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Old 01-11-2010, 04:58 PM   #1
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Default Battery run time?

Ok I'm trying to get a better understanding of the ratings on Batteries. Please correct me if I wrong, but If I have Trogon T-105, 25a - 115 min , 75a - 447 min. and I'm running a stock 36v ezgo with 275a controller. Then 275a(controller) / 6 (batteries) = 45.83amps. So my cart should pull 45.83 amp per hour from each battery. So if I use the T-105's only pulling 45.83a, I should get about 366 min. of runtime Right? or i'm I looking at it wrong?
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Old 01-11-2010, 07:04 PM   #2
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Default Re: Battery run time?

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Originally Posted by dutdut1981 View Post
Ok I'm trying to get a better understanding of the ratings on Batteries. Please correct me if I wrong, but If I have Trogon T-105, 25a - 115 min , 75a - 447 min. and I'm running a stock 36v ezgo with 275a controller. Then 275a(controller) / 6 (batteries) = 45.83amps. So my cart should pull 45.83 amp per hour from each battery. So if I use the T-105's only pulling 45.83a, I should get about 366 min. of runtime Right? or i'm I looking at it wrong?
Ok you are going about wrong with the right intentions.

First thing most folks do not understand is Mr. Peukert and his law of physics called the Peukert Effect.

Batteries are rated in AH, but there is a catch for lead acid batteries. They are rated at the 20 hour rate. Well a Trojan T=105 is rated at 225 AH at a 20 hour discharge rate. So the formula is Amps = AH/T. So for a 20 hour rate 225 AH / 20 hours = 11.25 amps. So in theory a 100% charged 225 AH battery should deliver 11.25 amps for 20 hours to completely discharged.

Then came along a real jerk about 100 years ago and ruined everything and they named a law after him called the Peukert Effect. What that means if you discharge a battery at a greater rate than specified, you have to de-rate the capacity. The amount you de-rate depends on how much greater you are discharging than the specified rate.. For a golf cart the controller amperage means nothing except how much current the controller can deliver with the motor at 0 RPM. So to try to figure out on average how much current the cart uses we have to convert to wh/mile and the speed. So in general 200 wh/mile at 15 mph. From that we can say the motor pulls 66 amps continuous average for battery de-rating purposes.

Ok 66 amps is a discharge rate of 225/65 = 3.46 hours. Ok Mr. Puekert says to de-rate by .57 turning your 225 AH battery into a 130 AH battery (.57 x 225). So now we can adjust and say 130 AH / 66 amps = 1.96 hours to fully discharged, and not 225/66 = 3.4 hours. as one might think.

But here is a better way to figure things out. Remember a T-105 is really a 130 AH battery in a golf cart because Mr. Peukert says so. From that we can determine the watt hour capacity by multiplying by the voltage. In your case 36 volts x 130 AH = 4680 watt hours. Your cart gets about 200 wh/mile. So in theory you should get about 4680 wh / 200 wh/mile = 23.4 miles.

Now for the last catch. You never ever want to discharge your battery more than 50% at any given time, so all those numbers are cut in half again. I will let you do the math now.
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Old 01-11-2010, 08:25 PM   #3
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Default Re: Battery run time?

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Originally Posted by sunking View Post
Ok you are going about wrong with the right intentions.

First thing most folks do not understand is Mr. Peukert and his law of physics called the Peukert Effect.

Batteries are rated in AH, but there is a catch for lead acid batteries. They are rated at the 20 hour rate. Well a Trojan T=105 is rated at 225 AH at a 20 hour discharge rate. So the formula is Amps = AH/T. So for a 20 hour rate 225 AH / 20 hours = 11.25 amps. So in theory a 100% charged 225 AH battery should deliver 11.25 amps for 20 hours to completely discharged.

Then came along a real jerk about 100 years ago and ruined everything and they named a law after him called the Peukert Effect. What that means if you discharge a battery at a greater rate than specified, you have to de-rate the capacity. The amount you de-rate depends on how much greater you are discharging than the specified rate.. For a golf cart the controller amperage means nothing except how much current the controller can deliver with the motor at 0 RPM. So to try to figure out on average how much current the cart uses we have to convert to wh/mile and the speed. So in general 200 wh/mile at 15 mph. From that we can say the motor pulls 66 amps continuous average for battery de-rating purposes.

Ok 66 amps is a discharge rate of 225/65 = 3.46 hours. Ok Mr. Puekert says to de-rate by .57 turning your 225 AH battery into a 130 AH battery (.57 x 225). So now we can adjust and say 130 AH / 66 amps = 1.96 hours to fully discharged, and not 225/66 = 3.4 hours. as one might think.

But here is a better way to figure things out. Remember a T-105 is really a 130 AH battery in a golf cart because Mr. Peukert says so. From that we can determine the watt hour capacity by multiplying by the voltage. In your case 36 volts x 130 AH = 4680 watt hours. Your cart gets about 200 wh/mile. So in theory you should get about 4680 wh / 200 wh/mile = 23.4 miles.

Now for the last catch. You never ever want to discharge your battery more than 50% at any given time, so all those numbers are cut in half again. I will let you do the math now.
****
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Old 01-11-2010, 08:29 PM   #4
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Default Re: Battery run time?

just peukert! and jam the biggest batteries in the space!
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Old 01-11-2010, 08:51 PM   #5
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Default Re: Battery run time?

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****
OK sorry that was a little long winded and technical. So here is the short version.

Take the battery AH rating and multiply by .289. So a 225 AH battery = .289 x 225 AH = 65 AH.

Now factor out hours by picking a current in amps so AH/A = H. So use something like 65 amps which is pretty close to actual. So 65 AH/ 65 amps = 1 hour run time. At 15 mph you get about 15 miles before you go below 50% DOD. Your mileage may very.
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Old 01-11-2010, 08:58 PM   #6
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Default Re: Battery run time?

see now even i understand it! thanks.
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Old 01-11-2010, 09:07 PM   #7
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Default Re: Battery run time?

Wow, what an answer!!!! I would need 5 degrees to comprehend all of that but I got the short Vinson, thanks Sunking. Does running the Cart at 1/2 throttle extend run hours X2. I realize it wont help the miles.
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Old 01-11-2010, 09:07 PM   #8
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Default Re: Battery run time?

The missing part of this thread is load. There is no constant current draw in the real world. Throttle position, passenger load and terrain change the current draw constantly.

Jim
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Old 01-11-2010, 11:04 PM   #9
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Default Re: Battery run time?

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. Does running the Cart at 1/2 throttle extend run hours X2. I realize it wont help the miles.
Well I have to be careful answering that, but in general yes it will extend the time, and distance. That is where Mr Newton's Law comes into play.

Electric motors are funny animals. Maximum current and torque occurs at stall speed or RPM's, and decays in a flat line to almost nothing at max rpm.

Voltage and RPM are directly proportional, so that the more voltage applied, the more RPM. Like torque rpm's are a flat linear line to voltage.

Because of the two characteristics noted above the maximum HP or electrical power is consumed at half the RPM rating of the motor. Once you go above have the rated voltage power decays.

Perhaps a graph will explain it better.
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Old 01-12-2010, 08:21 AM   #10
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Default Re: Battery run time?

There's only one part of that I didn't understand......


The part right after "Ok you are going about wrong with the right intentions"


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