Battery Charger Power Draw Questions

[cal40john]

Originally Posted by goboatingnow

Well it depends, in the case of linear regulation, a feedback loop effectively increases the series ( or shunt ) resistance and excess power is dissipated as heat. IN the case of switched mode, its about reducing energy transfer in magnetic coupling ( which has more of an analogy to mechanical regulators )


dave

The argument I was trying to make a comment on was about the difference between bulk and absorption. Only one thing is happening, the circuit is trying to maintain a certain voltage setpoint. If the voltage is at that setpoint it cycles the power (for this argument I don't care where or how the excess power is dealt with). If the voltage is lower than the setpoint the circuit stops cycling power and leaves it in the on state.

If you're going to say that this one circuit is doing the two different jobs of bulk constant current and constant voltage absorption fine, that's two of the 3 stages. If you define it that way then all internal regulators as well as old mechanical regulators are 2 stage regulators. They do bulk and absorption, but not float.

[zboss]

Originally Posted by goboatingnow

DO they , I wasn't aware of that


dave

Yes, check out the new mass combi's they are awesome. You connect them using CANBUS and they communicate with one another.

However, If I were to go around again I would probably favor victron.

[Saltyhog]

Originally Posted by zboss

Yes, check out the new mass combi's they are awesome. You connect them using CANBUS and they communicate with one another.

However, If I were to go around again I would probably favor victron.

Why???

[colemj]

Originally Posted by zboss

Yes, check out the new mass combi's they are awesome. You connect them using CANBUS and they communicate with one another.

However, If I were to go around again I would probably favor victron.

Wait a minute - that type of functionality is usually to synch the inverter outputs to provide more power. What is the advantage in charging vs two separate chargers?

Mark

[zboss]

Originally Posted by Saltyhog

Why???

They are more feature-rich and their electrical tolerances are tighter. For example, their voltage monitor has a resolution slightly higher than mastervolt.

Also they have direct to consumer support services, rather than requiring you first go through one of their vendors.

[cal40john]

Originally Posted by zboss

What about using dual chargers? We have a mastervolt and I know they support dual charging. So, when we upgrade to a larger battery bank and our single charger is no longer large enough for that bank, we will simply add a second 70 or 100 amp charger.

The other advantage to this is that if one charger goes out, we still have a second charger so we don't have to stop our plans to wait for a repair or replacement.

All I see is that the charger is compatible with their bus system and that you can view and change charge settings.
Manual for a Charge Master 70, see chapter 6:
http://images.mastervolt.nl/files/Ma...er070821EN.pdf

Do you have any other reference showing what is dual charging support?

[zboss]

Originally Posted by cal40john

All I see is that the charger is compatible with their bus system and that you can view and change charge settings.
Manual for a Charge Master 70, see chapter 6:
http://images.mastervolt.nl/files/Ma...er070821EN.pdf

Do you have any other reference showing what is dual charging support?

I believe you can "stack" any battery charger (others on here know more about that) and this is what I was planning to do. We do it everyday with our solar and it works just fine.

Although you are correct about the mass combi only being smart with AC.

I think Xantrex has a smart stacking feature for charging.

- z

[Saltyhog]

I'd think that for "simple" charge sources, stacking them is likely fine. There is nothing to get confused. However when "smart" chargers are just stacked up, I would think they could get confused as they are each seeing battery voltage change due to contributions from the other chargers. For example, if charger-A a switches from absorption to float, could that drop the battery voltage enough to cause charger-B to get confused about what to do next. Some of these chargers have a variable timeout on the absorption phase based on whether the charger believes the batteries were deeply discharged or not. The contributions from another charger might confuse that issue. What about some chargers that do an automatic absorption cycle on a weekly basis. If they are not in sync, the batteries would get 2 of these cycles. I can see where consolidating the "smarts" to one charge controller would keep things sane. I'm just not sure if any of the chargers are really *that* smart.

[goboatingnow]

Originally Posted by Saltyhog

I'd think that for "simple" charge sources, stacking them is likely fine. There is nothing to get confused. However when "smart" chargers are just stacked up, I would think they could get confused as they are each seeing battery voltage change due to contributions from the other chargers. For example, if charger-A a switches from absorption to float, could that drop the battery voltage enough to cause charger-B to get confused about what to do next. Some of these chargers have a variable timeout on the absorption phase based on whether the charger believes the batteries were deeply discharged or not. The contributions from another charger might confuse that issue. What about some chargers that do an automatic absorption cycle on a weekly basis. If they are not in sync, the batteries would get 2 of these cycles. I can see where consolidating the "smarts" to one charge controller would keep things sane. I'm just not sure if any of the chargers are really *that* smart.

That's not what really happens.

Note the mastervolt chargers I don't beleive are parallel-able.

When you connect separate charge sources. Generally they will not interfere. Chargers do not " drop" battery voltages. To do that they would have to sink current which they don't do. A charger regulates absorption mode voltage by effectively increasing its output impedance, resulting in less current flowing. As a result the battery voltage stabilises at a particular set point. It's not really the charger controlling things at all.

Hence two chargers won't confuse either other. The one remaining at absorption will determine the battery voltage , whereas the float one will just reduce its current and effectively do nothing.

What tends to happen when you parallel such sources is because the output impedances a d set points are not exactly matched a you get a " lazy" source effect. One charger will do the bulk of the work and the other will tag along. In bulk mode both chargers will more then likely be n CC mode ( using voltage foldback ) such methods means the chargers will share the bulk mode OK. In absorption mode typically one will do all the work.

Proper parallel charge sources have current steering to allow the work to be shared out between the two sources.

Dave


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[Saltyhog]

Originally Posted by goboatingnow

That's not what really happens.

Note the mastervolt chargers I don't beleive are parallel-able.

When you connect separate charge sources. Generally they will not interfere. Chargers do not " drop" battery voltages. To do that they would have to sink current which they don't do. A charger regulates absorption mode voltage by effectively increasing its output impedance, resulting in less current flowing. As a result the battery voltage stabilises at a particular set point. It's not really the charger controlling things at all.

Hence two chargers won't confuse either other. The one remaining at absorption will determine the battery voltage , whereas the float one will just reduce its current and effectively do nothing.

What tends to happen when you parallel such sources is because the output impedances a d set points are not exactly matched a you get a " lazy" source effect. One charger will do the bulk of the work and the other will tag along. In bulk mode both chargers will more then likely be n CC mode ( using voltage foldback ) such methods means the chargers will share the bulk mode OK. In absorption mode typically one will do all the work.

Proper parallel charge sources have current steering to allow the work to be shared out between the two sources.

Dave


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I normally let these things go, but there is enough confusion thrown around here WRT battery charging that I couldn't let this alone. A charger in absorption mode is simply a constant voltage source set to the absorption voltage. It does not regulate by "increasing it's output impedance". That makes no sense. A properly designed charger would keep its output impedance as low as possible. The batteries' equivalent series impedance goes up as it charges. *That* is why the charge current goes down as the batteries charge goes up. The charger does nothing but source a constant voltage supplying whatever current the battery will accept at that voltage.
You are correct about the "lazy source effect". There are potential instability issues in that case I believe, but I think that's beyond the scope here.
-Tom

[goboatingnow]

Originally Posted by Saltyhog

I normally let these things go, but there is enough confusion thrown around here WRT battery charging that I couldn't let this alone. A charger in absorption mode is simply a constant voltage source set to the absorption voltage. It does not regulate by "increasing it's output impedance". That makes no sense. A properly designed charger would keep its output impedance as low as possible. The batteries' equivalent series impedance goes up as it charges. *That* is why the charge current goes down as the batteries charge goes up. The charger does nothing but source a constant voltage supplying whatever current the battery will accept at that voltage.

You are correct about the "lazy source effect". There are potential instability issues in that case I believe, but I think that's beyond the scope here.

-Tom

Bandying around terms like " constant voltage " source without understanding regulation is of course misleading.

Equally so it talking about " effective series impedance " of batteries as simple Thevenin equivalent circuits also hide what's really happening.

If you treat a charger in CV as an imperfect voltage source and if you look at the way " regulation" works. You will see that the effect of the regulation is to in effect change the output impedance of the source. ( since all such impedances are Thevenin equivalents ) , think of it like this , if the chargers voltage stays the same and it's current flowing falls , then that is the same effect as increasing its equivalent ( note equivalent ) source resistance , Ohm will not be denied.

Think of a first order charger battery circuit , consisting of two perfect voltage sources each connected in series by two impedances , the equivalent output resistance of the charger source and the equivalent input resistance of the battery voltage source. Now these models are very basic of course. , now perturbate the voltage sources to take into account changes in chargers imperfect power supply and the need to regulate its output voltage ( note you can only source not sink current from the charger ) and the batteries EMF change as SOC changes. Do any of the equivalent impedances stay constant ????

A perusal of the principles of simple linear series regulation will proved plenty of additional information.

It's the same nonsense when people say " the charger reduces the voltage to a float voltage " in reality nothing of the sort happens electrically.

The accurate mathematical modelling of LA life cycle is still Doctorate level stuff

Dave


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[Saltyhog]

Originally Posted by goboatingnow

Bandying around terms like " constant voltage " source without understanding regulation is of course misleading.

Equally so it talking about " effective series impedance " of batteries as simple Thevenin equivalent circuits also hide what's really happening.

If you treat a charger in CV as an imperfect voltage source and if you look at the way " regulation" works. You will see that the effect of the regulation is to in effect change the output impedance of the source. ( since all such impedances are Thevenin equivalents ) , think of it like this , if the chargers voltage stays the same and it's current flowing falls , then that is the same effect as increasing its equivalent ( note equivalent ) source resistance , Ohm will not be denied.

Think of a first order charger battery circuit , consisting of two perfect voltage sources each connected in series by two impedances , the equivalent output resistance of the charger source and the equivalent input resistance of the battery voltage source. Now these models are very basic of course. , now perturbate the voltage sources to take into account changes in chargers imperfect power supply and the need to regulate its output voltage ( note you can only source not sink current from the charger ) and the batteries EMF change as SOC changes. Do any of the equivalent impedances stay constant ????

A perusal of the principles of simple linear series regulation will proved plenty of additional information.

It's the same nonsense when people say " the charger reduces the voltage to a float voltage " in reality nothing of the sort happens electrically.

The accurate mathematical modelling of LA life cycle is still Doctorate level stuff

Dave


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Wow! Your're really stretching things here. Voltage regulation, whether switched mode or linear, ALWAYS, strives to reduce the output impedance to as near zero as possible. The equivalent circuit (Thevenin if you prefer) is a perfect voltage source in series with some (very small) output impedance. You keep the output impedance as small as possible and set the voltage of the source to the target voltage via feedback. That's it. There is no controlling or setting of the output impedance. Not in the model circuit or in the practical implementation. It just does not work that way.
Again, I'm only responding to any of this because there often seems to be some confusion about chargers, smart chargers, bulk mode, absorption mode, etc. Generally folks get their answers here and all is good. But if someone down the line reads what you wrote, they're going to get the wrong idea and likely be more confused. I just don't understand where you're coming from on all this. Maybe it's a language or terminology thing. You post a lot here and generally are on the mark, so folks will tend to pay attention to what you write. But this got way off the rails. It's not serving anyone else WRT to understanding their battery chargers or how best to treat their batteries. I'm done.
With respect to the original question, I think that for many/most charge sources, it is fine to stack them and they will play together nicely. I think that there are some combinations that may give problems.

[goboatingnow]

I think it might be useful to have a basic primer in regulator , voltage source , power supply battery charger etc, so that people can actually see what the currents voltages , and resistance etc note all resistance computations are output resistance of the "charger " circuit. well ignore the battery for the moment.

Lets hypothesise the following

Billy has just arrived in college studying EE, he's played around at home with resistors and the like. His lecturer sets him a task, Billy, I have this special battery I want to charge , it has a nominal voltage of 5v and absorption voltage of 5,5 and a float voltage of 4.5V"

Futhermore he says "all you have is this 10V power supply ( say like a simple wall wart) and a potentiometer, a diode( more on that later), and a multimeter." oh and by the way , I want the circuit to indicate when its in "float mode,absorption & bulk", heres some indicators ( with a built in battery) and a switch ". " off you go" he says to Billy

So given the few components heres what billy does. ( see diagram) The diode he rekons will give him a bit of reverse polarity protection or something !. ( see later)

So , firstly Billy set the pot half way, reads the output voltage and as expected gets 5V

Q1. Whats the output impedance( resistance) of the source ( i.e. looking into billy circuit from the output side , ignore the wall wart for the moment).

The lecturer says , OK lets test it with a load. The lecture connects a restive load, and billy notices that the output voltage decreases to 4V. " its not regulating" says the lecturer. Billy realises he has to be the control circuit. so he tweaks the pot to restore the output voltage to 5V, Billy has become the regulator !.

Q2. Has the output resistance of the regulator( i.e. billy circuit ) increased, decreased or stayed the same.

The lecturer gives him the battery, he says , "its fairly discharged, around 4V", he says. Billy connects to to his circuit ( after removing the other load and restoring his pot to mid position) . He immediately notices his voltage on the output is 4V. So in the spirt of being a regulator, he turns his pot, Interesting he can turn his pot ALL the way up, and the voltage is still 4V and he can turn it all the way down and the voltage is 4V, hmmmm.

This must be bulk mode, so he turns on that indicator.

Measuring current, he notices, that when his pot is all the way up , he's outputing 2 amps, while all the way down he's outputting nothing. He realises he cannot "regulate the output"

Q3, is the output resistance ( the resistance looking into billy circuit ) the same irrespective of the pot position even though the output voltage remains the same.
Q3.1 why can't he change the output voltage


While pondering what to do, Billy notices that with the pot all the way up and current flowing, output voltage of his circuit is recovering, gradually increasing and he notices the current is reducing

Q4: is this a constant current circuit ?
Q5: if not what is happening ( hint batteries don't really have a linear bulk mode)


With a shock billy realises that the voltage has risen to 5.5V, , oh we're at the "absorption" point , he notices the voltage starts to climb to 5.6V and he can hear sizzling.

Quickly he turns his pot down, he notices the voltage and current falls and his battery voltage stabilised at 5.5V, He switches on the absorption indicator.

He finds he has to constantly adjust the pot "downwards" to keep the voltage from rising and he notices the current continues to reduce

Q6: billy is " regulating the circuit " to keep it in check, is this constant voltage mode
Q7:With such mode, is the output impedance of billys circuit, constant or varying. ? ( see previous posters contention)

Billy remembering the warning the lecturer mentioned ( " don't leave it in absorption mode forever"). Looks at his watch, notices two hours have passed and the current is down at 100 mA. He decides, "sure thats enough", Ill engage " float mode". he turns of the absorption lamp and turns on the float mode lamp.

Oh, he remembers, float is 4.5V , so he turns his pot down to try and set the voltage to 4.5V. To his surprise the voltage remains at around 5.2V, even turning his pot all the way down , he can't "set the float voltage at 4.5V

Q7: what can't billy set ( or regulate ) the float voltage to 4.5 ( hint the circuit cannot sink current per the diode, fwd its resistance is zero, reverse its resistance is huge)

Perplexed, billy notices that with his with his pot all the way down, the voltage of the battery is slowly dropping, after some time , he notices its at 4.4V, hah hah he say and he turns his pot till it read 4.5V and he notices some current flowing

After a while funnily he notices it reads 4.55V , no current is flowing and , even turning the pot down the voltage cannot be "dragged" down to the float voltage

Then after a short while, it drops just below 4.5v and he finds he can bring his pot up to 4.5V and some current flows again, and the cycle repeats.

Q8: Can Billys "regulator " actually force the battery into "float mode"
Q9: why not
Q10: Why do people say " my charger goes into float mode and keeps the battery voltage at XX"

Replace billy with a control loop and you have a smart three stage charger !!!

Understand this circuit and you understand smart chargers
Dave

[goboatingnow]

Originally Posted by Saltyhog

Wow! Your're really stretching things here. Voltage regulation, whether switched mode or linear, ALWAYS, strives to reduce the output impedance to as near zero as possible. The equivalent circuit (Thevenin if you prefer) is a perfect voltage source in series with some (very small) output impedance. You keep the output impedance as small as possible and set the voltage of the source to the target voltage via feedback. That's it. There is no controlling or setting of the output impedance. Not in the model circuit or in the practical implementation. It just does not work that way.
Again, I'm only responding to any of this because there often seems to be some confusion about chargers, smart chargers, bulk mode, absorption mode, etc. Generally folks get their answers here and all is good. But if someone down the line reads what you wrote, they're going to get the wrong idea and likely be more confused. I just don't understand where you're coming from on all this. Maybe it's a language or terminology thing. You post a lot here and generally are on the mark, so folks will tend to pay attention to what you write. But this got way off the rails. It's not serving anyone else WRT to understanding their battery chargers or how best to treat their batteries. I'm done.
With respect to the original question, I think that for many/most charge sources, it is fine to stack them and they will play together nicely. I think that there are some combinations that may give problems.

how at look at my previous post, ponder and return. it matters not what makes up the black box that is billy circuit.

[goboatingnow]

With respect to the original question, I think that for many/most charge sources, it is fine to stack them and they will play together nicely. I think that there are some combinations that may give problems.

That subject is both complex and simple, you either understand where the issues or you don't,

there are issues as to how regulation is done, source resistance matching, current steering, thermal runaway issues, switch mode interference, interference with logic decisions based on voltage , etc etc

its simple and complex.