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Discussion Starter · #1 ·
Talking to some friends and we were talking about chargers. Is it better to get a 40 Amp charger than a 10. Both being 3 stage chargers.

It's my thought that after the "bulk" charging, the remaining time to get a full charge is about the same for all chargers. AND, a bank can only accept so much during bulk without doing damage.

SOooo, unless you have a big bank (200 Ah or more), a bigger (read that as bigger $$$) will not save you all that much time.

So I guess my question is, is it worth it to spend the extra $ for the higher capacity charger?

Greg
 

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The real question is how much time do you have? At anchor with a gen, or at a dock with shore power? What are your DC loads when at the dock or charging?

Too small a charger, asked to do high an output duty for long periods, will result in shorter life, especially the fan less "waterproof" variants that are ideally designed for small bass boats...

Flooded batteries enjoy long slow charges at about 10% to 15% of "C" but can certainly be charged faster than that with no issues.

Ignore the term "smart" with chargers. Most chargers that claim smart are still as dumb as a box of rocks.... There is one well known charger brand that enters float at 4 hours from the time it turns on. That is, turn it on and in four hours it will be in float whether your bank should be there or not. With a large bank it may NEVER attain absorption voltage before dropping to float. SUPER DUMB...

Lots of other chargers use the simple "egg timer" approach to absorption timing. Smarter chargers use adaptive algorithms that calculate time in bulk, % of output etc. to determine time needed for absorption charging. Better "smart" chargers also revert to absorption voltage every few days or weeks to gas the batteries to prevent stratification and limit sulfation. Staying in float indefinitely can be bad for batteries and some charger makers have finally figured this out..

Some chargers will pop out of float with as little as 10% of the chargers capacity and then start an egg timer again. A good charger will run to 90% or more of capacity and hold float before triggering absorption. A good charger will also recognize that "bulk period" was very short and will drop back into float quickly as opposed to running out an egg timer.

Sadly most charger manufacturers are not open about their chargers true operational status and the vast majority of chargers actually suck at being smart.......

The Sterling ProCharge Ultra or ProMariner Pronautic "P" are two of the smarter chargers out there... (identical chargers jointly developed by Sterling in the UK and ProMariner in NH).
 

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Discussion Starter · #4 ·
THANKS for the quick replies!

I am not thinking about this for a full time cruising boat. More than a day sailor, but less than full time. I was also thinking about a boat that most likely goes into a dock that has power, and will stay at least the night or more.

I was just thinking about the real world difference in time required to charge a battery between a 10 or a 40 A charger. AND, the real value if the boat was going to spend a lot of time at a dock.

I HAD a 10 A charger in my boat for quite a while. I then put in a 40 A charger and just do not see that it did much better at charging, just emptied my wallet a bit faster. :mad:

Greg
 

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In your use 10 amps may be fine but it would depend on your loads. I'm installing a 10 amp charger on a family members 30' shortly. The boat lives on a mooring and has no refrigeration the only draws are a small gps vhf and a few cabin Lts and a 140AH bank. Basically the charger will top of the batteries when he's at the dock for a day two at the most, and to some times turn on when the boats on the hard being worked on. If the boat had refrigeration and lived on a dock I would up that to the 20 amp range of charger to better keep up with the more constant power draw.
 

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I agree with Maine on the Pronautic P or Sterling - great charger.

Size can mean a faster charge if you need to charge quickly during a short dock stay. Regardless of charger size the batteries are the determining factor - they will accept what they need and no more for a given voltage.
 

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SOooo, unless you have a big bank (200 Ah or more), a bigger (read that as bigger $$$) will not save you all that much time.
I guess we all have our reference points. A pair of 6 volt golf cart batteries in series is a 225 Ah 12 VDC bank. I don't think that's a big bank. Now eight golf carts in series-parallel is a 900 Ah bank, which I think is a big bank. *grin*

500 to 700 Ah banks are pretty common in the cruising boats I see, even weekenders.
 

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It also depends on the type of battery used in the bank. AGMs can take more charging current than other batteries. Full River recommends 25% of the Amp Hour capacity for the initial charge current (65A @ 14.5-14.9V) for my 260AH batteries.
 

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Discussion Starter · #9 ·
I guess what I was sort of trying to get a feeling for was something like;
Given the same battery bank of 200 Ah, 30% discharged
Given two of the SAME smart OR dumber chargers, one 10 Ah one 30 Ah

How long does it take each charger to bering the batteries to 100%

Something like (and this is just an example and has NOTHING to do with reality)
8 hours for the 10 Ah charger and
6.5 hours for the 30 Ah charger????????????

My point would be (IF the above was even close to real, and I am sure it's not) that if you were spending the night at the dock, the difference in time to charge would NOT make much difference! And if one charger was $100, and the other $300, I'd rather spend the extra $200 on sundowners :D

That is just me and I am NOT trying to tell any one what to do, just look at it logically.

Greg
 

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the difference in time to charge would NOT make much difference! And if one charger was $100, and the other $300, I'd rather spend the extra $200 on sundowners :D
Greg
Problem is that good quality chargers (Pronautic P for example) are not cheap. The chargers that are kind to your batteries are both larger and more expensive usually. I do not know of a really high quality charger that is low amperage and inexpensive.

If it is oversize there are no issues as the battery determines acceptance, not the charger.
 

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Discussion Starter · #11 ·
Brian,

I do understand what you are saying. I am trying to see what the extra dollars get you. Also, I know that the larger the battery bank, the bigger the difference.

I just did a quick look, the Pronautic P 10 Amp model (at Jamestown) is $260.61, the 30 Amp model is $512.53. The difference of $251.92 would purchase a LOT of sundowners at a remote anchorages.;)

OR, would it be better to get a spare to take along? The difference in price makes that an option.

Greg
 

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I guess what I was sort of trying to get a feeling for was something like;
Given the same battery bank of 200 Ah, 30% discharged
Given two of the SAME smart OR dumber chargers, one 10 Ah one 30 Ah

How long does it take each charger to bering the batteries to 100%

Something like (and this is just an example and has NOTHING to do with reality)
8 hours for the 10 Ah charger and
6.5 hours for the 30 Ah charger????????????
The question you ask is really easy to calculate to a point. Charging is not 100% efficient but for rough purposes, assume it is. So if the battery bank is 200AH and 30% discharged, that means it is down by about 60AH.

So, to get back to 95+%, the math is simply the number of amps the charger is producing (and the battery is accepting) x the time.

For a 10A charge current, it will take 6 hours to get 60AH.
For a 20A charge current, it will take 3 hours to get 60AH.
For a 30A charge current, it will take 2 hours to get 60AH.

Remember, the above is simplified. There are inherent inefficiencies involved with charging a battery so you will actually get slightly less than the above numbers.

Also, as the batteries become more fully charged, they cannot accept as much current so there is an exponential tail. That's why the most common algorithm today is 3 states, bulk, absorption and float.

In the bulk state, the charger holds the voltage high (14.5 - 14.9V for AGM) and tries to feed the battery bank as much current as it will take.

Depending on the battery type, the charger will change to the absorption state at around 80% full charge. In this state, the charger holds a constant voltage but the charging current will slowly decline.

When the battery is almost fully charged, the battery charger will enter the float state and continue to trickle charge the bank. The float state algorithm is where I've seen the most difference among different battery chargers. Some chargers will always try to trickle current into the battery whereas others will monitor the battery voltage and only turn on charging current if the battery goes below a threshold value and bring it up to a higher voltage (hysteresis).

A 200AH bank is relatively small and most reasonable chargers will easily bring it back to a full state over night assuming good battery management (never discharge more than 50%, etc.). I haven't checked lately but 40A chargers used to be about the knee on the price curve and would be more than adequate for a small bank.

The fun is in the larger banks. I have 4x260AH batteries for a total of 1040AH. If my bank is 50% discharged, I have to find a way to get 520AH of charge in a reasonable time (generator, shore power). So my inverter/charger is 120A. Same math as above, just larger numbers.
 

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Greg,
Given your stated usage (weekender/day sails) a ten amp will do you just fine.
Spend the rest on sun downers if you like, but I'd suggest a Victron BMX-600 series battery monitor.

There, simple answer.
 

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On my first boat I installed a Xantrex 20A truecharge. I loved that charger and used it all the time as a liveaboard and while out cruising. On my next boat, I went for the 40A charger. I usually would see the 40A charge light on for only a matter of minutes, then it would be 20A for a while, then less. I don't feel like I got a lot extra for my money with the upgrade.

My new boat has 3x8D deep cycle batteries (flooded) for the house bank and has the same Xantrex truecharge 40 charger. We'll see how long the 40A light is on for this boat when they are deeply discharged. Hopefully for a while at least....

MedSailor
 

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Discussion Starter · #15 ·
Chuck,

Thanks for the reply, but it's not for me. :)

I was just talking about the merits of the size/cost of chargers in real life usage. I have 300 Ah on our 27 foot Nor'Sea and have cruised full time 24/7 for years and am now cruising about half time. I have and LOVE my Link-10 battery monitor. Yes, I know there are newer and better ones, but it's not worth my $/time/effort to change out till this one goes bad. It works for my wife and I and is dirt simple to use. :D

Greg

Greg,
Given your stated usage (weekender/day sails) a ten amp will do you just fine.
Spend the rest on sun downers if you like, but I'd suggest a Victron BMX-600 series battery monitor.

There, simple answer.
 

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Discussion Starter · #16 ·
EXACTLY what I am talking about!

Greg

On my first boat I installed a Xantrex 20A truecharge. I loved that charger and used it all the time as a liveaboard and while out cruising. On my next boat, I went for the 40A charger. I usually would see the 40A charge light on for only a matter of minutes, then it would be 20A for a while, then less. I don't feel like I got a lot extra for my money with the upgrade.

My new boat has 3x8D deep cycle batteries (flooded) for the house bank and has the same Xantrex truecharge 40 charger. We'll see how long the 40A light is on for this boat when they are deeply discharged. Hopefully for a while at least....

MedSailor
 

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In the bulk state, the charger holds the voltage high (14.5 - 14.9V for AGM) and tries to feed the battery bank as much current as it will take.
Bulk is not a voltage limited stage of charging it is constant current or "CC". This is where the charger will put out the maximum that it can simply because it has not yet attained a voltage limit..

In bulk the charging is limited only by the capability of the charge source.

Depending on the battery type, the charger will change to the absorption state at around 80% full charge. In this state, the charger holds a constant voltage but the charging current will slowly decline.
The minute a battery bank has attained the "voltage limit" or absorption voltage, also known as CV or constant voltage, the current will begin to decline. In voltage limited charging the battery determines how much current will go in. All the charger does is limit the voltage and hold it steady. As the battery fills less and less current can go in at XX.XX volts....

In absorption/CV charging, float & equalization charging are also CV stages, the current is limited/dictated by the battery...

When the battery hits absorption is not as much dependent upon battery type but rather the relationship between available current and battery bank size. Of course type can play a role but between lead acid batteries they are not that far off compared to lead acid vs. Lithium.....

For example a 200A charger on a 100A AGM at 50% SOC will hit absorption/voltage limiting/CV almost immediately (often in 1 minute or two) yielding an extremely short bulk phase.. It can hit absorption at 50-51% SOC with a large enough charger.... Conversely a 2A charger would not hit absorption voltage until close to 99% SOC... So a 200A charger would have an approx 1 minute bulk stage then a long absorption/CV stage but the 2A charger would be in bulk nearly the entire duration and would not hit "limiting voltage" until well into the upper 90's... The relationship between your chargers size and your banks size plays the biggest role in when your bank will hit limiting voltage, then battery type..

When the battery is almost fully charged, the battery charger will enter the float state and continue to trickle charge the bank. The float state algorithm is where I've seen the most difference among different battery chargers. Some chargers will always try to trickle current into the battery whereas others will monitor the battery voltage and only turn on charging current if the battery goes below a threshold value and bring it up to a higher voltage (hysteresis).
This is where good vs. bad chargers come into play. More sophisticated chargers can supply very low mA level current and do this well where others need to cycle the power supply on and off at low current because the power supply simply can't run at mA levels. It essentially pulses on, voltage spikes, power supply turns off, voltage decays and it does it all over. The older ferro chargers were horrible at floating... Smaller chargers generally do batter at delivering small currents to batteries and holding the voltage extremely steady.
 

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Maine Sail,

Sorry, I was a little sloppy in my wording but didn't want to get bogged down in terminology of a "constant current source" vs a "constant voltage source". I was more focused on the idea that in bulk stage, the charger is putting in as much current as it can which of course is a combination of how much current the charger can provide and how much current the battery bank can accept.

Your terminology is exactly correct in that the when the battery bank is in some stage of depletion, the voltage is well below 14+V and the charger will provide constant current to charge the battery which brings the voltage back up.

Thanks for your clarification and keeping me honest.
 
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