SLA batteries and how to treat them

[tvtech]

Hi All

Much stuff has happened here recently. Frequent "load shedding" and all to protect the National Grid from total collapse.
I took advantage of it though. Where others fail I must show my mettle..

Climbed in and purchased a SLA battery just before Xmas last year. Mickey mouse 65Ah that is not a deep discharge battery...simply a well made normal 10 Year standby battery. Left it over Xmas and New Year. The battery never bugged me in spite of power failures in that time.

I knew, learning from past mistakes, never ever flatten a battery unless you can charge it properly. So I left it and let it be.

Roll on 2015. More load shedding. Battery but no charger = dumb. I have tried my own stuff but burned before.....

I start thinking.....maybe, just maybe there is a product out there that can do the charging properly without me going the whole Linear route again...huge Toroidals and lots of heat sinking and nah. Bugger that.

Investigate and find this gem right here in SA and 20 in stock and SMPS (which I normally hate)...

Anyway, I do not normally go "ga ga" as far a Tech stuff goes...but I am impressed.

I have so far taken the SLA 65Ah through around 25 cycles. I am busy with another cycle now and making notes. I am not afraid of testing.

Back to something else. I joined a local forum here in SA. People here have somehow learned you can take a normal UPS and give it super powers...like it came out with maybe 2X 7.2Ah batteries...they are modding them and hooking up 2X 100Ah batteries

How on earth do they think that a charger that cannot even charge 2 little 7.2 Ah batteries properly...could handle these massive batteries??

Sometimes I sit back and fold my arms and shake my head.

Regards,
tv

 

[JoeJester]

Assuming your hooking them up in parallel, 0.1C would be 20 amperes total for charging in 10 hours.

Most of those supplies are constant current devices until the batteries are fully charged, then shifts to float voltage charge.

Eventually, even those smaller chargers will charge larger batteries. What one needs to consider is the condition of the parallel batteries. If one has a higher internal resistance, the charger will shift to float voltage mode before it should, thereby "not doing a good job" of charging.

 

[tvtech]

Hi Joe. Good to see you again.

Any SLA given enough time will reach float charge conditions even with a crappy charger.

I am weary of this discussion. I have tried explaining stuff like this before to all that were prepared to listen. Many knew better

A classic example was a Guy in JHB that spent maybe R3000.00 on two new batteries. Around a Month later he was back saying he is not spending anymore money on batteries...the last ones only lasted him a Month.....

PEOPLE WILL SIMPLY NOT LISTEN.

I have walked the road. I have wasted. I have done the trials and tribulations.

I have learned. Meh, happily sitting here knowing my UPS will only drag the battery down as far as I want it.
And the proper charger takes over when I am done

Gives the battery all the Amps it wants when thirsty. Does not mess around...

Will people ever understand this??

I don't know.

Regards,
tv

 

[KeepItSimpleStupid]

How on earth do they think that a charger that cannot even charge 2 little 7.2 Ah batteries properly...could handle these massive batteries??

Well, how about these: **broken link removed**

5V at 0.500 mA is 2.5 W. If 1 Amp, try 5 Watts.

 

[JoeJester]

tvtech ... 0.1c always equals a charge time of 10 hours.

the 7.2 aH battery at 0.1c is .72 ampers per hour. So when you put two 7.2 aH batteries in parallel, the charger, assuming both batteries being equal, should charge them in 20 hours, as each battery is consuming 0.36 amperes per hour.

The problems always arise when you start putting batteries in series or parallel on a charger.

 

[MikeMl]

tvtech ... 0.1c always equals a charge time of 10 hours.
...

Actually about 12-14h, because of the charge efficiency of Lead-Acids (This from Powerstream):

Coulometric Efficiency. This is the efficiency of battery charging based solely on how many electrons you push in. If you compare watts in to watts out you have to take into account that the battery charging voltage is higher than the battery discharging voltage. The coulometric charging efficiency of flooded lead acid batteries is typically 70%, meaning that you must put 142 amp hours into the battery for every 100 amp hours you get out. This varies somewhat depending on the temperature, speed of charge, and battery type.


Sealed lead acid batteries are higher in charge efficiency, depending on the bulk charge voltage it can be higher than 95%.

 

[Tony Stewart]

As I recall SLA requires a temperature compensated CV level and not 14.4V shown in the MeanWell for FLA battery types, more like 13.8V~14V

Battery capacity must factor Load, duty cycle of no charger and charger power then max duration of outage.
If Load is say 100W and charger is 300W then with 100% efficiency, it might sustain a charge on an oversized bank of batteries with outage at 2/3 of the time..
If load is say 290W with 300W charger then only 10W is available to charge cells. so it can only sustain an outage of 3% of the time.

Then assume and factor 70% charger efficiency and outage ratio is reduced.

So increasing battery size is effective for extending outage duration only if the charger is much greater than the average load.[W]

 

[JoeJester]

Then I stand corrected. Mike and Tony certainly have pointed me in a direction to do some more research. Thanks.

 

[Tony Stewart]

Tvtech said "I knew, learning from past mistakes, never ever flatten a battery unless you can charge it properly. So I left it and let it be."

I believe 50% SOC min is optimal for total lifetime Ah output from research, I have analyzed. Going from 100% to 50% for LiPo was the case. Perhaps also relevant with SLA.

i also know low s.g. and SOC <50% on Lead Acid can promote sulphation which raises ESR permanently after extended periods... Unless rejuvenated with steady fast risetme pulses.. ~ 5A <100ns, > 20kHz (SolarTech)

 

[tvtech]

Hi Tony

I am here and watching

Maximum draw from the SLA with my setup is 8.5A. My charger can throw 20.85A at the battery if necessary to charge it quickly....battery wants a Max of 19.5A....my charger throttles (no cooling fans)...purposely so all balances out nicely.

I have taken this battery down to 50% DOD maybe twice....for testing purposes only. And no problems. Normally down to around 10 to 20% DOD with normal load shedding stuff here and all. Normally 2 Hours at a time.

And of course on Saturday, I decided to try and drive it down to 100% DOD( battery manual says it needs to be done every 3 Months)....UPS would not allow it but was interesting. No harm was done.

With the load shedding Today battery is still fine

Regards,
tv

 

[Tony Stewart]

The following graph shows the evolution of battery function as number of cycles and depth of discharge for a shallow-cycle lead acid battery. A deep-cycle lead acid battery should be able to maintain a cycle life of more than 1,000 even at DOD over 50%.

**broken link removed**
At tail-end of curve , use %DOD x Nc (number of cycles) for lifetime capacity = "Cap."
100% DOD, Cap. = 1 x 180
50% DOD, Cap. = 0.5 x 460 = 230
30% DOD, Cap. = 0.3 x 1220 = 366
so 30% DOD yields a 50% more life capacity than 50% DOD
but rate of charging also affects lifetime capacity, where cooler and slower is better.

 

[tvtech]

But I know that

That is why I said with my initial post" I am weary of this discussion".

Been there and done that

Too make things a bit simpler....theory and graphs are of no real value. You have to actually put said battery through it's paces...and test it in it's glory....with a matched charger....and that takes time and effort. And work. Every battery and every charger combination is different.

Theory is fine..but actual working conditions and all are different from setup to setup. I had the theory with Cyclons waxed in 2005/6 already. Nice Military Grade and all.

Saw my butt. Only realized years after that they died a slow death due to chronic undercharging. Takes time but it eats them.

So, I sort of know my around SLA now. Cuddling the cheaper ones with proper matched chargers and so far so good.

Regards,
tv

 

[Tony Stewart]

We used to build Solartech's Battery Rejuvenator when I was Eng Mgr in Contract Mfg.
Maybe made 25K units before he sold the company. I recall testing it on a older large motive power batteries for Air Canada. A full charged battery with this unit on it for a week, ended up improving capacity on a Sulfated cells and raised the specific gravity (s.g.) on the weak cells till they were all equal and normal for a new battery

It only drew 1 Watt of power when the Charger was on but delivered >10A repetitive spikes.

 

[tvtech]

I will never doubt your experience. Or stuff you have done. You know stuff..and so do I

How is that for a "shake hands" nice new friendship .

+1 for you.

Regards,
tv