Range Calculation

Have you made or bought a converted vehicle if so this is for you
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geekygrilli
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Range Calculation

Postby geekygrilli » Tue Aug 14, 2007 1:01 pm

My batteries started to drop off a little last night.....so my thoughts have turned to range!

By some quick calcs...

Assuming that the system runs at a steady state until the batteries are exhausted (obviously not what really happens):

If a steady 30mph draws 90Amps.

Batteries are 110Ah so in theory they will deliver 110A for 1 hour or 55A for 2 hours etc.

Pro rata they will deliver 90Amps for 1.22hours.

At 30mph I will cover 36.6 miles in 1.22hours.

The theoretical range is 36.6 miles at a constant 30mph. True range, i suspect will be about 20 to 25 miles. Which is OK, I suppose, but I WANT MORE!!!!!

I need to drop the current obviouslty. Maybe it doesn't draw that current. On my inductrial estate I can't really cruise at 30mph, I might welll be accelerating still.
I think i'll do some runs at 20 mph and see what happens.

What sort of currents do people pull at a constant 30 mph?

MalcolmB
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Postby MalcolmB » Wed Aug 15, 2007 7:58 am

Like you said: obviously not what really happens :cry:

The 110 Ah capacity of lead acid batteries is usually specified over a 20 hour discharge period. The faster you discharge them the less actual capacity you will get. If you discharge them over an hour or so, as is usually the case in an EV, you are only likely to get around 60% of the quoted capacity before the voltage sag tells you it's time to stop. You might be able to find manufacturer's tables for your batteries that will tell you what capacity you can expect for a given discharge period.

It's hard to say what range you can expect, but if you look in the Austin EV photo album you can probably find Wh/mile figures for vehicles of similar weight, which will give you some idea. I'd guess somewhere around 150 Wh/mile at a steady 30 mph, but that's a very rough guess!

What's the total voltage of your battery pack?

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geekygrilli
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Postby geekygrilli » Wed Aug 15, 2007 9:15 am

Total pack voltage is 96v. They are wet Lead Acid Deep Cycle Batteries.

ChrisB's Berlingo uses about 300Wh/mile, so I aim to be in in a similar area to that

I think I really need to get the car on the road, and 'suck it and see'.


Its such a nice feeling actually driving it out of the workshop in the mornings now - rather than having to push it!

MalcolmB
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Postby MalcolmB » Wed Aug 15, 2007 9:47 am

So roughly a 10 kWh pack. 20–25 miles range sounds about right. Still beats my measly 15-mile range. The fun factor is high though. I was tailed into Asda yesterday by a German guy who had noticed my bike was electric and wanted to know all about it. He was almost dancing with excitement :D

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geekygrilli
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Postby geekygrilli » Wed Aug 15, 2007 9:59 am

Yep, 10kWh.

I hope its more like 25 miles, my wife will be disappointed with less.
Its 10 miles from my house to Oxford street.
The whole point of the car is that she can drive into town for free and park for free. She might be able to get free NCP charging, though, if she is lucky.

It'll be alright for my 5 mile commute to work, so thats OK. Still means we can get rid of one of our ICE cars.

MalcolmB
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Postby MalcolmB » Wed Aug 15, 2007 10:42 am

300 Wh/mile sounds a little high to me. I reckon Chris must have a heavy right foot. :wink: I'd imagine that at average London speeds your wife should use less than that, as long as she doesn't do too many burnouts at the lights.

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aminorjourney
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Postby aminorjourney » Wed Aug 15, 2007 12:33 pm

Fret not!

I reckon it'll improve as you get used to the car. It took Kate and I about three months before either of us got 60 mpg out of our Prius. I'm guessing the same is true for any EV :)

Nikki.
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geekygrilli
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Postby geekygrilli » Wed Aug 15, 2007 3:37 pm

Cool

I just had to drop some forms off to the forklift people - the compnay that supplies the MEGA truck.

Its is quite smart. I got speaking to the salesman who was fixing the gear lever(!). Top speed of 'nearly' 40mph, range of about 30 miles.

They run at 48v, 12 x 6v Gel Lead Acid batteries - he couldn't tell me the Ah rating.

Makes me a bit happier cos mine is somewhere near that, considering they cost £10k plus vat!

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EVguru
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Postby EVguru » Thu Aug 16, 2007 1:41 pm

A rough rule of thumb on flooded lead acid batteries is that you will only get 55% of the 20 hour capacity when you discharge at the 1 hour rate.

In other words if you discharge a 100 Ah battery at 100 Amps, only expect to get 55Ah or a little over 1/2 hour run time. That's the Peukert effect at work.

It get worse as the current draw goes up and internal resistance adds to the loss of usable capacity at very high rates.

They run at 48v, 12 x 6v Gel Lead Acid batteries - he couldn't tell me the Ah rating.


12 * 6 = 72

I hope the salesman is better at maths when taking payment :D

I can see where the confusion might come from though, it's available in both 48 and 72 volt versions.
Paul

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geekygrilli
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Postby geekygrilli » Thu Aug 16, 2007 2:31 pm

Oh - 10 mile range it is then!

Maybe my current draw is all wrong though


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