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Old 05-19-2019, 06:50 PM
Bmr4Karts Bmr4Karts is offline
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Default Need some help calculating power requirements.

I've read over the sticky thread and can't get past figuring out the sin of an angle (I keep getting a negative number, lol).

So this is what I know and want.
  • My kart with me in it ready to go will weigh ~400lbs (less if I don't use heavy SLA)
  • Want to hit 25mph speed.
  • Will need the torque to easy go up a 20 degree incline.
  • Open to 48v or 60v brushless systems
  • I don't have a jack shaft so assume the axle gear is almost as big as the drive wheels.

Any help would be appriecated. I can't tell if an 1800w or 2000w system would be enough or I'm looking at something more like 10kw.
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Old 05-19-2019, 07:18 PM
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well, calculators use radians by default more often than not..
angles in the math you are refering to are in degrees!

A 20 incline? you sure? that is some heavy offroading you have in front of you there.

So
180 kg

Fi = m * g * sin(alpha)
=>
180kg * 9.81 m/s * sin(20) = 603.94 N (aka kgm/s)

604 Newton of force let's say just to round things a bit.

And that times the desired speed in m/s
(let's stick with 9m/s for simplicity's sake since I doubt you need to go up that hill at that speed)
makes
5436 Watts of power (MECHANICAL power at the wheel!)
means almost 7kW of electrical power draw if bad comes to worse..

So yeah.. a 10kW motor isn't a bad idea at all,
it won't be that much more expensive,
you have a nice backup
and run far from the limit and the risk of overheating motor or controller..

if you're so inclined (hehe) to go up that hill at 25mph we talk
6650 watts of mechanical power (~8.5 kiloWatts electrical)
still possible with the 10kW motor ...

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Old 05-21-2019, 03:05 PM
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Alright, not that I doubt you all but youtube is always a fun confirming device for me.

Edit. I don't think I'm going with the Leaf batteries only because they are so large and while a good deal, it's way more capacity than I think I will need.
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Old 05-21-2019, 07:19 PM
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Quote:
Originally Posted by Bmr4Karts View Post
Alright, not that I doubt you all but youtube is always a fun confirming device for me.
Alright, not that I judge you at all but people who need youtube to confirm a simple physics formula are usually badly educated.
See? doesn't read nicely that way either, does it?
and yes... same amount of truth

Okay, since the german wiki-page is far quicker explaining it..
here's the google translated version of it

AS simple as that.. we only need to counteract the downhill force (F.GH),
since we do not need to lift the kart off the road (F.GN)
both combined make up for the gravitational force of the kart (F.G)
which is mass (m) times gravitational constant (g : 9.81 m/s)


For the leaf batteries..
check for maximum discharge current per cell,
multiply that by the number of parallel cells for a total discharge current
and then by voltage and motor efficiency
as an example say 100A per cell 4 cells in parallel
400A * 48V *0.8 = 15360 Watts
for a motor with 80% efficiency [19200 Watts power draw max]


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Old 05-21-2019, 08:16 PM
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Pretty much I just watched all of Functional Artist's videos.

Now I'm trying to determine if the 20ah ford cmax energi battery cells have enough discharge capacity to handle my power requirements. I was going to go with the Leaf batteries but are huge.

According to this site they are good for 150 amps.
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Old 05-22-2019, 08:02 AM
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Quote:
Originally Posted by Bmr4Karts View Post
Pretty much I just watched all of Functional Artist's videos.

Now I'm trying to determine if the 20ah ford cmax energi battery cells have enough discharge capacity to handle my power requirements. I was going to go with the Leaf batteries but are huge.

According to this site they are good for 150 amps.
I would listen to Sid
He taught me most of what I (think) I know.

I experiment a lot & do lots of testing
...but, I'm just learning as I go

Sid knows his shirt

* as for batteries, I ran ElMoto, my electric motorcycle, @ 36V on (3) 12V 35AH SLA batteries
& then @ 48V on (4) of them.

It will pull over 500A (on hard acceleration) for a split second.

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Old 05-22-2019, 09:09 AM
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Quote:
Originally Posted by Functional Artist View Post
I would listen to Sid
He taught me most of what I (think) I know.

I experiment a lot & do lots of testing
...but, I'm just learning as I go

Sid knows his shirt

* as for batteries, I ran ElMoto, my electric motorcycle, @ 36V on (3) 12V 35AH SLA batteries
…& then @ 48V on (4) of them.

It will pull over 500A (on hard acceleration) for a split second.

What gauge wire did you use? What about connectors?

My plan is to build two 7s packs using buss bars and 4 gauge wire. I want them to be removable for charging and I'm trying to size out the connectors. I'd like to use Anderson Powerpoles, the PP120 Is what I'm thinking.


Also, battery has been ordered. Should be good for 150 amps and 225 max amps. Now I need a motor that has the potential to pull at least 100 amps and a slightly oversized speed controller.
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Old 05-22-2019, 11:34 AM
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Quote:
Originally Posted by Bmr4Karts View Post
What gauge wire did you use? What about connectors?

My plan is to build two 7s packs using buss bars and 4 gauge wire. I want them to be removable for charging and I'm trying to size out the connectors. I'd like to use Anderson Powerpoles, the PP120 Is what I'm thinking.


Also, battery has been ordered. Should be good for 150 amps and 225 max amps. Now I need a motor that has the potential to pull at least 100 amps and a slightly oversized speed controller.
I used regular 4g. automotive battery cables & standard battery cable lugs.

Here is an old thread (kinda the beginning of the El Moto story)

http://www.diygokarts.com/vb/showthread.php?t=33680
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Old 05-22-2019, 12:34 PM
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Thank you.

So I think I have some strong contenders for motor and esc. I have to admit they came from a youtube video. One of the videos that really got me wanting to build an electric gokart in the first place.

Motor Motenergy ME0201014201

Speed controller SABVOTON 72V150A

I'd start out with just 14 cells thinking I can add more later if I need more mph.

Is that proper logic?

https://youtu.be/zTjexuJE2us?t=177

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Old 05-24-2019, 09:30 PM
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That controller is for 72v — 95v I didn’t see where it can run on 48v like you planned.
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Old 05-27-2019, 12:30 AM
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Quote:
Originally Posted by voided View Post
That controller is for 72v 95v I didnt see where it can run on 48v like you planned.
Good catch. I am now focused on Kelly Controllers and will buy a KLS725H along with a ME1012 dual stator motor. I'd rather have too much motor and ESC than too little. Battery pack will get built up to 48v first quickly followed by 72v.
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Old 06-02-2019, 06:44 AM
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Alright, I'm very close to ordering a motor. At this point I'm torn between the Motenergy ME0201014201 and the ME1012. The latter is the same as the former with the addition of a 2nd stator for motor torque.

The Panasonic Prismatic cells are good for 150 amps continuous. The ME1012 can do 125 amps continuous. Just because it can doesn't mean it has to though right? Wondering how long my 20ah batteries will last.

If I take those two motors and apply the same load, won't they pull similar amps as long as that load doesn't go over the max power the weaker motor can handle?
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Old 06-05-2019, 12:07 PM
Bmr4Karts Bmr4Karts is offline
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My electric gokart project got real expensive real fast.

Motor - $600+
ESC - $600+
Batteries, $250 so far, will end up being closer to $500 once I go from 48v to 96v

Ended up going with a Motenergy BLDC 96v 200amp motor. Don't have to run that much volts or amps but I like having head room. Ordered a Kelly controller to match.

Still have to buy a bigger charger so it doesn't take 6+ hours to recharge.

I'll probably be able to do well over 50mph when I max everything out but I am at least a month away from having this done.
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Old 06-06-2019, 12:20 AM
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Yup. Electric doesn't come cheap
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