T-Pain Is On A Boat: [Electric Boats] Re: Comparing FLA to LiFePO4.

Thursday, February 21, 2013

[Electric Boats] Re: Comparing FLA to LiFePO4.

Hi Carter,

The only part of this that you might consider theoretical would be the cycle life. I usually leave cycle life out of the conversation, but every time that I do, someone else brings it up. However, the manufacturers don't just make the cycle numbers up. That said, I never had a marine FLA that lasted more than three years, regardless of the cycles. That was my fault, I have never been diligent in maintenance charging, my typical battery cycle life was less than 50 deep cycles for any brand of FLA.

However, when I built a few EVs in the mid 1990's, Trojans did deliver more deep cycles than their competitors and their cycle lifespans quoted were proven over and over. Likewise, I know EV guys with LiFePO4 battery packs that are already past 1500 cycles that are still within spec.

The rest of the calculations concerning Peukert's Effect and range under load are more than theoretical. All of this has been proven to be true, and the results are very predictable. I've personally measured the energy delivered compared to the energy put back for a number of different traction banks made of different battery technologies, and all of the data supports the work of Peukert.

A lot of people develop personal opinions about various batteries, but every time that I've done actual measurements using real monitoring equipment, the numbers come back close to the manufacturer's specs and plain old battery performance formulas.

I'm not trying to sell anybody anything. This is just my hobby. But there is a lot of subjective opinion and marketing hype out there that isn't exactly true. I try to cut through all that and provide substantiated data so that others can make informed decisions.

I am in no way faulting your choice; we all make choices based on our situation. Nor do I expect anyone else to editorialize my decisions. But as you can probably tell, I don't make this kind of decision lightly, and I am willing to share my research, thought processes that led to my decision and then follow up with actual performance to see if my predictions held true.

As they said during Saturday morning TV when I was a kid, "Knowledge is Power".

Fair winds,
Eric
Marina del Rey, CA

--- In electricboats@yahoogroups.com, Carter Quillen wrote:
>
> Eric,
>
> That's all theoretical and I will concede the numbers might actually play our in the end, who really knows. But for a lot of marine applications, weight is a non issue and if you can't afford to pay the premium for liIon performance, what do you do? And for the record, at an 80 amp draw, those T-125s are pretty much spent in about an hour and a half, even if the calc says 3.83 hrs. I don't have ANY experience with LiIon except in my cellphone and 12V Dewalt drill but I'd be willing to bet the theoretical does not match the actual for LiIon in a lot of applications. And I can tell you from experience of a thousand cycles, my 18V NiCad puts the 12V LiIon to shame. But that's another conspiracy theory story I won't get into now.
>
> Without a doubt, a good battery management system is the key to success with any battery chemistry but for the average consumer it can be a bit of a crap shoot with all the stuff on the market and there is a lot of money on the table. Lead acid is still a good starting point for many and is a time proven technology. A horse and buggy, a Volkwagan or a Farrari Testerosa will all get you to the grocery store but it's a matter of how much you want to spend to get there.
>
> You can run the same calcs for AGM vs lead acid but I know a lot of sailors that curse AGM and won't go near them. Twice the price for comparative performance is concensus among many despite what the numbers say. Even my golf cart battery guy, who sells the stuff for a living says go with lead acid over AGM. Maintenance and hydrogen outgassing is definitely a parameter to consider but with technology like, http://www.bfsgmbh.de/en/products/specialplugs.html, this from Germany, not available in the US market yet, the maintenance hassle and out gas hazard become a non issue as well.
>
> So more power to you, (no pun intended), if you want to spend the extra on LiIon and get the enhanced performance but I respectfully disagree if you're trying to tell me that LiIon is definitely best value at this point. Maybe, maybe not. The numbers are too close to the margin of error and the premium is still too high for my blood. But times are changing and LiIon is most likely to prevail in the end unless something even better comes along in the mean time. I'm still waiting for a Di-Lithium crystal battery or a matter/antimatter pod to hit the market.
>
> Carter Quillen, PE
> www.archemedesproject.blogspot.com
>
> From: Eric
> To: electricboats@yahoogroups.com
> Sent: Wednesday, February 20, 2013 9:09 PM
> Subject: [Electric Boats] Re: Comparing FLA to LiFePO4.
>
> Hi Carter,
>
> I know that your plan is largely solar and you've got generator and a full diesel driveline as backups, but here's some battery only performance data.
>
> So your eight T-125 (530 lbs) have a 20hr rating of 12kWh, but at a 25A load, the total capacity drops to 10kWh (that's the Peukert Effect kicking in). Put the load up to 50A and the total capacity is 8.4kWh. And at 80A (you said earlier that 80A = 3.8kts or 4.4mph), the total rated capacity falls to 7.5kWh, a loss of 37% to Peukert's effect. Limit your discharge to 60% of total capacity and you batteries will last 1.12 hours at 80A draw. At 3.8kts that works out to 4.25nm range on a full charge of your batteries.
>
> The Balqon pack with a 20hr rated capacity that is 67% higher than your FLA pack seems like a luxury, but let's check the same loads. Balqon doesn't list the weight, but it should be right around 500 lbs like your current pack. Starting with a total rated capacity of 20kWh, at 25A the rated capacity drops to 19.86kWh, very close to the 20 hour rated capacity. At 50A, the rated capacity is still 19.45kWh. Finally at 80A, the Balqon pack rates to 19.2kWh, losing only 4% to Peukert's Effect. Since LiFePO4 batteries can be consistently discharged to 80%, you could run the motor at 80A for 3.83 hours for a range of 14.5nm. That's 3.4 times the FLA range at 3.8kts under batteries alone.
>
> So at the cash register, the Balqon battery looks 8 times more expensive than the T-125s. But if you consider the increased range without any weight, the Balqon pack is only 2.3 times the cost of the T-125s. Trojan says that the T-125 is good for 650 cycles. At 2000 cycles for the Balqon, you would have to buy 3 sets of Trojans for the same number of cycles. If you factor in the full life span in cycles, the Balqon works out to 12% cheaper per mile than 3 sets of T-125s.
>
> I know that this doesn't change the fact that the original investment takes a bigger wallet, but that could ultimately save you money in the long run.
>
> I know that you didn't ask for this, but I like running the numbers, and it's been a while since anyone has done the math in front of the group. I figure that this exercise might be helpful for new mebers here.
>
> Fair winds,
> Eric
> Marina del Rey, CA
>