Lithium battery question...

[deacon]

You guys who use lithium batteries and have no axe to grind and no dog in the fight answer a couple of question for me please.

Form my screwing around with nimh I have come to the conclusion that it releases it's charge much differently. When you hit the throttle on a lead acid battery you get it all at once and thats all there is to it.

Nimh batteries which I have built way, way over the factory ratings deliver a comparable amount of energy, but in a different way. It just feels differently. It seems to get to speed more slowly but does deliver the same speed level once it is there. Is this also true with lithium batteries.

On hills that the sla battery pack will climb the nimh pack needs help, it just doesn't seem to dump energy like the sla does. Let me know I'm curious.

 

[Kevlarr]

From my understanding it really depends on the C rating of the battery. If you only have 10C batteries you have to be pretty careful about how many amps you're pulling out of them, get some 30C and you can draw off of them a lot harder.

Here's something I pulled off or Wikipedia:

Cell capacities are rated in ampere hours (A·h) or milliampere hours (mA·h). A 1000 mA·h battery is the same as a 1 A·h battery: both will supply 1 A for 1 hour. The C rating commonly associated with lithium ion batteries refers to the maximum current supply capability as a multiple of the cell's capacity: for instance, a 1 A·h, 20C battery should be able to supply 20 A continuously without damage. A useful way to calculate how long a battery will last for under heavy load is to multiply the A·h capacity by 60 to give ampere-minutes, so a 1 A·h battery is a 60 ampere-minute battery; to calculate how many minutes the battery will last, just divide by the average current drawn (e.g. a 10 A average current draw will mean that a 60 ampere-minute battery will last for 60/10 = 6 minutes).

So in other words the C rating is the safe amp draw capacity, multiply the Ah x the C rating and you have the "safe" continuous draw amp rating.

Here's a generic discharge curve for a li-po cell

As you can see it's pretty constant throughout the useful charge of the cell.

Something you should check out Deacon is the next new battery technology, Nickel/zinc

The Next Generation Battery | PowerGenix

A friend is very interested in them for his E-bike because they are a very low resistance cell. He showed me a report were they are pulling 15 amps out of a AA battery!
You'll appreciate this, there's a u-tube video out there where a guy is testing nickel/zinc cells in a flash, he actually had the flash go into thermal shutdown for the first time ever!

 

[motorbiker]

I tried nimh and sla on the ezip with a brushed motor

sla batteries can dump way more amps right now ! Makes for a torquey setup !

I'm thinking it would cost a lot to make a li ion pack that would be able to match the sla.

http://i180.photobucket.com/albums/x218/biodiesel_2007/Picture002.jpg

 

[deacon]

See thats where I am. I am in a area with lots and lots of hills. I can use a slow discharge battery fine, if I am willing to pedal assist up the hills, but I don't always want to do that. If I invest five hundred bucks in a set of batteries and have to pedal assist to get the bike started or to help it up a hill, I am going to be a very unhappy camper.

I can ride with the nimh I built, as long as I am willing to help it out here and there. I don't mind doing that on the bike trail. It's what I do for exercise. If I'm going into traffic to go to the bank, or to the home depot, I don't want to be forced to pedal assist just to get up the big hills. With a fresh sla it might slow a bit, but it will pull most anything around here.

If range is a factor of pedal assist, I'll just pull more batteries on my trailer and pedal assist with it. I need the trailer for balance anyway.

 

[Kevlarr]

Since you're using a trailer anyway have you ever put any thought into maybe using a couple of deep cycle marine batteries?

They're built to go though heavy charge/discharge cycles plus having 80Ah and the ability to occasionally draw 500 amps should offset the 80 lb. weight of a pair of them.

:edit:

Or maybe a golf cart battery.
http://www.apexbattery.com/mk-8au1-...m=shopping+engine&utm_campaign=googleproducts
It's about half the size and weight of a marine battery.

 

[deacon]

I need three but actually that's a good idea except that the controller would shut down at low voltage not low amps. I have no idea how that would work out. I am getting ready to test the nimh with the 12 speed bike to see how much pedal assist it needs. Probably too much but hey got to find out. I would never forgive myself if I didn't.

After that, I will probably piggy back it with a new 12ah set of sla I have coming. Batteries are the bane of my existence. I absolutely love me ebikes both of them, but the battery thing makes me crazy. When these guys talk about the twenty miles they get with a lithium battery and I do the math they have to be pedal assisting a lot on their aluminum bikes.

The ah and the miles they claim don't work out unless they are drawing tiny amounts from the battery over all. If so they don't live in a place called high point nor do they mostly ride the bike like I do.

 

[motorbiker]

A brushed motor can draw a lot of amps when starting from 0 rpm's.

A non brushed motor with a good controller will start off easier and save battery power.

Distance has a lot to do with driver weight too.

When they advertise how far an ebike will go on a charge the numbers will most likely be different for every driver.

I am learning how to go farther on a charge.

 

[zabac70]

Nickel/Zinc battery technology is old stuff. Maybe that is a new approach (or they've changed something , like electrolyte or design...). It is very similar to NiCd technology.

 

[deacon]

oh yeah I also weight a bit more than a hundred and twenty five pounds lol I guess I will just load my trailer up with batteries and ride into the sunset. Wonder how many alkaline I could fit in there lol...

 

[motorbiker]

oh yeah I also weight a bit more than a hundred and twenty five pounds lol I guess I will just load my trailer up with batteries and ride into the sunset. Wonder how many alkaline I could fit in there lol...

Me too ! I have lost about 40lbs though.

Now all my bikes are faster and will go farther !

 

[ferball]

I could be wrong (as usual) so electrical engineers feel free to ridicule me. When I was researching batteries for my 6v chargeing system I discovered that many of the newer rechargables aka Lithium and I believe also the NiMH have some circuitry built into the battery to prevent over charging, and to slow the "loss of charge" so it would stand to reason that this circuitry might try to smooth out a sudden spike in amp draw caused by accelertation. Just a thought, and it could be wrong.

 

[deacon]

I lost 60 two years ago and so far it hasnt found it's way home. I feel a heck of a lot better better but the bikes don't lol

Mine don't have the bms system it's just cheap batteries and they act like it. But I do think the drain is more level than with sla. Where I live, i need the burst more than anything to kick up those hills.

I rode the bike with the battery pack and it still is awful. I will wear the batteries out as a hybrid with the sla pack. They probably won't last long that way but so what, they are already paid for and pretty much useless on their own. I'm not sure exactly how they react with the sla batteries but they do make a difference in how the bike performs. Do they bring any range to the table? I'm not sure, but they seem to give it a little more push and what else am I going to do with them. I don't think even syrup would make them taste good. Maybe chocolate cake frosting would though

 

[SANGESF]

NIMH IS OK.. SLA IS BETTER (CHEAPER) Lithium is the best........
Lithium will hold it's FULL power until the very end.

Also, 36v of lithium is really 38.4 (12x3.2) as opposed to SLA which is 37.2 (3x12.4)
In the long run, NIMH, SLA and Nicard are all Lower voltaged. You will get more power and distance and speed from LiFePO4 than all the others.

In the long run LiFePO4, costs the same, because it lasts so much longer (usually 3x's or more) then all the others.. (Except for the other lithium types but those can be dangeroush with over drawing power or putting back power into them)

 

[jdcburg]

I started off with 2 12V 12ah SLAs to power my 24V 350W brushed Unite motor. I bought a 2nd set after I accidentally overcharged one. I converted to a 2 pack of 12V 20ah Lithium Iron Phosphate (LiFePO4) packs. As SANGESF says, they put out higher voltage. I usually start out at around 28V and they stay at around 26V for most of the charge. Also, they run longer before they start to sag. Yes lead will put out a lot of amps in a hurry, but I found even a moderate steady draw takes them down quickly. Everyone has had that experience with a car starter - it starts off quick but slows right down if the motor doesn't start. Then you let it rest for a minute and it comes back again but for a shorter period. Pretty soon it's just dead. Today I went 27 miles on my lithium pack, using 16 of the 20 ah available. It climbed the last hill to my house like I started off. It started with 26.88 and ended with 24.4V. YMMV but I like them - jd

 

[deacon]

how much did you pedal the bike and how is the geography where you are....

Here is my problem if you rode 16 miles and averaged 16 miles and hour then you would have been drawing only 16amps average. if you have four amps left. I can't ride my bike on an average of 16amps where I live and how I ride it. But every time anyone tells me about about litho batteries its twenty miles and twenty miles an hour. If that is the case they are running their bike on an average of twenty amps. I just can run mine on twenty amps I tried to run it on 25amps and it just wasn't enough for me personally. See my problem.

I know it will pull forty amps but it can't pull forty often if you are going twenty miles at twenty miles an hour. So either you are doing a lot of pedal assist or the ground is flat where you live or the battery does not adhere to the math profile.

 

[jdcburg]

I use a Turnigy WattMeter and a digital speedometer. I pedal assist quite a bit but when I broke a wire and had to pedal home the other day, I realized I don't really help all that much (LOL) I keep all my readings on a spreadsheet. I started after I got the Lithiums so I can't really compare them to the SLAs number for number. My peak draw was 27.97 amps today. That's 1.4C on the 20ah pack, which is rated 2C (40 amps) continuous and more burst (maybe 5C). Peak watts - 644.1. Avg speed 14.36mph. Top speed - 30.83 (downhill). I live in a hilly part of Massachusetts. I looked on a site called MapMyRide.com and found out on today's ride I had an elevation change of about 450 feet over the ride and the hills ranged from 4-6%. BTW, the 20ah Li pack weighs 13.2 lbs, while the 12ah lead weighed 16 lbs. The most I ever went with lead was 15 miles, and they were tired! Nearly twice the range and better power with less weight. They are not perfect. I will try to report some of the down side tomorrow, but they are definitely worth it in my book - jd

 

[motorbiker]

If I give the sla batteries a break and pedal I get more distance for sure.

At least on an ebike you can pedal and give the batteries a break now and then.

My ezip has a 450w at 24v motor and uses 24V 10 AH sla batteries.

The new Ezip setups with li ion batteries have motors rated at 250W.

With li ion http://www.currietech.com/currie-technologies-ezip-eco-ride-for-women-electric-bike.php 15 to 22 miles (Rider Weight, Rider Input and Terrain Contingent).

With sla http://www.currietech.com/currie-technologies-ezip-trailz-for-men-electric-bike.php 15 to 22 miles (Rider Weight, Rider Input and Terrain Contingent).

both have batteries 24v 10 ah.

The motors cost about the same so why did they do this ?

 

[deacon]

I have found that true when i ride the bike trail but in traffic i tend to stay on the throttle.

 

[SANGESF]

how much did you pedal the bike and how is the geography where you are....

Here is my problem if you rode 16 miles and averaged 16 miles and hour then you would have been drawing only 16amps average. if you have four amps left. I can't ride my bike on an average of 16amps where I live and how I ride it. But every time anyone tells me about about litho batteries its twenty miles and twenty miles an hour. If that is the case they are running their bike on an average of twenty amps. I just can run mine on twenty amps I tried to run it on 25amps and it just wasn't enough for me personally. See my problem.

I know it will pull forty amps but it can't pull forty often if you are going twenty miles at twenty miles an hour. So either you are doing a lot of pedal assist or the ground is flat where you live or the battery does not adhere to the math profile.

I don't understand why you would pull 16amps constant....
On my bike 36v, if i'm doing 20mph, i'm pulling at most 12 amps... on pulling up to that speed it will be a 16-18amp draw, but once going 10-12 amps.

My bike with me AND all my stuff is a total of 300+lbs and only draw a small amount.

If you got a 20ah lithium battery, i'm SURE you could do 20 mph and get at LEAST 25miles out of it.

IF you have a motor/controller, that can do 36/48v conversion, you're much better off at 48v and will pull MUCH less amps.

 

[deacon]

never mind lol we seem to be talking about different things entirely. I think I will stick to my sla but thanks for all the help