Maximizing Battery Life on a Budget

To start off, I have indeed read the wiki, some forum posts, build threads, etc. I have also done my own research independently, and come up with the following:

Ping batteries provide the maximum value in wh per dollar (48V, 30Ah pack produces a whopping 1.6 wh/$ !!!). If ping lives up to its ratings, it meets or beats everything including a123 after factoring in lifetime differences. Unfortunately, I can only take advantage of this if I have $1000 to spend. Which I do not.

I have $400 to spend on batteries for a starter electric bike. I have chosen this motor system:
http://www.leafbike.com/products/di...w-rear-hub-motor-bike-conversion-kit-613.html

All the reasoning behind my choice of motor system can be found here:
http://endless-sphere.com/forums/viewtopic.php?f=30&t=48202

I want to maximize efficiency. This means I can't be running a battery at its maximum rated continuous current - that would kill both capacity and lifespan. Can someone confirm that this is true?

The system is 48V, and I am fairly firm about that choice. That means the only ping battery in my price range is 48V and 10Ah. It may be found here:
http://www.pingbattery.com/servlet/the-48V-LiFePO4-Battery-Packs/Categories

Is it reasonable that I can run this battery at max for 3 minutes without damaging its lifespan? Should I opt for a less economical lithium polymer system in order to have a longer lifespan? After all, there's no point in spending hundreds of dollars on a battery and then toasting it within a month.

Here is a (polymer, I think) battery performance chart I found for a system that is running at a quarter of the power I will be using on a regular basis:
http://us.itselectric.ca/product_p/48v-lithium-polymer-10ah.htm

The battery appears to be roughly the capacity I am talking about. you can see that the temperature rises significantly for such a moderate load. If this is a polymer pack and it heats up so much, what would happen to a ping at four times that?? I'm guessing nothing good, but I may be wrong. That's what I want to find out.

You could always go lipo and make a 1.6kwh pack for about 600 bucks excluding the cost of the charger and harness. Or for about 300 bucks you could make a 48v 10AH pack out of lipo thats good for up to 200A peak and get an entry level power supply and rc charger.

Although the Ping is a high quality pack - 48V1000W will really tax a 10AH pack. Another option is a Sunthing28 48V15AH pack on Ebay for about $425. Delivery might take up to 2 months (depending on where you are located) but his pack seems to be a solid performer. Have mine for a few weeks now coupled with a 48V 1000W Yescom kit (highly recommend that too for the price!) and have taken it up to 30A bursts. Time will tell longevity but so far so good. FYI this set up gets me up to nearly 30 MPH on the flats and I am 235 lbs and usually carry a 20 lb + pack - not too shabby!

The bike kit looks ok, but your battery analysis is way off. And if you think you can get 52 miles from that lmc 10ah pak, you're dreaming. Well, maybe you can if you weigh 50lbs and only give it a max of 5.6A as they do in their chart. It's just pure marketing BS. The controller that comes with your kit is 30A max. It'll kill a 1C 10ah battery pack in no time. For max lifespan of a 1C pack with a 30A controller, you need a 30ah pack. You can get by with a 15ah pack, but don't expect to get more than 700 cycles out of it unless you never pull more than 15A from it. Cycle ratings for all these type batteries are using less than a 1C discharge. Some are rated at .5C. Check the specs.If you8 only need up to a 20 mile range, there's no better choice than a 10ah 20C 12s rc lipo pack for ~$150. Well taken care of it will last thousands of miles. And pulling 30A from it is nothing.

Yeah, whatever the marketing guys say cut it in half.

48v 10 ah battery can run that kit, but I strongly recomend you sell your platelets or whatever you have to do to get a 15 ah instead.

If you must go with 10 ah, you must avoid full amps as much as possible. Notice the significant difference that I did NOT say avoid full throttle. You can cruise at 25 mph using only about 10 amps of 48v, about 900w or so. But that is no hill, or headwind. Slow down and pedal harder for hills or headwinds.

You'd have to be very carefull how you climbed hills to avoid much use of more than 15 amps, and on stop signs just pedaling for 15 feet before you use full throttle would be enough. You will soon learn to listen to the sound of the motor, and try to avoid letting it grunt under full load. keep it silent, and you are likely ok.

Your range at 20 mph would be at least 15 miles. Closer to 10 miles if you run full throttle. 30 miles possible at 15 mph. Put a mark on the throttle, and just try to ride using 3/4 throttle. Another option would be to modify the controller to a lower amps. But you CAN use all of it for a short time if you need it, so I'd leave it alone and just avoid full throttle on starts and hills. Just use it when you must, and the battery will last long enough to buy a better one later. You should still get at least 2 years if you ride smart.

the problem is that I have to make this battery last five years to justify the investment, or else get a cheaper battery.

Sun Thing Battery has the capacity I need. It should come out to about $400 including shipping.
http://www.ebay.com/itm/LiFePO4-48V...ronics_Batteries_Chargers&hash=item20cc7c3df0

The other choice is to buy lithium polymers. Polymer batteries can handle the current without a sweat, and that might come in handy later. I have a decent 1-4 cell charger already, so I would buy 7 2S packs, since 2s is the only kind that comes in 10Ah sizes, and yields the most wh per dollar as far as I can tell. Then I could probably charge them in parallel without too much trouble. This solution would be lighter weight by about 3 lbs, but I would want to do it exactly right so I don't blow them up. Total cost would be $450 including shipping, so I would order through my local hobby shop instead. They might even beat the online price by a few dollars. Then the cost would be comparable.
http://www.hobbyking.com/hobbyking/...2854_Stampede_Rustler_Bandit_compatible_.html

All said and done, the sun thing battery is STILL a better and safer value because it has 15 AH versus the polymer pack at 10, prices being equal. So the only question left is, can I get away with using a 15AH 2C LiFePo battery and have it last longer than a polymer pack?

Based on what I am reading both here and elsewhere, yes, I think I can get away with buying the sunthing pack and not worry too much about cooking it. what do you think?

Well you can hope for 5 years, but it would be a pretty ,,, er, optomistic one for a 10 ah 2c battery (able to briefly stand 20 amps but best limited to about 15) to last 5 years on a 30 amps controller.

Your best option would likely be the 15 ah sunthing pack. 3 years would not be unusual then, 4 quite possible. 5, well depends on the controller you buy. Again, a 20 amps would be your better choice. Then you can ride any way you want with a 15 ah pack.

Lipo is generally considered a two year lifespan, half the cycles of lifepo4. So it's definitely lifepo4.

Your expectations are not so out of line, just the budget. Compared to bus or car, you'll have a $500 lifepo4 battery pay for itself in about 2000 miles. So consider the second year, and any more you get to be free riding.

I'm on my second pingbattery now, both lasted three years or more, getting lots of hard use. There may be a few out there that lasted 5 years, but three to four years is about average near as I can tell.

I just bought a supposedly new SUN-THING battery from a endless=sphere member. It was sold under auspicies of being a 48v 20 A.H. BATTERY. I had it tested at Hi-power cylces in Northridge. They charged it up and put in on a battery analyst and it came out as around 12 a.h. at best. Just my observation quality control. My next battery will be from PING.

I would think, given your parameters, the many advantages of a power/watthour meter would be of value to your project. You can get a simple meter that will display amps being used, or get a fancy one that will manage it automagically (CA type).

this would help manage the load in different situations, showing excess current loading and too deep of a discharge, both causing shortend life.

any thoughts?

d

Just that he can't afford a Cycleanalsyt. But there are some very cheap watt and volt meters on ebay from time to time. Look in the battery section threads for discussion of them.

But since he's got no money, he also needs to know how to do without one at least for awhile.
Most likely, his motor will make some noise, and learning to ride quieter will keep him in the lower amps. Mostly, it's 3/4 throttle and pedal hard on hills, and 3/4 throttle leaving stops. That should keep him under 15 amps nearly all the time. The motor will grunt more when he pulls 30 amps for sure. And get a 20 amps controller kit, or perhaps cut a shunt in the 30 amps controller making it into a 15 amps.

A wattmeter is priceless though. Particularly, you want to avoid discharging past 80% to help a battery last, along with avoiding big amps spikes. So there is really no substitute for a wattmeter if you want to monitor your depth of discharge. You can watch for the voltage drop with a very cheap voltmeter, but that will tend to tell you when it's 95% discharged with lifepo4. Lifepo4 will show the same voltage for miles and miles and miles, then the voltage drop tells you that you are already riding in the very last mile.

Agree with Dogman - a wattmeter is a very valuable accessory for your "dashboard" - got mine on Amazon for about $20 - shows me AH used during my ride and A & W usage while riding - if I am drawing too much; I can quickly adjust my throttle and/or pedal more to avoid damage to my battery. Would have loved a CA but I too was working on a tight budget and $20 was more than reasonable for the functionality!

I use Watts Up for my battery and now I wouldnt go without using something like it ever again. Its well worth the price I paid for it which was $49.99 shipped through amazon. I rode 36.38 miles today at an average speed of 15.0 mph on a 48v 18Ah SLA battery pack and used 11.008 Ah and 531.9 Wh and the ending voltage was 48.58V. I also have the same motor geee and wes have and the cool thing about this motor is its a 470rpm motor which is the same rpm that my old currie motor is and using its PAS system it netted me 40+ miles on a brand new 24v 10Ah pack but was never able to do it again on new 10Ah batteries. That same currie motor on an 18Ah pack like I have now got me from Newark to Buckeye Lake back to Newark on one single charge at 12.5 - 13 mph which is about 23 miles round trip. It is also about 75% throttle on the motor since the curries top speed for me was 17 mph. Anyhow itd be wise for you to get something that will tell you your energy usage on the battery pack while riding since you could manage your power with it better than without it.

duly noted. I will seriously consider buying some means of monitoring the power being used by the bike.

Also, it may be true that the battery is worth several times its cost in gasoline. It might not! Especially when buying from ebay. By low balling, I am minimizing the risk of experimenting in an area of technology I have never touched before.

Thank you all for your input. I will probably start work on this bike in the summer, and post a build thread on ES with pics 8) .