# ( controller ? or not )



## clintster7 (Jun 29, 2010)

hey new to the site .. good stuff 

Im in the process of designing a car for the drag strip and have read a few of the threads ..

From what I understand a controller is a pricy item .. but with my project I will not need a variable controller .. what I need is an on/off switch . is there a simple way to go about the wiring and switch .. I know this is fairly vague but with what I am going to try to accomplish i just need all or nothing .. 

I have not picked out a motor for sure yet as I am still researching .. any help would be appreciated .. 

the car will have a gas engine and an electric one that will turn on at full throttle ( like nitrous ) so the electric motor will only need to be equivalent to 75 hp or so .. but that would be 75hp more through the whole power-band 

thanks


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## TX_Dj (Jul 25, 2008)

Quoting your post in the "where do I get started" thread, this info may be missed otherwise.



clintster7 said:


> hi I jumped the gun and posted in tech and should of started off here ..
> 
> ok I will start with what requirements I am going for
> 
> ...


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## TX_Dj (Jul 25, 2008)

The short answer is yes, you will need a controller.

The controller's purpose isn't just varying speed. The controller also limits current to acceptable levels to prevent you from turning the motor into a big ball of plasma.

Motors cost as much, and in some cases, significantly more than a controller. And I doubt you really want to replace one before you hit the half-way line, yeah?

My question though is... why do you want to carry the weight of a useless ICE on a drag race vehicle? Seems pretty pointless to me, when the EV will beat the pants off anyone who has an ICE in their car anyway...


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## TX_Dj (Jul 25, 2008)

TX_Dj said:


> when the EV will beat the pants off anyone who has an ICE in their car anyway...


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## clintster7 (Jun 29, 2010)

TX_Dj said:


> The short answer is yes, you will need a controller.
> 
> The controller's purpose isn't just varying speed. The controller also limits current to acceptable levels to prevent you from turning the motor into a big ball of plasma.


So at no point none of those drag cars are at maximum battery out put ? I thought that if I wanted to go faster I would need more volts / amps .. and if all I wanted was to have a motor go as fast as it could wouldn't it make sense to not hold anything back ..? there would have to be some type of voltage regulator that could regulate the maximum output without spending 1000 bucks on a variable controller when I do not need it . 100 hp could be harnessed with a set of wide tires. on / off is all I need .. plasma ball would be if the batteries output exceeds what the electric motor can handle ( is this correct )


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## Guest (Jun 30, 2010)

Yes sort of but not all at once. If you dumped 2000 amps into your motor all at once you will most likely twist your drive line right off. So control the output to what your motor can handle and your drive line can handle. Those wide sticky tires will create a high torque load on the drive components at full on power. Talk to the experts on using full on or full off. It can be done on a low power system. The old Kaylor system was like that. On or off. But they used like 72 volts max and split that into two power packs. One at 36 and the other at 72 and used a small sepex starter/generator style motor on little light weight buggies and they still warned that full 72 volts and amperage from your pack in low gear will twist an axle right off. So you see you do need some control of the torque you will be producing. 

Pete


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## order99 (Sep 8, 2008)

Think of it this way-would you design an ICE dragster with no accelerator, just a starter switch going from 'Off' to 'AAAIIIIEEEEE!!!!'? Nope.

Having said that, you might be ok with a Contactor or Immersion array like the ones below(just for the drag strip mind you):

http://www.poormansev.com/id24.html


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## clintster7 (Jun 29, 2010)

order99 said:


> Think of it this way-would you design an ICE dragster with no accelerator, just a starter switch going from 'Off' to 'AAAIIIIEEEEE!!!!'? Nope.
> 
> Having said that, you might be ok with a Contactor or Immersion array like the ones below(just for the drag strip mind you):
> 
> http://www.poormansev.com/id24.html


well thats true to a point but think of this . some drag cars launch way harder than a direct drive EV would because ICE draggers are dumping their clutches at 3-4 k rpms or more .. with a direct drive Im not sure that is more of a violent launch than a pro street launch because ev's are so smooth . ( on a lower hp ev ) just my thoughts


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## clintster7 (Jun 29, 2010)

order99 said:


> Think of it this way-would you design an ICE dragster with no accelerator, just a starter switch going from 'Off' to 'AAAIIIIEEEEE!!!!'? Nope.
> 
> Having said that, you might be ok with a Contactor or Immersion array like the ones below(just for the drag strip mind you):
> 
> http://www.poormansev.com/id24.html


thanks for the link by the way


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## Qer (May 7, 2008)

Oh my... Ok, here goes!



clintster7 said:


> but with my project I will not need a variable controller .. what I need is an on/off switch


First you have to decide what kind of motor you want. If you're going for a DC-motor you could, theoretically, just switch it on or off, but an AC- or BLDC-motor you can't since they need active electronics to actually rotate.

You're not specifying what kind of motor you're planning to use, but I get the feeling we're talking series wound motors (especially since you state that it should be cheap too) so that's what I'll presume.



clintster7 said:


> So at no point none of those drag cars are at maximum battery out put ? I thought that if I wanted to go faster I would need more volts / amps .. and if all I wanted was to have a motor go as fast as it could wouldn't it make sense to not hold anything back ..?


That's correct. The controller holds the current down since you want to actually reach the goal too. If your whole car blows up after a fraction of a second there won't be much of a race, right?



gottdi said:


> If you dumped 2000 amps into your motor all at once you will most likely twist your drive line right off.


From the Z2K-logs I've seen that's exactly what most of those drag racers do; instantly dump (nearly) 2000 amps into a siamese motor in series. We're not talking ordinary family car transmissions here... 



clintster7 said:


> with a direct drive Im not sure that is more of a violent launch than a pro street launch because ev's are so smooth . ( on a lower hp ev ) just my thoughts


As I've said, I've read and analysed the logs. Nothing smooth over EV-drag racing. It's more of a sledge hammer approach.

Anyway, back to the question about an on-off-switch. In one of the logs I have from an actual drag racing run the motor current jumps from 0 to 1700 Amps in less than 0.1 seconds, during the same time the motor voltage jumps from 0 to 60 Volts (two motors in series) which gives about 35 mOhm. During the same time the pack voltage drops from about 380 to 350 Volt (about 17 mOhm).

So, what whould happen if you replaced the controller with a switch in the same situation? Probably something like this:



You get brutal arcing in the switch/contactor that might blow it up directly at start. That is if you're lucky. If you're unlucky, it survives.
IF the switch/contactor survives, your motor current will spike away to about 7500 Amps. This is when it's very probable that the switch/contactor welds shut which will be a slight inconvenience later.
Your car will probably skid like hell since you slam the transmission with torque that's way out of scale, that is if the transmission doesn't just snap instantly.
If you, despite all this, manage to control the car and transmission holds your brushes will overheat and the motors will turn into giant plasmaballs. This will short the motors and pretty much bypass the internal resistance.
Current will now ramp up to north of 15000 Ampere since the only resistance left in the circuit is the batteries and cables, which will make the batteries generate over 5 MW heat! They will instantly explode.
This is when the slow (relatively speaking) electro-chemical reaction in a human brain will start to pick up that something isn't quite right and you'll frantically try to break the circuit, realising the switch/contactors are welded stuck.
Ragnarok. Inferno. Emergency care. Rehabilitation. Medical bill. Or possibly funeral.

Unless you're aiming for the Darwin awards a controller is a pretty good thing to invest in.


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## GerhardRP (Nov 17, 2009)

Qer said:


> Oh my... Ok, here goes!
> 
> Anyway, back to the question about an on-off-switch. In one of the logs I have from an actual drag racing run the motor current jumps from 0 to 1700 Amps in less than 0.1 seconds, during the same time the motor voltage jumps from 0 to 60 Volts (two motors in series) which gives about 35 mOhm. During the same time the pack voltage drops from about 380 to 350 Volt (about 17 mOhm).


Lets see. Motor Voltage/ battery voltage= 60/350 = 0.17 = PWM
Battery current = PWM * motor current = .17 * 1700 = 289 Amps
Battery resistance = 30 volts/ 289 amps = 103 mOhm

Gerhard


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## clintster7 (Jun 29, 2010)

ok I get what your saying .. 
wow 7500 amps from one 12 volt battery .. Just kidding ya
so at the bare minimum I would need the correct size resistor to keep the current in check. But maybe a two stage one but not a variable one ( as a minimum )


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## clintster7 (Jun 29, 2010)

I need to do some more reading I'm kinda in the dark on the formulas above and what exactly they mean .


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## toddshotrods (Feb 10, 2009)

I love Qer's post ^^^ ROFLMAO!!! 

I think you guys are misunderstanding what he wants to do though. From what I gather he wants to run an electric motor as a powerbooster. He will already be moving under ICE power (he stated at full throttle). Nitrous systems are normally wired to only activate at *full* throttle (micro switch on the throttle). His electric motor would be wired this way. It would spin inactively until his foot was completely planted in the accelerator pedal, and would only be under power as long as he kept his foot buried in the pedal. Any variation from full throttle and the contactor opens again. You would need other safety systems though (rpm, temp, current, etc).

It's basically a "75(hp)-shot" of electric boost - pretty interesting idea. 

As for doing it without a controller, Qer has some valid (humourously stated) points. I'm not so sure it would end quite so dramatically. I would guess that, providing you have good racing instincts/quick reactions, you would be able to get the emergency cut-off pulled without physical harm - except maybe to your motor and/or pack. Just like N20 though, it'll likely be an expensive error. The problem is you are in uncharted waters. You might want to start off with 5-10hp, and work your way up - learn as you go. You might not get much in the way of faster ETs, but you will learn what works and what doesn't relatively inexpensively, and much more safely.

All that being said I would still run a controller.


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## clintster7 (Jun 29, 2010)

thanks toddshotrod I was just tryin to get a more tech answer in tech section about how an on off swich might be achieved . I kinda got 2 threads going . I was tryin to keep the 2 on different subjects but now it's all runnin together .. That's cool though . I am still a bit in the dark as to what a controller does .. Is the controller actually the only factor as far as amps and watts to the electric motor ..

on non EV 's ( other uses for electric motors ) where only one RPM is needed what kind of setup would be similer to that..


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## TX_Dj (Jul 25, 2008)

clintster7 said:


> some drag cars launch way harder than a direct drive EV would because ICE draggers are dumping their clutches at 3-4 k rpms or more .. with a direct drive Im not sure that is more of a violent launch than a pro street launch because ev's are so smooth . ( on a lower hp ev ) just my thoughts


They have to dump their clutch at 3000-4000 RPM, because that's where the engine generates max torque, and torque is what you need for the launch.

The EV generates max torque right off of 0 RPM, so that's why they don't do this (don't need to).

You'll get a better launch with an EV at 0 RPM, imho. Go back and watch as Scotty launches the Killacycle rocket ship.  BOOM, instant torque and power.


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## toddshotrods (Feb 10, 2009)

TX_Dj said:


> ...You'll get a better launch with an EV at 0 RPM, imho. Go back and watch as Scotty launches the Killacycle rocket ship.  BOOM, instant torque and power.


I love the potential of EV in racing, but that kind of information needs to be presented with full disclosure. KillCycle is fast, but it took a massive investment to get to that level of performance. Just to be honest and clear, it is still a full second behind its ICE equivalent (Pro Stock Motorcycle PSM = 6.847). In fact they run almost consistently in the 6's now. The same goes for the street-legal cars, maybe even a bigger performance gap.

I'm not knocking any EV accomplishments - just saying we have to keep things in perspective. To tell someone just do it with an EV is misleading because you won't go anywhere near as fast for the same money - yet. I could run in the 8's with ICE, for what I will be spending on the Inhaler's powertrain. It costs to launch that hard.


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## toddshotrods (Feb 10, 2009)

clintster7 said:


> I am still a bit in the dark as to what a controller does .. Is the controller actually the only factor as far as amps and watts to the electric motor ...


The controller gives you just what the name implies - a way to control the voltage and current being applied to the motor. Without it you have to control it with the size and configuration of the battery pack. You would have to make sure that your pack could never deliver more than a specified amount of power, and figure out how to control whether that power is delivered as pressure (volts) or volume (amps). A controller lets you decide that safely and adjust accordingly. Kind of hard to beat, and you will likely spend the money it cost replacing parts, trying to figure out how to get that on/off setup right.


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## Qer (May 7, 2008)

GerhardRP said:


> Lets see. Motor Voltage/ battery voltage= 60/350 = 0.17 = PWM
> Battery current = PWM * motor current = .17 * 1700 = 289 Amps
> Battery resistance = 30 volts/ 289 amps = 103 mOhm
> 
> Gerhard


Oups. Mea culpa.


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## Qer (May 7, 2008)

clintster7 said:


> so at the bare minimum I would need the correct size resistor to keep the current in check. But maybe a two stage one but not a variable one ( as a minimum )


Problem is, when you start to look at contactors, resistors and whatsnots to do some electromechanical way to control the motor it'll all add up and I doubt that it will get that much cheaper in the end. Also, a controller is much smarter and efficient than a resistor, which means that:


The controller can constantly monitor the current and continuously feed the motor the maximum power the motor and battery pack can handle. The resistor will never be fully optimal and you'll either risk to damage something or not get the full potential from the system.
The controller converts power to power, which means that if your motor uses 100 kW power the controller will convert Umotor*Imotor to Ubattery*Ibattery so that the pack is drained with 100 kW power (+ a few percent loss to heat in the controller) while the resistor will "convert" Imotor=Ibattery and the resulting (Ubattery-Umotor)*I is lost as heat.
If you, for example, have a pack of 200 Volt, the back EMF in the motor is 100 Volt and you drain 1000 Ampere, you'll get 100kW to the motor, but the pack will be drained with 200kW and the resistor will convert 100kW into heat. If you instead have a controller it will feed the motor with 100kW but since the controller converts power to power you'll only drain 100kW (+ some minor losses...), which means 500 Amps, from the pack!

So with a resistor:


You'll need a much bigger pack to compensate for the more brutal discharge, alternatively you'll get less power from the motor.
You'll have to manually monitor the motor current to make sure you don't blow something up and still get as much power out as possible.
A 100kW resistor isn't going to be easy to build or buy, it will probably be bloody big and it will quickly get uncomfortably hot and I wouldn't be surprised if you find out that you have to water cool it.
You will need several contactors to be able to change resistance a few times for optimal performance at different RPMs. Contactors for these kinds of currents are anything but cheap.
So, do the math and a controller will probably pay for itself pretty quick only by the smaller battery pack needed. Smaller pack does of course mean both less bucks but also fewer pounds.

Or you can go for the contactor/resistor setup and when you've learned the lesson the hard way by blowing up a few packs and motors we'll gladly sell you a Soliton.


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## clintster7 (Jun 29, 2010)

ok so controller is the way to go but there are lots to choose from .. I need the simplest controller ( and cheapest ) where would I start .. I seen someone who used a used golf cart controller .. Ok I will need something to handle more volts .. lets say I wanted to use exactly 2 times the voltage of a golf cart . could I use 2 golf cart controllers and put them on the packs before the on / off switch .. so that the 2 controls would split the volts .. Im grasping at straws here


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## Qer (May 7, 2008)

clintster7 said:


> lets say I wanted to use exactly 2 times the voltage of a golf cart . could I use 2 golf cart controllers and put them on the packs before the on / off switch .. so that the 2 controls would split the volts .. Im grasping at straws here


Apparently so.

No, trying to combine two controllers that aren't made to cooperate will lead to that you'll have two badly smelling and rather expensive paper weights.

Price, performance, reliability. Pick two.


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## TX_Dj (Jul 25, 2008)

Golf cart isn't the right place to be looking.

Try looking at the Soliton 1 (gosh Qer, someone else has to toot your horn for you) or the Zilla 2K or the WarPDrive.

All of these put out motor amps equivalent to what you'll need to get your boost (or to go pure EV).


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## Qer (May 7, 2008)

TX_Dj said:


> Try looking at the Soliton 1 (gosh Qer, someone else has to toot your horn for you)


You mean this was too subtle?



Qer said:


> Or you can go for the contactor/resistor setup and when you've learned the lesson the hard way by blowing up a few packs and motors we'll gladly sell you a Soliton.


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## TX_Dj (Jul 25, 2008)

Apparently, I totally missed it!


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## clintster7 (Jun 29, 2010)

hmmm I am not sold but it will take some more reading and understanding of resistors for me to come up with the correct components . think about a starter motor .. crank amps are brutal over 30 seconds or so . I am only wanting to boost for 15 seconds at the most. get back to the issue on a later date .. 

also I am not sold on the resistor using as much energy as a non resistor circuit . thats the point of a resistor .. like a heater blower has say 3 different settings .. that has 3 different size resistors and there is no way high uses the same power as med or low .. 
and I will not need 100 batteries I am not trying to drive to NY and back on one charge .I am going 1/4 of a mile and then to the pits to change the batteries for the next run. so I can stay consistent with my et


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## TX_Dj (Jul 25, 2008)

clintster7 said:


> also I am not sold on the resistor using as much energy as a non resistor circuit . thats the point of a resistor .. like a heater blower has say 3 different settings .. that has 3 different size resistors and there is no way high uses the same power as med or low ..
> and I will not need 100 batteries I am not trying to drive to NY and back on one charge .I am going 1/4 of a mile and then to the pits to change the batteries for the next run. so I can stay consistent with my et


Seems you still have a lot of research to be done, but you don't want anyone experienced (or holding engineering degrees) to help you learn.

That's OK, there's nothing wrong with experimentation. Advice: Experimentation costs more than a controller or fried motors.

In regards to point 1, the heater blower. When you turn the blower to low, where do you think the extra energy goes? Nowhere? I'm sorry, but that's naive. It is dissipated as heat. If the resistor is removed (as in the "high" position) then the only load in the circuit is the motor. The motor will draw as much current as is required to turn the load (fan). But you want it to run slower, so what happens when you turn it to low? The resistor dissipates some of the energy as heat, and the motor has less to work with.

As for point 2, the batteries requirement: If you have 1 battery that can sustain 50 Amps of current, you cannot then magically draw 1000 Amps of current from this battery, chemistry and physics prevent that. If you have 20 batteries wired in parallel, you can then pull 1000 Amps from the same type of battery, because each battery only must supply 50 Amps. Both solutions generate the same voltage (let's say 12). In the first case, you have 12 * 50 = 600 watts. In the latter case you have 12 * 1000 = 12,000 watts. Which provides you more power? It's obvious. Similarly, if you have 20 of these batteries in series, you can only take a total of 50 Amps, but your voltage increases from 12 to 240. 240 * 50 = 12,000 watts.

So yes, you may well require 100 batteries (depending on the battery's characteristics) in order to provide sufficient energy for your "boost" to work as you expect. 

In fact, you said you wanted 75 HP of boost. 75 HP = ~56 kW. Lets say you chose to work with 144v of batteries, 56kW out of 144v = 388.88 Amps. If you have a 100 Ah battery rated at 3C discharge, you have exceeded the discharge capability of the battery by 88.88 Amps (you won't reach 75 HP). On the other hand, if you worked with 288v, the same power requirement would draw only 194.44 Amps. You'd need twice as many batteries to reach 288v as you would 144v.

Since weight is an issue with a dragster, you'd want to use the lightest batteries you can. Lets say you use A123 cells like KillaCycle. Each of these cells is 3.3v, 1Ah, 10C discharge rating. That means each cell can push 10A. So, to reach 288v and the ability to push 200A, you would need 20 packs of 87 cells each to reach your voltage and amperage requirements at the 10C discharge maximum, that's 1740 batteries. 

Alternatively, you could use 100Ah Thundersky cells, these are 3.2v, 100Ah, 3C discharge. To reach 288v with a 200A load bearing ability, you would need 90 batteries.

Please yes, do some research, but if you're here to ask us to help, please let us help instead of telling us we're wrong and that you know better. After all, we're the people who are doing this every day (some of us as many as 30 years, myself nearly 15).


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## clintster7 (Jun 29, 2010)

TX_Dj said:


> Seems you still have a lot of research to be done, but you don't want anyone experienced (or holding engineering degrees) to help you learn.
> 
> That's OK, there's nothing wrong with experimentation. Advice: Experimentation costs more than a controller or fried motors.
> 
> ...


now thats a better answer than you will be a flaming plasma ball of pooo. 

so now I know what a controller does. but what is a (dc) controller made of ? I think I saw a diy controller once on this site but it was before I signed up .. Ill try to find it. 

thanks . sometimes you just have to have your mind picked or nothing useful gets posted .. many of you have seen all kinds of questions and have become accustom to the standard answer but I like to know why and how .. I am taking what has been posted and thanks for that but I am hardly saying I know more than anyone on this subject .. oh yes I did and ill do it again "" lol


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## clintster7 (Jun 29, 2010)

TX_Dj said:


> In fact, you said you wanted 75 HP of boost. 75 HP = ~56 kW. Lets say you chose to work with 144v of batteries, 56kW out of 144v = 388.88 Amps. If you have a 100 Ah battery rated at 3C discharge, you have exceeded the discharge capability of the battery by 88.88 Amps (you won't reach 75 HP). On the other hand, if you worked with 288v, the same power requirement would draw only 194.44 Amps. You'd need twice as many batteries to reach 288v as you would 144v.


Ok back to business ( or learning I should say )

ok in this example the discharge of the battery . Is the 88.88 amp capability based on what it would normally be used for or is their a short burst before it would resume the normal 88.88.. Im asking if the batteries can be pushed beyond the amp hr rating for a few seconds or so before the battery would be damaged ? or is it just impossible due to the set discharge rate of batteries .. ?


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## toddshotrods (Feb 10, 2009)

TX_Dj said:


> Since weight is an issue with a dragster, you'd want to use the lightest batteries you can. Lets say you use A123 cells like KillaCycle. Each of these cells is 3.3v, 1Ah, 10C discharge rating. That means each cell can push 10A. So, to reach 288v and the ability to push 200A, you would need 20 packs of 87 cells each to reach your voltage and amperage requirements at the 10C discharge maximum, that's 1740 batteries...


I'm in full agreement with your basic points and advice (to use a controller) TX, but your A123 facts are off. It's 2.3ah per cell, and the 10C discharge rating is not even getting started. The whole point of A123s for racers is the ability to push them up to 50C. Yes, we know they won't last as long, but they also keep the race from lasting as long.

1740 cells is just 60 shy of what I plan to run in the Inhaler for 330 volts and 2070 amps!


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## toddshotrods (Feb 10, 2009)

clintster7 said:


> Ok back to business ( or learning I should say )
> 
> ok in this example the discharge of the battery . Is the 88.88 amp capability based on what it would normally be used for or is their a short burst before it would resume the normal 88.88.. Im asking if the batteries can be pushed beyond the amp hr rating for a few seconds or so before the battery would be damaged ? or is it just impossible due to the set discharge rate of batteries .. ?


Depends on the batteries. The A123s TX mentioned would actually take 176 of them for your theoretical example. 44 in series x 3.3v = 145.2 volts. 4 strings of those paralleled, drawing the full 50C for a 1/4mile pass would get you 460 amps. That would cost you $2000-3000 for the cells, plus custom cases, connecting them all, BMS, charger... It would give you your 75-shot of e-power easily though for only about 27lbs of cells + all the aforementioned connections and accessories...


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## toddshotrods (Feb 10, 2009)

clintster7 said:


> Ok back to business ( or learning I should say )
> 
> ok in this example the discharge of the battery . Is the 88.88 amp capability based on what it would normally be used for or is their a short burst before it would resume the normal 88.88.. Im asking if the batteries can be pushed beyond the amp hr rating for a few seconds or so before the battery would be damaged ? or is it just impossible due to the set discharge rate of batteries .. ?


That 88.88 was how much you were over the capacity of the pack. Its capability was 300amps (100ah x 3C rating). I am not sure whether that was a continuous rating or short burst rating, as I am not very familiar with prismatic cells. The ability to be pushed beyond the amp hour rating is the C rating. Amp hour rating is one C. I hope I know what I'm talking about...


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## clintster7 (Jun 29, 2010)

toddshotrods said:


> Depends on the batteries. The A123s TX mentioned would actually take 176 of them for your theoretical example. 44 in series x 3.3v = 145.2 volts. 4 strings of those paralleled, drawing the full 50C for a 1/4mile pass would get you 460 amps. That would cost you $2000-3000 for the cells, plus custom cases, connecting them all, BMS, charger... It would give you your 75-shot of e-power easily though for only about 27lbs of cells + all the aforementioned connections and accessories...


ha I had to look up a123s because I had no idea of what they were .. I assume no one uses those little things for evs or do they ? I assume it was to make a point about my not needing 100 batteries or so .. but it would be cool to have batteries like that because you could build a drag car with all the batteries lined up under the frame rails. lol

is it true that you can get a bigger burst from non lithium batteries but the lithium will hold the chard better after a load .. like the lead car style batteries could give a larger burst of amps up front but pay for it later ? does the cold cranking amps listed on a battery have any thing to do with what would make the electric motor have a bit more power for a few seconds ? or is it the continuous amp rating the only thing that matters ?


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## clintster7 (Jun 29, 2010)

Voltage times Amps = Watts. right ..
can cold crank amp rating be included ?


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## clintster7 (Jun 29, 2010)

ok I was just browsing youtube and is this a direct hook up ? it looks like its just jumper cables on one battery 



http://www.youtube.com/watch?v=Ts6rUzPys7w&feature=related


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## clintster7 (Jun 29, 2010)

clintster7 said:


> ok I was just browsing youtube and is this a direct hook up ? it looks like its just jumper cables on one battery
> 
> 
> 
> http://www.youtube.com/watch?v=Ts6rUzPys7w&feature=related


I know thats not exactly what I am trying to do but what if two or 4 batteries were hooked up what would happen ?


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## TX_Dj (Jul 25, 2008)

Good points, Todd. I just simply grabbed specs for the first A123 cells I found, these were 1.0-1.1 Ah ratings... And claimed 10C discharge. Then again, I just grabbed that info off fleabay, so likely it was someone being honest about their dishonesty selling cheap chinese cells as A123 knock-offs.



clintster7 said:


> Ok back to business ( or learning I should say )
> 
> ok in this example the discharge of the battery . Is the 88.88 amp capability based on what it would normally be used for or is their a short burst before it would resume the normal 88.88.. Im asking if the batteries can be pushed beyond the amp hr rating for a few seconds or so before the battery would be damaged ? or is it just impossible due to the set discharge rate of batteries .. ?


388.88 is the number, 88.88 is just what's beyond the hypothetical battery configuration I was using as an example. If you're talking about wanting to sustain 75 HP boost, you're going to sustain a power draw from the battery (no matter what the actual amps are to hold you there.)

Amps are analogous to torque. As we know, torque is what does the work. The more torque you require, the more amps it will take. Horsepower, as we know, relates to torque and the rotational velocity of the mass generating the torque and also includes the magic number "5252". The speed of your motor relates to the volts it is realizing. To get more speed from the motor, you need more volts to overcome the back EMF of the motor so that you can make it go faster. So to make it go strong and fast, you need lots of amps and lots of volts. The slower the motor turns, the more amps you need.

A controller is *not* like a "big dimmer switch like what you use in the livingroom" as I've heard it described countless times, it's more like an on-off light switch driven by a spastic 4-year-old who is flashing it on and off very quickly. That _is_ different than your simple "binary controller" switch, because A) the controller doesn't *stay* on very long, and B) you cannot monitor your motor amps quickly enough or switch the switch on and off fast enough (human neurochemical/muscle limitations). The controller will do this tens of thousands of times per second if it has to.

So basically what you have in a controller is this (very basic):
- Throttle input = torque request, controller says "we need to make that much torque."
- Controller turns on the switch and watches the current rise.
:: if it rises too much, or too quickly for the program, it turns it off again.
Rinse lather repeat until the requested torque is reached, or the throttle input changes.

In the case like Qer described, the instant-on scenario of a dead-stopped vehicle, the motor is just about a dead short, very very low resistance, and it sucks up a lot of power. The controller, lets say it's set for 2000 amps, gets a drag-race launch request (pedal full high, or a special program trigger) and it flips on the switch, but the microsecond that the current hits 2000 amps, it turns the switch off again. Again, the microsecond that the current drops back under threshold, the controller "flips on the switch" again. It gives the motor the max power it can take in a short duration without frying it (usually  ) and will let it stay there so long as the program allows, you demand it, or battery voltage sags or battery amperage increases to the threshold.

Very very simply put. But that is it's function. It's more than just a big resister that bleeds off the excess energy, like a dimmer switch for a light, or like the blower speed knob for your heater. 

Here's something similar (though it doesn't look it at first glance) to what you're trying to accomplish: http://www.flickr.com/photos/mbarkley/sets/72157604901740784/

This is a "Pusher", an EV trailer that was built by an NTEAA & forum member. It is a motor connected to an old light pickup axle, carries its own batteries and has a controller and all the other safety/control equipment of an EV. He would get up on the freeway and watch his scangauge for MPG while he dialed up the amount of "push" from the trailer until he reached a MPG he wanted to attain. "boost", if you will. Different application and implementation, but the same concept you're talking about.


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## TX_Dj (Jul 25, 2008)

CCA (cold cranking amps) is a meaningless number made up by marketing people to sell car batteries. Well, not exactly, but it might as well be.

You are talking about an SLI battery (starter, lights, ignition). The internal composition of a starter battery is MUCH different than a deep cycle battery. A starter battery can pump out some amps, this is quite true. It doesn't put them out for long, and you'll replace the battery in a couple runs down the drag strip if you use them. (That's where Wayland started, nearly 30 years ago).

When we talk about EV batteries, we are talking about deep cycle batteries. This is more like what you'd find on an RV or boat. They can crank out a lot of power when needed, and the last longer (both on a charge and in terms of cycle life longevity).

The video you post shows the motor under very little load (drivetrain and wheel mass only). It is probably pulling 50 or more amps off that one battery just to do that. If you connect more batteries in series (upping the volts) you will increase the wheel speed, reduce the amps, but not increase the overall watts used, because the load didn't change.

Put those wheels on the road, where they have a load to push, and do the same thing and amps will go off the chart, because the motor needs more current to handle the workload it has been presented.


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## clintster7 (Jun 29, 2010)

Tx dj thanks very good info .. 

I thought I would give a little more info on what Im trying to cook up .. 

mine would be similar to the video but its more like an accessory with the electric motor shaft attached to a pulley much like how an alternator is on the belt system of any car. 
The thing I wanted to accomplish no matter what electric motor I use is to match the maximum recommended RPM of the electric motor to the maximum rpm (redline) of the ICE .. this can be done with pulley ratios .. if the electric motor only puts out 2500 rpm and the ICE puts out 5000 rpm then a pulley twice the circumference pulley is needed on the electric one. anyway ..


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## TX_Dj (Jul 25, 2008)

What you've just described works against you.

You've just suggested a 0.50:1 overdrive ratio from the electric motor to the engine. This cuts your torque in half while doubling the RPM.

Further, the method you describe may not be taking into consideration the size, weight, location or otherwise of the electric motor. Your ICE will be flexing under power, accessories stay aligned with the engine because they are firmly mounted to the engine. The engine isn't designed to support the weight of (not to mention the torque input of) the EV motor, so even if you could scab something together to support the EV motor along with the engine, it would add a lot of weight and still would consume even more room in the engine bay than just the motor alone.



clintster7 said:


> I assume no one uses those little things for evs or do they ? I assume it was to make a point about my not needing 100 batteries or so .. but it would be cool to have batteries like that because you could build a drag car with all the batteries lined up under the frame rails. lol







Yes, custom packbuilding makes it very easy to fit as much power into any tiny crevice of the car. Building traction packs of this magnitude out of these tiny powerful cells is still a pretty new art. People have been building packs in the size of RC cars and laptops for ages, this takes it to a whole new level, and is very similar to the way the packs for the Tesla are built.


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## Duncan (Dec 8, 2008)

Hi Guys

Is an SLI battery not ideal for this application?
The man wants to use heaps of amps for 15 seconds - this is what a starter motor does

One run will be 400 amps for 15 seconds - 1.66 Ampere Hours or 4% discharge on a 40AH starter battery

If he gets 100 cycles like that before it dies - it will probably last a season

I envisage 15 cheap car batteries to give his ex-forklift motor attached to the front of his IC engine a tickle on its way down the strip

If nothing melts he could try 20 cheap batteries! 

SLI batteries are no good for travelling a distance but they are designed for high current but low discharge levels


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## clintster7 (Jun 29, 2010)

it depends on how you look at it .. That motor rpm is an example not the exact motor rpm max. A 50:1 would be perfect for that rpm example because it would spread the power over the whole ice rpm range . If the ratio was a 1:1 ratio the electric motor wold have a burst but would stall when the rev limiter on the electric motor kills the power.. With the 50:1 rato in the example there is no possibility of the ice or the electric of over rev because they are tied together .. I'm not woried about the extra supports or there weight .. A whole chrome moly roll cage my dad has in his drag car weighs only 60 lbs.. So a chrome moly sub frame is only a fraction more weight .. Solid mounts on the engine would keep it fairly stable with the subframe design that also reinforces the mount area.. As far as space I'm not woried about that at all . As long as I have a reasonable diamiter electric motor I could just mount it directly above the engine (stickin out tha hood) like a blower with the blower style belt. This will also put it up in the fresh air to help keep cool.. So this is thought out well it's just I am missing some of the tech facts .. I can only use so much hp atached to the front of a crank so I'm not wanting to go crazy super high hp electric engines yet but there is more than one way of doing almost any part of the build.


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## ewdysar (Jun 15, 2010)

clintster7 said:


> As long as I have a reasonable diamiter electric motor I could just mount it directly above the engine (stickin out tha hood) like a blower with the blower style belt. This will also put it up in the fresh air to help keep cool.. So this is thought out well it's just I am missing some of the tech facts .. I can only use so much hp atached to the front of a crank so I'm not wanting to go crazy super high hp electric engines yet but there is more than one way of doing almost any part of the build.


You've just invented a BAS (Belt-Alternator-Starter) hybrid, albeit higher power than the ones that GM sold in the 2007-2009 Saturn Aura and Vue Hybrids and the 2008-2010 Chevy Malibu Hybrid.

"The BAS system is also capable of providing modest levels of power assist during launch/acceleration and similarly modest levels of "blended" regenerative braking during deceleration....The system is reasonably simple and inexpensive, making BAS equipped vehicles some of the least expensive hybrids available."

You're just talking about a bigger boost motor which will take a much more sturdy belt drive, perhaps the cogged blower belt that you suggest could take the 75hp without slipping or damage. But GM has proven with thousands of production vehicles that adding electric boost through the accessory pulleys on the front of an ICE engine is perfectly viable. As long as you're using the blower belt assembly, you might as well include an electric clutch (like the one in "Mad Max") so that you don't have extra rotational mass until you plan on using it. 

Funny how these ideas come back around from different directions...

Eric


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## Tesseract (Sep 27, 2008)

clintster7... You actually don't _need_ a controller for this application, as long as you make some good engineering/design decisions and enable the electric "boost" motor only after the drag race is well under way (ie - the shaft on the boost motor is already above 1500rpm).

You will want to pick a pack voltage and capacity such that it will sag just the right amount to automatically limit the current when the motor is at its lowest RPM (ie - when you first engage it). Having less Ah capacity will actually help you here, because you probably only need the boost for maybe 5 seconds. For that length of time you can easily pull 60C from A123 cells, and maybe as much as 100C. From our dyno testing of controllers we have found that a WarP9 motor seems to need about 100-110V across it when spinning at ~1900 rpm and drawing 1000A. That, btw, is 100kW of input power and given the reduced efficiency of the motor when cramming that much amperage through it, probably good for 55-70kW of actual mechanical output power. You would be better off shooting for a higher RPM and lower current here, but the downside is a narrower RPM band the boost motor will be able to assist... 

So, there are several trade-offs involved here - and there are even more that I haven't mentioned - but for this very limited application of supplying a power boost to a drag racer already under way I think you can make a case for skipping the controller. Whether you have the engineering chops to pull this off is another story - it's obvious you have little or no electrical knowledge - but maybe you are a halfway decent race car builder. Dunno, but you are definitely in the deep end of the engineering pool with this one... question is, do you know how to swim?


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## TX_Dj (Jul 25, 2008)

Jeffrey's right. In your application, you're already going to be turning the motor at some RPM, amp requirements will be less because you're not starting a load from stall. Hmm.

Very peculiar setup you're describing, unlike anything I've ever seen, but as pointed out, seems to be similar to something GM uses in a hybrid. Interesting.


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## clintster7 (Jun 29, 2010)

thanks for all the help so far .. excellent input ..

now i need to study batteries .. and 

after tesseract's post it has me thinking I would be better off looking at high rpm electric motors and setting it up more like this .

If higher rpm electric motors in general need to be turning before the amps are pumped into it then for example I could .

use a 8000 rpm electric and match the RPMs to a 6000 rpm redline ICE .. that that way that after launching off the line at 2500 or more rpm then at 3000 RPMs when the electric motor is activated the electric is already at 25% higher rpm than the ice due to the pulley ratio .. 

3000 RPMs on the ICE would be 3750 RPMs on the electric . 

time to research batteries and motors ..


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## TX_Dj (Jul 25, 2008)

Use the torque, luke!


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