# Reasonable performance from SLA (300V, 6kWh, 750lb, $1000)



## Ziggythewiz (May 16, 2010)

What kind of amps can those little batteries push?


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## PStechPaul (May 1, 2012)

The 4.5 Ah SLA batteries are probably similar to these:
http://www.power-sonic.com/images/p.../ps_psg_series/6volt/PS-640.pdf_12_July_9.pdf

So, at 2C, they have 1/2 the capacity, 2.25 Ah at 9A, to 4.5V. The maximum long term discharge current is 13.5A (3C) for 7 minutes. Peak burst current is 45A (10C) for 7 seconds.

Terminal voltage at full charge is 6.35V and drops to 5.95V at 1C, so ISR is about 0.4/4.5=0.0889 ohms. Using that, the peak short circuit current would be about 6/0.09=67A. The terminal voltage for the rated 45A burst would be 6-45*0.09=1.95V.

The rated life to 60% original capacity is 200 cycles for 100% discharge, 500 cycles for 50% discharge, and 1100 cycles at 30% discharge.

If you had 50 of these batteries as DC link voltage for a VFD which drops out at 200V, you could get a maximum of 22A or 4.4 kW. With 60 batteries you'd start with 360V so you could get 37A and 7.4 kW. You get maximum power transfer at 50% of nominal battery voltage, so this is about it. From 1620 rated capacity (1/20C) the absolute maximum power you can get is about 4.5x. You can get more current, but lower voltage. 

For a simple series wound traction motor you might be able to pull more torque, so you might be able to get 10x to 15x if you basically run a short circuit. In that case you'd be using them basically as disposable primary cells. Maybe get 10 cycles before they blow up.

There is another thread about using LiIon in parallel with lead. So in this case you could get 100 pcs (320V) of the SLAs for 1350 Wh (including adjustment for Peukert) for $560 and 50 pcs (320V) of the LiFePO4 of the same capacity for about $1200. So you can get a 2.5 kWh pack for $1800. You can use the burst capacity (30C) of the LiFePO4 for short term acceleration power of 40kW for 2 minutes total, which is enough for about 10 drag races. Of course it would only provide about 7 miles of range.


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## PStechPaul (May 1, 2012)

*Re: Reasonable performance from SLAs (360V, 6kWh, 750lb, $0.15/Wh)*

I found another source for inexpensive SLAs:
http://www.herbach.com/Merchant2/me...AR&Product_Code=TM96BAT2869&Category_Code=BAT

This is a a 12V 12A-h Panasonic SLA for $21.50, weight=8lb, actually two 6V units strapped together. That works out to 144Wh and $0.15/Wh which is about the same as the 6V 4.5A-h battery for $4. So 30 of these puppies would be 360V and 4300 Wh, for $645, and weighing 240lb. They are in Moorestown NJ so shipping should be not bad and if I wanted to get, say, 120 of them which is 1/2 ton I could just take a ride up there and pick them up. At that quantity I could probably get them for $2000 and I'd have about 16 kWh and at 330 Wh/mile I could get maybe 30 miles of range. At 30 MPH and 10kW that's 2/3C so real capacity is 9.3 kWh with Peukert=1.2.

I think I will order 4 or 6 of these for my tractor project(s). Pulling 2HP at 36V (3S2P) is 42A or about 2C, for about 1/2 hour, but mostly I'll be pulling 1/2HP so I should get 1.4 hours runtime.

How do SLAs compare to flooded lead acid deep cycle batteries? I can get a 12V 105 Ah battery locally for $85 which is $0.07/Wh. Could the SLAs be twice as good?


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## piotrsko (Dec 9, 2007)

unless you know the specific chemistry involved, it is difficult to compare the two. The chemistries do vary by manufacturer and even different types from the same place.

basically, a sla is a fla with pressure caps. More batteries equals more complexity which introduces interesting failure points like inadvertent plasma events.

my 202 vdc 25 kwh pack cost about $2200. Using all of one style battery could have shaved $500 at some decrease of longevity, but the jury is still out on that decrease because I haven't had a failure yet.


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## McRat (Jul 10, 2012)

Be real cautious. Lead acid batteries have vastly different qualities and a shelf life. This is spoken from a recent victim. I bought a battery for a motorcycle recently (SLA), and it would barely start the bike even though it said 12.5v. So I put it on the charge. It never recovered it's capacity, and was dead in 6 months. I come to find it's 5 years old.

I replaced it with a cheaper, fresh battery of the same rated Ah from another brand, and it works like it's supposed to. I see this alot with UPS power supplies for computers. The $90 ones have a limited life of about 3 years, but the $400 ones last 5+ years. Both use SLA.

I'd buy a couple first before buying a quantity, and test them.


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## PStechPaul (May 1, 2012)

I just bought 6 of the 12V 12AH SLAs. I should get them tomorrow. Looking more closely, they were supposed to be PANASONIC LCR12V10BP, but they are two BAT-0063 and the closest spec sheet I could find is:
http://www.apeximg.com/spec/D5736.pdf

They are UPS batteries and the graph shows discharge rates up to 3C for 8 minutes. At a 1 hour discharge the effective ampacity 7.2 Ah for a Peukert of 1.89. They should last for 1200 cycles at 30%, 500 at 50%, and 200 at 100%. 

I bought a 12V 17Ah SLA at a Hamfest about 8 years ago (2004?), and I used it intermittently with an inverter and for my low voltage induction motor experiments in 2005. Its date code was 1999, IIRC. When the battery in my old lawn tractor went bad, around 2008, I replaced it with the SLA, which was about half the size. I used it occasionally, but mostly let it sit. Several times I charged it up but mostly I forgot about it and then last Winter, after it had just been sitting for about two years, I decided to see if it had any life in it. Surprisingly, when I turned on the ignition, the light lit up fine and even the headlights worked OK. So I charged it up and used it to turn the engine, as shown here:





 
And it's the same battery that I used in this early test drive of my Craftsman riding mower project:





 
So if that's any indication of what to expect, I'm sure I'll be happy! 
.


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## PStechPaul (May 1, 2012)

Today I got two boxes from UPS, but neither of the boxes looked big and heavy enough to contain 6 8lb SLAs. Sure enough, they were not included.  The paperwork showed them as being discontinued.  So It looks like I'll order them from eBay.

Just did. Ordered three for $73 including free shipping:
http://www.ebay.com/itm/UPG-D5744-S...US_Rechargeable_Batteries&hash=item1e700ba3e8


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