Bike Power

System · November 2006

I'm a 69 year old geezer who has led a very active life. One of my interests has been long distance bicycle touring. This past summer I had two heart attacks that slowed me down a bit. But, I've rehabilitated to the point I can bike long distances on level ground but the hills still whip me. I live in the middle of the Smoky Mountains of North Carolina so this is a problem.

I've found a lightweight, battery operated, hub motor system that assists in the peddling effort and may be a solution for me. I'm so excited about this BionX system that I'm considering a long trip this summer.

The BionX gets up to 30 miles on a charge. That's great for local trips where it can be recharged overnight. On long tours in the past I usually pedaled 60 to 100 miles a day. Since I normally travel and camp in remote areas plugging in won't work. So, I'm looking for a solar charging system that would charge the battery while I'm travelling.

You might want to take a look at my recumbent trike at www.greenspeed.com.au and the BionX is at www.bionx.ca

I would build a canopy above the seat of the trike for a solar panel. This should be adequate for short trips. For long trips I pull a trailer that could carry an additional panel array. How many and what type of panels do you suggest?

The information I have is the battery is a lithium-ion 36V, 9.6AH. The Ac charger that comes with it recharges the battery in 3 to 4 hours at 2 amps. The motor is a brushless 350W with a peak of 600W. These numbers don't mean much to me. I'm an artist, not very technical.

The panels would be constantly bouncing and vibrating. What would be the best way to mount them? Could they be mounted ridgedly or should there be some sort of suspension?
Of course, "lightweight" is key. Reliability is more important to me than cost. What other equipment would be required?

Thanks for your help,

Rob

BB. · November 2006

Re: Bike Power

Good Afternoon Rob,

Welcome, and I will take a shot at this...

Some numbers, in a perfect world 1 horse power = 745 Watts--or your hub is 300/745 = 0.4 hp rating...

If it takes 4 hours at 2 amps and 120 VAC to charge, that is 4*2*120=960 watt*hours (4 hours at 240 watts)...

Just for the sake of discussion, lets assume that you would want two BP 175 watt solar panel:

http://www.bp.com/liveassets/bp_internet/solar/bp_solar_north_america/STAGING/local_assets/downloads_pdfs/pq/product_data_sheet_4175B_en.pdf PDF File

Size of one BP 4175 panel--recommending two panels as a starting point (one may work--depending on how much power you will really need).
Dimensions Length: 1595mm (62.8”) Width: 790mm (31.1”) Depth: 50mm (1.97”)
Weight 15.4 kg (34.0 pounds)

Roughly, those will generate about 1,000 to 1,500 watt*hours on a sunny day pointed at the sun, from, at least 9am to 3pm... This would probably be an appropriate place to start... Depending on efficiencies of conversion/charging, weather, how much power you use, etc., your exact values can be tweaked... (solar energy collected based on SF CA experience of my Grid Tied home using 20 BP 4175 panels for summer months--your location will be different).

So, you will need to tow that panel around (weight of trailer+panel+drag)--the panels are pretty strong, but it is still glass--very rough roads and/or a crash will break the panels. Plus, you will have to park most of the day, with the panel pointed towards the sun, to generate a full charge.

Or, you can get a Honda eu1000i gasoline generator + 1 gallon of gas (17.7" x 9.4" x 15.0" and 29lbs + 6lbs for a gallon of gas) for about the same (or a little less) cost as a solar panel... (~$700 for generator vs ~$900 for a solar panel)... And you can just charge at night (a gallon of gas should last your 4-5 days of charging). Plus you can charge in any weather/shade condition.

So, just being practical, you have to choose size/weight/daytime use of the charging (going green) vs the costs of going with a portable generator.

Obviously, the solar panel will require some sort of electronics to convert to your battery pack--won't be too heavy, but may be difficult to find an off-the-shelf unit that does what you need. You may be able to get some charging when trailing the solar panel during the day (no trees, good sun angle), but I would not count on more then 50% of rated charging while riding vs a fixed full sun set during the prime 9am-3pm solar charging hours.

Your thoughts?

-Bill

mike95490 · November 2006

Re: Bike Power

(try # 2, a power glitch just re-booted me at 90%)

After reading the first reply, I'll say I took a different approach in my guesstimate, by using motor usage.

Assume 500W usage for 1 hr per day.
Needs about 700W to recharge that usage. (recharge and conversion losses)
If parked for noon break, that's a lot of panels.
Your 120V 2A ac adapter, is it a heavy one (transformer) or feels light and almost empty (switching)
A switching one will handle a cheap square wave inverter (usually) 120V 2A = 240W 300W inverters might work, but I'd use a 500W inverter, and be sure it won't overheat. 12V battery:Deep cycle, maybe from Costco? Heavy.

Panels : I'd suggest Uni Solar 64's they are rugged, no glass, and slightly flexible.
PV panels, if they say 100W, count on getting 80W, just like EPA mileage estimates, they lie.
So the 64 w panels will actually give you about 50 watts. For lunch hour recharge, that's 14panels. Ouch.
Spread it out for 4 hours optimum sunshine in winter (2 hrs before noon, 2 hrs after, more in summer) and you only need 4 panels.

Cloudy days You could live with one cloudy day, but then your 12V deep cycle battery will be low, and need recharge.
2 cloudy days - you have to park or destroy your 12V deep cycle battery by over dischargeing it, with no recharge.

So you could build a little trailer, for your gear & PV panel rack and the 12V battery will apprecate some shock mounting, to keep the internal plates from being beat up.

Use the motor more, and need longer recharges.

Does the bike motor kit have a car (12V) recharger option ? That would be best, skip the other losses of charging 2 batteries and the inverter. You should have a small 12v gel/agm battery for the Charge Controller to work with.
You may be able to recharge "on the go" if that's the case.
Possibly consider re-fab the battery pack to work with 12V AGM cells, and direct charge off the solar. Anyone make a 36V charge controller ? 12, 24, and 48 V are common.

System2 · November 2006

Re: Bike Power

I'm a solar novice but long term cyclist (with increasingly worn out knees) and like the sound of your idea. FWIW here are my thoughts:

I am not sure about how many panels you would need - the Bionx can charge itself on descents so much would depend on the daily ascent/descent gradient profiles, as well as the time in the saddle. Having a few climbs spaced out over the day with flats and downhills in between would obviously require less battery / recharging than one all day climb. Also, if you are camping and can be flexible about your itineraries (i.e. don't expect to get so far on cloudy days), you should be able to do with fewer panels than Bill suggests. But from the sound of it you would still need quite a few panels for a lunchtime charge.

I think the key to it will be to design a lightweight trailer that can take the required number of panels, ideally this will be no wider than your trike, so it may have to be quite long. I would suggest using smaller panels (e.g. Kyocera 85s) which would be less likely to flex, and would probably mount these with zip ties on soft rubber pads, and also use a 1.75" fast rolling semi-slick tyre(s) on the trailer, at about 25-30psi to dampen the jolts. If your roads are very bumpy a Bob Ibex trailer (with suspension) would be worth thinking about - but I can't see how you could fit more than 1 or 2 panels onto an Ibex, and I am not sure if or how you could fit a Bob trailer onto a recumbent trike.

I still think a lightweight solution is paramount - and if it wasn't for the development of Lithium batteries would have suggested wiring the panels directly to the motor (no battery). and then waiting for some good sunshine before having a go at the climbs. Hope this is a help. Andrew.

BB. · November 2006

Re: Bike Power

Just for information... A Uni-Solar 64 panel:

# Rated Watts: 64.0 watts @ 25°:C
# Rated Power: 16.5 volts @ 3.88 amps
# Open Circuit Volts: 23.8 volts @ 25°:C
# Construction: triple junction, Tefzel glazing
# Warranty: 20 yrs.
# Weight: 20.2 lb/9.2 kg
# L x W x

53.8" x 29.1" x 1.25"

20 lbs is still not light (actually, I would have thought the Uni-Solar it to be much lighter, surprise!)...

For charging, I would suggest that using the AC transformer and an inverter (possibly with a 12 VDC storage battery) would not be the way I would go for a charging system... I would find a MPPT type controller and wire a couple panels in series to directly charge the 36 VDC Lithium cells. It might also be so much more efficient that you could get away with only ~175 watts of solar charging (36vdc*9.6 Amp*Hours = 345.6 Watthours)... It is possible that the AC charger is either not as efficient, or is not using the full 240 watt input for the full 3-4 hours, or some combination of both).

If you decide to charge the lithium cells with a MPPT solar charger--finding a small 36 VDC version might be difficult, and it probably would not be the correct voltage for lithium anyway--so you may have to look around for one that meets your needs (and probably manually monitor the charge voltage/current to ensure that everything is well).

If you cannot find a MPPT controller that meets your needs, I would get 36 VDC (like 3x 12 VDC or 1x 24 VDC + 1x 12 VDC panel sets) worth of solar panels and build my own simple charge controller (simply opens the circuit when maximum voltage is reached).

You can hook the panel(s)/charger to the battery and charge some while you are riding (assuming good sun). Won't be perfect, but it can work.

Reading the spec. sheet for BionX, it is not clear if the 2amp*4 hours is at 110VAC or 36VDC (I am tending towards 2amps at 36 VDC--so, there is not much known about the AC charger--but it is probably more efficient than I first assumed)...

If, you wanted to charge your bike in two hours, one 175 watt panel (or set of panels generating > 150 watts) would probably come close to 80% charging of your bike battery... However, it appears that the company recommends 4 hour charging (full or empty) for their Lithium-Ion batteries. You may violate their warranty if you try to charge in less time...

If you are interested in solar charging, then I would contact BionX and say that you have X amps of 48 VDC of solar power available, and you would like their suggestions on how best to connect it--Of course, the sales guy may not want an engineer to work on the problem and incur liability if something goes wrong.

At this point, I was not trying to get an exact solution for you--But trying to set the bounds of the problem (weight, physical size, cost, expectations of power output, etc.)... Once you have decided on a path to follow, then nailing down the "fine points" is much easier.

-Bill

mike95490 · November 2006

Re: Bike Power

BB wrote:

build my own simple charge controller (simply opens the circuit when maximum voltage is reached).

Home brew charging is fine for lead. ni-cad, ni-mh. Li-ion is VERY picky about chargeing, and just a few moments of overcharge, and it's history. I would not recomend bypassing the factory charge ckt.

BB. · November 2006

Re: Bike Power

Mike,

You are correct... There are some NiMH battery packs there too... Heavier and slightly less range--but may be easier to charge with solar panels.

-Bill

Frank · November 2006

Re: Bike Power

Another option is to try to identify a motor/controller package that allows regeneration: you can recover some of that energy going downhill. Usually permanent magnet motors can regenerate but I don't know if anyone offers such a package for bicycles. I think that carrying panels around will be more trouble than it's worth. You'd be better off looking for strategic places to plug-in a conventional charger (stores, churches, etc.) IMO.

Good luck!

System2 · November 2006

Re: Bike Power

WOW! I'm overwhelmed by the quantity and quality of your responses.

It seems from your suggestions the best route for me to pursue might be:

1. Forget about the Li-ion battery and go to NiMH for more reliability.
2. Find three lightweight, high efficiency panels to wire in series to produce 36V with an output of two amps or more.
3. Run this through a charge controller directly to the battery pack.

This type of setup would allow the battery to potentially be receiving a charge anytime there is sunlight as I am peddling along. Now I have to get down to the nitty gritty of actual numbers numbers and supply sources.

Thank you all for your thoughtful responses.

Rob

BB. · November 2006

Re: Bike Power

I would first focus on the size/type of solar panel you need... The BP 4175 panel I suggested was just a starting point in terms of size (surface area)... It is a reasonably efficient panel and any other type of lightweight panels (unless you go for some very expensive alternatives) are going to be physically larger (possibly, up to twice as many square feet in area)...

Also, using solar forces one to think about efficiencies and actual usage of energy... For example, all of the above numbers are based on the assumption that you will be using 100% of your battery pack's energy. In reality, it will be your own needs/patterns of use that will have a lot to do with how much battery power you will consume.

And, you may be approaching the laws of diminishing returns. The weight and wind resistance of the motor/battery pack/solar panels/trailer/electronics/etc. to the point where you are in need of the motive assist simply because you are dragging around so much extra weight to supply the motive assist.

I would suggest, that before you purchase/build the solar charging station that you may wish to purchase (or rent/borrow, if available) just the BionX system and experiment with it... See how much power you need, and mock up a solar kit and see how it performs (does it slow you so much, that BionX simply supplies the extra energy to pull the solar kit, etc.).

Monitor how much power (use the AC charger and a kill-a-watt meter, and/or directly monitor the charging current going into the battery pack for voltage/current/power/time) to see how much solar power you will need.

In the end, I would suggest that just the BionX kit and relying on the kindness of strangers to supply AC power for charging (campsite generator, campground office, nearby gas station, ranger station, etc.) to charge the BionX unit may work OK for you...

I, a few decades ago (bavk in the 1970's) I had a little airplane (Taylorcraft L2m--like a Piper Cub) that had no electrical system (hand prop'ed, build in 1943). And I flew around the SF Bay Area and the US (from SF to New York and back through southern US) with an aviation transceiver/VOR, a 12 volt motorcycle battery, and an AC wall-wort charger--and asked anyone I could for the occasional recharge. On occasion I could not find anyone, and once in a while I had to wait a few hours for somebody to show up and unlock the door to get the battery back--but it did work.

I understand that you will not be where AC power will always be available--and I like solar power as much as the next person--but you will have to be very committed to solar (money, time, and some interesting mechanical/electrical design challenges) to make this a genuinely useful product (with some very severe limitations)...

I had suggest that Honda eu1000i as the non-green alternative because it was--sort of light--and pretty quiet... But I would wonder if you could not get a small model engine (model ship, aircraft, vehicle--or even a weed whacker type motor) and attach an alternator/generator to build a very lightweight alternative power source for those times when AC is not available... It would be much lighter--but probably be almost too noisy to use (especially if you have to run it for 2-4 hours).

Looking forward to hearing more about your project.

-Bill

PS: I have not had time to read the whole article--heading out of the house right now, but here is, what seems to be, and interesting article on batteries (where they have been and where they are going):

http://wired.com/wired/archive/14.11/battery.html

Enjoy!
-BB

System2 · November 2006

Re: Bike Power

Bill

Your analysis of the situation is right on target and I am appreciative of your suggestions. Tomarrow I'm going to South Carolina to "kick the tires" on a demo BionX equipped bike. If I like it guess what I'm getting for Christmas.

I too, had a little airplane in the late 60's when living in Alaska. A very early Cessna 150 but it did have an electrical system. Your cross country trip must have been a blast.

Thanks again

Rob

System2 · November 2006

Re: Bike Power

Not sure a 350W motor will take you up a hill with all that weight.

Just throwing a few numbers around.

Rider weight = 170 lbf
bike weight= 50 lbf
solar + trailer weight = 80 lbf (3x 20lbf panels)

Lets assume you want to climb a hill that's 1000 feet high and takes 3 miles. And you're going 10 mph.

The power required is:

Power = height * weight / time (neglecting tire friction and air drag)

Power = 376 watts

Energy taken from battery = 376 watts * 18 min = 113 watt-hrs

If your battery has 345 watt-hrs, then you may be able to squeeze 3 1000 ft climbs out of the battery (one hours worth). That's not much if you're riding in the hills. And once your battery is depleted, you're dead meat. You'll never be able to climb with that weight.

I would travel as light as possible. Forget the motor assist and reduce your milage per day.

Cal

System2 · November 2006

Re: Bike Power

A couple of years ago I biked from Wash. DC to Gatlinburg, TN. Almost 600 miles of the trip was on the Skyline Drive and Blue Ridge Parkway. The total climbs on the trip exceeded 50,000 feet. Cal, believe me I know what "dead meat" is.

The BionX motor is a proportional, pedal assist system. You are always pedaling but when you turn the system on it allows you to select 1 of 4 levels of pedaling help. Using a microprocessor, the motor measures your thrusting power (through chain torque) at the rear axle and will boost your thrusting power by 25%,50%, 100% or 200%. This in combination with the 24 gears on the trike will spread the work out. On level ground, no wind, and a 170 lb rider the company claims the average distance covered with one battery charge (35V NiMH) is: Level 1 56 miles
Level 2 37 miles
Level 3 28 miles
Level 4 22 miles

Bill is right. I need to get the BionX, log some miles on it and get some real numbers to work with. I've got a great proving ground here. From my house I can start a 3500' climb up to the Blue Ridge Parkway. This will be a great winter project.

Rob

mike95490 · November 2006

Re: Bike Power

I see that the bike motor does have a regen capabelity, so that will be a help recovering on the downhills. From all I've seen here, perhaps going with P350 ni-mh battery is the best bet, and at least 3 panels with a loaded voltage of about 45V, will give you charging current. in cloudy conditions, expect no output from panels, only in sunlight. It's a tough balance, to consider panel weight, charge control, and how much it'll cost you if you fry something. At least ni-mh batteries are fairly commonplace now, and replacemnets will not be too big of a factor. And you are not a passanger, you are 90% of the propulsion system, with some assist form the solar. There are some other 36V nimh chargers, for larger batteries, that charge at higher current. nimh can take a pretty stiff charg till they reach 70%, then you have to start tapering off.
with it http://www.nycewheels.com/cha-voloci-nimh.html @ 4amps you could get a 3/4 charge in less than an hour into your 9A battery pack. Once the batteries start to get the least bit warm, you MUST switch to a lower current charger.

Another consideration, might be to carry a 300 - 500W automotive cig lighter inverter with you, and you could always run your charger off a friendly car in a pinch.

System2 · November 2006

Re: Bike Power

Rob,

Yes, the best way is to actually test it out. But putting the pencil to paper and doing some calculations may save you a lot of money. Renting one would be best. Be sure to connect your BOB on the test run and load it up with 70 lbs of rocks. LOL

I don't think the Level 1-4 data you provided is that far off of my calculation. The added 80 lbs will significantly reduce your climbing capability. It *could* be an albatross.

BTW, I'm a mountainbiker. Ridden many of the best trails out West and have done some mountainbike racing. Cal knows pain. ;-)

Calbiker

Bike Power

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