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Old 08-05-2013, 04:35   #16
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Re: battery charger mode explanation

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Originally Posted by noelex 77 View Post
OK I think we are agreed that a current set point will tend to overcharge the batteries on its own when a load is present.

I am still puzzled why you think a timed absorption phase will always undercharge the batteries with a load.
Even the cheap chargers operate the absorption countdown only when the battery is at the absorption voltage.
Normally the load will have no impact.
If the load is higher than the battery charger can put out and the battery return voltage is not reached it will result in slight undercharging. In the much more common situation where the load is less than the output of the battery charger, or the voltage drops down to the battery return voltage, it will result in overcharging.

This is why an adjustable absorption time is beneficial.

Where the battery charger cannot sustain the load and a charging current, obviously the charger cannot sustain its output voltage. where the charger is capable of sustaining the load, and charging the battery,, then the only thing that terminates absorption mode, is the timer. Since manufactures have to design for the safest situation, Inevitably they have to set it short ,hence in a load sharing most of the absorption mode current is being diverted to the load, unbeknownst to the charger , hence (a) The low current nevers trips (b) the timer does (c) the Battery has most likely only received a partial absorption charge due to lower current and hence (d) its undercharged

This is easily demonstrated by doing SG tests, I have done so on my Mastervolt chargers and I know that in a load sharing situation, the lights on the charger indication the charge state are very misleading and the SG indicates a lower charged battery then it indicates, Full charging tends to happen only when the boat is shut down and hence the load current falls away to close to zero.

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Old 08-05-2013, 04:50   #17
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Re: battery charger mode explanation

Dave I think you you are misunderstanding how the absorption timer works.
Even on cheap battery chargers it will only count down when the battery is at the absorption voltage.

If a load reduces the voltage below the absorption voltage the timer stops. If the battery charger has got a higher output than the load the battery is still being charged even though the timer is stopped. The battery will receive more amp hours before the timer runs out and the absorption phase is terminated.

If the load is greater than battery charger output but not high enough to take the battery to the battery return voltage the battery will be discharged with a stopped timer. This is an uncommon and narrow range of loads. Not many loads are higher than the battery charger output. Very high loads even for a short time will trip the battery return voltage zeroing the counter and restarting the clock, which once again will tend to overcharge the battery.

More batteries die from undercharging than overcharging but it is important to understand how the various factors work in an effort to select the most appropriate parameters for the charging algorithm (if they are adjustable, which hopefully they are). Absorption time is one of the most misunderstood parameters.
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Old 08-05-2013, 05:05   #18
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Re: battery charger mode explanation

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If a load reduces the voltage below the absorption voltage the timer stops. If the battery charger has got a higher output than the load the battery is still being charged even though the timer is stopped. The battery will receive more amp hours before the timer runs out and the absorption phase is terminated.
I was covering the situation where the absorption mode voltage is maintained. ( ie the common one ) yet there is load sharing. The charger beleives it is in absorption mode, yet the set point low current is never achieved, Hence absorption times out on the safety timer

Since the safety timer is designed to handle a wide range of batteries, it is typically set at quite low values, as a manufacturer is happy with an undercharged battery not one that overcharges.

Hence load sharing causes undercharging because the charger cannot determine the absorption current and hence its period.

Some chargers use a di/dt algorithm but its not much better.

IN a proper design , like in many electronics 'power path' charging, the battery current and load current are measured separately, this should really be done on boats.



Quote:
If the battery charger has got a higher output than the load the battery is still being charged even though the timer is stopped.
if teh battery charger drops below absorption voltage due to teh load, yes the timer stops, but the battery isnt now in absorption mode and hence will not overcharge ( battery acceptance remember)


In situations where the battery is repeatedly brought in an out of absorption mode by load sharing , you have to implement some clever strategies, Victron do this as does Mastervolt to a greater or lessor extent)

The key feature that a charger design whats to ensure is not to overcharge, and therefore it will err on the side of undercharging.

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Old 08-05-2013, 05:45   #19
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Re: battery charger mode explanation

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if teh battery charger drops below absorption voltage due to teh load, yes the timer stops, but the battery isnt now in absorption mode and hence will not overcharge ( battery acceptance remember)
Lets me use a simple example to show where the load will always charge the battery more (using a timed absorption phase) providing the load does not exceed the output of the battery charger.

The battery is held at the absorption voltage of say 14.4v with an hour left to run on the absorption timer.
We turn on a load for an hour that drops the battery voltage below 14.4v .
The timer will stop. The battery will still receive charge. If the voltage is close to absorption voltage say 14.3v it will receive a lot of charge, almost as much as would if was in the absorption phase. If the voltage is lower it will receive less charge, but providing the output of the battery charger is higher than the load it will be a net charge.
At the end of the hour we turn off the load and the battery charger will keep the voltage at 14.4v for another hour despite the extra charge it received while the load was on.
The battery will be in a higher state of charge at the finish of the absorption phase.

In the worst case when the voltage under load is only just below the absorption voltage the charging is close to what we would have achieved if we had extended the absorption time for an hour.


I agree most battery charger default value are a little low. It is frequently possible to adopt a more aggressive charging pattern. This can be especially beneficial for boats that use a generator. However it is important to understand the interaction of various factors.
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Old 08-05-2013, 13:20   #20
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Re: battery charger mode explanation

Lots of theory and lots of ifs and buts and maybes - but the easiest thing to do every time the charger/regulator drops to float is to force it back into absorption mode and see what the charge current is. If it is 0.5% of the battery capacity then the bank is fully charged. So a 400 Ah bank will have a charge current going into the bank of 2 amps at or near the absorption voltage, not at the float voltage.

If the battery is accepting a higher current when switched back to absorption then some adjustments to the absorption time can be made until this is always close to the 100% value. Some regulators will have other parameters that can also be changed to make sure the drop to float happens at the right time - not too early or too late. The only guaranteed way to get this to happen accurately all the time is with a controller that measures the return amps to the battery. Some expensive solar controllers will do this - and function as a battery monitor.

Switching the shorepower off/on is easy. The alternator can be reset just by cutting the power to the engine by turning the ignition off/on. Solar regulators can be reset by removing the fuse - or having a switch just to be able to reset them. Solar are the ones likely to cause the most problems because of the relatively low charge currents in most cases - compared to the shorepower and alternator.

The point to realize here is that when a charger/regulator says "FLOAT" don't assume the bank is 100% charged.
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Old 08-05-2013, 13:40   #21
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Re: battery charger mode explanation

It is difficult/impossible to achieve 100% charge in the absorption phase.

Termination of the the absorption phase is nominally at 2%. This can be reduced, especially for new batteries. 1 to 1.5% is commonly used.

0.5% is very aggressive. In some situations, especially with wet cell batteries where the water can be frequently replaced it can be appropriate, but it should be used with caution.

There is a considerable loss of charge efficiency with these very aggressive settings and a lot of the amp hours is converted into heating the battery, rather than charging it.

The reality is that a lead acid battery requires a long charging time to achieve 100% charge. A very aggressive absorption charge will reduce the amp hour counter to zero quickly, but some of this energy will go to heating the battery and boling the water out, so the real charge level will be lower than displayed.
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Old 08-05-2013, 14:59   #22
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Re: battery charger mode explanation

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Lots of theory and lots of ifs and buts and maybes - but the easiest thing to do every time the charger/regulator drops to float is to force it back into absorption mode and see what the charge current is. If it is 0.5% of the battery capacity then the bank is fully charged. So a 400 Ah bank will have a charge current going into the bank of 2 amps at or near the absorption voltage, not at the float voltage.

If the battery is accepting a higher current when switched back to absorption then some adjustments to the absorption time can be made until this is always close to the 100% value. Some regulators will have other parameters that can also be changed to make sure the drop to float happens at the right time - not too early or too late. The only guaranteed way to get this to happen accurately all the time is with a controller that measures the return amps to the battery. Some expensive solar controllers will do this - and function as a battery monitor.

Switching the shorepower off/on is easy. The alternator can be reset just by cutting the power to the engine by turning the ignition off/on. Solar regulators can be reset by removing the fuse - or having a switch just to be able to reset them. Solar are the ones likely to cause the most problems because of the relatively low charge currents in most cases - compared to the shorepower and alternator.

The point to realize here is that when a charger/regulator says "FLOAT" don't assume the bank is 100% charged.
Spot on. The vast majority of shore chargers I come across undercharge the batteries because they go into float far to early. It is a rare situation where the loads keep it bouncing in and out of absorption and if that is the case the charger was really sized incorrectly to account for use as a power pack / charger...

In the shop I use a DC switch mode power supply with adjustable voltage and current. I can leave a battery charging at float for many days then bump the voltage to 14.6V and it still takes a while to "charge" and drop the acceptance down into the sub .5% range.. Conversely if I leave it at 14.6V to 14.8V until the current drops to .5% the battery is truly chuck full....

I have my "yard battery" a battery I lug around connected to an inverter when working on vessels without shore power or close enough to an extension cord. I use it for my power tools, shop vac and heat gun. This battery has been BEAT ON... I have no clue how deep I discharge, don't really care, but many days after 8 hours of work my inverter is shutting off on low voltage just with the Dremel. I charge this battery every time I bring it back to the shop at 14.8V and quite often I forget and leave it on over night or sometimes for two or three days. I simply add some water if it needs it. This battery was 4 years old when I began using it and today is is 7 years old.. I don't think I have ever "float" charged it, just 14.8V every time I charge it. I charge to .5% - 1% acceptance then I terminate the charge. Full enough for what I need.

I the shop I charge and equalize manually and my human timer works pretty well. I also have a wall timer because I tend to know how long it will take with certain batteries so I set it and walk away when the timer shuts off the batteries are usually 100% full... Occasionally they are not so I flip it back on.

None of the numerous marine or auto chargers I have in the shop will get the battery as full as fast and some take two or three cycles to do so because the pop into float too early.

The idea that a little bit of excess time at absorption voltages will kill batteries is one I never really understood. We have millions of cars, trucks buses and tractors driving around at 14.2 - 14.6V for hundreds & thousands of hours/miles.

The boat we currently own is a good case study. She was cruised 24/7 for five straight years with only an 80 watt solar panel / charge controller, and the stock 50 amp Mitsubishi alternator with no smart regulation. Banks were charged combined via a Yandina automatic combining relay (ACR/VSR).

The batteries were not fancy. They were Wal-Mart / Johnson Controls group 29/31 deep cycles installed new at the beginning of the cruise. Norm, a retired electrical engineer, & his wife, lived & sailed comfortably, away from dock power, from Labrador to South America and through the canal to Alaska and back all with no smart regulation, just a single voltage alternator, and a "small" by today's standards alt and bank. Throughout this five year 24/7 cruise time period they logged over 2700 engine hours of charging time at the dreaded non-float voltage of 14.4V (+/-.1V).

If you figure that the average coastal cruiser might do 100 hours per year this represents 27 years worth of charge time with dumb regulation set to 14.4 Volts. The last three vehicles we've owned, charged at 14.2-14.6 for many, many years (all into the 6 figures mileage wise on the original factory batteries). My wife's 03 Honda Pilot had 151k on the original factory battery before we traded it, and the alt put out 14.4 volts all day long..

When we bought our boat from Norm the cheap Wal*Mart deep cycle trolling batts and stock 50 amp alt were still plugging along despite being used about 325 days per year more, over 5 years, than the average coastal cruiser does.

When we bought the boat the batts were in year six of hard use , andtired, so I replaced them. I retired the hardly ever cycled start battery to starting my brothers Mako which it did until last summer, which made it over 10 years old. Not bad for a battery charged for 2700 hours at 14.4V...

Up until last summer we still had that same stock alternator with no smart regulation and that replacement bank is still going very, very strong. It is in my barn only because I wanted to experiment with LiFePO4. That bank did 7 years at 14.4V + solar.


Even if you did get into a situation where the charger was held a few tenths below absorption it is probably not a big deal. Chronic under charging is what I see a lot more often than over charging... When I see over charging I am usually seeing an unregulated voltage. Recently it was a bass boat sitting in a drive way with unregulated solar panels.... When I showed up at noon on a mildly over cast day the batteries were at 15.1 - 15.2V and had been "fully charged" for about six weeks..

So like Dave & SL I do see chargers undercharge more than over charge..
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Old 08-05-2013, 21:35   #23
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Re: battery charger mode explanation

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Spot on. The vast majority of shore chargers I come across undercharge the batteries because they go into float far to early. It is a rare situation where the loads keep it bouncing in and out of absorption and if that is the case the charger was really sized incorrectly to account for use as a power pack / charger...

In the shop I use a DC switch mode power supply with adjustable voltage and current. I can leave a battery charging at float for many days then bump the voltage to 14.6V and it still takes a while to "charge" and drop the acceptance down into the sub .5% range.. Conversely if I leave it at 14.6V to 14.8V until the current drops to .5% the battery is truly chuck full....

I have my "yard battery" a battery I lug around connected to an inverter when working on vessels without shore power or close enough to an extension cord. I use it for my power tools, shop vac and heat gun. This battery has been BEAT ON... I have no clue how deep I discharge, don't really care, but many days after 8 hours of work my inverter is shutting off on low voltage just with the Dremel. I charge this battery every time I bring it back to the shop at 14.8V and quite often I forget and leave it on over night or sometimes for two or three days. I simply add some water if it needs it. This battery was 4 years old when I began using it and today is is 7 years old.. I don't think I have ever "float" charged it, just 14.8V every time I charge it. I charge to .5% - 1% acceptance then I terminate the charge. Full enough for what I need.

I the shop I charge and equalize manually and my human timer works pretty well. I also have a wall timer because I tend to know how long it will take with certain batteries so I set it and walk away when the timer shuts off the batteries are usually 100% full... Occasionally they are not so I flip it back on.

None of the numerous marine or auto chargers I have in the shop will get the battery as full as fast and some take two or three cycles to do so because the pop into float too early.

The idea that a little bit of excess time at absorption voltages will kill batteries is one I never really understood. We have millions of cars, trucks buses and tractors driving around at 14.2 - 14.6V for hundreds & thousands of hours/miles.

The boat we currently own is a good case study. She was cruised 24/7 for five straight years with only an 80 watt solar panel / charge controller, and the stock 50 amp Mitsubishi alternator with no smart regulation. Banks were charged combined via a Yandina automatic combining relay (ACR/VSR).

The batteries were not fancy. They were Wal-Mart / Johnson Controls group 29/31 deep cycles installed new at the beginning of the cruise. Norm, a retired electrical engineer, & his wife, lived & sailed comfortably, away from dock power, from Labrador to South America and through the canal to Alaska and back all with no smart regulation, just a single voltage alternator, and a "small" by today's standards alt and bank. Throughout this five year 24/7 cruise time period they logged over 2700 engine hours of charging time at the dreaded non-float voltage of 14.4V (+/-.1V).

If you figure that the average coastal cruiser might do 100 hours per year this represents 27 years worth of charge time with dumb regulation set to 14.4 Volts. The last three vehicles we've owned, charged at 14.2-14.6 for many, many years (all into the 6 figures mileage wise on the original factory batteries). My wife's 03 Honda Pilot had 151k on the original factory battery before we traded it, and the alt put out 14.4 volts all day long..

When we bought our boat from Norm the cheap Wal*Mart deep cycle trolling batts and stock 50 amp alt were still plugging along despite being used about 325 days per year more, over 5 years, than the average coastal cruiser does.

When we bought the boat the batts were in year six of hard use , andtired, so I replaced them. I retired the hardly ever cycled start battery to starting my brothers Mako which it did until last summer, which made it over 10 years old. Not bad for a battery charged for 2700 hours at 14.4V...

Up until last summer we still had that same stock alternator with no smart regulation and that replacement bank is still going very, very strong. It is in my barn only because I wanted to experiment with LiFePO4. That bank did 7 years at 14.4V + solar.


Even if you did get into a situation where the charger was held a few tenths below absorption it is probably not a big deal. Chronic under charging is what I see a lot more often than over charging... When I see over charging I am usually seeing an unregulated voltage. Recently it was a bass boat sitting in a drive way with unregulated solar panels.... When I showed up at noon on a mildly over cast day the batteries were at 15.1 - 15.2V and had been "fully charged" for about six weeks..

So like Dave & SL I do see chargers undercharge more than over charge..
The first and most simple way I determine if a Murdered Battery COD is from chronic overcharge, is to make a visual inspection of the batteries. A chronically overcharged battery will show signs of positive grid plate corrosion.

This is demonstrated by the positive battery post showing signs of bulging, and expulsion.

positive grid plate corrosion - Google Search

And yes, chronically holding any battery above it's design voltage can and will lead to a murdered battery.

It's the second leading "Cause Of Death", of a Murdered Battery, right behind Chronically Undercharging a Battery.

Lloyd
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Old 09-05-2013, 05:50   #24
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Re: battery charger mode explanation

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The first and most simple way I determine if a Murdered Battery COD is from chronic overcharge, is to make a visual inspection of the batteries. A chronically overcharged battery will show signs of positive grid plate corrosion.

This is demonstrated by the positive battery post showing signs of bulging, and expulsion.

positive grid plate corrosion - Google Search

And yes, chronically holding any battery above it's design voltage can and will lead to a murdered battery.

It's the second leading "Cause Of Death", of a Murdered Battery, right behind Chronically Undercharging a Battery.

Lloyd
But on boats, short of "plugged in" vessels using poor quality shore chargers, or worse yet "automotive chargers", I can't recall the last time I saw a battery die from chronic over charging like we used to...

Occasionally I see an unregulated solar install cook a battery or a 30 year old ferro charger do the same or a complete malfunction in a charger or alternator, but these are about .5% of the batteries I see killed on boats. The others tend to die due to under charging and other issues......


I tend to think we often blow way out of proportion how long it takes at say 14.4V to "over charge" (FLA) batteries on boats, especially sailboats... Our own boat did 2700 hours worth, our cars have done as much as 151k/7 years at 14.4V with FLA batteries....

Over the years manufacturers have upped the safe absorption voltages yet I see very, very few installations pushing much beyond 14.4V - 14.6V in absorption.

There is no doubt chronic over charging will eventually destroy batteries but on most boats I find that it is chronic under charging that kills them even when they have such things as "dumb" alternator regulators...

I have a trawler-cat that recently completed the Great Loop. He has twin dumb regulated alternators (did not want "fancy"). His four 6V Deka's are in as near perfect shape as I could ever hope for. He also has 240W of solar and MPPT but his alts feed 14.4V when the engines run.... I did not check the engine hours but I am sure he kept track...

With the newr "smart chargers" I can't recall the last time I saw one cook batteries except for a few that malfunctioned ( often with an "X" in the name).. I did have one that was an old single set point ferro unit and the batteries were in the hot engine bay with a fridge compressor, IT, water heater, gen set and many other heat producing items on top of two large Cats....... It still took nearly four years in that installation to cook the batteries and the owner had never even opened them to check electrolyte levels. IIRC that old charger was set at 14.2V but even tied to the dock that engine bay was usually pushing 90-100F.....

I suspect we can get too bogged down in the minutia of an hour here, or two hours too long there, at absorption voltages and we don't often step back and look at the big picture. Like millions of cars in the automotive world running around 24/7 with FLA batts at 14+ V..

When you put it in that perspective the occasional extra few hours at absorption may actually be beneficial in a world where most batts are chronically undercharged...

So far, well at least since Feb, I have replaced approx 36 batteries, none of which died from over charging all were chronically undercharged and most were heavily sulfated. I will replace many, many more as the phone has not stopped ringing..
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Old 09-05-2013, 06:37   #25
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Re: battery charger mode explanation

Automotive battery life is pretty short especially for a battery that is never discharged more than 10%. Of course they cheap and easily replaced so sophisticated charging regimes are not justified.

With a bit of care you can make a significant difference to battery life. More batteries die from undercharging than overcharging, but for the longest life you should aim to get it right. Be particularly careful with gel and AGM batteries these are more sensitive to overcharging than flooded batteries.

Boat batteries are expensive, especially in out of the way places. Lugging a 70kg acid filled box with the dinghy and getting them on and off the boat is no fun, once you have done this a you will want to know how to get the longest life possible.
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