Optimal Charging Regimen - Wet Cells

[akio.kanemoto]

Greetings Folks,

I've been searching the archives for the past hour trying to find this, to no avail: I remember having read something about the optimal "range" which full-time-cruisers use to maintain their batteries, but can't seem to find it. From memory it was something like "discharge to 50%, charge to 80% and do a full charge once per month" or something.

I have a 675Ah bank (6 x 6V T-105) and 250A of charging capacity off the engine/alternators, a Honda, and a small solar panel. No shore power.

I've been going from about 75% of capacity to about 87% capacity and start charging at 250A for a minute, then 150A for a bit, then rapidly taper down to 60A or so as I approach 85%. So it means that in one hour of charging, I get about 80Ah back (which seems very low compared to my charging capacity).

I was sure there was an optimal regimen I read ages ago which balanced charge time against cycle life?

Thank you!

[btrayfors]

Akio,

Good questions. You have exactly the same setup I have with six T-105's for my house bank.

What I believe you're getting at is charging efficiency, i.e., the percentage of applied current to the batteries which is actually converted into stored energy.

While there is pretty good data for AGMs and gels, real data for flooded batteries is a bit harder to find. The best data I know of comes from a study done by Sandia National Laboratories a few years ago, using a single Trojan flooded battery. They were specifically examining charging efficiency at the upper end of the state-of-charge (SOC). What they found and what they reported is interesting, if incomplete and based on a very small sample.

Basically, they found that at the upper end of the charging cycle, say 85% and above, charging efficiency falls way below 50%. That means that over half of the applied amperage is wasted in heat. Also, as SOC rises, the batteries will accept much less amperage, so you lose out in at least two ways :-)

Lesson: those who keep their batteries nearly topped off and operate at very high SOC (like between 90-95 or 97%) are wasting a lot of charging current in the form of heat.

Most cruising boats tend to cycle between about 50% and 80% SOC. In this range, you're not hurting the batteries by discharging below 50%, you have reasonable charging efficiency so you're not wasting more power than you need to, and you're not running the engine or generator forever trying to get the batteries up to near 100% SOC.

The downside of that plan is that all lead-acid batteries, most particularly AGMs but also gels and flooded, need to reach a full charge periodically to avoid sulfation of the plates and premature loss of capacity. There's no hard and fast rule about how often this should be, but in my experience and research I believe it should be once a week or more frequently whenever possible.

Thus the occasional overnite at a marina plugged into shore power is a good thing, as is powering for a long distance. And, it's why wind generators or sizeable solar panels are a very good idea as part of the charging complement, since if sized correctly these will be able to get the batteries to a high SOC fairly often.

Hope this helps a bit.

Bill

[akio.kanemoto]

Hi Bill,

Thank you very much for the reply!

Based on our current usage pattern (we're not on the move yet, so no instruments etc) - we use about 25-30Ah/day - which is basically the fridge, lighting (100% LED) and stereo - so to get down to 50%, we're talking almost 2 weeks. I expect that when we're more "active", we should be getting up to about 70-80Ah/day.

I've been planning for an engine based charge cycle of once per 3-4 days (and this will actually nicely line up with our water usage - i.e. we NEED more water every 4 days - small tank!) - so I will be making water at the same time as charging.

But I really don't think I will be able to do a full charge once per week. There is always a small "trickle" charge from the solar panel though.

Do you think by limiting the discharge to say 60% and going from 60-80%, istead of 50-80% and then fully charging monthly (I can buy a charger and can run the Honda for a while on "full charge day"...) - I am limiting sulfation or do I really need the full charge weekly?

Also - what are your thoughts on equalization? Monthly/Quarterly? Ever?

Thank you very much again!

Originally Posted by btrayfors

Akio,

Good questions. You have exactly the same setup I have with six T-105's for my house bank.

What I believe you're getting at is charging efficiency, i.e., the percentage of applied current to the batteries which is actually converted into stored energy.

While there is pretty good data for AGMs and gels, real data for flooded batteries is a bit harder to find. The best data I know of comes from a study done by Sandia National Laboratories a few years ago, using a single Trojan flooded battery. They were specifically examining charging efficiency at the upper end of the state-of-charge (SOC). What they found and what they reported is interesting, if incomplete and based on a very small sample.

Basically, they found that at the upper end of the charging cycle, say 85% and above, charging efficiency falls way below 50%. That means that over half of the applied amperage is wasted in heat. Also, as SOC rises, the batteries will accept much less amperage, so you lose out in at least two ways :-)

Lesson: those who keep their batteries nearly topped off and operate at very high SOC (like between 90-95 or 97%) are wasting a lot of charging current in the form of heat.

Most cruising boats tend to cycle between about 50% and 80% SOC. In this range, you're not hurting the batteries by discharging below 50%, you have reasonable charging efficiency so you're not wasting more power than you need to, and you're not running the engine or generator forever trying to get the batteries up to near 100% SOC.

The downside of that plan is that all lead-acid batteries, most particularly AGMs but also gels and flooded, need to reach a full charge periodically to avoid sulfation of the plates and premature loss of capacity. There's no hard and fast rule about how often this should be, but in my experience and research I believe it should be once a week or more frequently whenever possible.

Thus the occasional overnite at a marina plugged into shore power is a good thing, as is powering for a long distance. And, it's why wind generators or sizeable solar panels are a very good idea as part of the charging complement, since if sized correctly these will be able to get the batteries to a high SOC fairly often.

Hope this helps a bit.

Bill

[colemj]

Originally Posted by akio.kanemoto

Based on our current usage pattern (we're not on the move yet, so no instruments etc) - we use about 25-30Ah/day - which is basically the fridge, lighting (100% LED) and stereo

Wow! It is either cold where you are and/or you have a fantastically insulated fridge and/or a very small one and/or not being used much. That is a low number of daily Ah usage. I suspect you will get up to 100-125 Ah/day once out cruising. If you do get away with using only 70-80 Ah/day, you will be a very energy efficient/miser boat indeed!

Mark

[Billy Higgins]

Bill (btrayfors) has provided a very nice summary of the issues. The topic of charging is both outwardly simple, and yet very complex to get exactly right on all facets, including motor life. Unless you are powering for long durations, further research will reveal that using your main plant to charge to over 90% SOC is the most wasteful practice you can imagine.

I recommend the following two sources:
1. There is a very good section on charging protocols at the Morgans Cloud web site - www.morganscloud.com
2. Nigel Calder's great book on systems is another widely recommended source - 'Boat Owners Mechanical and Electrical Manual'.

[btrayfors]

I agree with the comment about your daily usage, i.e., when you become an active cruiser you're more likely to have a daily consumption in excess of 100AH.

Re: getting a full charge, it's kind of Catch 22. Understand this: even if you were plugged into shore power and floating your T-105's at 13.2-13.6VDC 24/7, slow sulfation of the plates would still occur.

I've found it beneficial to do a "repeat absorption" cycle every other day, kicking the voltage up to 14.8-15.0VDC for about 30 minutes.

These figures are strictly arbitrary...I chose them to try out with my 5-year old T-105 house batteries after observing the gradual sulfation and loss of capacity in three banks of T-105s kept at float level 24/7. Thankfully, I have a Victron Multi which is programmable to do this automatically. There was a marked improvement after a few months of this regime, vs. just leaving the float voltage for long periods. My five-year old T-105's recovered capacity and tested like new after a few months, and repeated tests for the following year showed this to be a real improvement not an imagined one.

The fact that you'll be exercising the batteries while cruising -- drawing them down and charging them up as well as moving them about in the wave action and sailing -- will help things, because the absorption voltage will be 14.4VDC or more (I recommend 14.8VDC for the Trojans).

However, I do believe that equalization can make a difference and should be done periodically, though not frequently as each time you do it you run the risk of damaging the plates a little.

With proper care you should get 5-7 years good service from the T-105s.

Is once-a-month charging to 100% enough? No, I don't think so. In your stead, I'd seriously consider adding a larger solar capability which could help you achieve high SOC numbers more frequently.

Bill

[akio.kanemoto]

Originally Posted by Billy Higgins

Bill (btrayfors) has provided a very nice summary of the issues. The topic of charging is both outwardly simple, and yet very complex to get exactly right on all facets, including motor life. Unless you are powering for long durations, further research will reveal that using your main plant to charge to over 90% SOC is the most wasteful practice you can imagine.

I recommend the following two sources:
1. There is a very good section on charging protocols at the Morgans Cloud web site - www.morganscloud.com
2. Nigel Calder's great book on systems is another widely recommended source - 'Boat Owners Mechanical and Electrical Manual'.

Thank you for the link - some very interesting reading there!

Originally Posted by btrayfors

I agree with the comment about your daily usage, i.e., when you become an active cruiser you're more likely to have a daily consumption in excess of 100AH.

Re: getting a full charge, it's kind of Catch 22. Understand this: even if you were plugged into shore power and floating your T-105's at 13.2-13.6VDC 24/7, slow sulfation of the plates would still occur.

I've found it beneficial to do a "repeat absorption" cycle every other day, kicking the voltage up to 14.8-15.0VDC for about 30 minutes.

These figures are strictly arbitrary...I chose them to try out with my 5-year old T-105 house batteries after observing the gradual sulfation and loss of capacity in three banks of T-105s kept at float level 24/7. Thankfully, I have a Victron Multi which is programmable to do this automatically. There was a marked improvement after a few months of this regime, vs. just leaving the float voltage for long periods. My five-year old T-105's recovered capacity and tested like new after a few months, and repeated tests for the following year showed this to be a real improvement not an imagined one.

The fact that you'll be exercising the batteries while cruising -- drawing them down and charging them up as well as moving them about in the wave action and sailing -- will help things, because the absorption voltage will be 14.4VDC or more (I recommend 14.8VDC for the Trojans).

However, I do believe that equalization can make a difference and should be done periodically, though not frequently as each time you do it you run the risk of damaging the plates a little.

With proper care you should get 5-7 years good service from the T-105s.

Is once-a-month charging to 100% enough? No, I don't think so. In your stead, I'd seriously consider adding a larger solar capability which could help you achieve high SOC numbers more frequently.

Bill

OK, I'm a believer now, so have started looking for a charger to use with my Honda (2kw).

I was initially looking for an Iota DLS-75 per your suggestion in another thread, but it appears to be only 110VAC... the 240VAC version only goes up to 55A.

Ideally, I'm looking for a 100A charger with a current limiting feature (so I can dial it back incase the Honda can't handle it), or a straight 75A (minimum) charger... with an equalization function.

I've looked at Victron Centaur, but it doesn't do equalization, and the Phoenix is also an inverter and too expensive. Mastervolt's MasterCharge 12/100 looks like it will do the trick, but is just a tad too wide for the space I have.

Any thoughts on a not-too-large charger which fits the bill?

Also - on installation location - I'm assuming that during equalization, one has to disconnect the house circuit to avoid frying equipment right?

Thank you again!

[akio.kanemoto]

Originally Posted by colemj

Wow! It is either cold where you are and/or you have a fantastically insulated fridge and/or a very small one and/or not being used much. That is a low number of daily Ah usage. I suspect you will get up to 100-125 Ah/day once out cruising. If you do get away with using only 70-80 Ah/day, you will be a very energy efficient/miser boat indeed!

Mark

Actually there's a story behind the fridge... it's quite large, but the bottom is something like 12" insulation (purely due to hull geometry, wasn't intentional!), the side wall (hull side) is again stupid.. around 12" and the other 2 remaining walls are about 4.5".

The lid however is a miserable 2.5", and is currently undergoing surgery to bring it up to 4.5".

[btrayfors]

Originally Posted by akio.kanemoto

......

Ideally, I'm looking for a 100A charger with a current limiting feature (so I can dial it back incase the Honda can't handle it), or a straight 75A (minimum) charger... with an equalization function.

I've looked at Victron Centaur, but it doesn't do equalization, and the Phoenix is also an inverter and too expensive. Mastervolt's MasterCharge 12/100 looks like it will do the trick, but is just a tad too wide for the space I have.

Any thoughts on a not-too-large charger which fits the bill?

Also - on installation location - I'm assuming that during equalization, one has to disconnect the house circuit to avoid frying equipment right?

Thank you again!

Sterling makes an excellent very smart charger which has been winning rewards and turning heads. Unfortunately, the largest in the series is 60A. But, it's power-factor corrected and will easily run on Honda EU2000i and will leave you enough slack to run other things simultaneously. It can work off 240VAC or 120VAC 50 or 60 cycles, and has a host of very useful features, including equalization. A bit pricey, but probably well worth it.
ProMariner has a similar line of chargers which appear to be Sterlings that have been re-branded.

MaineSail has done an excellent how-to series on installing a new battery charger, featuring one of the Sterling chargers. I think it's on SailNet.

Yes, during equalization you have to be careful of what you leave on, since 15.5-16.5V is enough to fry some stuff. Many things, though, will not be harmed by this voltage...you have to examine each piece of gear/equipment to be sure.

Bill

[s/v Jedi]

Originally Posted by btrayfors

Sterling makes an excellent very smart charger which has been winning rewards and turning heads. Unfortunately, the largest in the series is 60A. But, it's power-factor corrected and will easily run on Honda EU2000i and will leave you enough slack to run other things simultaneously. It can work off 240VAC or 120VAC 50 or 60 cycles, and has a host of very useful features, including equalization. A bit pricey, but probably well worth it.
ProMariner has a similar line of chargers which appear to be Sterlings that have been re-branded.

MaineSail has done an excellent how-to series on installing a new battery charger, featuring one of the Sterling chargers. I think it's on SailNet.

Yes, during equalization you have to be careful of what you leave on, since 15.5-16.5V is enough to fry some stuff. Many things, though, will not be harmed by this voltage...you have to examine each piece of gear/equipment to be sure.

Bill

In addition to this excelent advice: it is not a problem to use "just" a 60A charger because it will mostly be used for that last 15-20% of battery capacity, where the charge current will be way down anyway. Only when used for bulk charge fom 50% SOC up, a bigger charger makes sense.

ciao!
Nick.

[akio.kanemoto]

Originally Posted by s/v Jedi

In addition to this excelent advice: it is not a problem to use "just" a 60A charger because it will mostly be used for that last 15-20% of battery capacity, where the charge current will be way down anyway. Only when used for bulk charge fom 50% SOC up, a bigger charger makes sense.

ciao!
Nick.

I was just thinking in terms of efficiency and options down the road. I have 250A charging capacity on the engine, but understand the wear/tear associated and the lifecycle cost of an engine is WAY higher than a "disposable" Honda...

I don't have enough experience yet, but maybe the balance between "normal" charge cycles, the requirement for watermaking, "full" charges may dictate more usage of the Honda - so the more capacity the better... ?

Or maybe something like -

Every 3-4 days, charge to 80% with the engine (until it drops to ~80A).

Every 6-8 days (second charge cycle), charge to 80% with the engine (again until down to 80A) then charge with the Honda to 100%.

Every 5th to 6th charge cycle, equalize with the Honda...

?

Hmmm....

[akio.kanemoto]

Originally Posted by btrayfors

Sterling makes an excellent very smart charger which has been winning rewards and turning heads. Unfortunately, the largest in the series is 60A. But, it's power-factor corrected and will easily run on Honda EU2000i and will leave you enough slack to run other things simultaneously. It can work off 240VAC or 120VAC 50 or 60 cycles, and has a host of very useful features, including equalization. A bit pricey, but probably well worth it.
ProMariner has a similar line of chargers which appear to be Sterlings that have been re-branded.

MaineSail has done an excellent how-to series on installing a new battery charger, featuring one of the Sterling chargers. I think it's on SailNet.

Yes, during equalization you have to be careful of what you leave on, since 15.5-16.5V is enough to fry some stuff. Many things, though, will not be harmed by this voltage...you have to examine each piece of gear/equipment to be sure.

Bill

I was actually looking at the rebadged 60A one a littler earlier - I believe it's called the "Pronautic 1260". Nice form factor too. Only thing is that to start equalization, you need to remove the lid and fiddle a bit.

Do you have any thoughts on the Xantrex Truecharge2 60A unit? This is smaller (easier to fit) and appears to have an easier to use interface.

[s/v Jedi]

Originally Posted by akio.kanemoto

I was actually looking at the rebadged 60A one a littler earlier - I believe it's called the "Pronautic 1260". Nice form factor too. Only thing is that to start equalization, you need to remove the lid and fiddle a bit.

Do you have any thoughts on the Xantrex Truecharge2 60A unit? This is smaller (easier to fit) and appears to have an easier to use interface.

Nooooooooooo....... not the "X" !

Nick.

[btrayfors]

I would steer clear of Xantrex-anything (except the EchoCharge). There are much better choices and there is much better after-sale support from other manufacturers.

I think you are misjudging the rapidity with which you can recharge those six T-105s. A battery under charge will accept only so much amperage at any given voltage, regardless of the size of the charger or alternator.

Those 675AH total batteries are only going to accept between 20-25% of their capacity (135-169 amps) maximum, and that's only when they are in the bulk charging phase with a significantly discharged battery bank. And, they'll only do this for a few minutes, after which they'll cut back to around 12-15% (80-100 amps).

Charge efficiency of T-105's at 50% SOC is somewhere between 80-90%, judging from the above-referenced study and from my own observations over many years. That is to say, although you may have a huge alternator on the engine, it's NEVER going to use anywhere near the 250A capacity...at least not for more than a few seconds.

Given your 675AH battery bank discharged to 50% SOC, then, is 100A or 125A charge capacity better than 60A? Yes, indeed, it is. When my battery bank is down to about 50% SOC, I see my 100A Balmar alternator with Balmar MC-612 regulator putting out 80A for long periods of time, until the SOC reaches a level where the batteries won't accept 80A any longer. Then, it ramps down progressively until the final stages are reached at about 10A.

However, as earlier noted, once you're operating in the higher SOC range -- say, above 80-85% SOC -- the batteries won't accept much amperage at the recommended absorption voltage of 14.6-14.8VDC AND something less than 50% of the amps supplied to the batteries are going to be lost in heat anyway.

No way around it. Physics, chemistry, and Ohms Law at play here, with Peukert fiddling in the background :-)

Bill

[akio.kanemoto]

Originally Posted by s/v Jedi

Nooooooooooo....... not the "X" !

Nick.

That bad?