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Max The Magnificent
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I'm starting to think that...
Max The Magnificent   12/17/2013 4:53:10 PM
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Hmmm... I'm starting to think that picking the best battery option for my robot might not be as easy as I thought...

prabhakar_deosthali
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Deep discharge Batteries
prabhakar_deosthali   12/18/2013 6:46:53 AM
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This is a nice primer on Batteries. While working on Electrical vehicle project , where I was a novice as far as battery technology is concerned, I was bombarded with many of these terms. One fo the term often used was "Deep Discharge" batteries. Could you elaborate on this ?

eetcowie
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Re: Deep discharge Batteries
eetcowie   12/18/2013 10:25:31 AM
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Depth of Discharge (DOD) [%] The percentage of battery capacity that has been discharged, expressed as a percentage of maximum capacity. A discharge to at least 80% DOD is referred to as a deep discharge. Manufacturers make adjustments to the size and configuration of electrodes and chemistry, in order that there is less damage to cells when the battery is discharged to this high amount. Marine batteries are often of the deep-discharge type.

prabhakar_deosthali
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Re: Deep discharge Batteries
prabhakar_deosthali   12/18/2013 11:55:09 AM
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Thanks a lot for the information on Deep Discharge Batteries. Also it is said that the batteries have some kind of memory , which means it gets tuned to the charge/discharge pattern which is regularly used. If something out of the regular routine is tried later then the battery does not give optimum performance. e.g if you are doing only partial discharge every day and recharging again to full, then a sudden deep discharge may damage the battery.

What is your opinion on the same?

eetcowie
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Re: Deep discharge Batteries
eetcowie   12/18/2013 2:45:17 PM
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The 'memory effect' was initially denied by manufacturers, but eventually they reversed their stand after good science showed that certain chemistries had a preference for a terminal voltage where the battery spent most of its time. It results in a loss of capacity, since the battery quickly drops its terminal voltage after discharging, to the 'memory' point. To compensate, manufacturers began recommending that batteries always should be discharged to the end-of-cycle point (not partially discharged and recharged). This idea ran counter to system designers wishes, since most of the energy-transfer losses happen at the end of the rated-discharge cycle. What you mentioned, though, happens often enough about the pattern of cycles and optimum performance, even outside of the memory effect. Some manufacturers now include mention of how their batteries perform with regard to the memory effect, in order to differentiate their product from the competition.

Max The Magnificent
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Re: Deep discharge Batteries
Max The Magnificent   12/18/2013 3:46:33 PM
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@eetcowie: The 'memory effect' was initially denied by manufacturers, but eventually they reversed their stand after good science showed that certain chemistries had a preference for a terminal voltage where the battery spent most of its time...


Will you be elaborating on this later in the series, and also telling us how to mitigate against it? For myself, in th ecase of my iPad, I usually let it run down to around 10% and then charge it all the way back up to 100%. By comparison ,in the case of my notepads, it's onlt every "now and again" that I turn them on without plugging them into the wall first -- is this OK?

eetcowie
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Re: Deep discharge Batteries
eetcowie   12/18/2013 11:25:16 PM
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I will cover more on the memory effect later, but for now, Max, there may not be a substantial memory effect on the type of battery in your device. Suffice to say that for each chemistry and construction combination, there exists an optimum charging and discharging electrical and physical environment that will yield the greatest service life. But a high service-life comes with trade-offs in other performance areas -- this is no surprise, since "...you don't get something for nothing", they say. I tend to have the thinking that when something is really good, I ask myself about what does it compromise? Some comedian once said, "You can't have everything. Where wuould you put it?"

Keep those good comments comming!

Max The Magnificent
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Re: Deep discharge Batteries
Max The Magnificent   12/19/2013 9:00:30 AM
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@eetcowie: "You can't have everything. Where would you put it?"

Past experiance would say that the answer to this question would be "My Office" :-)

 

selinz
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Re: Deep discharge Batteries
selinz   1/14/2014 2:12:02 PM
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Since we're in the mode of asking, I would also request that you add (in the catch all summary page) a column of common form factors and price!

eetcowie
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Re: Deep discharge Batteries
eetcowie   1/14/2014 8:56:04 PM
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The final summary, will probably be pricing per kg of weight or by volume (L). I already include the price in each battery type, in WattHours per $, so it makes it easier to compare technologies for each kind.

Stargzer
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Re: Deep discharge Batteries
Stargzer   2/3/2014 1:56:31 PM
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@eetcowie:  "Marine batteries are often of the deep-discharge type."

As a boat-owner (Happiness is a Trojan that doesn't leak) I've seen two types of Marine batteries.  Some deep-discharge batteries are used for accessories on larger boats or electric trolling motors on small boats (e. g. Bass Boats).  They aren't designed to start a large gas or diesel engine.  Newer batteries in the last 10 years or so seem to be designed to handle engine starting as well as deep discharge.  If you are going to use a battery for starting, always check the CA (Cranking Amps) or CCA (Cold Cranking Amps) to make sure it can survive the load without destroying the cells, and also check the discharge rate for deep discharge (amps discharged over a period of time).  Marine starting batteries often use the CA value instead of the CCA; not many are (fool)hardy enough for below-freezing cruising!

A fully-charged deep-discharge marine battery, a 12V auto-receptacle three-way splitter, and a small inverter are quite handy when a blizzard or a storm (hurricane, thunder storm, or a derecho) takes out the power.  Only when the storm blows over is it time to crank up the generator!

eetcowie
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Re: Deep discharge Batteries
eetcowie   2/4/2014 9:38:34 AM
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Quite right. Thanks for that.

DaveC9316
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Re: Deep discharge Batteries
DaveC9316   12/19/2013 8:02:44 PM
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While looking up information on solar power for recreation vehicles I came across some great information on wet cell lead acid, and although archaici technology I "m guessing  the principles remain similar to other technologies.

Lifetime vs. depth of discharge, multi-stage charging vs. voltage and current vs temp, optimal maximum charging current, etc

Look up Trojan T 105, this is the workhorse golf cart battery (good for RV too!)

Between the 2 page datasheet and 24 page user guide  you'll learn the basics about flooded batteries.

eetcowie
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Re: Deep discharge Batteries
eetcowie   1/14/2014 8:48:58 PM
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nice flooded-type find.



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