# Making custom battery charge circuits for your electric vehicle



## electric_driver (Feb 4, 2017)

The alternators of the hybrid drive train I'm making will be using a voltage and amperage that is not very common (48V @ 145-155 A). As a result, it is difficult to find a charger which I can use in this system (since most chargers are meant to be powered from the electricity grid (so 230V or 110 V). Also, most chargers do not allow the batteries to be charged at the highest C-rate they can sustain. To resolve this, I hereby put up a post to let us solve this (and hopefully generate a solution that will benefit, not just me, but anyoone building an electric vehicle that uses unconventional voltages/amperages or batteries).

An obvious solution is that we just describe the procedure on how to create (a very simple) electric charging circuit, from scratch.

First off, here are the details of my electric vehicle system, which can serve as an example:

* the batteries I use are 4 NiFePo4 batteries of 12V, with 2,5Ah which I wired in series to make one 48V battery. I use two of these intermittently, but that's not important here. The C-rate of the batteries is 4C

* the input power is (as allready mentioned above), 48V @ 145 to 155 A

Let's start with calculating out some things based on the variables we allready know.
We know that:

* They're NiFePo4 batteries. The nominal voltage of NiFePo4 cells is 3,2V. Since we know the nominal voltage, we also know how much cells there are in the 12V battery. This is 4, since 3,2 x 4 = 12,8 V. So, it's a "4S pack". We don't know how many P's it has but that's not important. We also know the maximum charge rate with this, since the maximum charge voltage at which to charge LiFePo4 batteries is 3,6V per cell; since we have 4 cells, the maximum charge voltage is 14,4V for these 12V batteries.

* We know the C-rate of the 12V batteries is 4C, and the capacity is 2,5 Ah. So 1C= 2,5 and we have not 1 but 4 C, so maximum discharge rate is 10A (2,5A x 4). Charge rate would be a little less, but near that amount.

The charge curves for NiFePo4 tell us that we best charge them:
- from 10 to 90% of State of Charge (SOC) at the full C-rate the batteries can handle (in our case 4C or hence 10A)
- from 90% to 100% of State of Charge (SOC), at 0,5C (or hence 1,25 A)

So ideally, in my example, I'd need to make a charging circuit that is able to charge 4 NiFePo4 batteries of 12,8V from a 145A @ 48V input stream. The rate at which to charge the batteries would be 10 A @ 14,4 V for 10-90% of SOC, and 1,25 A @ 14,4 V for 90%-100% of SOC

How would I make such a circuit in practice ?

Also, I'll only be using a small part of the power (more precisely, the surplus power will be: 145 A @ 48 V - 10 A @ 14,4 V = 6960 watt - 144 watt = 6816 watt ). So where does this power go in such a charge circuit ? Is it normally just grounded ?

The above calculations can obviously be done for any type of battery (LiPo, NiCd, ...) -regardless of their C-rate- and for any other input stream. We just need to specify now how one can make the charge circuit in practice.


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## dcb (Dec 5, 2009)

electric_driver said:


> So where does this power go in such a charge circuit ? Is it normally just grounded ?


Lol .


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## Sunking (Aug 10, 2009)

I hope this is a thought only exercise as a learning experience because you have a lot to learn. 

To start I do not know of any LFP battery that can handle a 4C charge current. Even if one existed you would not want to do that as there is just to many things that can go wrong and all end in fire. 

Lastly what do you mean ground? Ground has nothing to do with anything or any function. If you are speaking of a Traction Battery Pack, there is no Ground as that would get you killed. 

Charing LFP or really any lithium battery is the easiest battery in the world to charge. All it takes is a CC/CV power source that you can control the voltage to within 1% which is extremely easy to do. For LFP any Float Charger with an adjustable output can be used. Set the voltage anywhere from 13.6 to 14.4 volts and you have a charger fo rlithium batteries. They are drop in replacements for lead acid. 

The only real trick is to decide if you want to fully charge them up to 14.4 volts which requires some sort of BMS to terminate the charge. Or use no BMS and just charge to 13.6 to 13.8 volts and let them Float.

What you are thinking is quite simply a bomb.


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## electric_driver (Feb 4, 2017)

dcb said:


> Lol





Sunking said:


> Lastly what do you mean ground? there is no Ground as that would get you killed.
> What you are thinking is quite simply a bomb.


Ok. I think you're having the wrong idea of my intentions here. My project intented to build a demonstrator to showcase my hybrid drivetrain (see my other posts). During construction however, it became clear the kart wasn't able to hold the extra weight of the alternators and the internal combustion engine I wanted to put on it. So, I changed my tactic to focus on building the generator (internal combustion engine + alternators) and the electric kart seperately. The generator will hence be a stationary charger. So it's placed on the ground and it would be able to ground excess power.

The fact that I seperated the generator and the kart is also the reason why I mention to possibly ground the excess power generated. In my initial design, I just intented to reroute the excess power to the electric motor, but now that both are seperated, that's not an option any more.

The current design (seperated generator and kart) will generate huge amount of power that is wasted, and so it's uneconomic and unecologic. That said, the generator too is just a device to help me demonstrate my drivetrain, so efficiency/ecology is of no importance here (it won't be the finished product anyway and it will hence never be replicated in exactly this way by others). 

I guess that it might be best to nonetheless look for different batteries (especially since I didn't buy them yet), but I don't know of any brand/model that would be 
* able to charge at a rate of 145 to 155 A or at a rate that is at least far greater than 10A
* are cheap
* are available off-the-shelf and easily obtainable

The batteries I inititially intented to acquire (which could indeed handle a 4C charge rate) were these: http://cs-batteries.de/LiFePo4-Motorrad-Starter-Batterie-PRO-12V-25Ah-150A-420g
I selected these mainly because of their other specifications:
* high discharge rate (140 A) so able to drive the 10 kW electric motor of the kart (note that although the charge/discharge rate is often about the same in batteries -both being specified by the C-rate -, the example of the cs-shop batteries show that this isn't always the case and the charge and discharge rate can vary considerably; here: 1400%
* low weight
* small size
* very small capacity
That said, since the kart will be seperated off (or even no longer done at all), these requirements all fall away, and only the charge rate and the cost are still important factors. Although some of these are of importance to my patent (of my patented drivetrain), the vehicle such a generator could be intented for can be of any size (even lightweight delivery vehicles -as UTV's, light commercial vehicles, ...-) so the whole can still be considered low capacity/small/lightweight.

If someone can tell me some suitable brands/models, that would be appreciated. I am mainly thinking of AGM batteries currently (since these seem to be used with starter motors too, so have a high output, which could mean that they can be charged quickly too (high C-rate) ?
The capacity of these AGM batteries are generally around 15 to 30 Ah I believe, but as said, that's not a problem any more, and actually, the higher the capacity the better (for the C-rate at least). A 30Ah battery has, even with a 1C rate, then still 30A. I would preferably need to get to 145-155 A, so AGM batteries would then still need to allow for a C-rate of 5. I'm not sure that's possible; if not perhaps someone of you can tell me what battery type _does_ allow such high C-rates, or I can just increase the capacity even more (using 2 batteries in parallel, which yields 60 Ah). One problem that does occur with very high capacity numbers is that it would then no longer comply with the "small capacity" claim of my patent, so I rather not make it too high neither. I mentioned that I consider 1 km of range (which is about 1 minute of driving time I guess) to be a "low capacity" for a vehicle, but a bit more (up to say 10 km or 10 minutes of driving time) can still also be considered low capacity. A 30 Ah battery still falls under this reasoning then and can be used without problem (1 minute of driving at say 127 to 145 Amps per hour makes 2,11 Ah to 2,41 Ah; 10 minutes makes 21,1 Ah to 24,1 Ah). When standardly, the motor is spun at double that amperage (254 to 290 Amps), even 42,2 Ah to 48,2 Ah is needed, so the battery can even be have a capacity of up to 48 Ah, and still fall within the definition. Also, if the torque is higher, it could be of great benefit to the light commercial vehicles/UTV's I'm aiming my system to be used in.

Aside from the batteries -which is uniquely my problem-, the question still holds I think: how is excess power dissipated in a regular charge circuit ? I have an enormous amount of power I would dissipate, but even in regular chargers (say a 5A, 6V charger working off the mains electricity grid -which still means an input of 3680 watt- (230V @ 16 Amps)), there is also surplus energy that is dissipated (in this case 3650 watt).


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## Duncan (Dec 8, 2008)

Hi Electric - driver
You need to sit down with some physics textbooks as you really don't seem to understand the real world

I suggest you have a look at this Thread which is where we put the threads that don't seem to understand the real world

http://www.diyelectriccar.com/forum...-free-energy-perpetual-motion-over-13449.html

As far as the "excess power" in a normal battery charger the mains supply is not 230v and 16 amps - it is 230v and - UP TO 16 amps - if the charger only needs 0.13 amps to feed the battery (as in your 5A -6v example) then that is all it takes - there are losses to heat in all energy transformation but in a well designed charger these should be about 5%


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## electric_driver (Feb 4, 2017)

Duncan said:


> As far as the "excess power" in a normal battery charger the mains supply is not 230v and 16 amps - it is 230v and - UP TO 16 amps - if the charger only needs 0.13 amps to feed the battery (as in your 5A -6v example) then that is all it takes - there are losses to heat in all energy transformation but in a well designed charger these should be about 5%


Yes, I thought this would be the case (that it just doesn't draw that much power at all). But then, the question arised to me that if this isn't used, the "excess power" still stays on the grid, and supply and demand of the power can never be equal I assume (ie the power is produced in a power plant, but I doubt the power plant owners calculate out the power that will be drawn by the users). So again, there is surplus power on the grid somewhere that isn't being used, so how is that dissipated ?


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## Duncan (Dec 8, 2008)

When you add lots of small variable uses together you get a smoother function
The water in you glass is lots of individual molecules but together they act as a liquid

The tens of thousands of consumers acting individually act as a much less variable whole and the power companies can cope with that - famously in the UK when popular programs were on the power companies had to have extra capacity for the advert breaks when half of the country would rush to the kitchen and put the kettle on


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## piotrsko (Dec 9, 2007)

It is not "excess" power. It is excess potential. It does not function until it is used. Like a battery: no current flow from chemical change occurs until a load circuit is connected.


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## ken wont (Jul 6, 2016)

electric_driver said:


> Yes, I thought this would be the case (that it just doesn't draw that much power at all). But then, the question arised to me that if this isn't used, the "excess power" still stays on the grid, and supply and demand of the power can never be equal I assume (ie the power is produced in a power plant, but I doubt the power plant owners calculate out the power that will be drawn by the users). So again, there is surplus power on the grid somewhere that isn't being used, so how is that dissipated ?


First, I believe you are Hyper-Focusing on a detail that you don't need to understand or worry about. Take a deep breath, relax and think instead about what you really want your project to accomplish. 

Is the Kart for short range high power, short range low power, long range low power, long range high power? How quickly do you actually need to charge the batteries? .... etc. Get a good idea of the big picture, then, think about each stage to accomplish that.

Right now you are very enthusiastic,(which we admire), but in this state it is very hard not to get caught in the swirl of Hyper-Focusing! When you find yourself getting frustrated and spending too much time on one detail, do something to distract yourself and look at your goal from a different direction.


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## electric_driver (Feb 4, 2017)

For the AGM batteries; here's a setup that would hence work (I think, not sure on the C-rates yet since I can't find any data on that):

I can wire 4 AGM batteries of 12V, 30Ah (or 40Ah or 50Ah) in series, yielding a 48V, 30-50Ah battery. I can drop the second battery pack alltogether so I only need 4 batteries, not 12 (else, it would become very heavy/big indeed). An added advantage will be that the electronics system will be much simplified this way. Downside is that charging and discharging will occur from the same 48V battery, so C-rate may be negatively affected a bit, but perhaps it's still sufficient. I'll also be able to run the electric pump for my watercooling on one of the AGM batteries, and be able to run the starter motor from yet another one of the AGM batteries (so I don't need to have a seperate battery just for that, and all batteries will be constantly recharged, so they will never run out of power neither).

One more thought I'm having is whether or not I really need a motor controller ? For my motor, the Sine-wave VEC500 would be needed as the motor controller. The price of that is almost as high as my electric motor (825€) and I rather avoid buying it. Can't I just run the motor by connecting the motor directly to the battery somehow ? I could do without engine speeds (so just use a single speed) and just propel the vehicle by activating and deactivating the motor as needed.

Oh right, and for the problem that the kart and the generator will be seperate (meaning they will need to be connected to a wire and the generator might not be able to move), I have one more idea:
can't I just put wheels under the generator frame and use the kart to tow it ? I guess it will look silly, but the whole is just for demonstrations anyway, so it would be workable, and it will be safer, since if the batteries catch fire, they will be in the towed section, which is further away from the driver.
The alternative is that I keep both stationary and just spin the kart's wheels (off the ground) with it, but that doesn't make for a good impression I think.


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## dcb (Dec 5, 2009)

You are trying to race ahead to a finished product with no idea how any of it actually works. This isn't web development.


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## electric_driver (Feb 4, 2017)

I looked what chargers there are available for AGM batteries. I specifically thought of using the Optima AGM batteries, and so looked at the website, but appearantly the charger they use is but a mere 12 amp (@13,8V-15V) charger, so that's only marginally better than the 7A charger with the 2,5 Ah NiFePo4 batteries I first intented to use. That means that the AGM batteries can only be charged (and discharged) at 0,25 C or so, which is pretty pathetic (I thought it would easily allow up to 5C, given that it can start a starter motor which requires much higher C-rates). It seems though that that's the "cold cranking amps" measurement, so this can't be sustained for long. In the case of the Optima AGM battery, the cold cranking amps were 900 Amps (so the cold crancking amps c-rate of these AGM batteries were 18C). 

The NiFePo4 batteries seemed equally good in this regard, since they too allow a cold cranking amp rating that equals say 10C (see http://www.lithiumion-batteries.com/products/12v-50ah-lithium-ion-battery/ ). The difference off course was with my other NiFePo4 batteries that I selected those with lower Ah ratings, so even at 1C, it didn't allow high amps for charging.


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## electric_driver (Feb 4, 2017)

I looked a bit further and there seem to be battery types that allow an even higher C-rate (up to 5C, without any danger), and they're even more environmentally friendly as AGM batteries. Downside is that they seem to come in voltages of just 1,2V. The 50Ah battery at 5C gives a possible output of 250A (@1,2V). That's even more than what I need. I could do with a 30Ah battery (output = 150A) -and 30 Ah is still more than the capacity I need; ie I can go as low as 2,5 Ah-.

However, I would need 48V, so I would then need to use 40 such batteries. That seems a bit overkill though.

One other possible way I'm thinking of is by just using a battery with much more Ah, and then using a DC-DC converter. Wouldn't that reduce the Ah rating too in a way ? More precisely: the voltage is but 1,2 V and I need 48V. So the voltage would be stepped up 40x. Wouldn't the amp rating be lowered 40x then as well ? So I could use say a 2000 Ah battery and have just 50 Ah left (2000/40 = 50). I could go even lower since I need but a minimum of 2,5 Ah, so could do with even a 100 Ah battery (100/40 = 2,5), or any battery with an Ah rating between 100 and 2000. This battery type is available in such Ah sizes, so it could be a real option, if my reasoning here is correct.

If the above isn't a correct reasoning, the best method would be my other proposed method in which I both charge the batteries (at a low amperage) and drive the electric motor with the surplus/excess energy. It should be possible now that I'm considering to connect the generator using a wire to the electric engine and tow the whole assembly with the kart. My only concern with the latter is: how do I make this circuit ?


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## dcb (Dec 5, 2009)

putting a tiny battery in a hybrid is counter to efficiency.

1. you cannot recapture as much braking energy
2. you have to cycle the engine more, and run it longer.
3. engine "switching losses" are fairly astronomical
4. You get zero benefit from plugging into the wall

There is absolutely nothing environmentally friendly about your proposal, and it makes zero engineering sense (except perhaps to you).

If your gasoline engine and alternator is making more energy than it needs to, then that is a failure on the designers (your) part.

If you can't even measure static torque, there is next to zero chance you have the skills and understanding to do an accurate accounting of the efficiency of such a system, let alone make efficiency improvements. You will be wasting time/money/fuel to prove nothing.

What point is there in discussing a tiny battery when it is such an awful idea in this application? Your only claimed benefit was weight savings. Then you add a starter, and a 12v system, and alternators, and a trailer, etc... what magic is going to make it make sense?

with parallel, you at least get rid of the alternators. And you can just bump start the engine, so you don't need such a heavy duty 12v system. But I think your liberty of discussing gas engines (given you don't really get them either) has expired. In which case a tiny battery discussion is even more pointless.


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## Sunking (Aug 10, 2009)

electric_driver said:


> I looked a bit further and there seem to be battery types that allow an even higher C-rate (up to 5C, without any danger), and they're even more environmentally friendly as AGM batteries. Downside is that they seem to come in voltages of just 1,2V. The 50Ah battery at 5C gives a possible output of 250A (@1,2V). That's even more than what I need. I could do with a 30Ah battery (output = 150A) -and 30 Ah is still more than the capacity I need; ie I can go as low as 2,5 Ah-.


Sorry but you really do not know anything about batteries. Not even the basics of series and parallel circuits. The batteries you linked to are NiFe aka Edison Batteries. You cannot charge them at 5C because the internal resistance will not allow it. They have extremely high internal resistance. They can be discharged at 5C but some really bad things happen that will rain on your parade. 

Due to the very high resistance of them at 5C discharge your voltage collapses from 48 volts to less than 20 volts. In addition to that thunderstorm raining on your parade comes the tornado call Mr Peukert blowing you away by turning your 50 AH cells into less than 5 AH cells. 



electric_driver said:


> However, I would need 48V, so I would then need to use 40 such batteries. That seems a bit overkill though.


Do not worry about it because it will never happen. NiFe batteries when it comes right down to it are worthless. Edison never reapplied for the patent, and no USA manufacture has made them for 40 years. Only Chi-Coms make them now for fools on solar energy who do not know anything about batteries like yourself. Here is what will really stop you. If you think AGM and Lithium batteries are expensive, NiFe cells cost 3 to 5 times more than Lithium. Nickel Silver is expensive because it is a semi-precious metal. If that does not stop you, weight and size will. A 50 AH Nife Cell is going to weigh 6 times more than Lithium and 5 times the size in volume. 

Time for some more embarrassment for you. You do not understand the simplest basic fundamental a first week student knows about series-parallel circuits.

Series: voltage and power adds
Parallel: current and power adds. 

Last comment, I do not think you even know what C-Rate really means. If you charge or discharge at say C/4 is 15 minutes. That means you can fully charge or discharge a battery in 15 minutes. So please explain to all of us in detail what application you have that only requires 15 minutes of power or be charged up in 15 minutes. 

There is no reason for me to answer the rest of your questions because you do not even have any basic fundamental knowledge a first week student has, and thus incapable of understanding the answers.


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## electric_driver (Feb 4, 2017)

dcb said:


> If your gasoline engine and alternator is making more energy than it needs to, then that is a failure on the designers (your) part.


The gasoline engine/alternators are not oversized. Compared to regular commercial hybrid vehicles, the generator-part is actually not very powerful at all. Most hybrids and electric cars have 11 and even 22kw chargers, and these charge a battery far faster than what I intent to do.

Anyway, I don't need to tell you guys this, you have more experience/knowledge on electric cars than I do. That's also the reason why I came here in the first place: to improve my demonstrator design since I also knew that the fact that I can't store power fast enough with my demonstrator is a big flaw, and as dcb pointed out: I'll prove nothing with it (except perhaps create some public awareness of my project). So, I really want to improve it (and I still can since I haven't bought the batteries or charger yet). I'll execute the project regardless. So if you guys can tell me a brand/model of a usable charger for my 48V, 150A system, I'll be glad to hear it and I will change the project accordingly. Even if you think the drive train will create no energy savings/improve ecology, there's still no reason why you shouldn't help me to at least prove it doesn't work. If I work the demonstrator out as how I planned it (which doesn't allow to charge the batteries at full speed), the test will not be a test at all, and other might replicate it still (given that the test was not done correctly).

So please give some examples of brands/models of chargers and batteries that you would use if attempting such a project.



electric_driver said:


> One other possible way I'm thinking of is by just using a battery with much more Ah, and then using a DC-DC converter. Wouldn't that reduce the Ah rating too in a way ? More precisely: the voltage is but 1,2 V and I need 48V. So the voltage would be stepped up 40x. Wouldn't the amp rating be lowered 40x then as well ? So I could use say a 2000 Ah battery and have just 50 Ah left (2000/40 = 50). I could go even lower since I need but a minimum of 2,5 Ah, so could do with even a 100 Ah battery (100/40 = 2,5), or any battery with an Ah rating between 100 and 2000. This battery type is available in such Ah sizes, so it could be a real option, if my reasoning here is correct.


No answer was given on whether my reasoning here was correct or not. Is this method valid or not ? I probably won't use the Edison batteries, but if the method above works, I could just adopt the technique and pick a different type of battery (AGM, NiFePo4, ...)

For instance, high-Ah AGM batteries (at 12V or 6V) seem to be common in the forklift-industry.
Let's take the 140 Ah, 12V AGM battery as an example:
12V x 4 = 48 V
DC-DC converter: x4, so 140 Ah/4= 35 A = 1C
at 4C = 140 A output continuously
48V, 100A chargers too can be obtained for them. They are not ideal though since most commercial 48V, 100V chargers are electricity grid powered (230V, 16A) and they're very large as well.


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## dcb (Dec 5, 2009)

it is invalid, you don't have the engine and alternators make more power than needed. You don't add a fancy charger, nobody does that. You just charge straight through the inverter/power factor corrector and software controls the throttle and generator magnetic status. In your case you have to sort that out twice as you have alternators and drive motors that can both generate. P.s. the 1930's called and they want their project back...



electric_driver said:


> I'll prove nothing with it (except perhaps create some public awareness of my project).


You seem more interested in attention than in sound engineering or reasoning (or homework).


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