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Old 02-17-2012, 09:37 AM   #11
scottyb
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Default Re: how to figure amp draw

This thread reads better than anything anywhere on the net on this subject ... well done gentlemen

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Old 02-17-2012, 05:22 PM   #12
sonnysmith
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Default Re: how to figure amp draw

Thanks everyone that had input into this subject.
All the info is great.Now with 3 number 2 pencils and a good calculator.I will put my cart together and not worry about how fast it will run OR care.After all this information all I need to work on is my golf game.
In all seriousness,I thank you for the good information,It will come in handy as I go forth with my other builds.
I have taken your advise and went with a 400 amp controller an all of the other parts need for my up date.

Thanks again
Sonny
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Old 02-03-2018, 06:54 AM   #13
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Default Re: how to figure amp draw

Quote:
Originally Posted by JohnnieB View Post
Warning: Technical content!!!.
May cause Brain Freeze if read before morning coffee kicks in.

1 horsepower = 745.699872 Watts (Commonly rounded to 746 for convenience)
1 Amp times 1 Volt = 1 Watt.
Therefore: 15.5A (not 7A) is required to develop 1 HP @ 48V. (Or 20.7A @ 36V)

Mechanically, HP = Torque times RPM divided by 5250

The stock rear end ratio for a TXT is 12.44:1 and the stock tire height is approximately 18", so with a little number crunching, you could figure out how many ft/lb of torque is needed to propel your cart at 14MPH and from that you could derive Watts needed per MPH and calculate the speed increase with a 33.3% increase in applied voltage, but there are many other factors involved, so it would only be approximate at best.

Basically, if it took about 70A @ 36V (2520W) to propel your cart at about 14 MPH, 70A @ 48V (3360W) will propel it at about 18 MPH. (28.5% increase rather that 33.3%)
Conversely, it would only take 52.5A @ 48V to propel it at 14MPH, hence the often mentioned statement that going to a 48V system reduces current and or increases run-time.

Hope this helps rather than confuses.

Back to circling on updrafts and looking for rabbits.

Excellent! Now for your help! I have a 700 Controller, a RS II that demands amperage and all the supporting equipment to give it what it wants. I’m upgradeing to lithium and don’t know what amperage pack I should go after? I found one that seems it would work well but only has a max short burst of 250amps. I don’t think this would be sufficient. My cart runs 32 with the t-875’s and will pull the front tires in a hole shot. It’s a great setup but we’re always looking for more!
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Old 02-03-2018, 10:48 AM   #14
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Default Re: how to figure amp draw

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Originally Posted by caylen17 View Post
Excellent! Now for your help! I have a 700 Controller, a RS II that demands amperage and all the supporting equipment to give it what it wants. I’m upgradeing to lithium and don’t know what amperage pack I should go after? I found one that seems it would work well but only has a max short burst of 250amps. I don’t think this would be sufficient. My cart runs 32 with the t-875’s and will pull the front tires in a hole shot. It’s a great setup but we’re always looking for more!
All a controller does is limit how many amps the motor is allowed to draw.
It is the motor that demands the amps and the number of amps a motor is capable of drawing is inversely proportional to the RPM.

In other words, you have an electrical valve that can pass 700A, but how many amps your motor can draw at 0RPM (stall) is unknown and that is the number you need to know.

Plum Quick (or whoever the motor manufacturer is if it isn't the motor listed in you signature block) might be able to provide the needed info, or you can insert an ammeter in series to measure the amps drawn, or you can estimate it by measuring individual battery voltage drops.

The batteries alone in a 48V Lead-Acid battery pack drops about 1.5V per 100A of current draw, but you cannot use battery pack voltage for estimating the amp draw since the cables and connections also drop voltage and how much they drop is unknown and varies from cart to cart, so you have to use individual battery voltage. Since there are six 8V batteries connected in series, the voltage drop for one of them is 0.25V per 100A.

It will be easier if you have a DVM that has a Min/Max setting.
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Old 06-19-2019, 10:20 PM   #15
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Default Re: how to figure amp draw

More rabbit food...

I don't mean to hijack this thread but it's the one that came closest to answering a similar question regarding amp draw.

I have a 48V club cart with a stock motor that does 12MPH, tops...going downhill with a tailwind. I live in Houston texas which is mostly flat and don't plan on using this cart for anything other than driving it on the golf course which is no more than 10 miles in a given day.

My 8-volt batteries have reached the end of their life and trying to figure out how to move forward.

I found a guy selling 9x9x9 lithium ion packs rated at 48v 45Ah and 2kwh.
(he also has a 66 Ah version) How many of these would I need to provide equivalent power/speed as the current setup?

I"ve done all kinds of searches involving Ah and all I can find is that the lithium ion batteries' rating are double of wet batteries but can't seem to find anybody that can tell me how many would equate to a 6x8V pack wet batteries.
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Old 06-20-2019, 02:23 PM   #16
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Default Re: how to figure amp draw

Beware the Ebay BMS units. The batteries may be fine, but the BMS they usually put on them is bunk.

Look in the lithium section and you'll see a lot of people who have converted their carts. 45ah 2kwh sounds like Chevy Volt modules. I'm running Chevy Volt modules at 14S2P for 94ah at 58v. Equivalency is difficult, but seems most people look for around 100ah capacity or more. I ran a 47ah pack for a bit, but the 94ah pack is much better. I have not run it from full charge to full discharge, but I've estimated my 47ah pack as having a range of 13 miles. So my 94ah pack should be double that. Mind you I don't fully charge or fully discharge which should make my pack last longer but I give up a little range because of that.
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Old 06-20-2019, 03:49 PM   #17
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Default Re: how to figure amp draw

When I did my initial testing, I found that a 100ah Li pack was nearly identical (within 2 minutes discharge time) to T-875 lead batteries on the Lester discharge machine when drawing both down to 20%. I have also read that when a lead battery is discharged at a 1-hour rate (not the 20-hour rate listed on the lead battery label), they are de-rated to 57% of their 20-hour rate. The one hour rate is much closer to the actual usage patterns found in golf carts, I can't imagine anyone driving their cart so slowly/modestly to allow it to run 20 hours of driving time until the batteries were dead.
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Old 06-20-2019, 04:26 PM   #18
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Default Re: how to figure amp draw

Quote:
Originally Posted by cgtech View Post
When I did my initial testing, I found that a 100ah Li pack was nearly identical (within 2 minutes discharge time) to T-875 lead batteries on the Lester discharge machine when drawing both down to 20%. I have also read that when a lead battery is discharged at a 1-hour rate (not the 20-hour rate listed on the lead battery label), they are de-rated to 57% of their 20-hour rate. The one hour rate is much closer to the actual usage patterns found in golf carts, I can't imagine anyone driving their cart so slowly/modestly to allow it to run 20 hours of driving time until the batteries were dead.
That's me. One of my two pedals is always to the floor.
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Old 06-20-2019, 09:17 PM   #19
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Default Re: how to figure amp draw

Quote:
Originally Posted by bronsonj View Post
Beware the Ebay BMS units. The batteries may be fine, but the BMS they usually put on them is bunk.

Look in the lithium section and you'll see a lot of people who have converted their carts. 45ah 2kwh sounds like Chevy Volt modules. I'm running Chevy Volt modules at 14S2P for 94ah at 58v. Equivalency is difficult, but seems most people look for around 100ah capacity or more. I ran a 47ah pack for a bit, but the 94ah pack is much better. I have not run it from full charge to full discharge, but I've estimated my 47ah pack as having a range of 13 miles. So my 94ah pack should be double that. Mind you I don't fully charge or fully discharge which should make my pack last longer but I give up a little range because of that.
This is perfect. It's all I needed. I should be able to use the 45 AH pack to do my 8 mile course without an issue. I only wish I could use my wet cells as backup to help out. Unfortunately, from all I've read, its a BBBAAADDD Idea to mix lithium with lead acid.

Thank you for all the replies.
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Old 06-21-2019, 03:28 AM   #20
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Default Re: how to figure amp draw

45ah is too small in my opinion. Have you considered what their max safe output is vs your controller amp rating is? Is your controller a little 245a one, is it higher? How do you plan on charging it (the charger you have now will almost certainly not be appropriate for the job)? This can set your garage on fire if you carelessly do this. Please crunch the numbers before you buy. It's not for the faint of heart to do correctly. Doing it wrong could do far worse than leave you walking home for exhausted batteries that didn't make the trip.
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