Slow or fast charge deep cycle batteries?

[BAD ORCA]

I finally got around to re-wiring my charge circuit, fusing everything and installing a good battery charger. My new charger (Sterling Pro Ultra 60 amp) has an option to change the power of the charger. I can charge my batteries at a full 60 amps, 45 amp, 30 amps or 15 amps.

Eventually i will upgrade to a 500-600 amp hour battery bank and will need the full 60 amp output from the charger, but for right now i have a small 130 Ah battery bank, two small West Marie group 24's.

Since i have the option to set the power level of the charger i started wondering which power level might be best? I have been playing around a bit with charging them at 15 amps and 30 amps and it seems i get more usable amp hours out of them when i charge at the lower setting. regardless of which power setting i use they get the full 14.5 volts it just takes quite a bit longer for them to get to float when charging them at 15 amps.

do lead acid batteries respond better to a slower charge versus a quicker charge? are my observations accurate and the slower charge is getting more usable power into the batteries before i turn it off?

Also a secondary related question. How long should i leave them in float? Is there a general rule of thumb based on battery bank size, charger size or something else to determine the float time? Im not a fan of unattended charging and turn off all power when i leave the boat, so i try and time my charging cycle to get the batteries as charged as possible, but i understand they do need a certain amount of time in float cycle to get the last 10-20% of chartge into the batteries, if i understand charging correctly.

 

[Davidasailor26]

When you’re seeing 14.5 volts it means you’re in the absorption (2nd) phase. At that point the charger isn’t really putting out its maximum current anyway. That phase is called the constant voltage phase because it’s limiting the amount of current output to hold a constant 14.5 volts. Once the current required to do that drops below a preset threshold the charger will drop to float. The only time you’re using the full current available (whether 15 or 60 amps) is before you reach 14.5 volts, in the bulk phase. That phase is called constant current because it’s when the charger is putting out a steady current (either its maximum output or your hard-limited amount). For the size of your current bank even 15 amps is still more than 10% of the bank capacity, so unless your batteries are deeply discharged they’re probably only pulling about that much for a brief period of time anyway before moving into absorption. One downside of the higher current is that you’ll reach absorption more quickly, at a lower SOC, which means the absorption phase might take longer.

For the second question I wouldn’t worry about keeping the batteries in float for extended periods. Plenty of people do that and the amount of current in float is so small that it isn’t a problem. Doing that certainly beats the alternative of having the batteries drained by a bilge pump or some parasitic load and sitting dead. The only downside is the risk for galvanic corrosion if you don’t have a galvanic isolator.

 

[dlochner]

The Sterling/ProNautic chargers are smart chargers and will adjust the current based on the condition of the battery. I have a 50 amp charger on my boat.

When the charger is first turned on, it will put out the full rated amperage at a fairly low voltage, somewhere in the low 13 v range. As the batteries charge, the voltage will slowly rise until it reaches a set point. That voltage depends on battery chemistry and the setting that is programmed into the charger. Once at that voltage, the charger will hold the voltage constant and the current will gradually decline. When it reaches a certain level of current, the voltage will drop to the float voltage and the charger will provide a small current to the batteries until the battery can no longer accept a charge. Then the charger shuts off. Unless there is some reason to not leave the boat plugged into shore power, there is no reason to turn the charger off until you unplug and go sailing.

To answer the other question about reducing the output current, that will depend on the battery. The rule of thumb for flooded lead acid batteries is about .1 C to .2C where C is the amp hour capacity of the bank, in your case 130 ah. The charger you have has 3 charging outputs. When multiple batteries are connected maximum output (60 amps) is divided across the three outputs at 20 amps each. To answer your question, there are a several pieces of information we need, what is the maximum recommended charging current? How are the batteries wired, as one large bank with the batteries in parallel or separate and only parallel with the 1-2-Both switch? And how do you have the charger connected to the batteries?

 

[BAD ORCA]

The Sterling/ProNautic chargers are smart chargers and will adjust the current based on the condition of the battery. I have a 50 amp charger on my boat.

When the charger is first turned on, it will put out the full rated amperage at a fairly low voltage, somewhere in the low 13 v range. As the batteries charge, the voltage will slowly rise until it reaches a set point. That voltage depends on battery chemistry and the setting that is programmed into the charger. Once at that voltage, the charger will hold the voltage constant and the current will gradually decline. When it reaches a certain level of current, the voltage will drop to the float voltage and the charger will provide a small current to the batteries until the battery can no longer accept a charge. Then the charger shuts off. Unless there is some reason to not leave the boat plugged into shore power, there is no reason to turn the charger off until you unplug and go sailing.

To answer the other question about reducing the output current, that will depend on the battery. The rule of thumb for flooded lead acid batteries is about .1 C to .2C where C is the amp hour capacity of the bank, in your case 130 ah. The charger you have has 3 charging outputs. When multiple batteries are connected maximum output (60 amps) is divided across the three outputs at 20 amps each. To answer your question, there are a several pieces of information we need, what is the maximum recommended charging current? How are the batteries wired, as one large bank with the batteries in parallel or separate and only parallel with the 1-2-Both switch? And how do you have the charger connected to the batteries?

right thats what i see happening on the display. the absorption phase takes quite a bit longer when i have the charger set at 15amps.

iv'e jumped the three outputs on the charger together and only have a single output to my house bank positive charge bus. battery cable conects directly from the bus to the house battery bank. there is a cable from the charge bus to a 1,2,B switch. the reserve bank gets charged via an ACR from the charge bus but currently is not connected (waiting for wire) so, only one house bank, 2 - batteries wired in parallel at the moment.

west marine recommends 14.5 / 13.5 float for my batteries which is what i have the charger set to. i have the battery temp sensor cable installed so its actually 14.6/13.5 right now with the weather. i have the remote display so i can see that the housebank is getting the full 15 or 30 amps when charging unless i have some things running.

the absorption phase seems about twice as long when at 15 amps. i have been running the batteries down to 12.2 volts before turning on the charger. i have the charger power savings mode turned off so the charger stays on/in float until i turn it off. my AC wiring is a bit sketchy and i dont trrust leaving AC power turned on when im not at the boat. thats a project coming up this year. the DC circuit was the first phase.

 

[BAD ORCA]

When you’re seeing 14.5 volts it means you’re in the absorption (2nd) phase. At that point the charger isn’t really putting out its maximum current anyway. That phase is called the constant voltage phase because it’s limiting the amount of current output to hold a constant 14.5 volts. Once the current required to do that drops below a preset threshold the charger will drop to float. The only time you’re using the full current available (whether 15 or 60 amps) is before you reach 14.5 volts, in the bulk phase. That phase is called constant current because it’s when the charger is putting out a steady current (either its maximum output or your hard-limited amount). For the size of your current bank even 15 amps is still more than 10% of the bank capacity, so unless your batteries are deeply discharged they’re probably only pulling about that much for a brief period of time anyway before moving into absorption. One downside of the higher current is that you’ll reach absorption more quickly, at a lower SOC, which means the absorption phase might take longer.

For the second question I wouldn’t worry about keeping the batteries in float for extended periods. Plenty of people do that and the amount of current in float is so small that it isn’t a problem. Doing that certainly beats the alternative of having the batteries drained by a bilge pump or some parasitic load and sitting dead. The only downside is the risk for galvanic corrosion if you don’t have a galvanic isolator.

so it sounds like it doesnt really matter that much which setting i choose.

no galvanic isolator yet but other than my sg-200 i dont think i have any parasitic loads but thats something i want to start learning how to test for using a multimeter.

 

[dlochner]

the absorption phase seems about twice as long when at 15 amps. i have been running the batteries down to 12.2 volts before turning on the charger. i have the charger power savings mode turned off so the charger stays on/in float until i turn it off. my AC wiring is a bit sketchy and i dont trrust leaving AC power turned on when im not at the boat. thats a project coming up this year. the DC circuit was the first phase.

It should take longer. Once the charger starts to leave the Constant current stage the charge current tapers off. If it is tapering off from 30 amps more current is going into the battery in the first few minutes than if it is tapering off from 15 amps. Some made up numbers for illustration purposes: Assume In the first 5 minutes after shifting from CC to CV, the current drops 10%. For the those 5 minutes the charger has been sending ~14 amps to the battery when starting at 15 amps or ~28amps when starting at 30 amps. Eventually the current will taper to the same level, but the higher starting current gives the 30 amp setting an advantage. Make sense?

 

[Stu Jackson]

Chargers do not limit the current, the batteries do that.

In addition to these links, do a search on "Battery+Acceptance" by Maine Sail on this fine forum.

Battery Acceptance by Stu Battery Acceptance

and

Why Going Into FLOAT is NOT Full

Why Going to Float is NOT Full

 

[BAD ORCA]

Chargers do not limit the current, the batteries do that.

In addition to these links, do a search on "Battery+Acceptance" by Maine Sail on this fine forum.

Battery Acceptance by Stu Battery Acceptance

and

Why Going Into FLOAT is NOT Full

Why Going to Float is NOT Full

Thanks Stu. will look through all this. i notice when i get to float my batteries are around the 2% Ah number according to my charger display so iv'e been turning it off pretty soon after it reaches float. i should probably pay closer attention to this number and see how far it drops the longer i leave the charger in float.

 

[marchem]

Chargers do not limit the current, the batteries do that.

In addition to these links, do a search on "Battery+Acceptance" by Maine Sail on this fine forum.

Battery Acceptance by Stu Battery Acceptance

and

Why Going Into FLOAT is NOT Full

Why Going to Float is NOT Full

Stu, is it safe to assume (always dangerous, I know) that a smart charger like the Sterling does a pretty good job of waiting to float until the battery is full, or almost full? I understand that a dumb, or kitchen timer charger has no chance, but I'm hoping the Sterling does.

 

[BAD ORCA]

Stu, is it safe to assume (always dangerous, I know) that a smart charger like the Sterling does a pretty good job of waiting to float until the battery is full, or almost full? I understand that a dumb, or kitchen timer charger has no chance, but I'm hoping the Sterling does.

It appears to. I have the remote display which show charge voltage and amps going in/out. it goes into float right about 2% of battery Ah capacity every time.

 

[BAD ORCA]

It should take longer. Once the charger starts to leave the Constant current stage the charge current tapers off. If it is tapering off from 30 amps more current is going into the battery in the first few minutes than if it is tapering off from 15 amps. Some made up numbers for illustration purposes: Assume In the first 5 minutes after shifting from CC to CV, the current drops 10%. For the those 5 minutes the charger has been sending ~14 amps to the battery when starting at 15 amps or ~28amps when starting at 30 amps. Eventually the current will taper to the same level, but the higher starting current gives the 30 amp setting an advantage. Make sense?

thank you. i had to read that a few times but yes. i appreciate your elaborating. im a little slow to absorb electrical knowledge for some reason. it can be a little confusing.

 

[Maine Sail]

Quote: "Lead Acid Batteries"

AGM = Lead Acid Batteries
GEL = Lead Acid Batteries
Flooded = Lead Acid Batteries

AGM battery cycle life benefits from high charge rates where flooded deep cycle generally do not get any added cycle life from charging at high rates.

Best to tell us exactly which batteries you have as "lead acid" includes AGM, GEL and Flooded batteries.

 

[Maine Sail]

The charger you have has 3 charging outputs. When multiple batteries are connected maximum output (60 amps) is divided across the three outputs at 20 amps each.

It is not divided that way with the ProCharge Ultra as it is not a cheap "autoformer" charger. It is simply distributed by demand. If the start bank is accepting 0.2A the house battery can be getting 59.8A..

 

[dlochner]

It is not divided that way with the ProCharge Ultra as it is not a cheap "autoformer" charger. It is simply distributed by demand. If the start bank is accepting 0.2A the house battery can be getting 59.8A..

RC, thank you for the clarification. The point I was trying to somewhat inaccurately make, is the maximum current that can be produced by the charger is 60 amps and that is distributed between the batteries and it was not 60 amps per battery.

 

[BAD ORCA]

Quote: "Lead Acid Batteries"

AGM = Lead Acid Batteries
GEL = Lead Acid Batteries
Flooded = Lead Acid Batteries

AGM battery cycle life benefits from high charge rates where flooded deep cycle generally do not get any added cycle life from charging at high rates.

Best to tell us exactly which batteries you have as "lead acid" includes AGM, GEL and Flooded batteries.

Ah yes sorry. Flooded lead acid.

 

[Stu Jackson]

Stu, is it safe to assume (always dangerous, I know) that a smart charger like the Sterling does a pretty good job of waiting to float until the battery is full, or almost full? I understand that a dumb, or kitchen timer charger has no chance, but I'm hoping the Sterling does.

Rob, unless a charger has a shunt, it cannot "know" what the amperage going into the batteries may be. The conclusion is that they are all egg timers otherwise, and based on voltage.
The definition of "smart chargers" means, essentially, that they the three stages or phases (i.e.,m bulk, absorption & float) AND THAT'S PRETTY MUCH IT.
You could go back and read Maine Sail's excellent review of these chargers, too.
Wiring a new charger From Maine Sail:

Marine Battery Chargers - Installation Tips & Considerations
and
Installing a Marine Battery Charger - Marine How To

 

[Davidasailor26]

Rob, unless a charger has a shunt, it cannot "know" what the amperage going into the batteries may be. The conclusion is that they are all egg timers otherwise, and based on voltage.
The definition of "smart chargers" means, essentially, that they the three stages or phases (i.e.,m bulk, absorption & float) AND THAT'S PRETTY MUCH IT.
You could go back and read Maine Sail's excellent review of these chargers, too.
Wiring a new charger From Maine Sail:

Marine Battery Chargers - Installation Tips & Considerations
and
Installing a Marine Battery Charger - Marine How To

The second link Stu posted has a very good section on “egg timer” charging, and does specifically call out the ProCharge Ultra as being smarter than that. As the article points out of anything the smarter chargers err on the side of undercharging, which would make it important to let the batteries float for at least some time.

 

[marchem]

Rob, unless a charger has a shunt, it cannot "know" what the amperage going into the batteries may be. The conclusion is that they are all egg timers otherwise, and based on voltage.
The definition of "smart chargers" means, essentially, that they the three stages or phases (i.e.,m bulk, absorption & float) AND THAT'S PRETTY MUCH IT.
You could go back and read Maine Sail's excellent review of these chargers, too.
Wiring a new charger From Maine Sail:

Marine Battery Chargers - Installation Tips & Considerations
and
Installing a Marine Battery Charger - Marine How To

Stu, both the Sterling and PROMariner “Smart” chargers display amps out, so I’m guessing they have a shunt.

 

[Stu Jackson]

Stu, both the Sterling and PROMariner “Smart” chargers display amps out, so I’m guessing they have a shunt.

I went and downloaded the manual for the Sterling. There is NO (zero, zip, zilch, nada) evidence that the ammeter on the unit controls anything, and none that there is a shunt that controls anything.

 

[Stu Jackson]

The second link Stu posted has a very good section on “egg timer” charging, and does specifically call out the ProCharge Ultra as being smarter than that.

@marchem, here's what it says:

The Sterling ProCharge Ultra uses a number of factors to adjust and adapt the duration of the absorption cycle to what it believes the battery needs. In terms of charge algorithms it works pretty well. A simple explanation is that the ProCharge Ultra examines the duration spent in bulk and can then add or subtract time spent in the absorption stage. This type of algorithm is certainly smarter than a simple egg-timer. While not perfect, it does a better job at keeping the batteries healthy than do many egg-timer based chargers.


In an ideal recharge a battery charger would not drop to float voltage until the battery bank had attained the 99.5% to 100% SOC point. Almost all battery chargers out there, for marine use, drop to float before the battery bank has attained 100% SOC. While this makes them “safe“, for the manufacturers lawyers, it also means that in order to get back to 100% SOC it just takes a bit longer. At a dock this is not a huge deal, if we are getting into the mid to upper 90’s before the float transition. Once the charger drops to float this dramatically extends the time it takes to get to 100% SOC. The absorption cycle is perhaps the most important stage of charging and if it is too short, due to an egg-timer, the batteries can become chronically under charged and suffer the effects of sulfation.