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Old 29-11-2011, 08:18   #31
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Re: Questions About Wind / Solar Controller

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Brain. Hurting. The pain. Head. Swelling. Information. Overload. Aaaaarrrrrr.

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Yes, this is the issue with common understanding of complex topics. As a fellow electrical engineer, I agree with what Dave is saying, but unfortunately it doesn't help most people grasp the issues. As a result, people distill it down to "multiple charge sources will interfere with each other" or "multiple charge sources will work fine together" and then argue for ever on web forums about which is correct without really knowing what's behind each statement :-)

So, at the risk of making things worse rather than better, let me offer a visual to help the non-electrical engineers better grasp and analyze what's going on.

Imagine a 55 gal barrel that is filled with water and submerged in the water. But the barrel also has a small hole in it. Your job is to lift the barrel out of the water and hold it at a designated height.

The work involved with lifting the barrel and holding it at a particular height is much like charging a battery.

The faster you lift the barrel, the harder it is. But after you lift it to a certain level, it gets easier and easier to hold it there as the water leaks out the hole. If you lift the barrel slowly, it's not so hard because the water leaks down as you lift, but it takes longer. The faster you want to lift the barrel, the harder you have to lift.

Charging a battery is very similar. The bulk stage is like lifting the barrel out of the water. If you are limited in your lifting ability, you will only be able to raise the barrel at a certain rate, having to wait for water to drain out enough to lift further.

If you have two people lifting, you can get the barrel lifted up faster. It's not so important whether one person is lifting harder than the other, just what the combined lifting force is. Both people will lift as hard as they can until the barrel is at the designated height. Three or four people lifting is even better.

The Bulk charge stage is much the same. One charger will charge the battery as fast as it can, and multiple chargers will charge it faster. It's their combined charge capacity that matters, not how much each contributes individually. And each will work as hard as it can until the battery reaches its bulk voltage.

Things get a little more interesting as the barrel arrives at the desired height and the job changes from lifting to holding. Each of the people lifting has a slightly different perspective on what the "correct" height is, so each starts backing off at slightly different times. Again, it's not a problem since the height is close enough to what we want. As the water drains out the barrel becomes lighter and lighter, and less effort is required by everyone to hold the barrel. Eventually, the barrel becomes light enough that one person is carrying all the remaining weight. Whichever person thinks the barrel should be the highest will be the one left holding everything.

The same thing happens as the chargers hold your battery at its Bulk/absorb voltage throughout the Absorb stage. Note that for simplicity, I'm going to assume that Bulk and Absorb voltages are the same. Each charger measures the voltage a little differently, and each contributes differently to maintaining Absorb voltage. As the battery becomes more charged, the chargers will back off typically leaving one charger doing most if not all the work.

Then things get the most interesting trying to conclude when the job is done. The people holding the barrel will let go when they either a) feel they are making no meaningful contribution to holding the barrel up, or b) conclude they have been holding it long enough and are going to just let it drop back in the sea. As long as one person keeps holding on, the barrel stays up, and after the last guy gives up, it drops back in the sea, eventually floods, and the whole process starts again.

Finishing up your battery charge is similar. It becomes easier and easier for the chargers to maintain the Absorb voltage, and eventually each drops out either because it's no longer producing more than some threshold of charge current, or because it's been in Absorb for longer than some time limit. Ultimately one charger is the last one operating, and it's the charger trying to achieve the highest Absorb voltage for the longest amount of time. Just because others dropped out earlier doesn't mean another charger will run longer. Each has a job to do and will stop when it's done. If anything, they finish up earlier because there were more of them helping throughout the whole process.

The real loophole in the system is if someone is leaning on the barrel while everyone is lifting. Those who are waiting for the load to lighten to a certain level will just keep on holding, unaware that they are holding up a leaning crew member, not the barrel. If waiting for a light load is the ONLY criteria for stopping, the poor guys holding up the barrel can be left there indefinitely. Note that it makes no difference how many people are holding the barrel up. As long as one of them won't stop until the load lightens, he just keeps on going.

Finishing up the Absorb charge has the same loophole, but it has to do with how your chargers operate, NOT how many of them there are. Good chargers will stop when the load gets light AND they will stop after some period of time. This is to protect against remaining in Absorb forever because your fridge is running and the charger is carrying that load PLUS your battery's final charge load.
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Old 29-11-2011, 08:22   #32
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Originally Posted by twistedtree

Dave, thanks for sharing the nuts and bolts, but I'm confused by the above.

Are you saying that it's OK to maintain a battery indefinitely at 14.2-14.4V and that it's below the gassing voltage? I though the gassing voltage was around 13.6 or so which is also the voltage for a constant voltage charger like in a car or many/most boat engines.

Also, I think noelex 77's point is that many regulators, for better or worse, only time the absorption mode and don't look at their output current as a criteria for switching to float.
Yes it's perfectly ok to remain in so called absorption mode indefinitely as long as you remain below the gassing point. This is from about 14.4 at ambient. Many car regulators are now set to 14.2.

I did a review of cheaper solar controllers some time ago. From what I could see they never exited absorption mode. ( there's no need , as float mode doesn't really exist on a boat ) using a timer is really an extradinary poor way of determining that mode as if there's a system load as well, which is typical of such installations the regulator would drop to float ( if one exists ) and never charge the battery properly.

Quickest way kill LAs is to undercharge them not leave them in absorption mode. Which is why my experience of simple chargers/ regulators is that what they do. They never leave absorption mode ( well they don't know anything about absorption mode they just regulate to 14.2 etc)

Dave
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Old 29-11-2011, 08:43   #33
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Re: Questions About Wind / Solar Controller

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Originally Posted by goboatingnow View Post
Yes it's perfectly ok to remain in so called absorption mode indefinitely as long as you remain below the gassing point. This is from about 14.4 at ambient. Many car regulators are now set to 14.2.

I did a review of cheaper solar controllers some time ago. From what I could see they never exited absorption mode. ( there's no need , as float mode doesn't really exist on a boat ) using a timer is really an extradinary poor way of determining that mode as if there's a system load as well, which is typical of such installations the regulator would drop to float ( if one exists ) and never charge the battery properly.

Quickest way kill LAs is to undercharge them not leave them in absorption mode. Which is why my experience of simple chargers/ regulators is that what they do. They never leave absorption mode ( well they don't know anything about absorption mode they just regulate to 14.2 etc)

Dave
More batteries die from undercharging than overcharging, but long periods of time at absorb voltage when there is little or no discharge from the batteries is not good for them, particularly sealed batteries.
A lot of simple one stage regulators use a single voltage that is a bit between the ideal absorption and float voltage. IMHO its worth getting a regulator that has a true float voltage setting.
These multistage chargers will virtually all use a timing system to drop down to float.
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Old 29-11-2011, 08:55   #34
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Quote:
Originally Posted by noelex 77

Dave that will not provide any regulation at all.
The controller has no way of knowing if part of the current the solar panels are producing is powering a load.

For example suppose the set point is greater than 14.2v with less than 5 amps into the batteries. When these parameters are reached the battery is close to fully charged and the controller drops back to float.

If there is no load and the parameters are just about to met. The solar controller is regulating just over 5a and the battery is above 14.2. If we turn the fridge on drawing 6a. The solar controller will adjust to now provide 11A. It will never reach the return current parameters with the fridge on.

If the system recognizes the net current into the battery turning the fridge on makes no difference. The system still recognizes that the battery is only receiving 5A so its very close to fully charged.

Return amps has to be net current into the battery. Some of the total current provided by the solar controller will go to driving the loads. The solar controller can be supplying a very large total current even if the battery is fully charged.
Only the net current (together with battery voltage and battery bank size) gives an accurate indication of the battery reaching close to a fully charged state.

This timed method is the way all the better solar controllers use to determine when to drop back to float..
The cheaper controllers maintain one voltage only as you indicate and never drop on to a float voltage.

99% of solar regulators in boats use one of these 2 systems.
There are very few that can use return amps.
Even probably the most sophisticated controller used on boats the Outback FX80 will not use return amps unless you purchase 3 additional products (which cost as much as the regulator again)
Noelex.

Chargers can not " drop back to float" unless the battery or the other connected sources allow it. They can regulate their current down, effectively raising their thevenin equivalent input impedance. In effect they just disappear off the battery circuit. ( sorry simplified)

As to absorption mode exit. ( I did design battery chargers) there are three ways

(a) dv/dt. - expensive circuit, not always reliable, detection point is battery specific
(b) di/dt. - easy ( most psu design requires current monitoring anyway )
(c) time - easy circuit, but no feedback from circuit possible.

There's a couple of more esoteric ones.

The majority of controllers simply use current with a backup timer for protection. This is especially true of smart battery chargers ( which is the same process for all regulators ). Since series pass , shunt or PWM controllers are all sensing current it's easy to implement.

Using a timer only, to take your example would actually cause constant battery undercharging as we are almost always charging with a load connected. Hence the regulator has no idea the battery is actually receiving current. At least in the di/dt situation the regulator will stay in absorption mode indefinitely while the load remains attempting to get the battery charged. Usually as a precaution there is a coarse timer running. ( see XW solar charge controller for a good description).

Again in a complex system of multiple sources, loads and batteries, it matters not that the situation you mention occurs once you don't exceed the gassing voltage. Once the regulator sees the current falling it " assumes" the battery is charged, reduces its current to the 20hr value ( or less) this effectively raises its input impedance and the battery voltage drifts down to the float value with a small constant current flowing into the battery. In my experience few cheap solar controllers bother with float, probably because solar has been a traditionally low power recharge mode.

It's worth noting that most alternator regulators don't have a float mode either. ( cause they get stopped after a while). Mains chargers tend to have it as they remain in circuit for a long time.

I fully agree with the net current concept, absolutely, and it's one argument for fully integrated charging controllers controlling all sources. However it's not widely used due to the inconvience of rigging external shunts.

I'm actually in the middle of a proof of concept system that uses nmea2k shunt and nmea2k linked charge controllers to talk to each other and synchronise their charging environment. Yet there's no single pint of failure as all controllers can revert to dumb control if the network or the shunt fails.

Dave
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Old 29-11-2011, 09:00   #35
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Quote:
Originally Posted by noelex 77
More batteries die from undercharging than overcharging, but long periods of time at absorb voltage when there is little or no discharge from the batteries is not good for them, particularly sealed batteries.
A lot of simple one stage regulators use a single voltage that is a bit between the ideal absorption and float voltage. IMHO its worth getting a regulator that has a true float voltage setting.
These multistage chargers will virtually all use a timing system to drop down to float.
Noelex they don't, read mastervolt xantrex, etc. they all use current monitoring with a protection timer. Look up the various ICs from maxim, TI and others and see the algorithms used

I fully accept that very long periods ( like days) at above about 14.1 ( ambient corrected) can cause issues with positive plate corrosion, shedding etc. but it's minor compared to undercharging. Cars now all use 14.1-14.2 and are all sealed systems. ( and since they are all at 100% anyway, they survive) deep cycle with stronger plates and more active material are even more tolerant see Trojans recommended absorption voltages as a case in point .

In a boat we rarely have a float situation, in fact most regulators are seeing transitions from absorption set point to bulk mode constantly as loads come and go and the battery SOC changes. Often the regulators spend a lot of time in absorption mode with current or protection timers tripping then re-entering absorption on load. Some have more sophisticated approaches with entry into bulk mode being required before another absorption mode begins. ( victron studer etc)

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Old 29-11-2011, 09:01   #36
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twisted tree, that was brilliant , it reminds me why I don't teach electronics and just design it.

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Old 29-11-2011, 09:45   #37
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Re: Questions About Wind / Solar Controller

Dave / noelex 77 & twisted tree - many thanks for your contributions. I am an aero engineer and clearly have enough knowledge of charging systems to stay in the gray area between trouble and no trouble.

Once a certain depth of knowledge is obtained it is very hard to keep the conversation in the realm where a layman can understand what to do.

In terms of absorbtion and float modes which may or may not exist depending upon the sophistication of the controllers we are predominantly now talking about maximizing battery life rather than "getting the thing charged" - right?

In real terms what is the impact on battery life for a "top end" controller vs. a "decent" controller? I suspect the other variables such as overdischarging, dirty connections, the hostile marine environment play just as big a factor in battery life.

My experience with charge systems is pretty simplistic engine operated generators and I recently installed a couple of very small solar panels on my boat. But I have been reading voraciously for a while.

It recently has become more of a priority because my brother just bought a boat and I am trying to help him figure out the systems on it.

For generation he has a 12v X 30 engine alternator, 12 X 80w of solar, a windgen of unknown species that appears to be about 12 v X 20amp. He also has a 240vac 3kva genset on deck. For the charging systems there appears to be no combiner and I have not really placed my hands on any of the regulators. The genset plugs into the shore power plug with an adapter.

On the 240vac side there is a 12v X 30 amp charger and a 24v X 50 amp charger. The house is 12v and the engine starter and gypsy is 24v.

There was an inverter that was stolen off the boat right before the purchase and that is the first decision to make on purchasing new equipment.

As it stands now the only way to charge the 24v system is to run the genset or plug into shore power to power up the 24v charger.

This discussion has been very helpful to me.

Cheers!
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Old 29-11-2011, 10:12   #38
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Re: Questions About Wind / Solar Controller

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Noelex.

Chargers can not " drop back to float" unless the battery or the other connected sources allow it
The solar controllers simply drop the regulation voltage from say 14.5 to 13.8v easy

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The majority of controllers simply use current with a backup timer for protection.
With respect I disagree. 99% of solar controllers do not use current at all to regulate. They regulate on voltage and time only.
Can you name some that use current to regulate ?

Quote:
Originally Posted by goboatingnow View Post
Using a timer only, to take your example would actually cause constant battery undercharging as we are almost always charging with a load connected. Hence the regulator has no idea the battery is actually receiving current.
You are misunderstanding how solar controllers work. The timer is on voltage only. Not current. When the battery voltage is maintained at the absorption voltage for the absorption time. The solar controller will drop back to float.
Say 14.4V for 2hr would be typical. They work this way because the load current does not disturb the regulation
If the voltage drops below 14.4V the timer stops. The cumulative time at 14.4v must be 2hr.
Some solar controllers use a slightly more sophisticated timer sequence that will extend the absorb time depending on the time to reach bulk etc, but it is timer based not current based.
This is how solar controllers fundamentally work.
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Old 29-11-2011, 10:37   #39
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Re: Questions About Wind / Solar Controller

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In terms of absorbtion and float modes which may or may not exist depending upon the sophistication of the controllers we are predominantly now talking about maximizing battery life rather than "getting the thing charged" - right?

!
The better 2 stage chargers will charge slightly quicker than the simple controllers. This is because their absorption voltage is higher forcing more current into the battery. They will then drop back to a lower float voltage which is better for long term storage with no load. Like winter storage.
The 2 stage chargers will charge at say 14.5v then drop back after say 2hrs at this voltage to 13.8v
A single stage charger will try to keep the battery at an intermediate voltage of say 14.2v

The benefit changing from a single stage charger to 2 or more stages will extend battery life and reduce charging times. The extra cost is justified IMHO for all but small boat systems.
Quote:
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For generation he has a 12v X 30 engine alternator, 12 X 80w of solar, a windgen of unknown species that appears to be about 12 v X 20amp. He also has a 240vac 3kva genset on deck. For the charging systems there appears to be no combiner and I have not really placed my hands on any of the regulators. The genset plugs into the shore power plug with an adapter.
This is a serious system but there is no need for a combiner. Separate controllers will be fine.
An integrated system that will shut off all the charge sources when charge parameters are met is possible, but gets more complicated and sacrifices some redundancy.
I would install the best multistage charge controllers and consider some refinements like using net battery current to terminate the charge.
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Old 29-11-2011, 14:02   #40
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Re: Questions About Wind / Solar Controller

Wow, you are really challenging much of what I've learned over the years. Below are the points I'm struggling with. There must be more to the story.

- You mention three triggers from exiting absorb; dv/dt, di/dt, and time. In absorb, isn't dv/dt zero by definition for the entire time you are there? I can understand di/dt being a sophisticated way to detect full charge, but from what I've seen most do it based on i, not di/dt. When i reaches 2% of battery capacity, the battery is considered charged and drops to float. This of course means the charger needs to know the battery bank capacity, adn better chanrges let you program it. Others just make an assumption and the i threshold is a fixed constant. Time is commonly used - sometimes by itself, and sometimes in conjunction with a lower limit on i.

- You are saying that a battery can be left at 14.4V indefinitely without gassing and subsequent loss of water. I always though gassing started in the 13.4V range (can't remember the exact number), but I understood the the whole point of the Float voltage was max voltage that was below gassing so it could be left on indefinitely. Could you be talking about AGMs? I could see how with an AGM it's not the gassing voltage that you need to worry about, but rather the max gassing rate that the AGM can re-absorb on a steady state basis. In other words some gassing is fine as long as it can recombine with out being released. This would allow AGMs to float at higher voltages without losing water.

- I get the car chargers that are constant voltage chargers. They are cheap and simple. And 14.x volts makes sense since a car typically doesn't get driven long enough to create an adverse over-charge condition. But I'm struggling with how this is a good idea for any charger that can run for extended time.
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Old 29-11-2011, 14:14   #41
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Re: Questions About Wind / Solar Controller

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Using a timer only, to take your example would actually cause constant battery undercharging as we are almost always charging with a load connected. Hence the regulator has no idea the battery is actually receiving current. At least in the di/dt situation the regulator will stay in absorption mode indefinitely while the load remains attempting to get the battery charged. Usually as a precaution there is a coarse timer running. ( see XW solar charge controller for a good description).
I don't think this is correct. If the charger is maintaining absorb voltage for say 3 hours, the battery will receive the same charge during that time regardless of loads. The key to my statement is that the charger can maintain the absorb voltage, which presumes that the loads are within the current capacity of the charger. The charge current will fluctuate to service both the battery charge and the loads, but at a constant voltage the battery will get the same current regardless of the presence or absence of parallel loads.

The whole issue of loads opens up the loophole where some current threshold is used to end the charge cycle. This only works in the absence of loads. Any load will trick the charger into thinking the battery still has a high acceptance current when it's actually going to a load. My understanding is that timers are used in conjunction with current limits precisely as a safeguard against this form of run-on absorb
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Old 29-11-2011, 16:59   #42
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Re: Questions About Wind / Solar Controller

Ex-calif, while a few of us wallow in the weeds, I can offer some simpler guidance on what to look for in a charger.

When picking any type of charger whether it's a pure mains charger, an inverter/charger, a solar charger, wind charger, engine alternator, or whatever, I'd look for the following as minimum criteria for buying:

- Three stage charging. This is typically called bulk, absorb, and float charge stages, but some manufacturers may get creative with terminology.

- Adjustable voltages. At a minimum there should be settings for flooded versus AGM batteries. Preferably, it's nice to be able to dial in any voltage for the different stages. This is particularly important if you are trying to set multiple chargers to the same settings.

- Multiple triggers to end absorption mode. I think the two most important are 1) charge current dropping below some threshold (usually 2% of battery capacity), and 2) a timer that limits absorption. And both should be adjustable.

With the above I think you'd be in pretty good shape.
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Old 29-11-2011, 17:13   #43
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Re: Questions About Wind / Solar Controller

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Wow, you are really challenging much of what I've learned over the years. Below are the points I'm struggling with. There must be more to the story.

- You mention three triggers from exiting absorb; dv/dt, di/dt, and time. In absorb, isn't dv/dt zero by definition for the entire time you are there? I can understand di/dt being a sophisticated way to detect full charge, but from what I've seen most do it based on i, not di/dt. When i reaches 2% of battery capacity, the battery is considered charged and drops to float. This of course means the charger needs to know the battery bank capacity, adn better chanrges let you program it. Others just make an assumption and the i threshold is a fixed constant. Time is commonly used - sometimes by itself, and sometimes in conjunction with a lower limit on i.

- You are saying that a battery can be left at 14.4V indefinitely without gassing and subsequent loss of water. I always though gassing started in the 13.4V range (can't remember the exact number), but I understood the the whole point of the Float voltage was max voltage that was below gassing so it could be left on indefinitely. Could you be talking about AGMs? I could see how with an AGM it's not the gassing voltage that you need to worry about, but rather the max gassing rate that the AGM can re-absorb on a steady state basis. In other words some gassing is fine as long as it can recombine with out being released. This would allow AGMs to float at higher voltages without losing water.

- I get the car chargers that are constant voltage chargers. They are cheap and simple. And 14.x volts makes sense since a car typically doesn't get driven long enough to create an adverse over-charge condition. But I'm struggling with how this is a good idea for any charger that can run for extended time.

twistedtree

Gassing ( corrected for ambient) occurs around 14.4, mind you some manufacturers set it higher, float is at around 13.6 - 13.9, most absorption set points are now around 14.1. Batteries can generally handle 14.1-14.2 without any problem or loss of electrolyte. Long term, where batteries are left without loads attached then floating them is a good idea. Solar gets away without float in that it gets dark

see Lead for a little background. ( simplified I know).

as to absorption mode exit.

" In absorb, isn't dv/dt zero by definition for the entire time you are there?"

no, LA have a definative and unfortunately slightly battery specific voltage curve characteristic that can be computed and absorption end point detected. See SmartGauge battery monitor for an implementation that effectively build a dynamic voltage versus SOC and can determine battery state from just voltage measurements. Its not a trivial computation task and generally your average PSU software engineer has more to do then implement that system. But it works,

Yes you can use the absolute value if i and its one I left out. in fact most good algorithms effectively use the value of i over time,

car chargers arnt simple, modern regulators are smart, they are very like low cost solar chargers in fact, just a simple voltage set point with current foldback. for charging batteries where float isnt needed, these are as "smart" as you need.

Remember anyway float isnt much use to man nor beast in a system where loads are connected all the time.

Dave
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Old 29-11-2011, 17:20   #44
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Re: Questions About Wind / Solar Controller

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I don't think this is correct. If the charger is maintaining absorb voltage for say 3 hours, the battery will receive the same charge during that time regardless of loads. The key to my statement is that the charger can maintain the absorb voltage, which presumes that the loads are within the current capacity of the charger. The charge current will fluctuate to service both the battery charge and the loads, but at a constant voltage the battery will get the same current regardless of the presence or absence of parallel loads.
"Hence the regulator has no idea the battery is actually receiving current."

Sorry I didnt mean the load drained the charge from the battery ( although kerchoffs will tell you a percentage obviously does , but typically the battery impedance dominates the load one.)

What meant is that in a load situation the charger cant determine absorption mode exit by using i, as it doesnt know what actual current is split between the battery and the load , as you say yourself in the "loophole" section. However at least I only sensing, does leave the absorption mode run on as is needed. Timer exits are typically in my experience set for 2x or 3x actual absorption time, but can be set closer or further in some cases.

Quote:
The whole issue of loads opens up the loophole where some current threshold is used to end the charge cycle. This only works in the absence of loads. Any load will trick the charger into thinking the battery still has a high acceptance current when it's actually going to a load. My understanding is that timers are used in conjunction with current limits precisely as a safeguard against this form of run-on absorb
we are agreeing here, its just a nuance, where the load is connected or not soley timer based absorption can leave a battery undercharged, especially a big bank. I know for a fact that several major smart chargers( and solars controllers) use current as the determining exit factor. Timers are used as a safeguard

Loads of course trick the charger into extending absorption mode, but in fact absorption mode shouldn't and generally doesn't cause gassing. Some controllers ( like sterling) can in some cases select a very high absorption voltage,( or the user can select the setpoint) which induces gassing but ensures fast charging, but these require battery maintenance and even perhaps watering systems.

Dave
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Old 29-11-2011, 17:31   #45
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Re: Questions About Wind / Solar Controller

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Originally Posted by twistedtree View Post
Ex-calif, while a few of us wallow in the weeds, I can offer some simpler guidance on what to look for in a charger.

When picking any type of charger whether it's a pure mains charger, an inverter/charger, a solar charger, wind charger, engine alternator, or whatever, I'd look for the following as minimum criteria for buying:

- Three stage charging. This is typically called bulk, absorb, and float charge stages, but some manufacturers may get creative with terminology.

- Adjustable voltages. At a minimum there should be settings for flooded versus AGM batteries. Preferably, it's nice to be able to dial in any voltage for the different stages. This is particularly important if you are trying to set multiple chargers to the same settings.

- Multiple triggers to end absorption mode. I think the two most important are 1) charge current dropping below some threshold (usually 2% of battery capacity), and 2) a timer that limits absorption. And both should be adjustable.

With the above I think you'd be in pretty good shape.
yes but these are available in some systems, but they are expert user stuff, setting overly high or low setpoints can have ramifications that lots of users dont understand, hence many manufacturers choose safe setpoints, that prevent tailoring. Given the tech level we are at, its strange that auto battery id systems havent arisen.
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