Can batteries be charged while the bike is on?

[Dolfino]

I'm about to begin a project and I wanted to know if a bike could be charged even when it is moving. If so, could I just plug in the voltage to the battery port on the controller? I could regulate the voltage so that's not a problem. By the way, I'm planning on using a 36V 750W hub motor, and the 36V 16AH battery, all electrical components from GoldenMotor.

[e-lmer]

The charging voltage for any particular battery is higher than the
voltage rating of the battery.

For example a 12V car battery charges at just under 15V.

The Golden Motor speed controllers are derated, you can run
them at a higher voltage than the rated voltage, so you can
run the system while being charged (assuming a regulated
input voltage) with no risk, but you will not be able to get
any accurate reading of the battery capacity in this way.

[Dolfino]

To charge the battery while using it, could I plug in a 50.8V power source into the charging outlet on the battery while the battery is simultaneously connected to the controller? 50.8V comes from the GoldenMotor website. After clicking the EV battery button on the left hand side and scrolling down to the solar charger section of the page it shows that the 36V solar battery chargers output 50.8 charging volts.

[Gregte]

You have to be very specific when you use the terms "outlet" etc. You mention plugging a power source into a charging outlet on the battery. I am not clear what you mean but I will assume that you mean plugging the power source into the charging input socket on the battery.

If you are using a battery that has a BMS built into it then you can do what you suggest. The voltage will never be higher than about 42.0 volts because the BMS will open circuit from the charging socket to the battery cells when that voltage is reached.

Whenever the charger is connected to the battery 50.8 volts will not be measure at the battery or charger since the battery is a load on the charger and will keep the voltage down to under 42.0 volts. But when the BMS opens the circuit between the battery and the charger the charger's output wire will show a voltage of 50.8 volts and the battery will show a voltage of 42 volts. They are no longer completely connected once the BMS has opened the charging circuit.

It is OK that the bike is ON because the BMS will keep the voltage of the battery to no more than 42 volts which is the safe upper limit of the battery.

[Dolfino]

You have to be very specific when you use the terms "outlet" etc. You mention plugging a power source into a charging outlet on the battery. I am not clear what you mean but I will assume that you mean plugging the power source into the charging input socket on the battery.

Sorry if I confused you. I was going to say charging inlet but this picture confused me and made me change my mind.

Anyways, from what I understand, it is perfectly OK to input any voltage over 42V into the charging inlet, regardless of whether or not the battery is on, and also regardless of whether or not the battery is being used. It would be much easier to input 48V than 50.8 into the charging inlet on the battery because I could easily get a 48V DC-DC converter. I think I understand it now, but I just want to clarify. Thanks so much for your help.

[ccbreder]

I am curious as to where you will get the power for the charging side.

Automobile charging takes place while the battery is "in use" for lights radio ect.
But the Alternator/generator must send higher voltage to the battery than the batterys voltage. Also must send more amps than the other circuits are using.
Would this be the case with LiFePo BMS. How about LiFePo without BMS?

[Bikemad]

I am curious as to where you will get the power for the charging side.

My guess is one of the following:

• A portable generator mounted on the back (or towed behind on a small trailer)
• Solar panels
• Wind turbine
• Wave energy (But severe arm ache is a major side effect with continual waving)
• Static electricity / lightning strikes
• Hydrogen cell
• Miniature nuclear reactor
• Overhead power cables
• A bigger battery pack
• Jumper leads connected to passing cars
• A wheel driven alternator
• a 48V DC-DC converter powered by the 36v battery discharging outlet

 

[ccbreder]

 

[Gregte]

Anyways, from what I understand, it is perfectly OK to input any voltage over 42V into the charging inlet, regardless of whether or not the battery is on, and also regardless of whether or not the battery is being used. It would be much easier to input 48V than 50.8 into the charging inlet on the battery because I could easily get a 48V DC-DC converter. I think I understand it now, but I just want to clarify. Thanks so much for your help.

What happens is this... to charge any battery you have to put in a somewhat higher voltage than the voltage you are trying to charge the battery to. The higher that input voltage is, the quicker the battery will charge. If the input voltage (charger voltage) is too high then the voltage measured at the battery while charging will also be too high. You do not want to charge your 36v LiFePO4 battery higher than 4.3 volts per cell. (I think 4.3 is the max, not absolutely certain.) So you can charge with as high of a voltage as you want as long as the cells never go above 4.3v each. The BMS in the battery is supposed to ensure that over voltage charging does not happen.

If you are applying your charging voltage at the output wires of your battery the BMS input charging circuitry will be bypassed and it will be possible to overcharge the battery and ruin the cells. I just mention this in case you intend to charge thru the output connector of your battery instead of the normal charging jack.

[Dolfino]

I am curious as to where you will get the power for the charging side.

My guess is one of the following:

• A portable generator mounted on the back (or towed behind on a small trailer)
• Solar panels
• Wind turbine
• Wave energy (But severe arm ache is a major side effect with continual waving)
• Static electricity / lightning strikes
• Hydrogen cell
• Miniature nuclear reactor
• Overhead power cables
• A bigger battery pack
• Jumper leads connected to passing cars
• A wheel driven alternator
• a 48V DC-DC converter powered by the 36v battery discharging outlet

I must say that I am impressed with the umm... interesting power sources you have come up with. However, I guess it's time to tell what power source I was really planning on using. Human Power. I planned to have a 12V pedal generator and step that up using a DC-DC converter to 48V, enough to charge the battery safely using the BMS and the charging inlet.
 By the way, I don't necessarily need to charge the battery, just extending the range is good enough. The goal is to have a series hybrid human-electric bike.

[Gregte]

I planned to have a 12V pedal generator and step that up using a DC-DC converter to 48V, enough to charge the battery safely using the BMS and the charging inlet.
 By the way, I don't necessarily need to charge the battery, just extending the range is good enough. The goal is to have a series hybrid human-electric bike.

In what way would this be better than just pedaling the bike in the normal way, with sprockets and chain, to get more range?

 Mechanically it may or may not be as efficient (or more efficient) for pedals to drive a generator than pedals driving the rear wheel would be. But even if that were a 'break even', there is definitely a loss of efficiency when pedaling a generator to charge the battery in that the generator is not 100% efficient electrically. It will produce heat which is wasted energy.

Or maybe you have something else in mind that precludes what I envision?

[muzza.au]

I don't see to point of it either as human legs can only produce 100-200 watts, 200 being more towards the athletic riders and your motor is 750watts. So in theory you would only being putting a small amount back in. But also you say you are going to use a dc-dc converter to step up from 12v to 48v. Usually when you step up the voltage the inverse applies to the current, the current goes down, therefore you would be putting very little current into the battery and its how much current you put in that really counts, not just the voltage. If you see lifepo4 batteries advertised on ebay they usually come with 2A charger, but they sometime have the option to upgrade to 5A chargers. The 5A charger would of course charge the battery alot quicker, but I've heard the higher the current then potentually the lower the long term life of the battery will be.

Muzza.

[Dolfino]

The idea is to have a series hybrid electric tricycle. The tricycle part of it makes it so that the pedaler can pedal while stopped. I know that there are a lot of problems with it but the project really is just a demonstration of it's potential. First up, regardless of how hard it would be to pedal, if I had a 48V pedal powered generator, most of the inefficincies of a DC-DC converter (and there are a whole lot of them) would be eliminated. Obviously no human is capable of continually generating enough wattage to charge the battery while riding, I have come up with a solution to that as well. The pedal generator can be detached from the trike and pedaled anywhere. For example, during an exercise program someone could pedal the generator and charge a 12V battery power pack connected to an inverter that the battery charger would plug into and charge the battery as if it were plugged into the wall. The key, however is that all of the electricity ever used to move the tricycle would be completely human generated, one of the most efficient power converters known to mankind. Basically you never have to use any power plant (aside from your body that is) to run the machine. Now of course, that's only half the benefit, a normal trike is exactly the same way. The other key to this project is that it can be a reliable form of short-range transportation. For destinations less than 5 miles away, you can expect to be there in under 15minutes. At first it can sound a bit crazy, but really it isn't. Anyways, that seems like a good answer.

In what way would this be better than just pedaling the bike in the normal way, with sprockets and chain, to get more range?

Here's a crude answer from Eltratech.com

Electric Bicycles currently on the market have a motor that drives one of the wheels in addition to the bike's pedals and derailleur. When these motors are running, the rider has to pedal faster than the motor or they're just spinning the derailleur's ratchet. Therefore, the rider must choose whether to pedal or run the motor, but cannot do both together efficiently. In addition, the old mechanical gears have to be constantly repositioned to stop the derailleur from grinding the chain. Whenever the bike is stopped, the gears have to be manually banged down to first gear while the bike is still moving.

Technically Eltratech isn't technically right because it isn't the derailleur with a ratchet, it's the freewheel. Also if the rider pedals at exactly the same speed of the motor, then he or she adds torque to the system (which is always nice to have). However, I am confident in the 750W motor's torque, and I don't think that will be an issue. So that's the answer to that question.

[Bikemad]

I don't see to point of it either as human legs can only produce 100-200 watts, 200 being more towards the athletic riders and your motor is 750watts. So in theory you would only being putting a small amount back in.

• The men who flew the man-powered aircraft could develop 400 Watts at the pedal crank for long periods.

Assuming you can maintain 100watts at a the required charging voltage (around 43.5v) you would generate 2.3Amps.
(if your generator was 100% efficient)

Realistically, I would predict a maximum of around 1.7Amps after losses.

So, if you can manage 10 hours of pedalling at this rate, you could (in theory) fully charge the battery!

One hour of hard pedalling would put 10% back into your battery.

Although it may be feasible, I would not under any circumstances describe it as practical.
(I'd rather use solar panels or wind turbines to generate the current and eliminate all that unnecessary hard work.)

Alan

[Gregte]

I always admire anyone looking for a more environmentally friendly way of producing energy but I will make one point that I found to be quite an eye opener. I have calculated that it would cost well over 100 times as much money for the food required for me to pedal my bike than the cost of electricity required to drive my bike's motor. Here are my numbers, and mind you, I am talking about the consumer's cost of two fuels, that being food vs. electricity.

At a moderate 10 mph you ought to burn around 300 kilocalories (300 food calories) per hour.

To go 10 miles would take 300  Calories.

A typical TV dinner has 300 calories and costs around $2 so you would go 10 mi. on the bike for $2 food.

I keep a record of kilowatt-hours (Kill-A-Watt meter) I have used to charge my bike and it has cost me 80 cents to go 600 miles. That's 0.133 cents per mile or 1.33 cents per 10 mi. (I pay 9 cents per kwh)

• Food=$2.00 per 10 mile.
• Electricity=$.0133 per 10 mile.
• 2.00 / .0133 = 150.37

Therefore "TV dinner fuel" costs 150 times as much money for me as electricity to power my bicycle.

You may get food a lot cheaper perhaps but even if it is free you will likely spend more money cooking it than that used to power a bike with electricity.

DON'T GET ME WRONG! I am not trying to downplay alternative energies. I am all in favor it. I am just pointing out that food energy fed to humans is quite expensive compared to virtually all other energy sources. I am talking about the dollar cost to the consumer.

And to top it off, over 2/3 of adult U.S. citizens are overweight, therefore carrying an excess of 'fuel' which would be well spent as bicycle fuel. But in the long term, if everybody did ride a bike, pedal a generator etc. that excess fuel would soon be depleted and we would be back to my comment that human food is VERY expensive fuel to power machinery.

To those who might advocate that there is a money savings to be realized in better health if people would power machinery, I will say this; that is true to a point. People should eat enough food to power their own bodies, including doing enough excersize to stay healthy. But beyond that, food eating is wasteful. It causes far more pollution to produce a watt's worth of food fuel than a watt's worth of electricity. For that matter, in most cases the amount of energy saved using 'human power' to power a machine will never pay for the cost of the machine, i.e. human powered generator. That generator will need replacement before the realized savings have even reached the break-even point.

My contention is that powering machinery with human power is only sensible as long as the human has excess fuel to burn. Beyond that, and the amount required for optimum health, human power is not economically practical or even environmentally friendly compared to directly burning fossil fuel.