New to EV motorbikes

An area for all you bikers who now run your two wheeler on battery power, scooter owners to.
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Fat-tony71
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Re: New to EV motorbikes

Postby Fat-tony71 » Tue Mar 08, 2011 9:41 pm

So all the ICE gear is on "that site", Looking like its gonna be a nice bidding war :D . So its looking good.

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Fat-tony71
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Re: New to EV motorbikes

Postby Fat-tony71 » Tue Mar 15, 2011 5:59 pm

So most of my bits have been sold, Just the engine and little bits left. They all end this weekend. So fingers crossed I can get the motor etc soon. Also been looking at batterys and found these on "the bay"
http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... 5630wt_907
Just wondering on if they are suitable and how many I would need.

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Jeremy
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Re: New to EV motorbikes

Postby Jeremy » Tue Mar 15, 2011 7:49 pm

The simple answer is that these won't deliver the current you need. The cells they are using are laptop cells, which have a low maximum current capability. The key things to look for when picking cells for a relatively high power system like this are the rated discharge capability of the cells and their internal resistance. The first figure tells you the peak power that you can expect to get from the pack. In this case, the rated discharge current is only 40A, so the maximum continuous power you can get would be 40 x 48 = 1920 watts. You really need to aim for around 10 to 20kw for reasonably good performance. Next, look at the internal resistance, as this tells you how much the voltage will drop when you load the battery down. In this case it's given as less than 50 milliohms (0.05 ohms). If you were to draw 40 amps from this pack, then the voltage would drop by 0.05 x 40 = 2V and the power lost to heating the battery pack, rather than driving the motor, would be 2 x 40 = 80 watts. If you were to draw the maximum continuous current that this battery can deliver, 80A, then the voltage drop would be 0.05 x 80 = 4V and the power lost as heat in the battery would be 320 watts. That's a lot of heat in a small volume, meaning that the battery pack would get unacceptably hot after a short time at this power level.

The added problem is that the battery management system for this pack has a 60A current limit normally, which fits well with the probably C rate, or discharge current rating, of these cells of around 1.5C (C rate is the maximum current divided by the battery Ah capacity, so a 40Ah battery discharging at 60A is 1.5C). For comparison, the cells that I was originally going to use on my RD50MX were rated at 10C, so the 40Ah pack I had was capable of running at 40 x 10 = 400A. The cells I've just bought are rated at 20C, but I've droped down to a 30Ah pack, so they should be able to deliver 30 x 20 = 600 A peak. In practice I hope that the average current will be no higher than around 50 to 60A, but you need at least a 5 to 1 or so ratio between the average current and peak current to give good acceleration and hill climbing performance.

Hope this helps, rather than confuses!

Jeremy

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Fat-tony71
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Re: New to EV motorbikes

Postby Fat-tony71 » Thu Mar 17, 2011 10:11 pm

Ok, Sort of understand. What do you think of the Heaway 40160S cells? just looking on http://eclipsebikes.com/headway-lifepo4 ... -1027.html at the single cells, Looks like I could build a good battery pack out of them. Looks like they are 160 A at 10C, So I guess I would need a few to get the correct output for the motor.

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hohisilver
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Re: New to EV motorbikes

Postby hohisilver » Thu Mar 17, 2011 11:34 pm

I was looking at those - I'm going to configure the pack as 2 cells in parallel, which with the 40160s would give 20C and 32AH (maximum current of 320A!), 25 of these in series to give 80V. In the end due to cost and space considerations I ordered 50 38140S which will give me 24AH, still a maximum of 240A!
Ian.

A train station is where the train stops. A bus station is where the bus stops. On my desk, I have a work station....

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Jeremy
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Re: New to EV motorbikes

Postby Jeremy » Fri Mar 18, 2011 8:08 am

I have a lot of Headway cells and have found them to be OK. I used the older 38120 10Ah cells and paid around $16 each for them direct from Headway in China. I think the current price for small quantities (less than 100) is around $18 each from most resellers (they are probably cheaper direct from Headway).

The 16Ah versions are probably better than the 10Ah versions, but do seem a lot more expensive (those you've linked to are around $2.35 per Ah, the 10Ah ones I used are around $1.80 per Ah). It would be well worth contacting Headway and getting a price, as the chances are they'd be a fair but cheaper than that site is asking for them.

I'd guess that you need around 30 to 40Ah as a minimum pack size, ideally a bit more, although it all really comes down to how much space you have available in the frame, under the seat, inside the old fuel tank etc.

Jeremy

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hohisilver
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Re: New to EV motorbikes

Postby hohisilver » Fri Mar 18, 2011 10:20 am

I got mine from here: http://www.evassemble.com/index.php?mai ... cts_id=151 and the 40160s work out at about $1.58/AH according to my calculations.
Ian.

A train station is where the train stops. A bus station is where the bus stops. On my desk, I have a work station....

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Fat-tony71
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Re: New to EV motorbikes

Postby Fat-tony71 » Fri Mar 18, 2011 12:48 pm

Thanks guys. I should have plenty of room for the cells, I'm gonna cut the bottom of the tanks off for starters. I was thinking 30-40 cells, But I need to mock the units up first. Seat is gonna be tight, Looking at putting the controller and small parts under there.

Daz

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Jeremy
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Re: New to EV motorbikes

Postby Jeremy » Fri Mar 18, 2011 1:15 pm

EVAssemble get some truly awful reports over on the ES forum, mainly for supplying very unreliable BMS systems and then being very difficult to deal with. There seem to be a lot of very unhappy EVAssemble customers about - a search on ES with the term EVAssemble will soon find all the tales of woe. If you're only buying cells from them and are putting together your own pack, with your own BMS, then I would think that EVAssemble is probably as good as any other supply. I still think buying direct from Headway is likely to get a better deal, overall. In my experience they were pretty good to deal with, the only slight problem being that payment needs to be wired to their bank.

Jeremy

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hohisilver
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Re: New to EV motorbikes

Postby hohisilver » Fri Mar 18, 2011 1:22 pm

I didn't go for any of their other products having heard a tale of woe about one of their BMSs, but I'd already decided to go the "Peter Perkins" route on that anyway! :)
Ian.

A train station is where the train stops. A bus station is where the bus stops. On my desk, I have a work station....


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