# Battery type explanation



## TEV (Nov 25, 2011)

The LiFePo4 seems to be the best for regular car performance. I got the CALB's SE100Ah, but my conversion is not ready yet so I can't do a review on them yet.

Take a look at this list to see more options :

http://www.diyelectriccar.com/forums/showthread.php/list-li-ion-cell-manufacturers-78881.html


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## major (Apr 4, 2008)

joamanya89 said:


> Battery type explanation...?


http://batteryuniversity.com/ I'm not saying there is anything wrong with this site, but in general.....Don't believe everything you read on the interweb  Battery U is a good place to start. Take the topics and buzz words from there and do further web search and build your knowledge base.


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## Siwastaja (Aug 1, 2012)

Shortly put;

There are _countless_ of different types of lithium-based batteries. You can try to divide them to a few groups, like the typical three you mention, but it is more or less wrong.

For example, the so-called "LiPo batteries", or what people mean by saying "LiPo", _are_ lithium-ion batteries contrary to common belief.

In reality, it is like this:

There are many different materials for positive electrode. LiCo, LiMn, LiNi oxides and their mixtures, and then we have LiFePO4.

There are many different materials for electrolyte. It can be non-aqueous liquid (many different chemicals can be used) or a polymer.

Then there are minor additives, and different micro structures.

So there are much more than three different combinations. Just one thing is common, they all fall under "lithium ion".

As a general rule of thumb, properly designed and manufactured LiFePO4 cells should give the longest service life in both cycle number (2000-5000) and calendar time (10 years?) and thus, it should be the best investment. 

Note that all lithium-based battery types seem to be in _about_ the same price range, on average. Hence, given the relatively high price and the ecological aspect of manufacture and usage of materials, LiFePO4 seems to be the winning technology. However, some of the others might be as good as well, but indeed we have read the news about calendar life problems in production EVs using non-LiFePO4 in warm climates.

Then there is "RC-LiPo", cells that are designed to have both maximal Wh/kg _and_ W/kg, at the expense of cycle life and calendar life. They also are less safe. AFAIK, they are LiCo cells with polymer separator. (Correct if I'm wrong). They might be a bit less expensive than LiFePO4 and can give enough current to make a usable low-range vehicle, but if they last only for 2-3 years, it will be very expensive in the long run.

I think this is often missed: for the battery selection, your planned _range_ will be very important. If you are designing a low-range vehicle (something like 20-30 km or less), you really need to pay attention to internal resistance or the C rating of the battery; you need to pull out 3C or more; otherwise, the acceleration will be sluggish. However, if your range will be about 100 km or more, you probably don't need to pay much attention to this; you can get some cheaper cells just because their large capacity will help giving the current you need.

To sum it up; look at the specs of the actual _cells_ instead of _types_, because there are many aspects. And, the real cycle and calendar life is IMO the most important spec, unless you are rich. At least calculate the _real_ price per year.


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## dragonsgate (May 19, 2012)

Siwastaja said:


> I think this is often missed: for the battery selection, your planned _range_ will be very important. If you are designing a low-range vehicle (something like 20-30 km or less), you really need to pay attention to internal resistance or the C rating of the battery; you need to pull out 3C or more; otherwise, the acceleration will be sluggish. However, if your range will be about 100 km or more, you probably don't need to pay much attention to this; you can get some cheaper cells just because their large capacity will help giving the current you need.


I would think it is the other way around. Cheaper Batts. for short range and bigger more expensive for higher C’s and longer range.


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## Siwastaja (Aug 1, 2012)

dragonsgate said:


> I would think it is the other way around. Cheaper Batts. for short range and bigger more expensive for higher C’s and longer range.


OK, let me show you...

Let's take an example of a 100V system. Let's say we would like to have 20 kW available for quick acceleration to higher speeds. This means 20 kW / 100 V = 200 A.

Now, let's make a long range vehicle with a 20 kWh battery (about 100 km / 60 mi of range), so we'll use some random Chinese prismatic LiFePO4, 200 Ah cells. For our acceleration current of 200A, it will be only 1C when we have 200 Ah cells. Practically all cell brands will be very fine with just 1C.

Now, let's make a small-range vehicle with a 4 kWh battery (about 20 km / 12 mi of range). So we will have 40 Ah cells. If we STILL want to have the same acceleration current of 200 Ah, we will pull out 5C from the cells (40 * 5 = 200). For most cheaper Chinese prismatics, this apparently is near the absolute maximum peak and causes a heavy voltage sag and is possible only at high State-of-Charge and at high enough temperature. So, we will use A123's, two 20Ah pouches in parallel; for them, 5C should be no problem.

But they are more expensive per Wh.

So, this example shows that when you up your range, it happens quite naturally that you will have high current output because of the sheer capacity of the pack; your C ratings will be low.

Of course, if you have money, you can afford high-C cells even for low-C usage and it will pay of as an extreme efficiency and low voltage sag, but the difference is not big.

RC toys are a prime example of where high C is needed; they have a very limited range. But real cars are easier, because usually we need the range anyway and will get high _current_ rating even with low _C rating_.

Furthermore, it can be shown that voltage is not part of the equation. It reduces to a simple equation; higher range (in km or mi) linearly reduces C rating, given the otherwise same conditions. (Naturally, a heavier battery pack increases the current somewhat and offsets the result a bit. If the car is otherwise very lightweight, this may be important to take into account.)

The same goes for charging, too. For example, take the Tesla's new supercharger. They charge at whopping 90 kW and say it will replenish 180 miles in just 30 minutes. Still, if you calculate it, it is just about 1C for the 85 kWh battery pack -- 1C is not always even considered quick charging. But due to their _really huge_ battery pack, they can afford relatively low-C charging and still call it supercharging. If their pack were to be half of that, they would need really go to 2C which could be very detrimental to the cell life in the long run, or require more expensive special cells which would still not give any extra range.


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## joamanya89 (Feb 13, 2012)

Alright, appreciate a lot all your answers, and taking advantage that you already talk about car range and stuff, I'd like to ask about two other things...

First, I know the voltage is going determinate the rpm, and the ampers determinates the torque (because it is what create the magnetic fields on the motor's inductance), but if you have keep the clutch and with it the gear box, is that important to use a high voltage? shouldn't it be better to use a 100V for a heavy car, but a 300Ah, and like 48V for a lightweight car and 200Ah?


And on second turn, what about lithium recycling? thinking about that, everything tells me that if I really wanna go green, you should use lead acid batteries


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## Ziggythewiz (May 16, 2010)

The voltage impacts your top speed. At 120V my car tops out at 45 in 2nd gear. If I were running 100V I couldn't get to 40 in 2nd. Obviously gearing could be changed, but more voltage means more top speed.

As for recycling, for now we think lithium will have a useful life of about a decade. When the capacity drops such that it's no longer useful in a car you could continue to use it as solar backup for another decade or three. I've heard of lead being anywhere from 95-99.9% recycleable. It's not 100%. So every time you run a cycle you lose some to the environment. If you do that every 3 years it will add up compared to the longer life of lithium.

Also, I don't know the economics of recycling lithium, but if it becomes rare enough to drive the price up, it will be more worthwhile to reclaim it, or to reclaim more of it.


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## joamanya89 (Feb 13, 2012)

Ok, I won't argue about something I have not clear yet...
But about the voltage, the situation is that I live in Uruguay, 3th World for a lot of people jaja, and here are no lithium batteries, or any ev stuff, so I'm trying to build my own controller, and trying to get the cheaper way, becaus, importing everything is just too expensive...

I'm going to convert a very lightweight car, a citroen mehari, it motor has 30hp, so I was considering use a 75v system, but then to reduce budget, I thought, that keeping the clutch, and the gear box too, I could use a 48V system and perhaps 200Ah, so I could get something like 150km range and perhaps 100km/h...


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## Woodsmith (Jun 5, 2008)

By lowering the voltage you will need more current to produce more torque to pull a higher gear to get the speed you want.

By raising the current you will get I^2R losses in the cables creating heat. Also you will make your motor get very hot as it runs slowly pulling high current.

For the same top speed it is better to use more voltage, giving a higher motor RPM in a low gear, rather then more current giving a lower motor RPM in a high gear.

Also motors are more efficient if they are spinning up to their maximum speed for the voltage due to the back EMF reducing current flow. If that maximum is high due to high voltage then you are able to reach a higher speed in a low gear efficiently.
If you have lower voltage then to produce the same power required for the same speed then a very low gear will be needed where the motor cannot reach maximum speed as it will need to slow down to pull more current to get the torque.


Once you have worked out the energy you need to meet your range and speed requirements you should then aim to get enough battery capacity to meet that. It is better to do that with more batteries of lower capacity then few batteries of higher capacity of the overall same energy.


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## mora (Nov 11, 2009)

If you want to put more amps to the motor at higher rpm you need more voltage (dc motors). This would allow you to drive longer in one gear. 75V will be fine but your torque (amps) will drop quickly as rpm rises. You will need that gearbox.

My guess is that 48V and 200Ah (9.6kWh) will not give 150km range unless you are converting a motorcycle. Even 100km might be struggle but then again I have no idea how much your car will weigh.


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## jumpjack (Sep 9, 2012)

Ziggythewiz said:


> As for recycling, for now we think lithium will have a useful life of about a decade.


I had not such luck: my 60V/24Ah Li-Ion battery is no more able to provide required 25A for my 1500W e-scooter; but I think it could be easily provide 2-3A to power lights at home.
Can you suggest any link/forum/blog where to find info about how to "recycle for home use" such a battery?




Woodsmith said:


> Also you will make your motor get very hot *as it runs slowly pulling high current*.


I didn't get this: why does it pull more current at lower speed?




Woodsmith said:


> [...] as it will need to slow down to pull more current to get the torque.


As above.


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## joamanya89 (Feb 13, 2012)

my car is arround 750kg, but It is to expensive for my to import lithium batteries (for a 75V and 100ah, it would cost $3000), so I'll do it by using lead acid, so de car will be arround 950Kg Ithink...

By the way, do you know what kind of lead acid baterry is better?, I know it must be deep cycle...


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## Ziggythewiz (May 16, 2010)

jumpjack said:


> Originally Posted by *Ziggythewiz*
> _As for recycling, for now we think lithium will have a useful life of about a decade._
> 
> I had not such luck: my 60V/24Ah Li-Ion battery is no more able to provide required 25A for my 1500W e-scooter; but I think it could be easily provide 2-3A to power lights at home.
> Can you suggest any link/forum/blog where to find info about how to "recycle for home use" such a battery?


I'm specifically referring to LiFePO4 which specs at 2000-5000 life cycles. There are many other lithium formulations that have much shorter life, and therefore are not of much interest to us in practical EV land.

To reuse a worn out battery you just need to reconfigure it for the appropriate voltage and have the necessary charge controller/monitoring. If you have a UPS or solar panels and inverter in a 12V, 24V, or 48V setup you would make your pack match accordingly.


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## Ziggythewiz (May 16, 2010)

joamanya89 said:


> By the way, do you know what kind of lead acid baterry is better?, I know it must be deep cycle...


The most economical lead batteries are usually 6 or 8v golf cart batteries. 6V will give the most range and life, but 8V do nicely if you don't have room for the additional weight/space.


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## joamanya89 (Feb 13, 2012)

so you would not recomend me to use 12v batteries? I'm just looking for arround 100km of range, and 90km/h, I would be quite happy with that, do you think it is possible with lead acid? rememmber it is a light car, and also has thin wheel...


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## joamanya89 (Feb 13, 2012)

I would like to know what is the real deal behind the BMS, What does it exactly do?
I've done a research on this forum, and a lot of people talks about it, but every body is saying something different...

What are the real risk on the lithium batteries so we should use BMS?

And is there a real risk or it is just use to be sure you are using all battery's energy, and no one is keeping a bit...?


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## jeremyjs (Sep 22, 2010)

joamanya89 said:


> so you would not recomend me to use 12v batteries? I'm just looking for arround 100km of range, and 90km/h, I would be quite happy with that, do you think it is possible with lead acid? rememmber it is a light car, and also has thin wheel...


You'd be lucky to get 50-60 KM out of almost any conventional lead acid conversion. When it's new.


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## Woodsmith (Jun 5, 2008)

jumpjack said:


> I didn't get this: why does it pull more current at lower speed?
> As above.


As the motor spins up to its maximum speed, for the voltage and load, it produces a back EMF that opposes current flow, so less current can flow into the motor then. That reduction in current results in a reduction of torque so the motor can no longer accelerate against the load that is imposed on it.
That is how its speed is limited when loaded and sets the maximum speed the motor can propel the vehicle in the given situation.

If you want to accelerate more, ie go faster in a given gear, you will need more torque and hence a greater current flow. That can only be achieved by increasing the voltage.

The alternative is to select a higher gear that causes the motor to run slower. The motor, when it runs slower, produces less back EMF and so more current is able to flow into it to generate the torque needed to accelerate to a higher speed.

That method works but there is a limit to how much torque a motor can develop and how much current it can handle before it over heats and melts.

As you can see, you could, in theory, run the car at 12v (at a slow rpm and high gear) but to power it up to road speed you could be pushing through a few thousands of amps. No motor is going to handle that.

It is easier and better to run the car at 120v (at a high rpm and a low gear) and a few hundreds of amps instead.


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## Woodsmith (Jun 5, 2008)

The over heating of the motor, and cables, comes from I^2R. This is current squared multiplied by resistance.

All the cables and the motor have resistance. As the current increases the heating effect is the square of the current. For each doubling of current the heating increased four times.

This is a very good reason to keep the current low.

Also the power is equal to current multiplied by the voltage. So for the same power you can have high current and low voltage or low current and high voltage.

The latter is better.


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## joamanya89 (Feb 13, 2012)

So it would be better also, to have like a 200V system and 50Ah batteries, than 50V system and 200Ah batteries?...



I would like to know what is the real deal behind the BMS, What does it exactly do?
I've done a research on this forum, and a lot of people talks about it, but every body is saying something different...

What are the real risk on the lithium batteries so we should use BMS?

And is there a real risk or it is just use to be sure you are using all battery's energy, and no one is keeping a bit...?


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## Ziggythewiz (May 16, 2010)

joamanya89 said:


> so you would not recomend me to use 12v batteries? I'm just looking for arround 100km of range, and 90km/h


Most 12V batteries not not true deep cycle ones (marine usually means hybrid) and will not last long. It's tough to get much range from lead because due to peukert you can only use about 60% of your capacity, and because deep discharges reduce lifespan you have to limit it to 50-80% DOD. So you end up with ~25% of the sticker rating. 

With my first pack I was happy while I was getting 15 miles.


A 200V system is capable of reaching speeds up to 4x that of the 50V system, but will require 4x the cell interconnects as well.

There are plenty of threads discussing BMS or no BMS. Either way, if you overcharge or overdischarge your cells they will die.


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## joamanya89 (Feb 13, 2012)

So, I would need to get a bigger motor, because all of 30hp motors are arround 75V...

Does some one know where could I get a PM brushhed DC motor to import...?


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## Woodsmith (Jun 5, 2008)

joamanya89 said:


> So it would be better also, to have like a 200V system and 50Ah batteries, than 50V system and 200Ah batteries?...


Yes.



joamanya89 said:


> So, I would need to get a bigger motor, because all of 30hp motors are arround 75V...


No. You can over volt a motor as it spends very little time running at a high voltage, or at high power, so it will survive.
But if your voltage is getting above 72-96v range you should be thinking about advancing the brushes to prevent arcing.

I run a 24v motor on 48v in my tractor (low speed, low power) and would have no concerns about increasing to 72v in due course.


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## jumpjack (Sep 9, 2012)

Thanks woodsmith, very interesting and useful explanations.
Maybe you can also answer another question: how can I calculate the maximum speed an electric vehicle can achieve on a slope? Intuitively it depends on vehicle weight and motor current (besides, of course, slope angle), but I can't figure out a formula. Let's ignore friction in a first instance.

Example: my e-scooter has:
Motor power P= 1500 W
Motor voltage V= 60V
Wheels: 2xR=10" 
Scooter weight: 85 kg 
Driver weight: 75 kg
Total weight: W = 160 kg

Which speed is it supposed to reach on a given slope (A= xxx degrees)?


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## jumpjack (Sep 9, 2012)

joamanya89 said:


> So it would be better also, to have like a 200V system and 50Ah batteries, than 50V system and 200Ah batteries?...


If I understand correctly, in first case you can reach higher speed, in second case you can ride greater slopes, as the more is the capacity, the more is the current you can pull from battery, the more is the motor torque (until it melts  )
(The onboard controller of course will prevent motor from pulling too much current from battery: if motor is rated 5000W, it won't be allowed to pull more than 100A from a 50V battery)


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## adeyo (Jun 6, 2012)

Woodsmith said:


> .... aim to get enough battery capacity to meet that. It is better to do that with more batteries of lower capacity then few batteries of higher capacity of the overall same energy.


Thanks for all the insight in this thread! Can you elaborate on this principle as well?


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## jumpjack (Sep 9, 2012)

Is this true?



> In brushless motors, unlike DC motors, there is no possibile regulation of current flow: current is constant, instead what can be changed is the percentage of time in each period T of time for which the current flows in the motor (PWM drive). At low speed, the percentage is low; at higher speed current flows for a longer time; at full speed, current flows 100% of time.
> This cause torque in electric motor to be constant versus motor speed (RPM), unlike Internal Combustion Engine, where torque is higher in a small interval of speed. Speed is changed by changing the T period length (hence the frequency)


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