Suggestions on Battery Backup for Harman Super Magnum?

lsayre · Post by **lsayre** » Sun. Jan. 15, 2017 2:17 pm

To calculate the Peukert Constant (also called Peukert's Exponent) you must have at your disposal the manufacturers "amp" rating for 2 diversely differing "hours". The more diverse the better.

For example, a battery with a 420 amp rating for "20 hours", and a 275 amp rating for "1 hour" has a Peukert Constant of 1.16.

http://planetcalc.com/2283/

Only from there can you begin to play "load" games (using the same site and scrolling down further to find two additional of three total calculators) and know how long your battery bank will really last for a given load:

Don't take it down below 50% of fully charged.

guysnydr · Post by **guysnydr** » Mon. Jan. 16, 2017 3:15 pm

I really appreciate all the great information. Here is an ad that I stumbled across for Harmans inverter/charger (which I believe is simply a SureFire Sentry model 512 that you can buy lots of places, but without the Harman logo on it). I wanted to share what they (Harman) are estimating for run times on stokers:

Stove Battery Backup - Part# 3-20-512
For Pellet Stove and Coal Stokers
When the power quits, Surefire 512H takes over. The Surefire 512H is designed to backup or replace utility power. When it is used with a common 90 A-hr, deep cycle marine battery, its highly efficient circuitry provides approximately 8 hours of operation from a wood pellet stove or stoker in the absence of electricity. It also works with automatic ignition stoves.

The Battery Backup will operate in the following:
Accentra Pellet Stove
Advance Pellet Stove
P38 Pellet Stove
P43 Pellet Stove
P68 Pellet Stove
PC45 Pellet / Corn Stove
XXV Pellet Stove
Super Magnum Coal Stoker
DVC-500 Coal Stove
VF-3000 Coal Boiler
Other models besides the ones listed may operate properly with the Surefire 512H.

Based on what I am learning here, an 8 hour run time (or even close) sounds unachievable on a single deep cycle battery. Are they crazy or? I think I am thoroughly confused now.

captcaper · Post by **captcaper** » Mon. Jan. 16, 2017 3:22 pm

Probably those 8 hrs are until it's drained down to zero... so 4 hrs would be the real time. 2 batteries might give you 8hrs..but if the hot air blower is running alot due to very cold weather like we get here I wonder..

lsayre · Post by **lsayre** » Mon. Jan. 16, 2017 3:36 pm

A single 12 volt and 80 AH (assuming 20 hour rated) battery with a more typical lower end Peukert constant of 1.30 will deliver 3.1 amps at 120 volts AC for only 42 minutes (to 50% discharged).

And in reality it will be more like 33 minutes, since a budget inverter will only be (if you are lucky) about 80% efficient.

You have to realize that what is a 3.1 amp load at 120 VAC is a whopping 31 amp load at 12 VDC.

3.1 x 120 = 372 Watts
31 x 12 = 372 Watts

And with AC there is also the Power Factor to consider, and if it is ~0.9, then the "real world" Watt draw is actually going to be 413 Watts.

Probably closer to 30 minutes to battery half discharged.

lsayre · Post by **lsayre** » Mon. Jan. 16, 2017 5:56 pm

Perhaps an easier (albeit incorrect) way to look at this problem is to simplify things by doing the following:

Take an 80 AH battery that can't be pulled below 50% charged too many times before killing it, and what you effectively have at hand is a 40 AH battery, or a battery capable of delivering (under some Peukert determined load which we are magically waving for this example) 40 amps over some period of time.

40 amps x 12 volts = 480 Watts of total energy at your disposal, sitting inside the battery (assuming that the inevitable "sitting drain" on the batteries stored energy is miraculously zero).

I have already eluded to the fact that due to PF considerations for AC combined with inverter inefficiencies the "effective" Watt draw for 3.1 amps at 120 VAC is:

3.1 / 0.90 PF x 120 / 0.80 Efficiency = 517 Watts per hour

480/517 = 0.9284 hours

0.9284 hours x 60 minutes/hour = 55 minutes and 42 seconds.

The conclusion is that if by some miracle (that is not going to happen) the battery earned its 80 AH rating via a draw of 3.1 amps at 120 VAC through an inverter, the best case scenario is 55 minutes and 42 seconds of run time (without destroying the battery).

I'm sticking with closer to 30 minutes.

CapeCoaler · Post by **CapeCoaler** » Tue. Jan. 17, 2017 12:21 am

So the site factors 50% draw down and 20 hour rate...

Battery Needed is rounded to nearest whole number, and is rated in AH at a 20 Hour rate. If you find a battery with at least this many rated Amp Hours Your Load will run for the desired amount of time at a safe 50% discharge level. - See more at: https://www.batterystuff.com/kb/tools/calculator-sizing-a-battery-to-a-load.html#sthash.aWbMYQ2V.dpuf

Just for shits and giggles...
Larry's real world inefficacies brings it to 517 watts...
4.5 amps AC...
47.61 amps 12VDC...
4 hr run time...
470 AH at 20 hr run...
Go with the golf cart batteries...
Now the stoker will not be running full out 100% of the time...
But when the power goes out it may be running 80% of the time...
So that is why an inverter/charger may be your best bet...
Add as many batteries to get the desired runtime...

lsayre · Post by **lsayre** » Tue. Jan. 17, 2017 6:26 am

Best bet in a power outage is a hand fed stove. After looking at it, that's what I went with. Instead of back-up batteries, I have a back-up stove. Stove costs about the same as only about 6-8 hours worth of giant batteries.

captcaper · Post by **captcaper** » Tue. Jan. 17, 2017 6:56 am

For my needs I can't see using a battery bank to keep the stove running a few hours.. I do have a Honda 2000i that runs quiet with the lower loads of the Super Mag.. and have an external tank hooked up to it for many hours of run time.. Also if the stove runs down the batteries because no ones there then your paying alot for such little in my book.
I figure if I'm not home the house won't freeze for a while..maybe days. As it takes a long time for the house to cool down enough to start freezing.. Enough time to get someone over to run the generator for the stove...
I often thought of letting the truck idle all night with an inverter hooked up to the truck for the stove but so much easier to start my Honda 2000i.

titleist1 · Post by **titleist1** » Tue. Jan. 17, 2017 7:19 am

lsayre wrote:Best bet in a power outage is a hand fed stove. After looking at it, that's what I went with. Instead of back-up batteries, I have a back-up stove. Stove costs about the same as only about 6-8 hours worth of giant batteries.

Even though I have a generator I think this is the best strategy for long power outages. I have a backup Mark III ready to be rolled into place and easy to move the flue pipe off the stoker to connect the hand fed. The clean out T is where it will connect. I have about a week's worth of bagged nut coal stored under the steps of the outside basement entrance and plenty of fire pit firewood ready to bring in. There have been a few times we lost power here for a week prior to installing the stoker but thankfully not since.

And guysnydr's already got the Mark III so he doesn't even need to fork out more money, just park it in a corner!

My stoker will hold a fire for about 1/2 hour and sometimes longer if draft conditions are just right to keep some air pulling through the firebed. If we got a lot of 1 - 2 hour outages where i'd lose the fire might get a small a battery backup to keep from having to relight often. I'd probably unplug the distribution fan to extend the battery.

captcaper · Post by **captcaper** » Tue. Jan. 17, 2017 11:28 am

For long periods a small gen at least is a must... a MkII or III will not keep the fridge going or anything else you might want to do during the outage.

guysnydr · Post by **guysnydr** » Tue. Jan. 17, 2017 11:31 am

I like the idea of using the Mark III as a backup but it wouldn't work well for me because of where my stove is located. It is basically in the corner of a family room sitting on a tiled area that I put in place just for a stove. To the right is a bar and there isn't room for a second stove there. The rest of the floor is carpeted, so my only option would be to operate it in front of the stoker sitting on carpet in the family room, or move the stoker out completely and sit the Mark III in its place during the power outage. Neither of those options would be desirable unfortunately but it is a good thought and would probably work well for others.

It sounds like, for me, the best option is going to be at least two 6 volt golf cart batteries hooked to a 500 Watt (minimum) inverter/charger. It doesn't sound like it will run long, but it will at least buy me some time and keep the fire going for a little bit until I either get the generator hooked up, or worse case, it goes out and when I get home I relight it and use the generator. The good news is that our power is pretty reliable for the most part. When it does go out it is usually back on reasonably quickly. I just want some peace of mind. I may look at adding a switch to the output blower so I can at least kill that for a bit to save some draw on the batteries.

Someday I may just invest in a whole-house generator with auto start. But that is down the road as they are incredibly expensive.

Captcaper is right-on regarding the Honda 2000i. They are awesome little generators and whisper quiet!

Thanks to all for the great information and time spent helping shed some light on this issue that can obviously get somewhat complicated. All input is greatly appreciated! You guys are great!

2biz · Post by **2biz** » Tue. Feb. 27, 2018 8:38 pm

Late to the thread to offer suggestions...This is what I use for backup....

https://www.amazon.com/Power-Inverter-Charger-450 ... dpSrc=srch

And thread here on the forum with all info.

Post by 2biz - Battery Backup With Pics

It backs up my AK-110 Stoker now and works great!

McGiever · Post by **McGiever** » Tue. Feb. 27, 2018 10:02 pm

Just some basic electric theory thrown in for readers...12 volt DC has a limited reach if going up for higher watt loads.

Consider connecting multiple golf cart batteries in series to get higher volts DC (24 or 48 VDC) so you can save some copper and also not suffer from voltage drop in the wires, even worse voltage drop if wires are not kept really short.

Surge ratings on inverters mean very little if the wire cannot handle it...too small of wire makes a "bottleneck".

Don't buy a 12 volt setup to start with and then discover later you really needed bigger and better, as these are not cheap to buy.
Just sharing some info for y'all.

coalnewbie · Post by **coalnewbie** » Wed. Feb. 28, 2018 6:59 am

Even though I have a generator I think this is the best strategy for long power outages. I have a backup Mark III ready to be rolled into place and easy to move the flue pipe off the stoker to connect the hand fed.

The only solution. I will disconnect the AK 180 chimney and my G 111 chimney will be connected and will just take over. The only solution as you will have limited gas/propane in inventory.

coalnewbie · Post by **coalnewbie** » Wed. Feb. 28, 2018 1:17 pm

The conclusion is that if by some miracle (that is not going to happen) the battery earned its 80 AH rating via a draw of 3.1 amps at 120 VAC through an inverter, the best case scenario is 55 minutes and 42 seconds of run time (without destroying the battery).

I'm sticking with closer to 30 minutes.

and then there is the issue of lead/acid batteries degrading and it's very finite life span.