Battery Backup With Pics

So this might not be posted in the right place, but it will be once I get my new Stoker in place!

I'm new to the forum and have been snooping around to see how many topics have been started about Battery Backups...Not as many as I would have thought...And many topics asking "How To" v/s ones offering up systems that actually work as designed.

I have been heating my house with a forced air furnace for about 25 years. Just a few years ago and after getting lucky for so many years, I set out to solve the problem of having an over-heated stove due to a power outage when we were away from home. My wife and I both work, so the backup system was designed to keep the furnace blower going long enough to avoid over-heating till we would get home from work...Minimum run time I was looking for was 8-10 hours. After that, the amount of fire and coals in the stove wouldn't be an issue.

So I'm here to share what I came up with....

Aims Power, 12v to 120v, 1500 Watt Pure Sine Auto Switching Inverter Charger, with 3000w surge, built in 35a auto-charger,
p/n PICOGLF10W12V120VR
(4) 242ah 6v deep cycle batteries wired 2 series 2 parallel to get 484ah @ 12v
Converting to 120v not counting for inefficiencies in the inverter is 48.4ah @ 120v
Mathematically, that capacity should run my furnace appr. 16 hours (Furnace Blower uses 3.0a)
The Inverter will shut down at 11.5v or @ about 50% battery capacity remaining that runs the furnace blower appr 8-10 hours

I tested the system after installation and ran the furnace for 5 hours continuous. Battery voltage never dropped below 12.5v. I'm sure it will go 8-10 hours easily! I built in a separate circuit to monitor battery voltage by flipping the switch. The switch also turns on an a 3" 12v fan to exhaust any fumes during the charge cycle. That's what the PVC pipe is for. But because of such a low charge rate, the batteries don't even get warm. I try to cycle the batteries about once a month even though the auto-charger conditions the batteries every 10 days if not discharged.

The backup system isn't cheap, but doesn't break the bank. I have a little over a $1000 in it. But gives me piece of mind when I'm not at home. Plus when I'm home, if the power goes out, I'm not in a mad rush getting the generator going to avoid a meltdown...Some Pics....BTW, the digital readouts also allow me to monitor how balanced the batteries are...They are still pretty close even after 2 years!

Nice Setup.

WNY wrote:Nice Setup.

A++

So it wasn't renewable energy after all, although adding some solar panels, a hydro or a wind turbines can make it fill that bill.

Very nice!

NOTE: 50% discharged is 12.1 volts (as properly measured for a battery bank that has been disconnected and left to sit idle for at least 4 hours with absolutely no load on it, which is not possible for your case (or mine)). 11.5 volts is closing in on a dead battery (10% remaining charge). You might consider changing the cut-off setting accordingly (to perhaps 11.9V or 12V for the cut off).

If your battery banks Peukert constant is 1.19 (upon first educated guesstimate), you will have 4.23 hours to 50% discharged for a 30 amp load at 12 volts. This would extend to 5 hours for a phenomenal Peukert rating of 1.14.

http://www.csgnetwork.com/batterylifecalc.html

With all of the various inefficiencies added in you are probably at about 3 hours max to 50% discharged. 3.5 hours if your banks Peukert rating is among the very best. Peukert's Law is brutal. But then again, your furnace blower will not run all the time. But that momentary ~5X current draw each time it starts up is also going to be a killer (ala Peukert) over time.

Nice, and neat........... Being a "stoker" stove / furnace, it'd keep the fire from going out, and coming home to a cold house, and ash pit full of fresh hopper coal. That is; if the electric comes back on, after the fire goes out. As far as over heating the stove / furnace; Should the electric go out, so doesn't the fire. No combustion air = no fire. Now that it's over, and done with, and the money is gone, You'll be happy you made the investment, SHOULD the power go out. You won't be running around, trying to get a generator hooked up, etc.. Like I said, VERY NICE!

Hmmmm....So the batteries advertisement led me astray!

http://usbattery.com/products/6-volt-batteries/us-125-xc2/

Product Name:
US 125 XC2

--------------------------------------------------------------------------------

Voltage:
6-Volt Deep Cycle – Golf, Multi-purpose

--------------------------------------------------------------------------------

Data:
20 Hour Rate: 242
Minutes of Discharge @ 75 Amps: 140
Minutes of Discharge @ 25 Amps: 517

Looks like I need to study up on Peukert's Law! (Actually didn't know it existed!) But doesn't explain 5 hrs run at 3.0a and still having 12.5v left under load. I am very close to the 20c discharge rate for the 4 batteries, though....Also, this particular inverter doesn't have a variable shutoff...Only 10.5v and 11.5v using a dip switch. The 11.5v cutoff would be actual under load, so nominal after cutoff will be higher, maybe closer to the 50%.

@ MCGiever....Nope, not renewable. Not yet anyway. My brother has an Array and gets a check from Duke after they deduct what he uses! He has a nice setup! Although, its attached to the grid....If it goes down, then what?

By downloading the PDF spec sheet for your battery (and finding its amp hour rating at various amp draws) I was able to calculate that your battery has a very good 1.18 Peukert exponent value. Lower means better.

This calculator says 7.8 hours for a 30 amp draw. The calculator at the top of the page gives you the Peukert exponent, and the calculator a bit below it gives you hours for various amp draws.

http://planetcalc.com/2283/

Unfortunately, Peukert values from online calculators are all over the place, since many of them have the math all wrong. I'm not sure which one is right between the two Peukert calculators I've now linked you to, but the one I attached here is probably closer to the values that US Battery quoted (though I did not take the time to verify this). If the one here is closer to US Battery's figures, this leads me to believe that the calculator on the link I first gave you is way off.

The essence of Peukert is that a battery has no such thing as a single one size fits all amp hour rating. The more demand you place upon it, the less battery you actually own (and visa-versa). And the relationship is exponential, not linear.

Unfortunately, voltage remaining under load is essentially a meaningless measure. It's all I (by choice, see below) have to go on also. My battery bank (same batteries as yours) is showing signs of aging at only 2.5 years old, but I have loads on them continuously. The lowest Ive ever seen for mine was 24.4 volts (only seen once), but most of the time they go no lower than 24.7 to 24.9 volts, with all of my measurements being under at least some minimal load, and not sitting for 4 hours disconnected. This leads me to tentatively believe that load monitored voltage is likely always reading a few tenths higher than the properly required 4+ hour sitting (rested) voltage (I.E., the real voltage).

The only way to actually measure discharge percentage under any level of load is to take the specific gravity of the battery acid (for each cell). I'm not fond of playing with concentrated sulfuric battery acid. And we both have 12 cells to check. Mine being all in series, for a nominally 24 volt system, and yours in series/parallel, for a nominally 12 volt system.

Thanks for sharing the knowledge you have on this! It’s truly appreciated! I can see you have studied it in a lot greater depth than I have. I was strictly doing the math from the Manufacture Specs of the batteries and designing the system around those advertised specs and what I was wanting for run time…(Since I was so close to the 20c rating). Even if I’m a little short on the 8 hours I was shooting for, the bank should run long enough to avoid a meltdown situation…

It was mentioned but I never thought about it with a stoker! Electric goes out, fire goes out (no combustion blower), electric comes back on…The stoker dumps a bunch of coal in the bucket! Having a Battery Backup! Priceless! Thanks!

It’s funny! I haven’t had a power outage since installing the backup 2 years ago! Cheap insurance I guess! Before then it happened quite often in the winter. Luckily I was home every time it happened! Hence scrambling to get one of the gen’s running!

Now I even have these little warning devices that plug into an outlet. If the electric goes off, an LED light comes on that illuminates the floor and an audible alarm goes off which “Should” wake me if I’m in “Rim” mode!! More cheap insurance!

Since adding the battery backup, I didn’t think I needed something that would “Text or Email” me during an outage. Even that would need its own battery backup! And it goes on and on! How far do you go?!

https://www.amazon.com/POWER-RELIANCE-CONTROLS-MfrPartNo-THP ... ing+device

Larry,

How are you switching load? I've read some of your old posts and see you were asking about relay logic?

The nice thing about the Inverter I have, it synchronizes the sine wave during transition (If I am saying that right?) I had thought about using a relay and inverter, but was concerned about the synchronization thing? There is absolutely no delay or missed beat when this inverter switches load. Its that quick...I had read where this transition could be an issue if not synchronized correctly when dealing with an electric motor. It would be different if the motor was allowed to power down before starting back up, I assume?

BTW, You say you have the same batteries as I do! I did a lot of research before settling on these! Great minds think alike! LOL!

2biz wrote:Larry,

How are you switching load? I've read some of your old posts and see you were asking about relay logic?

I'm not running my boiler off of my solar system and batteries (during an outage or otherwise). With my boilers 1/2 HP fan, I believe it would require something more than I have on hand for that task, and in an outage my system will be needed for refrigerator and a freezer, plus lights, and possibly some small and portable 120VAC induction stove top cooking type tasks. Perhaps it would work though. I'll need to play with the numbers. I haven't concerned myself with this because I also have a stove that can heat pretty much the entire house. And since I'm retired, and I have chickens, I'm generally near at hand on most occasions, so I would likely be here to start a fire and keep the house warm, while letting the boilers fire go out (which for my boiler, I'm told, can range from 1 to 3 days). Most power failures will not likely outlast my boilers fire...

You did great! I could only wish that my system layout was organized as nicely as you did for yours.

Just starting my 1/2 HP fan motor would likely trip my 1,500 watt inverter. Roughly 5X to 7X normal runtime amps to get it moving, albeit for only about 1/2 second to at most 1 second.

lsayre wrote: Just starting my 1/2 HP fan motor would likely trip my 1,500 watt inverter. Roughly 5X to 7X normal runtime amps to get it moving, albeit for only about 1/2 second to at most 1 second.

Check the surge capacity of your inverter. Mine has a 3000w surge capacity for up to 20 seconds. You might be surprised!

372 Watts = 1/2 HP

5 x 372 Watts = 1,860 Watts, and 7 x 372 = 2,604 Watts (before inefficiencies and AC PF are factored in)

It might work for the case of 5X (and due to PF + inneficiencies, would most likely not work for the case of 7X)!

But either for 5X or 7X, nothing else better be drawing inverter Watts simultaneously.

My inverter is a $189 (before shipping) gray market Chinese rip-off of a Cotek. Not much margin above 1,500 Watts. My 1,100 Watt microwave is hit or miss with it.

PS: For a microwave rated at 1,100 Watts, this is only for the magnetron, and it does not factor in the Watts required to rotate the platter, or to light up the lights, etc..., and it does not consider the AC PF (alternating current power factor). My microwave is drawing a measured 1,480 continuous Watts (before PF consideration) when I put my Kill-A-Watt meter on it. Sometimes I can heat a cup of coffee for 60 seconds with it off of the inverter, and sometimes I can't. Some of my lack of success may be due to massive voltage drop though. I never checked this, but I'd wager that at 1,480 Watts my inverter is delivering well less than 110 volts AC (whereas at more normal demand levels it meters right at 120 volts AC). Perhaps when the batteries are well charged the voltage drop is a bit less pronounced. ???

I was mistaken. Our batteries are a bit different. I actually have four of these.

http://usbattery.com/products/6-volt-batteries/us-l16hc-xc2/

My batteries Pukert exponent is well lower, at only 1.23, but they each have 420 AH at 20 hours (6 VDC). In your application that would yield 840 AH at 20 hours (12 VDC). I got mine on sale for $235 each (before tax).

I considered those batteries when I got mine. But 4 of them were somewhat outside the budget! $235 each before tax was a good price. They weren't that low when I purchased. I ended up getting mine from a "Battery Giant Store" for about $600 out the door.

I also considered a 24v system to be able to utilize lighter gauge wire and lower amp draw, but didn't have a backup charger that was 24v. I'd have to disconnect the batteries and charge 2 at a time if I ever needed to. Although 24v is optimum....I settled on a 12v system...