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| Thread ID: 80375 | 2007-06-20 11:22:00 | any electric motor experts out there? | motorbyclist (188) | PC World Chat |
| Post ID | Timestamp | Content | User | ||
| 561087 | 2007-06-20 11:22:00 | would a 24V DC 2.1 KW winch motor have any issues being used on a small bike? i'm not sure if they're designed for variable speeds or not, and i don't really want to invest in something i can't use so some knowledge would be appreciated:) |
motorbyclist (188) | ||
| 561088 | 2007-06-20 13:34:00 | Ok, to start with it's 24 volts . Most bikes are 12 volts, so you are going to need two 12 volt batteries to run it . Then you will need some means of charging said batteries - not to mention the weight factor . Next, it's rated at 2 . 1 kW . That's 2100 watts . Using round figures and assuming an efficiency of around 80%, it's going to draw 100 amps under load . That's a LOT of current . You will need HUGE cables to run it . Think welding cable . This all adds up to a lot of weight and a lot of power . The winch won't be able to pull anything of substance as you will end up dragging the bike along first . The only thing it would be useful for perhaps is pulling the bike out of a sticky situation . There are plenty of smaller winches rated at 12 volts, much lighter and lower current draw that would be more suited to a bike, if the above idea is in fact your intended application . |
supertrouper (6665) | ||
| 561089 | 2007-06-20 20:59:00 | Propulsion motors are pretty specialised, that means expensive. If the motor is used to propel the bike, the efficiency of the motor will be of concern. You might consider the duty cycle of a winch motor (A short burst with a prolonged cooling period) compared with the proposed use for powering a bike - a burst of high power followed by prolonged running at somewhat reduced power. Then there is the design life, you could probably use all the annual usage of a winch motor before the morning was decently started. It's favourable features appear to be price and availability plus the high torque at low RPM. (Most users of disability scooters would be pretty infirm, have you considered hijacking? Once you have whipped out the motor and controller, they couldn't chase you.) |
R2x1 (4628) | ||
| 561090 | 2007-06-20 23:39:00 | Ok, to start with it's 24 volts . Most bikes are 12 volts, so you are going to need two 12 volt batteries to run it . Then you will need some means of charging said batteries - not to mention the weight factor . Next, it's rated at 2 . 1 kW . That's 2100 watts . Using round figures and assuming an efficiency of around 80%, it's going to draw 100 amps under load . That's a LOT of current . You will need HUGE cables to run it . Think welding cable . This all adds up to a lot of weight and a lot of power . The winch won't be able to pull anything of substance as you will end up dragging the bike along first . The only thing it would be useful for perhaps is pulling the bike out of a sticky situation . There are plenty of smaller winches rated at 12 volts, much lighter and lower current draw that would be more suited to a bike, if the above idea is in fact your intended application . yeah, i know about batteries etc, i mean to drive the bike by electric power rather than petrol . perhaps i should've been more clear |
motorbyclist (188) | ||
| 561091 | 2007-06-20 23:42:00 | Propulsion motors are pretty specialised, that means expensive. If the motor is used to propel the bike, the efficiency of the motor will be of concern. You might consider the duty cycle of a winch motor (A short burst with a prolonged cooling period) compared with the proposed use for powering a bike - a burst of high power followed by prolonged running at somewhat reduced power. Then there is the design life, you could probably use all the annual usage of a winch motor before the morning was decently started. It's favourable features appear to be price and availability plus the high torque at low RPM. (Most users of disability scooters would be pretty infirm, have you considered hijacking? Once you have whipped out the motor and controller, they couldn't chase you.) thanks that was what i was concerned about. looks like i'm back to getting a motor from an electric moped (or visiting the local retirement village:lol:) |
motorbyclist (188) | ||
| 561092 | 2007-06-21 05:25:00 | The winch motor is probably a bit too powerful. That's a couple of HP maximum. However, it doesn't pull 2.1 kW all the time. It pulls enough power (current) to overcome the resistance. For a bike probably 50 to 100W would be all. But without a decent control the bike would get faster and faster.. Scary. The 24 V is not a problem. It's watts you need. Higher volts means lower current for the same power. (Many battery powered scooters use 24V -- two 4Ah 12V gels). A reasonably fit cyclist can maintain about 100W for a reasonable time. So a motor with a maximoum rating of 150W or so would be fine. The 2.1 kW one might be a bit heavy, and it might have a gear reduction to make you travel v e r y s l o w l y. |
Graham L (2) | ||
| 561093 | 2007-06-21 06:52:00 | ok, by bike i mean small motorbike, not a pedal bike. i understand power=current*voltage, and i know the 2kw is a bit overkill but it is equivalent to the petrol engine that it is replacing. crappy chinese mopeds are about 600w and reach 30kph while the decent european ones are 2kw and are actually ridable, which is about equal to a 50cc two stroke or 100cc 4 stroke petrol engine. my understanding is that the maximum torque is at 0rpm and max power at max rpm. the winch motor spins at 1700rpm, so i'll need to gear it down which i've already sussed. as for voltage it's batteries that are the concern, i want to keep the number of cells as low as possible for simplicity, likewise i don't want an AC motor because i'll need an inverter and controller, which i plan to experiment with in a second project really the only problem is finding suitable engine, which is why i'm asking about the winch motor because i was worried i'd kill it or it wouldn't perform as i want it to. |
motorbyclist (188) | ||
| 561094 | 2007-06-21 08:13:00 | as for voltage it's batteries that are the concern, i want to keep the number of cells as low as possible for simplicity, likewise i don't want an AC motor because i'll need an inverter and controller You will need some electronics for throttle control anyway, which fundamentally will be at least a switching unit to provide variable mark-space pulsed DC to control power and speed. The motor power rating is actually somewhat unimportant at this stage, so long as it has enough power at maximum demand. Like a 500kW V8, it will only be asked to generate full power at full noise, the rest of the time the V8 is idling along at sufficient power to maintain cruising speed, and that could be 50kW or less around town. Cheers Billy 8-{) |
Billy T (70) | ||
| 561095 | 2007-06-21 08:14:00 | Sounds like re-inventing the wheel or (in your case) fire . Just being silly here, where do you think you'll get sufficient electricity to run this moped? Hola! ¿Es tu loco? You can conceivably drive anything from a roller skate to an ocean liner with the escapement of a pocket watch . . but that's just silly too . (And it sure ruins the watch) . I think I'll convert a rather neat formula from a real equation to MY personal equation and show how it fits here: E = I - R § where E is the energy output by a motive device (electric motor in your case) . § where I is energy input from (again, in your case) a battery pack . § where R is the resistance and therefor motion lost to inefficiencies and waste (in your case) in the form of heat and friction and possible immolation of yourself, the moped and whatever field of dry weeds you land in . I suggest if you want to have fun disproving the laws of conservation and propulsion, then have at it . . I did it once too when I was younger and less educated (read: school of hard-headed persons) about perpetual motion and free energy from the tension of the rubber bands in a golf ball . (Confession time here: I try to create perpetual motion all the time when I trout fish . . . did I mention that I am going on a TROUT SAFARI soon?) I surely don't want to stifle an adventurous mind . . but this project is truly a dead-end unless you can find some really l-o-n-g extension cords so you don't have to carry (X³) number of batteries with you on a moped . . . . and/or/also set yourself or clothing on fire from a 5% duty cycle motor running at high amps for 100% of the time . . . . however long that turns out to be! Can I suggest that all trials and road-tests be done downhill toward a lake or river for refreshment value and the fire extinguishing properties of water? |
SurferJoe46 (51) | ||
| 561096 | 2007-06-22 03:27:00 | You need a controller, anyway, and the higher the voltage the less current you are switching. The fewer the cells (voltage) the lower your overall efficiency. "Simplicity" in the battery (few cells) is the last on the requirements list. If you want a couple of kW, you're talking about making a switch which will handle (and break) a lot of amps. At 12V that's something about 200A. 24 V motor is a good compromise (you don't want the "fun" of switching an inductive load with high voltages). Fractions of ohms in wiring, and forward voltages of switching devices add up to significant fractions of volts (losses) at high currents. The "toy" mopeds you don't like do have the advantage that they don't need registration, WOF, and other expensive things. I'd check up on the requirements for your grunt machine before you spend too much money. ;) |
Graham L (2) | ||
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