I'm making a little electric powered BMX bike and I'm using a 24V motor that I already have, so what do I use to power it? Due to cost (need to keep it low) lead acid is the only option I think anyway. I could buy 18Ah batteries that are the right size and easily mountable but can't go for very far but far enough. Or I can buy a couple of car batteries which are massive for less but go twice as far. What do I do?
What's wrong with two 12v motorbike batteries? Much smaller than car batteries and might work just as well
They're not as common and so cost about the same as a car battery, but with a car battery I can get a lot further miles out of them.
How about batteries from golf trolleys/carts/mobility scooters? Not sure about sizing but they may fit the bill.
how much is the rated ampere? basically, just check how much the motor uses and choose a battery accordingly. usually car batteries are rated with the Ah, ampere hours. let's say it's rated 60Ah (quite common), this means it could run a one ampere device for 60 hours on a full charge (assuming that the battery is rather new). a motor of that size probably draws around 4.5 amperes on full load. that combined with above battery would give you a range of approx. 267km (166,7 miles) between charges. you should look into using batteries from golfcarts since these are usually 24v. otherwise you'd need step up the voltage in order for you to run the motor att full speed.
Ahh you see this is where it gets interesting, batteries don't actually work like that! You can have a 10Ah battery and it will have different capacities depending on what you pull from it wether it be 10A or 1A (or whatever value you like), 10Ah is just the maximum it can hold at a given constant current draw say 1A, at 10A it may only be able to provide 8Ah! This is my other option but they are a lot more expensive you see. I think I might go for the car batteries as I can get them locally and don't have to pay postage! Thanks people!
sure, if you're talking 'bout real life. i, however, choose to live in a perfect world where theory rules practice, where there are no such things as losses and dissipation, only pure "mathness"! but sure, you'll always have losses, dissipation, changing weather conditions and whatnots. car batteries should do the trick (or if you don't have enough room, mc batteries). thought about implementing a recharge function? (would be rather cool to recharge the batteries a little while going downhill, although you'd loose some speed).
To begin, I will redirect you to the Endless-Sphere forums, it is the highest concentration of knowledgeable E-vehicle people I have found on the internet. So go post your question over there for them in the e bike forum. Be sure to do plenty of searching through the forums yourself before you ask your question, since there is a very very good chance that all of your questions have been answered previously, and if you don't their response to you, will largely consist of links to previous topics. But once you have done some searching around don't be afraid to ask them some questions. http://endless-sphere.com/forums/index.php Choosing your batteries is a rather complicated matter, and don't be so quick to resort to Lead batteries so quickly. A nice LiFePo4 pack which gives the highest amount of recharges, the most stable chemistry, a high C rating, and a good sized capacity can cost as little as 300-400 dollars for a small bmx bike pack. When your looking at batteries there are a few important things to consider: 1. Cost (pretty self explanatory) 2. Weight (Lighter the battery for the same power = Longer the range and faster the acceleration) 3. C rating ( This is the discharge rate of the battery. Take the Amp Hour rating and times it by the C rating, and this will give you either the Continuous discharge rate or the pulsed (momentary) discharge rate. 4. Amp hour rating (This is a measure of the amount of energy stored in the battery) 5. Nominal Voltage rating (This is the most common method of measurement. And is the measure of the median voltage over the batteries discharge cycle, a 12 volt nominal voltage battery will vary anywhere from 13-14 volts fully charged, to 10.5-11.6 volts discharged. I have a lot more information to give you, but alas it is late and I have to get up rather early tomorrow morning. So go to the forum I posted earlier, and poke around the battery forum a bit. And if you have any questions let me know and I'll do my best to answer them, or point you in the right direction. I am rather confused as to how you went from amp hours, to distance... but regardless. If you ran an e-bike at 4.5A with a battery voltage of 24 V, That would give you 108 Watts. That amount of power might just barley be enough to get him rolling slowly on a flat surface. so since he can run for ~13 hours on a 4.5A load, he could probably get ~13 Mile range going about 1-3 mph if the entire route was completely flat. ( your speed dies off the further a battery is discharged since the voltage drops as the discharge level gets higher. ) (less volts or amps = less power)
i figured he'd do a running start by using the pedals, then maintaining the speed using the motor. a quick calculation was done where i assumed that the speed to maintain was 20km/h, using a motor which draws 4.5A from a 60Ah (not real life, i know, but it's way easier to do number crunching in your head when your assuming a perfect world) battery gives a run time of approx 13 hours giving a range of 266 km. the voltage drops over time, of course, but he could maximise the amount of voltage that he uses. maybe he could implement a giant joule thief .
