Ebike Solar Charging How to

If you ever wanted to learn how to charge your ebike battery with solar panels while off grid, camping, …, this blog post will get you started. No inverter required!

Each week questions come in about charging my electric fat bike using a portable folding solar panel during camping, for the daily commute or for my off-grid ham radio adventures. This solar charger is quite simple, lightweight and doesn’t require the use of an inverter for our free, green and renewable eBike charging.

Portable Solar ebike Charger

There are only three primary components to my portable solar ebike charger. Depending on which solar panels you choose, the entire kit can come along with you, without adding much weight to your ebike touring load.

  • Solar panel(s)
  • Charge controller
  • The ebike battery

In my rather poorly drawn diagram, one can see the solar panel, charge controller and the ebike battery as a system. It is this simple! My charging plan can work in two ways: In the first scenario, the ebike battery can be charged while the ebike is stopped with its battery disconnected from the ebike system. We connect the ebike battery to the charge controller like we would any other battery. Then we connect the solar panel to the charge controller to charge the ebike battery. This is great for multi-day camping or for those times we travel to someplace, remaining there long enough to charge our ebike battery. Afterwards set off on the return trip or continued journey with the battery fully charged.

In both examples, pedal-assisted drive is used. Pedal-assist is a mode that doesn’t propel the ebike forward unless the rider is applying force (torque) on the pedals. The motor won’t engage unless the rider is peddling the pedals. The benefit of the pedal-assisted drive is much greater range. The range of an ebike in pedal-assist mode is the combined effort of the ebikes motor and the riders spent calories. The ebikes motor and our bodies are working in unison to propel the ebike forward. My preferred way to utilize pedal-assist is to engage the ebike motor, only during times it would be too difficult for me to pedal eg. “up the hill” under my own steam. This is an excellent way to extend the usable range of the ebikes battery while augmenting with one’s own effort. Another point about pedal assist is often misunderstood. This e-bike is not a motorcycle or moped. It won’t go on its own! It needs Force applied to the pedals, for it to be propelled forward. There’s no throttle engaging the motor, without the Rider applying Force to the pedals.

In the second example, we have two ebike batteries. One battery is in use on the ebike, while the other battery is being charged. This means we can use a smaller solar panel since the battery has many more daylight hours with which to charge. This is beneficial in a “keep moving forward” scenario, where we don’t want to take “days long” breaks to charge/recharge a flat battery. It also gives us the option to charge on the run, provided we have a large enough space to deploy the solar panel, while in motion.  I often use my bicycle trailer as a platform for a small portable rollable panel. We’ll cover This at some point during 2022, with a fat bike-powered expedition.

Mysterious Charge controller

For the 48-volt lithium-ion battery, we use a Genasun GV8 Boost charge controller. The GV Boost series of controllers allows a lower voltage panel, to charge a higher voltage battery. This is very straightforward physics. We sacrifice current from the panel, to increase charging voltage at the battery. This is what a boost controller does. In my case, a single PowerFilm 60-watt solar panel generating 3.6 amps at 15.4 volts at the panel output is used.  Keeping the boost conversion in mind, the charge controller can provide ~1-1.3 amps at 56.4 volts at the battery leads. If two of the 60-watt PowerFilm panels are combined in parallel, we can increase charge current to make up for conversion losses. If we connect the two 60-watt panels in series, we reduce the conversion losses by increasing voltage at the solar panel output.  The higher starting voltage results in more efficient conversion and higher charge current at the battery. The dual solar panels in series are my preferred solar charging strategy for off-grid ebike charging.

The Genasun GV8 Boost model used is the “54.2 volt model for 13S lithium-ion batteries”. You might have immediately noticed the voltage discrepancy!? This is caused by the Genasun charge profile being very gentle to the lithium-based batteries.  The Genasun rather risk shorting a full charge by a percent or two, versus over-charging the battery, leading to a reduction in its cyclic life. Trust this, and please don’t think it to death.

Off-Grid eBike charging go kit

My solar panel and charge controller gear take up very little space. One or two of the folding series from PowerFilm weigh nothing and pack flat. The Genasun charge controller is very small, taking up little to no space. Everything is stored together in a saddle bag or on the bike trailer if using one. I decided on 2x 60-watt FM16-3600 panels for their size, weight and capability. Utilizing two of these panels in parallel or series can help make up for the losses introduced by the charge controller during the Boost voltage conversion.

Connections & Charging

I use the Genasun GVB-8-WP-Lithium for 48 volt lithium ion batteries. This charge controller takes a lower voltage from eg a 15-30 vol solar panel, then boosts it to an adequate voltage for the 48 volt eBike battery. The Genasun GVB-8 has four wires coming out of it. Two are for connecting the solar panel, while others link to the ebike battery. The wires are confusing, so please pay attention (see image above).
From Right to Left:

  • Yellow wire: Solar input + (Positive)
  • Black wire next to yellow: Solar – (Negative)
  • Next black to left of solar – Battery Negative
  • Next black wire on left: Battery Positive 

Anderson Powerpoles are a perfect solution for quick, modular connections between the charge controller and ebike battery. 

GZR Raw

48 volt ebike battery

My electric fat bike is the GZR Raw Black 2020 model. It has a 48 volt (46.8v) lithium-ion battery pack in a 13S4P Hailong battery configuration, powering a Bafang Maxdrive mid-drive motor. This is 13x 18650 cells in series, with 4 cells in parallel. The individual lithium-ion cells making up the ebike battery, each have a voltage range of 3.7 to 4.2 volts. The voltage of a “48” volt lithium-ion battery pack when fully charged is ~54.6 volts or 4.2 volts x 13 18650 cells. This is our ~target working voltage for charging. It doesn’t have to be perfect, but a little less is better than too much. A little less is preferred to preserve the cyclic life of the battery.

For those of you using a 36 volt Bosch e-bike, I found a video reverse engineering the Bosch charging system. The video also explains how to 3D ptint the proprietary connectors required to charge your Bosch battery from any DC power source. https://youtu.be/d2r3jbL78iQ

Testing

Power for lights, phone, …

Many have asked about using the ebike battery to power other peripherals with the e-bike battery. Definitely! This ebike battery charge port has DC output directly on the charge port. You can see the baby Fluke connected to the charging port of the e-bike battery, that the wrong voltage from the e-bike battery. The Flukes display shows DC voltage present on that port. That port is protected by a BMS (Battery Management System) preventing tricksters or mishaps from damaging the battery.

To make use of the “charge” port we need to regulate the voltage coming out of the first and not something useful. If we connect a 12v device to the 48 to 54 volts available from the battery pack charge port, we’re going to see a lot of smoke. We can use a buck voltage reducer or wide voltage regulator to reduce the voltage down to something manageable. That’s usually 12 or 24 volts. Ensure your buck or regulator can handle Ty the current of the device you’d like to power.

Assumptions

We often assume placing enough solar panels in series to reach 48 volts would be ideal for charging. Although this is logical, isn’t wrong and would be quite efficient, we still need to ensure our voltages “add up”. We do this by regulating the voltage coming from our solar panels to reach the target charge voltage. Regulating the voltage ensures we don’t damage our battery while charging. Regulating the voltage from our solar panels presents the right voltage for the battery, stops the charging cycle when the battery is fully charged and uses the right charging profile for our lithium-based batteries (CC/CV no floating charge!). To regulate the charging, we need a solar charge controller between our solar panels and the battery. Since there is also a voltage mismatch, we will leave this job to a “boost charge controller“. More on this later.

Another assumption we make (because it is often done at home), is using an inverter to convert power coming from our solar panels to AC. This is so a home AC electric ebike charger can be used in the field. This is fine for a large off-grid home, cabin, RV. Not so much for portable work! In regards to portable solar panels and off-grid charging, we don’t want to recreate grid power (AC) while off-grid. Not only does this add more weight to our off-grid solar charging system, but it also adds unnecessary components for the conversion. What we don’t want is converting the DC voltage from our solar panels to AC at the inverter, then back to DC for the e-bike battery. This is ridiculously inefficient. Firstly, we want to keep things DC since our ebikes work on DC voltage. Second,  we want to ensure we use as few components for charging as possible. Trust me, the inverter is not required! A solar charge controller will take its place. This is the basis for achieving our portable solar electric bike charging goals. Nothing more, nothing less.

Expectations & limitations

We must understand and reconcile our expectations and limitations of solar ebike charging off-grid. From the perspective of OH8STN, we use an electric fat tire bike to augment portable ham radio and camping expeditions. This usually means we are going to hang around awhile, once we arrive at our destination. We will never be able to sustain an ebike purely on solar power and it shouldn’t be our objective. My singular goal is to have the ability to recharge my ebike off-grid, in the field if necessary.

Electric Fat Tire Bike Background

Human mobility and independence from grid power are big aspects of my life. Fat tire e-biking has enhanced the man-portable ham radio and camping experience, by extending the range and load-carrying capability of my off-grid adventures. It makes sense to use the fat tire e-bike as a platform for rapid, green and cost-effective mobility, but only if we can solve the ebike solar charging problems while away from the electric grid. The fat tire bike is like the Willys Jeep of biking. These high geared mountain goats can traverse areas that stop a traditional bicycle, in its narrow-tire tracks. The wide 4-5 inch wide tires make snow, sand or unmanaged tracks easier to navigate while carrying larger loads. A fat tire bike is a utilitarian tool and an excellent platform for multi-day camping, preparedness, or ham radio micro-expeditions.

Augmenting fat-tire bikes’ capabilities with an ebike system makes lots of sense. The combined fat tire bike gearing and ebike motor to augment the rider will keep it moving forward, albeit slowly, despite the terrain under its tires. Adding off-grid solar charging capabilities to the ebike save money on electric bills and increases the already pragmatic capabilities of this utilitarian platform in the field.

Final thoughts

Back in the day, off-grid solar charging of electric bikes was a complex affair. Large rigid solar panels on trailers meant to extend the range of a touring ebike were anything but practical. Today we have extremely portable, lightweight & flexible solar panels. We have the Genasun GV8 Boost charge controller series, compatible with 36, 48 & 52-volt ebike batteries. We can now carry a netbook-sized solar go-kit, without compromising on the other gear we carry. Pragmatic on-demand solar charging solutions for field deployments are a reality.
For my deployments, having the option of being completely human-powered, augmented by an electric motor and or recharged if or when necessary. These are huge steps in the right direction. Bottom line. I am already carrying the solar panels. Why the heck wouldn’t I use them to charge my ebike as well!?


Lots of effort goes into these posts. Researching each component, software application, pragmatic field testing. When you see these posts, the mistakes and blunders have already been filtered out. If you find any value in that, share this post and/or buy me a rootbeer.

73
Julian oh8stn
YouTube http://www.youtube.com/c/oh8stn
Buy me a rootbeer: https://paypal.me/oh8stn/2usd

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15 Comments

  1. Very interesting and timely. I have been a cyclist since ’71 and did ultramarathon events (200ks-1200kms) between ’85 and ’15. The last few years I started riding back/logging/fire roads in the wilderness of British Columbia. I bought a little electric last year so am interested in this subject. It has 16×2.25 tires but i have used it a lot on rough roads like my gravel bike with 700×38’s. The electric only weights 35 lbs so is quite reasonable to pedal with no power and the low weight extends the range (about 75kms).

    But I have been intrigued by solar power. I have 36v 7.5A battery so I think three 40W in series would do the job, but I haven’t found panels of this size which are both light enough and inexpensive enough for this application. I ride about 75kms a day and don’t want to take off too many days to recharge.

    • Hi Barry. In the old days of course we would have put solar panels in series to make up the voltage. Now thanks to boost charge controllers, we can give up some of the current, to make up the voltage. I’m using to Powerfilm panels to make up for the conversion losses. I’m almost certain Genasun has a 36v version.

    • I’m not sure if I mentioned this in my earlier reply. The Boost charge controller removes the need for so many solar panels in series. The Boost controller uses some of the current coming from the solar panel to boost the voltage going to the battery. This is the reason I have 2x 60-watt panels in parallel. Using the Boost charge controller in this way is definitely cheaper than buying so many solar panels and stacking them in series. The same charge controller I’m using as a 36 volt version as well. The battery output from that charge controller connect to the same Barrel connector charge input on my battery. Definitely give it a go! 👍

  2. Hi Julian,
    Now that you have all that energy in the bike batteries, have you thought of a way of powering the radio kit from that? After all, power to the radio could be more important than power to the bike (especially if you’re on a mountain top and it all goes downhill from there). As it now seems, the energy in the bike is something of a one-way road.
    Also, did I spot it right that you inverted all your PowerPoles at some point in the past? It appears that now you have them the “right’ way around.
    73, András

  3. Hi Julian, have you thought of a way of getting the charge from the bike back into the radio if you ever needed it? I’d rather get the message out and push the bike home whenever required. (Also, if you’re on a summit, home usually is downhill from there.
    Also, is it possible that you reversed your PowerPoles at some point in the past?
    73, András

    • Excellent questions. Yes I still have some power poles which are reversed. That is on purpose not a fault.
      I’ll do some tests on the e-bike battery. The only adequate port on the battery is the port used to charge it. Since I already carry lightweight lithium iron phosphate batteries, the idea of slaving off of the e-bike battery wasn’t a very high priority. The output port on the e-bike battery is a 5-pin bafang/hailong port. If we could tap that Port, it would still need to be regulated down to ~12 volts for the radio.

  4. Would this charge controller work well for the bike battery and the battery pack you use for radios, or do you carry two different charge controllers?

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