SLA vs. LiFePO4

[safe]

The fact of the matter is there are more factors than cost.

Oh I agree 100%.

In fact my designs tend to be "sport oriented road racer" designs that are not really all that practical compared to other options. I suspect the ultimate "cheapskates special" would be something like that guy building a tricycle and placing the SLA's in the back. That allows you to carry the weight with plenty of stability and would not cost much to do. He was planning to add some strong mag wheels to support the weight.

There are a lot of very practical chinese scooters and cargo transport vehicles that follow similiar design principles... but they don't look like that much fun to ride.

If fun is the goal and startup price is not a problem then the advantages of less weight with LiFePO4 opens a lot of doors.

Eventually I'm going to build the "dream road racer bike" where I put some serious money into it... but I want to refine my designs cheaply for now. Until all this stuff stabilizes in price and design I'm trying to make my way through without having the "dot.com disease" of splurging on all kinds of stuff that don't add value towards anything worthwhile.

After all... we are in a tough economic environment... it's good to think in frugle terms even if your goal is pleasure. It's hard to enjoy something that is hemoraging money all the time...

 

[EMF]

The fact of the matter is there are more factors than cost.

Oh I agree 100%.

What the....

 

[Patrick]

I think of battery life as three different variables:
cycle life (at a given DOD)
shelf life (self discharge rate at given temp)
calendar life (how many years they last. may be affected by temp and DOD cycling)

Cycle life has been documented, but calendar life isn't proven yet for the latest lithium cells.
(edit: TS claims 5-10 years for their scoots)

But some people love to see the math, so here's mine:

16 ThunderSky 40 Ah cells in my scoot.

30 miles range is 75% DOD, at the 40 amps I pull flat out.

ThunderSky claims 3000 cycles at 75% DOD, but let's say I only get 2000. So, 60,000 miles on a pack.

The pack costs $1200. So 1200/60,000 = 02 cents per mile.

With a 30 mile commute each day, that's 8 years of use. Obviously 4 years if I do 60 miles a day.

If the calendar life is there, lithium is half the cost of your "cheap" lead.

Just my two cents worth.

 

[safe]

The pack costs $1200.

The pack costs $1200.
The pack costs $1200.
The pack costs $1200.
The pack costs $1200.
The pack costs $1200.

If I could just get past the startup costs then I agree that the price starts to look pretty good... it's the "safe" thing to do to want to take the lower cost road though. It won't be long before true knowledge about "calender life" comes out... I'm glad you brought up that term "calender life" as opposed to "shelf life". I think I've been using the wrong term for a while. (hey I was calling "Armature Current Limiting" by the phrase "Motor Current Limiting" for a few months, so I do get the words wrong sometimes)

From now on I'll use the phrase "calender life" when I want to describe the total time before batteries decay.

 

[Ypedal]

All these years.. i've had to read instruction manuals with paragraphs that make me scratch my head and think " Who on earth writes this stuff ? "... i think i found my answer ! :lol:

About cost.. it's only money, can't take it with you when you die.. :wink:

 

[safe]

About cost.. it's only money, can't take it with you when you die.. :wink:

I can remember during the dot.com days a fellow programmer in San Francisco had rented an apartment for something absurd like $5,000 a month and his attitude was that money is something to be spent. Well they all seemed to have spent it and ended up broke and I was the "tight wad" that saved it and managed to stop working at 40 years old. (I'm 47 now)

Time is money and money is time.

If you spend all your money you will need to spend all your time making more of it... which means less time exploring your own interests like ebikes.

So I'm still concerned about the "bottom line" on everything... you know the saying:

"A fool and his money are soon parted."

...I leave the fast parting of money to others.

Going to the gas station and spending $40 to just fill the tank is getting to be a real shock, so anything is looking better than gas these days...

 

[Toorbough ULL-Zeveigh]

By a staggering coincidence I'm exactly the same age.
I sold my computer service company at age 30 & retired at 35.
Do I 'win' ?

 

[TylerDurden]

Do I 'win' ?

Whoever dies with the most debt wins.

I believe the Merrikans are in the lead. (LEED)

 

[safe]

By a staggering coincidence I'm exactly the same age.
I sold my computer service company at age 30 & retired at 35.
Do I 'win' ?

Yes you do... you beat me by five years.

It's good to have really smart guys like us that decide to not just throw our time away grinding away at some boring corporate work. The computer thing is "solved" and anyone that has any brains right now is into "Going Green". It's the place to be, the "new frontier".

So you need to get into something... are you doing any pet projects? The world needs smart guys meadering their way towards a solution so that they might stumble on it by accident. I figure that eventually I'll use all this accumulated knowledge for some productive purpose... whether in something I might make or if I do want to work on something again for someone else it will help me get the job. If nothing else just knowing the technical stuff and passing it around helps the "collective".

It's nice not be worried about survival all the time... that's the best thing about not having to work, you can pursue your own interests.

 

[andrew]

safe, have you considered gel cells for replacements?

SLA (sealed lead-acid) seems to be another term for valve regulated lead-acid (VRLA), which can mean either gelled electrolyte (gel cells), or absorbed electrolyte in glass matting (AGM).

Being so concerned with cost, did you research the cycle life of gel cells, which appears to be at least twice that of AGMs?
http://www.mkbattery.com/techref.php
MK Battery Gel Brochure

And, what about "Silicon" lead-acid which are really just a variation of gel batteries? Also VRLA, and supposedly last 400 full cycles, at a cost that is cheaper than high-quality AGMs from siliconebatteriesusa.com .

I contacted Trojan Battery Co., a long time manufacturer of large EV batteries. Their opinion was not very good at all about AGMs in terms of cycle life, especially for deep cycles. They recommended their gel batteries instead. Some of their flooded batteries in a Renault electric car that my family owned lasted 18,000 miles.

Have you really found the cheapest of anything?

 

[EMF]

It's good to have really smart guys like us that decide to not just throw our time away grinding away at some boring corporate work.

In my life, I have found that the "really" smart people are the ones that don't try to give that impression. Let alone proclaim it in writing. To me, money or wealth is not a good yardstick for measuring intelligence or wisdom. My grandfather was poor by many peoples standards, but he was one of the wisest men I ever knew. I just wish I had written down a lot of the things he said to me when I was a kid - as I forget them now...

 

[Link]

It's good to have really smart guys like us that decide to not just throw our time away grinding away at some boring corporate work.

In my life, I have found that the "really" smart people are the ones that don't try to give that impression. Let alone proclaim it in writing. To me, money or wealth is not a good yardstick for measuring intelligence or wisdom. My grandfather was poor by many peoples standards, but he was one of the wisest men I ever knew. I just wish I had written down a lot of the things he said to me when I was a kid - as I forget them now...

+1. My grandfather was only average when it came to income. He died when I was like 6.Too bad, too. He was a certified genius; we would have got along well.

 

[safe]

I have found that the "really" smart people are...

I only run with the "smart crowd"...

 

[EMF]

I only run with the "smart crowd"...

Me too....now. It just took me a bit longer to figure out who they were and I wasted some years in the process. :wink:

+1. My grandfather was only average when it came to income. He died when I was like 6.Too bad, too. He was a certified genius; we would have got along well.

That's too bad Link, but even at 6 somehow you knew he was of great value and this is just the way my grandpa was. You were lucky to know him even for that short time, I'm sure of that.

 

[TylerDurden]

I only run with the "smart crowd"...

You only "run" with the drunk crowd... you simply annoy the other crowds.

 

[Toorbough ULL-Zeveigh]

Yes you do... you beat me by five years.

Wrong answer.
Where you end up has more to do with the cards you're dealt than skill or brains.
That's why I've never felt the need to mention at what age I retired at except in rebuttal to a faulty premise.

Now I'm getting off this flight to Havana.

 

[rf]

By a staggering coincidence I'm exactly the same age.
I sold my computer service company at age 30 & retired at 35.
Do I 'win' ?

If your ebike doesn't run on those gawd awful SLAs you win hands-down!!!

 

[EMF]

Yes you do... you beat me by five years.

Wrong answer.
Where you end up has more to do with the cards you're dealt than skill or brains.
That's why I've never felt the need to mention at what age I retired at except in rebuttal to a faulty premise.

Now I'm getting off this flight to Havana.

I think this is right too and it's how I think things are pretty much. Seems like to me as well, that results come of a combination of things and also personal decisions we make and this is also the point I tried to make. Having said that, for you guys to be able to retire at such an early age is most impressive and shows what is possible if you set your mind to it and work hard!

I guess my favorite saying that speaks to this, is one I heard once on TV during a professional golf tournament. At one point, a player made a fantastic shot from what seemed an imposssible position, to place the ball only a couple feet from the pin. One announcer in hushed tones, made the comment that the guy got "lucky". Immediately, the other announcer who was British said: "Luck is the residue of skill". :wink:

Like Toorbough ULL-Zeveigh - I would also like to get off the plane and get back to the thread subject.

 

[safe]

Where you end up has more to do with the cards you're dealt than skill or brains.

Momma always said that "life is like a box of chocolates, you never know what you are going to get."

The secret to life is to follow the obvious when all others follow what other people expect of them. (then exploit your finds to your advantage)

The "Emperor has no Clothes". :wink:

The "wisdom" in life is to avoid what everyone else accepts as truth and see things as they really are... it's simple... but people keep missing the obvious again and again and again... because they lose the ability to value their own ideas and insights. People become intellectual cowards... sheep... swept up by trends and media created views.

Some things never change. :lol:

I like the other chemistries that are emerging, but I stand by SLA for what it is. I've proven that it CAN perform better than most people imagine if you do your homework. While all others accept being a "loser" because they failed with SLA I stand as a "winner" in that I've proven that it can work. It's not the problem with SLA that made your attempt fail (if it failed)... it was you.

Hey, I'll be using all kinds of chemistries over time... but my point is not to allow public "fads" to make you believe that which is not true. SLA done right can perform very well. And when it comes to startup cost verses performance you really can't beat it with anything out there.

Just don't be a moron and try to run an ebike on 10Ah batteries... that's just never going to work very well. Do your homework first.

The Simple SLA Rule:

Your Current Limit Needs To Be No More Than 1C.

 

[andrew]

The Simple SLA Rule:

Your Current Limit Needs To Be No More Than 1C.

Unsupported, and wrong. I'm running my motorcycle with a current limit of about 17C (actually it's higher, but I don't exceed about 17C). Electric motorcycles and large EV conversions commonly go more than 5C current limit.

For some reason safe never responds to my posts

 

[Eric G]

Moron Huh!!!
I've been using 7.2ah sla for over a year now and they're still fine and more than likely still will be for this summer,I've logged over 1000 miles on these so far.Short bursts of ~3c are acceptable as long as you don't do it all the time.If you don't have or use your pedals pedals then yep you'll suck as many amps as the controller is rated for and large AH batteries will be better.It's all in how you use what you've got.Sure I'd like to use a lighter and newer chemistry that discharges with a flatter curve but for now the wallet says no,and SLA will have to do and they do!You can't be calling people morons because they don't do as you,it's not nice!

I retired at 40,but it wasn't by choice,LOL...

Eric

 

[Battboy]

This trhread seems to have derailed after the first page of responses.
Getting back to the original author's question and the answers provided -
I tend to support the answers given. As a more thorough explanation I offer
this explanation.

The comparative disadvantage with PbA chemistries is the dynamic internal
resistance of each cell that increases as more current is discharged while the
electrolyte, anode and cathode components undergo a chemical transformation that
has to be reformed during the recharging period. The results of this non-linear
chemical change is called the "Peukert" effect of lead-acid batteries, where
cell voltage drops off exponentially as more current is drawn and internal
resistance continues to increase with more rapid chemical transformation. A
more rapid exponential voltage drop reduces the overall capability of PbA
chemistry to supply the rated power to a load consistently. For instance, a
battery pack with a 260Ah rating may provide current for 20 hours if the battery
discharges current to a light load with steady current draw. However, a heavier
load like an electric motor that draws current from the battery within 5 hrs,
accompanied by sharp increases or decreases in current demand, may cause the
pack voltage to drop off more quickly as internal resistance rises. The battery
pack may only have an effective rating of 215Ah per charge cycle for this
application.

The more constant internal chemistry and voltage characteristics of LiFePO4
battery packs provide a more constant supply of total power to a system, as a
function of the balance between voltage and current where Power = Voltage *
Current. Since the voltage does not drop out as quickly in LiFePO4 chemistries
as it does in PbA chemistries, the current does not need to increase
proportionally in order to maintain power. This means the power delivered to the
motor will be very consistent until the very end, and less power will be lost
when accelerating and cruising in an electric motor vehicle.

Because the PbA cell internal resistance increases and causes the pack voltage
to drop, more current must be drawn from the battery to produce the same power.
Current draw continues to increase over time as more internal resistance is
formed with further chemical transformation of the battery components, resulting
in an accelerating discharge of the total power available within the PbA battery
pack.

When attempting to compare LiFePO4 to PbA chemistries, the first major advantage
of LiFePO4 cells are their ability to discharge power in terms of voltage
(volts) and current (amps) over time (hours or seconds). LiFePO4 chemistry has
far greater power discharge capability than PbA chemistry because electricity is
generated more efficiently from the movement of ions rather than from a chemical
reaction and transformation.

For these reasons PbA chemistries have been ruled out for EV Automotive use
entirely other than as a "car start" battery. PbA can still find a place in e-bike
& particularly scooter applications due to it's low entry cost level. I hope this
helps anwer the original author's question ?

Don Harmon



Don Harmon

 

[Link]

Your Current Limit Needs To Be No More Than 1C.

Don't think I could fit 30Ah of lead on my bike if I tried, and that's not even a very high current limit.

 

[rf]

Don't think I could fit 30Ah of lead on my bike if I tried, and that's not even a very high current limit.

One of the advantages of an ebike in my area is that the buses have racks for bikes. So if you break down or would like to travel a longer distance the bus can be a real asset. But you need to be able to lift your bike onto the rack.

Lead makes that very difficult.

Richard

 

[safe]

Unsupported, and wrong. I'm running my motorcycle with a current limit of about 17C (actually it's higher, but I don't exceed about 17C). Electric motorcycles and large EV conversions commonly go more than 5C current limit.

For some reason safe never responds to my posts

Okay, I will respond this time.

My point is that going above 1C creates a Peukert Effect that is more than 50%. If you are going above 50% in losses then you just aren't getting much out of the battery in terms of amp hours or watt hours. It's a question of how efficient your machine is going to be... how much range you can get.

You also need to think in terms of "peak power" verses "average power". I've heard that SLA is pretty good with short term bursts of power, but they need time to "rest" between those surges. If you ride in such a way where you "lurch and coast" a lot then you can get pretty good performance even at higher "C" rates.

My "peak power" is only 1C and that means that if I'm in a more conserving mode I run at more like 0.5C which means that I'm only losing about 35% of the total energy in the battery. If I work really hard at it I could make it 20 miles which is how that race in Portland is set up... more based on range and endurance than peak power.

My original point was that if we are talking about startup costs and long term costs you want to find the optimal point where you get the most energy out of your investment. LiFePO4 CAN achieve good economic numbers... but it can take 10,000 miles before you begin to break even compared to a well designed SLA system.

On my bike I've passes 3,300 miles and after replacing one bad cell (of three) I've only spent $200 so far. It's possible that I could go to 5,000 miles or more for $200. That's low startup costs and hard to beat even at high mileage for LifePO4. (SLA can still be a bargain if done right)