Wanted: ~20Ah battery

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MikeG
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Wanted: ~20Ah battery

Post by MikeG » Fri, 07 Nov 2008, 15:17

For a electric lawnmower project.

Trying to avoid a Lead Acid battery for ethical reasons (disposal, lifespan)

Does anyone have something they want to sell or giveaway?

The rolls royce solution might be a Thundersky LFP40AHA I guess...

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Richo
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Post by Richo » Fri, 07 Nov 2008, 21:09

TS are in 20Ah on alibaba's
SLA 20Ah will be at most corner stores!

SLA are recyclable in Australia.
Lithiums need to be sent overseas for recycling.
How is lithium more ethical then?
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acmotor
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Post by acmotor » Sat, 08 Nov 2008, 21:15

Mike,
What voltage pack are you planning ?

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Wanted: ~20Ah battery

Post by MikeG » Mon, 10 Nov 2008, 15:08

Fairly boring actually. A single 12V battery, to be fed into a 500W modified squarewave inverter, to power the 240V motor. I've been told that the anything but a sine-wave inverter will see a much lower efficiency, but I already have the 500W inverter, so I think I'll just plug it in and see...

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Post by Mesuge » Sat, 15 Nov 2008, 00:19

Richo wrote: TS are in 20Ah on alibaba's
SLA 20Ah will be at most corner stores!


Has anyone got confirmation from the parent chinese factory or the official US/EU distributor that 20Ah LFP (TS) is indeed for real?
I doubt it exists in "LFP", perhaps in their other chemistries..

Besides this would be <<<100km range commuter car, 40Ah seems to be the realistic mimimum also in terms of secured better cyclelife (<60A discharge application), but obviously 2x more expensive though.
I can see the only valuable benefit of high voltage 20Ah batt. setup in ultralight cars (<600kg, aero drag <.26) or various odd 2-3wheel projects..
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Richo
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Post by Richo » Sat, 15 Nov 2008, 05:13

I actually really only need a 15Ah pack for my daily commute with plently left over.
220 cells @ 15Ah = 10.5kWh total capacity.

So 20Ah would be great.
However the TS cell spec is pretty low considering acceleration would still require 80-100kW for 10 secs.
So the TS cell would not cut it.

Car weight 1100kg
Cd 0.385
fA 1.86m^2
4 wheels

If I had to drive 50km to work everyday I'd think about moving...


Although Mike might have the right idea - ride on lawn mover. Image
Plus he could get some pocket money with the odd-job on the way home Image
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Post by Johny » Sat, 15 Nov 2008, 05:37

I'm seriously thinking 20ah LiFePo4 also.
I've followed up a few Chinese LiFePo4 pack-makers now. All except the jack guy only rate them (20ah cells) to 3C (he has a more expensive higher rated alternative I think). 3C is just a bit short. 25ah would be good. 30ah gets too expensive again (I've had quotes on 20 and 30ah).

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Post by Richo » Sat, 15 Nov 2008, 05:49

To me finding the balance between weight, range and performance is the problem.
Don't forget the right one must specify the Ah, C rating, internal impedance and be a resonable weight and price.
If I can't find it then I'm gunna start gluing AA batteries together Image


But I'm sure 1-2C would be fine for the lawnmower project.
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Post by MikeG » Mon, 17 Nov 2008, 14:00

BTW, this is a push mower project (not ride-on), so the biggest issue we'll have is getting the blades turning...

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Post by acmotor » Mon, 17 Nov 2008, 16:35

Be aware of the ESR of a battery.
Even though it may be rated at 3C or more, they are not much use if the voltage has drooped to less than half !
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Post by Richo » Tue, 18 Nov 2008, 06:18

Saw a 240V plug in lawn mower at the local flee market and I thought of you Mike Image

Hey don't the 240Vac "universal" motors run on DC as well?
Sounds tricky trying to get 28 x 12V SLA's on there.
Lets say I was using a 12V3.3Ah(C20) lead acid battery.
Typically you would get 1.98Ah for 1hr.
So this would be 28*12*1.98=665W continuous for 1hr.(Ignoring internal losses)
Peak is about 50A for 5sec which is well over the 2.4kW from a power point.
So the motor should start everytime!

For about 7min use you could get 9.9A.
So this would be the 2.4kW continuous.
But I doubt that a 240V mower would be expected to do 2.4kW continuous.

In any case they weigh 1.2kg each or 33.6kg for the pack.
size 134 x 67 x 67 mm ea = 17L for a pack (9 x 2L icecream containers)

So size and weight is doable but a bit much for the poor mower.
Price would be around $600-1000 for the pack.


I guess the eqv pack in Lithium would be 9 cells 3.2V 40Ah.
So would be 28.8V 40Ah = 1152Wh
So you could use a 36V 700W oatley style motor

Still at around $2/ah would be around USD$720 for the pack.
Unless someone bought enough extra when they by their eV pack.
Then you might get it cheaper.

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Post by MikeG » Tue, 18 Nov 2008, 16:40

I was thinking an inverter actually... But I'm coming to the realisation that 250W might just be too little for a lawnmower...

I've looked at various motors, such as the Oatley ones and even cheap 6hp winch motors... The issue is motor speed. A lawn mower needs to turn the blades at roughly 2800rpm. The Oatley one you included the link for spins at 450rpm, and winch motors don't get beyond about 1500rpm. The 240V AC motor I have spins at 2860rpm which is ideal, as was the $30 (delivered) price tag...

The motor idles at 1.375A but the startup current could be up to 10A (240V).
Converting these to the 12V battery source, we're talking idle at 26A and up to 100A starting current. Scary numbers for such a small motor.

A 20Ah battery would see a mowing time of up to 35 mins, keeping the battery above 20% capacity.
Last edited by MikeG on Tue, 18 Nov 2008, 05:41, edited 1 time in total.

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Post by moemoke » Tue, 18 Nov 2008, 19:17

MikeG, I'm interested in your e-mower project, I was thinking along the same lines using a 3/4 horse 240V motor through an inverter or get a new 1000W 240V plug in mower from local hardware $120 ditch the plug and run motor through inverter, not sure what size inverter I would need though, as 1000W ones seem to be a few hundred dollars.

Please keep us posted with your project.


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Wanted: ~20Ah battery

Post by MikeG » Tue, 18 Nov 2008, 19:27

I've been told that induction motors don;t like cheap modified sine wave inverters, so you need a true sine wave inverter which could be quite expensive.

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