Looking for some guidance - E gocart

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Jake Z

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So I'm looking to convert a gas powered racing cart to electric for my daughter. I think I will get far less complaints of her riding around on an E-cart through the subdivision. I've done some research and I'm looking at the following set up:

Motor: motenergy me0909

Controller: Sevcon Millipak 4Q

Batteries: either (4) 50ah Agm or yellowtops part # 8171-767

Throttle: PB-8

The couple things I am having an issue is figuring out is how to charge/maintain the batteries. My last build was a 36v razor dirt quad, and was much simpler. It doesn't seem from my understanding I will be able to charge through the controller like the quad. It does seem like the controller will monitor for low voltage though. I may be completely over complicating/over thinking things, but it be nice to plug the kart in at night and not worry about overcharging as well. So how is everyone taking care of charging/battery management?

Thanks,
Jake
 
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mikkelibob

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I'm right there in the same boat. Have a manco roller (pending purchase) that looks pretty clean. I figure its heavy enough (as is my rear) to require a good motor, and that a 1000W and 1500W scooter motors are too weak.

I have the same motor in mind, although could be tempted into the similar cost ME0907 (or ME3201 or ME 4201) for a brushless system. The motor price is similar, but I think brushless 300amp controllers are a bit more expensive. The Millipak 4Q was already on the nicer/expensive side.

I saw some guys on youtube do a Alltrax SPM-48225 Motor Controller (much cheaper at $208) with that me0909. I'm guessing pumping 200amps is slower than a nicer 300 amp controller, but I'm not sure how much slower. Personally I'd be happy with 12mph over grassy dirt roads. Forum experts, how cheap can one go on a controller and hope to move 500 lbs at 12mph over grass? Can a kelly mini controller like the KDS72200E ($140) provide enough juice?

Cheaper throttle option:
http://kellycontroller.com/simplified-5v-throttle-pedal-p-1028.html

I have the same question as you re: battery charging.
 
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itsid

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first you cannot (should not!) power a 300Amp motor (and yes, peak Amperage IS important)
with a 200AMp controller, if the motor wants 300Amps it'll draw 300 Amps... overheating and frying the controllers MOSFets in an instant. (result: no power at all.. worst case: a literally burning controller)
So a 300Amp or bigger controller is what you should use!
If you're keen to go as cheap as possible, at least find a self resetting temp fuse that cuts of the power in case too much is about to be drawn.
(controllers come with inbuild fuses mostly nowadays.. but since a fuse is ~5bucks and a new controller is slightly above that ;).. why not one more level of safety)

To know what power you'll need to move at 1mph over grss..
just check my essence thread here
you'll need to convert some numbers to metrics of course... but hey at least that's scientific ;)


'sid
 
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mikkelibob

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I'll take a stab at doing the math.

Mass = 250
curb weight of manco scorpion = 344lbs (156kg) - maybe 25 lbs less with engine/gas/clutch
me = 190 lbs + some batteries and motor (95kg)
total: ~250 kgs

Fi = m * g * sin(alpha)
G= 9.81 m/s²
alpha = if you want to go offroad you can assume 10°,
Fi = 250 kg * 9.81 m/s² * sin(10°) = 456 N

Fr = m * g * Cr * cos(alpha)
Cr = .05 (0,050 cart on dirt track)
Fr = 250 kg * 9.81 m/s² * 0.05 * cos(10°) = 121 N


Fa = Ca *m *a
an acceleration of 2 m/s²
Fa = 1.2 * 250 kg * 2 m/s² = 720 N

Fw = 0.5 * Da * Cw * A * v²
air density at 20° C is 1.2 kg/m³
Cw = 1.2; adult in a cart is possibly even worse than a chubby on a chopper?
A = 1 m2? Just guessing.
7 m/s are 32.4 km/h btw (~15.5 mph)
Fw = 0.5 * 1.2 kg/m³ * 1.3 * 1.0 m² * (7 m/s)² = 38N

Pm(Fi) = 456 N * 7 m/s = 3200N
Pm(Fr) = 121 N * 7 m/s = 850N
Pm(Fa) = 720 N * 7 m/s= 5000N
Pm(Fw) = 38 N * 7 m/s = 270N

http://www.thunderstruck-ev.com/Manuals/ME0909 Plots.pdf
36v, 140amp = 5040W @ 0.7 efficiency 3500W
45v x 180amp = 8100W @ 0.9 efficiency 7300W

So it looks like I’d need at least about the 36v set up (possibly sacrificing acceleration) and should plan on possibly having to do 48v.
 
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mikkelibob

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I think this old thread answers the battery charging question we both had:
http://www.diygokarts.com/vb/showthread.php?t=27511

Basically, you can get a charger for each battery and disconnect them (more work, but maybe cheaper) or charge them with a single charger (matching voltage of course, so 36v charger for 3x12v batteries).

Anyone able to double check my math? In the Pm(FI) calculation, I'm wondering if I was happy with 10mph (so about 4.3 m/s) if I could get along with the me0909 at 24v. In one place I read you can assume about 83w per volt (so about 2000W with 24v), but I don't know how that jives with the efficiency power curve. My goal is to just putter around my ranch - more or less going faster than a good jog seems like enough speed.

Also, can I get some help on throttle? I see lots of folks get those PB6 units, but those are $90. Has anyone had good luck with the kelly simplified 0-5v hall pedal and an alltrax controller? http://kellycontroller.com/simplified-5v-throttle-pedal-p-1028.html

Do folks usually fab up their own motor mounts, or buy an off the shelf solution? The best deal I've found is an etek L bracket on ebay for $75 or so. I have a welder and a dremel, but not a drill press.
 
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HelloYOU

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Jake Z said:
So I'm looking to convert a gas powered racing cart to electric for my daughter. I think I will get far less complaints of her riding around on an E-cart through the subdivision. I've done some research and I'm looking at the following set up:

Motor: motenergy me0909

Controller: Sevcon Millipak 4Q

Batteries: either (4) 50ah Agm or yellowtops part # 8171-767

Throttle: PB-8

The couple things I am having an issue is figuring out is how to charge/maintain the batteries. My last build was a 36v razor dirt quad, and was much simpler. It doesn't seem from my understanding I will be able to charge through the controller like the quad. It does seem like the controller will monitor for low voltage though. I may be completely over complicating/over thinking things, but it be nice to plug the kart in at night and not worry about overcharging as well. So how is everyone taking care of charging/battery management?

Thanks,
Jake
Click to expand...

Should work perfectly. I had one of those PM DC motors before going series wound, but I returned that motor because when I looked at the end turn windings that curved around back into the slots of the armature at the front shaft end, there was no enamel insulation on them!! They bent them so tight that it broke the insulation enamel off the windings. That was about 6 years ago, so maybe quality control has improved since then.

For charging I use a multi-channel charger like a Pro series charger: http://www.dualpro.com/project/professional-series/ made by Dual Pro Systems. All the channels are electrically isolated from each other, so you just hook up each channel to each battery without worry of shorting out anything on the charger.
 
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