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Old 26-11-2014, 12:00   #16
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Re: Battery Charger Output Amperage

One item that hasn't been mentioned is that using a Honda gen to charge the batteries will take 8 or so hours for a full charge as the batteries internal resistance increases and they accept less current.

Best to invest in some solar for a quiet full charge. Batteries do not do well if not fully charged.
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Old 26-11-2014, 12:04   #17
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Re: Battery Charger Output Amperage

I use the mnemonic pac-n-sav. Easy for me to remember, because I used to frequent a grocery store of that name.

Parallel Adds Current -n- Serial Adds Voltage

So, two 6 volt batteries, of 260ah each, wired in series, adds the voltage but not the current. You end up with a 12 volt battery of 260ah. Wiring them in parallel would add the current but not the voltage, and you would end up with a 6 volt battery of 520ah.
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Old 26-11-2014, 13:58   #18
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Re: Battery Charger Output Amperage

Better to look at thia from the other end. L/A batteries are self limiting for charge rate. You batteries like a charge current of 10% of their capacity so 10A for each 100A/h. To get more in you need excessive voltages and can damage batteries and attached kit. You can go a bit bigger which will give a slighty faster overall change but in reality the gain is negligible. Having a bigger charger does not cause problems but wont charge faster, it just costs more! Yes you genset will charge those batteries irespective of the charger size because you will only draw about 40A @ 12v (480W)
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Old 26-11-2014, 17:14   #19
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Re: Battery Charger Output Amperage

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Originally Posted by roland stockham View Post
Better to look at thia from the other end. L/A batteries are self limiting for charge rate. You batteries like a charge current of 10% of their capacity so 10A for each 100A/h. To get more in you need excessive voltages and can damage batteries and attached kit. You can go a bit bigger which will give a slighty faster overall change but in reality the gain is negligible. Having a bigger charger does not cause problems but wont charge faster, it just costs more! Yes you genset will charge those batteries irespective of the charger size because you will only draw about 40A @ 12v (480W)
While some manufacturers recommend 10% of bank size it isn't the maximum liquid acid batteries will accept. They will accept 20% or so of capacity, for a while at least, in bulk charge.

Xantrex lists their 40 amp Truecharge 2 at 9 amps AC. 4.5 amps for the 20 amp version and 13.5 amps for the 60 amp charger.
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Old 26-11-2014, 20:13   #20
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Re: Battery Charger Output Amperage

While some manufacturers recommend 10% of bank size it isn't the maximum liquid acid batteries will accept. They will accept 20% or so of capacity, for a while at least, in bulk charge.

Yes it is perfectly true that a heavily discharged L/A batter will accept more charge. It can be useful if, for some reason, you need to get charge into the battery rapidly and don't have time for a full charge. The down side is that by doing the rapid charge you drive up the voltage more quickly so instead of getting to the trigger for step 2 on the charger cycle at about 80% you get there sooner and have to spend more time at step 2. In step 2 the charge rate is lower so the overall time to FULLY charge the batter does not go down by much. Haven't done the maths but I know in practice it makes little difference to the overall time. If you have good solar or wind input and can do all of step 2 with it you may shorten engine run time which might be worth it.
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Old 26-11-2014, 20:21   #21
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Re: Battery Charger Output Amperage

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Originally Posted by roland stockham View Post
While some manufacturers recommend 10% of bank size it isn't the maximum liquid acid batteries will accept. They will accept 20% or so of capacity, for a while at least, in bulk charge.

Yes it is perfectly true that a heavily discharged L/A batter will accept more charge. It can be useful if, for some reason, you need to get charge into the battery rapidly and don't have time for a full charge. The down side is that by doing the rapid charge you drive up the voltage more quickly so instead of getting to the trigger for step 2 on the charger cycle at about 80% you get there sooner and have to spend more time at step 2. In step 2 the charge rate is lower so the overall time to FULLY charge the batter does not go down by much. Haven't done the maths but I know in practice it makes little difference to the overall time. If you have good solar or wind input and can do all of step 2 with it you may shorten engine run time which might be worth it.
The goal should be to put in as much as the batteries will accept at proper bulk charge voltage (14.8 for Trojans for example) to shorten engine/generator time. No matter what you do the last 15% or so will take 8 hours approx. Best to leave that to solar or wind gen unless you want the engine or gen to run all day.
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Old 26-11-2014, 22:44   #22
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Re: Battery Charger Output Amperage

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Originally Posted by mitiempo View Post
The goal should be to put in as much as the batteries will accept at proper bulk charge voltage (14.8 for Trojans for example) to shorten engine/generator time. No matter what you do the last 15% or so will take 8 hours approx. Best to leave that to solar or wind gen unless you want the engine or gen to run all day.
Exactly right!

Buy the largest capacity charger your EU1000i will handle (40 amps is about right) and think about adding solar power for getting your batteries to a full charge.

Bill
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Old 27-11-2014, 03:37   #23
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Re: Battery Charger Output Amperage

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Originally Posted by roland stockham View Post
The down side is that by doing the rapid charge you drive up the voltage more quickly so instead of getting to the trigger for step 2 on the charger cycle at about 80% you get there sooner and have to spend more time at step 2. In step 2 the charge rate is lower so the overall time to FULLY charge the batter does not go down by much.
is that correct? a battery charged to 14.4v at, say, c/6 will have a soc less than one at c/10 to the same voltage?

Interesting, havenīt heard of that before.
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Old 27-11-2014, 06:54   #24
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Re: Battery Charger Output Amperage

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............ Just another observation: you said you have a capacity of 440 Amp hr; if so, then these are 2 enormous 6 Volt batteries, weighing up to 60 kg each? Or do you have two 6 Volt batteries with a capacity of 220 amp/hr each? Indeed, you can add the voltage when connecting in series, not the capacity.
That was my thought also. It's a common mistake to think that two batteries in series doubles the capacity. It does not, it only doubles the voltage.

Two batteries in parallel will double the capacity but not change the voltage.

(Assuming identical batteries of course)
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Old 27-11-2014, 06:57   #25
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Re: Battery Charger Output Amperage

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is that correct? a battery charged to 14.4v at, say, c/6 will have a soc less than one at c/10 to the same voltage?

Interesting, havenīt heard of that before.
I'm not sure what Roland Stockham is trying to say, but it doesn't seem right to me, either.

A battery will accept what it's going to accept at any given voltage, and it won't accept more no matter the size of the charger.

Here is an example for AGM batteries, developed in a research effort with the Concorde Battery company on one of their new 4D Lifeline batteries. Clearly, during the first 1-2 hours of charging a larger capacity charger puts more AH back into the battery than a smaller one. This is important if you are cruising and don't have an infinite charging source and need to get as much capacity back into the batteries as you can in a relatively short period of time.

This graph shows the charging curves for four different size chargers, all kept at the same charging voltage (14.4VDC).

Click image for larger version

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The graph was developed from real test data with an AGM battery, but the same holds true for any lead acid battery....flooded, AGM, gel, TPPL, etc.

It is a common misunderstanding that you can have too large a charger, and that this will fry your batteries. NO, that's not true. Provided that the charger has controlled voltage limits as dictated by the battery type (e.g., 14.8 for flooded, 14.6 for AGM, 14.2 for gels, etc.), then ANY size charger with a capacity larger than the amperage a battery will accept at any given voltage will do exactly the same thing.

And, when your battery charger is much smaller than the amperage a battery will accept at any given voltage (or SOC).....as in the graphic above....you'll get less capacity back into the battery at any given time.

What's more, there's good evidence that faster charging at specified voltages is actually good for the health of the battery.

Bill
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Old 27-11-2014, 12:02   #26
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Re: Battery Charger Output Amperage

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It is a common misunderstanding that you can have too large a charger, and that this will fry your batteries. NO, that's not true. Provided that the charger has controlled voltage limits as dictated by the battery type (e.g., 14.8 for flooded, 14.6 for AGM, 14.2 for gels, etc.), then ANY size charger with a capacity larger than the amperage a battery will accept at any given voltage will do exactly the same thing.
Once at absorption that certainly seems to make sense.
Back at bulk most recommendations seem to be around the C/10 C/8 mark with little info as to why that is. The only thing a bit of time on google came up with was to limit heat stress causing plate shedding.
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Old 27-11-2014, 18:06   #27
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Re: Battery Charger Output Amperage

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Originally Posted by conachair View Post
Once at absorption that certainly seems to make sense.
Back at bulk most recommendations seem to be around the C/10 C/8 mark with little info as to why that is. The only thing a bit of time on google came up with was to limit heat stress causing plate shedding.
The bulk/absorption thing is mostly a red herring. Provided that you not let voltage exceed the recommended limit for the type of battery you're charging (say, 14.8VDC for a flooded lead-acid golf-cart battery), then the limiting factor in charge acceptance is the battery itself.

Is this safe? I think so, as do most authorities in the field. Overheating won't occur unless you've not taken account of the ambient temp, or the batteries are too low on electrolyte, or there's a damaged/shorted cell in the battery.

Fact is, batteries are more often charged too slowly than too fast. This is especially true of AGMs and, to a lesser extent, gels and TPPL batteries. Consider the graph above: at a 50% SOC, the AGM battery under charge will initially accept more than 100% its CA rating!

At a deeper state of discharge, say at 20% SOC, that same battery can initially accept five or six times its CA rating, i.e., 500-600 amps! Nobody has that kind of charging capacity, but guess what? Concorde says they've found that charging at that rate is actually good for the longevity of the battery.

Again, the bottom line: a battery will itself limit how much current it will accept at any given voltage.

A corollary rule, drawn from my own experience and research: charging a battery at the maximum amperage it will accept at any SOC -- given the prescribed voltage limit -- is actually good for the battery.

Happy Thanksgiving!

Bill
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