RFC - Building first E-bike from scratch

[assaf]

Hello respected forum!

I've been lurking here for a year or so, reading & getting educated, and this is my first post.
I must begin by saying that the level of involvement by members here, and the feel of the place, is unique, and I value your contribution very much, you keep a wonderful forum, and it benefits so many people who're interested in this field.

I have a build plan made up, and before I put down a considerable amount of money, I'll really appreciate some peer review.

Background: I've been riding for over a year a Gary Fisher hard-tail with a 350W Bafang (running 500W) and 2 packs of LiFePo4 36V 8Ah hooked in parallel, with various mods & installations (soldered shunt, self-made torque arms, watt meter, 2nd battery pack retro-fitted, XT60/deans connectors where needed). It's time to take it a step further

Objective: A high-end bike (DH frame), with a decent & reliable system that can deliver 40-60 KM/h, with short periods (like 2 minutes) of ~70KM/h. Most of the time I'll be cruising ~45KM/h so as not to arouse suspicion, but I'll want that 70 for whenever I have the whole road to myself 8)
My terrain is mostly flat. I plan to use the bicycle as my primary vehicle to work & back. Each way is ~30KM and I can charge at each end.

So here's the recipe:
* Bike: Downhill/Freeride bike with space in the triangle (yet to decide on one, perhaps Felt Redemption) (around 1000$ here).
* Motor: Crystalyte H40 Cruiser from Ilia @ebikessf (great communication, btw). 460$ + 85$ shipping.
* Battery pack: Hook up this LiPo in 4S5P pattern: "ZIPPY Flightmax 3000mAh 6S1P 20C", amounting to 24S 15Ah in total. 588$ + 90$ shipping.
* Controller: LYEN Edition 12 FET 4110 MOSFET Extreme Modder Controller. 129$ + shipping
* Charger: Turnigy 4x6S 400W Lithium Polymer Battery Charger. 124$ + shipping.
* Power supply: Hobbyking PS35 DC Power Supply for Chargers 35A (350W)
* 3-speed switch. 15$
* Cycle Analyst V3 (with the temp control). ~150$
* Wires, Connectors, solder, more tools: ~200$?

The battery pack shall be 24S 15Ah and the controller set to 50A max, which according to ebikes.ca simulator (BIG THANKS for that, a friend and me played with that thing for hours!) should give a 44KM range @50KM/h.

How does this look in general? Anything missing or miscalculated? Appreciate any comment before I put the big buck!

Thanks in advance,
Assaf

 

[dogman dan]

Should work out ok for a solid 40 mph bike. I'm not sure what your actual top speed will be, but I'm sure you will see 70kph. (43mph)

Range might be a bit less than you think, depending on how much of your 15 ah you are willing to actually use, and if you charge to 4.2v or not. You ought to have 13-14 ah there for sure. Calculate your expected range based on 13 ah, and you should get that far.

Charging. You will of course need a power supply or several to run that charger. You might start with just one of that charger, before spending a huge amount on 3 more of them. You might decide you like another charger better later.

Tools. A cellog 8 is just about indispensable. At first, you might even want some of the cheapie lvc warning devices. 4 of them, one for each set of 3p x 6s bundles. They suck for running all the time, since they actually throw a pack out of balance. But for that learning curve time of getting into lico, they can save your ass. Using just the CA readout is fine once you know you have all good packs, and you are not discharging deeply that ride.

Later on, if you must discharge deep you can pull that cellog out of your pocket and make a quick check of your packs before pushing below 3.65v per cell. Or still use the buzzers for a ride you know will push the pack all the way to 3.5v. The cheap buzzers I got are adjustable, so you can set them for whatever you want, based on your known voltage sag under load.

 

[Drunkskunk]

Looks like a good start on the plan.

Breaking 60kph takes a couple of amps more than average. That 12FET may be fine once modified, but you'll pe pushing it very hard. You're in the grey area where the 18FET may still be overkill, but if you plan to do any off road riding, It wouldn;'t be a bad idea. You might also consider using the 4115 FETs, since they handle the higher voltage better.

1332 watts of lipo is a big @ss pile of batteries, and Lipo aren't real friendly when bounced around. Strapping that many bricks to a bike is a problem. you'll need a rigtid box of some kind. I'm running that much Lipo myself. Building a battery box isn't so hard, but you may want to look at a dedicated frame like the Raptor.

Lipo are short lived. you may well be able to get 15 amps out of them this year. next year you'll get 12 or 13 amps, the third year you'll get 9 or 10. the 4th year you may get 5, and they'll start looking like puffer fish, regardless of how much you use them. So plan your battery or your speeds accordingly.

 

[assaf]

Thanks dogman for the detailed reply!

As for range, I'll give it a test when the bike is finished. Anyway the cool thing about custom packing of the battery is the flexibility!

4 x Celllog-8's added to the list. Does that thing feed off the balance taps for power?
Power supply: 350W from HK: http://www.hobbyking.com/hobbyking/store/__9205__25A_14v_DC_Power_Supply_for_Chargers_350W_.html.

I definitely want an audible alarm LVC alarm. You said "I got" - do you sell them? I would also like a visual alarm.

Battery protection: I believe the Cycle Analyst and the balancing charger take care of HVC / LVC for me, rendering a BMS redundant. Is that the way to go?

Assaf

 

[assaf]

DrunkSkunk, thanks!

I think it was Luke somewhere that said that actually 12x4110's are better than 18x4115's? Or did he mean amps rather than volts...

Unfortunately I've already pushed the budget as far as possible with the Mrs., so I can't order the custom frame. I'll rig up some kind of metal cage for the pack, using old tubes to soften the inner walls. Be very interested to see how you designed your box.
The pack will ultimately be 18*13.5*2.15cm, a tad beefier than what I currently have on the gary fisher so I guess I'll be on familiar ground there.


The battery holding good for only two years is definitely a downside. But LiFePo4 are way too expensive / haven't got the C rating for my needs.

Assaf

 

[Drunkskunk]

Luke was right, but not in the same context. IRFB4110 have less than half the RDS on resistance of 4115s, but they're rated for 100 volts Max. 4115s are rated for 130 volts. Your 24S Lipo maxes at 100.8 volts. Every time you hook them up, its like slamming the FET's head against the wall. while some of the FETS may be into that sort of hard core S&M, others are just going to quit on you. Its a risk.

Now for racing, or trying to build a high performance, no compromise bike, 4110 are the way to go, but those who do it know they're beating the hell out of their controller and are prepared to replace it or rebuild it when it dies.

You're building a commuter/primary transportation bike. you want it to work reliably tomorow, next week, next year, and for a long time to come. That means chosing parts that arn't functioning by hanging over their jagged edge of the failure point. 4115s will handle that kind of voltage without astressing, and the performance impace is something that only matters on the racetrack. Now if you ran 20S, or 18S, 4110s are the way to go.

My battery box is built into the frame. its the bike in my sig pic, but there a bunch of pics in the build thread in my signature line. Its so tight of a fit that I actualy had to build a battery press to compact the 100mm wide batteries into the 100mm wide hole.

 

[assaf]

Very good & accurate points! Indeed reliability is paramount as this will replace my current primary vehicle. This thing need to function as much as possible without flaws.

So lower Rds = slightly better performance which only counts in races (like paying an extra 2000$ for a bike frame that's 200g less).

Well, I'll probably have lots more questions as I start to build. Now I need to order the parts and find me a bike

PS
The picture of the motor with the panties - LOVED it I showed it to my wife so she'll understand what I'm going through. Her reaction expressed that she did.

Assaf

 

[heavymetalthunder]

I think your set up is good except on the batteries. When exceeding the 25 MPH barrier you will really see your power usage go up. On my current 1000 watt 48 v set up at 25 MPH I use about 760 watts and 1200 watts of power at 34 MPH. I think you need you add an additional brick or use more 5000 MAH, plan to move your AH to at least 20, the 20c rated batteries should perform OK. I use 8 5000 MAH 6S 25C to 40C and have a range of 15 miles with a 15% spare power reserve, of course my bike is fairly heavy and I tend to travel at 30 MPH.

 

[assaf]

Thanks heavymetal, it looks like I'm gonna add 5Ah like you say. You say you cruise at 30mph, just wondering, does law enforcement not notice? That's kind of the part that scares me about this adventure.

 

[John in CR]

I'm with Drunkskunk. The controller seems a bit light unless you mount it fully in the air under the downtube. I don't like RC Lipo for a commuter with deep discharges twice a day. They'll wear out quicker, and with your charging plan you're looking at a lot of man hours fiddling with charging battery instead of park, connect one plug, and charge like you're used to. I don't know about you, but I don't want a second hobby called fiddling with batteries, not to mention the high likelihood of some kind of connection mistake or connector or wire failure with those many hundreds of connects and disconnects a month.

 

[assaf]

Hmmm.. so the problem is the chemistry?