Size of Battery Charger

[ranger58sb]

Originally Posted by Maine Sail

For the best longevity of your expensive TPPL batteries Odyssey suggests at least 40% of "C"... It is in their technical manual... These batteries like to be hit hard and Odyssey has determined that 40% of capacity is what is minimally needed. Hitting these minimums with Odyssey can get very hard when banks get large so you often just suck it up and take the cycle life hit..

Sounds like I should get on with my charger upgrade sooner rather than later, thanks for the wake-up call

In the meantime, I guess we've been lucky enough, maybe partly because we don't use them hard. Anyway, we're getting though our 8th season on the oldest bank and they still act like new.

(Sorry, all, for diverting the thread a bit for a minute or two...)

-Chris

[ranger58sb]

Sorry, slightly more diversion...

These from the Odyssey manual:

In order to achieve the full design cycle life of ODYSSEY batteries in cyclic applications the charge current must be a minimum of 40% of the battery’s 10-hour rating (column 8 of the chart on page 5). Thus the minimum charge current for a PC925 battery in a cycling application is 10.8 amps (40% of 27Ah). Please refer to Figure 6 of the ODYSSEY Technical Manual for a detailed discussion of the recommended charge profile for ODYSSEY batteries in cycling applications. The manual may be downloaded from www.odysseybattery.com.

To fully charge a 31-PC2150 battery that is routinely discharged deeply, a minimum of 40 amps are required with charger voltage within the range of 14.1V to 14.7V.

Specific points: The calculation uses the 10-hour rate (92-Ah for PC2150s) vs. the 20-hour rate (100-Ah). Also, "discharged deeply" seems to be key, in our case.

Presumably a 3-battery bank would need 110.4 amps to fully charge from a deeply-discharged state? So 220.8 amps required for two banks of 3 batteries? Hmmm...

FWIW, the charger I had intended to upgrade to is on Odyssey's list of recommended chargers... but it's only a 60-amp 3-bank charger... but it's also the largest charger on Odysseys recommended list.

BTW, 100-amp inverter/chargers were mentioned; most of those don't seem to be recommended for installation in the engine room (the easiest installation I could do, simply replacing the existing converter).

In the meantime, our batteries seem fine, perhaps because we seldom deeply discharge either of the big banks.

I have the option of eventually combining the battery currently used as a genset starter into one of the main banks (which are also main engine starters) when that bank needs replacement, giving us one bank of 300-Ah (20-hr rate) and one bank of 400-Ah... and in that case the parallel switch would like protect the genset/main engine starting function. That would give us 700-Ah (or 644-Ah at the 10-hr rate), presumably requiring 257.4-amps for charging?

I suspect there's something critical here that I haven't understood -- after all this time <sigh>...

-Chris

[lancelot9898]

I'm also having a hard time in understanding the rational for needing a large amp charger for those AGM's. One of the benefits of the AGM is that it can accept a higher amp charge over the wet cell or even the gel. For that reason, I upgraded the alternator with Balmar and an external regulator to limited the run time on the engine. However, when I go to a marina and plug in, I'm there for more than a day and while it may take me a long time to bring that battery back up with the small 20 amp "smart" charger...I will eventually get there as long as my usage is limited there at the dock. Even with the lifeline AGM's which require equilization which my small charger can do, requires a high voltage and not necessarily high amps. I don't have the lifelines and other AGM's do not require equilization....not sure why? Anyway, my 5 year old AGM's bank of 500 amp-hours are still doing fine with only a 20 amp "smart" charger on them. It would seem to me that if in fact a high amperage is needed for the AGM's to prolong the life span, then solar panels might not be a good idea.

[twinboat]

It would seem to me that if in fact a high amperage is needed for the AGM's to prolong the life span, then solar panels might not be a good idea.

No, AGM's might not be a good idea, with solar panels.

[goboatingnow]

The key with AGMS is to ensure they do not spend too much time sitting discharged, ie below 80%. They need to be restored to 100% on a regular basis. IN reality unless you have very high current charge sources, AGMS are not a good fit for boats.

dave

[Saltyhog]

To clear things up just a bit: I don't think anyone is saying that generic AGMs require a high charge rate of of 0.4 * AMP-Hr rating. This is specifically regarding TPPL batteries from Odyssey per their tech sheet. I believe generic AGMs like to have a good strong shot every now and then and per Lifelines specs, a shore charger of 0.2 * AMP-Hr rating is preferred. Saying that AGMs and solar don't mix is silly. If you don't deeply discharge them, solar is perfect. If you do discharge deeply, you might be better off if you occasionally give them a good strong slug from a big alternator or other high current charger. For many, an hour of high current charging in the morning (via say, a big alternator) and the remaining charge from solar is perfect. Lots of other potential use profiles, with a sliding scale of effectiveness. It all depends on you, your usage, your habits, your boat setup, and your wallet. It's a system comprised of all the parts. You cannot consider 1 or 2 independent of the rest.

[zboss]

So, are the % ratings on the total system capacity or the amount of charge you have used?

For example: using 40% of a Lead Acid 100 AMP battery. At 10% Lead Acid charger... do I need a 4 AMP charger or a 10 AMP charger?

Also, does it vary based on 6V in series vs. a single 12 V in the same capacity?

For example: Lead Acid 100 AMP 6V x 2 in series still gives you 100 AMPS in 12 Volt but the overall capacity @ 6V is 200 AMPS

Using the 10% figure for Lead Acid batteries, I would need a 10 AMP charger vs. a 20 AMP charger.

[ranger58sb]

I think I would understand the math better if I knew what "C" means. Overall capacity? Or amperage required to bring a bank up to full charge? Or...?

600-Ah discharged only 20% should mean only 120-Ah are required to bring the bank up to fully charged (disregarding inefficiencies in the process, to simplify discussion). My current 40-amp charger seems to handle that easily enough, given initial bulk charge and then over the course of the 4-hour absorption period.

???

Given our schedules (including her pesky day job), we're rarely able to anchor out for more than 2-3 days at a time. Two 2-hour charging sessions each day seems to handle everything well enough (and given our all-electric galley, most hot meals require genset for a while anyway).

-Chris

[rw58ph]

You know for DC, NOT AC, you can have more than one charging source. So you can gang charge the batteries. On the house bank for quicker charging time we have to 60 amp chargers. When at dock only one is used.

[Patacha]

Originally Posted by ranger42c

I think I would understand the math better if I knew what "C" means. Overall capacity? Or amperage required to bring a bank up to full charge? Or...?

-Chris

Chris.

Please refer to my explanation on page 2 of this thread.
C is the capacity of a battery from fully charged to fully discharged, over 20hrs. If a battery is rated 150ah, it means it will provide this capacity at a discharge rate of 7.5A over 20hrs.

If you discharge at a lower amps, you will get more ah out of the battery; at a higher discharge rate you will get less ah out of the battery. This is due to the nature of the batteries, AKA Peukert effect.

[ranger58sb]

Originally Posted by Patacha

Chris.

Please refer to my explanation on page 2 of this thread.
C is the capacity of a battery from fully charged to fully discharged, over 20hrs. If a battery is rated 150ah, it means it will provide this capacity at a discharge rate of 7.5A over 20hrs.

If you discharge at a lower amps, you will get more ah out of the battery; at a higher discharge rate you will get less ah out of the battery. This is due to the nature of the batteries, AKA Peukert effect.

Thanks, I did see that. I understand the simple math, but I haven't yet twigged on to how that computes at a specific time or at a specific discharge state (if it does).

IOW, if I have only discharged two 600-Ah banks to about 80%... is C at that point essentially 120-Ah? Or is it still the whole 600-Ah?

Another IOW, should I calculate required charger size based on the total, or the difference between total and used? (Realizing that my usage may sometimes exceed my norm.)

No too many 600-amp chargers out there Yep, could have multiple chargers; good idea. Yep, as MS says, sucking up the cycle life is a likely option...

I'm on a track to upgrade chargers anyway, but I'd be more comfortable if I better understood the limits the math is telling me (if it is).

-Chris

[Patacha]

Originally Posted by ranger42c

IOW, if I have only discharged two 600-Ah banks to about 80%... is C at that point essentially 120-Ah? Or is it still the whole 600-Ah?

Another IOW, should I calculate required charger size based on the total, or the difference between total and used? (Realizing that my usage may sometimes exceed my norm.)

-Chris

1. Ideally, If you start at 600ah and consume 80%, you have 20% capacity left - 120ah. C is only the ORIGINAL rating.

2. Charger size sould be C/5 to C/10 of the RATED capacity; say, 600ah bank - 120-60A charger.

Hope I was of help.

[twinboat]

Amp output from a charger and Amp Hours in or out of a battery are 2 different things.

If you have 600 Amp Hour bank and you want to charge it at C/10 then you need a 60 "AMP" charger.

If you run down your battery bank to 80% then you need to replace 120 Amp Hours.
That mean you need to run your 60 AMP charger for 2 hours to replace 120 Amp Hours.
That is the simple explanation. Of course it will take longer because the charger Amp rate drops off after the battery nears full charge.

[ranger58sb]

Originally Posted by Patacha

1. Ideally, If you start at 600ah and consume 80%, you have 20% capacity left - 120ah. C is only the ORIGINAL rating.

2. Charger size sould be C/5 to C/10 of the RATED capacity; say, 600ah bank - 120-60A charger.

Hope I was of help.

I actually meant it the other way around: start at 600, usually discharge that only by 20% (i.e., remaining with 80% of original capacity).

-Chris

[ranger58sb]

Originally Posted by twinboat

Amp output from a charger and Amp Hours in or out of a battery are 2 different things.

If you have 600 Amp Hour bank and you want to charge it at C/10 then you need a 60 "AMP" charger.

If you run down your battery bank to 80% then you need to replace 120 Amp Hours.
That mean you need to run your 60 AMP charger for 2 hours to replace 120 Amp Hours.
That is the simple explanation. Of course it will take longer because the charger Amp rate drops off after the battery nears full charge.

Yes, and we would have to run our current 40-amp charger for 3 hours (still ignoring the rate drop). Which is easy enough to do.

That doesn't get me anywhere near the C/40 thing for Odyssey AGMs... or even C/20 for Lifelines...

-Chris