Batt Capacity

[paulo]

Hi all,

Tried a search with no luck.

I'm getting a new battery to run a fridge, lights etc. I'm tossing up between a 105amp/Hr and 120amp/Hr capacity battery.

The question is am I splitting hairs or is the little bit more capacity really going to make a difference?

Cheers,

Paul

[jwb]

for a single battery system I would aim for the 120ah if you can accommodate any size difference (if any?)

what size/type of fridge btw?

cheers

[evaredy]

At 50% discharge you only get an extra usable 7.5 ah, Depending on the price difference it may not be worthwhile getting a 120ah.

[paulo]

for a single battery system I would aim for the 120ah if you can accommodate any size difference (if any?)

what size/type of fridge btw?

cheers

It's a 40l Waeco fridge.

At 50% discharge you only get an extra usable 7.5 ah, Depending on the price difference it may not be worthwhile getting a 120ah.

That's they way I was looking at it. And the plan would be that it never goes anywhere near 50% discharge, so the benefit would be even less. Even at that, to my way of thinking, it would only be a couple of hours extra power. Please correct me if I've got this wrong

[Goose]

Should still be 12.5% more Ah (and thus run time) in the larger battery.... except that different battery companies will rate their batteries slightly differently, so its not going to be exact comparing batteries from different companies. If its 2 batteries from the same manufacturer, from the same product range, then its pretty safe to compare. Also try work out the $/Ah and see which is better value per Ah.

[richee]

what about the physical size of the batteries and the battery case, do you have room?

[Jeepers Creepers]

Any battery over 110 of those ampie things, are usually very heavy batteries and quite larger in physical size.

[chisel]

If you have space, get the bigger one

[gronk]

If you have space, get the bigger one

Same as solar, you can never have too much  !!

[theins]

Your usage will depend on so many factors, e.g. use of fridge and temperature setting, ambient temperature, etc...

... my view would be - if in doubt - go for the bigger one if you can. No such thing as too much power 

[Andy_Q]

A quality battery should be good for hundreds of discharges at 100% depth of discharge.

If you are not cycling the battery daily you will not likely kill it by cycling well below 50%. I use 11.0 volt as my cut of.


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[gronk]

A quality battery should be good for hundreds of discharges at 100% depth of discharge.

If you are not cycling the battery daily you will not likely kill it by cycling well below 50%. I use 11.0 volt as my cut of.


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Have you discharged yours to 100% hundreds of times ?

That is advice completely opposite to what is considered normal !!

[theins]

A quality battery should be good for hundreds of discharges at 100% depth of discharge.

That's an interesting comment. Could you please let me know what it is based upon? I have always been told to avoid discharging to less than 50%, hence I tend to use 12V as cut off...

Any information appreciated.

[HKB Electronics]

A quality battery should be good for hundreds of discharges at 100% depth of discharge.

If you are not cycling the battery daily you will not likely kill it by cycling well below 50%. I use 11.0 volt as my cut of.


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Technically a true statement, but at looking at the below graph would you want to?

[Andy_Q]

I rest my case.

No I have not done it nor will 99% of camper owners ever have the opportunity to get hundreds of trips out of batteries.

That is why I'm happy to occasionally go to 11v and not be too precious about the possible long term effects. Cold beer is more important than if I'll get an extra 10 years life of of the batteries.
Additional note for the op Paulo,  Batteries die with heat vibration and time as well as cycles so depending on your circumstances this is all academic anyway.


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[gronk]

I rest my case.
That is why I'm happy to occasionally go to 11v and not be too precious about the possible long term effects.

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When people invest up to and over $1000 in batteries, they mightn't be so happy to abuse their batts like you.

You might get 100 recharges out of a battery that's been taken down to 100% discharged...or you might get 5 ??   But seeing as 100% discharged is approx 11.6V, your 11V is not a reading too many people want to follow..

I know beer is very important, but maybe not as much as a set of batteries !!  You sound like you need another battery ??   

[Andy_Q]

This is the voltage curve for my batteries. Yours might be different.

After 20 hours at 5 amps, 11 volts. Still 10Ah capacity left.




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[Andy_Q]

Edit double post for some reason so I'll add the following

[gronk]

This is the voltage curve for my batteries. 

After 20 hours at 5 amps, 11 volts. Still 10Ah capacity left.

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What batteries do you have ?

How many times have you discharged the batteries down to 11V ?

[Andy_Q]

Hi Gronk

The battery is a GNB M83CHP12V27.

Made in USA by Exide.

Still quite new so not a lot of cycles on them.

I'm happy to be convinced that I'm wrong on this but as far as all of the manufacturers data I've seen. A few hundred cycles to 100% dod should be expected.

It may be that many cheap batteries are over rated and not capable of this... But that would be fraud in my book.


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[gronk]

I'm not going to convince you of anything....but those batteries are designed for golf carts .....and are engineered for a 80% DOD and 400 cycles and 2 year lifespan..

I see nowhere in the specs about discharging them to 100% ??  Which by the way is still 11.6V...not 11V..

No reason not to use them for camping, but if you treat them right, they MAY last 6 yrs instead of 2 !!