Charging an Ebike with solar question?

[Tomcor]

Thinking about buying an 36v 8.8ah ebike. I have a 175w mppt solar setup on my van.
What size and type of invertor would I need to charge the ebike? How long would it take to charge the battery pack? Anyone charging a 36v ebike with your solar?
Also have a separate Renogy 30w mono panel that I was thinking of using to charge with a dc to dc stepup voltage converter at 42v. Instead of using an invertor and my other large panel.

 

[KathyC]

I charge my 48V ebike battery using a simple 300W modified sine wave inverter. The key is the actual charger that you use for your ebike battery. Mine came with a 2A charger that states it requires 120 watts. This works fine for recharging.

 

[AreWeLostYet]

Thinking about buying an 36v 8.8ah ebike. I have a 175w mppt solar setup on my van.
What size and type of invertor would I need to charge the ebike? How long would it take to charge the battery pack? Anyone charging a 36v ebike with your solar?
Also have a separate Renogy 30w mono panel that I was thinking of using to charge with a dc to dc stepup voltage converter at 42v. Instead of using an invertor and my other large panel.

I would avoid using an inverter. An inverter converts DC power to AC power. Your solar panel's charge controller puts out DC. Your ebike's battery is DC. Best to stay DC and avoid the conversion an inverted does for things that have to have "house current". This is more efficient and simpler. So your charge controllers probably puts out 12 volts DC. You can probably get an adapter that your e-bike's charger can plug into car current (12 volts DC). It might have that cigarette lighter type plug. This is a more direct method of charging that's is more efficient and likely to be a faster charge that doesn't involve an inverter. Simply put - no need to 'invert', just step the current up or down.

 

[tx2sturgis]

Thinking about buying an 36v 8.8ah ebike. I have a 175w mppt solar setup on my van.
What size and type of invertor would I need to charge the ebike? How long would it take to charge the battery pack? Anyone charging a 36v ebike with your solar?

Look at the UL label on the charger (or call them and ask) because it should have a wattage rating. Or maybe amps @ 120v. 

If it says 200w (or under) then you will need at least a 300 watt inverter. 

If it is 300-400w then you would need a 600w inverter. 

As always, for inverters powering chargers, I always recommend a pure sine wave inverter and for anything above about 100 watts, it is always best to hardwire the inverter, avoiding a cigarette lighter plug. 

With 175 watts of max solar, flat mounted, you will need to do most or all of the charging during daylight hours.

 

[AreWeLostYet]

The ideal setup if you already have a vehicle with batteries being charged by sloar is to hard wire a connecting link with connectors like an these from your battery bank. Then a connecting length of wire long enough to reach where you'll charge your e-bike. Taking power directly from the battery (which is being constantly charged by solar) eliminates the need for any kind of specific type of power like "square sine wave". And your vehicle battery bank is going to have plenty of power to charge any e-bike made.

It's nice to be seeing more e-bikes on the roads these days. They provide mobility to people who, for whatever reason, don't own a car or drive yet need to get to the grocery store, library, etc. Particularly for the elderly or others not fit enough to use 'pedal power'. And when gas prices teach the sky, their popularity is going to skyrocket. E-bikes seem like a natural fit for nomads and RVers.

 

[QinReno]

What Kathy says makes sense. The charger that comes with the bike is made to plug into 120VAC, which could be a 12VDC-to-120VAC inverter capable of handling the wattage, so Kathy has it covered - even if the conversion efficiency (solar->DC->AC) is not 100%. It never is.

You have to realize that you're messing with Lithium batteries here, which can catch fire and potentially explode if not charged properly. Before trying any jury-rig, I would talk to the people who manufacture the bikes. They should know.


BTW, Tomcor, which bike are yo looking at getting. I was looking Pedego recently,
https://www.pedegoelectricbikes.com/products/#trail

 

[AreWeLostYet]

What Kathy says makes sense. The charger that comes with the bike is made to plug into 120VAC, which could be a 12VDC-to-120VAC inverter capable of handling the wattage, so Kathy has it covered - even if the conversion efficiency (solar->DC->AC) is not 100%. It never is.

You have to realize that you're messing with Lithium batteries here, which can catch fire and potentially explode if not charged properly. Before trying any jury-rig, I would talk to the people who manufacture the bikes. They should know.


BTW, Tomcor, which bike are yo looking at getting. I was looking Pedego recently,
https://www.pedegoelectricbikes.com/products/#trail

An e-bike battery pack with lithium batteries is going to have a battery management system (BMS) whicn will manage charging current and eliminate any chance of lithium explosion. When you plug any power source into the charge input of the e-bike, that power has to be filtered through the BMS before going to the batteries.

Don't fall for the "only use the official, original, approved charger" BS or you'll never be able take advantage of all the options. And you'll pay thgough the nose - which is the whole point of manufacturers insisting you use THEIR adapters, THEIR batteries, THEIR adapters etc.

If you're really stuck on adhering to manufacturer's equipment, they probably make an adapter from bike to car battery. You can cut off the cigarette lighter plug (a good idea) and solder or crimp on a coronet you can bolt to one of your vehicle battery pack. Some kind of quick-disconnect link somewhere in the line would be ideal. Or, even alligator clips to attach this line to the vehicle battery (assuming you have a battery other than you vehicle's starting battery). Walmart has nice copper alligator clamps in their boat supply section for $2/pair.

 

[QinReno]

Eye R an electrikul injanear, and the one thing I know is that you don't want to screw up when dealing with lithium batteries. If I were going to spend $3000-$4000 on an electric bike, I would check with the manufacturer first, and then do what they say.

 

[AreWeLostYet]

Eye R an electrikul injanear, and the one thing I know is that you don't want to screw up when dealing with lithium batteries. If I were going to spend $3000-$4000 on an electric bike, I would check with the manufacturer first, and then do what they say.

Lithium batteries and e-bikes are a relatively new technology. Many of the denizens of these forums are not.

I can assure you that any manufacturer is going to urge you to use only their products and related accessories and parts. This is so that they can continue working at and receiving a pay check from that manufacturer and has nothing to do with what is best for YOU.

 

[DLTooley]

I've yet to see a definitive answer on this question. Yeah, theoretically staying DC makes sense, but that doesn't mean there is a car adapter solution actually available at a reasonable cost. Does anyone know the basics of dc-dc voltage conversion for an inquiring mind?

 

[QinReno]

I've yet to see a definitive answer on this question.  Yeah, theoretically staying DC makes sense, but that doesn't mean there is a car adapter solution actually available at a reasonable cost.  Does anyone know the basics of dc-dc voltage conversion for an inquiring mind?

If you want a definitive answer, you need to know a lot more information first:

1. is the actual charging electronics inside the battery unit on the bike, or in external electronics? (and don't assume you know the answer ahead of time).

2. Kathy's unit says 2A and 120W. That would indicate it gives a 60V DC output, which would charge the 8.8AH battery up in somewhat more than 4 1/2 hours.

3. it's unlikely that her unit gives a 12V output at 2A, and there is a boost circuit inside the battery box, as it would take 4X to 5X as long, or 18-22 hours, to recharge the battery. 

You need to know all of the parameters first, and not simply assume them. Then you can figure what you're doing.

EDIT: a couple of extra items:

4. it would make sense to actually have the charging electronics, per se, inside the battery box, as then the electronics can more easily perform "balanced charging", meaning all the different cells in the battery are monitored during the charging process, and balanced evenly.

5. OTOH, the complete charging circuitry could be in the external box, but then it would need a multiconductor cable to plug into the battery, so that once again all cells could be monitored and charged evenly.

 

[tx2sturgis]

Does anyone know the basics of dc-dc voltage conversion for an inquiring mind?

To charge a 36v lithium battery, (which will need around 40 volts or maybe 50v to charge it) the 'car charger' or DC- DC solution still inverts the DC to a high frequency AC, (400hz is common) then thru a boost converter, essentially a toroidal style transformer, steps this high frequency AC up to a higher voltage, then rectified and filtered, and turned back into DC at the higher voltage.

There is no free lunch. The 'inverter' is still present, with some efficiency losses. 

If the OP buys a common off-the-shelf PSW inverter, probably not more expensive than the bike's OEM proprietary DC charger, then they also have an inverter which can be used for other AC items within it's power range.

 

[QinReno]

To charge a 36v lithium battery, (which will need around 40 volts or maybe 50v to charge it)
...........

Offhand, Mr Pirate, whatdayathink? We know that 120VAC @ 2A would kill you pretty darn dead, pretty darn quickly. Might 40-50VDC at 2A be a bit of danger, or not? Especially for someone who is not really sure of what they're doing? 

(you and I are shirley a couple of professionals and wild men, and used to taking our lives in our own hands on an every day basis!).

 

[tx2sturgis]

lol....

There is an anti-inverter theme that is constantly expressed on this forum. Nothing wrong with them, as long as the user understands the limits. They are a tool for a job.

Now, using one 24/7 to power a fridge might not be the best use for them, I get that.

However, for intermittent use, charging batteries, running a blender, a microwave, TV, or whatever, and sacrificing a few percentage points of efficiency, but gaining ease of use, low voltage monitoring, multiple applications, and very reasonable cost seems to be a good solution in some cases.

I do wish that off-the-shelf inverters included a time-based auto-power-off feature, like we had in our commercial trucks.

 

[QinReno]

For people interested in e-bikes, I just ran across this site where he does reviews on e-bikes.
https://www.youtube.com/user/ElectricBikeReview/videos
https://electricbikereview.com/

 

[AreWeLostYet]

If you want a definitive answer, you need to know a lot more information first:

1. is the actual charging electronics inside the battery unit on the bike, or in external electronics? (and don't assume you know the answer ahead of time).

2. Kathy's unit says 2A and 120W. That would indicate it gives a 60V DC output, which would charge the 8.8AH battery up in somewhat more than 4 1/2 hours.

3. it's unlikely that her unit gives a 12V output at 2A, and there is a boost circuit inside the battery box, as it would take 4X to 5X as long, or 18-22 hours, to recharge the battery. 

You need to know all of the parameters first, and not simply assume them. Then you can figure what you're doing.

EDIT: a couple of extra items:

4. it would make sense to actually have the charging electronics, per se, inside the battery box, as then the electronics can more easily perform "balanced charging", meaning all the different cells in the battery are monitored during the charging process, and balanced evenly.

5. OTOH, the complete charging circuitry could be in the external box, but then it would need a multiconductor cable to plug into the battery, so that once again all cells could be monitored and charged evenly.

All lithium battery e-bike power packs have a battery management system (BMS) which takes care of all charge rate, balancing, auto shut-off functions. Just feed them the correct current - typically 24, 36 or 48 volts DC. There are chargers that use 12VDC (automobile battery current) to charge 48 VDC batteries without unnecessarily adding an inverter (which develop a lot of heat, so have noisy fans and often fail) into the system. Here's one:
http://www.powerstream.com/dc-input-charger-12-48v.htm

 

[tx2sturgis]

Thank you for helping to make my point.

That DC-DC converter IS an inverter in disguise, and its $804! And the efficiency rating is around 75%. Many off-the-shelf inverters surpass that. 

The OP could buy an additional e-bike battery AND a common 12vdc to 120vac inverter for that amount of cash.

There is no 'free lunch' on this stuff, there just isn't.

 

[tripper]

This really inexpensive mppt controller can charge the battery directly off of solar.

MPT-7210A
You will have to do a little research on forums for your setup, the info is out there, it a neat little upconverting mppt controller.  I think you need around 42volts to charge that 36 volt pack.
Personally I would just get a nice inverter as you will find that useful for many things, and just charge of the inverter thru the battery charger to the 36v pack, the loss will be minimal and you wont have to worry about anything. 
Also, charge the bike battery someplace SAFE, outside away from flammables or in an oven or metal pot with lid etc.  18650 cells can and do catch on fire occasionally, they even make fire bags you can put the battery in to charge it. No need to risk your life or burning your rig down.

 

[AreWeLostYet]

This really inexpensive mppt controller can charge the battery directly off of solar.

MPT-7210A
You will have to do a little research on forums for your setup, the info is out there, it a neat little upconverting mppt controller.  I think you need around 42volts to charge that 36 volt pack.
Personally I would just get a nice inverter as you will find that useful for many things, and just charge of the inverter thru the battery charger to the 36v pack, the loss will be minimal and you wont have to worry about anything. 
Also, charge the bike battery someplace SAFE, outside away from flammables or in an oven or metal pot with lid etc.  18650 cells can and do catch on fire occasionally, they even make fire bags you can put the battery in to charge it. No need to risk your life or burning your rig down.

Just get one of these.

It's made to charge one of these which has a 36 volt lithium battery pack.

If it bothers you, cut off the cigarette lighter plug and solder/crimp on the connector of your choice to connect to the 12VDC battery of your choice.

 

[tx2sturgis]

One of the things we don't know about this 'roll-your-own' solution:

Does the lithium battery on the bike in question have a built-in BMS or not?

Some do, and only need a 2 pin connector (normally) to supply the required voltage and current. Sometimes there is a third pin for voltage or temperature sensing.

Those are what are referred to as 'smart batteries'.

Others have external controls built-in to the 'smart charger'...they will have multiple pins on the battery connector.