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Recommended Amperage, 3x12v


TruthWalleyes

Question

I'm going to replace my 3 12v batteries today with 3 new 27ah. Batteries are currently hooked up in parallel, and will be when i put in the new 3.

My question, What size charger would you recommend. 10A, 15A, 20A? And, how many hours would it take to charge 3 12v batteries, say half drained, with said charger?

Thanks for any input.

I don't think i'm interested in an Onboard.

Also, since i'm looking at a new charger, any brand recommendations for a charger that LASTS.

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I'm wondering why you would not want an onboard charger. The convenience is a no-brainer to me. Completely automatic, you never have to worry about shutting it off or overcharging. It's always connected, just plug it in and forget it. Go to the Cabela's website and click on the Minn Kota onboard chargers. Scroll down to the chart which shows recovery time for each charger. (Yes, those are generalities. Specific times will vary by battery type, size and age). As the amps per bank increase from 5 to 15, recovery times get shorter. The Minn Kota portable chargers are only 5 amps per bank. There are other brands of portable chargers but make sure they have automatic shut-off. For onboard chargers, other brands are Dual Pro, Guest, Pro Mariner and the Cabela's line, which I think is made by Pro Mariner.

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Reason for not going to on board is cost. Today i keep my charger in the boat, hooked up and in a water tight area. Simply plug it in. If i do take it out, it takes me 3 minutes to hook up, which i have time to do. I can also use a charger with an auto-shutoff. I've heard too many horror stories with on board chargers going bad, and i've had my fair share of non-on board chargers going bad as well. I think i'd just like to avoid the expensive charger.

Also, if i were to get an on board charger for 3 batteries in parallel, why would i get more than 1 bank? If you used a 3 bank you would be charging all 3 batteries in a parallel circuit which just doesn't seem right to me.

Last charger i had go bad was minnkota, and that only took 3 months to kick the bucket on a $70 charger.

I guess the convienence difference to me is like buying bottleed water, or filling up a bottle of water. One costs more, but doesn't take that much less time.

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I'm wondering why you would not want an onboard charger. The convenience is a no-brainer to me. Completely automatic, you never have to worry about shutting it off or overcharging. It's always connected, just plug it in and forget it. Go to the Cabela's website and click on the Minn Kota onboard chargers. Scroll down to the chart which shows recovery time for each charger. (Yes, those are generalities. Specific times will vary by battery type, size and age). As the amps per bank increase from 5 to 15, recovery times get shorter. The Minn Kota portable chargers are only 5 amps per bank. There are other brands of portable chargers but make sure they have automatic shut-off. For onboard chargers, other brands are Dual Pro, Guest, Pro Mariner and the Cabela's line, which I think is made by Pro Mariner.

X2

I have AGM batteries and like them a lot, I also have the C's battery charger, 3 bank 20amp this is a nice charger. Just plug it in and not have to worry about over-charging. Much nicer to only plug in one chord and not have to worry about a portable charger and all the chords and clamps.

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My question, What size charger would you recommend. 10A, 15A, 20A? And, how many hours would it take to charge 3 12v batteries, say half drained, with said charger?

I've always been told (hearsay of course), that the slower the battery is charged, the better. So. say you had a 2/10A charger, if you dont need it right away, you're better off charging at 2A vs 10A. Smart chargers will also vary the amount going in, but I'm not sure the rates, varies with every charger as far as I'm aware.

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Quote:
I've always been told (hearsay of course), that the slower the battery is charged, the better. So. say you had a 2/10A charger, if you dont need it right away, you're better off charging at 2A vs 10A. Smart chargers will also vary the amount going in, but I'm not sure the rates, varies with every charger as far as I'm aware.

This is old school thought. I've done quite a bit of research into this and well over 80% of all the information I can find says to recharge as soon as possible and use a smart charger. A smart charger typically uses three charge modes or cycles. The first cycle delivers a constant current determined by the limits of the charger until the battery reaches about 90% of full charge. In many cases this will be about 15A. After that it goes into a second mode where it puts out a higher voltage but limits the current to a small amount until nearly fully charged. After this it goes into a maintenance mode where it maintains the battery charge.

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The time it takes to recharge a battery is dependent on the battery's state of discharge and the charger's output amperage. A 105AH battery at 50% state of charge will take approximately 3-1/2 hours to recharge using a 15A charger. The problem with normal "non-smart" chargers is that they never really obtain a complete and full recharge because they don't have the right technology to do it. They get close.

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So at the store, how do i identify a "Smart" vs Not. Are they labeled as such, or maybe "variable Charge" or something of the sort?

Thanks

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3 Batteries = 3 bank charger, using a single bank on 3 batteries will increase charge time by at least 3x, not sure the horror stories you have heard but an onboard charging system is a must in any boat I own... Mines plugged in at all times when not in use...

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So at the store, how do i identify a "Smart" vs Not. Are they labeled as such, or maybe "variable Charge" or something of the sort?

Thanks

When looking to purchase my on-board I couldn't find one that wasn't a smart charger. They indicate this in their features list.

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So at the store, how do i identify a "Smart" vs Not. Are they labeled as such, or maybe "variable Charge" or something of the sort?

Thanks

Look for "Multi-stage" charging or ones that have a Maintenance Mode. Something along those lines. I've been told that the Minn-Kota on-board chargers are linear and those types reduce battery life.

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There isn't much point to getting a 3-bank charger for a three batteries in parallel setup, unless you separate/isolate the batteries for charging. When all the batteries are in parallel the charger sees them all as one battery. So, one of the key/primary benefits of a multi-bank charger of seeing each battery individually and charging each according to its need is defeated right out of the box, so to speak (again, unless you separate them for charging, which could be done fairly simply with two switches in the negative leads between the batteries).

If your batteries are truly 27Ah then I'd probably go with 5A per battery or 15A total/parallel charge rate. That would be recharge time of theoretically 2.7 hours at 50% discharge but it takes somewhat longer, maybe 10-15%, than theoretical time to recharge.

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Thanks for the replies. I also though a 3 bank was useless with 3 batts in parallel. I'm not going to isolate them, and an 8 hour charge time i would be fine with, so i'll look for a 15amp-20amp multistage charger.

I got real busy last week with a softball tournament, and the next few days i'll be in Chicago so i'll look into a 1 bank on board next week.

THanks,.

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No need to isiolate them on a multiple bank charger just hook a set of leads to each battery....

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all the information I can find says to recharge as soon as possible and use a smart charger.

Charge as soon as possible and "charge as fast as possible are two totally different things.

Yes, charge as soon as possible, but slow as possible is still the standard, especially for deep cycle batteries.

When purchasing new batteries for my RV I did the same research and asked many of the same questions. Everything I found said get a variable amp smart charger, but find ones with an adjustable Amp setting. So, after the average trip where I won't haul it for another week or more, I can set it to 2amp trickle charge and it can slow charge it all week. If I was coming home and needed to leave the next day, then I use the 10amp setting and can replenish my 200 A/h capacity in ~20hrs.

To the OP, you said 27A/h batteries, are you talking about a Group 27 battery? Because that is not a 27ah battery, 27 is the size. It is likely rated for 60-80a/h depending on who makes it. Three Group 27's would net you 180-200 a/h of storage. At half discharge, I would want at least a 15amp for an overnight charge.

ANd I will also echo what has been said about the smart chargers. Look for something that says smart charger, maintenance or float mode etc. These will not "overcook" the battery. The model I bought is a Schumacher brand with a 2, 6, and 10amp charging. I can also choose 6v or 12v for my 6v batteries. It was $40.

Get something good cause it would suck to burn up $250 in batteries with a $25 charger.

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No need to isiolate them on a multiple bank charger just hook a set of leads to each battery....

Right. You don't have to isolate them but if you don't then all you effectively have is a one bank charger looking at one big battery. OTOH, it's tough to find a smart charger that'll do 15-20A (or more) without getting a multi-bank unit.

I have my rig set up with a three bank system. One battery for starting and low draw accessories, two batteries in parallel for trolling; fairly common in and of itself. The somewhat unique thing is the way the trolling power is set up. The two trolling batteries automatically isolate for true three bank charging when the trolling motor is unplugged. A 24V or 36V system is easier inasmuch as they're typically self-isolating by nature.

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Quote:
Yes, charge as soon as possible, but slow as possible is still the standard, especially for deep cycle batteries.

Sorry, but I must disagree with this. Based on my research of many various battery manufacturers and charger manufacturers the slow recharge is not necessrily the best. Give the batteries what they need to bring them up to 90% quickly and then the slow down begins is what my research has taught me. That's why the multi-stage smart chargers do what they do.

Besides, if you're correct then everyone that has an on-board charger has probably done their batteries a serious disservice because most, if not all, are smart chargers using the 3-step recharging process.

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Quote:
Right. You don't have to isolate them but if you don't then all you effectively have is a one bank charger looking at one big battery. OTOH, it's tough to find a smart charger that'll do 15-20A (or more) without getting a multi-bank unit.

Either way it's the same result. Batteries connected in parallel are essentially one large battery.

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One thing that needs to be clarified. At no time did I suggest a battery should be recharged “as quickly as possible.” There is a limit to the current rate that should be applied. In most cases, about 20% of the batteries AH rating will be safe and not produce too much excessive heat. For example, a 105AH battery should not be charged at more than a 20A rate or over-heating could result.

Here's some of the information from a quick search. Note these are all in regard to wet cell batteries. Gel Cell batteries require different processes.

Deep Cycle Battery FAQ from "Northern Arizona Wind & Son"

Quote:
Battery Charging

Battery charging takes place in 3 basic stages: Bulk, Absorption, and Float.

Bulk Charge - The first stage of 3-stage battery charging. Current is sent to batteries at the maximum safe rate they will accept until voltage rises to near (80-90%) full charge level. Voltages at this stage typically range from 10.5 volts to 15 volts. There is no "correct" voltage for bulk charging, but there may be limits on the maximum current that the battery and/or wiring can take.

Absorption Charge: The 2nd stage of 3-stage battery charging. Voltage remains constant and current gradually tapers off as internal resistance increases during charging. It is during this stage that the charger puts out maximum voltage. Voltages at this stage are typically around 14.2 to 15.5 volts. (The internal resistance gradually goes up because there is less and less to be converted back to normal full charge).

Float Charge: The 3rd stage of 3-stage battery charging. After batteries reach full charge, charging voltage is reduced to a lower level (typically 12.8 to 13.2) to reduce gassing and prolong battery life. This is often referred to as a maintenance or trickle charge, since it's main purpose is to keep an already charged battery from discharging. PWM, or "pulse width modulation" accomplishes the same thing. In PWM, the controller or charger senses tiny voltage drops in the battery and sends very short charging cycles (pulses) to the battery. This may occur several hundred times per minute. It is called "pulse width" because the width of the pulses may vary from a few microseconds to several seconds. Note that for long term float service, such as backup power systems that are seldom discharged, the float voltage should be around 13.02 to 13.20 volts.

Chargers: Most garage and consumer (automotive) type battery chargers are bulk charge only, and have little (if any) voltage regulation. They are fine for a quick boost to low batteries, but not to leave on for long periods. Among the regulated chargers, there are the voltage regulated ones, such as Iota Engineering, PowerMax, and others, which keep a constant regulated voltage on the batteries. If these are set to the correct voltages for your batteries, they will keep the batteries charged without damage. These are sometimes called "taper charge" - as if that is a selling point. What taper charge really means is that as the battery gets charged up, the voltage goes up, so the amps out of the charger goes down. They charge OK, but a charger rated at 20 amps may only be supplying 5 amps when the batteries are 80% charged. To get around this, Xantrex (and maybe others?) have come out with "smart", or multi-stage chargers. These use a variable voltage to keep the charging amps much more constant for faster charging.

Deep Cycle Battery FAQ’s from Marine Electronics dot net.

Quote:
6. HOW DO I RECHARGE (OR EQUALIZE) MY BATTERY?

There are up to four phases of battery charging: bulk, absorption, equalization and float. The bulk stage is where the charger current is constant and the battery voltage increases. You can give the battery whatever current it will accept not to exceed 20% of the ampere-hour rating and this will not cause overheating. The absorption phase is where the charger voltage is constant and current decreases until the battery is fully charged. This normally occurs when the charging current drops off to 1% or less of the ampere-hour capacity of the battery. For example, the ending current for a 100 ampere-hour battery is 1.0 amp or less.

The optional equalizing phase is a controlled 5% overcharge, which equalizes and balances the voltage and specific gravity in each cell, the effect of increasing the charge voltage. Equalizing reverses the build-up of chemical effects like stratification, where acid concentration is greater in the bottom of the battery. It also helps remove sulfate crystals that might have built up on the plates. The frequency recommendation varies by manufacturer from once a month to once a year, from 10 to 100 deep cycles, or when a specific gravity difference between cells reaches .03 (or 30 points). To equalize, fully recharge the battery; next, increase the charging voltage to the manufacturer's recommendations (if you cannot find one, add 5%). Heavy gassing should start occurring (be very cardeful about safety precautions). Take specific gravity readings in each cell once per hour. Equalization has occurred once the specific gravity values no longer rise during the gassing stage.

The optional float phase is where the charge voltage is reduced, held constant and used indefinitely to maintain a fully charged battery. Please refer to Section 9 for more information about storing batteries and float charging them. An excellent and easy to understand tutorial on battery charging basics can be found at http://www.batterytender.com/index2.html by drilling down through Charging Tutorials & Charging Basics. The following are multi-stage charging algorithms from Deltran (Battery Tender) for three different types of deep cycle batteries:

From The Battery Equilizer, Inc.

Quote:
Battery Charging

Battery charging, remember you must put back the energy you use immediately, if you don't the battery sulfates and that affects performance and longevity. The alternator is a battery charger; it works well if the battery is not deeply discharged. The alternator tends to overcharge batteries that are very low and the overcharge can damage batteries. In fact an engine starting battery on average has only about 10 deep cycles available when recharged by an alternator. Batteries like to be charged in a certain way, especially when they have been deeply discharged. This type of charging is called 3 step regulated charging. Please note that only special SMART CHARGERS using computer technology can perform 3 steps charging techniques. You don't find these types of chargers in parts stores and Wal-Marts. The first step is bulk charging where up to 80% of the battery energy capacity is replaced by the charger at the maximum voltage and current amp rating of the charger. When the battery voltage reaches 14.4 volts this begins the absorption charge step. This is where the voltage is held at a constant 14.4 volts and the current (amps) decline until the battery is 98% charged. Next comes the Float Step, this is a regulated voltage of not more than 13.4 volts and usually less than 1 amp of current. This in time will bring the battery to 100% charged or close to it. The float charge will not boil or heat batteries but will maintain the batteries at 100% readiness and prevent cycling during long term inactivity. Some AGM batteries may require special settings or chargers. Battery Charging

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Either way it's the same result. Batteries connected in parallel are essentially one large battery.

Not sure what you mean by "either way". We are in 100% agreement that batteries in parallel are effectively one larger battery. But, that's the problem...

If the batteries can be isolated for charging then each will be charged according to its unique need with a multi-bank charger. If they're not isolated, meaning still connected in parallel for charging, the ability for the multi-bank charger to sense each battery individually and charge each accordingly is lost (more like wasted).

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Maybe I'm misunderstanding what you mean by isolated. I was thinking perhaps leaving them connected in parallel and connecting a three bank charger to each battery. Technically, I would be incorrect in that assumption because they would not really be isolated. My mistake.

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By isolated I meant break the connection(s) between the batteries that are in parallel, so they're no longer in parallel (for charging). Isolated might be a bad choice of word but I couldn't think of anything else to describe having each battery separate from the others for charging.

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Check out the B&D smart chargers 6/10/25 amp charge.Set at 25 A it will only give the charge the battery needs.Excellent charger!! It works better and faster than my Promariner 2 bank @6A per.

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By isolated I meant break the connection(s) between the batteries that are in parallel, so they're no longer in parallel (for charging). Isolated might be a bad choice of word but I couldn't think of anything else to describe having each battery separate from the others for charging.

No, you got it right. I was wrong.

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Alright a few more clarifications...Thanks.

Yes Group 27, i was mistaken by calling them 27ah.

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Well i picked up 3 Interstate group 27's.

After doing some research into on board chargers, i'd have to separate the 3 batteries from parallel and go with a 3 bank. I have not found a 1 bank charger that delivers 15-20amps.

I'll probably go pick up a black and decker smart charger as recommended above as i do not want to isolate the batteries. Also, 3 brand new batteries should all drain equally when always hooked up in parallel, so each battery really shouldn't require different recharge times.

My only concern with the B&D is that it will not charge if batteries are drained too far. I will run them batteries to absolute dead if necessary (long weekend trip or something of the like) and i'm wondering if a new battery could fault this charger, or if it only "Faults" when your batteries need replacing?

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Running the batteries to dead is VERY VERY hard on them. Actually, below 50% even shortens their life quite a bit.

The automatic battery chargers I've used won't start the cycle with deeply discharged or completely dead batteries. I have an old manual charger to bring them up a bit in that rare occasion.

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I hear ya on running them dead. I guess i'll use them as much as i want and if they go dead while on the water for 3 days then so be it...GOt a good deal on them interstates anyway.

I'm more concerned with the level at which the smart charger won't charge. Is it 25%, more or less? I didn't see it on the outside of the box, but will have to read instructions tonight to see if it specifies.

Dang it's warm today!

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This is a Raider charger 12/8/2 smart. $40. Nice small package. I may even install as an on board. I found it at FF, not what i was looking for but the price was right. We'll see if it lasts.

Manual says that if the charger goes into float stage (The final charging stage where battery is maintained)and a voltage of 13V is not achieved. The charger will recondition the battery. After reconditioning the battery, if a voltage of 10V is not achieved through 5 charging cycles then the battery charger will say replace battery...

So long story short. Anything that doesn't charge above 10v is a dead battery to the charger...That is one dead battery if it can't be charged up to 10V!!

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