Lithium, Lead, Amp-Hours, and EVs

by Kurt
(Wyoming)

Lithium electric car battery

Lithium electric car battery


I was wondering what the differences would be between doing a conversion using Lithium Iron Phosphate batteries that have 100 A/h and one that uses golf cart batteries like the Trojan T-105 that have 225 A/h.
I know the LiFePO4 batteries are the favored batteries if your budget can handle them. but it seems to me that the higher the A/h rating the better for an EV. Is this correct or would the lithium batteries still be the better choice.

Hi, Kurt -
It's a matter of weight and distance you can travel, but oh, this is not simple.

The LiFePO4 batteries at 100 AH will not take you as far as lead batteries at 225 AH, but they'll be a lot lighter - and AH for AH, you'll get more miles from the lithium. (See my remark in the comments below.)

As you know, amphours, AH, are a measure of how many amps your batteries can deliver times the number of hours they can deliver the amps.

And as you've also figured out, AH are notoriously heavy little devils; comparing the same battery chemistry, more amp-hours means more weight.

But a lithium amp hour doesn't equal a lead amp hour. A 200AH LiFePO4 battery pack, you may notice, will take you a lot further than a 200AH lead battery pack.

Oh, and about the price, well - lithium is coming down in price all the time. Now, in 2011, lithium is as cheap or cheaper than lead per mile. So go ahead and get the LiFePO4. You know you want to; )

Regards,
Lynne

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Understanding amp hour ratings
by: jerry hart

I have a 48 volt electric cart that uses 6 Trojan t 890 8 volt batteries. I think that I would like to convert to the Lithium Ion batteries for my next replacement. I am having a rough time understanding how many amp hours the lithium batteries should be. The specs on the T890 are as follows: Capacity Amp Hours:
5 Hr rate: 155
10 Hr rate: 175
20 Hr rate: 190
100 Hr rate: 211
Which rate should I use to estimate the equivalency between lithium and flooded acid. Also, is there a simple formula that I can use to get to the amp hours required with the lithium?

Hi, Jerry -
You don't have to adjust anything, amp-hour wise, if you convert to lithium.

The pack that you are using now has the number of amp hours it does because of space available, weight of batteries (the more amp hours, the more your batteries will weigh), and money (more amp hours means more money).

Your lithium batteries will be much lighter, so you can increase your amp hours accordingly.

Hope this helps!
Lynne


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Lithium amp-hrs
by: David Hrivnak

I would love for others to repeat my testing. But I tested a 12V Lithium FePO4 battery (4 cells) rated at 40 amp-hrs against a Optima Yellow top 38 amp hr and against a 100 amp-hr gell. I put my truck on jack stands and connected one battey and ran (at about 15 MPH) until the voltage reached about 10.5V.

To my surprise the Lithium lasted about 28 minutes versus 10 minutes for the Optima and 32 minutes for the 100 amp-hr gel. So it seems like the lithium lasts far longer than lead.

Hi, David -
You're right about that.

In practice, those LiFePO4 batteries, amp hour for amp hour, will move your car more miles than the AH equivalent lead battery pack.

The LiFePO4 doesn't seem to mind so much if you put your foot in it.

And the LiFePO4 pack will forgive deeper discharge than the lead, the lithium has more usable energy.

- Lynne

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