Author Topic: Deep cycle battery question  (Read 272 times)

Offline kid_couteau

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Deep cycle battery question
« on: September 25, 2017, 05:07:57 PM »
Hi All

Ok I am building a backup battery bank and a question arose

On some batteries I see the term initial current, example on 33AH battery it was less than 8.25 amps. Now if I have say 5 33AH batteries with this reading would the increasing AH also increase the initial surge amps?  I plan to run a pellet stove with this and it uses about 700 watts to get started and then settles down a lot

Please advise
Kid Couteau

Offline Carl

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Re: Deep cycle battery question
« Reply #1 on: September 26, 2017, 06:04:55 AM »
  The 700 watts means (allow my rounded number math as you will discover it includes inefficiencies and losses) will require about 70 Amps from
a 12 volt battery bank and the typical wet cell battery ,as chemical storage of power,should be limited to C10 (ONE TENTH battery Amp hour rating)
While C10 can be exceeded by a good margin in charge and discharge,not without damage to the life of most batteries.Wet cell batteries should not be discharges beyond 50 to 70 percent ,though read the specs for your chosen battery to determine it's designed charge/discharge parameters .

  A  battery should not be discharged below 60% state of charge ,with exception of DEEP CYCLE cells and they survive a bit more discharge ,though not without suffering length of usable life as deeper discharge cycles stress the plates and chemistry.

NOW ,to your question...FIVE of the 33 Amp Hour cells (let's call it 150 Amp hours total as if it is one battery) will do OK at C10 or 15 Amps (150 to 175 watts) for about 6 hours ,slightly more without damage to the cells. I figure the feed motor will be about this much once the stove is started.. and the
INITIAL CURRENT should be limited to a few seconds so as to not buckle the battery plates will give a total of 40 Amps for a very brief time or only about 400 watts..

Bottom line is this 5 X 33 battery bank may work for up to 5 or 6 hours but will suffer a bit as it is about HALF the size battery that you really need for a TEN HOUR run time and the health of your expensive battery bank.

  My fridge runs at about the same power level (700 -800 watts to start and 140 watts to run) and while a 100 Amp hour battery will start and run the fridge for 3 to 4 hours...not without suffering loss of lifetime cycles. My 'regular bank' of batteries is 550 Amp Hours and will only run the fridge for 24 to 30 hours without charge help as my fridge is a low power compressor ,it runs about 20 out of 24 hours ,many fridges need over 300 watts for say 14 out of 24 hours.

  It should work for 5 to 6 hours but I bet you want longer run time.

  Just my old man's opinion as a battery user and sometimes battery killer for the last 40 years or so.
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Offline kid_couteau

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Re: Deep cycle battery question
« Reply #2 on: September 26, 2017, 07:06:32 AM »
Thank you!  ;D

My main worry is the stove uses 700 watts for about 5 to 10 minutes while starting up to get the pellets burning.

After that it cuts way back in power draw.

Kid

Offline Carl

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Re: Deep cycle battery question
« Reply #3 on: September 26, 2017, 09:08:13 AM »
Thank you!  ;D

My main worry is the stove uses 700 watts for about 5 to 10 minutes while starting up to get the pellets burning.

After that it cuts way back in power draw.

Kid

Then I would look for about 500 to 800 Amp hours of battery for say 24 hours run time or a bit more and the ability to get it started without over stressing the batteries as that is way longer initial current that batteries are rated for as about 30 seconds and not several minutes.But it sounds like a workable project.
Stop complaining about life and start Celebrating it .

I've reached the age where there is little left to learn the hard way.

If you had only one year,one month,or one day...Would you live your life differently?