Best New House Battery

Dennisail

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Brisbane
Im not even fully certain temp sensor have prevented what happened in my case? Is there a point where once a certain temp is reached it will cut off all current rather than just lowering the charge voltage? Say the battery short is bad enough the max charge voltage at max temp compensation may still allow massive current?

Its almost like you need a temp cut out to prevent this sort of fault.

 
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Maine Sail

Anarchist
555
4
Im not even fully certain temp sensor have prevented what happened in my case? Is there a point where once a certain temp is reached it will cut off all current rather than just lowering the charge voltage? Say the battery short is bad enough the max charge voltage at max temp compensation may still allow massive current?

Its almost like you need a temp cut out to prevent this sort of fault.

Yes properly done a temp cut off is really how it should be implemented. No battery should really even be charged at much above 100F, its just not healthy for them, so 115F - 120F would be a good full cut threshold. If you have a dead cell, with charge current behind it, the temp will get to 120F pretty easily.

Even if I start at 85F and throw 1C at an AGM battery I rarely see them break 100F....

 

Pukka

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NZ
Throw 1C?

I'm about to buy batteries- This interests me.

+ battery monitor etc.

 
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Dennisail

Anarchist
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Brisbane
1C =

300amps into a 300ah bank,

540amps into a 540ah bank

etc etc

The reality is the battery compartment will go to close to 100f pretty easily on a hot day around here. Which is yet another reason lithium is good in hot areas. I wish they didn't install the HWS in the same compartment as my batteries to make matters worse.

 
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Pukka

Member
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NZ
Thx legend. (giggle) So a portion of an 1 hour to full charge.

Want to elaborate on "C"?

 
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Dennisail

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C = Charge rate AFAICT

So if you have a 100Ah bank, charging at 2C would be charging at 200A. Charging at 0.5C would be charging at 50A. C applies to charge and discharge.

 

DDW

Super Anarchist
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C is capacity. So a 100AH battery has C=100. Charge rate of 0.5C would be 50 amps.

 

Maine Sail

Anarchist
555
4
C is capacity. So a 100AH battery has C=100. Charge rate of 0.5C would be 50 amps.
Exactly "C" is capacity.

When we use "C" in context of cycling marine batteries it is usually at the 20 hour rating.

When we use "C" in the context of charging or discharging it is as a % of "C" or % of capacity..

If talking Charge Rate:

.03C = 3% of 100Ah or 3A Charge Rate

.1C = 10% of 100Ah or 10A Charge Rate

.25C = 25% of 100Ah or 25A Charge Rate

.5C = 50% of 100Ah or 50A Charge Rate

.75C = 75% of 100Ah or 75A Charge Rate

1C = 100% of 100Ah = 100A Charge Rate

 
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Chasm

Super Anarchist
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As explained above using fractions of C is a convenient shorthand.

They are also used to express (dis)charge rates because -for a given battery chemistry and type- they stay pretty much the same over a wide band of capacities.

 

Pukka

Member
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0
NZ
Thanks for explaining.

"For this application I see no benefit to AGM other than preamture hole in the owners wallet.. For other applications AGM's can and do make a lot of sense.

The worst thing about AGM's is that the vast majority of folks I see buy them, buy them for the wrong reasons. They also don't take advantage of their benefits, don't charge and use them correctly then complain when they are dead in two years and they have a a big fat hole where their wallet used to be.

*If you want a sealed long lasting, long cycling battery then GEL wins.

*If you want a sealed high charge acceptance medium cycle life battery then a premium AGM such as Odyssey, Lifeline or Northstar wins. (perhaps FireFly too but they are new)

*If you beat around cans and don't invest in taking care of an expensive battery, the way they should be cared for, then flooded wins.

*If you want long cycle life and don't care about high acceptance rates then deep cycle flooded, like golf cart or floor scrubber/fork truck, batteries win..

*If you have an unlimted budget, and want to out perform lead by multiple times over, LFP wins....

Theres a lot to buying batteries but for the OP I would suggest sticking with a good deep cycle flooded battery..."

Wow! That seem to nail the OP,s questions & mine for that matter. Par for the course from MS.

 

Dennisail

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Brisbane
Something else to note about C rates is how they effect usable capacity in respect to Peukert's law. http://en.wikipedia.org/wiki/Peukert%27s_law

The more current you draw, the less capacity you get out of the battery thanks to internal battery losses (hence there is a need to define a specific discharge rate to get an oranges to oranges capacity comparison, which why we have the standard 20h rate). Not sure how this effects charge rates but I assume it would be the similar? IE high charge rates create the same kind of losses in the battery as high discharge rates? Can anyone confirm? Another plus for lithium as lithiums are hardly bothered by Peukert's law.

I just rigged up a walker bay with a trolling motor and an old N70 start battery (which has another obscure way of measuring capacity called reserve capacity. RC is how many minutes the battery can supply 25 amps at usable voltage levels.) Ah rate is roughly 70ah. The trolling motor uses about that much current, so that is a C rate of 1. At that current the battery is getting well abused and has a very low capacity. Putting in 2 batteries gives a C rate of 0.5, so it gets me something like 3 times the range not just 2 as you might first expect.

 
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DDW

Super Anarchist
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Something else to note about C rates is how they effect usable capacity in respect to Peukert's law. http://en.wikipedia.org/wiki/Peukert%27s_law

Another plus for lithium as lithiums are hardly bothered by Peukert's law.
Another plus for the otherwise useless AGMs, good ones have a Peukert much closer to one. So to summarize, AGMs are completely useless except:

* Don't spill acid

* Don't spew corrosive and toxic fumes

* Don't outgas and occasionally explode and have to be externally vented

* Have a much slower self discharge rate

* Have much higher charge acceptance rate

* Have lower internal resistance and lower Peukert coefficient

Reminds me of a Monte Python scene:


 

Moonduster

Super Anarchist
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But the fact remains that LFPs do all those things substantially better and weigh a lot less. I just don't see how anyone can rationalize the cost of AGMs for their fairly small incremental return on investment when, if those things were important, they could use LFPs and get a substantially better return.

 

Alex W

Super Anarchist
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322
Seattle, WA
AGMs fit on their side, FLA don't. That is a huge thing for me, where I have plenty of space that is under 9" tall to fit batteries. I could buy a lot of FLA U1 batteries to fit there, or I can buy a couple of group 24 AGMs and lay them on their side. I can't get additional height clearance without either removing my fuel tank or raising the aft bank.

Pearson intended for my single house battery to fit under the galley sink, where I prefer to keep a trash can (keeping a battery under a sink seems stupid too). Some other owners keep their batteries in the lazarette, but the boat is already heavy on that side (cooler, hot water heater, and head are on the side, there is nothing heavy on port to balance it out) and adding 100lbs of batteries makes it worse. This is a light boat, so 100lbs off center makes a big difference in the boat's trim.

It's worth the $100-$150 price penalty to make the best use of my interior by using AGMs compared to FLA. I'm sure the same occurs on other small cruising boats.

I am interested in LiFePO4 next time I need to replace batteries. The deeper DOD, lighter weight, and ability to fit in unusual spaces are all nice features on smaller cruising boats. I have a line on some cheap lightly used ones, and may upgrade before it's really necessary as a result.

I disagree with your assertion that smaller cruising boats are always on a tight budget. There are a lot of reasons why I have a 28' boat, not a 35' one, and budget is only a part of the consideration.

 
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Dennisail

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Brisbane
But the fact remains that LFPs do all those things substantially better and weigh a lot less. I just don't see how anyone can rationalize the cost of AGMs for their fairly small incremental return on investment when, if those things were important, they could use LFPs and get a substantially better return.
Thats my own thoughts.

BTW I have AGMs on my boat which I actually purchased. But they were used (in very good condition)and going cheap. They are quite good for what I paid for them. If I had to pay sticker prices I may as well get some real sticker shock and make it really worth it. The Peukert exponent of them is still no where near good enough (for me) for things like using an electric oven or high wattage HWS.

 
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Spin Echo

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No doubt that LFP is the best by all parameters, however the price is astronomical and so AGM is a great compromise in stepping up from flooded.

 
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axolotl

Super Anarchist
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184
San Diego
Flooded or Lithium. The stuff inbetween hardly seems worth it it most cases unless there is a particular compelling reason that sealed needs to be used.

BTW my boat nearly caught on fire thanks to a faulty lead acid start battery. Eventually it developed an internal short/dead cell which dragged down the voltage of charger terminals absorbing the full 44a of charge current from my large solar array. The current turned most of the electrolyte into hydrogen gas and boiling acid, and it was too hot to touch. A spark would probably have caused a large explosion. So lets not pretend that lead acid batteries are fully safe either.
Had almost exactly the same thing happen to me, except I noticed a lot of gassing when charging and an inability to hold @ 12.5v. Finally popped the caps off when charging and one cell was gassing like crazy. A VOM showed it was partially shorted out. Now if a bank is behaving badly, I'm right on top of it.

The bad thing about flooded is sometimes they'll limp along when damaged and make a mess later to inform you.

 

DDW

Super Anarchist
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I'm mainly just stirring the pot. If my Lifeline batteries ever die (9th year now?) I will look pretty hard at LiFePo4. I already switched over for the glider instrument battery and I have been pretty happy with that choice. Lasts longer and keep the voltage up higher, longer. Don't have to worry about recharging it right away as you do with LA.

 


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