Battery pack placement

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

Post by Xmoht » Thu, 16 Nov 2017, 07:22

Thanks for your reply Paul.

I haven't been able to find many people running the lower voltage systems so it's hard to know what the actual outcome will be.

Did you find your acceleration improved just between swapping the lead acid for lithium when it was the same voltage?

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Re: Battery pack placement

Post by Paul9 » Thu, 16 Nov 2017, 07:29

Yep acceleration improved noticeably with lithiums vs lead acids. Just the weight reduction helped! Lead acids weighed about 265kgs whereas the same voltage for lithiums was just over 100kgs. Losing 160kgs of weight helped performance in every area.

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Re: Battery pack placement

Post by antiscab » Thu, 16 Nov 2017, 11:30

nearly all the series DC motors used in conversions *are* 48v motors from forklifts. you can easily go to 120v on a "48v" motor

my experience with an impulse 9" motor in my mazda was that the motor voltage rarely got above 70v (at 4000rpm), even though my battery voltage was around 140v (250A battery limit, but 650A motor current limit)

Lower battery voltage probably won't affect performance, as long as you are still able to draw enough amps from the battery (600A minimum I would suggest)
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1999 Prius - needs batt

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Re: Battery pack placement

Post by Xmoht » Thu, 16 Nov 2017, 11:55

antiscab wrote:
Thu, 16 Nov 2017, 11:30
Lower battery voltage probably won't affect performance, as long as you are still able to draw enough amps from the battery (600A minimum I would suggest)
And aside from the battery and motor, it's my choice of motor controller that will allow me to draw enough amps to give it that requisite performance?

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Re: Battery pack placement

Post by Richo » Thu, 16 Nov 2017, 12:29

Yes - correct.
Amps -> Torque (acceleration)
Voltage -> RPM (top speed)
The available Voltage will decrease as the Back EMF increases with speed so this will limit the AMPS you can draw.
So a higher voltage battery pack will mean you can draw the peak AMPS over more RPM giving better acceleration.

In either case Power IN is Power OUT.
If your small battery back can only sustain 30kW peak then the voltage isn't so much of a factor in the initial acceleration.
Even my Handi which was 700kg had 40kW.
30kW on a 1000kg Rolla won't be exciting - but it will get you to the shops...
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Re: Battery pack placement

Post by Xmoht » Thu, 16 Nov 2017, 13:36

Richo wrote:
Thu, 16 Nov 2017, 12:29
Yes - correct.
Amps -> Torque (acceleration)
Voltage -> RPM (top speed)
The available Voltage will decrease as the Back EMF increases with speed so this will limit the AMPS you can draw.
So a higher voltage battery pack will mean you can draw the peak AMPS over more RPM giving better acceleration.
Forgive me as I'm still trying to get my head around some pretty basic concepts but..

If the weight of the car and the speed (the load on the motor) are known, is it possible to work out exactly what voltage battery pack is required (in context of overcoming back emf)? Or are there a lot more variables in play?

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Re: Battery pack placement

Post by Richo » Thu, 16 Nov 2017, 15:41

Yes it can be calculated.
But you will need to look at it on a case by case basis for each motor selected.
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Re: Battery pack placement

Post by poprock » Thu, 16 Nov 2017, 18:38

Hi again; Still banging on about weight distribution:3.2 Brakes and Steering

Version 2.0 - 1 January 2011 Page 20/29
/

"Because mass distribution is an important factor in maintaining good handling and braking
characteristics of a vehicle, it must be considered carefully in the design of a conversion or ICV.
For example, a significant reduction of front axle mass may lead to poor cornering behaviour as
a result of loss of traction together with deterioration in braking performance.
Care should therefore be taken to minimise changes in mass distribution. Where this is
unavoidable, brake bias must be adjusted to take into account the changes in mass distribution.
Locating the battery pack entirely behind the rear axle should be avoided as it may lighten
steering and/or cause the vehicle to yaw in a dangerous manner, particularly if the vehicle has a
relatively large rear overhang. Vehicles with front wheel drive may also lose drive traction.
Vehicles displaying any of the above undesirable characteristics will be rejected by Registration
Authorities."
Hope this helps.

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Re: Battery pack placement

Post by Xmoht » Thu, 16 Nov 2017, 19:00

poprock wrote:
Thu, 16 Nov 2017, 18:38
Hi again; Still banging on about weight distribution
Hi poprock, thanks for that.

I've got all the light vehicle modifications guides printed out and neatly presented in little green folders for me to study!

Definitely concur about weight distribution. Once I've removed the ICE I'll be weighing each corner. In hindsight and after talking to the engineer, my choice of batteries (and motor etc.) and their placement will be contingent on keeping it under weight and evenly distributed.

But I'm still loving all the advice so I appreciate it!

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Re: Battery pack placement

Post by Richo » Fri, 17 Nov 2017, 12:43

The handi lost 140kg of iCE junk.
Lets assume that the rolla is about the same.
45kg was around the back area.

SO IF you had 100kg of lithium.
You would need to put about 50kg of battery in the back of the car somewhere.
50kg of battery in the engine bay.
Then motor controller etc in the engine bay...

This should be roughly back to where the original distribution was.
You would only go over weight if you decide to stick with SLA.

Did some of the old rolla's have the fuel tank in the boot on the side or were they underneath?
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Re: Battery pack placement

Post by Xmoht » Fri, 17 Nov 2017, 13:56

Richo wrote:
Fri, 17 Nov 2017, 12:43
The handi lost 140kg of iCE junk.
Lets assume that the rolla is about the same.
45kg was around the back area.

This should be roughly back to where the original distribution was.
You would only go over weight if you decide to stick with SLA.

Did some of the old rolla's have the fuel tank in the boot on the side or were they underneath?
As far as I know all under. Mine was 15kg dry, 50L capacity. It's a bit of a boy racer so it's got very little interior, no sound deadening etc. So as you say if I avoid lead acid it'll come in under weight, but if I'm trying to be as budget conscious as I can be every kg is going to count and I am keen on trying to aim for 50/50 weight distribution.

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Re: Battery pack placement

Post by Richo » Mon, 20 Nov 2017, 12:37

Richo wrote:
Tue, 14 Nov 2017, 12:14
So the (SLA) pack would be 2.4kWh useable, 30kW peak, ~15km range, 108kg, $1,200.
So the (Lithium) pack would be 60V 60Ah 2.8kWh useable, 30kW peak, ~15km range, 31kg, ~$1,300.
Richo wrote:
Fri, 17 Nov 2017, 12:43
SO IF you had 100kg of lithium.
You would need to put about 50kg of battery in the back of the car somewhere.
50kg of battery in the engine bay.
Sorry NOT 100kg of lithium...
Even a small SLA pack would be under weight - just.

The GVM takes into account a full tank.
0.75kg/L x 50L = 37.5kg fuel
+15kg dry tank weight.
52.5kg.

So for a Small SLA half the pack needs to be where the petrol tank used to be.
The rest of the SLA in the engine bay.
For Lithium the entire pack would be where the petrol tank used to be.


You may have to put a 12 or 15 inch sub in the boot to offset the reduced weight of lithium to keep 50/50 8-)
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Re: Battery pack placement

Post by Xmoht » Mon, 20 Nov 2017, 14:20

Richo wrote:
Fri, 17 Nov 2017, 12:43
So for a Small SLA half the pack needs to be where the petrol tank used to be.
The rest of the SLA in the engine bay.
For Lithium the entire pack would be where the petrol tank used to be.

You may have to put a 12 or 15 inch sub in the boot to offset the reduced weight of lithium to keep 50/50 8-)
Haha yes, it's going to be fairly light in the end.

I spoke to Graeme from Suzi Auto and batteries comparable to Leaf ones in cost and size are available, and these would fit in the engine bay.

But as you say given the low weight, I could easily fit in lead acid into the boot and it would hang the same depth as the petrol tank and weight distribution would be good. I think ultimately the deciding factor would be how cheaply could I get SLA batteries, particularly if I could find a source for them used?

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Re: Battery pack placement

Post by Adverse Effects » Mon, 20 Nov 2017, 16:53

you dont want to go leadslead you will burn way more power dragging there HUGE mass around and you will only have about 1/3 the power to mass not to mention lead dont deal well with the torcher of heavy discharges

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Re: Battery pack placement

Post by Xmoht » Mon, 20 Nov 2017, 17:03

Adverse Effects wrote:
Mon, 20 Nov 2017, 16:53
you dont want to go leadslead you will burn way more power dragging there HUGE mass around and you will only have about 1/3 the power to mass not to mention lead dont deal well with the torcher of heavy discharges
With the low weight of lithium or NCM though, do you think being so light in the rear will be problematic? No spare tyre, petrol tank, rear seats etc. means that it'll already be heavily weighted to the front end.

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Re: Battery pack placement

Post by Adverse Effects » Tue, 21 Nov 2017, 08:16

dose a car get all out of balance when the tank is almost empty (~-40Kg)?

dose the car get all out of balance when you have 3 adults in the back and a full tank of gas (~400Kg)?

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Re: Battery pack placement

Post by Xmoht » Tue, 21 Nov 2017, 08:18

Adverse Effects wrote:
Tue, 21 Nov 2017, 08:16
dose a car get all out of balance when the tank is almost empty (~-40Kg)?

dose the car get all out of balance when you have 3 adults in the back and a full tank of gas (~400Kg)?
The car doesn't move when you have 3 adults in the back and a full tank of gas, it's a Corolla! (But good point, thanks)

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Re: Battery pack placement

Post by poprock » Tue, 21 Nov 2017, 11:42

And the 3 adults are still forward of the rear axle :) ( unless you are sneaking them into an old style drive- in movie lot and they are shoehorned into the boot) :P

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Re: Battery pack placement

Post by Richo » Tue, 21 Nov 2017, 12:13

Richo wrote:
Tue, 14 Nov 2017, 12:14
If the Rolla was doing 8L/100km then to break even on petrol prices the petrol would have to be $1.37/L. (For SLA)
So eqv 8L/100km that is $0.50/L. (For lithium)
I wouldn't buy SLA just based on the numbers above.
It would be like saying NEW12V 90Ah are HALF price - who would do it.
Even if you got 2nd hand ones with half capacity you would need QUARTER price.
$55 for 12V 90Ah SLA..

Sure it would be cheaper to get it going - initially - by what $300-400.
But it would be more expensive to run that putting premium in it all the time now.

Well I guess if you put SLA in it now you can always think about a Lithium upgrade in 2-3 years time..
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