Battery rating

[Kakalina]

Will a battery rated at 220 AH really produce that many amp-hours @ the current it was rated at.

[john61ct]

Depends on the type of battery and quality of the manufacturer and sales channel.

Generally yes, in fact at the high end with true deep-cycling as opposed to hybrid (actually starters), rating specs are often very conservative, especially with LFP4.

Walmart so-called "marine" lead, not so much.

[DeepFrz]

But, in the case of all lead acid batteries, you only get a usable amount of approximately 1/2 of the rated amp hrs or you will very quickly kill your batteries. Lots of information on 1 1/2 million threads...oops, was that political?

[john61ct]

LiFePO4 are happy to let you cycle down to 80% discharge, and don't want to be kept 100% full either like lead.

They may - if properly cared for - be cheaper than high-end lead in the long run, but require a **much** bigger up-front investment, and not just money but research/learning time.

[Kakalina]

I am using 4 Trojan T105 batteries. Trojan's information indicates 20
Hr rating 225AH. That would indicate testing at 11.25 amps for 20 hrs at 80 degrees F. But when you look at their performance chart @ 10 amps you only get 1000 minutes or 16.7 hrs. This is considerably less than 225 AH.
I am not interested in critizing their ratings, I'm only interested in understanding my battery capacity to determine what size battery I need for a 130AH load.
I do know you should only deplete your batteries 50% in order to prolong their life.

[sailorboy1]

You will never really "know" that. All you can do is make assumptions. The larger the capacity to the amount you routinely take out is part of the life factors of the battery. So if you normally take 130AH out of your 260AH batteries for 50% they will probably last a shorter time than if the bank was 520AH. But that doesn't mean the larger bank costs less overall.

I'm been meeting lots of cruisers who don't know how much they use and only have a voltmeter on the boat. Their batteries are lasting long enough for them.

On internet forums people talk about batteries like they are gold instead of lead.

[a64pilot]

You need as a min 260 AH if you will draw them down over a 20 hr period, however that is when they are at their very best brand new, and batteries slowly dergade.
So I would say if overnight you need as a min 300 AH, however if you have 400 AH, they will last longer because you will cycle them shallower.
However there is a general rule that it is best to size for two days draw especially if using Solar to recharge, so now we are at a 260 AH draw which means a 520 AH bank to stay within the 50% discharge rule.

Long story short, as big a bank as you can afford and can fit, and can carry the weight will be your best bet. If a very large bank, it can go for many years longer than one marginally sized, cause give it a few months and the bank will lose enough capacity so that it is no longer marginal, but inadequate, then its death accelerates.

Do google custom search on battery bank sizing, sit down in a comfortable chair and do a lot of reading, there is a lot out there

[john61ct]

Round up, get a bigger bank than you think you need, given space or weight limitations of course. Invest up front to save $ long term, bigger banks are more efficient and last longer.

130AH is not a measure of load itself, but capacity, load over time. Might be better if you post your list of appliances, what they consume, estimate daily usage for each.

Also your recharge sources and how often/long you are running your motor(s), frequency shore power is available are all important.

[Stumble]

You need to look at the chart again, if you follow the 10amp rate over its appreciably over 1,000 minutes. It's a fat line on a skinny chart, with varying scale (which is why it's labeled for estimate only) but I wouldn't guess it's indicating about 13-1400 minutes (at this scale each verticle tick is 1000 minutes).

https://www.thesolarbiz.com/media/ca...ata_Sheets.pdf

[StuM]

Originally Posted by Stumble

You need to look at the chart again, if you follow the 10amp rate over its appreciably over 1,000 minutes. It's a fat line on a skinny chart, with varying scale (which is why it's labeled for estimate only) but I wouldn't guess it's indicating about 13-1400 minutes (at this scale each verticle tick is 1000 minutes).

https://www.thesolarbiz.com/media/ca...ata_Sheets.pdf

It's a logarithmic scale, which can be very confusing to read (unless you are old enough to have used a slide rule regularly ). I'd say your top estimate of 1400 is a bit high, but, yes, it is well over 1000.

Halfway between the 1000 and 2000 lines is about 1320 and 1/3 of the way is about 1215. It looks as though the red line crosses just a bit below 1/2, but well about 1/3 - so yes, 1300 is about it.

That makes it about 217Ah @ 10A which, given the "estimation purposes only" nature of the graph is near enough.

[StuM]

Originally Posted by Kakalina

I am using 4 Trojan T105 batteries. Trojan's information indicates 20
Hr rating 225AH. That would indicate testing at 11.25 amps for 20 hrs at 80 degrees F. But when you look at their performance chart @ 10 amps you only get 1000 minutes or 16.7 hrs. This is considerably less than 225 AH.
I am not interested in critizing their ratings, I'm only interested in understanding my battery capacity to determine what size battery I need for a 130AH load.
I do know you should only deplete your batteries 50% in order to prolong their life.

Depends on what you mean by load.
Load is an instantaneous demand and is measure in Watts or Amps.

Presumably you mean a 130Ah draw and the question then becomes over what period. If you mean 130Ah over 24 hours, then your average load is about 5.4 Amps.

You need to look at your charging source. If it is solar, then during the day there will generally be no load on the batteries and they will be charging so you need to look at your overnight draw. If that is say 80Ah then as a minimum, you only need to size your batteries to supply that without your SOC dropping below 50% (i.e 160Ah bank).

But as a rule of thumb, you should size your bank to be at least double your total daily draw and x3 gives you a nice margin, so 260-390Ah would be good.

Note that the about figures assume that your load/draw is at 12V. The T105 data is for 6V batteries. So each 225Ah T106 will only give you a bit over 100Ah at 12V - that means that you will need 4 of them hooked up in series/parallel in the above scenario

[Maine Sail]

Originally Posted by Kakalina

Will a battery rated at 220 AH really produce that many amp-hours @ the current it was rated at.

Here is a shot of a 105Ah battery near the very end of a 20 hour capacity test. Note the 5.25A load and the voltage about to be cut off at 10.499V... This battery, freshly broken in, slightly exceeds the 105Ah rating..


Good quality deep cycle batteries, broken in, and discharged at the 20 hour rate at between 75F and 80F will certainly deliver the rated Ah capacity. Some deliver even slightly more but keep in mind this is an ever moving target so the length of time they will deliver the actual rating is a relatively short period, especially in a PSOC application. With good care and good charging practices you can slow the demise but they are still continually fading after they have cycled up to rated capacity.

Sadly there are far too many batteries out there that I have never, ever seen meet the claimed Ah capacity rating. These are most often "automotive cased" batteries stickered up as "deep cycle marine"...

Good quality 6V GC2's or GC12's generally meet their rating after being broken in. Break in can take 10-75 cycles depending upon the battery.

[john61ct]

Originally Posted by Maine Sail

Break in can take 10-75 cycles depending upon the battery.

Aside from initial balancing, have you come across any preliminary protocols for "breaking in" LiFePO4 banks yet? Or is there no need?

I understood that's what you meant by "commission charging" elsewhere?