Battery pack placement

Technical discussion on converting internal combustion to electric
Xmoht
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Battery pack placement

Post by Xmoht » Fri, 10 Nov 2017, 12:35

Hi all,

Looking at the basic design elements for my EV conversion.

It's a 1984 Corolla sedan. Based on my estimated battery pack size, there will be room in the boot or the rear passenger area as it'll only have the two front seats.

Neither placement will be any closer to being directly over the rear axle in terms of weight distribution. Being in the rear passenger areas is easier in terms of leaving the boot free for groceries (primary purpose is grocery vehicle) and allows access to spare tyre.

Are there any specific considerations I haven't considered for this? It's a four door sedan so easy access to rear passenger area.

Appreciate any advice!

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Re: Battery pack placement

Post by antiscab » Sat, 11 Nov 2017, 00:42

Depends a bit on what batteries you are using.

Remember a car interior acts like a greenhouse, on a 40 deg c day the internal temperature can get to 80 deg c.

Using lithium batteries is easiest to get enough range, but mounting the battery within the passenger compartment necessitates cooling while parked, or never parking the car in the sun on a hot day. If you live in an area that's rarely hot. You'll be fine

Depending upon how much space you have, in the engine bay or under the car is better. Mounting batteries where the fuel tank and spare tyre used to be is a popular choice.
Matt
2008 Mazda 2 - EV Shop convert
2011 Blade Electron mk6
2007 vectrix - 117'000km
1993 Electrolux - needs batt and charger
1998 Prius - needs batt
1999 Prius - needs batt

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Re: Battery pack placement

Post by Xmoht » Sat, 11 Nov 2017, 06:58

Thanks for your reply.

I'm planning in using lead acid batteries. I'm in Tasmania so it's rarely very hot and I'm looking at decent ventilation and insulation of the box.

Are you suggesting I don't worry about having a spare tyre, cut out the spare tyre well in the boot and weld in a low hanging battery box?

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Re: Battery pack placement

Post by antiscab » Sun, 12 Nov 2017, 05:15

You should be okay for heat then.

Battery box location is always a trade off. Low hanging battery box in the boot helps you retain much of the car interior space, at the expense of probably more work and possibly unfavourable weight distribution. Although should be easier to keep cool.

I'd suggest measuring weight distribution of the car as is, and then measuring again once you have all the ice bits out.

What kind of lead acid batteries are you looking at getting?
Matt
2008 Mazda 2 - EV Shop convert
2011 Blade Electron mk6
2007 vectrix - 117'000km
1993 Electrolux - needs batt and charger
1998 Prius - needs batt
1999 Prius - needs batt

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Re: Battery pack placement

Post by poprock » Sun, 12 Nov 2017, 06:12

Hi, just a thought that one of the regulations is that as little weight as possible be placed behind the rear axle line to avoid spinout . With lead that is a lot of leverage in a corner. :o

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Re: Battery pack placement

Post by poprock » Sun, 12 Nov 2017, 07:25

NCOP LAN 2011 Version2.0-1 "Mass distribution should be as low and CENTRALLY located as possible in the vehicle to assist with vehicle stability". In the Govspeak dialect MAY= we don't really care; SHOULD=we would like you to do this but it's up to you; MUST=MUST. :D Check for later versions of NCOP.

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Re: Battery pack placement

Post by Xmoht » Sun, 12 Nov 2017, 09:40

Thanks for all your great replies!

Weight distribution in the car is pretty equal and balanced which is one reason they're popular for drifting. The version with a slightly heavier performance motor is weighted as follows:

FL, 275kg FR, 260kg

RL, 210kg RR, 210KG

Interior cabin space isn't a concern as it won't have rear seating either way. My primary concern with interior battery box and lead batteries is effective venting. If I have an aluminium box bolted in place in the cabin, how can I vent out effectively?

Aluminium box in boot (a la the popular RX7) allows a few options for venting but as you guys note will affect weight distribution negatively (though I can compensate by modifying my brake bias and a few tweaks).

I don't drive my ICE most days of the week and when I do its generally sub 10km in a trip. So I've looked at the ForkenSwift as a spec basis, 48v of batteries with a DC motor. Tentatively speaking I figure I would use something like eight Trojan T-105 6v batteries. I'm guessing that with the box they'll have a weight around 250-300kg.

I'm in North West Tasmania and it has so many hills that to make it practical for my occasional further trips (100-400km) would be an exponential leap in requirements so I'm focusing on turning it into an electric grocery cart for my weekly shop.

Really appreciating all your great advice as I'm trying to work out as many kinks as I can before I get started with my engineer.

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Re: Battery pack placement

Post by Richo » Mon, 13 Nov 2017, 13:02

From a safety point of view I would not recommend wet cells such as the T-105's for an eV.
Do you have any other options for batteries?
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Re: Battery pack placement

Post by Richo » Mon, 13 Nov 2017, 13:15

Sounds similar in build to Simons Niki.
http://www.aeva.asn.au/forums/viewtopic.php?t=602
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Re: Battery pack placement

Post by Richo » Mon, 13 Nov 2017, 13:18

Depending on variant of corolla a flexi-tube from the battery box to side vents of the car.(rear pillars)
Then a fan on the battery box pushing cabin air into the battery box.
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Re: Battery pack placement

Post by Xmoht » Mon, 13 Nov 2017, 13:51

Richo wrote:
Mon, 13 Nov 2017, 13:18
Depending on variant of corolla a flexi-tube from the battery box to side vents of the car.(rear pillars)
Then a fan on the battery box pushing cabin air into the battery box.
Thanks for your replies, I will have a read through the other build thread.

Your suggestion on using the rear pillar vent is absolute genius, I hadn't even considered it as on option but could potentially be perfect.

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Re: Battery pack placement

Post by Xmoht » Mon, 13 Nov 2017, 14:53

Richo wrote:
Mon, 13 Nov 2017, 13:02
From a safety point of view I would not recommend wet cells such as the T-105's for an eV.
Do you have any other options for batteries?
I'm entirely open to everything at this stage but cheaper and simpler is better given my low ambitions. A 48V battery pack using lead acid batteries is my goal tentatively and I have no particular batteries in mind to achieve this, I simply heard that 6V batteries were a good compromise for weight/size/power and that Trojan T-105s are a popular choice for this.

Looking at something like the ThunderSky 12V batteries, at 48V they would still only cost a few thousand dollars and even with the battery box these would potentially weigh under 100kg (easily getting me under weight for the cars total).

Will a 48V battery pack be sufficient for my purposes at this time? Slow acceleration and a low top speed being acceptable.
Nation Code of Practice Section LV wrote: HAZ: Hazardous Voltage. Any voltage that may be greater than 60V DC or 25V AC at any time
The code of practice used by the engineer for compliance says any voltage below 60V is extra low voltage. If I go 48V I should avoid the additional requirements that go with high voltage systems right? (Namely having the system inspected and certified separately by a second electrical engineer)

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Re: Battery pack placement

Post by antiscab » Mon, 13 Nov 2017, 15:24

How fast and far do you want to go on a charge?
Matt
2008 Mazda 2 - EV Shop convert
2011 Blade Electron mk6
2007 vectrix - 117'000km
1993 Electrolux - needs batt and charger
1998 Prius - needs batt
1999 Prius - needs batt

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Re: Battery pack placement

Post by Xmoht » Mon, 13 Nov 2017, 15:31

Based on my current driving habits, 15-20km range would be adequate as a range, 40-50kph would be adequate as a speed.

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Re: Battery pack placement

Post by Richo » Tue, 14 Nov 2017, 10:06

The voltage really only matters in relation the to the motor back EMF for a given speed.
48V sounds realistic for your expectations.
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Re: Battery pack placement

Post by Richo » Tue, 14 Nov 2017, 12:14

Just crunching some numbers:
A 12V 90Ah 27kg SLA battery Rated 55Ah for 1hr, 27A charge, 800A discharge 5sec.
So the pack would be 2.4kWh useable, 30kW peak, ~15km range, 108kg, $1,200.
If you assume a 2 year life so 730 cycles that's 10,950km or $10.95/100km.
If the Rolla was doing 8L/100km then to break even on petrol prices the petrol would have to be $1.37/L.
Not too the price of Petrol in Tassie but in Perth it's normally around $1.15/L.
So economically SLA is a tad worse than petrol.

Looking at 8 Leaf cells.
7.6V 60Ah 3.8kg 240A/540A.
So the pack would be 60V 60Ah 2.8kWh useable, 30kW peak, ~15km range, 31kg, ~$1,300.
If you assume a 6 year life so 2190 cycles that's 32,850km or $3.96/100km.
So eqv 8L/100km that is $0.50/L.
Much better than petrol for not much more than SLA.

TBH you could fit all that in the engine bay, no venting and keeping the back seat.
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Re: Battery pack placement

Post by Xmoht » Tue, 14 Nov 2017, 12:52

Richo wrote:
Tue, 14 Nov 2017, 12:14
Just crunching some numbers:
A 12V 90Ah 27kg SLA battery Rated 55Ah for 1hr, 27A charge, 800A discharge 5sec.
So the pack would be 2.4kWh useable, 30kW peak, ~15km range, 108kg, $1,200.
If you assume a 2 year life so 730 cycles that's 10,950km or $10.95/100km.
If the Rolla was doing 8L/100km then to break even on petrol prices the petrol would have to be $1.37/L.
Not too the price of Petrol in Tassie but in Perth it's normally around $1.15/L.
So economically SLA is a tad worse than petrol.

Looking at 8 Leaf cells.
7.6V 60Ah 3.8kg 240A/540A.
So the pack would be 60V 60Ah 2.8kWh useable, 30kW peak, ~15km range, 31kg, ~$1,300.
If you assume a 6 year life so 2190 cycles that's 32,850km or $3.96/100km.
So eqv 8L/100km that is $0.50/L.
Much better than petrol for not much more than SLA.

TBH you could fit all that in the engine bay, no venting and keeping the back seat.
The Leaf cells idea is excellent, but it seems like finding them can be difficult. Is it just a case of keeping an eye out for group buys and things? I'm entirely open to changing my plans as I'm still learning the basics.

I've had a good read through your Handivan build thread Richo but couldn't see any photos or information about your Headway battery pack? Looking at the information on EVWorks they seem like they could be lighter and cheaper still?

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Re: Battery pack placement

Post by Richo » Tue, 14 Nov 2017, 12:54

Looking at the T-105 specs all I can see is a peak of 250A.
So 48V 250A is 12kW.
Which isn't good either - half anything I was suggesting above.
The reason frankenswift used them is because they came with the forklift they purchased to scab the motor out of.
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Re: Battery pack placement

Post by Richo » Tue, 14 Nov 2017, 13:09

Yeah my thread is WAY out of date.
When I have actually done something on the Handi I'll update the thread.
Soon I hope - I have a couple of weeks off over XMAS to play with it.

The Headway cells are quite good.
So 110 cells of headway 2.8kWh useable, ~35kW peak, ~15km range, 36kg, $3,000.
So perhaps a little better than leaf but cost is way more.
For the same price you'd be better off going with more leaf.

In my opinion to make a cheap conversion you have to be patient and get the batteries at a good price.
Wait until you can score some Leaf or even Tesla cells.
Then get everything else in a hurry to suit the batteries.

This IS backwards to what other ppl say as they have a specific higher power requirement which limits their motor and controller selection.
Last edited by Richo on Tue, 14 Nov 2017, 13:14, edited 1 time in total.
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Re: Battery pack placement

Post by Richo » Tue, 14 Nov 2017, 13:13

Just as a side thought a 250W panel on a roof rack is about 4km of recharge range per day in Tassie.
So if you only use to go to the corner shop every other day you may not have to even plug it in...
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Re: Battery pack placement

Post by Richo » Wed, 15 Nov 2017, 12:52

How 'bout motors?

Motenergy ME1003 23kW
Motenergy ME1114 24kW
Motenergy ME0913 30kW
Motenergy ME1115 30kW
DLC-20 30kW

There is a 72V Forklift on dumtree for $1k in Tassie. 1164538895
I dont see any specs anywhere so no idea if it'd work for your conversion.
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Re: Battery pack placement

Post by Xmoht » Wed, 15 Nov 2017, 17:55

Still don't entirely understand motors at this stage. I got lost at magnetic flux (in the first chapter :lol: )

I figured I'd call up the forklift sales place that I believe deal in used forklift stuff too and go from there, but looking at other peoples build threads there's so much variety and choosing an appropriate used forklify motor is tricky.

So short answer is I don't know!

I'll get the body work and rust repair finished, remove ICE, weigh the four corners, and plan from there to make sure it's all going to be under weight and distributed appropriately. I think this thread has shown me that even going for a cheap and simple system is going to be more complicated than I first thought.

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Re: Battery pack placement

Post by poprock » Wed, 15 Nov 2017, 19:13

Ebay salvaged vehicles, 2012 corolla C

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Re: Battery pack placement

Post by poprock » Wed, 15 Nov 2017, 19:15

Correction, prius

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Re: Battery pack placement

Post by Paul9 » Thu, 16 Nov 2017, 07:11

My gut feel about a 48v system is that acceleration may not be slow but embarrassingly slow.
I finished my conversion in 2010 with a 96v motor and controller with 8 x 12v SLA batteries in a 1993 Suzuki Swift. Battery weight was about 260kgs. One of my regular trips was to the golf course 10km away and did not involve much in the way of hills. A 20km round trip. Acceleration was embarrassingly slow and, though top speed was about 75km/hr, it seemed to take me half an hour to get to that speed. Though the battery capacity was 100amp hours, I was only getting about 35 amp hours from the batteries due to the Peukert effect. I was using about 1.4 amp hours per km so my 35 ah capacity only got me 25kms at best.

In 2012 I swapped out the SLA batteries for 100ah CALB lithiums and the difference was chalk and cheese. Since then I have regularly added lithiums to the car to the point where I am now running it at 130v with the old 96v motor.

My worry about your "plans" are:
a) Only a 48v system
b) Lots of weight due to lead acid batteries
c) As you say your area "has so many hills"

I realise 48v forklift motors are well priced and reasonably readily available. Have you thought of running the 48v motor with 5 x 12v lead acid batteries (60v) or even better 60v worth of lithium batteries? Though to be honest I think 48v (and maybe even 60v) will be too low a voltage.

Just my 20c (if that) worth.
Cheers
Paul

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