Solar battery charging for ebikes.

[Nealh]

So here goes I would be interested in the idea of setting up a solar charging system for an ebike battery or two, might be pretty useful on the sunnier days. Wheezy menioned it on the thread of " Battery charging - cost of".
Also with Matthew slacks 30 odd day tour of Scotland with his solar trailer and seemingly getting some charge energy even on low sun or less desirable days.
So guys/girls no useless cut & past links from utube and other media, just post your method and way of setting up such a system.
Detailing item/components needed to knock up a kit to do so.
Pic, drawings would be useful for those of us interested.

 

[StuartsProjects]

So here goes I would be interested in the idea of setting up a solar charging system for an ebike battery or two, might be pretty useful on the sunnier days.

Me too.

Hope to build a bike storage locker near the from of my house. Getting a mains cable there for battery charging might not be low cost.

However a Simple solar charger setup would be another possibility.

 

[georgehenry]

https://www.amazon.co.uk/BLUETTI-Portable-Generator-Regulated-Wireless/dp/B09M9ZD4BF/ref=pd_rhf_dp_s_pop_multi_srecs_sabr_cn_sccl_4/257-7353902-0884856?pd_rd_w=rpFRO&pf_rd_p=f5d9521c-870e-48e1-8eeb-16653f6f5464&pf_rd_r=1TJ3ZBZB133CEEH358DC&pd_rd_r=96ea1131-0b75-4e9c-8aee-b1880d3dda6e&pd_rd_wg=IoHEn&pd_rd_i=B09M9ZD4BF&th=1

 

[Plas man]

Just a thought , would a Sturmy Archer type hub front dynamo do any good ? Charge spare bat on the move .

 

[WheezyRider]

So here goes I would be interested in the idea of setting up a solar charging system for an ebike battery or two, might be pretty useful on the sunnier days. Wheezy menioned it on the thread of " Battery charging - cost of".
Also with Matthew slacks 30 odd day tour of Scotland with his solar trailer and seemingly getting some charge energy even on low sun or less desirable days.
So guys/girls no useless cut & past links from utube and other media, just post your method and way of setting up such a system.
Detailing item/components needed to knock up a kit to do so.
Pic, drawings would be useful for those of us interested.

Sounds like a good idea Nealh. For my setup I have a 180W solar panel charging a 40Ah LiFePO4 battery through a MPPT charge controller. I have it powering a 12V camping fridge. I have a 300W modified sine wave inverter to get the mains for small items like a bike charger or laptop. The charge controller also has USB outputs, so you can recharge USB power banks etc.

Here are some old pics of the the setup, where I was using an old car battery and before I added the inverter:





However, running a bike charger from a 12V battery to power a mains voltage inverter and then step that back down again to charge the battery is not very efficient, so using one of these would be a good idea if you plan to use it mainly for charging bike batteries:



Most solar setups are designed for charging 12V and 24V systems (with lead acid as the default battery type), so one of these combined MPPT and boost charge controllers would be very useful. I think MatthewSlack has this sort of setup on his solar trailer. It takes the 12 V or 24V typical of most solar panels and steps it up to a higher voltage. I assume it has a CC/CV setting for the charging process, and you set the required voltage, but I have not bought one of these yet.

I'll take some more up to date pics tonight and add an update.

 

[Nealh]

Apart from cost it appears pretty simple a decent size PV panel of what ever wattage 180 - 300w, a mppt variable/adjustable solar boost charge controller suitable for up to 60v and a bit of wiring and one could be away. Static or on the move it is wholly acheivable.
The addition of an expensive static storage battery (lifepo4 it would have to be) is an idea for storing excess charge and one then could use the mppt booster to also charge the battery or what ever device. Roll on power cuts one would be self sufficient on the bike front.

 

[WheezyRider]

Apart from cost it appears pretty simple a decent size PV panel of what ever wattage 180 - 300w, a mppt variable/adjustable solar boost charge controller suitable for up to 60v and a bit of wiring and one could be away. Static or on the move it is wholly acheivable.
The addition of an expensive static storage battery (lifepo4 it would have to be) is an idea for storing excess charge and one then could use the mppt booster to also charge the battery or what ever device. Roll on power cuts one would be self sufficient on the bike front.

Yeah, it's not difficult to cobble something together and although it does cost, when you consider what is happening to energy prices, I think it will pay for itself. Plus, it gives you that independence if the power does go down.

My simple system:
180W solar panel. I bought this over 10 years ago and it was £500 then, but now would cost you only about £100 to £150. (£0.7 to £1 per peak Watt is typical these days, depending on the panel size).
Solar cable, about £1 per m
Scrap Wood to make the frame for the panel - free
MPPT charge controller about £25
12V 40Ah LiFePO4 battery about £175
300W inverter 12V to 240V. Bought it about 15 years ago for about £20.

So for about £400 I put together a basic system.

I have about 1300W of panels lying around and a BMW i3 4kWh battery module I someday hope to rig up, but it's a case of lack of time. A lot of this stuff has been sat around for ages untouched

A word of warning about panels. You will see a lot of panels on eBay etc that claim huge numbers of Watts, but they are so small, there is no way they could give that power. So look at the claimed output and efficiency and the panel size and see if that is realistic assuming a 1 kW/m2 solar irradiation.

I normally use it for powering my fridge and mostly just top up my bike with it, doing the main charge at work. But sometimes I have done a more significant charge of 200Wh or more. I'm not sure what the inverter efficiency is, probably 80 to 90% then the Sans charger is only about 80% efficient, so there is quite a lot of waste. Having something to go direct from 12V to 42V for the bike would be a lot better. I do have some booster modules with CC/CV functionality, but again...another project and no time...

 

[Nealh]

Matt did have some advise on panels which to buy so I will have to see if I can find the info, it may have been on his earlier solo trip to the land of the leeks and daffodils.

Storge batteries are expensive so the more ah the better if going down that route, I have seen bolt together 3.3v 280ah modules at £130 each so 4 for a 12v battery is £520, for 280ah it is by far the cheapest I have seen.

 

[matthewslack]

Well done Nealh, good idea to get up to date coverage all in one place.

Static charging and my self sufficient bike have both similarities and substantial differences too.

Static system, efficiency is nice to have, but not the end of the world if not too high because component costs are much lower than 10 years ago. You might use what you already have as a starting point, and go in stages, learning along the way.

Mobile system, light weight and high efficiency are essential. So here, it has to be best panels that can be afforded, best charge controller, and straight to the battery. There is little sense in going via a buffer battery, inverter and charger. Too much weight, too much lost in conversion.

Apart from wiring, connectors, fuses and measuring equipment, there are only five components involved.

1. Panels

Solar PV panels, also often called modules. For static systems, glass surfaced, heavy and fairly cheap. For mobile systems, lightweight, plastic surfaced, and if any good, quite expensive.

Small glass panels get increasingly expensive per W as size gets smaller. Anything less than 50W not worth bothering with. 100W not much more expensive, and cheapest option is secondhand 250W panels from solar farm upgrades. Try Bimble Solar and I have used triplesolar on eBay.

For mobile use, Sunpower cells, ideally in Sunpower modules. I bought a batch from Bimble, and they were really helpful.

2. Charge controller.

DIFFERENT depending on your requirements.

Direct charging of bike battery usually requires STEP UP or boost controller, a relatively uncommon thing. Elejoy MU400SP for cheap, adjustable voltage, built-in display, robust, or Genasun for state of the art, not adjustable voltage, no display, very expensive.

Charging intermediate battery of 12 or 24 V lead acid or LiFePO4 usually needs STEP DOWN charge controller, which is the normal kind. Good makes are Victron, and Steca. Victron is almost a 'Hoover' like name in off grid circles. Be careful to choose right model according to maximum panel voltage, max current, and check LiFePO4 support if relevant.

3. Battery

If a buffer battery, and lead acid, needs to be pretty big. Ideally double or more the nominal capacity of your bike battery so that it is not run too low in use, which can drastically shorten life.

Otherwise it is your spare? bike battery, ready to swap out. Worth seeing if a spare bike battery, directly charged is the cheapest option if starting with a blank page.

4. Inverter

I have used Sterling Power mostly, and for my Shimano chargers have had no problems with their quasi sine wave models.

I run a 1.8A charger off a 150W inverter, and the 4.6A charger off 1000W inverter, as I don't have anything in between.

5. Battery charger.

Which you already have.

 

[StuartsProjects]

There are several Videos on YouTube about the MPT7210A charger, and whilst it does appear to charge batteries OK, there is doubt that actually does maximum power point tracking (MPPT).

So for a fixed installation, which is what at I am thinking of doing, a 12V solar panel charging a lead acid leisure battery via a proper MPPT, would be the way to go.

With a lead acid battery acting as the storage, if you did not need to charge the eBike battery every day, you could use a smaller\cheaper solar panel.

 

[WheezyRider]

Just a thought , would a Sturmy Archer type hub front dynamo do any good ? Charge spare bat on the move .

A hub dyno of that type only generates a few Watts, maybe enough to power a phone or some lights. Then you'd still have to put energy in to drive it...which comes from you, or the battery, or if you are lucky, coasting downhill.

 

[WheezyRider]

I decided against lead acid after much deliberation. Yes, they are cheaper, but you have to get a massive one if you want to have a reasonably long cycle life. Plus, there are so many brands and not all the well known brands are as good as you might think and there are lots of different models from the same brand...so how do you choose? There is a leisure battery association which gives a grading:

NCC Verified Leisure Battery Scheme

The NCC is the UK trade body for the tourer, motorhome, caravan holiday home and residential park home industries. We represent the collective interests of our membership base, which spans the entire supply chain: Caravan manufacturers, motorhome manufacturers, caravan holiday home...

www.thencc.org.uk

So there are A, B and C grades. But even getting an expensive A grade battery might only give you 300 cycles at 50% DoD, and fewer than that if you go to an even deeper DoD.

Hence I chose a medium size LiFePO4 battery of 40Ah that wasn't cheap, but not overly expensive to do some testing. They can give between 2000 and 4000 cycles at 80% DoD and much more than that at 50% DoD:



Even after thousands of cycles there is still 80% useable capacity left, even though the battery is considered at "end of life".

This one was the cheapest I could find in this size. Note the added fuse, to improve over the car battery set up



The downside is the availability of the right charge controller. Not all of these are good for LiFePO4 packs, as most were made for lead acid. These nominal 12.8 V batteries have an internal BMS and will accept up to 14.6V and have LVC protection too. They are meant to be a drop in replacement for lead acid, but there are some differences. The LVC of the charge controller is usually set a bit high for this type of battery, but I think that's not a bad thing, you just get a bit less capacity out, but it should mean the battery will last longer. The main thing is the max voltage when charging. Mine will disconnect the panels at 14.6 V, which is great, but not all charge controllers are well calibrated, so what it thinks is 14.6, might be more than that.

You can get more sophisticated charge controllers which you can select the battery type, or programme all the parameters, but they tend to be more expensive.

 

[WheezyRider]

Here is my Belkin 300W inverter and the power monitor I bought many years ago.

It has no trouble running the Sans bike charger, which seems to pull about 85W and give out about 65W. I haven't looked at the power drawn by the inverter when doing this yet to get an idea of overall efficiency. But as I said, I have a booster with CC/CV capability, so at some point I will go directly from 12V to 42V for the bike battery.

The inverter is fine for charging the bike and I have used it to power a 200W slow cooker, but going up to the full 300W would mean about 25A from the battery, so you wouldn't be able to do that for long. I do have a 1100W inverter, but that would be about 92A at 12V, so too much for this 40Ah setup.

The inverter is a modified sine wave. I have used it to power a 100W 240V fan motor and it was fine, but my understanding is if you want to power stuff like mains motors without them over heating, or running inefficiently, you should use a more expensive pure sine wave inverter.

 

[WheezyRider]

Well done Nealh, good idea to get up to date coverage all in one place.

Static charging and my self sufficient bike have both similarities and substantial differences too.

Static system, efficiency is nice to have, but not the end of the world if not too high because component costs are much lower than 10 years ago. You might use what you already have as a starting point, and go in stages, learning along the way.

Mobile system, light weight and high efficiency are essential. So here, it has to be best panels that can be afforded, best charge controller, and straight to the battery. There is little sense in going via a buffer battery, inverter and charger. Too much weight, too much lost in conversion.

Apart from wiring, connectors, fuses and measuring equipment, there are only five components involved.

1. Panels

Solar PV panels, also often called modules. For static systems, glass surfaced, heavy and fairly cheap. For mobile systems, lightweight, plastic surfaced, and if any good, quite expensive.

Small glass panels get increasingly expensive per W as size gets smaller. Anything less than 50W not worth bothering with. 100W not much more expensive, and cheapest option is secondhand 250W panels from solar farm upgrades. Try Bimble Solar and I have used triplesolar on eBay.

For mobile use, Sunpower cells, ideally in Sunpower modules. I bought a batch from Bimble, and they were really helpful.

2. Charge controller.

DIFFERENT depending on your requirements.

Direct charging of bike battery usually requires STEP UP or boost controller, a relatively uncommon thing. Elejoy MU400SP for cheap, adjustable voltage, built-in display, robust, or Genasun for state of the art, not adjustable voltage, no display, very expensive.

Charging intermediate battery of 12 or 24 V lead acid or LiFePO4 usually needs STEP DOWN charge controller, which is the normal kind. Good makes are Victron, and Steca. Victron is almost a 'Hoover' like name in off grid circles. Be careful to choose right model according to maximum panel voltage, max current, and check LiFePO4 support if relevant.

3. Battery

If a buffer battery, and lead acid, needs to be pretty big. Ideally double or more the nominal capacity of your bike battery so that it is not run too low in use, which can drastically shorten life.

Otherwise it is your spare? bike battery, ready to swap out. Worth seeing if a spare bike battery, directly charged is the cheapest option if starting with a blank page.

4. Inverter

I have used Sterling Power mostly, and for my Shimano chargers have had no problems with their quasi sine wave models.

I run a 1.8A charger off a 150W inverter, and the 4.6A charger off 1000W inverter, as I don't have anything in between.

5. Battery charger.

Which you already have.

Good info there

Could you say something about system sizing?

How big a panel should you get to battery size to have reliable charging for a typical bike battery through out the year?

 

[matthewslack]

There are several Videos on YouTube about the MPT7210A charger, and whilst it does appear to charge batteries OK, there is doubt that actually does maximum power point tracking (MPPT).

 

[WheezyRider]

There are several Videos on YouTube about the MPT7210A charger, and whilst it does appear to charge batteries OK, there is doubt that actually does maximum power point tracking (MPPT).

So for a fixed installation, which is what at I am thinking of doing, a 12V solar panel charging a lead acid leisure battery via a proper MPPT, would be the way to go.

With a lead acid battery acting as the storage, if you did not need to charge the eBike battery every day, you could use a smaller\cheaper solar panel.

I've seen stuff saying it's not MPPT, some saying it is and still others saying is is pseudo MPPT. While there are chips out there that are MPPT and boost capable, until you have one opened up it's difficult to say for sure what this manufacturer has put inside it.

LT8490 MPPT Buck-Boost Multi-Chemistry Battery Charger – Beyondlogic

Here is the instruction manual:

https://gotronik.pl/images/MPT-7210A.pdf

 

[jimriley]

I have a solar system on my narrowboat, capable of charging the bike. There is also a wealth of info on boaty forums about systems, batteries etc, eg https://www.canalworld.net/forums .
The system on a live aboard boat is likely to be bigger than needed for charging an ebike, but all grist to the mill.
I have 135w flexible panel, stuck on roof, no room for more. Combined with 20a mppt and 1500w inverter, 450ah LA batteries. It does all I need. I do not have room to carry the ebike, just a Brompton, but one day might get a woosh kit for that.







We are currently at Lemonroyd, just south of leeds

 

[Benjahmin]

I have some questions.
So in order to avoid the inefficiencies on an inverter the bike battery has to be charged either direct from the solar panel or a lifePo or L.A. leisure battery. So we need to get 42v or 41.7v from 12v. The e-bay mppt linked to earlier has voltage increments of 12v. I assume that neither 36v or 48v is suitable. So how can the right voltage be arrived at, powered from 12v the source?
If the bike battery is reverse charges via the output port (presumeably bypassing the bms), what protection is there and would cell balancing still be achieved?
I'm interested 'cos I have a panel on my shed powering an old van battery just for a few leds (used when winter log splitting).
Also we take our bike away camping and hook up isn't always available. I have a 40w panel that keeps the van battery up to scratch whilst standing.

 

[StuartsProjects]

The e-bay mppt linked to earlier has voltage increments of 12v. I assume that neither 36v or 48v is suitable. So how can the right voltage be arrived at, powered from 12v the source?

The MPT 7210T can be set to charge up to any voltage, its not limited to 12v,24V,36V etc. From the manual;

"The product parameters
1. Input voltage: DC12-60V
2. Output voltage: DC24V-72V can be the key to set voltage is continuously adjustable to accommodate 24V / 36V / 48V / 72V battery pack
3. Output Current: 0-10A key settings can be continuously adjustable "


Check out some of the Youtube videos.

 

[WheezyRider]

I have some questions.
So in order to avoid the inefficiencies on an inverter the bike battery has to be charged either direct from the solar panel or a lifePo or L.A. leisure battery. So we need to get 42v or 41.7v from 12v. The e-bay mppt linked to earlier has voltage increments of 12v. I assume that neither 36v or 48v is suitable. So how can the right voltage be arrived at, powered from 12v the source?
If the bike battery is reverse charges via the output port (presumeably bypassing the bms), what protection is there and would cell balancing still be achieved?
I'm interested 'cos I have a panel on my shed powering an old van battery just for a few leds (used when winter log splitting).
Also we take our bike away camping and hook up isn't always available. I have a 40w panel that keeps the van battery up to scratch whilst standing.

If you want to use a 12V battery as a standby and sometimes use it to charge your bike direct (without a mains inverter), then you need to get a booster module that will go from 12V to 42V. Ideally, one with Constant Current (CC) and Constant Voltage (CV) capability. This will mean you can then charge the bike battery at a constant current until a set voltage is reached and then the current will decrease. When the current has dropped to a few tens of milli Amps, then the charging is effectively over. If you use a LA battery, it is quite forgiving in terms of balancing between the cells. Commercial 12.8 V nominal LiFePO4 batteries contain a BMS to organise the balancing. If you build your own from cells, you will need to add a BMS.

You may also want to consider a 24V standby battery rather than 12V, as it more efficient.

Of course, to charge the standby battery from a solar panel of a meaningful size, you ought to use an MPPT step down module, to go from 18V or 36V open circuit voltage of the panel to the voltage needed to charge the battery. You can see this in my post above.

If you want to charge direct, with no 12V standby battery in between, then you need to use the combined MPPT/Booster module - such as the 7210 module, or the ones that Matt uses on his trailer.