# Very basic questions



## Benjamin515 (Apr 12, 2012)

Hi,

After lots of research the conclusion I think is that the warp 11 will be best engine to use for my car.

I do have a set of very extremely basic questions. (English is not my mother language so maybe some of the terminology won’t be correct but here goes)

1. When NetGain gives engine stats about the warp 11 how do those stats relate to what batteries to use? Can you give an example from these engine stats?
-120-170 Volts
-43 horsepower @ 72 Volts, 453 Amps

2. Can more batteries produce a higher input in the engine? How do these two relate to each other? Weaker type of batteries equal less horsepower to the same engine as high-grade batteries to that same engine?
3. Most people say they use a 144V “system” in their EV. Why? Is this the sum of all batteries used?
4. What role does the engine controller have in relation the overall current flow in your EV? 
5. Does the controller keep a certain level of current throughout the system and lets it out when you put max input to the throttle?

Thanks!

Benjamin


----------



## evnz (Jul 24, 2010)

Hi i am like you a beginner
I choose a warp 11 as I am building a heavy truck so i got a big motor.
43 horsepower is a constant (an i.c.e horsepower is it's peak) i guess the i.c.e equivalent of 120 horsepower motor
A good controller and a good set of batteries will give you a quick takeoff but doing that to much will lower your range, In some controllers you can set max speed (rpm's) max amps and other things so you don't damage your batteries or motor.
If you go 72 volts the amps will be 400 if i get this right and you go 144 volts the amps will be 200 and some batteries have a internal resistance and as you start off the volts may drop eg 144 down to 130 
Keep reading and asking questions and this site has a wiki page with lots of information
Owen


----------



## ga2500ev (Apr 20, 2008)

Benjamin515 said:


> Hi,
> 
> After lots of research the conclusion I think is that the warp 11 will be best engine to use for my car.


OK I see from your other posts that you are planning on converting a Saab with an expected weight of about 4000 lbs, top speed 70 MPH, with 50 mile range.



> I do have a set of very extremely basic questions. (English is not my mother language so maybe some of the terminology won’t be correct but here goes)
> 
> 1. When NetGain gives engine stats about the warp 11 how do those stats relate to what batteries to use? Can you give an example from these engine stats?
> -120-170 Volts
> -43 horsepower @ 72 Volts, 453 Amps


Not really. All battery chemistries can be configured to deliver the required voltage and amperage, so the battery type is independent of these parameters above. In general the voltage is defined by the chemistry. The amperage by the internal resistance of the construction of the cell.

The final item to understand is that the maximum power requirement (and since the voltage is fixed, this means maximum amps) occurs at stall, which for a vehicle is when it is at a standstill. As soon as it starts moving, the amperage requirements drops off.

So the two ratings you need to examine are the continuous amperage rating, which is the maximum current that can be drawn indefinitely, and the maximum (or pulse) current, which is what can be drawn for a period of 5-10 seconds. Both of these are measured in terms of the Ah capacity of the cell/battery, marked as C. So for a 100 Ah cells the C rating is `100 A. So if the continuous draw is 3C and the maximum draw is 10C/10 seconds, then you can run this cell at 300 amps indefinitely and draw up to 1000 amps for up to 10 seconds.

So for example the 453 amps would be 4.5 C. If this is the standstill power required, then the 100 Ah cells can handle it.

With a big vehicle, you need to watch more for the continuous ratings as opposed to the peak ones. 


> 2. Can more batteries produce a higher input in the engine? How do these two relate to each other? Weaker type of batteries equal less horsepower to the same engine as high-grade batteries to that same engine?


You need to define *input* and *weaker* before this question can be answered.
In short the high the voltage you apply to a motor, the faster it spins. The more amperage you apply, the torque (force) goes up. Motors have both a maximum voltage and power rating. So there are limits to the amount of voltage and amperage that can be provided. Any battery pack can be constructed to provide this energy. It becomes a question of weight and cost, not "weakness".



> 3. Most people say they use a 144V “system” in their EV. Why? Is this the sum of all batteries used?


I've been saying that batteries can be constructed to provide the required voltage/current. This is done by stringing together cells in series to increase voltage, or in parallel to increase capacity. Take two 3.2V cells that are 100 Ah in capacity. Connecting them together makes a battery. If we connect both positive terminals together and both negative terminals together, this is a parallel configuration. In that case the capacities add while the voltage stays the same. So we would end up with a 3.2V 200 Ah battery. On the other hand, if we connect the negative terminal of one to the positive terminal of the other, then the voltage adds between the two remaining terminals. In that case we'd have a 6.4V 100 Ah battery. With enough cells both can be done at the same time. So with 4 cells it's possible to create a 6.4V 200 Ah battery by connecting two pairs of cells in parallel, then connecting those two parallel sets together in series. This would be called a 2 parallel, 2 series battery configuration, labeled 2P2S.

So with 144V you would need 144V/3.2V/cell = 45 cells.


> 4. What role does the engine controller have in relation the overall current flow in your EV?
> 5. Does the controller keep a certain level of current throughout the system and lets it out when you put max input to the throttle?


The controller uses the fact that motor RPM is related to voltage. It does this by pulsing the battery voltage to the motor, known as pulse width modulation or PWM. The percentage of the time of the on time of the pulse to the total time, is the same average percentage of the voltage of the motor to the voltage of the battery. So if the battery voltage is 144V and the PWM is 20%, then the motor will see 144V * .2 = 28.8V and will spin at 20% of it's maximum speed at 144V.

So the controller doesn't really control the current. The battery and controller will provide whatever current the motor is demanding up to a limit. This is the amperage rating on the controller. So a 500 A controller will allow the motor current to rise to 500A, while a 1000A controller will double that amount. Remember that current and torque are related, so the higher the current rating on the controller, the more torque that can be generated from the motor.

The final item is that the motor current and battery current are related by the power equation: P=IV where I is the current and V is the voltage. The power provided by the battery is equal to the power used by the motor:

Pm = Pb (m is for motor, b is for battery)
Im * Vm = Ib * Vb

remember that the motor voltage is the PWM percentage of the battery voltage:

Im * (Vb * PWM) = Ib * Vb

Ib = Im * PWM

So in short to get more power to the motor both the battery current, and the amount of current the controller can pass through must be high enough.


> Thanks!
> 
> Benjamin


Now some questions for you:

1. All of the questions you are asking seem to be related to acceleration. Are you planning on racing this car in a drag race?

2. What is your budget? Many of the choices are limited moreso by cost than anything else.

3. Of all of the parameters (speed, acceleration, range, cost) what exactly is the most important thing to you?

I'm just wondering where exactly are you trying to get to with all of this. Your initial posts started talking about speed (70 MPH) and range (50 miles). Yet this post seems to be all about acceleration, which is the only parameter affected by torque/current.

ga2500ev


----------



## Benjamin515 (Apr 12, 2012)

Thanks evnz and thanks ga2500ev!!

This helped allot and I understand everything accept the part where you draw the conclusion a 100Ah cell can run 453 Amps.

Besides that, everything is very clear, thank you again. 

Now to answer your questions:

_1. All of the questions you are asking seem to be related to acceleration. Are you planning on racing this car in a drag race?_
No. The choice for the Warp 11 engine is based on the maximum recommended vehicle weight from this overview: http://www.evsource.com/tls_warp11.php

_2. What is your budget? Many of the choices are limited moreso by cost than anything else._
Our country installs a free electricity pillar at your house and the government pays also a part to promote electric driving. Besides that I’m the first in my county to be driving an electric vehicle and I’m getting sponsored because of that. This does not mean it is going to be a 15K+ project.

_3. Of all of the parameters (speed, acceleration, range, cost) what exactly is the most important thing to you?_
The most important in this project is to have a maximum range of 50 miles and to not be a snail. All costs will be aimed to achieve that with a fast recharger. However, it is not necessary when I pull up at a travic light to see the front of my car break off and go airborne due to the humongous amount of torque. On the other side I don’t want to wait 20 seconds to go from 0 to 60. Would love to have all in the middle. Not to slow, not fast, it doesn’t have to have a maximum range of 100miles but is has to have a range of 50miles. It doesn’t have to go faster than 85mph but has to go faster then 50mph.


----------



## mora (Nov 11, 2009)

You need to size your batteries so that you don't go over recommended C-rating. Let's say you have 100Ah batteries. 1C is 100A, 2C is 200A. 0.5C is 50A. Battery manufacturers give you some information about batteries and will tell you not to exceed 3-4C (most common for prismatic LiFePO4 cells). In previous example 453A from 100Ah cell is 4.53C.

Aim for 1C or less being your continous current draw at your desired speed (60mph?). If battery manufacturer says 3C is maximum current draw for cell you can't hold that 3C too long. 2-3C (or higher) should be for short periods only.

Go as high on voltage as you can (or feel comfortable). You will soon notice that 170V and 0.5-1C advice given will result in costly battery pack. If budget is an issue you could get low Ah cells and build to desired voltage right away. Then later add similar pack and put it in paraller with your existing pack to get more Ah.

Your car will probably consume something like 20kW at 60mph. Maybe more. Do you need that 50 mile range at that speed? 20kW at 170V is ~117A. (power = voltage * current).


----------



## ga2500ev (Apr 20, 2008)

Benjamin515 said:


> Thanks evnz and thanks ga2500ev!!
> 
> This helped allot and I understand everything accept the part where you draw the conclusion a 100Ah cell can run 453 Amps.


Just to be clear, just because the motor can pull 453 amps at 72V does not mean you'll ever get there under normal driving conditions. As I said before, the maximum torque is at stall. You'll pull the most amps pulling off from a start. The motor voltage will be very low (say 15V or so) with very high amps. At 156V pack for example, the battery current will be 1/10 the motor current. So even if the motor is pulling 2000A in a stall, the battery is still only providing 200A of current. This is reason that controllers always measure motor current and not battery current.



> Besides that, everything is very clear, thank you again.
> 
> Now to answer your questions:
> 
> ...


OK, not drag racing. Trust that the motor will be more than enough. Warp 11s are usually used to drive pickup trucks. There's more than enough power with the motor. You'll have to work to find a controller that can deliver the power so you can use it.



> _2. What is your budget? Many of the choices are limited moreso by cost than anything else._
> Our country installs a free electricity pillar at your house and the government pays also a part to promote electric driving. Besides that I’m the first in my county to be driving an electric vehicle and I’m getting sponsored because of that. This does not mean it is going to be a 15K+ project.
> 
> _3. Of all of the parameters (speed, acceleration, range, cost) what exactly is the most important thing to you?_
> The most important in this project is to have a maximum range of 50 miles and to not be a snail. All costs will be aimed to achieve that with a fast recharger. However, it is not necessary when I pull up at a travic light to see the front of my car break off and go airborne due to the humongous amount of torque. On the other side I don’t want to wait 20 seconds to go from 0 to 60. Would love to have all in the middle. Not to slow, not fast, it doesn’t have to have a maximum range of 100miles but is has to have a range of 50miles. It doesn’t have to go faster than 85mph but has to go faster then 50mph.


OK back to basic parameters.

Speed is related to volts. Get your battery pack to a high enough voltage, then you'll get the speeds you require.

Acceleration is related to torque/current. This is a function of the motor (no problem), controller (unknown), and max battery current (buildable). Here you need to get the highest amp controller you can afford. Shoot for a 1000A controller. It'll deliver all of the current/torque you need to accelerate as you wish.

It really only comes down to range, what is based on the capacity of the battery, the weight of the car, and the speed you drive it. This is really where your problem lays. You want long range on a very heavy car, driving at highway speeds. You need to get a rough estimate of how much a battery to meet these requirements will be. The usual energy consumption metric is called Wh/mile which is the average amount of energy it takes to drive the car 1 mile. It varies on the weight of the car (lighter takes less power) and the speed of the car (slower takes less power). For cycles it's usually about 100 Wh/mile. For pickups and heavy cars up to 500 Wh/mile at various speeds.

I'll come back with a calc later...

ga2500ev


----------



## Benjamin515 (Apr 12, 2012)

Explanations are very clear, you guys help me alot, thanks mora & ga2500ev.

@mora

So basically all EV’s have a set of cells in series for capacity and a set of cells in parallel for power. Is there something like the most effective ratio of series to parallel? Or is this all depended on the need of the vehicle? Or is it all money related? In the sense that the more money for better cells the more efficient your ride? 

@ga2500ev

_Trust that the motor will be more than enough. Warp 11s are usually used to drive pickup trucks. There's more than enough power with the motor. _
In your opinion the Warp 11 is overkill for the Saab? With this engine, do I need over 55 100Ah lithium cells to achieve my goal? 

_Speed is related to volts. Get your battery pack to a high enough voltage, then you'll get the speeds you require._
Is there something like a general Volt to Weight equation related to speed so I can calculate the amount of Volts and amps required for the vehicle's goal?


----------



## mora (Nov 11, 2009)

Benjamin515 said:


> So basically all EV’s have a set of cells in series for capacity and a set of cells in parallel for power. Is there something like the most effective ratio of series to parallel? Or is this all depended on the need of the vehicle? Or is it all money related? In the sense that the more money for better cells the more efficient your ride?


Many people seem to have found 144V and 100Ah+ the best starting point. Of course this is vehicle dependant (weight being the issue). I had 96V before and went to 144V a year after finishing my conversion. I've been happy so far. I managed city traffic easily at 96V though.

You get voltage by putting cells in series. Let's say 144V. Each cell is 3.2V nominal, so 3.2 * 45 = 144V. When fully charged cells can be something between 3.6V and 4.0V. So after full charge your pack voltage will be higher than at nominal. It will settle down to 3.2V per cell very soon after you press the accelerator few times.

Power is voltage times current. Remember my previous advice regarding discharge rates? 144V and 300A (3C for 100Ah) will give you 43200W (43.2kW). Voltage will drop a bit at that load and your transmission and other losses will eat that power a bit before it reaches wheels. Battery pack is your only power source in EV.

You get the same power at 288V and 50Ah or 72V and 200Ah cells. Also your battery capacity is the same. (capacity in Wh = voltage * Ah)

Crudely put: voltage is speed and more amps is more acceleration/torque. Capacity is range. More capacity = more pack cost.

If you go high voltage your acceleration might be lower but it will be more constant. Meaning you can maintain a certain torque for most of the rpm range your motor can provide. How about 100-150Nm torque from 0 to 4000rpm? At lower speeds maybe even more? Your stock transmission will prefer this option. If you go high amps and low voltage your torque at 500rpm might be 300Nm but will drop soon. Smoking tires? Yes, hehehe.

Needs are different. Money available is mostly the biggest barrier here.


----------



## Ziggythewiz (May 16, 2010)

Benjamin515 said:


> So basically all EV’s have a set of cells in series for capacity and a set of cells in parallel for power.


You have to have a string of cells to get the voltage you need. No one (yet) makes a battery over 100 V. You don't have to parallel your cells unless you're using small cylindrical or pouches. With the larger prismatics you just size it appropriately and use one string.


----------



## ga2500ev (Apr 20, 2008)

Benjamin515 said:


> Explanations are very clear, you guys help me alot, thanks mora & ga2500ev.


Happy to help.


> @mora
> 
> So basically all EV’s have a set of cells in series for capacity and a set of cells in parallel for power. Is there something like the most effective ratio of series to parallel? Or is this all depended on the need of the vehicle? Or is it all money related? In the sense that the more money for better cells the more efficient your ride?


All good questions. quickly:

series is for voltage. parallel is for current. power is the product of the two. I always view a battery as a rectangle, with the height as the series voltage and the width as the parallel current capacity. The energy/capacity is the area. So if you make the battery "taller" or "wider" then the area increases (i.e. more capacity). Usually the motor will dictate the maximum voltage while the motor and controller will dictate the maximum total current. However, even if your motor/controller limits the current through the system, you can still widen the battery for capacity. So say a 500A controller/motor combo is paired with a battery that's 1000 Ah wide. There's no way to get 1000A out of the battery at any one point, but the capacity (area) of the battery is still twice one that only is 500 Ah wide. All of this presume the same voltage (height).

The capacity defines your range. The motor limits your voltage. Factors such as weight, space, and cost limits your capacity. The rule of thumb is to get the maximum voltage that will need (see below for more), and then use the other factors to widen the battery as much as you can to gain the maximum capacity for the weight, space, and cost available.

More is always better. More is always more expensive. You have to create a space/weight/cost budget, then fit the highest capacity you can into it.

One last thing: the battery needs to have a minimum amperage too, otherwise you won't get the torque necessary to accelerate properly. You have to make sure that your current draw doesn't exceed either the continuous or maximum allowable current. Widening the battery always helps with these. In short if you use 2 60 Ah cells in parallel, then you get double the continuous and maximum current draws than only using one. Sometimes this will limit your voltage. Say you have 44 40 Ah cells. You can make a 140V x 40 Ah battery if you put all the cells in series. However, 40 Ah cells do not have the current values to move the car properly. You can reorganize into a 22S2P which ends up being 22 80Ah cells giving a battery with 70V x 80 Ah. Now you may get this current you need. However, your voltage is limited and the top speed of the car is cut.

It's all a balancing act unless you have unlimited money and space for cells.


> @ga2500ev
> 
> _Trust that the motor will be more than enough. Warp 11s are usually used to drive pickup trucks. There's more than enough power with the motor. _
> In your opinion the Warp 11 is overkill for the Saab? With this engine, do I need over 55 100Ah lithium cells to achieve my goal?


The two items to look for are torque and RPM. Too small a motor will not give you the torque you need. A motor that's limited in voltage may not give you the RPMs. As outlined above the battery organization is independent of the motor, other than limiting the maximum voltage, and keeping the current within both the range of the motor and the battery. The question you should be asking is "Will 55 100Ah lithium cells give me the range that I need". 55 cells * 3.2V/cell * 100Ah/cell = 17600 Wh. A heavy car will consume 450 Wh/mile or more. Also you can only use up to 80% of the available capacity with lithium. So the real available capacity is a touch more than 14000 Wh. Divide that by the consumption 14000 Wh/ 450 Wh/mile = 31 miles. So you cannot reach your range goal with this.

Another item is that 55 cells is probably high. The discharge voltage will be about 176V. That 170 is an absolute maximum. Don't want to push it. Drop it to 50 cells to be safe. Up the cells to 180 Ah and you get 28800 Wh with about 23000 Wh usable. now your range is 51 miles. Could bump it up a cell or two, but not 5.

Just pulled a random quote from here with cells running about $260 USD. So your battery will cost a bit more than $13000 USD.

This is why a budget for range, space, weight, and cost is crucial. Big car is a lot of cash. This is why I'm converting a Geo Metro. It'll consume close to 250 Wh/mile which means that I can go nearly twice as far with the same battery.




> _Speed is related to volts. Get your battery pack to a high enough voltage, then you'll get the speeds you require._
> Is there something like a general Volt to Weight equation related to speed so I can calculate the amount of Volts and amps required for the vehicle's goal?


It's not volts to weight. It's volts to RPM. It's a spec that most motors will have on their spec sheet in a chart. Or in the case of the Warp, they specify everything at 72V and you ca scale. So if the RPM is 2000 at 72V, then it'll be 4000 RPM @ 144V for example.

The top RPM is specified by the voltage limit. So with a Warp 11 @ 170V, then the top RPM would be 4720 RPM for the example above (170V/72V * 2000 RPM).

The best place to look is at the torque and RPM specs of the original engine. You can scale down a bit because unlike ICE, maximum torque is at 0 RPM. ICE specifies torque in the power range (2000-4000 RPM).

The NuWiki has motor specs. Also you can check out EV archives of cars similar to your and see what motors they used.

The Warp 11 isn't a bad choice at all if you can afford it. It has both the high voltage and torque required to more a large load. No need to rethink that decision.

ga2500ev


----------



## Benjamin515 (Apr 12, 2012)

Thanks ga2500ev for your time. Now I understand the subject fully.

On the type of random cell you posted. The characteristics of that cell shows a life cycle of ‘2000’. Is this value considered ‘long life’ as some manufactures give?


----------



## Ziggythewiz (May 16, 2010)

You should really stick with manufacturers that publish actual life cycles. The term "long life" typically means relatively short life. If it was long enough for them to be proud of it, they would publish it.


----------



## Benjamin515 (Apr 12, 2012)

Thanks Ziggy.

Do you know what a cycle of '2000' means?


----------



## Ziggythewiz (May 16, 2010)

It means discharge to a given depth, then recharge. Assuming you only charge at home, you'll typically use 1 cycle per day of use. So a cycle life of 2000 means you can do that for 2000 days before your cells drop to whatever the rating is (maybe 80 or 90% of capacity)

One example would be a cell may be rated for 2000 cycles at 80% DOD and 3000 cycles at 70% DOD. I would recommend sizing your battery pack so that your typical usage falls around 65% and your max usage is under 80%.


----------



## Benjamin515 (Apr 12, 2012)

Thanks Ziggy. I didn’t knew the link you posted existed.

Here’s a small example of a calculation I made. (We have Euro’s here but I’ll calculate back to dollars.) 

After the conversion the only thing I’ll be saving is of course gas money but also road taxes. I’ll be saving a total price of at least $4462,60 per year. This price will be higher because of annual checkups, maintenance etc etc but to be calculating from a minimum it will be $4462,60 a year. (Gas prices here are 8,80 a gallon.)

If I use the example as given before, with the $13.000 battery pack, I need to drive it every day for 2,9 years long to be even. Only after that I’ll save money. And that’s not even including the costs of the total conversion. For the example lets say the total conversion will cost $16.000. Then I’ll have to drive it for 3,5 years to get even. It would be a real bummer that when you reach that point, or even before that, the $13.000 battery pack will be dead. So it will be crucial to choose batteries with a very very long life cycle. 

Is a life cycle of ‘2000’ considered high or low?


----------



## Ziggythewiz (May 16, 2010)

Haha, I didn't even post that link. I don't know if the mods added that or if the system autodetects an exact title and links it.

2000 is very high compared to old lithiums, and average for LiFePo4. Multiple vendors quote their batteries at 2000 cycles for 80% DOD. Some quote them for 3000 or even 5000 cycles for 70% DOD, which is why I would size the system to stay under that. If you get 3000 cycles, that's about 10 years of use.


----------

