Reality check on motor/battery/donor combo please!

Technical discussion on converting internal combustion to electric
Post Reply
Peter C in Canberra
Senior Member
Posts: 494
Joined: Sun, 27 Jul 2008, 04:05
Real Name: Peter Campbell
Location: Canberra

Reality check on motor/battery/donor combo please!

Post by Peter C in Canberra » Mon, 11 Aug 2008, 20:53

Hi,
I am converting a Charade. I have just started pulling bits out and have not yet made any major purchases. I thought I had decided on the Impulse 9 motor since it should certainly give plenty of performance in a car starting (and probably finishing) with a weight of about 800Kg. I don't want to be underpowered. Zippy is nice, but I don't need over the top performance either. Similar to our 1.4L petrol 2006 Hyundai Getz would be about right. Range is important. I will almost certainly use 144V of LFP90AH lithiums since that seems the only way to fit in sufficient KWhs, not lose the back seat and keep some space for shopping in the back. Then I was told that I'd be better off with the ADC 6.7" X91 motor since I wouldn't be able to supply enough current to the Impulse to make it worthwhile and would instead just make the syncro work harder (without clutch) for the larger rotating mass. Indeed it was suggested I should set a current limit in the controller to be nice to the batteries.

If I have the larger motor and drive moderately would there be any range penalty compared with having the smaller motor? IE is smaller more efficient than big, even when both are driven moderately, like with petrol motors?

So, I guess, I'd like some feedback on what to expect (range and performance) from a combination of 800Kg car with 13KWh of LFPs and either the ADC 6.7" or Impulse 9. Pros and cons? (price difference is minor in the overall scheme)

Thanks,
Peter.
Daihatsu charade conversion 2009-18, iMiEV 2013-2019, Holden Volt 2018-present, on the ACT's 100% renewable electricity. Kona on order.

User avatar
Richo
Senior Member
Posts: 3737
Joined: Mon, 16 Jun 2008, 00:19
Real Name: Richard
Location: Perth, WA

Reality check on motor/battery/donor combo please!

Post by Richo » Mon, 11 Aug 2008, 21:14

Impulse9 should have a better torque/amp ratio than the 6.7" motor.
I doubt the 6.7" would be grunty enough to get the performance you ask.
Go the 9".
So the short answer is NO but the long answer is YES.
Help prevent road rage - get outta my way!

User avatar
woody
Senior Member
Posts: 1715
Joined: Sat, 21 Jun 2008, 02:03
Real Name: Anthony Wood
Location: Mt Colah

Reality check on motor/battery/donor combo please!

Post by woody » Mon, 11 Aug 2008, 21:53

A sydney guy has converted a holden combo. It's a lot heavier (lead-acid) but he's regretting the 8 inch ADC and would have preferred the 9 inch because he's thrashing the 8 inch which is inefficient and heats it up, making it worse.

The downsides of bigger DC motor off the top of my head:
1) bigger - might not fit
2) heavier
3) costs more
4) may be slighly less efficient (not sure)
5) peak power at different RPM (may be better or worse)
6) Draw more current (can be controlled by the, um, controller)

All of which will probably be outweighed by the advantages.

Kearon is going LFP90s + Netgain Impulse 9, but his car is 25-30% heavier.

cheers,
Woody
Planned EV: '63 Cortina using AC and LiFePO4 Battery Pack

zeva
Senior Member
Posts: 422
Joined: Sat, 15 Dec 2007, 05:09
Real Name: Ian Hooper
Location: Australia
MSN: sigmunky@hotmail.com
Contact:

Reality check on motor/battery/donor combo please!

Post by zeva » Mon, 11 Aug 2008, 22:14

You probably can't fit anything bigger than an Impulse 9 in a Charade (due to the narrow engine bay) but I tend to think they're the way to go.. Of course, as a NetGain reseller I would say that Image but here's some justification on woody's points above:

1) The ImPulse 9 is the same length as the ADC 8, which are actually both marginally shorter than the 6.7" L91 or X91.

2) True, but its not too significant compared with the vehicle mass (i.e 10-20kg more motor in a ~1 tonne vehicle)

3) ImPulse 9 is cheaper than the ADC 8 Image

4) Bigger motors are usually more efficient in EVs due to lower heating (where the motor doesn't feel as overworked, as you suggest in the case of the Combo)

5) ImPulse 9 do have their power band at a higher RPM, so may feel less "punchy" off the mark - but you can just take off in a lower gear to compensate.

6) Bigger motors can handle higher current (equals more torque and power), but yes it's the controller's job to manage/limit this.
Ian Hooper
--
"Never doubt that the work of a small group of thoughtful, committed citizens can change the world." - Margaret Mead
http://www.zeva.com.au

User avatar
Richo
Senior Member
Posts: 3737
Joined: Mon, 16 Jun 2008, 00:19
Real Name: Richard
Location: Perth, WA

Reality check on motor/battery/donor combo please!

Post by Richo » Tue, 12 Aug 2008, 00:37

^ Listen to the man ^

If it fit's put it in.
So the short answer is NO but the long answer is YES.
Help prevent road rage - get outta my way!

Goombi
Senior Member
Posts: 532
Joined: Sun, 10 Aug 2008, 17:59
Real Name: Eugen
Location: Gympie

Reality check on motor/battery/donor combo please!

Post by Goombi » Thu, 14 Aug 2008, 17:34

Just info.
What is the average speed of a say 9" motor at 50 Km/h (I realise it depend what gear one uses and the power)
Is there a limit how fast same motor will run? 3-4-5-6-7K rpm?
personally 2500rpm/ motor should be most ecconomical.
chinese cars that use 96 volt system only run at 2000-2500 rpm-- reaching 60-70 km/h and doing around 100km distance plus..
I would say electric motor doing 5000rpm must drain the batteries pretty fast. I would like to compare snyone's chart.
Same a combustion engine --faster you run the more fuel it needs elementery....

antiscab
Senior Member
Posts: 2486
Joined: Mon, 26 Nov 2007, 05:39
Real Name: Matthew Lacey
Location: Perth, WA

Reality check on motor/battery/donor combo please!

Post by antiscab » Thu, 14 Aug 2008, 18:50

from memory, a warp 9 has max power point around 4000rpm, if you can feed it the full 1000A at 170v.

the resistance loses in a electric motor are more significant than the mechanical friction loses.
at a higher rpm you have to feed the motor less current for the same mechanical power output.
the losses are therefore lower.

a warp 9 is designed to take just shy of 200A continuous.
staying below this rating results in a cooler more efficient motor.

say you need 10kw. at 200A thats 50v.
if you spin the motor twice as fast, it becomes 100v, 100A.
the effect of halving the current is reducing the resistance losses to a quarter.
the mechanical friction losses go up aswell, so there will be a "sweet spot".

If you retain the gearbox, just put it in the gear that requires the least battery side A to do the job (ie watch the A guage) :)
Matt
2017 Renault zoe - 25'000km
2007 vectrix - 156'000km
1998 prius - needs Batt
1999 Prius - needs batt
2000 prius - has 200 x headway 38120 cells

User avatar
woody
Senior Member
Posts: 1715
Joined: Sat, 21 Jun 2008, 02:03
Real Name: Anthony Wood
Location: Mt Colah

Reality check on motor/battery/donor combo please!

Post by woody » Fri, 15 Aug 2008, 00:34

AFAIK Internal Combustion engines use more fuel at higher RPM because higher RPM means more air going through the system, and you need to keep the fuel/air mixture rich enough to avoid nasty problems like putting holes in pistons from burning too lean.

There is also more friction due to the pistons traveling faster/further.

In electric motors, the friction element is there, not to any where as big an extent, but the air/fuel problem is not there at all :-)

That said the efficiency curve for a DC motor is very flat, I think netgain and advanced dc both plot efficiency.

The difference between highest and lowest efficiency is about 10%, which is about the same as a gearbox.

It's still a good idea to keep the gearbox for torque multiplication (low gears) but it doesn't give you the efficiency gains you get for an ICE.
Last edited by woody on Thu, 14 Aug 2008, 14:38, edited 1 time in total.
Planned EV: '63 Cortina using AC and LiFePO4 Battery Pack

drowe67
Groupie
Posts: 147
Joined: Fri, 18 Apr 2008, 20:14
Real Name: David Rowe
Location: Adelaide
Contact:

Reality check on motor/battery/donor combo please!

Post by drowe67 » Sun, 17 Aug 2008, 14:50

Peter,

I have just got a Charade on the road with the lower power X91-4001 6.7 inch motor:

here is the evalbum entry, here is a picture of the motor installed.

Image

Plenty of room for a 8 or 9 inch motor, as long as they aren't much longer. Only about 1 inch spare lenghth-wise on the X91, although there would be 2-3 inches spare if you had a single shaft motor.

I have 330kg of lead in the thing (curb weight around 1100kg) and it accelerates better than the ICE (no gear changes, pulls 3rd easily from stand still), at least up to the 70 km/hr I have taken it so far.

It does feel and ride heavy, so with Lithiums and massing around say 900kg I would guess your Charade will be quicker than a ICE Getz around town. With an 8 inch motor you will be quicker than most ICE cars off the line.

Even with the X91-4001 motor (which is the lower power, range orientated X91 motor) my biggest problem is my clutch is slipping under even modest acceleration. So consider a clutch upgrade when you have the gearbox out.

It pulls over 200A under reasonable acceleration (I can't floor it with the current clutch).

Cheers,

David

Peter C in Canberra
Senior Member
Posts: 494
Joined: Sun, 27 Jul 2008, 04:05
Real Name: Peter Campbell
Location: Canberra

Reality check on motor/battery/donor combo please!

Post by Peter C in Canberra » Mon, 18 Aug 2008, 04:27

Thanks for the feedback. I'll be interested to hear how it goes and may get in touch if I run into anything tricky as I dismantle the petrol-associated stuff. I had planned to not keep the clutch and removed the clutch pedal today. There seemed to be a fair consensus that one can do without it. Since you are pulling over 200A for reasonable acceleration I may not get much better in spite of the more powerful motor. The rated limit for the LFP90AH cells is 270A. If the controller is set for a limit of (say) 250A to be kind to the battery I may not see all that the motor is capable of doing. Still it is encouraging that you get "reasonable acceleration" for this sort of current with a little more mass that I would have. That suggests that I should not be hampered too much be the current limit of the battery. Does that sound right to the others here?
Thanks,
Peter.
Daihatsu charade conversion 2009-18, iMiEV 2013-2019, Holden Volt 2018-present, on the ACT's 100% renewable electricity. Kona on order.

antiscab
Senior Member
Posts: 2486
Joined: Mon, 26 Nov 2007, 05:39
Real Name: Matthew Lacey
Location: Perth, WA

Reality check on motor/battery/donor combo please!

Post by antiscab » Mon, 18 Aug 2008, 05:55

a few points of clarification:

assuming your controller has good ripple caps on the battery side, and the motor has a reasonable amount of inductance, the controller will trade volts for amps.

lfp90aha can do 270A continuous, but 450A for several seconds (with 500A+ for milliseconds if the ripple caps arent rated for enough current.)

even at the conservative 270a, a 144v pack would give 31kw.
even a curtis 1231C could give the motor constant power over the majority of its operating range (lots of current, high torque to start with, low torque at higher speed)

the motor wont have alot of voltage applied to it until it has spun up a fair bit. the smaller the motor the faster it has to spin for the same voltage and current drawn.

the other point is that a x-91 is only rated for a 120v pack (that sags under load). so that motor shouldn't ever see the full pack voltage (assuming the common 144v pack).

an x-91 is more efficient at lower currents than the L-91, it is true.
however, at higher currents (200+) the L-91 wins out.
so keep that x-91 spinning.

Matt
Matt
2017 Renault zoe - 25'000km
2007 vectrix - 156'000km
1998 prius - needs Batt
1999 Prius - needs batt
2000 prius - has 200 x headway 38120 cells

Peter C in Canberra
Senior Member
Posts: 494
Joined: Sun, 27 Jul 2008, 04:05
Real Name: Peter Campbell
Location: Canberra

Reality check on motor/battery/donor combo please!

Post by Peter C in Canberra » Mon, 18 Aug 2008, 16:13

Thanks for the comments. I plan to use an Impulse 9 rather than the L/X-91. The general indications above make me think I should not loose any efficiency so long as I don't get heavy footed.
I have wondered if it is possible to have some form of current limit between the batteries and the controller so that one can never exceed their limits. If the constant current source were followed by a lot of capacitance the voltage could then sag while the current increases beyond the limit without stressing the battery. I did a back of envelope calculation and came to the conclusion that one would need 100s of Farads to sustain (say) 500A of which only 250A came from the battery for a minute with the voltage sagging from 144 to 96V. Does that sound right? Can you buy a cheap 300F cap with a 144V rating? ( I suspect not!). Do controllers really have anything approaching this much capacitance on the battery side? Is the internal resistance of the battery sufficient that one wouldn't need the current source I proposed above? Is such a current source actually a feature of a good controller anyway? IE is the maximum current in the controller set at the battery side of some caps rather than at its output side? I had hoped to buy a ZEVA controller if they are ready when I have the rest of my car done.
thanks for any further comments on my speculations,
Peter.
Daihatsu charade conversion 2009-18, iMiEV 2013-2019, Holden Volt 2018-present, on the ACT's 100% renewable electricity. Kona on order.

antiscab
Senior Member
Posts: 2486
Joined: Mon, 26 Nov 2007, 05:39
Real Name: Matthew Lacey
Location: Perth, WA

Reality check on motor/battery/donor combo please!

Post by antiscab » Tue, 19 Aug 2008, 04:11

a few points of clarification:
assuming the control has good ripple caps on the input side, and the motor has a reasonalbe amount of inductance, the controller controls, motor and battery side current independantly.

so 200A at the motor may be only 30A at the batteries at low speed.
under cruising conditions, the voltage on the motor side is almost always lower than the pack voltage (unless you happen to be running a pack voltage of 72v or less).

the other point is that lfp90aha are rated to 270A continuous. they are capable of 450A for a few seconds, and 900A for microseconds.

on my own 288v 90AH lithium pack, i will be running a battery side current limit of 450A, and a motor side current limit of 2000A.

144v of 90AH lithiums will give driveable (ie wont be left behind in traffic) acceleration for mid-sized vehicles.

Matt
Matt
2017 Renault zoe - 25'000km
2007 vectrix - 156'000km
1998 prius - needs Batt
1999 Prius - needs batt
2000 prius - has 200 x headway 38120 cells

antiscab
Senior Member
Posts: 2486
Joined: Mon, 26 Nov 2007, 05:39
Real Name: Matthew Lacey
Location: Perth, WA

Reality check on motor/battery/donor combo please!

Post by antiscab » Tue, 19 Aug 2008, 04:19

Hi Peter,

most controllers allow you to set battery and motor current limits independantly.
i know for a fact, the zilla controllers can have independant current limits.

a 90AH cell only sags to 2.6v at 270A. (or 117v for a 144v nom pack, 31.6kw)
at 450A, cell voltage is 2.2-2.3v (or 99v for a 144v nom pack, 44.5kw)

capacitors are spectacularly expensive.
from a cost/kw perspective, it is cheaper to buy lithium batteries.
so if 144v 90AH isnt enough power, for for 160AH cells, or go for more voltage.

controllers are almost always rated as motor side max current (zillas included).
the only time you ever see battery side current approach the rated motor side is when the back emf of the motor has approached the pack voltage.

Matt
Matt
2017 Renault zoe - 25'000km
2007 vectrix - 156'000km
1998 prius - needs Batt
1999 Prius - needs batt
2000 prius - has 200 x headway 38120 cells

Post Reply