battery backup for a Rinnai space heater(installation complete and successful)

[47sawdust]

I am looking for some feedback on powering a Rinnai space heater during a power outage.I need to keep a 10x 20 well insulated room warm enough to keep a water supply to a sink from freezing.
The Rinnai is a model EX11CTP,very small unit that requires 44 watts for ignition and fan.
What size battery would be needed to keep this going for 2 days and what would be a suitable inverter?
Initial thoughts are to trickle charge with utility power, but a small solar panel is also in the plans.
The owner does not want to use kerosene as temporary heat.
Thanks

[Ljohnsaw]

44 watts on 120vac?  Probably want a smaller inverter so there is less losses.  Probably something in the 200 to 500 watt range.  So for 2 days of coverage you would need 1,056 watt-hours of storage.  You need to convert that back to DC watt-hours taking into consideration of losses in the system.  Someone better versed in that will come along soon.  You would do well to have a 200 watt solar panel.  I have one on my camp trailer with a good controller.  Pretty maintenance free.

[Ianab]

So for 2 days of coverage you would need 1,056 watt-hours of storage.

That's the basic calculation, Now divide that by the battery voltage (12V) and add in a fiddle factor for the inverter efficiency. Comes out with about a 100 A/H deep cycle 12 V battery.  So it's in the "sensible" range.

Might also be worth checking the average draw of the heater, It may need more for the igniter, but once it's running the fan alone might need only 1/2 that power. If it draws less when only the fan is running, then you get a longer run.

But inverters generally run best at maybe 1/2 power. They aren't at the best efficiency at 5% capacity. Hence the advice of a smaller unit, not a 2,000 watt unit that needs 20w just to keep it running.

Edit, also check that the system is "fail safe" and the mains power will switch it back on if the battery runs flat.  If the UPS shuts down for flat battery, make sure it will power up again when mains is restored. It would suck if the power is off for 49 hours and you run out of battery. 

[47sawdust]

Great info.,thanks. I was thinking along the same lines of using a 200watt panel to trickle charge.I have a similar setup to power led lights at my saawmill.
Any brand of 500 watt inverter to recommend ? Panel? Battery?

[John Mc]

44 watts on 120vac? Probably want a smaller inverter so there is less losses. Probably something in the 200 to 500 watt range. So for 2 days of coverage you would need 1,056 watt-hours of storage.

I think you miscalculated. 1056 Watt-hours would be just 24 hours of continuous operation. 2 days of continuous operation would be 2112 watt-hours. Though in reality, I', guessing he would need far less, since it's unlikely the heater would need to run continuously to heat a well-insulated room.

Sounds as though a Jackery Explorer 2000 Pro portable power station might do the job for you. It's basically a battery storage and inverter in one. Capacity is 2160 watt-hours. It has a couple of 110VAC outlets. Just plug the Rinnai into the unit when needed. Since your heater probably doesn't need to run continuously to keep the room warm, you might get away with a significantly smaller, lighter, less expensive unit if all you need is 2 days of run-time.

They can recharge via solar panels (they have a built-in solar charge controller) or 110VAC. Some models can also charge via a car cigarette lighter (though the car charger takes along time to recharge). IF there is an extended power outage, just take it somewhere that has power, plug it in for a couple hours and you are fully recharged.

As a bonus, you can use it a portable power source the rest of the year, when freezing is not a concern.

[mudfarmer]

That Jackery thing is cool! Possibly overkill on features and budget for the ask though?

$2k for the Jackery but you could get 2x 100AH AGM batteries (Renogy, etc) for <$500 and a pure sine 500w inverter for around $100. You would not have the built-in charge circuits or the ability to run much larger loads though.

[47sawdust]

I'm monitoring the electrical use now as we go through a cold spell. I'm somewhat optimistic that a 100amp hour lithium battery and a 300-500 watt pure sine wave inverter will keep the Rinnai going for at least 3 days.The means of trickle charging are up to my client.She likes the idea of a small solar panel so will probably go in that direction.

[Joe Hillmann]

Instead of going through the expense of buying a battery backup why not just install a ventless heater that doesn't require electricity.  You can get a 10,000 BTU one for $112.  It runs without electricity, and you can fit a thermostat to it.

Or if you want something a bit nicer look into a direct vent wall furnace.  They can be run with no electricity and use a thermostat.  10,000Btu units start around $500 + the cost of instillation.

Both options will be cheaper than any battery back up that will power your heater for a couple days.

Another option is a MR. Heater with 20 pound or 100 pound tanks.

Is there a reason the owner won't go for Kerosene?  Do they have experience with old heaters running diesel stinking the place up?  A heater in good condition burning clean kerosene only produces smell when it is lit and put out.  To solve that problem I light mine on the porch, let it get up to temp, then carry it inside.  And when I want to turn it off I carry it out to the porch and turn it off out there.  That way almost all the stink stays out there.

Solar panels are great, but the sun doesn't always shine.  Usually in my location January is sunny.  But this year we have only had 4 or 5 sunny days since Christmas.  At the moment I have 640 watts of solar that I have been monitoring since Monday.  On Monday the peak out put was 7.4 watts, yesterday it it 24 watts, and today is a bit brighter and it hit 34 watts.  And I am only able to get that much power because I am using MPPT controllers.  I love solar, but it isn't a magic bullet.  And I wouldn't want to rely on it alone to prevent tens of thousands of dollar of plumbing and flooding damage without also having a good generator to back up the solar.  Also power tends to go out during storms.  Storms usually means cloudy skies, and solar doesn't put out much power when it is cloudy.

[47sawdust]

In 48 hours of continuous use this heater consumed 940 watts.I feel pretty confident in the battery/inverter route.My client is 76 years old,some times stubborn and very busy with other than the practical matters of living on her own.This approach appeals to her and she is paying the bills

[Joe Hillmann]

In 48 hours of continuous use this heater consumed 940 watts.I feel pretty confident in the battery/inverter route.My client is 76 years old,some times stubborn and very busy with other than the practical matters of living on her own.This approach appeals to her and she is paying the bills

What was the outside temp when you did the test?  Can you expect it to be colder when in actual use?
Lithium batteries can only use about 70% of there rated capacity.  And lead acid only 50%.
Also check how much power it draws at ignition.
I have a small diesel heater that can run for hours and hours on a regular car battery but can only start 3 or 4 times on the same battery because starting takes  way more power than running.  
I am not trying to steer you away from battery backup, just pointing out possible pitfalls that hopefully you can avoid if you are expecting them.

[Joe Hillmann]

If you are set on battery back up. I would go with 12 volt,lead acid, golfcart, batteries.  If you go with batteries around 100 amp hours or 200-240 minutes RC. Each battery of that size would give you about 24 hours of runtime on your heater.  You can wire them up in a 12 volt bank with as many batteries as you want.

I would go with the smallest inverter that can run your load.  Ideally one with auto on so it only runs when something plugged into ot calls for power.  Before buying an inverter I would try borrowing one to see if the heater will run on a cheap modified sine wave or if it needs a pure sinewave.  I have several fans that REALLY dont like modified sine waves.

Also some furnaces will NOT run with a floating neutral so to run them off a inverter you need to bond the inverters neutral to the buildings.  

If you want to trickle charge the battery of solar just to keep it topped up any cheap PWM controlled will work as long as the panel output is designed to match your battery charging voltage.  With such a set up the only time the battery will charge is when the panel is in FULL sun.

If you want to scavenge as much power as possible to keep it running as long as possible when the power is out go with a MPPT controller.  As long as it is daylight it will put some power into the battery.  I personally have "make sky blue" brand controlers.  They are a cheap brand from China.  I have used mine for about 4 years and have abused them in ways they shouldn't be used and am very happy with them.  MPPT controllers dont care about matching panel and battery voltage.  They will take any voltage from the panels and convert to any voltage the battery needs

[47sawdust]

Thanks Joe. The Rinnai service rep said the pure sine wave inverter was definitely needed.I am looking at a couple 300watt inverters.The choices are a little confusing.

[Joe Hillmann]

Does the owner of the system live on site.  When the power goes out will she be able to go to the heater, un plug it from the wall and plug it into the inverter and turn the inverter?

Or does it have to be automatic?

Will the owner be able to do basic monthly checks on the water level in the batteries and there voltage?  As well as add water if necessary?

[47sawdust]

She does live on site and can physically do the change over.I am hoping to use a sealed type of battery.

[peakbagger]

Morningstar has made a slick small sine wave inverter for years that might be the ticket Suresine 300 Watt Off-Grid Solar Inverter l Morningstar Corp. About as bulletproof an inverter that is probably available. 

[Joe Hillmann]

If you do instal solar panels I would recomend installing them straight up and down on a south facing wall, ideally under an overhang, but low enough so they get full sun in the winter.  

I have some panels that are at 78 degrees on the roof and some that are mounted on the south wall.  The ones on the roof need to be cleared after every snow fall, snow builds up at their base and jas to be shoveled away.  The vertical ones needed to be cleaned one time this winter from a strange south wind snowstorm.

[47sawdust]

I am planning on mounting the panels vertically for exactly the reason you mentioned.
Thanks

[Sod saw]

.


The recommendation to mount the solar panels is spot on for some one who may not be able to get out and clear them off every time it snows, although those panels will not have as much output when the sun is high in the summer.   They will not be needed to keep a discharged battery up in the warmer summer because if the power goes out the pipes will not freeze any way and the batteries should not be discharged.

As for batteries:  any battery must not be discharged too far.  Lead acid batteries can only be discharged about 50% of their rated amp hour capacity.  Ideally they should never see a 50% discharge.

AGM type of batteries can be discharged somewhat further without doing permanent damage to the inside parts.

The newer lithium type of batteries can be discharged even further but must not go below their lowest designed state of discharge and therefore must have a Battery Monitoring System in the circuit to automatically disconnect the battery form all loads when that battery reaches its lowest allowed state of discharge.

The lead acid type are least costly with the AGM sealed type of batteries costing more than lead but less costly than the most expensive Lithium type of batteries.

It's a balancing act to provide the customer with the best system for their lifestyle and their abilities to watch over the system on a daily basis without having the cost be so high that they can not afford that system.

Now, let look at safety.  If you have the heater operating from the 115 volt house main utility electric system (plugged into the wall) it will not run when the electric utility goes down (storm).  Therefore, your wish is to have a battery backup electric system to power the heater when the electric utility goes down.  

If that battery backup system automatically comes on line when the electric utility goes down and the heater is still connected to the utility, the battery system will back feed into the electric utility system and could kill someone who is working on that utility electric system.  Further more if the battery backup system output is connected directly to the utility electric system the battery backup system inverter could be damaged from back feeding .

Your battery backup system inverter must be designed to automatically switch the load (heater) from deriving its electricity from utility electric to battery backup without directly connecting the utility electric system to the battery backup system.  Not all inverters are capable of isolating those two electric systems.  Please do not buy a cheap inverter and expect it to be safe in all instances.

Legally; where are we now?  Most electric companies require an engineering study and formal application to be able to connect an alternative source of electricity directly to their utility system for safety reasons.

You can get around this requirement by installing a physical  transfer switch to manually or automatically disconnect the utility electric system from the heater and connect the battery backup system to your heater.  Thereby isolating your battery backup system from the utility electric system always keeping the folks working on the main power lines safe.

have fun and be safe


.

[Magicman]

Something like this might be an option:  LINK or LINK

[John Mc]

That Jackery thing is cool! Possibly overkill on features and budget for the ask though?

$2k for the Jackery but you could get 2x 100AH AGM batteries (Renogy, etc) for <$500 and a pure sine 500w inverter for around $100. You would not have the built-in charge circuits or the ability to run much larger loads though.

Certainly it's overkill. However, if you have it, you can use it to power other things as well, or take it camping instead of a generator. Granted, those extra uses may not be of interest to this customer.

[47sawdust]

Where I'm at today is this set up.
100watt panel with controller,100 ah agm battery,500 watt true sine inverter,fuse,cables and automatic transfer switch.
My hope is to have this be a seamless operation as my client may or may not remember to make the switch manually.
Total materials cost is less than $650.then I have to do a clean installation.

[Joe Hillmann]

Where I'm at today is this set up.
100amp panel with controller,100 ah agm battery,500 watt true sine inverter,fuse,cables and automatic transfer switch.
My hope is to have this be a seamless operation as my client may or may not remember to make the switch manually.
Total materials cost is less than $650.then I have to do a clean installation.

Do you mean a 100 WATT panel?
What inverter did you decide on?
If you haven't bought it already have you looked into uninterruptible power supply(UPS)?  You can swap in a 100 amp hour battery.  Then plug the UPS into the wall and the heater into the UPS. 
The UPS will act as a battery charger and always keep the battery charged, and when the power goes out it will automatically switch over to battery power.  When the power comes back on it will switch back to grid power and recharge the battery.  UPS's are designed for electronics so are pure sine wave.  UPS's are designed not to back feed the power grid.  Other than checking every so often that the battery is still holding a charge it is very little maintenance.
Then if you want to add a solar panel you can but it really isn't necessary.

[47sawdust]

I am not familiar with  the process you describe but I am curious.
What UPS size,brand and how would it be connected to a 100ah battery.?
Sounds slick.
Thank you.

[Joe Hillmann]

Do you know what a UPS is?

It is basically a battery charger, a lead acid battery about the size for starting a small atv and a high quality, pure sine wave, power inverter all built into one unit.  You plug it into the wall then plug your computer equipment into it.  The charger charges the battery, the battery powers the inverter and the inverter powers your computer.  That way if the power goes out your computer stays running and you can save what you are working on and shut it down.  UPS's also have built in surge protection. 

You could buy a regular ups, remove the battery and extend the leads with longer wires and battery terminals or alligator clips and connect it to a larger 12 volt battery of your choice and capacity.  You will have to drill a hole in the case to run the wire to the battery.  If you do a clean job wiring it this can look very professional or if you are sloppy it can look pretty bad.  UPS's have a built in pezo electric buzzer that alarms anytime it is disconnected from grid power to warn you.  Since I use mine mostly as a pure sine wave inverter where I don't have grid power I clipped one of the wires to the buzzer when I had it open.  For the way you want to use it you should re wire the buzzer to an external switch.  That way it it will alarm when the power goes out but she can turn it off when it gets annoying.

They also make UPS's designed to  have external batteries connected to them but they tend to be much higher wattage and more expensive.

Or look into something like "Growatt, all in one"  it is basically a UPS for external battery with a spot to connect solar panels.  The problem is Growatt doesn't make one for a 12 volt system, there smallest is 24 volts.


I think a modified UPS  would fit your needs if the heater only draws  44 watts. It is almost what they are designed for, to sit there for years unnoticed and unmaintained until the power goes out and they kick on and do their job so well they need an alarm to worn you something is wrong.  You can buy a 330 watt one with 6 plugs for $110.  I have two of them that I modified.  I think they are both Belking.  One is around 900 watts the other is around 500.  The bigger one I removed the power cord from and only use it as an inverter(I kind of regret removing the cord from it)  The smaller one still has the cord and can be used as a battery charger, a inverter or a UPS.  The smaller one has a clip in lid where the battery used to be so I am able to tuck all the wires neatly into it when it isn't in use.  The larger one has a couple winters of use powering my hunting/fishing/syrup shack because I had it in storage with a dead battery and didn't want to spend money on an expensive pure sine wave inverter.

[Joe Hillmann]

If you need pictures to describe it better I have one right here I could take apart to show you how I wired it.

[47sawdust]

Thanks Joe.I think I will stick with my original plan.I don't mind modifying equipment for my own use,but can't do it for a paying customer.

[Ljohnsaw]

Joe,
I like your idea!  I see free UPS' on CL every now and then that have a dead battery.  I think I may pick up a couple to use as inverters for my cabin (off grid) to charge my laptop!

[scsmith42]

I have done what Joe suggests above.  The computer that I am typing this on is connected to an old UPS that I've wired external batteries to for longevity.

For the OP, UPS units are available with connectors for external battery packs.  They are commonly used in the computer world for extending longevity during an outage.  Many of them are rack mounted and you can add multiple battery packs.

I have one that backs up the computer network for my wife's veterinary practice.  The nice thing about this setup is that your client will have factory warranty, etc.

[mudfarmer]

Those sealed UPS batteries are also good replacements for solar electric fence chargers, FYI ;D Doubled up two of them when the OEM fence charger battery died and now have twice the storage crammed in there.

[47sawdust]

I finished the solar battery backup today and the initial results are very promising.
The Xantrex transfer switch works instantaneously.
The panel,monitor,battery,inverter and all cables and hardware came from Windy Nation Solar and Wind.
They were very easy to deal with,designed the system and everything arrived promptly with no damage.
The transfer switch and lighted cord ends were sourced elsewhere

100watt panel







 


Rinnai running off house current.Both cord ends lit.

 


Rinnai running off battery right hand cord end only lit.