sla question

[jeohearn]

Which is best:
One, to charge sla batteries twice a day (at work and upon returning home) or
Two, to charge them once a day at home after each round trip to work.
Brief background: currently I charge twice daily because I'm not sure my 3x12v 12ah will make the 14 mile round trip. But it's occurred to me that they might, and so I am inquiring about any problems with having them sit uncharged at my workplace for 8 hours (I've heard slas should always be charged 'immediately' after each use.)
Thanks for helping a relative newbie.

 

[v_tach]

Let them cool down after use then recharge. No reason to let them sit in a depleted state.

 

[amberwolf]

I'd always keep SLAs topped off, to prevent sulfation. Otherwise you risk damaging the battery, depending on the depth of depletion, even sitting for just a few hours, especially if you do this basically every day.

 

[morph999]

I didn't think there was anything wrong with letting SLA's sit for a few hours as long as they are charged. I'd definitely charge them twice per day if I were you, though. ONe on each trip because, yeah, they aren't supposed to sit in an uncharged state. Also, the least amount of depth used, the longer the life span. I started using my SLA's to 90 - 100 % of capacity and they only last a month after that.

 

[dogman dan]

Charging immediately, as soon as they aren't hot, is best. It prevents sulfation crystals from hardening while the battery waits for the next charge, and with sla's the shallower the depth of discharge the better. sla chargers can be found real cheap on ebay, so get one to keep at work.

 

[RTLSHIP]

I always charge my SLA batts ASAP. Never thought about waiting for them to cool down. After discharging ,charge up at first opportunity or ASAP.
Bring a charger along for the ride. Even if you are only visiting someone for 1/2 hour or so, you can still
get a partial recharge. The idea is to avoid deep discharges and delays in recharging.

 

[pgt400]

Always charge immediatley after use and keep on float....If I'm not riding my bike, its on the charger. I'm going on 3 years and over 2,500 miles with no noticable loss in capacity.

 

[RTLSHIP]

We have a Crown Forklift at work. It uses an Exide Hog battery. It could be over 10 years old. I know we bought the forklift used
back in 04. Still works. We add distlled water. The battery goes at least 3 or 4 hundred lbs.

 

[dogman dan]

The forklift proves the dictum, bigger the better with batteries. Probobally so big it gets discharged at .10 C.

You can charge the batteries warm, but when real hot, a cool down is not a bad idea. So in summer it might be good to cool em first, if they got as hot as nicads like to get.

 

[RTLSHIP]

One other difference with the forklift is that it can be left half charged. We charge it up when it's low.
If you add to much distilled water to the batts, it will bubble up and leak out onto the floor. acid or elotrlytes are lost.
I'm wondering if anybody has opened up a regular SLA and improved it's capacity etc by adding water???

 

[Lock]

Which is best:
One, to charge sla batteries twice a day (at work and upon returning home) or
Two, to charge them once a day at home after each round trip to work.

Hi Joe
A little 36V 3A charger like this:
http://www.powerstream.com/1PAA545-36V.htm

Costs $50 and weighs 1.25lbs... Ya can leave it at work or carry it with you. Idea is to keep your discharges as shallow as possible for longer batt life. Plus yer commutes are not always gonna be only 7 miles one way. There'll be side trips, EVen just for the joy of riding power-assist (grin.) Ya didn't mention where you can park at work - indoors or out - so whether hot/cold ambient temps might be a factor...
Cheers
Lock

 

[Cold-E-Commuter]

I have also heard that leaving SLA batteries in any state of discharge for any duration of time is bad. As dogman stated, it causes sulfation. I also use SLA batteries and have learned a lot form this site and reading the specifications of the batteries at the manufacturers web sites. Here is an example of the specs on one of the sets I have.
http://www.efirstpower.com/PDF/FP12120.pdf
This battery has a 12Ah rate like yours do but that is at a 20 hour discharge rate. As seen there is a 7.49 Ah rate for a 1 hour discharge and a 5.87 Ah discharge for 15minutes. Also on this sheet you can see the cycle life depending on the depth of discharge (DOD). As you can see keeping the DOD to a minimum gives a larger cycle life. With this set of batteries I have determined that a ride of 7 miles over 35 minutes is roughly 50% DOD for the set up that I am riding. So the one way commute you have of 7 miles with a charge at each end should result in a total of close to 400 charges or 200 round trips. The furthest I have pushed this set of 12 Ah batteries is 13.6 miles and did not have the controller shut down. I have also found a set of 14 Ah batteries that are exactly the same size and fit into the original bag. See here: http://www.tempestbatteries.com/html/td14-12.html. This set cost about $130 with shipping from batteryspec.com and are worth it to me for the increased range. Hope this has been helpful.

 

[RTLSHIP]

I recently(ebay) purchased 4 12v 11ah SLA batteries for $106(shipping & taxes incl). They can be bought for 6% less if your outside of Fla. I can only speculate or surmise that the ride range on these is probably more than what you get with 36v 12ah SLA.
the weight is about same, they fit into the same battery bag, and the price is about the same. Of course, you need a 48 v sla charger. Went to work this morning on my brushless outfit. Very little pedal assist during the ride.
Approx 52 volts when the pack is "resting." 50.2 volts after a 4.4 mile ride to work. With a 2.5amp 48v charger, it took about 1hr 20 minutes to recharge, so I guess approx 3.4 amps were drawn?
By the way, there was a 10 to 15 mph headwind most of the way.
I figure a 10 to 12 mile ride/range will drop pack down to 48v. with wind resistance maybe 8.5 miles.
this is better range than ordinary 36v 12ah SLA.

 

[Lock]

Hi RTLSHIP

...think of your pack size in Whs - V x Ah ... the four 12V 11Ah batts give you 528Whs versus the three 12V 12Ah at 432 Whs... so 22.22% greater capacity. Ya will use the same amount of Whs to travel the same distance at the same speed so a smaller percentage of the larger pack. Shallower discharges = longer SLA life. With the higher volts of the 48V versus 36V, for the same wattage you will be using lower amps. Lower amps = lower losses in wiring etc, so there're savings there also. Offsetting this, the larger pack will be heavier a bit, so more energy needed for acceleration or hill climbing.

Enjoy the fresh lead! Best to shallow cycle things for the first dozen or so discharges and recharges.
Lock

 

[RTLSHIP]

thanks Lock. I always try to not go beyond the nominal capacity of 12v. this translates into 45% DOD maximum.
A DOD of 30% is ideal for battery life.
today's 4.5 mile trip is the furthest I've gone with it. This is the 4th recharge. When brand new, it took over an hour to fully charge this pack. A brand new pack is usually not fully charged, so a full charge is important before initial use.
I had heard the opposite about breaking in SLA: go deep early so that you get more range over life of the battery.
these Powertron 12v 11ah batts weigh approx 6.4 lbs each (>26lbs total); the typical 12v 12ah weighs around 9.2 ea (<27 lbs)

 

[Lock]

I had heard the opposite about breaking in SLA: go deep early so that you get more range over life of the battery.

Pretty sure this is NOT correct! Hopefully others will weigh in here... Disclaimer! I am really just an "end user"... I just wanna hop on and ride! Others here are far more knowledgeable than I about this stuff. I have ridden a lot but abused batts etc big time. Coulda saved lots of money over the years with better behaviour but have been happy to charge the excess off to entertainment!
Lock

 

[RTLSHIP]

One correction: the 48v 11 ah sla weighs (with bag) 26lbs; 36v 12 ah weighs 24 lbs. So Lock is right about the weight.
Shallow discharges make sense for SLA, especially while breaking in. Lifepo4 should also be broken in gradually as well as left on charger for some a while.

 

[dogman dan]

Never heard of that go deep early one before. Sounds like a variation of the nicad myth that stuck around 30 years about fully discharging them. Now we know what we really should have been doing is fully charging them, after letting them cool off. It makes "common sense" though so I could see how such a myth might get started.

 

[Cold-E-Commuter]

Nice tid bit from Lock. Increasing to 48V at 11Ah pack gets better range than the 36V 12Ah . Thanks. I guess I have been focused on Ah and not the available Wh. I guess that speed will make the difference according to the majic 26mph I have read about in many posts here. This may change my mind from the 36V 20Ah Ping I am looking at to the 48V 15Ah pack. 36*20=720Wh available vs 48*15=720 Wh. The same Wh availability but a higher speed if desired or same range at same speed. Seems to have more options. What can anyone tell me about getting a BMS for a Ping battery if needed? Just something for the future. SLA's are getting the job done for now.

 

[Lock]

Hey Cold-E
... Ping packs come w/a BMS.

Whs measure absolute capacity... available stored energy as how many watts can be delivered in one hour. Volts times amps give ya watts (power) but each is important with plusses and minusus. More Volts gives ya more RPMs - higher speeds - while more Amps gives ya better torque - acceleration and hill climbing. More amps means more losses (heating of motor/electronics/wiring/connections...) So it's a little dance juggling the mix of volts and amps to get watts.

Also, the (SLA) batt manufacturers LIE about their batts (Ah ratings.) Their ratings are based on a discharge rate over TWENTY hours. In an EV world life ain't like this. Faster discharge rates means ya see less actual Ahs from the batts. Then there's the fact ya shouldn't run the batts down below 20% of their rated capacity w/out reducing their claimed life (number of cycles, discharge plus recharge usually claimed as 300) and really running them down to only 50% does mean a longer life (more cycles before they get too tired.)

Then there's cold weather... where the Whs ya see get cut again.

I have a LiFePO4 pack to play with now, but if yer sizing a SLA pack, basically ya need to figure out the Whs ya need to get the job done. Lots to consider there, including the fact that power needs to cut through the air are not linear. Once yer hitting the high 20mphs (or hit real head winds) power needs per mile rise quite a bit (slowing down takes longer to get places, but you consume less Whs per mile, so have longer range.) What is your mix of pedalling versus battery really?

Then double this to allow for not running the batts down to empty. Then double that again to allow for cold batts in winter... Then decide on the split between Volts and Amps. (Actually, really I have this backwards. Figure out how many volts (RPMs) ya need, then how many Amps (how much ya want to show off yer power-assist) THEN figure out how long ya need to be burning up these Watts - watthours.)

Then add some more Whs to allow for play, `cause you'll end up spending more time having fun w/yer power-assist bike than you imagined

And yer SLA pack isn't fresh lead forever... allow for the fact that after 100-200 cycles they will already be feeling a bit tired compared to when they were new.

Gawd I love fresh lead... the way the vehicle feels alive again when ya plug in a new pack after the last daze and weeks of trying to squeeze a bit longer life out of the old, tired pack just replaced!
lL0K

 

[dogman dan]

As a general rule I suggest the 36v 20 ah size or the 48v 15 ah size for a ping. Why? they both weigh a reasonable amount and fit nice in old toolboxes and trunk boxes on rear racks. The 48v 20 ah is 5 pounds heavier and harder to fit in avaliable containers. The 720 wh is enough for long rides when you want one, and shorter rides that make shallower cycles don't hurt the battery.

Sometimes you get a guy who thinks 1000 20 mile cycles is the same battery wear as 1000 10 mile cycles. So they want to buy just the right size battery. But in fact, at 50% discharge on a ping you might get 2000 cycles.

The 20 ah battery can put out 40 amps continuous, so it's even suitable for 35 amp controllers on most motors.

The 15 ah battery can put out 30 amps continous, so its ok for up to 25 amp controllers.

I recomend keeping the 2c discharge rate to be above the controller rating so you never spend much time at the actual continuous discharge rate, but rather stay below it most of the time.

If something happens to your ping bms, he can send you another.

Meanwhile, adding one more sla is pretty easy and affordable. Back in the 4 buck gas summer, everybody was adding another sla to run 48v on thier Wilderness Energy kits. 48v is the only way to go with sla's. After they sag you still have a bit of speed.

 

[RTLSHIP]

the odd thing about my 48v 11ah SLA pack is that it weighs nearly the same as many of the 36v 12ah packs, but it has quite more energy density. I don't know the quality of these" Powertron" SLA. They are definitely for cycle use (not just standby).
Maybe SLA batts are getting lighter.
This 48v sla setup is nice on the Aotema Brushless kit. There seems to be additional efficiency as I'm using a limited 48v controller.
these 12v 11ah SLA's say 11ah on them. True, manufacturers misrepresent amp capacity on SLA's, but could I have gotten a
8.5 or 9.5 ah pack with 11ah written on it. Seems unlikely. Clearly, the weight & dims on these 11 ah packs is 6.4 lbs. 6x3x5 "
9ah batts have same weight and dims. Maybe Powertron is making high tech SLA.

 

[Cold-E-Commuter]

Is it possible to mix SLA batteries for a higher voltage? I have (3) 12V 12Ah batteries and (3) 12V 14Ah batteries and am wondering if it is possible to create a 48V pack by mixing. I have thought of creating this new pack using 2 of each wired in series of course. I don't know what having different Ah ratings in a pack might do. Can anyone tell me what this might do or if this is a bad idea?

 

[amberwolf]

The only problem you face when seriesing different capacity batteries is that you only get the capacity and current-draw capability of the lowest rated cell.

So your 12Ah batteries will limit the peak amount of current you can draw to whatever their max is, and they will also limit the total Wh you can draw from the pack to their limits.

The former means that although a 14Ah battery could probably normally face a higher current draw without much sag vs the same draw in a 12Ah, the 12Ah will still sag at that draw, being pulled in series.

The latter means that for Wh and Ah purposes, you should treat all of the batteries as 12Ah, even though the 14Ah would provide a little more power, doing so while seriesed with the 12Ah would cause over-discharge of the smaller batteries.

So do your Wh calculations for how much total power you can pull out of the pack as if you used 4x 12Ah in series, x2 of those strings in parallel, or 48V 24Ah.

 

[RTLSHIP]

I've read that an SLA pack is only as potent as its' weakest battery. This is consistent with amberwolf's comments.
There are people who ride with a 36v 12ah pack and bring along a 12v 8ah battery to use as a "power booster."
I'm not sure how to do the wiring on that.