SLA vs. LiFePO4

[Battboy]

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)

If you figure SLA will deliver on average 300 Life Cycles, while LiFePO4 will deliver 3,000 Life Cycles - wouldn't that mean you will replace the initial SLA investment 10 times by the time you reached a certain end point ? And in fact there is a good chance that LiFePO4 can deliver twice that number depending on the way you use them.

Don Harmon

 

[safe]

If you figure SLA will deliver on average 300 Life Cycles, while LiFePO4 will deliver 3,000 Life Cycles - wouldn't that mean you will replace the initial SLA investment 10 times by the time you reached a certain end point?

It all depends on your SLA design.

This has been my point... most people have failed to design their SLA's to be limited to 1C. If you keep the drain rates to lower levels then the battery lasts longer. (and don't drain too deep either)

Long term storage of SLA can last for 20 years (under ideal conditions), so if you are willing to treat them delicately they will last a long time.

If it cost $1000 for LifePO4 and $100 for SLA and you have to replace SLA 5-10 times to get the same range (which is probably true) then it's all about what startup cost you are willing to pay.

If you have lot's of startup $$$ buy LiFePO4.

If you want to pay low startup $$$ then buy SLA.

...over the long term they are close to the same price.

 

[Battboy]

I agree to a point. If you shallow cycle LiFePO4 like you are talking about doing with SLA, we can get projected life cycles of 20,000.

The voltage sag is also much less with LiFePO4 in that you keep a flat discharge curve, where as with SLA it drops off very fast under electric motor loads.

The weight of LiFePO4 is 1/3 the weight of SLA.

You only need half the Amps with LiFePO4 that you do with SLA (generally speaking).

LiFePO4 is Enviro - friendly.

It's all in how you look at things ???? If start-up cost is your sole important issue - then by all means use SLA. Your really have no other choice.

Don Harmon

 

[EMF]

If start-up cost is your sole important issue - then by all means use SLA. Your really have no other choice.

Don Harmon

Right! Plus, I like it when folks use lead acid as it helps to keep demand down on LifePO4, which until supply catches up with demand, helps keep the price down. :wink:

I wish everybody used lead. :lol:

 

[Link]

I wish everybody used lead. :lol:

Correction: "I wish everybody ELSE used lead. :lol:"

:wink:

 

[EMF]

I wish everybody used lead. :lol:

Correction: "I wish everybody ELSE used lead. :lol:"

:wink:

Right!!

 

[safe]

If start-up cost is your sole important issue - then by all means use SLA. Your really have no other choice.

Let's think of a typical person that might buy an ebike. They could probably handle some extra weight in the form of batteries if the overall bike is designed strong enough for it. Now let's say they ride the bike once each weekend for the summer and so we get a total of:

6 months (late spring / summer / early fall)
4 weekends per month

24 cycles per year.

Now if you rode that bike for five years (which is about when the calander life of the battery forces a replacement)

24 cycles * 5 years = 120 cycles.

In such a scenario for LiFePO4 it would take many, many years to start to pay back the startup cost.

On the other hand if you had someone that used their ebike to ride 10 miles each way to work you would get cycles like:

5 days * 4 weeks * 12 months (all year) = 240 cycles

...and then in five years you would have used up about 1200 cycles.

The fact of the matter is that is takes real effort to make up 1000 cycles. Calender life is the main concern and that's part of why SLA with it's low startup price makes sense for many people. I'm a frequent rider and I've gotten a lot of mileage out of SLA, so I know it can be done, but there are special precautions in the design that most people ignore and so they end up with failure.

The moment I learn the true "calander life" of LiFePO4 is the moment I will have full knowledge of it as an investment. That's the piece of knowledge no one knows yet.

The true "bottom line" on LiFePO4 is unknown...

 

[Battboy]

Well if it's of any value to you we offer a 3 Year Warranty on our LiFeBATT Packs, but we don't sell them for e-bikes. So if you go by the Warranty the Calendar life would be 3 Years. In reality you will most likely get double that, but at least you are covered by the Warranty for 3 Calendar Years.

I believe most Lead batteries come with a 1 Year Warranty but I could be wrong about that?

Don Harmon

 

[rf]

Let's think of a typical person that might buy an ebike. They could probably handle some extra weight in the form of batteries if the overall bike is designed strong enough for it. Now let's say they ride the bike once each weekend for the summer and so we get a total of:

6 months (late spring / summer / early fall)
4 weekends per month

24 cycles per year.

Wow!

Perhaps you meant to say non-serious rider. How about someone that rides 10 or 20 miles per day commuting to work? A really wonderful, potentially Earth-changing, application for an ebike.

Five times a week ... 20 to 40 cycles per month, 200 to 400+ cycles per year.

Now it all makes sense. This crazy, unreasonable insistence on Lead over reality. It was all geared towards occasional weekend rides. Oh!

For the rest of us: Lead clearly makes no sense.

Richard

 

[Battboy]

I think Richard "gets it"

 

[safe]

On the other hand if you had someone that used their ebike to ride 10 miles each way to work you would get cycles like:

5 days * 4 weeks * 12 months (all year) = 240 cycles

...and then in five years you would have used up about 1200 cycles.

As you can see I covered that.

Yes, for someone that uses an ebike for work then it starts to make sense because in three years you could conceivably begin to pay back the startup costs.

But think of how many people own bicycles that ride them very rarely?

I used to work at a bike shop as a young man (25 years ago) and people didn't ride their bikes very often. They might go for a ride about once a week at best and often it's far less than that. The "hardcore" rider is rare and if you are looking to build a product to sell (like I'd like to) then you need to able to hook the beginners with a teaser low price. SLA allows you to sell the bike at a low price and then if that person goes "hardcore" they could replace the SLA with LiFePO4 later on.

It's the natural "upgrade path".

...but my point remains, for the first time buyer that isn't sure about their purchase and just wants to get into ebikes it would be nice if they had really well built (sturdy) ebikes that properly used SLA. They don't exist right now... but they could and they should. It's the "missing design" that needs to be filled.

On the practical level... SLA for people without a welder is not very good. (all the success stories are all by people like me that are custom builders)

LiFePO4 makes the MOST sense for people that have limited means and options for anything else. It's nearly impossible to strap on SLA cells to a regular bike. (not recommended)

So you "lose" on the abstract concept (SLA is workable if you are wise in your design) but you "win" on the practical level because for an ebike purchaser your options are limited.

 

[rf]

Okay, so Lead Acid batteries are for losers.

People that buy ebikes but aren't going to use them. And for the vendors that cater to losers.

Great.

 

[safe]

Okay, so Lead Acid batteries are for losers.

If you are in America we have this election going on where the two liberal candidates are divided over two types of voters. There is the wealthy, urban "elite" crowd that votes for Obama (as well as blacks because Obama is black) and then there is the poor, working class, often rural crowd that votes for Hillary.

People who are not wealthy and need basic transportation are better suited for SLA.

People who are wealthy, urban, and want to appear "elite" would go fo LiFePO4.

For the same reasons the "common man" hates Obama the "elite" folks love him... elitism in anything (politics or batteries) becomes like a fashion statement.

It's like driving a Ferrarri (Tesla?) verses a subcompact car... the subcompact is more practical, but less sexy.

I'm trying to reach out to a broader audience (the common man) and think about selling something that everyone could own. I guess that makes me care about the "losers" and not just the wealthy. :?

 

[safe]

Why Motors Love Peukert's Effect

Peukert's Effect with SLA means that if you pull more energy out of the battery faster (higher "C" rates) you lose some of the total battery capacity. When your battery has a significant Peukert Effect (like SLA does) it means that if you use up a lot of energy really fast that your ride will come to an end earlier... more than just because you used the energy up faster, but the total energy is less... so it's a double reduction in range. Without the Peukert's Effect your motor wil have to endure the heat of higher power for a longer period of time. This amplifies the overheating issue that all motors deal with.

So in an "irony" of design... SLA actually PROTECTS the motor in that the harder you push the motor (higher peak current) the less time the battery is able to deliver the energy. The cumulative heating is reduced in direct proportion to the increased heating rate.

The Peukert's Effect might be seen as an "advanced motor protection scheme" if people didn't hate it so much. :lol:

 

[rf]

Okay, so Lead Acid batteries are for losers.

[...]
For the same reasons the "common man" hates Obama the "elite" folks love him... elitism in anything (politics or batteries) becomes like a fashion statement.

I'm trying to reach out to a broader audience (the common man) and think about selling something that everyone could own. I guess that makes me care about the "losers" and not just the wealthy. :?

Sounds more like you're accusing the less well off of being stupid. Unable to see past a tantalizing sticker price to the less expensive (and more functional) option. Like mistaking thoughtful, well-spoken intelligence for elitism.

 

[safe]

Like mistaking thoughtful, well-spoken intelligence for elitism.

I guess you're "Wright". :wink:

Reposted:

Why Motors Love Peukert's Effect

Peukert's Effect with SLA means that if you pull more energy out of the battery faster (higher "C" rates) you lose some of the total battery capacity. When your battery has a significant Peukert Effect (like SLA does) it means that if you use up a lot of energy really fast that your ride will come to an end earlier... more than just because you used the energy up faster, but the total energy is less... so it's a double reduction in range. Without the Peukert's Effect your motor wil have to endure the heat of higher power for a longer period of time. This amplifies the overheating issue that all motors deal with.

So in an "irony" of design... SLA actually PROTECTS the motor in that the harder you push the motor (higher peak current) the less time the battery is able to deliver the energy. The cumulative heating is reduced in direct proportion to the increased heating rate.

The Peukert's Effect might be seen as an "advanced motor protection scheme" if people didn't hate it so much. :lol:

 

[TylerDurden]

Because of voltage sag, the operator will continue to call for more power and draw more current... the lower voltage will increase the power more slowly, so the motor will stay longer in the high current mode.

Or, have you forgotten how you smoked your first motor.

 

[safe]

Or, have you forgotten how you smoked your first motor.

Well, if you want to be technical is was 18 verses 14.

My old gearing had an 18 tooth front sprocket and now I have a 14 tooth front sprocket. So overheating was a result of too tall of a gear. (that and that bizarre 6th gear test I did... that was dumb... but it did prove my point about how gears are better)

However, you do have a point... as the voltage sags your first gear might not be low enough to cover the steepest hill and since it would become "too tall" a gear relative to the remaining voltage it would heat more because it would bog down into the low rpms.

Actually I've discovered this to be true with my hybrid 36/48 volt setup. After 10 miles at the highly energy efficient (but lower powered) 36 volt mode I can switch to 48 volt mode and make it up the hills on my way home.

Too few gears equals more heat - This is Valid!