# Choosing battery help



## UCF_students (Jan 25, 2011)

Greetings!
I am building an electric go-kart and would like advice/tips for selecting the battery and charger. I am considering LiFePO batteries from Sky Energy but we have a tight budget so I may opt to go to deep cycle lead acid if I can find the right deal.

The motor is the the brushless dc Mars0913 24-72 V with 12kw rms and 30kw peak.
http://www.kellycontroller.com/mars-0913etek-comparablepmsmbldc-motor-p-874.html
The controller is a Kelly controller, KHB72701,24-72V,700A,Opto BLDC Controller/With Regen
http://www.kellycontroller.com/khb7270124-72v700aopto-bldc-controllerwith-regen-p-838.html

I'm thinking I need a minimum of 8 batteries 2 packs of 4 batteries in series connected in parallel.

Can anyone offer any advice or wisdom of what time of battery configuration I'm going to need for decent performance? Anyone??


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## UCF_students (Jan 25, 2011)

*choosing battery helpp*

Greetings!
I am building an electric go-kart and would like advice/tips for selecting the battery and charger. I am considering LiFePO batteries from Sky Energy but we have a tight budget so I may opt to go to deep cycle lead acid if I can find the right deal.

The motor is the the brushless dc Mars0913 24-72 V with 12kw rms and 30kw peak.
http://www.kellycontroller.com/mars-0913etek-comparablepmsmbldc-motor-p-874.html
The controller is a Kelly controller, KHB72701,24-72V,700A,Opto BLDC Controller/With Regen
http://www.kellycontroller.com/khb7270124-72v700aopto-bldc-controllerwith-regen-p-838.html

I'm thinking I need a minimum of 8 batteries 2 packs of 4 batteries in series connected in parallel.

Can anyone offer any advice or wisdom of what time of battery configuration I'm going to need for decent performance? Anyone??


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## Sutitan (Feb 23, 2009)

*Re: choosing battery helpp*

What is this kart for? Are you looking to race or just play around? At any rate, you would need abit more then just 4 lithium batteries in series. Depends what voltage you are planning on running your motor at.

If I were you, I'd take a look at lipo batteries. The folks over at endless sphere can give you plenty of info. Look at the turnigy nano tech batteries. They have something like 45-90C. As long as you get the voltage right, the batteries should be able to deliver. However the ride won't last long if you don't size the pack approprietly.


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## Yabert (Feb 7, 2010)

UCF_students said:


> !!tight budget!!


Hum! not exactly tight with 1750$ only for motor and controller!!

In conparaison, my budget for my motor/contoller 100 Kw set-up is 2000$. And I put 70% of my budget on battery to have 100Kw from it.
With your set-up you theorically have 30Kw peak but if your battery are only able to push 5kw you can't have more than 5Kw at the wheel.

I think you can find cheaper motor and controller for a kart.

For batterie you can use Odyssey AGM. Go higher in voltage will help the performance instead lower voltage and high amps.


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## Woodsmith (Jun 5, 2008)

I have merged your threads as there is little to be gained by posting the same question in different forums.


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## UCF_students (Jan 25, 2011)

Sorry for the duplicate post. im new to the site. THANKS for the replies. we are building the go kart as part of project for school. the motor/controller price is driven up because we will be using regenerative braking. we also want to be able to achieve a top speed of at least 50 mphs. I realize the power output is reliant on the voltage but im just worried about the operating current of the motor. can u offer any advice about current? thanks


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## DIYguy (Sep 18, 2008)

It's important to know the specific use of the kart. Will it be used for endurance racing? distance/time? drag race? just for fun with a few goals like top speed? Can u offer more specifics? As for regen... u won't get too much energy back from a kart... unless this is a project requirement for learning.... may not be worth it....?? depends again on requirements...


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## Sutitan (Feb 23, 2009)

> we also want to be able to achieve a top speed of at least 50 mphs.


Thats dependent on the gearing. the sprockets on the go kart axle are ussually interchangeable. Calculate the max rpm (at the voltage you choose to use), then figure in the gear ratio's between the drive sprocket, final sprocket, and wheels. there are calculators online that could help you out 



> I realize the power output is reliant on the voltage but im just worried about the operating current of the motor. can u offer any advice about current? thanks


Power is reliant on voltage and current (P=VI). In your situation, the most power you will be seeing is about 50kw. I figured this by using the controllers' max voltage and current which is 72v and 700A respectively. 50kw is pretty serious as far as power goes for a go kart. here's a pretty popular youtube video showing a 50kw electric go kart
http://www.youtube.com/watch?v=-xitMWUfeLk . I dont know what you want to hear about the current. Im not that sure about for how long the motor can sustain 700A (im assuming not very long). You probably will using be using alot less most of the time.

my suggestion remains the same. these are the batteries
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=14617
Each pack is 37v. 2 packs in series make 74v which is just what you need. the packs at 5Ah and can supply 45-90C which means 450A peak. so two in parallel and then two in series means a 74v 10Ah pack that can supply 900A bursts. for some reason hobbyking is offering me a one time discount right now while viewing the page. $152.56. strange. the normal price is $161.24 so x 4 = $645. only $610 in my cart currently. Email hobby king. maybe the can give you the offer that im currently seeing. Keep in mind this is only a 740w battery pack. this will on take you a few short miles depending on driving style.

BTW, what kind of project is this? Im guessing from your user name that a UCF student (central florida). Are there any EE's in the group?

EDIT: Didnt notice your motor is limiting you on power a bit. looks like it will be 30kw max for your build. oh well. my suggestions remain the same


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## UCF_students (Jan 25, 2011)

The kart will be used simply as a fun/fast learning vehicle with a few design requirements including:

weight < 500 lbs
top speed > 50 mph
range > long enough to have fun. oh and to learn of course 

yes, regen is a requirement that we will have to incorporate and explore. also, i plan on using a super capacitor in the system to achieve greater accelerations. the hope is to be able to make sort of an "electric nos" (hit a button and recieve extra power from the discharging super capacitor) let me know what you think.

thanks for the battery suggestions. i will look into it. what i dont get concerning current still is.. for example the turnigy battery pack u suggest, if the pack has a 10 Amp-hour configuration.. how would do you calculate its performance with respect to the continuous power and peak power of a motor? my motor is capable of 10 KW at 72 VDC (150 amps continuous), and 25 KW peak at 550 amps for 1 minute. 

i appreciate the help, by the way


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## Guest (Jan 27, 2011)

For the controller, be sure your heat sink has a flat surface. I mean perfectly flat. Make sure your controller has a good flat surface too. Use good thermal compound but not too much but evenly placed. You don't want hot spots and you want the heat to be moved away from the controller. I am just finishing up fixing a heat sink problem that killed a few controllers. I don't want the new one to die. I am sorry that the person who owned this vehicle before lost those controllers thinking the controllers were the problem. The problem was with the heat sink. 


http://greenev.zapto.org/63ev/63_EV/Kelly_Control_Sink.html


Pete


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## Guest (Jan 27, 2011)

By the way, go lithium for your batteries. I can get 100 AH Hi Power cells for a decent price. PM me.


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## Sutitan (Feb 23, 2009)

Id forgo the super capacitor bank. the batteries themselves should be able to provide more then enough current when you want it. money would be better spend on more batteries, which would most likely be much cheaper as well as lighter. A reasonably sized "NOS" bank would most likely cost outside your budget. 

Ill try explain the current a bit better. The C rating given the batteries is used to indicate a batteries continous current draw. this number is multiplied to the batteries current rating. In your case, the batteries current rating is 5Ah and the C rating is 45C continuous and 90C peak. this means that one pack should be able to put out 225A continuous and 450A peak. All those nano-tech batteries I was point you towards have a C rating of 45-90, but come in different current ratings, such as 2200mAh and such. you would take there current ratings (given in Ah) and multiply it types there C rating to get how many amps the batteries can provide.

now, this are specs just for the batteries. you need to look at the motor and controller spec sheets to see what the can do. from a quick glance, your motor can handle 350A continuous and 700A peak (1 minute). you batteries will be more then happy to supply that. next in line is your motor which you said can do 150A continuous and 550A peak. So it seems that your motor is limiting everything, then your controller, and lastly your batteries. 25kw is still very respectable for a go-kart. Im not sure if you can control the acceleration ramping, but if you could make it instant, you could stand still just burning tires. 

Before you buy the batteries, please read about lipo and their safety. they are known to be a little more volatile then some other lithium types. cell monitors with a low voltage alarm is a must. just keep a close on the voltage when charging and you should be find


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## UCF_students (Jan 25, 2011)

Greetings! 
We are going with 6 x AGM/SLA (B.B. EVP26-12)which are 26Ah/12V each.Opted againsted the LiFePo due to money constraints. Heres the link:
http://www.electricmotorsport.com/store/ems_ev_parts_batteries_agm-sla_bb_evp26-12.php

Can any one suggest a suitable charger that is not over-priced?

By the way, we just stripped our go kart chassis and have officially ordered our motor and controller!! =)

controller:
http://www.cloudelectric.com/product_p/co-kbl72301.htm
motor:
http://www.cloudelectric.com/product_p/mo-me-0913.htm


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