Bulk-Absorb-Float what are we missing?

vtmaps · February 2012

In another thread, Trojan battery charge specs were discussed:

BB. wrote: »

Trojan recommends a fairly nominal charging voltage of 2.35 volts per cell until the last 95-100% and finish at 2.45 to 2.7 volts per cell (at 10-13% * C rate of charge as the current limit) until the battery hits around 90% state of charge.

Here is Trojan's charging graph:
Attachment not found.
In the other thread, this information was not well received by members of this forum.

This next chart is from Interstate battery:
Attachment not found.
The 24 volt Absorb voltage is obviously a typo (should be 28.8 volts). But more importantly, they obviously have a different idea of the meaning of Bulk, Absorb, and Float.

This next image is from US Battery. It is a clipping of a larger image that gives charging information for different types of chargers. The clipping is of their instructions for a 3 stage charger:
Attachment not found.
Note that they do not consider Equalization or Float to be part of a three stage charging profile!

Finally, this is from the Iota IQ4 manual:
Attachment not found.

It is common advice on this forum that one should follow the manufacturer's recommendations. Is anyone on this forum (with Trojans, Interstates, or US Batteries) following these recommendations. If so, what chargers are you using and how is it programmed?

I wonder if we are all missing something here.....
--vtMaps

westbranch · February 2012

Re: Bulk-Absorb-Float what are we missing?

well the first thing I saw was that Trojan and USBattery seem to have the same idea finish at 3% of C/20.
I hope that is what I read...(could see by squinting)

VT what does you MNCC actually do when charging?

vtmaps · February 2012

Re: Bulk-Absorb-Float what are we missing?

westbranch wrote: »

VT what does your MNCC actually do when charging?

Does MNCC = Midnite Charge Controller? If so, I have an Outback fm60. When I bought my Outback, the Midnite Classic had been announced, but wasn't yet shipping. I would like to have a Classic for the arc-fault protection and the higher Voc (my four 235 watt panels could be in series, rather than series-parallel).
--vtMaps

westbranch · February 2012

Re: Bulk-Absorb-Float what are we missing?

OOPs, Memory ffffffailing, faulty disk... time for a reboot.

change that to FM60 then, and I suspect it is Voltage governed (like the MX60 is)

Blackcherry04 · February 2012

Re: Bulk-Absorb-Float what are we missing?

vtmaps wrote: »

This next chart is from Interstate battery:
Attachment not found.
The 24 volt Absorb voltage is obviously a typo (should be 28.8 volts). But more importantly, they obviously have a different idea of the meaning of Bulk, Absorb, and Float.

--vtMaps

You would think that 31 Volts was a type'o, but that is not what they say. They want you to do a equalize charge on every cycle. This their reply when questioned about it. In the real world your kind on your own to figure out what works best on your system. My guess would be from a warranty situation, in 24 months or whatever, they probably come out better having the High voltage and then they can blame you for not following it.

""Dear Bob,

We understand your concern and after testing multiple batteries we have found that the absorption stage has really helped the battery perform better and even run longer between cycles. The cycle life testing has also proven to be better than that of our competitors in the field by using the higher absorption setting.

Thanks,

Jeff Barron

Engineering & Technical Service Specialist

Interstate Battery System of America

10200 Plano Rd.

Dallas, Tx. 75238

Ph. 469-221-4655

Fax 469-374-6117

Email: jeff.barron@ibsa.com ""

westbranch · February 2012

Re: Bulk-Absorb-Float what are we missing?

you also need to 'flip' your mind as that is a C/10 table and not C/20. No easy comparison.

Vic · February 2012

Re: Bulk-Absorb-Float what are we missing?

vtmaps,

Well, I'd always recommend using the battery manufacturer's specs for charging parameters. AND, if this was ambiguous, confusing or unbelievable, would contact the manufacturer of your batts for clarification.

Each manufacturer has somewhat unique plate alloying and construction. They should and hopefully DO know what are the best charger parameters.

Very few users have the capability of bettering the wisdom and experience of any of the mainstream battery manufacturers. JMHO, but very good observations on your part, Vic

vtmaps · February 2012

Re: Bulk-Absorb-Float what are we missing?

Vic wrote: »

Well, I'd always recommend using the battery manufacturer's specs for charging parameters. AND, if this was ambiguous, confusing or unbelievable....

Vic, I am stuck with understanding Bulk-Absorb-Float the way it is defined in Home Power Magazine, WindSun FAQ, Outback, Magnum, and others.

I don't find the battery manufacturer's instructions for charging to be ambiguous or unbelievable. But I confused because they don't use the terms Bulk-Absorb-Float the way I am accustomed to using them. Trojan, especially, with their graph is clear about how they want their batteries charged. I suppose that I could set the absorb on my Outback to 2.35 volts per cell, and then set the float to the higher voltage. The point of my post is that many mainstream charger manufacturers do not seem to be on the same page with many mainstream battery manufacturers.
--vtMaps

Cariboocoot · February 2012

Re: Bulk-Absorb-Float what are we missing?

Battery manufacturers' charging specifications are more what you'd call "guidelines" than actual rules.

niel · February 2012

Re: Bulk-Absorb-Float what are we missing?

you know the only way you can find out how it's done is to ask them what they charged it with as most controllers, let alone battery chargers, will not accommodate such an arrangement without some extra components to modify the charge that to my knowledge is not available premade. ask them what commercially made cc or charger would meet their crazy configurations so that you can do so too. if they can't say then imho it's baloney to think they could ask you to do it that way.

stephendv · February 2012

Re: Bulk-Absorb-Float what are we missing?

The differences are because of different charging profiles - different applications use different charges, there's a standard DIN naming convention for these, like IUoU, IUIa, WoWa, etc.
The one used by all renewable energy chargers that I know of is IUoU:
I = Constant current (Bulk)
Uo = Constant voltage with a timeout (Absorb)
U = Constant voltage (float)

The profile posted by Trojan is similar to what I've seen for some forklift batteries and is the IUIa profile:
I = Constant current
U = Constant voltage
Ia = Constant current until the final voltage is reached, then charging is stopped.

As far as I can make out, the choice of the charging profile has more to do with how the battery is used, rather than the type of battery. In my view, this is why Trojan and forklift batteries reference the IUIa profile: because that's the charging profile used for traction batteries. Battery manufacturers who focus on producing a "renewable energy" battery tend to reference the IUoU profile.
Similarly, when looking at the manuals for forklift batteries not a single one lists the bulk, absorb, float values, because no forklift charger uses that profile. They tend to use the WOWa profile which is a "taper" profile, basically a long slow decreasing current charge curve. Again, that appears to be because that's the best way to charge a forklift battery which is at 20% SoC at the end of it's shift, and has 10 hours available before the start of the next shift. And it doesn't mean that that's the only way to charge a traction battery. If the batt is used in an RE system (i.e. relatively shallow discharges) - then an IUoU profile seems fine.

vtmaps · February 2012

Re: Bulk-Absorb-Float what are we missing?

Stephen, thanks so much for the DIN naming info. It has provided me with what I need to search for much more info. Its all starting to make sense!
--vtMaps

stephendv · February 2012

Re: Bulk-Absorb-Float what are we missing?

I found some more info on the IUIa method in the "Battery Technology Handbook" (there are a few copies floating about on the torrents). It describes it as follows:

"Charging is initially conducted with constant current until gassing voltage is reached (first I part). Then the voltage is kept constant (U part), and the current decreases permanently as the battery’s state of charge increases. As soon as the current has dropped to the allowed end- of-charge current (see Table 12.3), the final charging phase (second I part) is activated. Upon reaching the fully charged state, the battery has to be disconnected."

Table 12.3 attached (The battery types are also in their DIN designations, I think the flat plate bats like the trojans and surrettes are GroE types).

It seems that the main difference is that they shorten absorb phase a bit by using a higher end-amps current value than what RE chargers use. Then instead of dropping into float when it hits that current, they initiate another constant current charge to finish the charging. The RE chargers on the other hand keep absorb going until the end-amps reach 2A out of 100Ah, and then drop into float.

Attachment not found.

SolaRevolution · February 2012

Re: Bulk-Absorb-Float what are we missing?

FYI:
The XW system by the-company-formerly-known-as-Trace (AKA Schneider) has seperate voltage settings for Bulk and Absorb. (At least on some of the firmware versions)

westbranch · February 2012

Re: Bulk-Absorb-Float what are we missing?

GiS are traction type and golf cart type . http://www.bannerbatterien.com/banner/files/FolderTractionBullBlocGiS_gb.pdf

aglicknmex · February 2012

To muddy the waters even more----

Thanks for all the good input. After reading and "absorbing" I think Im seeing a basic reason for the IUIa and IUoU charge scenarios. A forklift being charged has no load and the currents flowing are entirely due to charging the battery. No complications here.

In a dynamic off grid system, the charging is complicated by the fact that the inverter may be pulling current in varying amounts all day. The poor charger does not have any way of determining where the power( charging amps) are going!! The final charging must be a function of voltage, not current.

I think that is why "the one used by all renewable energy chargers

is IUoU"

I see a potential problem in the bulk(constant current) stage. My inverter is often using 10-25 amps during the charging cycle. The battery is not getting that power for recharging.
Im thinking of upping my bulk cycle amperege (Midnite classic controller)

What do you guys think of my analysis?????

BB. · February 2012

Re: To muddy the waters even more----

I think you have a good handle on the whole battery / load issue...

It is one reason that we are pushing for larger solar arrays--To ensure there is sufficient energy going into the battery during daylight hours while assuming there will be some loads too.

A battery monitor is the best tool for watching what is happening to the battery. Logging current into and out of the battery bank reflects what the battery is seeing. Charge Controller loggers/meters/etc. cannot really figure out where all that energy is going other than it is being supplied by the solar array.

The Voltage Only battery monitors--Again, only part of the issue. Batteries have fairly complex physical/chemical interactions and it is difficult to just monitor bank voltage and really know what is happening.

-Bill

aglicknmex · February 2012

Re: Bulk-Absorb-Float what are we missing?

Could you recommend a couple battery monitors that you like?

BB. · February 2012

Re: Bulk-Absorb-Float what are we missing?

I do not have any (not in the solar biz)--From reading here:

The Trimetric seems to be a good "low cost" meter (and you have to read the instructions closely to set it up. No pretty setup interface).

The Xantrex models seem to be nice. Both include programmable output (use to turn on generator, turn off loads, turn on alarm, etc.) and the more expensive one has temperature correction (hmm--just check NAWS website, they do not currently list the more expensive model).

The Victron units have had some very nice things written about them here (and do have an aux contact too).

Call NAWS for the first too above and ask them what they see customers more satisfied with. Victron--I don't have any suggestions other than to search the web.

You can study the above units and then look for others that may better meet your needs too... There are more than I have listed above. And feel free to ask questions about any of the above or others that you find and other posters here can give you more information.

-Bill

vtmaps · February 2012

Re: To muddy the waters even more----

aglicknmex wrote: »

I see a potential problem in the bulk(constant current) stage. My inverter is often using 10-25 amps during the charging cycle. The battery is not getting that power for recharging. I'm thinking of upping my bulk cycle amperage (Midnite classic controller)

BB. wrote:

It is one reason that we are pushing for larger solar arrays--To ensure there is sufficient energy going into the battery during daylight hours while assuming there will be some loads too.

aglicknmex, be careful... what if your inverter load stops? You may then be pushing more amps into your battery than is good for it.

This recent thread morphed into a discussion of how to protect the batteries from too much current during bulk charge:
http://forum.solar-electric.com/showthread.php?14524

--vtMaps

jonr · May 2014

Re: To muddy the waters even more----

I was looking for a charge controller that implements Trojan's recommended 3 stage profile and ended up here.

aglicknmex wrote: »

the charging is complicated by the fact that the inverter may be pulling current in varying amounts all day. The poor charger does not have any way of determining where the power( charging amps) are going!! The final charging must be a function of voltage, not current.

I agree that knowing the amount of current flowing into the battery is necessary to implement the recommended profile. But it would seem that the easy way to do that would be an external current sensor mounted on the battery lead. But I don't see that typical charge controllers do that. So they must be implementing some other profile (using voltage and time?) - which I doubt is as optimal as the manufacturer recommended one. Why? Batteries are expensive and current sensors are cheap. So I want whatever treats the battery best. Is it available in cases where the battery is also in use?

westbranch · May 2014

Re: Bulk-Absorb-Float what are we missing?

Jon, I think the closest you are going to get is with a MN Classic with WhizBang jr, not quite exactly, but close.

vtmaps · May 2014

Re: Bulk-Absorb-Float what are we missing?

westbranch wrote: »

Jon, I think the closest you are going to get is with a MN Classic with WhizBang jr, not quite exactly, but close.

There's been an interesting discussion of exactly that:
http://midniteforum.com/index.php?topic=1811

--vtMaps

jonr · May 2014

Re: Bulk-Absorb-Float what are we missing?

Thanks to both. I see it's called IUI charging and I think even the Kid supports it??

I can think of an even worse scenario involving typical (non battery current aware) controllers. Say I have done a good job of shifting most of my load to daylight hours. I have little night load. So I buy a 100 AH battery bank and a 60A charge controller. It works fine, because 50A goes to my load and 10A (ie. C/10) to the battery. Then one day I turn off the load. The controller doesn't know this and sends 60A to the small battery. Not good...

The Bogart SC-2030 sounds like it might do some things right - but specs aren't available.

inetdog · May 2014

Re: Bulk-Absorb-Float what are we missing?

jonr wrote: »

... Then one day I turn off the load. The controller doesn't know this and sends 60A to the small battery. Not good...

Yup, bye-bye battery bank.
That is one good reason why the MN with Whizbang was recommended, since the Whizbang (Jr.) is a smart shunt which digitally sends the actual battery current information to the CC.

AuricTech · May 2014

Re: Bulk-Absorb-Float what are we missing?

westbranch wrote: »

Jon, I think the closest you are going to get is with a MN Classic with WhizBang jr, not quite exactly, but close.

Bogart Engineering has announced a charge controller (the SC-2030)* that is designed to work in conjunction with their TriMetric TM-2030 battery monitor. Do y'all think this might do the job?

*Their Web site says that it was due to be out in February 2014. I don't know what might be delaying its introduction, but I'm hoping our hosts have it for sale by the time I'm ready to build a system.

BB. · May 2014

Re: Bulk-Absorb-Float what are we missing?

I believe this is the link:

http://www.bogartengineering.com/products/sc-2030-charge-controller/sc-2030-charge-controller

Preliminary—detailed specifications coming soon
The SC-2030 is a PWM charger that works in tandem with the new TM-2030 TriMetric battery monitor. In constant communication with the TriMetric, the charger adjusts its charging current based on real-time battery information. The SC-2030 is designed for use with a 12V panel (36 cells) and a 12V battery, or a 24V panel (72 cells) and a 24V battery with efficiency comparable to that of MPPT charge controllers, but without the high cost of MPPT. The charger can handle solar currents up to 30A, and is ideally suited for RV and other small off-grid applications. The SC-2030 works optimally with a TM-2030 monitor, or can also work on its own with reduced performance.

One distinguishing feature is the ability to program the amount of excess amp-hour overcharge, as recommended by US Battery, Trojan, and other major battery manufacturers. A four-stage charging algorithm optimizes both battery life and charge-discharge cycle depth.
Delivery: February 2014

-Bill

Photowhit · May 2014

Re: Bulk-Absorb-Float what are we missing?

Here's the manual for the SC-2030; http://www.bogartengineering.com/sites/default/files/docs/SC-2030-UsersInstructions%20-%205-8-14%20%283%29.pdf

Looks like it sells between $100-150, $250-300 with trimetric and shunt, target for RV and small systems.

vtmaps · May 2014

Re: Bulk-Absorb-Float what are we missing?

jonr wrote: »

Then one day I turn off the load. The controller doesn't know this and sends 60A to the small battery. Not good...

inetdog wrote: »

That is one good reason why the MN with Whizbang was recommended, since the Whizbang (Jr.) is a smart shunt which digitally sends the actual battery current information to the CC.

What jonr needs is NOT yet available on either the Classic or the Kid, but will be (according to Midnite folks). Jonr needs to be able to set a battery current limit that is separate from the controller limit. This is available in the Outback line, but requires their flexnet DC with hub and mate3.

Jonr, the scheme you present (small battery with large daytime loads) does present a possible risk of exceeding your battery's current limit, but ONLY during bulk charging. If the morning sun can get this small battery up to absorb voltage before the midday sun (and loads), there will be no issue.

btw, an AGM battery (typically very high charge rates) could probably function well in your scheme.

--vtMaps

stephendv · May 2014

Re: Bulk-Absorb-Float what are we missing?

jonr wrote: »

Then one day I turn off the load. The controller doesn't know this and sends 60A to the small battery. Not good...

Thinking out loud here, but wouldn't the voltage and temperature limits on most modern MPPT controllers prevent battery damage? High current would mean high temperature, so if you could set the high temp threshold of the charge controller low enough you could perhaps avoid overcharging? Also, wouldn't such a high current also push the battery voltage up to the absorb limit quite quickly, at which point the controller will start backing off on the current to keep the voltage steady?

More questions than answers

jonr · May 2014

Re: Bulk-Absorb-Float what are we missing?

Are there charge controllers where the desired (you might get less) output voltage is easily set by another micro-controller? An Arduino with a voltage and a current sensor (Allegro ACS758 200A Hall Current Sensor?) could implement a proper/safe charge profile and provide the additional benefit of tracking DOD and turning off my inverter when it gets too low. Or maybe it's easier just to do the whole thing.

With (evidently) only one company getting it "right", I have to say that I am disappointed in the state of charge controller engineering.

Bulk-Absorb-Float what are we missing?

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