Electric go kart help :)

[Ahmed_bilal]

Hi guys before starting my go kart project i need some advice and answers please.

I have two 48 volts 750 watt DC motors connected to a live axel.

what battery Ah ratting shall i use if i plan on using 4x 12v batteries connected in series and the two motors connected in parallel( so they both get same voltage)???
I want the kart to run for about 4 hours max and was wondering what ah rating batteries to use.
Will 7ah not be enough? I understand that i cant use 7ah for 7 hours as that would discharge the battery and thats bad. Or do i need to use 20ah or 30 or around 40?

And should i use 5 12v batteries and over volt at certain times for added power or is this a silly thing to do? Would that be good or damage motors?

Thanks for help!


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[dcastillo]

Im not the expert here, but youre not looking at the math correctly...

rough estimating...
each motor can draw about 15 amps, assume you average 10amps while driving...
Thats 20 amps (for two motors).
so if you used 20AHr batteries (which do to their inefficiency) would probably only give you 30 minutes run time max...

I was using a 2000W motor with 19AHr of batteries and barely got 20min runtime.

I personally dont think its possible to get 4hrs runtime on a cart.

If im not mistaken, the Tesla has over 200AHr in its batteries and can barely get 4hrs of run time...

-Danny

 

[Ahmed_bilal]

Thanks for your reply i just got confused reading some other posts. That makes more sense than what i read. By the way if i totally drain the batteries and run them till the kart can barely move would that damage the batteries?


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[dcastillo]

im definitely not the battery expert either

but the general consensus is yes, its bad to fully drain your batteries...
Ive drained mine a few time enough to require my 5yr daughter to drive the cart home while I walked by it... probably not very good for my batteries.

-Danny

 

[itsid]

Well first off..

About what Danny already said, if you connect batteries in series you only increase the voltage, not the capacity.. 4x 12V 20Ah = 1x 48V 20Ah
20Ah technically give you one hour of driving time assmuing you draw no more than said 20 Amp average (10 per motor).

BUT the motors can draw as much as 20Amps each (maybe even more)
if you run them in parallel your controller needs to be rated @ 40Amps min!!

And that's where the 30mins come in..

Also the controller (most controllers do) comes with a battery protection, you cannot drain them; the controller will prevent that by shutting off the motor(s) as soon as you reach a certain lower voltage (for a 48V controller maybe 38V or so)
So a 20Ah batpack can only deliver ~17Ah to the motors in the first place.
But the batteries will be kept in working condition (that's the good news)

If you want 4hrs of running time, you'll end up with a 90Ah battery pack at the very least.
And that means four large (and heavy) truck batteries to carry around.
Not really a good idea if you ask me.

'sid

 

[dcastillo]

To add to sid
A 20AHr battery can deliver 1A for 20hrs, but it cannot delivery 20A for 1hr, the more current you draw the lower is true capacity is....
This is assuming you are using lead and batteries of course

 

[itsid]

Well a 20Ah battery can deliver 20Amps for an hour, just not an hour straight
but with say a 5% duty cycle you'll still have the full hour
(or you'll need to actively cool the battery to increase the duty cycle)

A bigger battery is less sensible, so an uncooled 60Ah battery can have a duty cycle of 10% or more at 20Amps...



'sid

 

[dcastillo]

I give
Your getting to technical now...

 

[Ahmed_bilal]

Thanks for all the great replies guys! I didn't think electric go karts seemed that complicated.

The new plan is i get 3x 12v 60ah AGM TECHNOLOGY - DEEP CYCLE BATTERIES
(Each battery weighs 11kg)
and 2X 800W 36V motors each motor also has a 19.5 Amp rating
Are these batteries any good or just over rated? I can get 3 of them for £200
Would this take my runtime to at least 1hour?
I heard that i need a controller that can deal with a max of up to 4X the amp rating of the motors. What amp rated controller shall i get?
Do any aspects of the controller affect run time?




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[itsid]

I don't know about the quality of AGM Batteries,

but 800W 36V motors will draw 26Amps (and more)

I assume you're talking about a unite my1020 motor (since it's all over ebay and cheap)
that specific motor has an efficiency of roughly 85% @ it's rated power
and it's 800W rating is mechanical output power.

Sooo it draws 800/0.85 = 941Watts of electrical power
941 Watts / 36V = 26.xAmps

plus it peaks at 980W mechanical IIRC with a 75% efficiency so it draws 36Amps up there.

so yeah, you need at least a 60Amp controller to power two 800W 36V motors

and let's just stick with the 60Amp rating of the controller for a second..
a 60Ah batterypack will last about an hour (a little less) because of the battery protection and heat drawing the high Amps.
Since the motors will not run at their full load all the time, it's more or less safe to assume you'll get your full hour.
To be on the safe side.. I'd get maybe a 72Ah set.


the controller has nearly no influence on the run time at all
(well every controller draws a tiny amount of power.. but compared to the motor it's not even noteworthy)

'sid

 

[Ahmed_bilal]

Ok great thanks for your help.
Can you please help me find where i can buy a suitable 60a 36v controller? I dont want to get 72a batteries as they are a bit too expensive.
I found this, would it be any good? http://www.ebay.co.uk/itm/310962678274



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[itsid]

I wouldn't use a motor controller like that, they're intended for stationary use
at constant speeds...

So not really made for a moving vehicle
no brake circuit, no battery protection etc.

You need to find a controller specifically made for electric vehicles (e scooter, e bikes etc)
Most of them are listed in wattage.. just find a 36V 1600W (or more) controller
(the wattage is listed as nominal motor wattage.. so the 36V 800W controller will cover up for the overshooting amps up to 32Amps for example)

Maybe you'll need to get a kelly controller for what you want.
http://kellycontroller.com/kds36100e100a24v-36v-p-270.html

maybe you can find a cheaper one *shrugs*

'sid

 

[Ahmed_bilal]

Thats an awesome controller much better than the rubbish one i found lol.
What is the maximal watt rating for that controller?


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[itsid]

constant rating is 60A.. so 2160Watts for a 36V
(electrical power! roughly 1850W mechanical power)

'sid

 

[Ahmed_bilal]

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[Ahmed_bilal]

Should i buy this one or the kelly one?


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[dcastillo]

ive never used a curtis before, but I have no issues with my Kellycontroller (I have the 24-48V 200A model)

now I just need a bigger motor

 

[itsid]

Well.. if you can get the Curtis for a good price, go for it.

As far as I know they're virtually bulletproof, reliable and powerfull
(and unfortunately expensive )

But make sure it's able to power brushed DC motors..
AFAIK some curtis controllers are meant for brushless motors only.

'sid

 

[Ahmed_bilal]

Ok thanks,i got the controller. But i also need a throttle, can you please suggest what types of throttles are best for the Curtis controller?
Would something like this work? http://www.ebay.com/itm/171125691520

I dont want fancy led indicators i just want one thats best for no more than £50 please.
Thanks


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[Ahmed_bilal]

Sorry i meant best function


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