AGM battery max voltage whilst charging

[frackers]

Greetings all

Just landed on my feet!! Tonight I get to unload 21 12v 100amp-hr UPS batteries from my trailer having picked them up yesterday. They aren't very old (couple of years I think) so should have plenty of their 10 year life left. Perfect timing as the 8 golf cart style batteries I bought new 4 years ago have just about died

These AGM batteries came out of an 80KVA UPS that was operational until last week so they all have a reasonable state of charge (all 13.2<>13.3 volts) apart from one which is sitting at 12.95V.

I don't have a great deal of experience with AGMs so the question is, when I'm doing a *Bulk Charge*, what should I limit the charge voltage to or should I allow them to sit at whatever voltage they like provided the charge current is within spec. I realise that once I get to *Absorption Charge* I should limit the voltage and just keep an eye on current, similarly *Float Charge* should be constant current with an eye that the voltage doesn't get too high.

I want to make sure I characterise these batteries before I wreck them!! I'll be using a charge counter to track where in the charge cycle they are, the problem being they are AGM so I can't check the SG to see what the starting point is. What I *don't* want to do is just go out and buy a controller where I have no knowledge of the algorithms being used - I trust my own software development skills better than that!!

This is my starting point for moving from wind to solar power so I'd like to get it right - there is another few KW of Oztules  panels about to take shape

[Wolvenar]

I am no expert but I know a lot of batteries of a lot of types seem to depend on the manufacturer.
Who made them? Maybe they have some charge guidelines we could find

[tomw]

Like Wolv said, there is a lot of difference between manufacturers of similar chemistry batteries on how they like them charged.

Must be differences in how they are made.


Flooded batteries seem to be the same but SLA, VRLA and AGM  manufacturers seem to vary a lot on how they think you should do it.

Tom

[frackers]

These are Century UPZ 12.100 VRLA batteries. The 2 page spec sheet has most info but not charging voltage - only float.

[Wolvenar]

For reference
Spec sheet obtained from here

[dang]

I've lived with this same type awhile now. Hope you got them for free or near free 

Float may be the only charging scheme permissible, but note the C/5 max charge rate makes for rapid bulk charging.

The 10-year warranty batteries I have suggest a high-rate float at 0.15 or 0.20V increase from normal float is allowable ONLY if another UPS 'outage' use period is scheduled that will draw the battery SOC down and damage the plate chemistry worse than cooking them at a higher charge rate.  Looks like 13.56V at 30°C (86.0 F) is it.. and accurate temperature compensation is MANDATORY.

http://tinyurl.com/7tudlec <---  "Effects of AC Ripple Current on VRLA Battery Life"

http://tinyurl.com/7oce4fz  <---  "Thermal Runaway in VRLA Batteries"

^^ You can't dump 'wild' rectified three phase into the 10-year VRLA/Gel batteries without consequences. These are thoroughbred pedigreed batteries made to be maintained by lab quality chargers.

There are hybrid SLAs etc. that use some qualities of different designs that can accommodate automotive spec charging, the 14.4 or 14.7V and no temp compensation, but then they are designed around a shorter warranty and no special equipment etc.

So if you're feeding wind power you get to invent a constant voltage - constant current charger AND filter the AC crap out of the DC charge lines - And you need to fine tune it for accurate temperature compensation.

[frackers]

Thanks Dang

Some very useful information there and stuff I'll be able to use in my controller one way or another!! I can monitor volts, current, temperature and state of charge (from charge counting) so now I have the start of a set of tables I can construct suitable charge/divert algorithms.

Since its pretty easy to do, I might split the battery strings a bit so I can monitor current and temperature in separate blocks (I run a 24 volt system).

With the current turbine its unlikely I'll be able to push more than C/20 (50 amps) into the bank and max discharge is about C/5. Assuming I get some solar onto it and start moving loads off grid then those numbers will change somewhat but so far I don't expect to suffer any thermal effects although the ripple current effects are something to think about...

Cheers

[shawn]

Good score on those AGMs are there any left?  
you will injoy the power 2kw of solar gives, my system is keeping up with the house needs on pv alone in these frosty days.

[oztules]

"This is my starting point for moving from wind to solar power so I'd like to get it right - there is another few KW of Oztules  panels about to take shape "

............... you do realize that your social life will suffer making panels.... they use up a lot of time.

But once you get up into the 3-4kw of solar, you will sadly lose any interest in wind made power..... except to see it turning.

Even today, only a handful of days past the shortest day of the year, mine made over 20000 watt hours today.. 20kwh. Both my 4 meter mills are in the shed...... to re-pot  the magnets  to stop them from deteriorating ......initially,...... but I just can't get excited about putting them back up, as I have too much power all the time now..... very sad really :'(

When they do go back up..... they will only be shorted I suspect and spinning very slowly...... just for memories............

When you can't use the power...... you can't use the power.


................oztules

[frackers]

Just reading the pdf for these batteries again and I see they can be used on their side - that would make getting to the terminals easy especially as I was thinking of having a 2 tier rack of them to save on floor space.

I wonder if they will also be OK on their short side - I can pack more side by side then!! Anyone any ideas or is it best to just have them right way up...

Cheers

[rossw]

Just reading the pdf for these batteries again and I see they can be used on their side - that would make getting to the terminals easy especially as I was thinking of having a 2 tier rack of them to save on floor space.

Here's mine, and generally being on their side makes lots of things easier I think.

[ksouers]

Ross,
That installation is much too clean 
You're going to have to do something about that!


Kevin

[tomw]

Ross,
That installation is much too clean 
You're going to have to do something about that!


Kevin

Yep, Ross does nice work. Don't tell him I said that tho.

Tom

[rossw]

Ross does nice work. Don't tell him I said that tho.

Aww, shucks guys....

There's an easy answer. I only post pics of the stuff that turns out reasonable

[ghurd]

"You can't dump 'wild' rectified three phase into the 10-year VRLA/Gel batteries without consequences"

I don't think the ripple they are talking about is related to rectified 3-phase.
To me, it looks like they are talking more about unfiltered rectified single phase.

Not sure how poorly a system would have to be designed to have 5A of ripple current on a 100AH battery from rectified 3-phase charging.
I'll leave that for Ross' calculator.

Could put a cap on the DC side of the rectifiers, asuming the wire run between the rectifiers & cap to the battery was fairly long (like tower to battery distance).  That would keep the ripple down to "almost none"?
G-