Solar Bicycle Trailer: Adjustable Solar charge controller

SolarStu · July 2017

I have a LG 37V 250W solar panel mounted on a bicycle trailer. I want to do three things with it:

1. Drive my 48V ebike motor directly (through a throttle), without using a battery. I want to do this purely for pedagogical purposes. I want my students to experience the amount of energy hitting the panel viscerally, by experiencing how fast the bike will go directly powered by the sun.

2. I want to charge my 52V lithium ion 11.5ah ebike battery for normal use.

3. I want to be able to charge other batteries of other voltages.

I bought an inexpensive MPPT Solar Charge Controller: MPT-7210A. The problem I have with it is when I try to run my ebike motor directly from the panel through the controller, the controller surges on and off every few seconds. It seems to have a capacitor or battery that has to fill and then it dumps the charge to the motor.

QUESTION 1: IS THERE AN ADJUSTABLE MPPT SOLAR CHARGE CONTROLLER THAT DOESN'T SURGE, THAT DIRECTLY CONVERTS THE LOWER PANEL VOLTAGE TO THE HIGHER MOTOR VOLTAGE?

QUESTION 2: IF I BOUGHT A CUSTOM GENASUN, WHICH I UNDERSTAND IS NOT ADJUSTABLE, WOULD IT SURGE?

THANKS SO MUCH!

Marc Kurth · July 2017

What is the power draw of the motor?

mcgivor · July 2017

Wants....

1. A single panel rated at a lower voltage than the motor simply won't work, the voltage would need to be equal, being that solar panels are current sources the voltage would collapse, so many more panels would be required in order to support the load, which at this point is unknown to all, other than yourself at this stage.

2. Fort the same reasons as above, the panel voltage is too low to accomplish this, with a single panel, charge controllers need to have a higher voltage than the target, in the case of MPPT, double or more,

3. Multiple voltage charging is generally not a good idea

Questions

1. Using a MPPT controller to drive an electric motor is asking it to do something it was not designed to do, it is designed to charge a battery, higher voltage than the battery is essential, they do not boost voltage, they "buck" or reduce voltage, whilst tracking the maximum power point, so the answer, unfortunately is no, won't work, to the best of my knowledge.

2. The surges are caused by the controller hunting, because it's being asked to do an impossible task.

Could a bicycle be powered solely by photovoltaic? In theroy yes but the sheer number of panels required would produce more aerodynamic drag, lost energy, than it could produce, unless of course the drag is transposed into lift, as with the solar airplane.
Sorry if my coments rain on your parade, but they are my opinions, others may prove me wrong.

Estragon · July 2017

IIRC Genasun makes boost controllers that might be able to take the ~35v output of the panel and supply the ~57v required to charge a nominal 48v battery. Without a battery though, the panel voltage would still likely collapse under the motor load. Depending on the motor load, you might be able to get away with quite a small battery.

Another possibility would be the sort of gear used to drive pumps directly from solar. My understanding is this can get costly though. Others here may have better insight on this than me.

BB. · July 2017

Most solar charge controllers are designed to charge batteries. Many will not even properly operate unless there is a (relatively) fixed battery bank voltage (12/24/48/custom voltage). The charge controllers generally use there DC output bus ("the battery") to run their internal electronics.

There are a couple possibilities that may work. One is the LCB (Linear Current Booster). These are used between solar panels and DC motors, typically for water pumping or fans. They run the solar panel following the Pmaxpower=Vmp*Imp) equation. The output is set to convert to Iout=Pmp/Vmotor ... Basically, providing maximum current to the motor and the motor can now output maximum torque without "collapsing" the solar array output voltage.

As far as I know, the few LCBs I know about seem to be all "buck converter" (down converter) based. You would have to have a solar array Vmp-array > motor voltage to operate correctly.

https://www.solar-electric.com/catalogsearch/result/?q=linear+current+booster

I don't know the voltage of your e-bike motor. Above link are for 12/24 volt motors.

Another method is the VFD... Variable Frequency Drive. These units are typically designed to take AC power in (120/240 VAC 50/60 Hz) and output variable frequency 3 phase power. These can be 3 phase induction motors or 3 phase Permanent Magnet Motors (non-brush/non-universal motors).

https://www.youtube.com/watch?v=DiKcKYbJ1A4

What is becoming more common are VFD's that can take DC voltage in (battery bank, or solar array). This may be beyond your initial design goals, but it would be a pretty efficient operation--Assuming you can find a VFD+motor that fits your needs. Many VFDs have auxiliary input(s) that can be used to set motor speed/torque/etc. Nice way to give you throttle control.

http://www.machine-controller.com/DC-input-VFD-solar-inverter-with-CE-certificate-WE_p441.html
http://www.diyelectriccar.com/forums/showthread.php/high-voltage-ac-motor-electric-bikei-133825.html
http://www.schneider-electric.com/en/product-range/62208-solar-water-pumping-system/

There is a big issue finding the right size VFD for your installation, and the "right" PM motor (voltage/wattage). It may not be possible to find commercial parts that will meet your needs (it is pretty difficult to find "small"/lower voltage fractional HP 3 phase induction motors). But, it is certainly practical from a "black box" design point of view. At this point, the market may not support such a device/setup.

-Bill

Photowhit · July 2017

I would think just bypassing the charge controller to run the bicycle motor directly will work, Most motors will run in a range of acceptable voltages. I would check to see if your motor has a range of acceptable voltages, of then electric bike will list a range as lead acid and lithium battery banks are used and rarely have a specific common voltage and lead acid voltages will have a range of voltages as the battery losses capacity.

The motor should also run in a range of powers, weather a 250 watt panel that will typically produce @180 watts will be powerful enough to 'drive you bike by it's self is questionable. Particularly understanding that the panel will NOT be optimally angled toward the sun. Most 48 volt systems are capable of using 600+ watts. There are lower voltage kits for bikes, if your serious about setting up a bike to run directly from solar I would think a low wattage/voltage drive would be more desirable.

Powering directly from the panel/sun should be possible while the panel is in the sun. As an example in a controller sunny area would likely work, but long distance dealing with normal shading, from trees and your bike/body would not be practical without some energy storage. I've run fans and a water pump (small) directly from the sun. both worked fine.

The control you have purchased is interesting, designed to boost voltage. Here's a link for other's, like myself who are in familiar with a boosting MPPT controller;

https://www.amazon.com/MPT-7210A-Controller-street-charging-system/dp/B01DP57PYA

Available for direct ship from China much cheaper, I have purchased from GearBest before, shipments take slightly longer than mountains crumbling to the sea, unless you pay for faster shipping.

http://www.gearbest.com/other-instruments/pp_353503.html

mike95490 · July 2017

Simple brushed motors will run from a PV pane of sufficient size. Often automotive radiator fan motors are wired to a panel for venting a house or greenhouse, they seem robust and may be able to be modified to a bike.
Brushless DC motors rely on a stable voltage source to generate a rotating magnetization field, a solar panel would have to be grossly oversize to be stable enough for a brushless motor to reliably work.

Solray · July 2017

With and without batteries is possible and has been done, just copy what others have already done or experiment yourself. Never listen to anyone that says you can't.

https://www.youtube.com/watch?v=P5pCY8SOEjw

https://www.youtube.com/watch?v=GAuVco35tzI

https://www.youtube.com/watch?v=5_SGoka_LzI

bill von novak · July 2017

Solray said:

With and without batteries is possible and has been done, just copy what others have already done or experiment yourself. Never listen to anyone that says you can't.

I have to wonder how that first design will handle in any sort of wind . . .

Solray · July 2017

Things on edge to the wind have very little drag. That's why folks that drive pickup trucks remove the tailgate, lower it or add a bed cover to improve mileage.

Try this: next time you are in your car on the freeway at 75mph, put a hand out the window and orient it so it is flat with the palm forward in a vertical orientation, then rotate it 90 degrees to a horizontal position and you will see how it will handle the wind.

bill von novak · July 2017

Solray said:

Things on edge to the wind have very little drag.

And that's the problem. You are fine with a crosswind - until you have to turn to avoid someone. And at that point you suddenly have a lot of lift in one direction or the other that wasn't there a tenth of a second ago.

Or a car passes you and the angle of the wind changes dramatically. Or the wind is gusty, or you are on a bridge and the wind is coming from slightly beneath you.

Muller's bike used a two-wheel trailer and I think that's in general a better way to go; you need to generate a lot of lift to be able to flip a two wheeled trailer.

Solray · July 2017

Do you do a lot of bicycle riding? I do and it would not be a problem in the conditions that a bicycle would be normally used. If you are forced to ride in a gale, I'd take the panels and any trailer off anyways, I guess if you use common sense it isn't a problem.

Solray · July 2017

If you are worried about the wind on a small panel on a bike, what do you think of this thing?

Image: http://sonsoz.com.tr/wp-content/uploads/2016/03/Solar-Boat.jpg

BB. · July 2017

Let us not get too far off track here... The original poster was looking for an experiment/example of solar energy and variability for his students (as I understand). Not to make a vehicle to drive around on the streets.

-Bill

mike95490 · July 2017

Solray said:

If you are worried about the wind on a small panel on a bike, what do you think of this thing?

That panel overhang, is minor, compared to the mass of the the rest of the vessel . Not at all a fair comparison,

bill von novak · July 2017

mike95490 said:

That panel overhang, is minor, compared to the mass of the the rest of the vessel . Not at all a fair comparison,

And, I suspect, furled in high winds.

Solray · July 2017

> @BB. said:
> Let us not get too far off track here... The original poster was looking for an experiment/example of solar energy and variability for his students (as I understand). Not to make a vehicle to drive around on the streets.
>
> -Bill

Exactly and I don't think high winds will be part of the experiment.

Thanks for being a voice of reason.

Photowhit · July 2017

Solray said:

Do you do a lot of bicycle riding? I do and it would not be a problem in the conditions that a bicycle would be normally used. If you are forced to ride in a gale, I'd take the panels and any trailer off anyways, I guess if you use common sense it isn't a problem.

As someone with serious bicycling chops, (35,000+ miles, Over 10K loaded touring) YOU ARE WRONG!. It will create issues, particularly with light bikes and riders.

No automatic alt text available

As to the PlanetSolar ship. It is a trimaran It only extend the 'wings' when reasonable calm. Much different situation.

Solray · July 2017

I don't see any solar panels on that bike. What is your experience with those on a bike? The video shows the bike with panels working just fine. Was that trick photography? Lol
From the evidence presented, it looked like it works.

As BB said, I don't think wind is an issue on an experimental bike to show students a concept.

Have you toured Europe by bike? If not, it's worth doing. I did for 6 years and loved every minute of it even the cold wet minutes.

Also have you tried the Rohloff speed hub? It's so nice to get rid of the floppy chain and external derailleurs and all the headaches they create.

Photowhit · July 2017

Solray said:
As BB said, I don't think wind is an issue on an experimental bike to show students a concept.

I will agree with this.

We don't know the conditions in the video, doubt it was wind.

I've got a bad hip now, Did @7000 miles one trip loaded touring, guerilla camping on the 'crack-n-fail' From Key West to Maine Cincinnati to St Paul and down to Misery (Missouri) where I was going to winter back in '99.
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Picture is from the trip in Ohio. I actual do have a 10 watt 12 volt solar panel on the bike! I did a total loss system with 2 - 6 volt AGM batteries. Charged in series and used in parallel for a few things. You can see it in this photo of the tunnel on Sparta Elroy.

Image: https://us.v-cdn.net/6024911/uploads/editor/sb/25hn1d1pxfbq.jpg

Bicycled back to Home, for my dad's 80th birthday in 2004 and considered finishing the original trip, but had a bad trip, some physical and had my bike stolen when I was home. Came home on an old police 'Rock Hopper'. At 57 it's unlikely I'll add to my 1000 mile rides. May shoot to add to my states from home, since I could do Oklahoma and Kansas pretty easy...

...but my mind set and hip would have to change...

Europe sounds great! on a recent visit to my brother's, I saw he still has my windshield, required for the Al-Can Hwy... never made that trip!

Solray · July 2017

I've never used a trailer on my bikes, just panniers, rack bag and handlebar bag. I travel as light as possible so if needed, I can pick up and carry the bike to cross rivers, etc. I carry a collapsible fishing rod and everything is the lightest weight made.
It looks like you even took the kitchen sink along.

Photowhit · July 2017

Yeah, I 'economized' in other ways. I wasn't in a hurry and paid for all but $1000 of 9 months of traveling but doing refrigerator magnets from photos I took along the way. While no kitchen sink, I had a cut down mat cutter, pieces of mat board (I'd pick up scraps and spend some time cutting down right away. Rarely had more than a shoe box full, lots of weight. Camera gear (back in the film days!) I did manage a couple centuries with that rig! but mostly 40-60 mile days. I'd nurse a cheap burger in a fast food place and work on making magnets, often with the rain fly drying over my rig. It was a rare day when someone wouldn't come talk, buy a magnet or 2...

I did travel light on an earlier trip, I did Natchez Trace and Blue Ridge Pkwy and Sky Line drive. I did several trip lightly loaded. If I head out again, it will be without the trailer, unless I decide to become a hermit (not entirely out of the question...lol) If you are still traveling I recommend Americans 2 longest parks!

If you think about going, check out the bike house in Afton, VA. It was once run by June Curry, a bit of a legend among touring cyclist. During the bicentennial there was a bit of a cycling craze and Bikecentenial (now Adventure Cycling) developed a cross country route on somewhat safe rural road. The East-West route went through Afton, which is also where Blue Ridge Pkwy continues as SkyLine Drive. June would watch cyclist pass and started giving out cookies and water. Later (I think after her father pasted, she made an old building into a hostile. June pasted about 5 years ago. I was proud to have met her and even went to church wither on my wet trip along the Ridge roads.

http://www.crazyguyonabike.com/doc/page/?o=1mr&page_id=31540&v=2Av

Not much of a gear photo. I have one at the highest point. But this one is important to me as June took it back in May 1991. No trailer in the hills! Small front and rear panniers on a Fuji Touring bike.

A rare shot of me in regular cycling shorts, others are Trek Mountain bike shorts with a hidden liner and pad.

Solray · July 2017

Your photo does not show up here.

SolarStu · August 2017

How do I wire it?

Now I have a 36V electric bike without the battery. A 36V solar panel on a trailer and two 1.5ah 18V lithium drill batteries.

What I want to do: Have the batteries buffer the panel's output so that the panel is continually charging the batteries and the batteries are driving the motor. Could someone direct me to a wiring chart? or describe it? Any pointers are welcome.

SolarStu · August 2017

Here are photos:

Image: https://us.v-cdn.net/6024911/uploads/editor/kr/n84pwqcnvars.jpg

Photowhit · August 2017

Stu, Please stop for a while...

Do you know the battery chemistry of the battery packs? Remember some lithium chemistries do not handle over charging well! May explode!

Do you know the battery voltage and charging parameters of the battery packs? I think most Lithium batteries run around 3.6-3.7 volts per cell, an 18 volt battery pack is likely something other than 18 volts.

I even thing that putting 2 lithium batteries in series could be dangerous without a management system. I don't know enough about Lithium batteries on this...

Do you have a charge controller on them?

bill von novak · August 2017

SolarStu said:

How do I wire it?

Now I have a 36V electric bike without the battery. A 36V solar panel on a trailer and two 1.5ah 18V lithium drill batteries.

What I want to do: Have the batteries buffer the panel's output so that the panel is continually charging the batteries and the batteries are driving the motor. Could someone direct me to a wiring chart? or describe it? Any pointers are welcome.

Use a Genasun controller for the 36V battery.

Do NOT use tool batteries without a BMS. Much better to get a real 36V battery from an outfit like Batteryspace or Lunacycle. It will come with a BMS.

Do NOT use 1.5ah batteries on a system that will have a charge rate of 8 amps. Most lithium chemistries cannot handle more than 1C.

I would also recommend a meter, like a Cycle Analyst or a Watts-Up to monitor your use, so that you do not over-discharge the battery.

Solray · August 2017

I'd have those bombs...I mean batteries at the back of the trailer as far away from me as possible in a non flammable container to help stop the flames from spreading too fast.

In wood,with an open top, inches from your rear end is not a good idea. Not without a battery monitoring system as a charge controller anyways.

mike95490 · August 2017

Solray said: ....with an open top, inches from your rear end is not a good idea......

It's a way of developing a brand

Solar Bicycle Trailer: Adjustable Solar charge controller

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