Electric trail bike

[DaBit]

Aren't these cells handier to assemble a pack?
http://www.ev-power.eu/index.php?p=p...lls-%283.2v%29

I used the 200Ah cells in a project and they seem to hold up fine. Cells are from Thundersky.

[Tweaker]

Originally Posted by UngaWunga

Have any links on sites where I can read up on what's needed?

http://www.diyelectriccar.com/forums/
Youtube


To the OP, A123 is now selling 20ah pouch cells to the public. www.mavizen.com who also sells conversion kits, There are plenty of other battery options as well.

[Luke]

Originally Posted by DaBit

Aren't these cells handier to assemble a pack?
http://www.ev-power.eu/index.php?p=p...lls-%283.2v%29

I used the 200Ah cells in a project and they seem to hold up fine. Cells are from Thundersky.

I'm sure they're much easier to work with and they are definitely a lot cheaper, but I thought they'd be a little lacking as far as power output.

Originally Posted by Tweaker

http://www.diyelectriccar.com/forums/
Youtube


To the OP, A123 is now selling 20ah pouch cells to the public. www.mavizen.com who also sells conversion kits, There are plenty of other battery options as well.

Nice. They don't seem to like small-scale sales. Do you know of any distributers that are US based? As an Oregonian I am allergic to any sort of sales tax, but especially at UK rates.

There are a lot of batteries out there, all with about the same energy/weight ratio but few that can deliver enough power.

[Luke]

There's not much news recently, but I've been working on getting the battery management right. I was running without it which ruined a couple of cells. The BMS boards that I built didn't working quite right, so I'm fixing them (with a knife and a lot of extra resistors) and integrating them into the battery packs.

[DaBit]

Originally Posted by Luke

I'm sure they're much easier to work with and they are definitely a lot cheaper, but I thought they'd be a little lacking as far as power output.

In my experience there are a few ways to significantly shorten the life of lithium cells, including the 'power' LiFePO4's:
- Overcharge (Vcell>3.65V) or underdischarge (Vcell < 2.5V) it.
- Charge them at low temperatures. Below 0C/32F is a a no-go area.
- Run them down more than 80-85% DOD. Lithium cells like microcycles.
- Draw excessive currents out of them. Much more than 1-2C continuous and 10C bursts will significantly shorten cycle life.
- Let them get hot.
- High discharge currents when cold. They should be threated the same as a petrole engine: medium loads only when cold, let it rip once warmed up.

Yes, they can provide 30C worth of current. Yes, you can charge them with several C's. Yes, they will work at 70 degrees C.
But that doesn't mean one can expect a long useful life for all cells, as you already experienced. Lies, damn lies, datasheets.

You're far better off purchasing a higher capacity pack and loading it less (1-2C cruising, 10C peak maximum). Much more kWh's per $ out of the pack during it's useful life. And a much more acceptable runtime.

Also: a voltage clamp is not a BMS.... for a certain application I have been using active charge redistribution to prevent the weaker brothers in the chain from overcharging/underdischarging. Charge inductor from the strongest cell, discharge in the weakest. Works extremely well in exctracting the last useable mAh out of cell string and keeping the cells healthy.

[TheGreatHareafter]

This is cool!

[Bronco638]

Hey Luke,

This has been a very interesting read. It's so far over my head (the details) that I wouldn't begin to comment. But, I'm curious about the "run time". I'm thinking this would make a great commuter bike (not what you originally had in mind). My commute is 11 miles on surface streets. It usually takes about 30-40 minutes depending on traffic.

Given what you've developed so far, would you think your set-up would work in a situation such as this?

What, if any, effect would temperature have on the battery life?

Of course, I'd have to have turn signals and brake lights (perhaps a headlight, too). So, there would be that current draw to consider.

And, yeah, I could take the cells inside and charge them during the work day so that I'd have a full charge for the ride home.

Thanks, Dave.

[Luke]

So I've spent the last few days fixing up the battery management. The circuit boards needed some cutting and rework, but should be better now.



The circuit on the breadboard is controlling the charging current, it is connected to the BMS. It needs a little more refinement, then turned into a permanent version.

There also needs to be a similar circuit set up to shut down the bike when the battery runs down. Then there can be more riding.

[Luke]

Originally Posted by Bronco638

Hey Luke,

This has been a very interesting read. It's so far over my head (the details) that I wouldn't begin to comment. But, I'm curious about the "run time". I'm thinking this would make a great commuter bike (not what you originally had in mind). My commute is 11 miles on surface streets. It usually takes about 30-40 minutes depending on traffic.

Given what you've developed so far, would you think your set-up would work in a situation such as this?

What, if any, effect would temperature have on the battery life?

Of course, I'd have to have turn signals and brake lights (perhaps a headlight, too). So, there would be that current draw to consider.

And, yeah, I could take the cells inside and charge them during the work day so that I'd have a full charge for the ride home.

Thanks, Dave.

I suspect a commuter would be pretty straightforward, check out ElMoto.net . There are a bunch of street bike projects on there and I think most of them can get more 20 miles on a charge. Once I get the battery concept set I'll go to a much bigger pack- the setup I have now is just for experimenting.

I don't know much about the battery temperature range yet. The datasheet says they don't put out much power below freezing, and don't last long above 140F.

Lights should be no big deal. Just get a dc-dc converter that will give you 12V from your battery pack and run your lights off that. I'm drawing around 1200 watts cruising at a modest speed, drawing another 60 watts for lights would probably be barely noticeable.

[Bronco638]

Thanks Luke, I'll have a look at that web site. I try to ride when morning temperatures are at or above freezing. That's usually from mid-March to late-November here in Chicago. Given the effect of temperature on the battery pack, I might have to wait until the weather is warmer (no biggie). Until then, I'll be keeping an eye on your progress!

[nulluser]

I converted an old GS-750 to electric. It was fairly easy, ended up costing around 2000 total.

http://www.junklet.net/html/make_page.php?n=ebike
http://evalbum.com/3500

Here is a video of a test ride: http://www.youtube.com/watch?v=kvG82ycbm4E

It is practical for my commute, which is about 3 miles each way. I ended up using AGM batteries and a Kelly Controller,

A couple things to remember about range. Because of Peukert's law, you are only going to get about half of the expected energy from the pack. Combined wit the depth of discharge limitation, you really need to oversize the pack. For my bike, the pack is around 4000 Wh. Assume I can get 1000 Wh out of the pack (50 percent from Peukert's law, 50 percent DoD) , at 65 Wh per mile that's about 15 miles, which is close enough for an off hand calculation.

The regenerative breaking also helps, but the circuit is kind of complex if you are rolling your own controller. The 400A controller was a good value for me, even though i have designed motor controllers in the past.

I have the regen kick on at 50 percent when I activate the front brake switch. This gives me some back breaking before the hydraulic front break grabs.

[toolfan]

Incredible project Luke!

[boney]

[knary]

Originally Posted by toolfan

Incredible project Luke!

What he said. Wow.

[Agent2]

This is such a cool project.
I would love to have an electric dirtbike, no worries about radiators, clutches, fluids, carbs/injection, noise, etc.
Bob's ev has a conversion online, they converted a Honda 250 to electric power, something that didn't look like an oversized electric bicycle. http://www.evdrive.com/Emoto_project/moto_project.html
Whatever happened to KTM's electric dirtbike?