# Stupid Question



## PhantomPholly (Aug 20, 2008)

As long as I'm asking stupid questions, when I look at those specs (4.25v maximum, 100 ah) does that mean that I calculate the KWh as 80 * 4.25 * 100 = 34 KWh? Or, do you use a lower voltage number to calculate "nominal power?"


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## peggus (Feb 18, 2008)

there's 30kWh of energy in a gallon of gas. Electric drive trains are around 3 times as efficient as their ICE counterpart. 

So, take the MPG of the car you're planning on converting, lets say 25MPG, this means you'll need 30/3=10 kWh to go 25 miles.

Those particular batteries have a nominal voltage of 3.3V, lets say 3.2 to account for sag under load so and for long life you don't want to use more than 80% of their capacity. So you'll have 3.2*100*80*0.8 = 20.5 kWh of everyday usable energy.


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## Bowser330 (Jun 15, 2008)

peggus said:


> there's 30kWh of energy in a gallon of gas. Electric drive trains are around 3 times as efficient as their ICE counterpart.
> 
> So, take the MPG of the car you're planning on converting, lets say 25MPG, this means you'll need 30/3=10 kWh to go 25 miles.
> 
> Those particular batteries have a nominal voltage of 3.3V, lets say 3.2 to account for sag under load so and for long life you don't want to use more than 80% of their capacity. So you'll have 3.2*100*80*0.8 = 20.5 kWh of everyday usable energy.


http://www.plasmaboyracing.com/bluemeanie.php
Lightweight but not very aerodynamic...

168V * 47AH (AGMs) = ~8kw
Agressive driving still nets 25-30 mile range
35-40 mile range @ 55mph

With 24kw (usable) in a more aerodynamic donor you could see 90+ mile range...(agressively driving).
Over 100 mile range driving @ 55mph...if John's estimates are correct...and who is going to challenge the developer of the white zombie...


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## PhantomPholly (Aug 20, 2008)

So what voltage number would I use for those batteries? It says 4.25 max, 2 something min - is it normal to use a much lower voltage than "charged state?" 

Even using the 3v figure, my example has 3X the kWh of the second poster's car using Optimas. Does that mean that 75-90 miles would be a reasonable range for a similar weight vehicle? That would be enough for all of my non-distance commuting. If not please speak up! I have to be able to count on 60 miles for a round-trip to the airport, including A/C.

For those of us with more money than brains, I think I've figured out how to do this at a reasonable price. I'm going into the EV conversion business, and my first will be a demonstrator vehicle. That makes everything a business expense, so out-of-pocket costs are reduced. There's always a vehicle in good shape with too many miles on it for reasonable price, and once I've built the thing and sell my own car my out of pocket (including tax credits) should be reasonable.


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## peggus (Feb 18, 2008)

Look at the discharge curve in the datasheet, you'll find that they spend most of their time at 3.2-3.3V or less if you draw high currents, 4.25 is the charge cutoff voltage.

Start with a vehicle that can get 40mpg, like a civic. and you'll get a comfortable 80 miles of everyday range with that battery. North of 100 miles if you drive conservatively and go to 100% DOD, just don't do that on a daily basis.


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## JRP3 (Mar 7, 2008)

Glad to hear you're going ahead with your project, even using "inferior" batteries 
You don't want to charge to 4.25, ever, just as you don't want to go to 2.0, ever. It seems as if after about 3.7 or so there is little capacity gain and the chance of the voltage taking off into unhealthy territory is high. So using 3.7 fully charged, 3.2 nominal, 2.5 or so max discharge seems pretty safe.
Something to consider if you are going to use the AC55 you linked to, those units come with the older UMOC controller as opposed to the newer DMOC, and some people have had difficulties getting them setup properly. I don't know the details but it's something to check into.


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## ZEVUtah (Apr 10, 2008)

PhantomPholly said:


> For example - this motor and 80 * these batteries look like they should be able to propel any of these "best used economy cars" (all are under 3,500 lbs curb weight) for SOME distance - and their respective mpg figures should reasonably account for the relative weight / drag values.


On another thread I was reading that for these batteries to last a long time you do not want to pull more than 3 * the AH rating. For a 100ah battery that would mean that on climbing steep hills you would be limited to 300 amps. That may not be enough. 

My car will often pull 500 amps on a steep hill even in first gear. The 160ah battery might be a better fit if you can afford the extra $$. That would give you a safe discharge rate of 480 amps.

KJD

http://www.evalbum.com/2058 
http://www.zevutah.com


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## JRP3 (Mar 7, 2008)

Actually the newer SE series can do 4C, 12C max. The TS cells are 3C, 10C max, so you can pull higher amps for short periods.


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## david85 (Nov 12, 2007)

PhantomPholly said:


> As long as I'm asking stupid questions, when I look at those specs (4.25v maximum, 100 ah) does that mean that I calculate the KWh as 80 * 4.25 * 100 = 34 KWh? Or, do you use a lower voltage number to calculate "nominal power?"


Always calculate energy content with the NOMINAL voltage, not peak cut off voltage. In reality, the charger should not allow the voltage to even get as high as 4.25V. Because of the charge curve, you don't really get significant energy content for going much higher than 3.6-3.7V per cell.

The minimum/maximum voltages are just that, the safe limits of the battery, but not the ideal limits, which are more.....well, limited.

Clear as mud?


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## PhantomPholly (Aug 20, 2008)

JRP3 said:


> Glad to hear you're going ahead with your project, even using "inferior" batteries
> You don't want to charge to 4.25, ever, just as you don't want to go to 2.0, ever. It seems as if after about 3.7 or so there is little capacity gain and the chance of the voltage taking off into unhealthy territory is high. So using 3.7 fully charged, 3.2 nominal, 2.5 or so max discharge seems pretty safe.
> Something to consider if you are going to use the AC55 you linked to, those units come with the older UMOC controller as opposed to the newer DMOC, and some people have had difficulties getting them setup properly. I don't know the details but it's something to check into.


Yep - they are inferior, but I've figured out my own "stimulus plan" to make it worthwhile. Still won't power a pickup truck (my preference), but the wife will keep her humongous SUV for a while.

The controller says "Max Operational Input voltage" = 400. Does this mean that it explodes if input voltage exceeds this? 

Example: 400/3.7v = ~108 batteries (more than I originally figured, expected only 80). If I used 100 batteries and never exceeded 3.7 voltage, will that provide enough head room to insure I don't burn up the controller?


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## PhantomPholly (Aug 20, 2008)

ZEVUtah said:


> On another thread I was reading that for these batteries to last a long time you do not want to pull more than 3 * the AH rating. For a 100ah battery that would mean that on climbing steep hills you would be limited to 300 amps. That may not be enough.
> 
> My car will often pull 500 amps on a steep hill even in first gear. The 160ah battery might be a better fit if you can afford the extra $$. That would give you a safe discharge rate of 480 amps.
> 
> ...


In your link the car mentioned is a VW rabbit with a 120v system - is that the car you are referring to?

If I am running a 400v system, won't my amps be about 1/3 for the same power?


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## PhantomPholly (Aug 20, 2008)

JRP3 said:


> Something to consider if you are going to use the AC55 you linked to, those units come with the older UMOC controller as opposed to the newer DMOC, and some people have had difficulties getting them setup properly. I don't know the details but it's something to check into.


I'm not "sold" on any particular combination, just saw this as a "special" and liked the idea that the controller and motor were already "sized for each other." I figured it was as good a starting place as any to "size" my motor and battery, and I also liked the fact that it will accept up to 400v from the battery pack. I fully expect to invest about $15k for parts, and that is going with a car that already has manual steering and brakes (no need to power those).

Once I actually get to the point of making final decisions I'll start picking your (the board members') collective brains for a good match for my use. I'm pretty well set on a 1999 Civic sedan - I owned one previously and loved it. That model year increased the interior space to equal the prior years' Accord, so it isn't a total "econo-box."


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## TheSGC (Nov 15, 2007)

PhantomPholly said:


> Once I actually get to the point of making final decisions I'll start picking your (the board members') collective brains for a good match for my use. I'm pretty well set on a 1999 Civic sedan - I owned one previously and loved it. That model year increased the interior space to equal the prior years' Accord, so it isn't a total "econo-box."


I have a 1996 Civic sedan (LX) EV that I just got on the road. The 1996-2000 Civic's have power steering and power brakes, and they are basically all the same, except for a few exterior modifications. Check out my blog in my sig. PM me if you want to know more about them!


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## JRP3 (Mar 7, 2008)

PhantomPholly said:


> The controller says "Max Operational Input voltage" = 400. Does this mean that it explodes if input voltage exceeds this?


Possibly, there may be some headroom above that but I don't know. I don't see why you'd even need to get close to that.


> Example: 400/3.7v = ~108 batteries (more than I originally figured, expected only 80). If I used 100 batteries and never exceeded 3.7 voltage, will that provide enough head room to insure I don't burn up the controller?


Sounds reasonable but I think the AC55 is typically run around 320 volts or so.


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## Nomad (May 8, 2009)

ZEVUtah said:


> On another thread I was reading that for these batteries to last a long time you do not want to pull more than 3 * the AH rating. For a 100ah battery that would mean that on climbing steep hills you would be limited to 300 amps. That may not be enough.
> 
> My car will often pull 500 amps on a steep hill even in first gear. The 160ah battery might be a better fit if you can afford the extra $$. That would give you a safe discharge rate of 480 amps.
> 
> ...


From what I was understanding these bats can pull 5c without a serious problem for short periods.(Does anyone know what a short is considered? 1 min 5min? 10secs?) 100AH 500amps, 60AH 300Amps so a 160AH would give 800amps and that is a hell of alot of pull.


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## Nomad (May 8, 2009)

ZEVUtah said:


> My car will often pull 500 amps on a steep hill even in first gear.


Your also @ 3600lbs


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## Nomad (May 8, 2009)

PhantomPholly said:


> Example: 400/3.7v = ~108 batteries (more than I originally figured, expected only 80). If I used 100 batteries and never exceeded 3.7 voltage, will that provide enough head room to insure I don't burn up the controller?


I've been doing it off 3.2 is this incorrect? So off your 400v system you would need 125.


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## david85 (Nov 12, 2007)

Again, when sizing a controller, you want to use the NOMINAL voltage rating of the pack, not the peak charged, resting voltage. Yes, the resting voltage can exceed the controller rating when the battery is fully charged, but by the time you are drawing enough current to possibly harm the controller, the voltage will sag down to the nominal voltage.

That is the general rule, however it would be best to double check with the manufacturer of the controller to see what their recommendations are. Generally, they will offer free downloads for the operator's manual for your reference.


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## PhantomPholly (Aug 20, 2008)

JRP3 said:


> Possibly, there may be some headroom above that but I don't know. I don't see why you'd even need to get close to that.
> Sounds reasonable but I think the AC55 is typically run around 320 volts or so.


Right, but with an inverter setup the output voltage is independent of the input voltage, isn't it? (This is an AC motor / controller)

So, to get the best range / minimum amp draw on your batteries you would want to get as close to the max allowable pack voltage, yes?


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## PhantomPholly (Aug 20, 2008)

david85 said:


> Again, when sizing a controller, you want to use the NOMINAL voltage rating of the pack, not the peak charged, resting voltage. Yes, the resting voltage can exceed the controller rating when the battery is fully charged, but by the time you are drawing enough current to possibly harm the controller, the voltage will sag down to the nominal voltage.
> 
> That is the general rule, however it would be best to double check with the manufacturer of the controller to see what their recommendations are. Generally, they will offer free downloads for the operator's manual for your reference.


Thank you! That's what I was trying to understand. 

Calculating the pack at "nominal voltage" means 125 cells to reach "max input voltage" of 400v, but that results in 530v if I ever actually charged them to maximum capacity. I may not know much about electronics, but I do know you only get to let the smoke out once...

Anyway, point taken and I will contact the manufacturer before I purchase. Who knows, I'm still a couple months away and someone may introduce something better before then...


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## JRP3 (Mar 7, 2008)

PhantomPholly said:


> So, to get the best range / minimum amp draw on your batteries you would want to get as close to the max allowable pack voltage, yes?


Yes but probably within reason, there may be a point of diminishing returns. Is it worth spending the extra money on batteries to run right at the very max to save a few amps? Also finding chargers at higher voltages my be problematic, you may have to get 2 chargers and split the pack.


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