Wiring brushless Etek, cable guage?
I am in the process of wiring up a brushless Etek to a Sevcon Millipak for my electric mountainbike conversion. What guage of welding cable would you guys recommend? I was looking at the stuff from electricvehiclesusa.com. I will be running 100 amps continuous and up to 250 amps for a 30 second burst. The batteries I am using are three B&B HR22's, for a 36V system. Thanks!
Awhile back I'd done some yahoogling for normal recommendations and there are charts out there saying that for a 100A current you need 00 welding cable (I think). However it seems those recommendations are for days-on-end "continuous" and somehow that doesn't apply to an EV.
On my Lectra I'm using 4 gauge wire and run current like what you say. This works fine. I'm using a different motor and controller however I think that those aren't important and what's important is that a given wattage corresponds to a given wire thickness.
4 AWG should be fine. My question is, how are you possibly going to draw 250 amps at 36v on a bicycle for 30 seconds? Are you gearing it for over 60 mph?
Yee hah! 250Amp * 36V = 9 kW = 12 HP. On a mountain bike?
You might want to see the thread where folks are defining how fast is too fast. Oh, and I recommend you take out a good life insurance policy as well...
I didn't catch that mountainbike part. That's crazy! Seriously, we're having to start modding parts once we hit about 5kW peak. There's a YouTube video of a guy who did something like that. They were having problems with the chain snapping.
eep! mountain bike? ohmygosh. This is the "Motorcycles" section, not "bicycles".
Whilst we are at it:
Is there a 200W rated bicycle motor that can produce a lot more power than that?
I'm thinking about having the option to use several battery packs in parallel for range on the road (200W legal limit in Oz) and switch them to series once on private land.
If using a good quality mountain bike with disk brakes it should be reasonably safe....
I am in the process of wiring up a brushless Etek to a Sevcon Millipak for my electric mountainbike conversion.
Tommy, you go, dude! However, you need to go to http://www.electricrider.com/custom/index.htm and look at the Insane-A-Cycle videos. The Insane-A-Cycle is/was powered by a (brushed) Etek, and you need to consider gearing and robustness when you build your bike. Otherwise, the dropouts become ripped-out, if you get my drift. An Etek / Mars motor has a ton of go, so make sure you also mount sturdy 200mm discs on your bike, so you can stop, too.
The motor, controller, line contactor, and tensioning mount is supposed to arrive on Thursday, so I will start mocking it up then.
If you have access to Solidworks CAD software, I can provide you (for your own personal use only) with exact dimensional models of the Mars brushless motor, Thundersky 90AH batteries, and even front and rear bicycle wheels. Recently, I discovered that they make 165mm-wide rear MTB hubs with a disc mount, which is perfect for a hybird: normal derailleur drive on the right and a motor drive (and even disc) on the left.
I've been designing something vaguely similar (a trike) for some time now.
I am mainly concerned with the 6 small bolts that hold the sprocket to the hub. I am afraid they might shear under full load, but I think as long as I can find a quality set of grade 8 bolts, I will be good to go. I am also concerned with the integrity of the spokes and nipples, but I will stick with the original spokes and rims until I see any hints of problems.
You are doing the same thing that I am, namely using the ISO 6-bolt disc bolts to hold on a sprocket. That is 44mm circle of M5 bolts, each of which is about 75% the area of a 1/4" bolt. A grade 8 1/4" bolt has a tensile strength of about 5000 lbs, so the tensile strength of the M8 bolt should be ~3750 lbs. A common rule-of-thumb is to rate the shear strength of a bolt at 60% of the tensile strength, so each M5 bolt should be good for about 2250 lbs in shear. The Mars brushless can output 200 in-lbs of torque max, and say you are geared 4:1 with a 2" driver sprocket and an 8" driven sprocket, you arrive at (roughly) 800 lbs of shear at the 44mm bolt circle. The 6 M5 bolts would yield at 6 x 2250, or about 13,500 pounds, so the bolts will hold. Will the hub? The spokes? This is left as a exercise for the student. MechE 101 is over for the day ;-)
I would recommend at least 13ga spokes and 3 cross lacing, though. 12ga spokes are available (but would probably require your hub to be drilled) and 4 cross lacing is even stronger in torque. Keep an eye out for loose spokes, since that would indicate a nipple that has stripped.
Let me know how it works!
PS - I'll also be interested in how you mount the motor!
Tommy - keep us posted - I'd love to see your finished product. I'd even like to ride it. It sounds like a hoot. Ignore us folks in the peanut galleries!
I know people have seen this bike, and it is basically an etek powered 20 inch wheeled downhill mountain bike without pedals.
I'd be concerned about the 26 inch mountain bike wheels. They built the jackal with motorcycle grade 20 inch wheels as the smaller wheels are stronger.
I like the idea, but wonder if a free-ride or downhill bike might be a better choice to convert. That Trek bike, does it have any suspension? None on the rear, right? Hitting a bump hard with the rear tire at 45 MPH with no suspension could get interesting.
I've got a lookup table, and for 20% duty cycle, you can do 280A on 6Ga and 358A on 4Ga. If you go 30% it drops to 228A and 292A respectively. At 60% it moves to 161A and 207A. 100% is 125A and 160A.
Its page 4. Its roughly what you're going to get with copper cable.
It's also helpful to calculate the power loss due to resistance to help make a decision, and give an idea how much the wire is going to heat up.
6 AWG: .0003951 ohms/foot * [wire length, 10 ft guess] * [current=250] * [current=250] = 247 watts at 250 amps, and 39.5 watts at 100 amps.
4 AWG: .0002485 ohms/foot * 10 * 250 * 250 = 155 watts power loss at 250 amps. ~25 watts at 100 amps.
2 AWG: .0001563 ohms/foot = 62.8% power loss of 4 AWG or 97.5 watts at 250 amps, and 15.6 watts at 100 amps
1 AWG: .0001239 ohms/foot = 77.3 watts power loss at 250 amps, 12.5 watts at 100 amps.
So you can kind of see that the advantage of going to larger and larger wire size gets smaller for a given amount of current flow in terms of power loss and heating. And, wire can really handle a lot, it'll just heat up, and waste some power. I bet even 8 AWG would work fine in your application, it would just heat up some and waste power. Take my motorcycle:
2 AWG .0001562 ohms/foot * 18 feet * 600 * 600 = 1021 watts loss at 600 amps, or 56 watts/foot. It gets nice and warm, but it does the trick. If I went to 1 AWG this would be 810 watts at 600 amps, and or 45 watts/foot, and 0 AWG would be .0000983 ohms/foot or 643 watts at 600 amps, and 35.7 watts/foot.
Not worth it for me to go to the larger wire size at 600 amps. On the other hand at 1100 amps these figures go to:
2 AWG: 189 watt/foot or 3402 watts
1 AWG: 149.9 w/ft or 2698 watts
0 AWG: 118.9 w/foot or 2141 watts
I think it'll get pretty hot, but maybe it won't melt. We'll see. I'll need to upgrade the batteries before that'll happen, as the B&B's would melt at 1100 amps.
Sorry for the rant, just my 2 cents on wire sizing.
Using the V-brake (I still call them cantilever) bosses for a motor mount is very resourceful. Will you be able to mount a rear disc brake?
Tommy, it's our policy generally to not change titles because this can be confusing to readers. Also, the initial focus of the thread is geared toward the original title, so this will not make much sense for new readers.
It is perfectly ok to make another thread, and repost whatever you want from this thread. Also, it might help to put a link to this thread in.
One of your shots above gets me exactly the info I was looking for (the stator fixing bolt locations on the fan side of the Mars brushless). Thanks. Good work. I look forward to the results of all your hard work.
Nice work, but are you sure about that chain? I mean, that's a beast of a motor you've got there. I'm not sure a bike chain could take it. Might have breakage problems.
37V sounds a little low. Should be like 39V or a little higher.