# Max possible batteries



## Tommahawk (Sep 28, 2008)

Theoretically (given unlimited space) how many lead acid batteries could an ev support before their is no longer any range benefits due to either new batteries pushing the weight of existing batteries rather than contributing to more mile per charge or resistances or something else and what is that range?

Given a standard 12v battery weighs about 25kg/55.13lb


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## TheSGC (Nov 15, 2007)

There deifnately a point of optimal battery/weight/range and it all depends on the conversion. 

For instance, I have a Honda Civic 96 volt conversion using an ADC K99-4007 and wally world MAXX29 12 volt 125 Ah batteries. Using Jerry's EV Calculator and inputting my exact gear ratios and specs, I have found that using the MAXX29s at 96 volts will yield the best range overall, with the 8 volts being the next best, and 6 volt going down in range because of the extra workload on the motor due to weight.

Of course my EV is running YET, but it will be soon as my last part is being ordered this afternoon!


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## madderscience (Jun 28, 2008)

The SGC,

when you did your battery weight / range tradeoff calculation are you sure you considered the higher AH capacity of the 8V and 6V batteries and not just the extra weight? What about the reduced peukert effect? If you need 100 amps to go at freeway speed you would be pulling about 1C from the 12V batteries and 0.5C from the 6V batteries, enough for a measureable nonlinear increase in range. 

A car with 96V of 200AH 6v batteries is going to have better range (probably around double) despite the extra weight vs. 96V of 125AH batteries. This has been well proven in real life driving. 

In my experience you will run out of safe carrying capacity in your chassis for batteries long before you stop seeing the increased range by carrying more. 

I've got 21 Trojan T-105 6v batteries stuffed in a 1985 toyota MR2 and I don't regret it at all. I'd go to 24, but there isn't any more room.

Not that there aren't reasons to go with a smaller pack: easier, cheaper conversion, better performance due to reduced weight. If you never plan longer drives, then there might not be any reason to carry extra batteries to enable it.

my $0.02


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## TheSGC (Nov 15, 2007)

I used this calc here: http://www.evconvert.com/tools/evcalc/

I do have a small motor (6.7 inch), so that had to be taken into account. The max system voltage is 96, so that was a baseline and then I started inputting the different batteries and looked at the ranges and amp draws at the motor side to compare. I couldn't fit enough of the 6 volts in even if i wanted too (It's a 4 door sedan and some trunk spare was a requirement), and the estimated difference in range between the MAXX29 and the T875 was a measly 4 miles, according to the caclulator with a 1% grade. 

I am starting my front battery rack now, and I think I will be lucky if I can get three batteries in there, and I am hoping to 4.

As for my commute, its 32 miles round trip and I am going to try to get a charging port when I get there. But my estimations put the range of the pack at 35-40 miles at 40MPH and below, and most of it is at 30 MPH and 20 MPH in the city/college grounds.


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## bblocher (Jul 30, 2008)

Tommahawk said:


> Theoretically (given unlimited space) how many lead acid batteries could an ev support before their is no longer any range benefits due to either new batteries pushing the weight of existing batteries rather than contributing to more mile per charge or resistances or something else and what is that range?
> 
> Given a standard 12v battery weighs about 25kg/55.13lb


There is a point of efficiency for a vehicle, but you asked at what point would more batteries yield no further range increase. Assuming a vehicle could support any number of batteries, there isn't a limit. More batteries would be more range. Of course this isn't practical


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## Astronomer (Aug 7, 2008)

bblocher said:


> Assuming a vehicle could support any number of batteries, there isn't a limit. More batteries would be more range. Of course this isn't practical


You would also need a motor that could take a limitless number of amps to get a limitless number of batteries moving. But, yes, in theory, there is no limit.


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## chamilun (Jun 17, 2008)

Madderscience,
after being told by everyone that my 94 eclipse couldnt hold 6 volt batteries, youve been an inspiration that this can, in fact, be done, and not be driving a lead sled.

would you mind plugging in your setup into the calculator and compare your real world numbers with the calculator?

many, many thanks!


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## Qer (May 7, 2008)

chamilun said:


> Madderscience,
> after being told by everyone that my 94 eclipse couldnt hold 6 volt batteries, youve been an inspiration that this can, in fact, be done, and not be driving a lead sled.


The problem is that at a certain weight the structure of the car won't hold it anymore and will start to take damage from it, so if you go for 6 Volt batteries you might end up with a so low voltage that the top speed suffers. With other words, all cars can use 6 Volt batteries but it might end up impractical due to the weight of the batteries.

How much cargo can the Eclipse handle and how many 6 Volt batteries can you fit in there, considering weight and volume?


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## TX_Dj (Jul 25, 2008)

The "biggest lead sled" to date has been the Red Beastie, to my knowledge.

It had two strings of 6v trojans at 120v, and could travel 120 miles or more on a charge, depending on conditions.

It was also about 1000 lbs over GVWR.

At some point there is a diminishing return. Perhaps beastie hit that point, but we don't know because it still had great range.

Alas, we'll NEVER know, since it no longer exists due to being consumed in an (unrelated) fire.


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## madderscience (Jun 28, 2008)

The EVconvert calculator gives my car (a 1985 toyota MR2, specs available at http://www.diyelectriccar.com/garage/cars/33 ) a range to 80% DOD of 78 miles at 50mph, and 53 miles at 60mph, both in 3rd gear. My own calculations (independent of any online calculators, and before I built the car) said 60 miles at 55mph. 

The longest real drive I have done was 66 miles. 56 miles of this was at 55mph on interstate 5 near everett, WA. the last 10 miles were on surface streets. I was at 80% DOD on the weakest cell, by specific gravity measurement. I don't have a watt-hour meter (yet) so I can't say what my actual WH/mile is but my best estimate for that drive (not including charging losses) was about 200 wh/mile.

So at least under those conditions, the theoretical and actual values are pretty close for my car.

I _DO_ consider my car a lead sled; it is built for range and not performance. However with the upgraded springs, shocks and brakes it handles fine though certainly not as nimble as it would have been as a gas car. I never drove it that way though. It weighs about 1000lbs more than it did stock, and it is about 500lbs over its original GVW.

I should also point out that I did have to make several sheet metal modifications and redesign my engine/transmission mounts in order to cram that many T-105s into the car. However other MR2's have been done with NO body modifications and they could still get 16 T-105 or equivalent form factor into the car; though they took the entire trunk for batteries to do it. I can still get 3 bags of groceries and my tool box into my trunk.


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## judebert (Apr 16, 2008)

Of course, regardless of whether you use 6V, 8V, or 12V batteries, the capacity is governed by the amount of lead in the battery. We can measure that most easily by weight.

As I recall from my days on the EVDL, the rule of thumb for the optimum battery load is about 1/3 of the total vehicle weight. So, if you take the weight of your car without batteries, and divide it by two, you'll find the optimum weight of batteries your car could carry. Then you can start worrying about space and GVWR.

Of course, this applies only to lead-acid chemistries. I'm not sure it will even apply to the lead foam version.


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## abudabit (Sep 18, 2008)

This motorcycle-esque tadpole I'm building is 150 lbs with out batteries, I'm planning on 200 lbs of batteries.  Hopefully judebert's equation only applies to conversions. 

Think I can set my current limiter to 75 A if i'm using 55 ah batteries? Or will that be too damaging to lead acids?


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## Gary Sconce (Oct 4, 2008)

madderscience said:


> "...measureable nonlinear increase..."


Ooooooooooo! Say it again (*shudders with scientific/EV/physics joy*) 
Hehehehe!


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## waldoz (Oct 1, 2008)

judebert said:


> Of course, regardless of whether you use 6V, 8V, or 12V batteries, the capacity is governed by the amount of lead in the battery. We can measure that most easily by weight.
> 
> As I recall from my days on the EVDL, the rule of thumb for the optimum battery load is about 1/3 of the total vehicle weight. So, if you take the weight of your car without batteries, and divide it by two, you'll find the optimum weight of batteries your car could carry. Then you can start worrying about space and GVWR.
> 
> Of course, this applies only to lead-acid chemistries. I'm not sure it will even apply to the lead foam version.


So is this the car with the ice or with out? Or is this a roller? 

I am looking at volvo and they come in at about 2900 stock. If you strip the motor mufflers and trans its around 2200 or so. 
Thanks 
Chris


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