Inverter as backup power

[Fod01]

I'm pondering the 'what if the power goes out' scenario, and am considering a small generator, but....

I've seen several posts where folks have run the blowers on their stoves by running an inverter from their truck. I assume these are deep-cycle batteries. I imagine we wouldn't get a lot of run time from the starter batteries in the cars. True? Also, I've read in some automotive forums that the car's alternator will not to a good job of recharging a badly discharged battery. It's primarily used to maintain charge That being the case, how long would you have to idle the truck to recharge? -Thanks

 

[Gooserider]

I'm pondering the 'what if the power goes out' scenario, and am considering a small generator, but....

I've seen several posts where folks have run the blowers on their stoves by running an inverter from their truck. I assume these are deep-cycle batteries. I imagine we wouldn't get a lot of run time from the starter batteries in the cars. True? Also, I've read in some automotive forums that the car's alternator will not to a good job of recharging a badly discharged battery. It's primarily used to maintain charge That being the case, how long would you have to idle the truck to recharge? -Thanks

How long the battery will last is essentially a function of how big the power draw is, along with how big the battery is... To figure this you need to find out what the power consumption of the load is when it's running - the label on most appliances really won't tell you this as the label will have the maximum power draw, which is usually just a few seconds at startup...

The key problem with trying to recharge a battery in a vehicle by idling is that the alternator output is dependent on engine speed, and at idle your alternator will barely put out enough juice to "break even" with the power demand of the vehicle's ignition system, if that... Typically you would need to get the engine up over 2,000 RPM before the alternator really starts to put out enough juice to seriously charge the battery, which translates to 20-30mph driving speed. While you could do a very fast idle to get some charging, it wouldn't be very fuel efficient, and would be really hard on the engine...

Essentially the question boils down to how long do you expect your power to be out for? You can do various inverter related things like computer UPS units (possibly after replacing the battery with a bigger one) or plugging something into your vehicle, but it gets really difficult / expensive to get more than a few hours on battery power without some sort of recharging method, and vehicles are intended for traveling, not battery charging... Also the longer the power is out, the bigger your load demands get - you have to start worrying about the fridge / freezer, possibly other electric dependent appliances, lack of lights gets more annoying, etc.

On the flip side, a power loss for just a few hours might let you get a bit chilly, but probably wouldn't be putting you at risk of pipes freezing or other serious problems, so how much expense is justified in planning for a short outage? A generator will keep the power on for as long as you can keep it fueled, and will probably be able to handle all your loads to some degree if sized properly and you do things like load rotation and so forth....

Our approach is that we have a few things in the house, such as the computers, the clock in the bedroom and the GF's CPAP machine, and a few other items where even a few seconds of power loss can be an issue on UPS units that will keep them going for long enough to do graceful shutdowns or otherwise deal with them, and / or give me time to drag the generator out of the garage and get it running if we have reason to think it will be a prolonged outage...

Gooserider

 

[smokinj]

here is where i fill the china gen-set work for me,in 3 years I only neened mine 1 time for about 4 hrs. (i start it ever coulpe months) 299.00 3500 watt

 

[Fod01]

Thanks for the in-depth response Goose. There's lots of good info there.

I'm not really thinking past heat from the insert, and that inverter trick sounded way too easy.
Further pondering is in order (coffee first). Thanks again.

 

[YZF1R]

I bought a little 2-stroke generator from HF for that very purpose. $129.95. Sips fuel and is very quiet. I know you're supposed to be able to burn without the blower, but besides not getting the heat out of it, I'm worried about not getting the heat out of it. In other words, I'm worried that if the insert can't get rid of the heat, the unit itself might overheat, besides the house not getting the heat. I pack mine up full for long burns and I've seen a couple of the secondary tubes looking cherry red at times, hence the concern of overheating the insert if the blower is not running.

Steve

 

[Gooserider]

I bought a little 2-stroke generator from HF for that very purpose. $129.95. Sips fuel and is very quiet. I know you're supposed to be able to burn without the blower, but besides not getting the heat out of it, I'm worried about not getting the heat out of it. In other words, I'm worried that if the insert can't get rid of the heat, the unit itself might overheat, besides the house not getting the heat. I pack mine up full for long burns and I've seen a couple of the secondary tubes looking cherry red at times, hence the concern of overheating the insert if the blower is not running.

Steve

I doubt that would be a major concern, especially for an occasional incident... I seem to recall that part of the testing is to do multiple full power burns w/o power, both to make sure that the insert doesn't get damaged, but even more importantly, to ensure that the heat reaching adjacent structures doesn't get to unsafe levels... Part of any solid fuel appliance design theory is "fail-safeing" and power outages are a pretty much guaranteed "failure" that has to be designed for - either by a guaranteed shutdown, or a design that can handle the heat and / or get rid of any excess, without requiring power or outside intervention.

Gooserider

 

[Fod01]

I hear that Steve. Last season I turned the blower off, packed it full for overnight, but never turned it back on. The next day you could feel the heat radiating off the entire hearth. Must've gotten toasty. I don't think I did any harm, because the manual instructs not to run the blower if the air is shut all the way down. As if any owners of flushmount inserts do this. They should have added a footnote that states 'When blower is off, give wood to neighbor, as you'll get no benefit from it!'.

Gabe

 

[LLigetfa]

My fireplace is not a retrofit insert per se but it throws out good heat without the blower. I use a 650 CFM blower in the crawlspace, which moves the heat through the whole house. We've had power outages that lasted for hours in bitter cold and the fireplace performed well enough that we don't worry about a genset. With my luck the generator wouldn't start in the cold anyway. I've seen my neighbors out struggling with theirs while I can just sit comfortably by the fire without the noise of either the fan or the genset.

I'm waiting for the price to drop on CHP systems. There are some reasonably priced whole house standby natural gas gensets now but I'd still worry that they won't start in the cold.

 

[YZF1R]

Gooserider: Glad to hear that. That makes me feel better to the safety issue.
Fod01: Yea, not much heat without the blower.
LLigetfa: I know NG powered engines are hard to get going if outside in the cold. The standby NG generators usually have an electric carb. heater as an accessory if not standard.

Steve

 

[kevin j]

small generator has several other advantages: portable tools, running the well, etc.
but if you don't have one, how about the thermoelectric or sterling cycle fans that sit on the stove. They are pretty small though.

Skipping the invertor, can you make up a panel with a 12vdc heater fan from a car that would fit near the stove, and run it direct from battery? you could lift off or otherwise adapt it to work in parallel with the original fan.

 

[Gooserider]

small generator has several other advantages: portable tools, running the well, etc.
but if you don't have one, how about the thermoelectric or sterling cycle fans that sit on the stove. They are pretty small though.

Skipping the invertor, can you make up a panel with a 12vdc heater fan from a car that would fit near the stove, and run it direct from battery? you could lift off or otherwise adapt it to work in parallel with the original fan.

Yes, that isn't a bad idea but once again, you are looking at the issue of getting more than a few hours of power from it, and how do you recharge after that... In addition there is also the question of getting the power from the battery (presumably in the car that's out in the drive) to the stove in the house - likely a lengthy powercord will be needed, and fairly heavy guage to minimize the power drop along the way...

The stove powered fans might work, except that there is the question of where do you put them on an insert to get the required heat? Also will that put the fan where you need to move the air... (IDEA :exclaim: - how about one of the thermo electric units where the fan part is separated w/ a short cord from the power producing part? not sure it would work?)

Gooserider

 

[burntime]

If you have a tractor just charge it off of that. Still not the most efficient but better then running the car. I think my simplicity is like a 15 amp charging system...some are 3 amp. If you have the larger it charges about 3 amps just outside of idle...

 

[Highbeam]

You can certainly do this with an inverter. Don't use your truck battery though, those starting batteries will be ruined by running them flat. Go to walmart and buy a deep cycle battery for 50$. This battery will have a number on it called amp-hours, like say 500 amp-hours. This rating means it will put out 500 hours of 12ish volt power at 1 amp. Thats a 12 watt load for 500 hours. So a watt is a watt. If you need 50 watts for your blower then thats 4 amps and the battery would only last 125 hours. The inverter that you need will consume like 10% of the juice just to get 110 volts but it will still work for a long time.

Put the battery(s) in the garage on a trickle charger. When the power goes out, plug in the inverter to the battery in the garage and run a normal 110 extension cord to your insert. You want to keep the batteries out of the house since they make some nasty gasses.

You have a small load to keep running. Folks try this with pellet stoves that require hundreds of watts and have only marginal success but you are in a better situation.

I have an RV with lights, a water pump, and a furnace that run off of my two 12 volt deep cycle batteries from walmart. Same deal, limited battery power but plenty for several days.

The off-grid people live off of a bank of many deep cycle batteries and charge them with solar, wind, or an occasional generator and then use an inverter to power their whole house.

 

[d.n.f.]

But a generator will run your deep freeze and your fridge. We had a twelve hour power outage this summer with 33C temps. Generator helped keep my meat collection stored properly.

 

[pilot-werx]

I have tried every scenario you can imagine... Marine batteries with solar, pto generator for my tractor, just old fashion lanterns, etc..... I live in an area with frequent power outages and finally got sick of messing with everything including throwing out $100's of food... Last summer I had an Onan 12kw generator installed with the transfer switch. In last December's ice storm, when the power went out at 2am and the generator come on automatically I was happy I took the plunge. It ended up running solid for 7 days.

By the time you get done messing around with the inverter, batteries, and running a vehicle, you can buy a small portable generator and a disconnect switch. You may only need it once a year, but it sure is nice knowing your house is not going to freeze up and you can make coffee in the morning!

 

[Wet1]

I agree that a generator is the way to go. I bought a larger unit (I think it's a 7500 watt) to power the entire house. Just picking up a small 2 stroke unit makes a lot of sense if you don't need a lot of juice. The little $100 units are quiet, light, and sip fuel. It's easy to sit them outside a window and run appliances directly off them with an extension cord.

 

[Highbeam]

We're talking about two things here.

1) Can an inverter work for a stove blower? Yes.

2) Should you buy a genset? Maybe, but I don't think that was the question.

I own a genset and a whole house tranfser switch and used it recently to keep the food cold during a 6 hour daytime power outage in the heat. I like gensets and don't own an inverter but I know how inverters work and there are some limited cases where they are superior. Running a 12kW genset to power a 50 watt stove blower is one of those times.

 

[Gooserider]

We're talking about two things here.

1) Can an inverter work for a stove blower? Yes.

2) Should you buy a genset? Maybe, but I don't think that was the question.

I own a genset and a whole house tranfser switch and used it recently to keep the food cold during a 6 hour daytime power outage in the heat. I like gensets and don't own an inverter but I know how inverters work and there are some limited cases where they are superior. Running a 12kW genset to power a 50 watt stove blower is one of those times.

I agree that getting a genset JUST for the stove blower is kind of silly, but my feeling is that by the time you start getting into the sort of scenario where you really need to have the stove blower going, you are likely to have enough other loads that need power to justify the genset...

My logic -

1. The insert may get hot, but is not going to be damaged by running w/o the blower, and it will still put out SOME heat.

2. Unless you spend the sort of money that it would take to get a genset, you will be hard pressed to get more than a few hours out of an inverter setup, and you will then be hard pressed to recharge the battery.

3. In an outage less than 12-24 hours, you really don't need ANY power - your fridge / freezer will stay cold that long, the house won't cool to the point of risking pipes freezing, etc... It may be uncomfortable, but you'll live through it...

4. In an outage over that length, most inverters will be running out of steam, and even if they aren't, you may be needing to power additional loads as the house cools down, and the fridge / freezer heats up, not to mention the convenience of having electric lights instead of candles, wanting to hear news & weather reports, etc... An inverter sized for the stove blower won't handle those other loads, again unless you start spending money in the genset price range...

I do have a genset, but our practice is that we won't even drag it out until either the power has been out for at least 5-6 hours, or there are strong indications that we won't be getting it back any time soon, such as news reports of major outages, or equivalent...

Gooserider

 

[YZF1R]

Actually, I intend to get a larger portable gen with transfer switch to run 2 refrigerators and one freezer, lights, TV, etc. The little one will be for overnight just for the insert blower and a couple lights, maybe a TV. I'm in a neighborhood and don't need the overnight noise or fuel usage of a larger one lunger pounding away all night just for the insert blower. BTW, the little one did start and run one of the refrigerators, but wouldn't start the freezer. No load voltage is 118v. I could turn it up to 128v or so and it may start the freezer, but then you need to worry about something small you may add after the large load is running. When the large load unloads from the generator, the voltage spike as the gen goes over the governor for a split second might damage the other thing. (Like a small TV or whatever.)

Steve

 

[Highbeam]

We're talking about two things here.

1) Can an inverter work for a stove blower? Yes.

2) Should you buy a genset? Maybe, but I don't think that was the question.

I own a genset and a whole house tranfser switch and used it recently to keep the food cold during a 6 hour daytime power outage in the heat. I like gensets and don't own an inverter but I know how inverters work and there are some limited cases where they are superior. Running a 12kW genset to power a 50 watt stove blower is one of those times.

I agree that getting a genset JUST for the stove blower is kind of silly, but my feeling is that by the time you start getting into the sort of scenario where you really need to have the stove blower going, you are likely to have enough other loads that need power to justify the genset...

My logic -

1. The insert may get hot, but is not going to be damaged by running w/o the blower, and it will still put out SOME heat.

2. Unless you spend the sort of money that it would take to get a genset, you will be hard pressed to get more than a few hours out of an inverter setup, and you will then be hard pressed to recharge the battery.

3. In an outage less than 12-24 hours, you really don't need ANY power - your fridge / freezer will stay cold that long, the house won't cool to the point of risking pipes freezing, etc... It may be uncomfortable, but you'll live through it...

4. In an outage over that length, most inverters will be running out of steam, and even if they aren't, you may be needing to power additional loads as the house cools down, and the fridge / freezer heats up, not to mention the convenience of having electric lights instead of candles, wanting to hear news & weather reports, etc... An inverter sized for the stove blower won't handle those other loads, again unless you start spending money in the genset price range...

I do have a genset, but our practice is that we won't even drag it out until either the power has been out for at least 5-6 hours, or there are strong indications that we won't be getting it back any time soon, such as news reports of major outages, or equivalent...

Gooserider

Good points goose. I'm a genset man. In fact, I need to change the oil in mine to get it ready for another season.

 

[jebatty]

Many good points made. I got a 5000W, 240V, inexpensive gen and put in a 10 circuit transfer switch. The circuits include most house lights (and most of these are CFL's); an outlet circuit for the computer and entertainment center; an outlet circuit for the kitchen microwave; refrigerator and freezer; the well water pump (240V); and the basement sump pump are all covered.

Also use full syn oil in the gen and exercise it periodically; stabilized fuel which I change out once a year. One reason for syn oil is that it flows well in really cold weather, and -30F where we live is not unusual.

Consider the gen an insurance policy. If you buy one, you may never have to use it; but if you don't have one, power outages become a contagion.

 

[Wet1]

Inverters are very inefficient and almost useless unless you have a decent bank of batteries, they will only cover your limited needs for a few hours. This is why I suggested the small 2 stoke gen above if you don't want to go with a larger genset. You can survive for weeks with one of those $100 generators. If you wanted to, you could even isolate your central heating system and install a receptacle on it, this way you can plug your boiler/furnace into the small genset and have emergency heat.

 

[daveswoodhauler]

I have an insert, and was looking at exactly what you are thinking exactly one year ago....looked at the cost of deep cycle batteries and an inverter...cost was just too steep to just run the blower.
We then had the ice storm here in the northeast in dec 08...lost power for 9 days....on day 4 I bought a 8350 watt start/5500 running generator from home despot....was $700...it runs everything in the house, except the oven and clothesdryer......and we have a 300 ft deep well.....I think a small generator might be a good fit for you.

 

[Dregan]

Another consideration about inverters (particularly when you look at use for electronics) is sine wave output. 99% or the inverters I've seen are modified sine wave, whereas a genset will usually put out pure sine wave (or at least, more correct sine wave)

Without getting into a physics or electronics diatribe, using a modified sine wave output can damage solid state electronics (circuit boards and electric motors - like what's in your fridge or blowers) A $200 Chinese-made genset won't (or at least, not as bad.)