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Old 29-11-2012, 09:57   #16
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Re: Confused..What size charger?

Given the OP's requirement that a Honda 2000 power the charger the only important specification is how much AC current does the charger draw. Some chargers are very inefficient and draw a lot of AC current.

One of the cheapest and most efficient chargers is the Iota series. The 55 amp unit draws a maximum of 13.4 amps at full output which is exactly the Honda's continuous output specification. Anything more will overload your Honda.

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Old 29-11-2012, 10:14   #17
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Re: Confused..What size charger?

Quote:
Originally Posted by sailinglegend View Post
Your quote is only true if you take into account the TOTAL charging time to 100%. Up to 80% - especially if you are running the engine or a generator - then there is a big difference. Above 80% let a big solar array take over.

If I change from my 100 amp engine alternator which is charging at 80 amps, to my DC generator, I get 250 amps going into my batteries. Only when they reach about 80% charge do they both put in the same current. So you will get from 50-80% of charge much quicker. That's 60% of your usable capacity.

If you have AGMs then their faster charging time with a higher current WILL get the bank up 80% much quicker. To put 100 Ah into an AGM will only take 102 Ah. To put 100 Ah in a flooded battery will take 120 Ah or more because of the difference in their charge efficiency.

With AGMs it makes sense to optimize your charging systems to justify their increased cost. Lifeline say do NOT charge their AGMs at less than 20% of C.
All true, except only that the bulk phase is usually over by about 70% charge with regular open cell lead acid batts, so if you're only discharging down to 50% of capacity, then you're using max current for only 20% (or so) of the batts' capacity.

I went from a 40 amp (* 24v) to a 70 amp charger for a 420 amp/h bank, and it didn't change my life, in real practical terms. That's 16% of C. The further you go, the more you run into diminishing returns.

Agree with you about solar.
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Old 29-11-2012, 10:19   #18
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Re: Confused..What size charger?

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If I'm understanding this correctly, the relationship b'twn batt capacity & charger size is only really pertinent to the "bulk" charging phase, i.e. up to 80-85%. After that, the batts are then into the "absorption" & finally the "float" stages so the charger capacity -- whether a charger or solar, etc. -- no longer really matters since it's all about the batt acceptance rate vs. the charging source output. Is this right?....
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"Lifeline say do NOT charge their AGMs at less than 20% of C," is this total batt capacity or each batt that the smart charger is charging at any particular time....
C is the total capacity of your 675 Ah bank. So you need a charger of 135 amps.
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....I have 3 Lifeline AGM's with 225ah each, but my smart charger will only charge one at a time based on need. So in my case is the 20% calculation based on 225ah, or the combined 675ah?
I don't understand how you smartcharger can charge one at a time?
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Old 29-11-2012, 10:28   #19
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Re: Confused..What size charger?

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All true, except only that the bulk phase is usually over by about 70% charge with regular open cell lead acid batts, so if you're only discharging down to 50% of capacity, then you're using max current for only 20% (or so) of the batts' capacity.

I went from a 40 amp (* 24v) to a 70 amp charger for a 420 amp/h bank, and it didn't change my life, in real practical terms. That's 16% of C. The further you go, the more you run into diminishing returns.

Agree with you about solar.
This is entirely dependent upon things such as age and the current available.

With a small solar system and low current a flooded lead acid bank won't hit 14.4V until the upper 90's as a percent of charge. With more current you can hit absorption voltage earlier, normally in the 80-85% SOC range for healthy batteries.

As batteries age and sulfate you can hit absorption voltage as low as the minute you turn on the charger, I see this quite often and is but one of many ways to determine if the batteries are toast or not..

If you are hitting absorption voltage (14.4V - 14.8V) at 70% SOC with 16% of "C" then the batteries are likely getting sulfated and building a surface charge early. An equalization cycle may help this and may not...
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Old 29-11-2012, 13:02   #20
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Re: Confused..What size charger?

hlev, i wasn't discussing charge times. That will vary with many things including acceptance rate AND charge profile, and if you've got the profile set for a long charge, the high rate won't matter, it will still be a long slow charge.

Most of the printed sources, including the battery makers, put the acceptance rate for wet lead at around 1/5th C, and for AGMs at 1/4C.

Yes, wide variations have been observed depending on battery condition and the phase of the moon, but those are the standard numbers to use on the back on the envelope.

Since the OPs Trojans are AGM...bump the charger up by 25% to allow for the extra absorption, if the budget allows for it and time requires it. Or don't bump it up, and they'll just take a bit longer to charge.

Charging on shore power, an extra hour isn't going to make a difference, he's still well under 8 hours, i.e. overnight. Charging on a genset, it won't make a difference either, unless he springs for a genset that has enough power for the bigger charger.
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Old 29-11-2012, 14:34   #21
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Re: Confused..What size charger?

Quote:
Originally Posted by sailinglegend View Post
Correct

C is the total capacity of your 675 Ah bank. So you need a charger of 135 amps.

I don't understand how you smartcharger can charge one at a time?
The charger is supposed to sense which battery needs to be prioritized for charging based on how depleted it is. It has a monitor that displays which one it's charging at any given time, which charging phase is being used, and how many amps & how much voltage are being delivered. It often rotates quickly b'twn the 3 batts. so they all come up to charge evenly.

I thought most of the smart chargers worked this way. Maybe the confusion is that each of my 3 batts are only combined at the main switches, and only for consumption purposes. The charger is wired to each of the batts individually, and they all get charged regardless of the position of the switches.

Does this make any sense?
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Old 29-11-2012, 23:06   #22
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Re: Confused..What size charger?

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....... Charging on shore power, an extra hour isn't going to make a difference, he's still well under 8 hours, i.e. overnight....
A contentious issue this charging! The back of an envelope and the phase of the moon don't help the argument!

You may think your batteries are charged in well under 8 hours but don't be fooled by the little light that says "FLOAT". They may still only be at 95% - that's 10% of their usable capacity that hasn't been fully charged and is then going to sulfate.

All chargers switch to float before batteries are 100% charged because they don't know what current is going into the batteries or what capacity they are. When the charge current is 0.5% of the battery capacity and the charge voltage is 14.2 volts or more then the bank is 100% full. The trouble is a charger will never allow you to see this situation because it switches to float too early - so next time it goes to float turn the charger on and off and watch the charge current go back up to well over 0.5% of C. At a float voltage it is going to take another 8 hours to put the last 10 % of usable capacity back in. Try it!


Quote:
Originally Posted by hellosailor View Post
Charging on a genset, it won't make a difference either, unless he springs for a genset that has enough power for the bigger charger.
If you double the size of your charger you will halve the time you run your genset to get the batteries from 50% to 80%. Past that its not worth running the genset.

Lifeline AGMs have a charge acceptance of 1.3C at 50% DoD. AT 100% discharge that goes up to 5C. Not all AGMs are the same so you can't generalize.
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Old 29-11-2012, 23:39   #23
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Re: Confused..What size charger?

Don't put all your battery eggs in the charger basket. I had one of those dinosaur of a charger weighing 50 lbs. in my boat. Found a new/old stock Phase three charger (15amps). I have added 300 watts of solar and rarely turn on the charger.
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Old 30-11-2012, 09:48   #24
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Re: Confused..What size charger?

"All chargers switch to float before batteries are 100% charged because they don't know what current is going into the batteries or what capacity they are."
Only if they don't have lunar phase detection.<G>

Cutting off the bulk charge early is a safety factor. Undercharging the batteries a little will do less harm thatn boiling them off with an overcharge, and given that there's no fast simple way to really tell exctly when the change should be made--that's not such a bad idea.

As to chargers not knowing battery capacity, surely there are chargers that are are smart as the typical mid-end MPPT controller, where the battery size and capacity ARE in fact user-programmed? Of course, that's not going to be a $99.99 charger from the auto store.

Which is another advantage to adding a solar panel, with proper controller, sitting there patiently and finishing off the charge in a liesurely fashion.

But within the original constraints, using a typical charger and a typical charging scenario, a 95% charge is perfectly acceptable for daily use. Not perfect, but without discussing equalization and other issues, it is still good enough for gummint work.
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