# Three-Wheeler commuter EV



## Ziggythewiz (May 16, 2010)

Sounds fun!

Is your 50km range to be the marketing number or real world daily range? I think it would be doable with a slightly more powerful lithium pack, but with lead acid I think you'll have more of a 15-30 km range.


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## 3WheelerUni (Feb 7, 2013)

Ziggythewiz said:


> Sounds fun!
> 
> Is your 50km range to be the marketing number or real world daily range? I think it would be doable with a slightly more powerful lithium pack, but with lead acid I think you'll have more of a 15-30 km range.


The aim is a real world range of around 50 km, but it is not the exact range that is most important at this stage. If the concept becomes reality maybe there will be money for a lithium battery pack 

From our simulations with real world driving cycles from the roads were the car is supposed to be driven, the consumption stayed below 0.8 kWh/10 km, giving a range of a little less than 50 km, with a battery buffer of 30 %. But of course, although the simulations are quite thorough, it's always going to be a simplification of reality. Though, when considering range for this type of urban/suburban electric car, an important factor is the low travelling speeds (seldom above 70 km/h), giving an advantage for the EV over ICE. 

Thanks for your response!

edit: Nice car by the way! I love the old Bug. What is the weight of your car?


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## Ziggythewiz (May 16, 2010)

I don't think your calculations for power needed are far off, but unless you've taken those sims and ran the batteries you've selected through the same power requirements I doubt you'll get as much out of them as you expect.

Due to peukert you can't get the full sticker rating (usually a 20 hr rate) from a battery while using it in an EV application (1 hr rate). Also, most lead shouldn't be discharged past 80% DOD or its cycle life will be significantly shortened, and less than 50% DOD is ideal for long life. I usually use 30% of sticker as an estimate for daily usable energy,


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## MalcolmB (Jun 10, 2008)

Sounds like a fun project, but not a lot of time to do it in, so I'd suggest keeping things as simple as possible.

Taking the energy density of lead acid batteries as 35 Wh/kg, and reducing that by 50%, as Ziggy suggested above, gives 17.5 Wh of usable energy per kilo of lead. For a 600 kg vehicle with top speed of 80 kph I would guess the energy requirement at around 1 kw per 10 km, a little higher than your calculated figure. So to get a range of 50 km, you would need just under 300 kilos of lead/acid batteries.

I've heard that the Golden motor is pretty good, but I think it is likely to overheat if you ask it to drive a 600 kg vehicle at up to 80 kph. I'd suggest you start out with a gear ratio that gives you a lower top speed (perhaps 60 kph) for initial testing. If you are using a chain drive it should be easy to increase the gear ratio later, if everything goes well.

It sounds like you already have some ideas for the chassis design, but a quick solution would be to connect an existing front subframe from a lightweight car to the rear end of a motorbike by a central box chassis. The central box could also provide storage for some of the batteries.


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## 3WheelerUni (Feb 7, 2013)

MalcolmB said:


> Sounds like a fun project, but not a lot of time to do it in, so I'd suggest keeping things as simple as possible.
> 
> Taking the energy density of lead acid batteries as 35 Wh/kg, and reducing that by 50%, as Ziggy suggested above, gives 17.5 Wh of usable energy per kilo of lead. For a 600 kg vehicle with top speed of 80 kph I would guess the energy requirement at around 1 kw per 10 km, a little higher than your calculated figure. So to get a range of 50 km, you would need just under 300 kilos of lead/acid batteries.
> 
> ...


hmm, interesting thoughts. Didn't know about the Peukert's law, more used to lithium batteries. I think we, in the first stage, settle for around 5 kWh of lead acid and see what range we get. You guys are probably right, due many real-world parameters the range will be quite limited. 

Regarding the gearing, we will have to do some more simulations and calculations to determine whether the motor will manage 80 km/h. As I see it, this is a matter of having enough power for the given motor speed (which in turn of course is dependent on gearing), i.e. under normal conditions the power need must be below 10 kW at 80 km/h. We have discussed limiting the top speed to 70 km/h, but like Malmcom suggests maybe 60 would be a good start. 

Another question - is it harmful to the motor to run it near its maximum speed (6000 rpm) for long periods? I mean, efficiency and torque wise it's probably beneficial to set the gearing such that the motor speed is as high as possible at low speeds (in town)?


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## Yabert (Feb 7, 2010)

3WheelerUni said:


> ... having fun and learning stuff,


If it's to learn, Lifepo4 cell are to consider. Lead is obsolete technology.

An easy way to learn about charging of lithium cells is to use a hobby charger with an integrated BMS.
24 cells in serie is considered like a 72v battery and I think charge two 36v with a 12S charger is simple.
The weight of 24 40Ah cells is only 34Kg and give you a good power and range.


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## 3WheelerUni (Feb 7, 2013)

Yabert said:


> If it's to learn, Lifepo4 cell are to consider. Lead is obsolete technology.
> 
> An easy way to learn about charging of lithium cells is to use a hobby charger with an integrated BMS.
> 24 cells in serie is considered like a 72v battery and I think charge two 36v with a 12S charger is simple.
> The weight of 24 40Ah cells is only 34Kg and give you a good power and range.


Yep, lead is really obsolete, but also cheap. The GWLs where not that bad though, but to get 5 kWh we would need more like 70 Wh per cell. To start with we have found a number of starting batteries (no pun intended ) for free. I know they are not for deep charge but at least they can get the car moving and hopefully registered. 

We did some more simulations on power need today and at 80 km/h, with some uphills, we seem to need around 8 kW to maintain speed. For acceleration it's more like 11 kW. Sounds like 10 kW with 20 kW peak would be enough then? Reasonable?

Thanks for all the response by the way!


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## Yabert (Feb 7, 2010)

5 kWh lead-acid battery pack = roughly 2.5Kwh of lithium.

70Ah Lead acid: Around 30-35Ah of usable energy, 150 Kg and $$$ (or $$$$)
40Ah Lifepo4 : Around 32-40Ah of usable energy, 34 Kg and 1100-1400$ (US price)

Free battery is another story...


Your power calculation is reasonable since my 860 Kg Smart can maintain 70-80 Km/h with 10-11 Kw (battery power, flat road, light wind).


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## 3WheelerUni (Feb 7, 2013)

Yabert said:


> 5 kWh lead-acid battery pack = roughly 2.5Kwh of lithium.
> 
> 70Ah Lead acid: Around 30-35Ah of usable energy, 150 Kg and $$$ (or $$$$)
> 40Ah Lifepo4 : Around 32-40Ah of usable energy, 34 Kg and 1100-1400$ (US price)
> ...


Yes, I was actually a bit surprised about the relatively small difference between lead and lithium, especially if you consider usable energy. Though, to get decent lifetime from a lithium pack it should be kept above 30 % SOC, right? And the energy comparison isn't really fare since the lithium cells are 3.2 V each, while the lead cells are 12 V. So for a 72V battery pack the 23*40Ah Lifepo4 would have an energy content of around 3 kWh, while 6*70 Ah leads would have 5 kWh. But again, that is rated, usable is another story. 

Nice to get a comparison of power demand! Actually, some of the specs from the Smart have been used for simulations.


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## 3WheelerUni (Feb 7, 2013)

We have a question about gearing. Since we want to have direct drive without gearbox and aiming for 80 km/h with a 6000 rpm motor, the gear ratio will be tough to manage if we want to wind out the motor (~1:9). 

In order to not put too much strain on the chain, the front sprocket's circumference will have to be big enough, while the back sprocket is limited by the size of the back wheel. 

A 5XX (5/8" pitch) chain will be impossible if we don't go lower than 10 tooth front. A 4XX (1/2" pitch) with 10/90 tooth could work, but we are a unsure if the 4XX chain will manage 20 kW? I can imagine that there will be other problems having such a big difference front/back?


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## Siwastaja (Aug 1, 2012)

Don't buy lead acid, it's the most expensive technology in the long run in EV use, in addition it's the worst. If you get lead acid for free, it's a different story then and you may be able to do initial testing with those. (That's what we are doing, by the way.)

About gearing, calculate the gear ratio so that you will get the maximum speed realistically possible with maximum RPM specified for the motor. For realistic maximum speed with the given motor power, try to use some online calculators for aerodynamics and other losses.


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## Yabert (Feb 7, 2010)

3WheelerUni said:


> A 5XX (5/8" pitch) chain will be impossible if we don't go lower than 10 tooth front. A 4XX (1/2" pitch) with 10/90 tooth could workk


Dual gear reduction!
http://blog.cycletrader.com/2008/09/swiss-made-quantya-electric-bikes-get.html


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## 3WheelerUni (Feb 7, 2013)

Siwastaja, the top speed has been simulated from somewhat realistic numbers of weight, aerodynamics etc. 

Yabert, nice reduction gear! That is of course one way to solve it, but dual reduction gear means dual loss, dual work and dual cost  

So, the question remains: Do you think 4XX chain with 10/90 tooth sprockets will work?


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## Yabert (Feb 7, 2010)

3WheelerUni said:


> So, the question remains: Do you think 4XX chain with 10/90 tooth sprockets will work?


Work? Yes. Well? No!
Is that it would be my choice? No

If your motor peak torque isn't over 30 lbs-ft (41 Nm), the #40 chain can theoretically work.

But I think you can live with the 1% extra lost and the small amount of work to add. Extra cost??? And the custom 90t sprocket don't cost something?

90/10 = 9:1 ratio
(36/12 x 36/12) = 9:1 ratio


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## 3WheelerUni (Feb 7, 2013)

Yabert said:


> Work? Yes. Well? No!
> Is that it would be my choice? No
> 
> If your motor peak torque isn't over 30 lbs-ft (41 Nm), the #40 chain can theoretically work.
> ...


Hehe, okey okey. Dual reduction gear then  I guess the extra loss will be compensated a little because of smaller losses due to bigger "front" sprocket.


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