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Old 02-24-2013, 12:59 PM   #1
Oneunder
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Default LiFePo4 conversion

I have a 2004 EzGo TXT freedom. After pushing my cart home from my last outing, I have been reading as much as I can on my options. I found this product and am prepared to pull the trigger.

http://optimum-china.en.alibaba.com/...sotherproduct1

My question is: Can I just take out the old and drop this in? Or is it a bit more complicated than that. I understand I need a different charger. But as far as compatability...whats the verdict?
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Old 02-24-2013, 08:32 PM   #2
JohnnieB
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Default Re: LiFePo4 conversion

A typical 36V battery pack in a golf cart is rated at 225AH.
Looks like these batteries are rated at only 100AH.

Even if you could get them to fit, you'd have less than half the normal run-time and minimal performance.
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Old 02-24-2013, 08:53 PM   #3
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Default Re: LiFePo4 conversion

A lithium AH rating is different then a lead acid AH. Sure the lithium is rated at 100AH but the rate is the unknown so it is unfair to say it is half the battery of the lead acid. Also it can be discharged to 80% SOC and still give 2000+ cycles so its range is even more comparable as well as cost. You'll have to replace the lead acid 3 times vs lithium.

Just a couple things to think about.
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Old 02-24-2013, 10:14 PM   #4
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Default Re: LiFePo4 conversion

well tell us about that 100 ah, verses the 225 ah, iam sure everyone would like to know what your talking about
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Old 02-24-2013, 10:28 PM   #5
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Default Re: LiFePo4 conversion

A Trojan t-105 is 225AH at a 20 hour rate. That is published. They even publish 10 hour and 5 hour rates which have much less AH. Hardly no manufacture published their 1 hour rates, that's the one that seperates the men from the boys.

You have to compare apples to apples. If a lithium battery has a 10AH spec you have to know at what rate it's taken at to compare to a Trojan 20 hour rate of 225AH.
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Old 02-25-2013, 04:58 AM   #6
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Default Re: LiFePo4 conversion

In post 3 I mistakenly stated lithium batteries can be discharged to 80% SOC, I meant 80% DOD (or 20% SOC). They can go this low for 2000+ cycles too.

Another benifit to lithium is their ability to hold voltage under load much better then lead acid.

Weight is the main reason people are using lithium more and more. The energy density of lithium for size and weight is great.
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Old 02-25-2013, 07:09 AM   #7
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Default Re: LiFePo4 conversion

Quote:
Originally Posted by sportcoupe View Post
A Trojan t-105 is 225AH at a 20 hour rate. That is published. They even publish 10 hour and 5 hour rates which have much less AH. Hardly no manufacture published their 1 hour rates, that's the one that seperates the men from the boys.

You have to compare apples to apples. If a lithium battery has a 10AH spec you have to know at what rate it's taken at to compare to a Trojan 20 hour rate of 225AH.
The variance in Amp-Hours at different discharge rates is due to the Peukert Effect and the Peukert Number for Lithium batteries varies with the chemistry.

The Peukert Number for the type of Lithium battery (Lithium Cobalt Oxide)that caused the grounding of Boeing 787 Dreamliners, is very close to 1, so varying the discharge rate does not significantly vary the AH capacity. On the other hand, the Lithium batteries linked to (Lithium Iron Phosphate) do have a Peukert Number >1, so the AH will vary with discharge rate.

However, manufacturers tend to display the products in a favorable light, so I'll stick with my assumption that a 100AH battery will have less run-time than a 225AH battery.
It may not be less than half as I originally said, but it is betting odds that it will be less.

As for reduced performance, I might have been unfair because I overlooked the fact the Lithium batteries have a nearly flat discharge curve while the terminal voltage of Lead-Acid batteries decreases as discharge rate increases. Due to that electro-chemical attribute, a 100AH 36V Lithium battery pack might be able to produce the same amps at the same volts during acceleration and hill climbing as a 225AH 36V Lead-Acid battery pack.

Hopefully, at some point in the near future, Lithium battery manufacturers will publish more meaningful specs on their products and some valid comparisons can be made.
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Old 02-25-2013, 09:09 AM   #8
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Default Re: LiFePo4 conversion

What is the best way to measure DOD? I was quoted for both 100ah and 200ah but since there was no price break for the 200ah, I thought I might get the 100ah first and test the run time.
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Old 02-25-2013, 10:30 AM   #9
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Default Re: LiFePo4 conversion

Quote:
Originally Posted by Oneunder View Post
What is the best way to measure DOD? I was quoted for both 100ah and 200ah but since there was no price break for the 200ah, I thought I might get the 100ah first and test the run time.
That is a question that an army of scientist and engineers working in the electric vehicle industry have been trying to answer for years and have yet to succeed.

To name a few of the issues:
Different Lithium chemistry has different volts per cell and different discharge curves.
In Lithium batteries, collectively, the volts per cell don't vary very much between nearly fully and nearly fully discharged.
The discharge curves change as a Lithium battery ages.

There are more issues, but what I am trying to say is that it isn't an easy task.
Plug "SoC Lithium Battery" into your web browser and read the articles on the subject and you'll find quite a few paper written about the complexities.
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Old 02-25-2013, 10:51 AM   #10
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Default Re: LiFePo4 conversion

One under, is your cart modded? do you have say an alltrax controller that is 48V compatible? Here's why I ask.....

I know I am a newbie on a lot of the cart electronics but not new to DC. but here is my thoughts.(JohnnyB jump in if I am wrong) Looking around at the site you posted, I noticed that they carry a 48V 400 aH battery. would it not be worth it to got with that one and just run @ 48V? if the cart is set up to run both and the 100ah is not enough
would this not work well for you and get some performance gains as well?
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