bretterzsp said:
I'm new to this forum and curious if anyone can answer a simple question that I can't seem to find the answer to. I'm trying to buy a ping battery with the most energy density for a long range bike I plan on putting together. I'm getting a mac geared hub kit that comes with an Infineon IRFB3077 controller that has different FET configurations (6,9,12). I know this controller is programmable and can easily except 60 volts but I would like it to step down my volts going to the motor to around 48v so I get more range instead of speed. I have not used one of these controllers before and I don't know if I just need a cycle assistant or whatever it's called that displays info on the system. Can a controller lower amps AND volts going to the motor or am I only able to lower the current? I planned on getting the 12 FET to be able to handle this battery.
I am assuming you plan to use a throttle. Throttles can turned to a specific degree which will cause your configuration to aim for a specific RPM (which relates to a specific speed). What this means is instead of imagining finding a special way of modulating the voltage, you can instead simply modulate a throttle using your wrist. Magical stuff, right? It gets better.
http://em3ev.com/store/index.php?route=product/product&path=41&product_id=91 This is one of my favorite throttles, buy two. On it, you see a three speed switch built into it. By default the controller you are acquiring will limit the throttles full twist to 50, 75, and 100% depending on where you flip the switch to. This is probably going to be the way to go for you. You can also change the settings within the controller to change where each of these switches limits the throttle to. So if you wanted to change settings of position one of the 3 speed switch to 20%, you could do that.
To make sure you fully grasp what I am saying, this three speed switch doesn't limit how much you can turn the throttle, it's range of motion is always the same, the three speed switch changes what the maximum percentage of throttle you turn to when you twist the throttle as far as it goes. So say you flip the three speed switch to 50% and twist the throttle half way, you will be telling the controller to put out 25% maximum RPM.
Definitely get the cycle analyst(or whatever it's called, who needs to be specific when writing, right?). Either a version 2.3 or 3. Completely worth it. If I was selling someone an electric bicycle, I wouldn't make something like this optional. Using a cycle analyst you can change the maximum power output on the fly. Really useful. Over time I eventually limited my maximum to 300w. Using this I was able to maximize range and still achieve an ideal speed, setting up an ideal(Ideal for me) low maximum power also really helps with preventing lazy riding. The number of important features and ideas fulfilled through a cycle analyst would take a while to explain and would be best known through experience.
You also might consider other chemistries if you are most concerned with energy density. em3ev.com sells packs as well, as I am sure you know, that are far, far more energy dense. Just look at the packs total weight and compare it to others of similar capacity. Maybe there is some reason I don't grasp as to why you want to buy those lifepo4 packs, kind of feels like you are feeding off old information. To illustrate, a 48v20ah lifepo4 pack from ping weighs 9.9kg, a 50v19.3 18650 29e pack from em3ev weighs 5.2kg, cost is pretty similar but energy density for the 29e pack is clearly wildly better.
You should also look closely at the controller you have or are getting. It's maximum voltage input is 60V, a 60v pack has a voltage range that goes above 60v. Using a pack that goes above this specific voltage limit will destroy the controller. In summary, you want a 48v pack with that controller.
One last thing to note, aerodynamics is probably the most important element when concerned with range. You go around twice as far on a watt hour using a fully recumbent bike as you would on an upright. In my mind, recumbent bicycles are like some sort of hidden(but not really hidden, just seems like so few know or care) method for doubling the energy density of your pack(I know energy density doesn't work this way, but you get what I mean). I am guessing that based on the capacity of your pack that you may already know this because you won't achieve that range on an upright unless you are going fairly slow, but it's worth repeating.
