Battery Charger Power Draw Questions

[Maine Sail]

Originally Posted by colemj

To test this, does your charger produce the same current throughout the entire bulk charge phase until the battery voltage reaches the absorption point? Ours does not - it starts out pretty much flat out at 100-110A, but slowly tapers down to ~90A by the time the absorption set point is reached. It is the variable internal resistance of the batteries during the charging that controls this output.

Mark

Like an alternator this is often due to heat. It is working as flat out as it can but is limited in its ability, most often due to heat... (note: some have a built in max bulk/CC time limit too).

In my shop I have an old Freedom 25 that will run at max output for as long as the internal egg timer allows but this is when my room temp is in the 50's.

In the summer flat out is about 80-85A once it heats up... On many boats the fans simply can't move the air through fast enough to keep it cool or they are mounted in the wrong orientation....

Zanshin's graph above is a good example of this (if that is what is happening, and it looks to be). It ran flat out for quite a while, then as it heated up it likely dialed current back to self protect, all this before the batts were at absorption voltage. If you could keep it cool you would very likely see the bulk stay pretty constant until CV was attained....

Even my lab grade power supplies can't run at full output for hours on end and I need dial them back by about 15% to keep them cool and running at max set current until absorption is reached....

[sailinglegend]

Originally Posted by DotDun

...If you want to think of this initial charging stage (bulk) that your 'constant current' charger is doing something different than any other charger, that's fine by me. My only point is this is the way battery charging works.

Why can't you understand that a "Smart Multi-Stage Charger" is both a Constant Current charger AND a constant Voltage Charger, but not at the same time!!!!! It is ONLY a constant current charger during the Bulk Stage.

Just to confuse things even more Balmar regulators allow you to set a BULK voltage to rise to say 14.6 v and hold it there for say 32 minutes before dropping down to an constant Absorption voltage that could be @ 14.3v - below the battery gassing voltage.....

[conachair]

Originally Posted by sailinglegend

. If it didn't change over to a constant voltage charger at the absorption voltage then the voltage would go higher and higher - Ohms Law. Is that clear?

Maybe a little bit simplistic, as the voltage rises above the gassing point and more and more of the energy being transfered from the charger into the battery is used to split apart water molecules into hydrogen and oxygen atoms, doesn't the concept of resistance and ohms law break down a bit?

Sent from my SGP312 using Tapatalk

[Maine Sail]

I love this graph recently published by Nigel Calder in Pro Boat.

It shows that even with Lifeline AGM batteries the current you throw at a battery will determine when and at what point in the SOC curve you hit CV or voltage limiting.



Lifeline 4D Battery 210Ah Discharged to 50% SOC

2.0C = CV Attained almost instantly @ approx 52% SOC (420A Charge Rate)

0.5C = CV Attained @ approx 70% SOC (105A Charge Rate)

0.25C = CV Attained @ approx 78% SOC (52.5A Charge Rate)

[btrayfors]

MaineSail,

Yes, that graph comes from research Nigel and I did with the Concorde-Lifeline company.

Here's a companion graphic which shows the charge curves by length of time and by size (capacity) of the charging source. We repeated the charge test from 50% SOC using four different size chargers to obtain these figures.

Bill

[Maine Sail]

Originally Posted by btrayfors

MaineSail,

Yes, that graph comes from research Nigel and I did with the Concorde-Lifeline company.

Here's a companion graphic which shows the charge curves by length of time and by size (capacity) of the charging source. We repeated the charge test from 50% SOC using four different size chargers to obtain these figures.

Bill

Attachment 78958

Thanks Bill. I knew the time data was out there. Looks like .1C did not hit absorption until after the two hour time limit which would put it well into the 90's SOC wise...?

2.0C Less than 1 Minute Bulk
.5C Approx 23 Minutes Bulk
.25C Approx 66 Minutes Bulk
.10C Over 120 Minutes Bulk

[goboatingnow]

Interesting, shows that there is a "right" size charger for the bank. too large an absorption is reached too quickly,

Li is really the only way !

Dave

[btrayfors]

Originally Posted by goboatingnow

Interesting, shows that there is a "right" size charger for the bank. too large an absorption is reached too quickly,

Li is really the only way !

Dave

Nope. Wrong conclusion.

The "right size" charger for an AGM battery is the largest one you can fit. As said before, it's good for the battery to be charged at or near it's maximum charge acceptance rate (and with AGMs that's a very high rate) AND it's much less expensive in terms of fuel, wear and tear on engines, etc.

However, in the real world very very few boats have this kind of charging capability. Most are under .25CA (say 100 amps charging capacity for a 400AH bank).

Bill

[goboatingnow]

Originally Posted by btrayfors

Nope. Wrong conclusion.

The "right size" charger for an AGM battery is the largest one you can fit. As said before, it's good for the battery to be charged at or near it's maximum charge acceptance rate (and with AGMs that's a very high rate) AND it's much less expensive in terms of fuel, wear and tear on engines, etc.

However, in the real world very very few boats have this kind of charging capability. Most are under .25CA (say 100 amps charging capacity for a 400AH bank).

Bill

Its true that thin plate VRLA AGMs can be charged very fast, 2C to 8C has been done. However on any sort of deep cycle thick plate, surface charge build s up and the battery goes into absorption mode prematurely . Maine sails data would seem to evidence this.


Dave

[cal40john]

I think of most 3 stage chargers as actually 2 stage. Ignoring the overtemp and time limits some have, people are saying there's constant current until the absorption voltage is reached at which time the charger goes into constant voltage.

Electrically how is this achieved? The charger or regulater is monitoring the voltage whether in constant current or absorption. As far as the charger is concerned it can be one circuit identical to even the old mechanical regulators. If the voltage is below the set point the alternator is turned on and left that way, when the voltage setpoint is reached the switch starts turning the alternator on and off as needed to maintain that voltage. That one circuit is doing one thing, trying to maintain a voltage setpoint, if that setpoint isn't reached the circuit just leaves the power on until it is reached.

Now to sell it, it's doing something different, the always on is one stage, and once the voltage has risen enough to start turning the power to the charge source on and off is another stage.

If you want to call that 3 stage, you have to call internally regulated alternators 2 stage regulators because they've been doing that since they were springs and mechanical switches.

https://www.youtube.com/watch?v=UxXuKOQTASE

Things like Balmers could be called 3 stage (or 4) because they can have a higher setpoint voltage to leave the charger/alternator 100% on longer in their first stage.

[btrayfors]

Dave,

There's no such thing as "going into absorption mode prematurely". BTW, Maine's data (from Nigel Calder) is also my data (from Concorde-Lifeline).

AGMs can absorb a huge charge for awhile, that's why we specified 2X charging as the first (top) curve. This is good for the battery as said earlier.

The battery doesn't know anything about bulk mode or absorption mode. It simply accepts whatever charge is provided at the given voltage and, as its SOC rises, so does its internal resistance.

Bill

[goboatingnow]

Originally Posted by btrayfors

Dave,

There's no such thing as "going into absorption mode prematurely". BTW, Maine's data (from Nigel Calder) is also my data (from Concorde-Lifeline).

AGMs can absorb a huge charge for awhile, that's why we specified 2X charging as the first (top) curve. This is good for the battery as said earlier.

The battery doesn't know anything about bulk mode or absorption mode. It simply accepts whatever charge is provided at the given voltage and, as its SOC rises, so does its internal resistance.

Bill

Accepted wisdom, is that surface charge builds up. less so on thin plate AGMS, hence there is an issue with absorption mode arriving too soon.

How can you explain that under 2C, the absorption voltage was reached very very quickly, at a lower SOC. ( 50% approx) , thats suggest surface charge.

Bulk and absorption modes are names we give LA batteries , based on points on there charging curve. Talking about internal resistance is somewhat misleading as any say 2nd order impedance model of a LA battery will demonstrate. its simply not a "single " impedance. its a very complex model.

[goboatingnow]

Originally Posted by cal40john

I think of most 3 stage chargers as actually 2 stage. Ignoring the overtemp and time limits some have, people are saying there's constant current until the absorption voltage is reached at which time the charger goes into constant voltage.

Electrically how is this achieved? The charger or regulater is monitoring the voltage whether in constant current or absorption. As far as the charger is concerned it can be one circuit identical to even the old mechanical regulators. If the voltage is below the set point the alternator is turned on and left that way, when the voltage setpoint is reached the switch starts turning the alternator on and off as needed to maintain that voltage. That one circuit is doing one thing, trying to maintain a voltage setpoint, if that setpoint isn't reached the circuit just leaves the power on until it is reached.

Now to sell it, it's doing something different, the always on is one stage, and once the voltage has risen enough to start turning the power to the charge source on and off is another stage.

If you want to call that 3 stage, you have to call internally regulated alternators 2 stage regulators because they've been doing that since they were springs and mechanical switches.

Things like Balmers could be called 3 stage (or 4) because they can have a higher setpoint voltage to leave the charger/alternator 100% on longer in their first stage.

All this is true for mechanical regulators, its not really relevant to modern electronic regulators, they don't really work the same.


dave

[btrayfors]

Originally Posted by goboatingnow

Accepted wisdom, is that surface charge builds up. less so on thin plate AGMS, hence there is an issue with absorption mode arriving too soon.

How can you explain that under 2C, the absorption voltage was reached very very quickly, at a lower SOC. ( 50% approx) , thats suggest surface charge.

Bulk and absorption modes are names we give LA batteries , based on points on there charging curve. Talking about internal resistance is somewhat misleading as any say 2nd order impedance model of a LA battery will demonstrate. its simply not a "single " impedance. its a very complex model.

What "accepted wisdom" is that, Dave? Who says you can reach absorption mode "too soon"? I'd like to see the objective data to support that conclusion.

Absorption voltage was reached sooner in each case by virtue of the fact that the battery was accepting more charge current than with the smaller charger in the curve below. As the battery accepts charge current, its SOC and its internal resistance go up, complex impedences or not. As seen by the charger, the battery will only accept so much current at a given voltage and no more.

Bill

[DotDun]

Originally Posted by sailinglegend

Why can't you understand that a "Smart Multi-Stage Charger" is both a Constant Current charger AND a constant Voltage Charger, but not at the same time!!!!! It is ONLY a constant current charger during the Bulk Stage.

I understand it just fine.

Since, "Constant Current charger AND a constant Voltage Charger, but not at the same time" can't physically happen at the same time, it makes one wonder why the distinction.

The accepted term - Bulk stage - has been used by the industry for years. In a contest of one-up-manship, the marketeers started using the term Constant Current to replace Bulk stage. It's a fancy term that does exactly what chargers have been doing for years (and calling it Bulk stage).