# How to determine minimal LiFePo4 battery Ah for 72V golf cart.

1622 Views 6 Replies 4 Participants Last post by  john61ct
Converting my 2013 BBB 72V Recoil to LiFePo4 battery setup, Have a 72V AC induction motor with a 300amp AC controller. Limited to 30HP (22.4kW peak). Not surehow to determine the minimum or optimal ah for this 72V system. For example, do I require 280ah or 200ah or 100ah to achieve performance comparable to the original 72V lead acid system (six 12v batteries connected in seried).

If the question is silly, pardon my ignorance as I am just begun learning. TX
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#### floydr

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What Ah were the LA battery? divide Ah of LA by 2 + 20%= needed Ah of LifePO4 Are you building the 72v battery pack with individual cells or 12v LiFePO4 batteries? if 12v LiFePO4 batteries make sure they can be put in series many can't some are limited on how many in series. Just a guess but min size would be in the 175- 200 Ah range.
Later floyd

#### brian_

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There's nothing silly about the question.

Automotive lithium-ion batteries can routinely handle about 3 A of discharge for each Ah of capacity, and even more very briefly, so to handle about 300 A of discharge you would need about 100 Ah of capacity. More wouldn't hurt, of course.

100 Ah @ 72 V would be 7.2 kWh. That sounds reasonable for a golf cart, although of course this style of "golf cart" isn't typically used for golf, and capacity depends on how it is used. Again, more capacity is good.

For those who didn't recognize "BBB Recoil", that's the Recoil model of the Bad Boy Buggies line, which is (or was) part of the E-Z-Go division of Textron. Stock, it appears to use nine 8 V golf cart batteries, which are typically rated at 100 Ah to 200 Ah, depending on the rate of discharge; lithium-ion batteries (even LiFePO4) can handle higher sustained discharge rates and deeper (to a lower state of charge) discharge than lead-acid, so the comparison is reasonable.

#### pmousso1

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There's nothing silly about the question.

Automotive lithium-ion batteries can routinely handle about 3 A of discharge for each Ah of capacity, and even more very briefly, so to handle about 300 A of discharge you would need about 100 Ah of capacity. More wouldn't hurt, of course.

100 Ah @ 72 V would be 7.2 kWh. That sounds reasonable for a golf cart, although of course this style of "golf cart" isn't typically used for golf, and capacity depends on how it is used. Again, more capacity is good.

For those who didn't recognize "BBB Recoil", that's the Recoil model of the Bad Boy Buggies line, which is (or was) part of the E-Z-Go division of Textron. Stock, it appears to use nine 8 V golf cart batteries, which are typically rated at 100 Ah to 200 Ah, depending on the rate of discharge; lithium-ion batteries (even LiFePO4) can handle higher sustained discharge rates and deeper (to a lower state of charge) discharge than lead-acid, so the comparison is reasonable.
I can;t thank you enough Brian for the feedback and direction. Most helpful and greatly appreciated.

#### john61ct

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Ah has a nebulous connection to "performance"

All about longevity and range whether miles or hours.

Put a coulomb-counter wattmeter on a unit drive it around at higher speeds higher duty cycle and longer hours & miles than you expect.

Say it uses 80Ah in a day

Then a 120Ah bank would be minimum IMO.

if can you put in more without adding too much weight

so less capacity per day is used

then the pack will last much longer before needing replacement

#### brian_

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Obviously the range requirement determines the minimum energy content. Amp-hour capacity is irrelevant to energy without voltage for context, but yes, given a fixed voltage energy is proportional to amp-hour charge capacity.

Since this is an existing operational vehicle with no change being made in anything other than the battery, energy capacity (or amp-hour charge capacity for the same voltage) can be determined in relation to what it already has - want the same range, need the same capacity...

#### john61ct

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Well properly designed, lead banks are often big enough so their usual DoD% is around 50% for longevity.

With LFP since they can last ten times longer, people often let them get depleted to an average of 80% DoD or even all the way to say 3.1Vpc

Nameplate rating can often be less exaggerated

So LFP usually has more usable energy compared to the nameplate Ah than with lead.

Also being twice the energy density (half the weight and volume) if those factors were limiting before, the owner may choose to increase total Ah capacity.

Finally, if the weight is a lot lower, that may impact stability if the system as a whole, increase risk of car rollover, might want to restore some of that reduced weight

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