Another EV bike :)

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mattcarr
Posts: 389
Joined: Sat May 12, 2007 2:27 pm
Location: Hampshire

Re: Another EV bike :)

Postby mattcarr » Thu Aug 29, 2013 9:18 am

Hi Chris - have you worked out your total pack size at all. I have done some quick maths from your posts and it seems that you have got a fairly small overall pack size. You lead acid pack would be 900 watt hours and your lipo pack roughly 1200 watt hours - so about a 2.1kwh pack. Now if you say your lipo's are set to 1amp max maybe 2 amps? then the max power out of those will be 1 - 2 kwatts. You said your lead acid is good for 40 amps so the max power out of them will be roughly 7 kkwatts. This is not taking in to account any voltage sag under load - so I would expect this to be a realistic 4 kwatts from the lead. So roughly 5 kwatts max power - which is not a huge amount - and then as the pack is fairly small you should be able to maintain this level of power for about 20 -30 minutes.

I know you wont use this amount of power all the time, but I was also interested in working out how far you could go on a charge. Say you can do 1 mile on 150 watt hours, then you would get about 14 miles. Again, these figures are working on using all of the available energy in the pack.

I do like the look of the cell control boards on ebay - it would mean making a 12 volt lithium battery very easy. I am after a light and controlled lipo 12 volt pack. May well go down this route myself.

Matt

ChrisBarron
Posts: 244
Joined: Tue Dec 11, 2007 11:26 pm

Re: Another EV bike :)

Postby ChrisBarron » Thu Aug 29, 2013 9:51 am

Are we using the same methods Matt ?

I have over 700 cylindrical cells, and could realistically expect 1400mAh per cell, conservatively

Adding 100 prismatic cells to that and allowing 1Ah per cell, I estimate 80Ah at 37V nominal. (10 series packs, each pack consisting of 80 parallel cells), so about 3kWh before adding lead ?

In terms of kW, 80A at 37V is about 3kW, however, what is the maximum current the pack will produce ? all of the cells are happy to give over 30Amps for short bursts and although 10Amps means they're warm, they can all go to 10Amps (and have a shorter life !) But lets say the current limit of the motor controller is 250A, then thats over 9kW and only just over 4Amp per cell, which I think they can cope with in short bursts

Of course, I can only use 42V down to 29V = 13V, at 80Ah so that's probably what you're talking about ? (just over 1kWh)

I expect the cruising current to be about 80 Amps at 45mph (based on field averaging of many other electric bikes) and expect a realistic range of 20 to 35 miles depending on conditions. Ideal for my weekend playabout. (I've got a thyristor chopper speed controller which isn't going to help any, so I'll be looking for some large capacitors to help with smooting)

Chris

mattcarr
Posts: 389
Joined: Sat May 12, 2007 2:27 pm
Location: Hampshire

Re: Another EV bike :)

Postby mattcarr » Thu Aug 29, 2013 11:12 am

Hi Chris - my mistake, I did not take in to account the voltage of the lipo in my calculations. A single cell is what 3.2v nominal voltage, by 1400 mah = 4.48 watt hours ( call it 4.5 ) and you have 700 which make a total of 3.1 kwh. I stand corrected.

Will be interesting to see what performance you get out of the pack. I am sure that the cells should be able to handle bursts of 4 amps each with out any problems.

Matt

ChrisBarron
Posts: 244
Joined: Tue Dec 11, 2007 11:26 pm

Re: Another EV bike :)

Postby ChrisBarron » Thu Aug 29, 2013 11:38 am

Maybe I made a mistake somewhere too, I don't have any lipo.
The flat red cells I'm calling prismatic, because I've commonly seen them sold as such, but actually they're flatted cylindrical lithium ion with 3.7 nominal voltage.

If I can expect 1500mAh from 800 cells at 1.5A each (ideal, based on last set of tests) , then that means an 80 cell pack has 80 x 1.5Ah = 120Ah capacity at 120Amps continuous.

It seems rather high, but it is in keeping with what I've measured of a few of the rectangular cells. The nominal voltage is 3.7V, ten of those in series is 37V(nominal) so that's a potential 4.44 kWh. At 150Wh per mile thats a range of about 30 miles

(Not sure now why I considered the useful voltage range of 4.2-2.9, because the capacity results which I already measured were made from within that voltage range !)



Because of the existence of so many unknowns, still, I'll aim for 20 fast miles just now :)

mattcarr
Posts: 389
Joined: Sat May 12, 2007 2:27 pm
Location: Hampshire

Re: Another EV bike :)

Postby mattcarr » Thu Aug 29, 2013 2:59 pm

What chemistry are the cells that you now have ?

ChrisBarron
Posts: 244
Joined: Tue Dec 11, 2007 11:26 pm

Re: Another EV bike :)

Postby ChrisBarron » Thu Aug 29, 2013 5:24 pm

I only have the cells pictured plus a few lead acids.

I have the bike, without an engine, the motor, controller and these cells, lithium ion.

I did have a huge lot of lipoly, probably 120 packs 3.7V 10Ah (4 x 2500mAh in parallel) , but under load testing even a 2C burst caused a lot of heating. They were designed for portable electronics and low discharge rates, high discharges would have killed them or started a fire.

I started looking elsewhere and bought into these 'faulty' laptop cells after selling the lipoly's for about the same price I paid for them.

mattcarr
Posts: 389
Joined: Sat May 12, 2007 2:27 pm
Location: Hampshire

Re: Another EV bike :)

Postby mattcarr » Fri Aug 30, 2013 12:04 pm

Well, I for one will be interested to see how you progress with your pack. How will you assemble it? Will you be using the cell holders and have them all wired up that way?

I used to work for major electronics company in IT - and we used to have piles of defunt laptop battery packs. I used to dismantle them to use the cells for home made torches. This was in my dog walking days when me and the kids would go out of an evening with the dogs. I built several 12 volt packs that would run the 50 watt halogen bulbs. Amazing how much of a field these can light up. I even had one torch with twin 50 watt bulbs on it. I used to say so the kids, as soon as you see it begin to dim, switch it off. I used to use my 12 volt car battery charger to charge them back up - only ever had one go bad on me - and that was because I forgot about it. I was sat in the front room thinking, what is that smell !!!!! - s&^t.... I had forgot I had put a pack on charge and when I ran to check, it was bubblingaway, and it was rather hot as well. The packs lasted some time as I seem to remember. Best pack I build was using nicad D cells, I built a torch that was like a maglite - nice and big, with a 20 watt halogen bulb on the end. I attached a 12volt car socket on to it so it could be charged in the car - nicads were much more forgiving.

Matt

ChrisBarron
Posts: 244
Joined: Tue Dec 11, 2007 11:26 pm

Re: Another EV bike :)

Postby ChrisBarron » Mon Sep 02, 2013 10:17 pm

I agree that nicads are a bit more tolerant, but then NiMH is more tolerant again. The abuse I've thrown at some NiMH cells here in camera flashes is amazing and they keep going, despite one of the chargers which likes to cook them if I forget about them. I probably should throw it out !

For assembly I've been in touch with this company, and off eBay they'll do a great deal on high volumes of these things, they do 2-cell and single cell versions too.
http://www.ebay.co.uk/itm/321114252941? ... 1438.l2649

They seem well engineered. They're interlocking and so it should be possible to make a top and bottom endplate of the right size. The gap between cells will help with cooling.

As an alternative I thought about getting some fibre embedded sheet material (temperature resistant) and drilling a hole pattern in it to form endplates which would become top and bottom spacers and pack support all in one.

The idea, next, is to sort my tested cells into piles of cells with similar capacity and then see how many I should put into 3.7V pack, and then order the holders. The last thing will be to spot weld nickel strip in rows, and then probably add a couple of copper (or aluminium) busses, with a nut and bolt terminal, to each 3.7V pack.

The rectangular cells will be a bit more interesting, I think I can get fibre embedded temperature resistant plastic strip which ca be used as a small spacer between each cell.

Both types of cells will be in vented enclosures, possibly with a coupe of fans and some ducting, it all depends how they perform on bench testing. I get the feeling that some temperature monitoring is almost compulsory !

mattcarr
Posts: 389
Joined: Sat May 12, 2007 2:27 pm
Location: Hampshire

Re: Another EV bike :)

Postby mattcarr » Tue Sep 03, 2013 7:36 pm

well, I for one am looking forward to seeing this pack being built. and it will be interesting to see how it performs.

Another question I was just thinking of - do you have any idea on the size ( volume ) the pack will be, and an estimated weight at all?

ChrisBarron
Posts: 244
Joined: Tue Dec 11, 2007 11:26 pm

Re: Another EV bike :)

Postby ChrisBarron » Tue Sep 03, 2013 8:14 pm

No I haven't got the final volume worked out, I'm waiting for some of the cell spacers to arrive and then I'll better be able to envisage it. I thoroughly expect that I won't get away wioth making all the packs the same shape !

As for the weight, I can lift all the cells with greater ease than I could lift the engine and gearbox, I guess with the weight fo the motor the final build will be close to stock weight.

Each cell is 45g, so 1000 cells weigh 45kg, which isn't too bad, if the range is 30 miles. IF !


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