Small, short-range battery??

[c_4]

Is there a small 36V battery that has enough capacity to run an eZee geared hub up a single hill, about 600m at up to 15% grade.

Here's the situation: I bike to work with the 36V 10AH eZee Li-Ion battery, and it works quite well. Our office complex is located on top of a hill and the geared motor gets me up there easily. Great, but once in a while, I don't want to bring lunch or eat in our cafeteria, and if I want to go to lunch, the closest mall is about 2 km away, at the bottom of the hill. Going downhill is not an issue obviously, but going back uphill is sheer hell without a battery.. I've got a good lock for my bike and the motor is a rear hub, so I'm not too concerned about that, but if I'm going to the mall, I don't really want to carry my big battery pack around, and I definitely don't want to leave it on the bike, so this is where my request comes in: I'm looking for a small battery pack that could be easily carried around.. It doesn't have to have much range- as I mentioned, the mall is only about 2km away, and most of it I don't actually need the battery for, just the last climb up, and I don't have to be able to do full speed with it, but it should be able to help me back up the hill..

Is there anything out there that would work? What springs to mind immediately are perhaps cordless tool packs- there are a number of 24-36 volt tools out there, but I don't think any of these could sustain the roughly 30A draw necessary to power a bike up a steep hill..

 

[swbluto]

Yep, I was going to recommend cordless drill packs. If you're battery savvy, take them apart and build your own custom pack from the cells - I would highly recommend the a123s from the dewalt batteries. If you're not, you can still hook multiple batteries together in parallel in their stock cases to get the amps you need using shottkey diodes.

For your application, I might recommend 2 DC9360s, a dual common cathode Schottky diode and a heat sink to bolt it to. The last two can be found at a place like Digikey.com or Mouser.com. Also, it seems that the Bosch fatpacks are an incredible deal and you could probably get the amps you need with 3 or 4 or them. You'd need two "dual common cathode Schottky diodes" for that.

 

[Russell]

You don't need diodes to use Bosch Fatpacks in parallel but they aren't the smallest or lightest batteries around however they are definitely cheap and easy. They don't have a BMS so you rely on the controller's LVC to keep the pack from going too low. Charging is easy with a standard lithium charger tweaked to around 41V or use a Bosch charger. I use a three-pack http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=7569&start=75#p147245 but guys have run on one http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=7569&start=165#p163546

The lightest solution would be to buy a couple of cheap high C-rate 5S 18.5V LiPo's and put them in series. Of course then you have to buy a balance charger, or two if you want to charge both at the same time. Once again there is no pack protection other than the controller's LVC circuit though you can buy modules which connect into the balance charging plug to alert you of a cell under-voltage condition.

An expensive solution but a compact one is to buy a high power 37V LiPo pack with BMS like the ones from Batteryspace.com which are capable of 40A output. http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=4035

-R

 

[swbluto]

You don't need diodes to use Bosch Fatpacks in parallel but they aren't the smallest or lightest batteries around however they are definitely cheap and easy. They don't have a BMS so you rely on the controller's LVC to keep the pack from going too low. Charging is easy with a standard lithium charger tweaked to around 41V or use a Bosch charger. I use a three-pack http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=7569&start=75#p147245 but guys have run on one http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=7569&start=165#p163546

If they don't have a BMS, then that would indeed work. But... if they don't have a BMS, what prevents them from over-discharging in power tools? Or wait, it probably has an LVC and it isn't affected by reverse polarity and back currents.

 

[pwbset]

A single Bosch fatpack will deliver 30A sustained, but you have to make sure your controller LVC is lower than 29v or you'll trip everything. Under full throttle I'm slurping ~1,200 watts from a single fatpack, but voltage sags <30v. As far as LVC I just stop using the fatpack when the resting voltage is around 30v. This pack has no BMS (and I'm guessing any LVC is in the tool or uses a pin I'm not using) and will let you drain down to death so be careful. I've taken the pack down to ~20-22v under load and that was a good warning to pay attention. I have no doubt cycle life is being destroyed the way I'm running this pack, but for $45 you can't beat the price for around 70-80wh of high amp madness. And you should be able to get 600m out of it no problem.

 

[chet]

I like my Golden Motor LiFePo 36V 10ah. It slides in the rack and locks with a key. It has a handle to carry.
Why not have a 2nd battery to charge at work and 1 to charge at home?

 

[GTA1]

You are bringing up a very important point, which is that a high valued, relatively portable package (battery) is a ripe target for theft or vandalism.

I would like to hear more from people who have had their e-bikes / batteries, etc. stolen / damaged / vandalized.

It seems to me where I am, there is a much lower threshold to such activities compared to stealing or damaging a motorcycle or car.

 

[billvon]

You are bringing up a very important point, which is that a high valued, relatively portable package (battery) is a ripe target for theft or vandalism.

Had my TF750X stolen once, but was recovered with secondary battery intact. Very few people know what the battery even is, so the odds of it being on the short list of a bike thief are pretty low.

 

[swbluto]

You are bringing up a very important point, which is that a high valued, relatively portable package (battery) is a ripe target for theft or vandalism.

Had my TF750X stolen once, but was recovered with secondary battery intact. Very few people know what the battery even is, so the odds of it being on the short list of a bike thief are pretty low.

Indeed. E-bikes will have to become more substantially more popular for the average bike thief to recognize that it's a battery and its subsequent value.

 

[miro13car]

I don`t even think about leaving my equipment loaded ebike for 1 minute not attended.
If I cannot push bike into shop I don`t use that shop.
Some shop like Safeway, Home Depot don`t care

 

[c_4]

I like my Golden Motor LiFePo 36V 10ah. It slides in the rack and locks with a key. It has a handle to carry.
Why not have a 2nd battery to charge at work and 1 to charge at home?

You misunderstood my query.. It's not about carrying the battery or its capacity/range or lack thereof.. My existing 10Ah battery pack is plenty for my commute, it's not huge, but it *is* a bit bulky and heavy to have to carry around if I go down the hill for lunch at the mall, and I don't want to leave it attached to the bike for fear of theft (I'm not too worried about the motor because it's a rear hub and between the chain and torque bars, and the bike lock through it, it's not coming off without some effort, and the motor is cheap to replace compared to the battery).. If it weren't for the hellish uphill climb back up to the office afterwards, I would just bike down and back manually, and leave the battery in my office, but that hill climb, although fairly short, is enough that if I didn't have the electric motor, I would not be biking to work at all- it's just too much effort first thing in the morning..

What I was asking about was whether there was available, a very small battery pack, something that was either cheap enough that I wouldn't worry too much about leaving on the bike, or if I decided to take it off, small enough that it's easy to carry and unobtrusive, and since I'm not going far, it would have just enough juice to make it back up the hill after lunch.. This would be in addition to my regular big 10Ah battery, which I'd use for the trip home..

Those Bosch packs are reasonably inexpensive, so I might give one of those a try.. I was mainly concerned about whether something that small could source the 20-30A needed by the motor for the climb up hill..

 

[swbluto]

There are lipo packs which are fairly light and somewhat cheap. For just a short jaunt, I'm sure you could well with that (Like, look for a 5 Ah 10C version). The only other thing is that you have to source an special extra charger and LVC, if you wanna protect your investment - the higher powered chargers are definitely not cheap.