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Old 02-04-2016, 00:25   #1
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Is high current draw bad for deep cycle batteries?

Background: I have 690AH of 12v sealed lead acid batteries and a large solar array plus wind generator so have plenty of power for my needs. To conserve bottled gas I use a 240v electric kettle to boil water via the inverter. This draws around 160 amps @ 12v when on but actually only consumes 7 to 12 amps based on the AH level of the batteries before and after (as shown by my battery monitor). I virtually never let my batteries drop below 80% of capacity and most of the time they are at 90% full or better (I'm a Captain Bligh on the electricity usage).

Question: is it bad for the batteries to have such a high power draw for the 5 or so minutes it takes to boil a kettle several times a day, especially given they are deep cycle not starter batteries?

TwT
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Old 02-04-2016, 04:53   #2
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Re: Is high current draw bad for deep cycle batteries?

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Originally Posted by Toys_with_time View Post
Background: I have 690AH of 12v sealed lead acid batteries and a large solar array plus wind generator so have plenty of power for my needs. To conserve bottled gas I use a 240v electric kettle to boil water via the inverter. This draws around 160 amps @ 12v when on but actually only consumes 7 to 12 amps based on the AH level of the batteries before and after (as shown by my battery monitor). I virtually never let my batteries drop below 80% of capacity and most of the time they are at 90% full or better (I'm a Captain Bligh on the electricity usage).

Question: is it bad for the batteries to have such a high power draw for the 5 or so minutes it takes to boil a kettle several times a day, especially given they are deep cycle not starter batteries?

TwT
A not so minor correction You draw power at 160 Amps but you consume 7-12 Amp hours each time you boil your kettle.

No, that sort of drain will not have any appreciable long term affect on your battery bank.
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Old 02-04-2016, 05:19   #3
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Re: Is high current draw bad for deep cycle batteries?

Your discharge rate is .23C which is nothing for this type of battery.
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Old 02-04-2016, 05:29   #4
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Re: Is high current draw bad for deep cycle batteries?

As long as you cables do not get hot and your voltage does not drop below 11 VDC, all is well!
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Old 02-04-2016, 09:30   #5
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Re: Is high current draw bad for deep cycle batteries?

As long as the cables, fuses and other connections are sized to handle the amps, no issues. You can hook them up to start your engine pulling even more amps and there is no issue.

Standard deep cycles have no issue with short bursts of high amp output. The only reason they aren't used for starting is they peak at a lower amp output so you need a bigger bank. Of course on a lot of cruising sailboats, a small engine combined with a large battery bank for house loads makes it viable as long as the bank isn't too far from the engine.

This all assumes you aren't drawing the batteries down too low but sounds like you have that under control given the limited amp-hr draw and not going under 80% charge.
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Old 02-04-2016, 16:34   #6
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Re: Is high current draw bad for deep cycle batteries?

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Originally Posted by Maine Sail View Post
Your discharge rate is .23C which is nothing for this type of battery.
Thank you - not sure what .23C means but it sounds low
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Old 02-04-2016, 17:32   #7
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Re: Is high current draw bad for deep cycle batteries?

690Ah is your rated capacity at 0.05C, or 5% of capacity usage over 20h
That is, you can discharge them completely in 20h at 34A (de facto, stop at 50% of SOC, after 10h0
As far as discharge rate (A) gets higher, your rated capacity is lower than 690Ah

Discharging at 160A, is exactly 23% of nominal capacity.

You can stay within say 0.4C without damaging batteries, and accepting lower capacity overall

You can use the kettle for say 1h1/2, thus drawing 240Ah, for an estimated 50% SOC, if reduced capacity at 0.23C is approx. 500Ah (guess)
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Old 03-04-2016, 10:14   #8
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Re: Is high current draw bad for deep cycle batteries?

a cranking battery can discharge high amps without loosing voltage and can be recharged faster as the plates are thinner. a deep cycle has thicker plates. it can discharge high amps but only for a short time in comparison to it's AMH rating, but can discharge lower amps longer than a cranking battery. But takes longer to recharge from the same state of charge.

as long as you don't go below 80% charge and are recharging within 24 hrs, sulfating is not likely to occur on the plates.
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Old 04-04-2016, 00:55   #9
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Re: Is high current draw bad for deep cycle batteries?

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a cranking battery can discharge high amps without loosing voltage and can be recharged faster as the plates are thinner. a deep cycle has thicker plates. it can discharge high amps but only for a short time in comparison to it's AMH rating, but can discharge lower amps longer than a cranking battery. But takes longer to recharge from the same state of charge.

as long as you don't go below 80% charge and are recharging within 24 hrs, sulfating is not likely to occur on the plates.
Thank you (and everyone else) for your comments. Since the current consumption is presumably being spread across the 6 x 12v 115Amp batteries that are wired in parallel ie about 25 amps per battery does this make it better (or not since the % draw stays the same and I would have to add another battery to reduce the %)?

I do find that plumbing makes more sense than electrical circuits!

TwT
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Old 04-04-2016, 03:55   #10
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Re: Is high current draw bad for deep cycle batteries?

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Thank you - not sure what .23C means but it sounds low
23% of the total capacity or 23 amps from a 100 amp hour battery, I think.
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Old 04-04-2016, 04:45   #11
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Re: Is high current draw bad for deep cycle batteries?

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Quote:
Originally Posted by Toys_with_time
Thank you - not sure what .23C means but it sounds low

23% of the total capacity or 23 amps from a 100 amp hour battery, I think.
In simple terms, C is the rate of discharge related to your battery Capacity.

1C means fully discharging the battery in 1 hour. 2C is twice as fast, i.e. fully discharge in 1/2 hour. 0.5C in 2 hours etc.

.23C means that you would discharge the battery (bank) fully in about 4 hours (it's not exact, because the faster you draw, the less Amp hours you can extract).
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Old 04-04-2016, 07:27   #12
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Re: Is high current draw bad for deep cycle batteries?

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Originally Posted by Toys_with_time View Post
Thank you (and everyone else) for your comments. Since the current consumption is presumably being spread across the 6 x 12v 115Amp batteries that are wired in parallel ie about 25 amps per battery does this make it better (or not since the % draw stays the same and I would have to add another battery to reduce the %)?

I do find that plumbing makes more sense than electrical circuits!

TwT
With multiple batteries run in parallel, the draw is not always equal on all batteries in the circuit. Its funny you mention plumbing, as it's very similar in many respects.

In a plumbing situation, say, you have two equal tanks sitting on a level plane. you plumb a 1/2 drain pipe from both tanks to a 1 inch pipe at the same point, one foot below the level of the tanks. one tank is two feet away and the other tank os 100 feet away. Due to the friction/resistance in the pipes the nearer tank will empty first.

in a battery bank run in parallel whilst a draw is present the last battery will contribute the least and like wise receive charge last. electricity flows the path of lest resistance or the shortest path. in essence, the successive batteries from the back foreword would drain into the previous battery. If all the batteries in a parallel circuit were wired to a single point respective of + and- with all cables the same length and size and the load taken from that point, then you would have an equal draw and recharge of the batteries in that bank

unlike plumbing, if you increased the wire size of the jumper from the back battery the resistance in the wire would increase too. A physicist might be able to figure a balance, but electrolysis in the wire would change the balance in time. Its easier and longer lasting to wire it to a central point. Say #4 jumpers coming into a #2 wire or #2 jumper wires into a 00 wire and so forth.
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Old 04-04-2016, 08:18   #13
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Re: Is high current draw bad for deep cycle batteries?

As others have told you (and Maine Sail is a great authority!!), there will be no damage from this.

HOWEVER, I would advise you to switch to a smaller kettle. It will take longer to heat up, but it will discharge your batteries less, than doing it at 2.3kW or whatever your kettle is. That's because of Peukert's Law, which says that lead-acid batteries lose more charge, producing a given number of A/H of power at a higher rate of discharge, than they do producing the same total amount of A/H, at a lower rate of discharge.

I use a 900 watt one, which is quite ok, in terms of boiling time, for a couple of cups of tea.
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Old 04-04-2016, 11:36   #14
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Re: Is high current draw bad for deep cycle batteries?

All I know is that my Mr Coffee uses 17 AH to brew a pot of coffee using the inverter. The battery monitor goes into low voltage alarm during this and goes back to normal right after. No big deal at all!

When I was in the Navy we had standard wet cell batteries (but a lot of them) and could power the whole sub off them from the motor-generator (think of a big rotating inverter) and it didn't damage the batteries.
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Old 04-04-2016, 21:28   #15
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Re: Is high current draw bad for deep cycle batteries?

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As others have told you (and Maine Sail is a great authority!!), there will be no damage from this.

HOWEVER, I would advise you to switch to a smaller kettle. It will take longer to heat up, but it will discharge your batteries less, than doing it at 2.3kW or whatever your kettle is. That's because of Peukert's Law, which says that lead-acid batteries lose more charge, producing a given number of A/H of power at a higher rate of discharge, than they do producing the same total amount of A/H, at a lower rate of discharge.

I use a 900 watt one, which is quite ok, in terms of boiling time, for a couple of cups of tea.
I did have a smaller one but I dropped it and now, in the words of Monty Python, it is a deceased kettle. As a sailor who is used to the vagaries of wind and current I'm in no hurry for the water to boil and have been looking everywhere for a replacement with a lower power draw but seems that as in many things in life, bigger is perceived as better and the lowest I have found is 1800W. What sort of shop did you buy yours in?

TwT
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