Need Help Calculating Motorcycle Charge

I'm looking into the **broken link removed**. It says that at 70 mph it will deplete its 6 kWh battery in 43 miles, which is about 36.8 minutes of run time. I'm trying to figure out if I would be able to put a gas generator I have on it to give it more range.

The bike has a 6kWh/60V battery, a 1kW charger (that takes 6 hours to charge it fully plugged into the wall 110V), and a 420 amp "controller" that meters the flow of electricity to the motor.

My generator puts out up to 55V of AC or 18V of DC power at 500 rpm. The most amps I've gotten out of it is 60 amps into a 12V battery, which is about 700 watts. The generator is home made, so there's not really any factory output numbers to use, just my measurements.

I would really appreciate it if someone on here could help me figure out if my generator would make a difference in range or not at that speed.

If the bike's battery is a lithium type, I wouldn't try anything without some manner of voltage/current control between it and your charger. Lithium batteries are notorious for catching fire if subjected to excessive charge/discharge rates or voltages. Hence the regulator already in the bike's electrical system.

I can't imagine the batteries are lead/acid due to the weight penalty they represent.

That said, you'd first have to jack up the output of the generator to no less that 60 VDC (to at least equal the bike's battery level). Then tie it into the bike's electrical system (not an easy task).

Other than that, you'd be augmenting the battery with the 700 watts (minus any power used to jack up the voltage output level), i.e., 6000/700, or approximately, 12 %.

This does not take into account the additional weight of the generator and fuel.

At 70 mph you are going a mile in 0.85 minutes (60mph/70mph), so 43 miles would be 36 minutes (.85*43). 36 minutes to flatten a 60 kwh battery is (60m/36m)*60kw = 100 kw!

100,000 Watts. Gee, what a nice round number. So very round it makes you wonder if it was a ballpark figure. Anyway, as you can see - your generator is 700w vs. 100,000w, or 0.7%. Doesn't seem to be worth the effort.

Thanks for the help guys.

Duffy, your numbers are a little off because it's a 6kWh battery, not 60kWh, although I wish it was. That said, your numbers would go up to a 7% increase at 70 mph, which is initially another three miles. My generator could use some tuning as well and I bet I could get the numbers higher.

Cowboybob, in order to jack up the output to 60V DC, would I be able to use some sort of device? Like an amplifier or something? (please forgive me, I'm new to this) Or would I have to improve the performance of my generator to get those numbers?

Either way, I feel pretty optimistic now after both your help, thanks again.

You said the generator puts out 55v AC, right? What frequency? Boosting the voltage might be as simple as adding a transformer, higher frequencies use smaller transformers. What kind of generator is this?

duffy said:

At 70 mph you are going a mile in 0.85 minutes (60mph/70mph), so 43 miles would be 36 minutes (.85*43). 36 minutes to flatten a 60 kwh battery is (60m/36m)*60kw = 100 kw!

100,000 Watts. Gee, what a nice round number. So very round it makes you wonder if it was a ballpark figure. Anyway, as you can see - your generator is 700w vs. 100,000w, or 0.7%. Doesn't seem to be worth the effort.

Click to expand...

It's a 6 kWh battery, not 60.

So to use that in 36 minutes means that you are using around 10 kw or 15 hp, which sounds a lot more sensible for a motorbike doing 70 mph. I think that I remember a figure of 25 hp at 70 mph for some car.

The 700 W generator is 7% so still not much use when riding, but it would charge the battery in 9 hours.

By simply rectifying and filtering the raw 55VAC output of the generator (which should give you in excess of 60VDC), then running that through DC voltage and current regulators set appropriate values, you'll should then be able to use it to charge (augment) the bike's battery system.

That said, in all honesty, I'd recommend against attempting to augment the power available on the bike. Again, lithium batteries are extremely sensitive to charging characteristics and not a little dangerous as a result. I know that manufacturer has modified the basic Li-ion battery they use with some "salts" that reduce fire hazards and overheating, but they have not eliminated them. and there is still the issue of mating the generator to the existing electronics of the bike.

And add into the equation the additional weight of the generator and its mounting system (something other than bungee straps, I would think), and add the effects on center of gravity and general handling characteristics, it most probably would make the bike unacceptably unstable.

Its a great idea you have, sort of a two wheeled "Prius", but the practicality of the modification gives me pause.

Here's an idea. You might get with the manufacturer and see if they can modify the electronics to allow "passive" charging of the battery when braking. One of the reviews of the bike mentioned that braking system felt "soft", which could be improved by making the motor a generator while braking or coasting (just as the Prius does).

But is IS a really sweet idea.

Ever think about building your own generator using a high-powered model engine? For instance, a ZDZ80B2RV is less than a foot wide and 4" tall -

- but it develops over 8 hp. **broken link removed**
That's about 6kw right there.

A 53cc twin boxer engine is considerably smaller, a third the price and develops 5.5hp - 4.1kw.
A 4kw motor/generator is under 6" diameter and less than a foot long. Not sure what your plans were for mounting the generator, but another advantage to building it yourself is that you might more easily integrate the components into the frame.

You should be able to cheat the battery some by limiting the generator output voltage to what ever the battery's no load voltage is. As the drive motor loads the system the battery voltage will dip a bit letting what ever the generator has available for power to be taken first.

If it was me and I was looking to make a compact high power engine driven power booster system I would start with a slightly modified commercial alternator reconfigured for 60 volt output being directly driven by a small high powered engine.

I have worked with many Leese Neville commercial alternators and I can say with good certainty that th they are very easy to reconfigure the stock windings to put out well over 60 volts on the output and still carry up to several KW's of usable power at that level.

Their regulators are rather easy to cheat or replace with a custom PWM type design that can work with the higher than stock output voltage but still keep the rotor voltage from going above the stock 12 or 24 volt input it was designed for as well.

Its just a thought.