that the user can make the necessary compensations in the application.

Floor Scrubber batteries are perfect for the OP's application. These batteries are ideal for moderately high discharge rates.

See this link: http://www.worldwidebattery.com/lit/T605_Trojan_Data_Sheets.pdf

Good lead acid battery resource: http://www.solarnavigator.net/lead_acid_batteries.htm

 

[fields_mj]

Finally, thanks for someone actually addressing the question. Obviously a generator would be a better option IF I new that I was going to be home to start it. The problem is that I have a wood burning furnace, and in the winter I normally run it 24/7 all week long. I leave for work around 7 and get home around 6:30. Wife leaves for the sitter around 1 and gets home round 3 AM. So there's a 5~6 hour period where there's no one here to start a generator, and she adds wood before she leaves to make sure that I have something to work with when I get home. Normally if the power goes out, I just go down and close the damper on the forced draft blower. During the day, I normally don't have it open very far anyway, and it can sit there and burn with no power for hours on end with no problem. The problem for me is that my wife doesn't understand this. So, if I can develop a reliable solution for under $200, it's worth it for her peace of mind.

Now back to my original question.

Whitespider - you got me. Transformer wasn't the right choice of words. I was thinking of the inverters that you can get about anywhere. I know that I need to see what the amp draw is for my blower, but I wasn't at home at the time and couldn't go down to check it. I've since checked it and the motor has a 2.8 amp rating. I'm not terribly worried about start up time. If the battery has to go straight into use immediately, then the blower is already running and should be trying to draw a pretty small load. The thermostat on the furnace will still be part of the system, so having an hour of continuous run time available is actually going to be capable of providing a lot more run time that what I'm calculating. TSC has a 120 AHr deep cycle marine battery for $80. I have a pair of 120V motor starters out of an electrical cabinet that I can use for relays. I just need to get some wire, a battery charger/maintainer, an inverter, and a small electrical enclosure to mount the wiring and relays in.

Here's a rough diagram of what I'm thinking.

One of the relays (R1) would be controlled by the house voltage. The other (R2) would be controlled by the voltage supplied by the inverter.

Under normal conditions the house power would run through a set of normally closed contacts on R2, and supply power to a battery charger and the furnace blower. A set of normally closed contacts on R1 (which would be open at this point) would prevent the house power from being run back to the inverter.

From the battery charger, the DC lines would run through a set of normally open contacts on R1 (which are now closed) allowing the battery to be charged/maintained. The power would then branch off and run to another set of normally closed contacts on R1 (which are now open) preventing the batteries from supplying power to the inverter.

When the power goes out, the R1 contacts after the battery charger would open, disconnecting the battery charger from the battery(s). The R1 contacts between the battery and inverter would close, supplying power to the inverter. The inverter would supply power to Relay 2 which would open the R2 contacts and prevent the inverter from feeding back into the house. The R1 normally closed contacts are now closed again allowing the Inverter to supply power to the blower.

This circuit should allow for the system to shut back off when the power comes back on, and could be modified slightly to work with a generator as well.

 

[v8titan]

Finally, thanks for someone actually addressing the question. Obviously a generator would be a better option IF I new that I was going to be home to start it. The problem is that I have a wood burning furnace, and in the winter I normally run it 24/7 all week long. I leave for work around 7 and get home around 6:30. Wife leaves for the sitter around 1 and gets home round 3 AM. So there's a 5~6 hour period where there's no one here to start a generator, and she adds wood before she leaves to make sure that I have something to work with when I get home. Normally if the power goes out, I just go down and close the damper on the forced draft blower. During the day, I normally don't have it open very far anyway, and it can sit there and burn with no power for hours on end with no problem. The problem for me is that my wife doesn't understand this. So, if I can develop a reliable solution for under $200, it's worth it for her peace of mind.

Now back to my original question.

Whitespider - you got me. Transformer wasn't the right choice of words. I was thinking of the inverters that you can get about anywhere. I know that I need to see what the amp draw is for my blower, but I wasn't at home at the time and couldn't go down to check it. I've since checked it and the motor has a 2.8 amp rating. I'm not terribly worried about start up time. If the battery has to go straight into use immediately, then the blower is already running and should be trying to draw a pretty small load. The thermostat on the furnace will still be part of the system, so having an hour of continuous run time available is actually going to be capable of providing a lot more run time that what I'm calculating. TSC has a 120 AHr deep cycle marine battery for $80. I have a pair of 120V motor starters out of an electrical cabinet that I can use for relays. I just need to get some wire, a battery charger/maintainer, an inverter, and a small electrical enclosure to mount the wiring and relays in.

Here's a rough diagram of what I'm thinking.

One of the relays (R1) would be controlled by the house voltage. The other (R2) would be controlled by the voltage supplied by the inverter.

Under normal conditions the house power would run through a set of normally closed contacts on R2, and supply power to a battery charger and the furnace blower. A set of normally closed contacts on R1 (which would be open at this point) would prevent the house power from being run back to the inverter.

From the battery charger, the DC lines would run through a set of normally open contacts on R1 (which are now closed) allowing the battery to be charged/maintained. The power would then branch off and run to another set of normally closed contacts on R1 (which are now open) preventing the batteries from supplying power to the inverter.

When the power goes out, the R1 contacts after the battery charger would open, disconnecting the battery charger from the battery(s). The R1 contacts between the battery and inverter would close, supplying power to the inverter. The inverter would supply power to Relay 2 which would open the R2 contacts and prevent the inverter from feeding back into the house. The R1 normally closed contacts are now closed again allowing the Inverter to supply power to the blower.

This circuit should allow for the system to shut back off when the power comes back on, and could be modified slightly to work with a generator as well.

Ok. Your circuit should work fine provided there isn't a momentary situation where the relays are in the state change mode and you damage the inverter by back feeding it with a short pulse of ac. Assuming this does not happen you will need approximately 35 Amps of current from that 12 V 120 AH cheap marine battery you are talking about. These batteries are usually combinations of starting and deep cycle cells and use porous plates. You don't want to take these hybrid marine batteries too far below 50% capacity or you will irreparably damage them. If you want to do it right, you should invest in a true solid plate deep cycle industrial battery. It will last longer and can be discharged past 20% capacity with no ill effects. They may cost a few bucks more but they will last longer and be more reliable....this is a must in an emergency backup system.

One more point: you will need an inverter that will tolerate the inrush current your blower motor wants to pull on startup. It's hard to calculate this but can be twice the boiler plate wattage.
so in your case 2.8A x 120v =336 watts. Your inverter might need to be able to handle 500 to 600 Watts to get that started. You are just going to have to try and see what works. Another thing, you don't want to oversize the inverter by a huge margin or you will just be wasting energy in the device due to inefficiencies. Modified sine wave inverters will run small induction motors with no problem.....I have my circulator pump running on one.

Good luck.

 

[ancy]

Rather than tell you to buy a generator I’ll answer your question.

First-of-all you can’t use a “transformer” with DC voltage, the battery supplied 12v DC must first be inverted to AC voltage. The inversion of 12v DC will yield around 9v AC (approximately 80%), which will need to be stepped up to 120v by a “transformer”. Whenever you increase AC voltage through a “transformer” you decrease amperage, wattage remains the same. So, for example, if you start with 50 amp/120v AC and “transform” it to 240v you will only 25 amps; both will supply 6000 watts of power (amps x volts = watts). Possibly you meant one of those boxes (called inverters) you can plug into the cigar lighter of your vehicle that supply 120v AC, which are actually an “inverter” and a “transformer” built into the same box.

OK, you need to determine two things…
1 – What size inverter/transformer to use.
2 – What size deep-cycle battery will run it for 1 hour.

To determine the inverter size you’ll have to read the label on the blower motor. If for example the motor is rated at 10 amps (10 amps x 120v = 1200 watts). Now, that 1200 watts would be maximum, the only time the motor would probably pull that much would at start-up. But at the same time you don’t want to be short on power when you need it, causing the internal breaker on the inverter/transformer to kick out. In practice, 80% is a good number to use, so a 1500 watt inverter would be a good choice (1500 x .80 = 1200).

To determine the size of the deep-cycle battery (in amp-hour rating) you’ll need to read the label on the inverter/transformer. An amp-hour (Ah) is 1 amp at 1 volt for 1 hour. A 100Ah 12v deep-cycle battery can supply 12v at 1 amp for only 8 hours (100Ah / 12v / 1 amp = 8.3 hours). So, if the inverter/transformer uses 10 amps your battery run time becomes greatly reduced (100Ah / 12v / 10 amps = o.8 hours). Again, the 10 amps would be maximum, the inverter/transformer would only be drawing the full 10 amps when producing the full 1500 watts of power. So once again, using the 80%, a 100Ah deep-cycle battery would probably run the blower for a full hour, maybe more (1 hour x .80 = o.8). Using two 100Ah batteries would provide 2 hours of run time.

Something to keep in mind is that an inverter/transformer also has a start-up time when both voltage and amps start low and build to rate; they do not instantaneously produce full wattage. IF the blower was in start-up phase at the exact same time the inverter/transformer starts-up there is the potential for damage to both, especially if it happens time-and-time-again. The chances of that are almost nil though… more likely the blower would be running, and momentum would keep the cage turning as the inverter/transformer starts-up… greatly reducing, or eliminating any chance for damage.

Hope this helps.

Yes and no you know a small gen would be the way to go. Easy, quite, safe, and cheaper!

 

[KsWoodsMan]

They make such a device, self contained all in one package.
Its called an Uninterpretable Power Supply.
A UPS has a gell cell battery and switches in or out automatically. Also has a built in charger designed just for it.

I have added auxiliary batteries to them for extended runtime.
Back when I needed them I had a pair of 250AH batteries attached to a 175 VA UPS and ran the back room and transmitters of a wireless iSP for a week on backup power. It took almost 2 weeks to bring them back to a full charge at a trickle rate though.

The blower should have a tag describing it power consumption, size your UPS/inverter accordingly.

Best of Luck !

 

[stumpy75]

They make such a device, self contained all in one package.

Its called an Uninterpretable Power Supply.

A UPS has a gell cell battery and switches in or out automatically. Also has a built in charger designed just for it.

I have added auxiliary batteries to them for extended runtime.
Back when I needed them I had a pair of 250AH batteries attached to a 175 VA UPS and ran the back room and transmitters of a wireless iSP for a week on backup power. It took almost 2 weeks to bring them back to a full charge at a trickle rate though.

Best of Luck !

+1
KISS method

 

[v8titan]

+2 on the UPS solution......makes life real easy and you won't need your relay circuit You can pick up a fairly high wattage model with a modified sine wave output relatively cheap. It's the true sine wave versions that get pricy. As others have said, you can crack it open add additional batteries to these and and greatly extend the run time. Be careful in selecting the wire gauge for the remote bank of batteries. If you are going to store them away from the UPS you will need to calculate the voltage drop in the cable to insure the UPS doesn't shut down prematurely (it will think the batteries are "empty" before they are due to the added losses in the cable). This is a important since you will be running at least 30 to 50 amps of current an therefor will have high I x R voltage drops.

 

[Whitespider]

+3

Not exactly correct here on your assessment of the 12V Amp-Hour rating…

As v8titan points out, I had my amp-hours and watt-hours mixed up. As soon as I started reading his reply I got a bit of a hot-flash of embarrassment… ‘cause I knew that. What’s even worse, we’re installing a wind turbine at work right now (boss is gonna’ try and sell ‘em) that uses batteries for power storage and I’ve had to do the calculations. Evidently I hadn’t had enough coffee when I posted… just goes to show ya’, and like I’ve said here before, never believe anything you read on the web without do your own verification. Although, through some sort of lucky math, my calculation ended with the correct number?? A 12v 100Ah battery can supply 1200 watt-hours of power (theoretically) (12v x 100 amps = 1200 watts) and the blower in my example uses 1200 watts (120v x 10 amps = 1200 watts). Where the 80% comes in is the efficiency of the inverter (most run around 85%, give-or-take) and the battery loss because of the higher (than test specs) load. In other word, if you put x amount of power into an inverter you can expect 80% out. So, because the blower will use 1200 watts in an hour, and the battery can only supply 1200 watts in an hour (1 hr x o.8 = o.8 hours run time).

But let’s forget all that and get back to the original question… using the new information from the OP.

...the motor has a 2.8 amp rating.

Wow, that’s smaller than I was thinking. At that rate we’re only looking at 336 watts (120v x 2.8 amps). Even figuring start-up I doubt it would ever pull more than 500 watts. It looks like your circuit would be just fine… but there isn’t any need for all that when you could just use one of these…

APC Power Saving Back-UPS 750

Just like KsWoodsMan posted, and others are agreeing, an Uninterruptable Power Supply is perfect for that type of load.
One single device that contains all your proposed wiring, relays, inverter and battery, capable of 450 watts (they will handle a bit more momentary surge, like at blower start-up)… just plug it in and you’re done! If you check the provided chart it will run your blower (at 336 watts) for over 5 hours without any added batteries. I have my 55-inch LCD television, sound system and satellite tuner plugged into one of those (has to be near 350 watts) and they’ve ran just fine when the power was out for over two hours. You can buy them all over the place for under $100.oo (got mine at Sam’s Club for 65 bucks). You can even connect it to your home network and check status/manage it from your computer. You can’t buy a battery, inverter, wire, enclosure and whatnot anywhere near that cheap.

 

[atlarge54]

Tripplite makes inverter/charger systems, my guess would be around $250 for the unit. All the automatic switching is built in. Then you'll need a couple good batteries. I've used one on my boiler for several years now. I use the batteries out of my boat which helps share the cost. Look on ebay to see what's available.

 

[Valkyrie Rider]

+3


One single device that contains all your proposed wiring, relays, inverter and battery, capable of 450 watts (they will handle a bit more momentary surge, like at blower start-up)… just plug it in and you’re done! If you check the provided chart it will run your blower (at 336 watts) for over 5 hours without any added batteries. I have my 55-inch LCD television, sound system and satellite tuner plugged into one of those (has to be near 350 watts) and they’ve ran just fine when the power was out for over two hours. You can buy them all over the place for under $100.oo (got mine at Sam’s Club for 65 bucks). You can even connect it to your home network and check status/manage it from your computer. You can’t buy a battery, inverter, wire, enclosure and whatnot anywhere near that cheap.

Actually the chart for the UPS in your link says it will only run his 336 watt load for approximately 6 minutes assuming (min) stands for minutes.