My Emergency Power Source / Question

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Mossy Beard
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Post Mon. Aug. 18, 2008 11:37 am

Hi,
I'm getting my Mag Stoker ready.
I've purchased a Tripplite 750 watt inverter,charger, transfer unit.
My question is:
How long would a 125 amp hour battery run the Harman ? ( I think the current draw on the Mag is 3 amps.)

Thx, Mossy Beard

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gambler
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Post Mon. Aug. 18, 2008 12:09 pm

A battery with a capacity of 1 amp-hour should be able to continuously supply a current of 1 amp to a load for exactly 1 hour, or 2 amps for 1/2 hour, or 1/3 amp for 3 hours, etc., before becoming completely discharged. In an ideal battery, this relationship between continuous current and discharge time is stable and absolute, but real batteries don't behave exactly as this simple linear formula would indicate. Therefore, when amp-hour capacity is given for a battery, it is specified at either a given current, given time, or assumed to be rated for a time period of 8 hours (if no limiting factor is given).

A battery’s amp-hour rating indicates the total amount of energy it will deliver at a constant rate of discharge over a period of 20 hours before it reaches a voltage at which it is stone dead for all practical purposes.A 12-volt battery, the most common nominal voltage, is fully discharged at 10 volts. A 100-amp-hour, 12-volt battery will run a 5-amp motor (or a 60 watt light) for 20 hours, and a 200-amp-hour battery will run a constant 10-amp (120 watt) load for 20 hours.That’s the theory. In fact, if a 100-amp-hour battery is discharged at a rate greater than 5 amps, it will not deliver all the advertised amp-hours before it goes dead. On the other hand, if you discharge it at a steady rate of less than 5 amps, you’ll get more amp-hours than the manufacturer’s rating shows—not a whole lot more, but some.That principle applies to most lead-acid batteries found on boats—the faster the discharge rate, the fewer amp-hours delivered. The more slowly energy is taken from a battery, the longer it will last.Sometimes a battery’s work capacity is given in reserve minutes. In the absence of any other definition, this is the number of minutes you can discharge a fully charged battery at a whopping 25 amps before its voltage drops to 10.5.
Last edited by gambler on Mon. Aug. 18, 2008 12:14 pm, edited 1 time in total.

sandman
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Post Mon. Aug. 18, 2008 12:12 pm

if your load is [email protected] it will be [email protected] with a modified sine wave inverter it might be a little higher.

you don't want to discharge your batt past 50% with 62ah's it would give you two hrs

Mossy Beard
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Post Mon. Aug. 18, 2008 2:43 pm

Thanks for the response.
Hang with me on this but the replies seemed to be at "odds" to each other. ( I may have miss read)
The battery is a Wally World deep cycle marine. ( 12v) I would like to get about 6-8 hrs. run time. The triplite has an adjustable output ( I think) which I set @ 105v. So, should it not stop the process when incoming voltage drops to low ? ( weather ac or dc)
I've asked the same question to some folks at work ( that should know) but I get answers, from several hours to 10-15 hrs. , with this set up ??

Thx, Mossy Beard


sandman
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Post Mon. Aug. 18, 2008 3:16 pm

if you want the battery to last more than a year I wouldn't run it for more than 2hrs. or discharge it past 50%

my preference is to only discharge my batteries by 10% 20% at the most.

but then again I have a house I run on batteries, inverters and charge the batteries via pv panels

if you want it to be able to run it for 6hrs I would want three new batteries that were all the same hooked up in parallel

you really need to find out what the actual draw is gong to be. get an amp meter and put it on the dc side.
if your using 3a on the 120v side it will be around 30a on the 12v side.

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Highlander
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Post Mon. Aug. 18, 2008 8:16 pm

Mossy
Your battery capacity will depend on what you are trying to supply. My backup battery is a size 29 deep cycle marine battery with 125AH , also a Wally World Everstart.
When we had a power outage, it held up for about 7 hours till the power was restored. I think it had a couple of hours still left in it. Besides the stoker, it was running the circulator pump on low speed continuously for that time. The draw on the DC side was between 10 and 20 amps, depending if it was stoking or not.
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rberq
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Post Mon. Aug. 18, 2008 9:47 pm

Sandman, you discharge your batteries only 10 or 20 percent because you use them day in, day out to power your house, and you want them to last as long as possible. Mossy, on the other hand, might discharge to a far higher percentage, but far less frequently -- at least we hope his power failures occur rarely. So, could he get by with fewer than your recommended three batteries, and still expect them to last four or five years?

Just speculating here: Would a "retired" fork-lift battery be suitable, if one could be found from a battery dealer? They are big suckers, presumably with a high amp-hour capacity, and I'm guessing the coal stoker would draw current at a much lower rate than the fork lift. So a battery that was no longer up to snuff for running the warehouse equipment, might still be more than adequate for a stoker, and maybe obtainable at scrap prices????

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farok
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Post Mon. Aug. 18, 2008 9:58 pm

Granted I'm no expert, but I hear they actually recycle old batteries because of the lead in them. If you can find a used forklift battery, that may work (not sure), but it may not be as cheap as you like. If I replace the deep cycle batteries I have now for my backup system, they hope to get the bad batteries back at the same time. (not sure if there is a surcharge for no return, as I've not tried this). Just something to watch out for, that's all.

Chris


sandman
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Post Mon. Aug. 18, 2008 11:43 pm

a used fork lift batt would be great if you can find a good one, but it's scrap value would be more than your whole system.

it all comes down to your load and your reserve capacity in amp hrs.

if you want the batteries to last use 50%-60%

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ceccil
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Post Tue. Aug. 19, 2008 1:44 am

Not sure if it applies in other states, but I think in NY when you purchase a new batt. you must pay a core charge unless you have an old one to turn in at the time of purchase. On the topic of the battery, I used to use a deep cycle batt. and trolling motor on my canoe. When we went on the river we would be there all day, by the time we got back to the launch the batt. would be dead and we would have to paddle some. This occured about 6 times per summer and the batt. lasted for 4 yrs.

Jeff

Mossy Beard
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Post Tue. Aug. 19, 2008 7:51 am

Highlander wrote:Mossy
Your battery capacity will depend on what you are trying to supply. My backup battery is a size 29 deep cycle marine battery with 125AH , also a Wally World Everstart.
When we had a power outage, it held up for about 7 hours till the power was restored. I think it had a couple of hours still left in it. Besides the stoker, it was running the circulator pump on low speed continuously for that time. The draw on the DC side was between 10 and 20 amps, depending if it was stoking or not.
Your set up looks almost exactly like mine.
I "like" your response of about 7 hrs... Thats what I'm looking for out of my system.
Again, the only load I'll have is 3 a @ 120v. ( or so the literature says)
Our power goes out several times a month in winter. I never know if it's 10 min. or 3 hrs ? the clocks are just flashing when I get home :?

Thx. for the input.

Mossy Beard

McKoker
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Post Tue. Aug. 19, 2008 4:01 pm

This link (Understanding Amp Hours) give good info on how the rate of discharge affects the actual amp hours you can expect.
Last edited by McKoker on Sat. Apr. 01, 2017 12:42 am, edited 2 times in total.
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TGMC
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Post Tue. Aug. 19, 2008 9:22 pm

3a @120V IS APPROX 300 WATTS . did anyone think to try a UPS for a computer. some of them have good time ratings, and you could hook up a deep cycle batt. to them. as far as forklift batteries most are too big and combersome, my batt.of choice would be from a large stationary genny. most get changed every 3-5 years and start with amp hr ratings above 1500 for small ones. the genny at my work has 2 rated at 2100 amp hr. this could run a stove fo at least 48 hr?

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