Solar battery charging for ebikes.

[Neilgtis]

So am I right in thinking to use a Solar panel
I need a mppt/ booster connected to a suitable
Plug to fit my battery and a output of 36/42 volts
Do I wire it to the battery or load terminals
How do I check if it fully charged look at display
Disconnect when full
Does the mttp stop letting power through
As I assume the panel is still producing power
Neil

 

[WheezyRider]

So am I right in thinking to use a Solar panel
I need a mppt/ booster connected to a suitable
Plug to fit my battery and a output of 36/42 volts
Do I wire it to the battery or load terminals
How do I check if it fully charged look at display
Disconnect when full
Does the mttp stop letting power through
As I assume the panel is still producing power
Neil

1) Set up the output voltage of the MPPT/Boost charge controller. 2) Set a max charging current. To be safe, start with just a couple of amps max. Then, when you connect a discharged battery, it will supply a voltage needed to push 2 amps of current into the battery. As time goes on, the voltage will rise in order to keep the current at 2 amps (as the battery gets charged, its voltage increases). Eventually, you get to the set max voltage point. It will then operate in the Constant Voltage mode and the current will start to drop, eventually to next to nothing. The end point of charging will be essentially when the current is very small. This is what happens in a normal battery charger, the indicator light goes from red to green when it switches into Constant Voltage mode. However, with one of these MPPT/Booster charge controllers, you should get a real time display of supplied current and output voltage.

If the power going into the MPPT/Booster is more than is needed by the battery, it will simply not do anything with the extra power, the input part might even shut the solar panel off completely, until the battery voltage is low enough to require charging again.

As for where to connect it, that depends on the type of battery you have and it's fittings/connectors. Essentially you would wire it up to wherever you would connect a normal charger. Be sure to add an inline fuse for safety. But if you are not sure, take a photo and post it here.

 

[matthewslack]

There is nothing like trying it at home before you go, and under no time pressure to get the hang of these things!

I have only used the Elejoy MU400SP, I am sure there are other options also at a budget price.

These are really easy to use, and do maximum power followed by constant voltage charging, and you can set in increments of 0.1V the finishing voltage.

Mine are set to 41.0V, and the displays clearly show diminishing current when that voltage is reached. I am trusting them to charge via my generic battery output port, so BMS can do balancing but cannot stop the charge.

Any solar panel intended for 12V lead acid will work fine, so if you already have one, it is s very low cost setup.

 

[Benjahmin]

Thanks Matthew, that helps.
I'm an electrician by trade but solar is a new field to me.
Here's what I'm trying to achieve.
I have a van with a tent box on top, bikes travel inside. No leisure battery just a 40w panel to keep vehicle battery up so I can use radio and leds whilst parked. At the mo use electric hook up to charge bikes but it's not always available.
So, having looked at the Elejoy spec, it seems I can set this to 41-41.5 or 42 v, and connect it to the normal charge port on my batteries so the battery bms would balance and limit charge as usual. Is that right?
The Elejoy would deliver constant current up to set voltage than switch to mA constant voltage. Is that right?
I'm guessing I would need a bigger solar panel but the 40w will do to test feasability.
Our two bikes have 3 batteries between them amounting to some 46Ah in total. We never run them flat (or at least not yet) 'cos our legs and bums give up before that happens.
The Elejoy spec claims 97% efficiency which seems really good, so going at it this way avoids the charger and inverter inefficiencies. What's not to like? So this might work with a days riding followed by a day resting/walking whilst the batteries charge.
Do the numbers stack up? I would have a concern that there is some safety issue I'm not aware of. Reverse feed possibility? Overcharging if left connected whilst out walking?
I know enough about electricity to be circumspect and D.C. in particular needs careful handling even at sub 50v.

 

[matthewslack]

Thanks Matthew, that helps.
I'm an electrician by trade but solar is a new field to me.
Here's what I'm trying to achieve.
I have a van with a tent box on top, bikes travel inside. No leisure battery just a 40w panel to keep vehicle battery up so I can use radio and leds whilst parked. At the mo use electric hook up to charge bikes but it's not always available.
So, having looked at the Elejoy spec, it seems I can set this to 41-41.5 or 42 v, and connect it to the normal charge port on my batteries so the battery bms would balance and limit charge as usual. Is that right?
The Elejoy would deliver constant current up to set voltage than switch to mA constant voltage. Is that right?
I'm guessing I would need a bigger solar panel but the 40w will do to test feasability.
Our two bikes have 3 batteries between them amounting to some 46Ah in total. We never run them flat (or at least not yet) 'cos our legs and bums give up before that happens.
The Elejoy spec claims 97% efficiency which seems really good, so going at it this way avoids the charger and inverter inefficiencies. What's not to like? So this might work with a days riding followed by a day resting/walking whilst the batteries charge.
Do the numbers stack up? I would have a concern that there is some safety issue I'm not aware of. Reverse feed possibility? Overcharging if left connected whilst out walking?
I know enough about electricity to be circumspect and D.C. in particular needs careful handling even at sub 50v.

Assuming generic batteries, not Shimano/Bosch etc first of all.

Yes, if you set the Elejoy to full battery voltage, you should be able to charge through the charge port, and so have full BMS protection.

I prefer to charge a bit below, 41V for my 36V bike, and I found my BMS didn't like that, and would not accept charge sometimes. So for knowing it will always charge, and trusting the Elejoy to stop at 41V and then current limit until full, I am charging via the output port. This is one of those things to find out and understand before depending on it.

Overcharging risk is always there, you need to form an opinion of how great it is, and consequences, and if need be have a second means of disconnecting if something is not right. On the road, I don't.

The Elejoy does not care how much current it stuffs into the battery. Just now I had 8 amps from my 330Wp array, into battery at 38V. So panel size vs battery capacity is the way to control maximum charge current. My solar battery is only 13Ah. I'll do a capacity test when I'm home to see how much this pretty concentrated use affects it.

Take the 97% efficiency claim with a pinch of salt. There are two efficiencies involved: the DC/DC conversion and the quality of the MPPT tracking algorithm. They are not always clear what is meant!

Your use case is perfect. I can say from my trip so far, you can expect at least 2Wh per Wp of panel on a fairly overcast day, rising to more than 6, maybe even 8 or 9, on a blue sky day from an unshaden horizontal panel.

Start with your 40W, but you will probably want to go somewhat bigger.

 

[Nealh]

So the elejoy modle Matt isn't current adjustable manually ?

 

[matthewslack]

So the elejoy modle Matt isn't current adjustable manually ?

No, only the full charge voltage is adjustable. Maximum current is max panel output divided by battery voltage, so if wanting to limit charge rate, just keep panel size down.

In my situation where what I generate determines how far I go in the day, those short high current bursts are vital, but may not be the best for the battery.

 

[Benjahmin]

I'm really enjoying this thread.
So, if I'm understanding the maths, my 40w panel might be capable of 80Wh on a dull day? That would seem to be enough to charge all 3 partially discharged batteries.
The lack of current limiting does concern a bit, don't want to damage my expensive batteries. (They are all generic. All recelled by Jimmy. Two are Boston Power cells, the other is 21700 something or others.)
I did wonder about parallel charging two, or even all three on a bright day, to split the current produced.
Not an electronics buff so can't think of another way.
Presumeably the Elejoy has some limit, so won't melt itself.

 

[Benjahmin]

Just looked at the Elejoy spec again and it's stating an ' Output to battery current limit' as Max 15A.
Wow!
OK, so that'll be with 400w panel, on a bright day. So I'm thinking a maximum panel size of 100w, so should give a max current of 3.25A. Is that how this is gonna work?

 

[StuartsProjects]

If I'm understanding the maths, my 40w panel might be capable of 80Wh on a dull day?

In general solar panels are advertised at the power under full sun.

So a 40W panel might only put out 10-20w on a cloudy day.

10w would only be enough power to charge a '36V battery' at circa 0.3A, so a 10Ahr battery might take 33 daylight hours to charge.

 

[matthewslack]

I'm really enjoying this thread.
So, if I'm understanding the maths, my 40w panel might be capable of 80Wh on a dull day? That would seem to be enough to charge all 3 partially discharged batteries.
The lack of current limiting does concern a bit, don't want to damage my expensive batteries. (They are all generic. All recelled by Jimmy. Two are Boston Power cells, the other is 21700 something or others.)
I did wonder about parallel charging two, or even all three on a bright day, to split the current produced.
Not an electronics buff so can't think of another way.
Presumeably the Elejoy has some limit, so won't melt itself.

80Wh, not 80Ah. So at nominal 36V, 80Wh is 80/36 = 2.2Ah.

The simplest way would be two panels, an Elejoy on each, and either each to a different battery, or parallel the Elejoy outputs to a single battery.

If you have space, maybe two 100W panels.

The panels could also be used via a standard charge controller to charge a leisure battery for your van, when not needed for the bike batteries.

My system is all plugged together with Anderson powerpole connectors, which make it easy to reconfigure.

 

[matthewslack]

In general solar panels are advertised at the power under full sun.

So a 40W panel might only put out 10-20w on a cloudy day.

10w would only be enough power to charge a '36V battery' at circa 0.3A, so a 10Ahr battery might take 33 daylight hours to charge.

In dull overcast, output goes through the floor. My 330Wp array in rain a while back was producing 6W!

However, the light intensity changes throughout the day, and if outside and just left connected, it is sometimes surprising how much is accumulated.

My worst day so far is 365Wh from my 330Wp.

 

[cyclebuddy]

It's interesting to hear what others are using. I admire @matthewslack innovate set-up where high generation, compactness & low weight, and conversion efficiency is important, but I don't think that's so important if you're basing your solar in a static garage/shed/house or mobile vehicle/van/campervan to tour. It also creates charging issues for "communicative" bike batteries (Bosch, Yamaha, MS's own Shimano and my own TranzX etc).

For my own bike-in-a-van application, I started off using a simple inverter directly off my van starter battery; it worked but was too power hungry. I then migrated to a simple Acid storage battery with a basic PWM controller and 100w panel; it didn't generate enough energy during a typical day, was too "Heath-Robinson" in execution, and wasn't easily portable/ took too much space/weight in my van to justify... and I didn't like the drag of having a fixed solar panel on the roof.

I've more recently migrated to a Bluetti EB70 (£570), which is a simple one-box solution. It has an MPPT controller, (enough for me) 700w LiFeP04 storage, and USB/12v/240v 1000w pure sine inverter outputs in that one box. It's not perfect by any stretch, but being input/output versatile and highly portable is for my uses a big advantage: Charge from van battery when driving, house/pub/hotel room/camp hook-up... or just throw a 100w foldable solar panel on the roof of my van when parked up and off cycling (which ironically generates about 80w on a good day, almost the same rate as my e-bike charger uses charging my bike battery). It also powers the fridge/tyre pump/lighting in my van. Take it to the shed or end of the garden to use electric tools, or in the house in case of a power cut... and of course easily charge the bike(s). I've sometimes even taken it with me in the boot of the car with my foldable bike in case I need a top-up. That portability/versatility is for me really useful - different priorities to MS's and others here more dedicated set-ups. I'll probably add a couple of £80 Renogy 100w fixed panels to my shed roof when it's at home as the foldable panel isn't intended as a permanent/fixed solar solution, but good enough as it is when on the move.

The Sunpower cells MS is using really are lovely/the best, but I'm not sure you need to pay for such good cells/that extra % gain if you're in a static situation when you can easily over-panel for less cost.

 

[mr_ed]

I have a new bike shed going in down my garden, could someone give a 'shopping list' with ballpark costs if I wanted a solar setup on the roof to charge my 52V 17.5ah battery? Happy for it to take as long as it takes to charge.

 

[StuartsProjects]

Happy for it to take as long as it takes to charge.

The Solar panel size could be a significant part of the cost, so some idea of an acceptable charge time, in Winter say, is needed.

 

[Nealh]

Reading Matt's reply reguarding current supply, I wouldn't want to be charging my cells much above 3a for cycle life and longevity, so sounds like small size panels are the answer for low current but then one will be waiting an age for charging directly.
The answer may be a storage battery but tbh the cost is then already getting quite high for a static option.

For my 44v nom batt's a 120w panel should give about < 3a max charge rate.

One has to be guided by the cell charge spec's if wanting decent cycle life, the lower the current input the better the life.
For touring one has little choice but to go for a higher current charge unless one has enough wh not to worry so much.

 

[StuartsProjects]

Reading Matt's reply reguarding current supply, I wouldn't want to be charging my cells much above 3a for cycle life and longevity, so sounds like small size panels are the answer for low current but then one will be waiting an age for charging directly.

If you have only a single battery then that could be an issue.

If you have two batteries, then you can readily alternate them, perhaps charging only on 1 Amp for long cycle life.

 

[mr_ed]

The Solar panel size could be a significant part of the cost, so some idea of an acceptable charge time, in Winter say, is needed.

Good point! Say 58V @ 500 - 1000 mA as a charge rate?

 

[Benjahmin]

Reading Matt's reply reguarding current supply, I wouldn't want to be charging my cells much above 3a for cycle life and longevity, so sounds like small size panels are the answer for low current but then one will be waiting an age for charging directly.
The answer may be a storage battery but tbh the cost is then already getting quite high for a static option.

For my 44v nom batt's a 120w panel should give about < 3a max charge rate.

One has to be guided by the cell charge spec's if wanting decent cycle life, the lower the current input the better the life.
For touring one has little choice but to go for a higher current charge unless one has enough wh not to worry so much.

This is about where I'm coming to.
Having let my brain roam around the elegance of Ohm's law overnight, I'm now seeing this.

A 100Wp panel ( assuming a 12v ouput)is capable of delivering 100/12=8.3A
Assuming no losses in th Elejoy (ridiculous I know) then this becomes 100/42=2.38A. A much more acceptable charge current. Of course this would only happen in full bright sunlight, so averagely would be less.
Considering that this would be for the occaisional van camping trip I think it would be more cost effective to pay the £5/night hook up fee, sting though it does.

I have looked at some combined battery/inverter combo's (they seem to be mislabelled as generators) and they are too expensive just for camping/bike use.
However, in consideration of the growing possibility of scheduled power cuts (think 1970's all over again), I may consider one. I have domestic P.V.'s which, in a power cut, will not generate as they receive no A.C. signal. With the installation of a suitable isolation switch to isolate from the grid, it may be possible to trick the solar controller into thinking it has mains by back feeding from a battery inverter, so allowing the panels to generate. Thus keeping freezers ,full of my veg garden produce, going, at least in daylight.
Control and safety implications need carefully thinking through here.

 

[WheezyRider]

Reading Matt's reply reguarding current supply, I wouldn't want to be charging my cells much above 3a for cycle life and longevity, so sounds like small size panels are the answer for low current but then one will be waiting an age for charging directly.
The answer may be a storage battery but tbh the cost is then already getting quite high for a static option.

For my 44v nom batt's a 120w panel should give about < 3a max charge rate.

One has to be guided by the cell charge spec's if wanting decent cycle life, the lower the current input the better the life.
For touring one has little choice but to go for a higher current charge unless one has enough wh not to worry so much.

One thing to bear in mind, the charging rate stress will depend on the number of cells you have in parallel in your pack. For a 6p or 8p pack 3A is not that high, 0.5 A per cell or less. A usb bank charger will often charge at 1 A per cell. Of course, the more amps you charge at the more heat and more risk you run.