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Paul9 - Once upon a time...

Posted: Sat, 25 Jun 2011, 04:56
by Paul9
Once upon a time (about two years ago) there was a little boy called Paul. Paul lived in an evil naughty place called Sydney. Sydney was an evil naughty place because it had thousands of cars with internal combustion engines which gave off even more gas than Paul gave off when he sat in the bath. Then one day little Paul read a magazine. Not one of those magazines he hid under his bed but an environmental magazine which had an article about how to build your own electric vehicle. Paul asked another little boy called Johnnie, who owned a motor mechanic business, to help build the EV. Little Johnnie was full of glee and suggested that if Paul bought two sets of components, little Johnnie would build two EVs and they would have one each.
Little Paul saved up all his pocket money and even pulled out one of his teeth each night for the tooth fairy. Little Paul eventually saved up enough money for two sets of components but now sucks his meals up through a straw and is difficult to understand when facing into the wind.

For any little kiddies out there unfamiliar with the Chinese kit from Eugen (Goombi):
Motor 96volt DC F series, 8.5 kw continuous 2800 rpm
Controller 300 amp
Pot Box and 15amp Charger
DC-DC Converter

(I believe the kit is now distributed by Graeme at Suzi Auto in Brisbane)

The two little boys also imported batteries:
SANTAKUP A.G.M. 105 amp hour capacity approx $170 AUD each
Other minor parts purchased from ZEVA in Perth
Adaptor plates purchased from Suzi Auto.
The donor car was a 1993 two door Suzuki Swift for $150.

Over the last two years the two little boys spent some of their spare time building the EV. As you little kiddies out there would expect, many goblins and evil nasty wizards would sneak in at night, when the little boys were asleep, and disconnect the wires so the car would not work properly (that's all we could put it down to!)

In December 2010 the first car was ready to drive. The two little boys called in an engineer who was basically happy with the vehicle except for a couple of minor changes.

When little Johnnie received his trade plates they decided Paul would do some testing. Paul decided to drive it around the quiet, but hilly, streets near his mother's place. Little Paul decided to define a few different "circuits" and drive them a few times. On each trip he recorded the kms travelled, amp hours used, starting and finishing voltages and start and finishing State of Charge. He would vary the gear used and driving style and got the following results:

3rd Gear ........1.24 amp hours per km (119 watt hours per km)
5th Gear ........1.35 amp hours per km (129.6 watt hours per km)
Heavy Traffic ...1.58 amp hours per km (151.7 watt hours per km)

As a result of his testing, and his very low IQ, little Paul has a few questions which you may be able to help with:

1) I find it strange that I get better (more economical) "fuel" consumption in 3rd gear than in 5th gear. "Fuel" consumption is about 8% lower in 3rd gear than 5th. Fuel consumption is lowest in 5th in an ICE. Is this better consumption figure for 3rd gear in the EV my imagination?

2) Closely related to the above, 3rd gear seems to be weaker up hills? A few hills cause the EV to slow down to approx. 40kph in 3rd gear but if I climb the same hill in 5th I do not get as severe a decrease in speed?

3) My battery monitor (TBS e-xpert pro) seems to think I have only about 60 amp hours capacity in my battery. After I use say, 30 amp hours, my battery monitor reads my State of Charge (SOC) as 50%. The batteries are 105 amp hours capacity and this figure has been input to the monitor. Could the monitor be automaticaly adjusting for the discharge rate ie. 105 amp hour capacity at C20 rate but 60 amp hour capacity at the C1 rate?

4) I assume we have incorrectly wired the battery monitor as it correctly measures my discharges (so to speak) but does not recognise the increase in SOC when I recharge overnight? The next morning the voltage will be back up to around 104.6 volts, which is how I know the battery has filled overnight, but the SOC will still read last nights figure say 61%?

5) As a hypothetical question has anyone experimented with Low Rolling Resistance tyres? Do they make a difference? How about thinner tyres and tyres pumped up high?

I would post a few pictures but I can't get them uploaded.
Thanks in advance,
Paul

Paul9 - Once upon a time...

Posted: Sat, 25 Jun 2011, 15:23
by coulomb
Paul9 wrote: 1) I find it strange that I get better (more economical) "fuel" consumption in 3rd gear than in 5th gear. "Fuel" consumption is about 8% lower in 3rd gear than 5th. Fuel consumption is lowest in 5th in an ICE. Is this better consumption figure for 3rd gear in the EV my imagination?
Not your imagination. Motors have a "sweet spot" of maximum efficiency; higher or lower speeds than that spot cause it to use more electrical power for the same mechanical power output. In other words, efficiency drops off away from the sweet spot.

What happens is that lower motor speeds require higher motor torque for the same mechanical power output (power equals speed times torque on the mechanical side; voltage times current on the electrical side). Higher torque requires higher current. Higher current means more copper loss (I^2R losses). Conversely, higher speeds cause more friction and windage losses, not just in the motor but part of the transmission. So there is a speed that the motor is most efficient at, where the copper losses are not too high, and the friction and windage losses are not too high. For your vehicle and those hills, fifth gear puts the motor closer to the sweet spot than third.
2) Closely related to the above, 3rd gear seems to be weaker up hills? A few hills cause the EV to slow down to approx. 40kph in 3rd gear but if I climb the same hill in 5th I do not get as severe a decrease in speed?
This is something unique to series DC motors. By choosing fifth gear, you put a bigger torque load on the motor. This causes the speed to drop more (from the no-load speed) and this increases the voltage across the motor windings (the motor windings see the difference between the pack voltage and the back EMF of the motor; the back EMF is proportional to motor speed). The net effect is that the motor sees more current; this increases the field current (and hence the field magnetic strength) and the armature current. Both of these effects increase the torque from the motor. This doesn't come "for free", rather, fifth gear makes the controller and pack "work harder" as the load increases. The net effect is that you lose less speed up the hills.
3) My battery monitor (TBS e-xpert pro) seems to think I have only about 60 amp hours capacity in my battery. After I use say, 30 amp hours, my battery monitor reads my State of Charge (SOC) as 50%. The batteries are 105 amp hours capacity and this figure has been input to the monitor. Could the monitor be automatically adjusting for the discharge rate ie. 105 amp hour capacity at C20 rate but 60 amp hour capacity at the C1 rate?
Yes. It will have a default "Puekert constant" that it will be using, and typically at EV currents, the effective capacity (for lead acid batteries) will be around half the C20 capacity. You may find it useful to enter an exact figure for this from your battery specifications (if you can find them), or adjust the exponent up or down depending on whether it seems to be adjusting too much or too little with heavy loads (drives where you have more hills and/or acceleration).
4) I assume we have incorrectly wired the battery monitor as it correctly measures my discharges (so to speak) but does not recognise the increase in SOC when I recharge overnight? The next morning the voltage will be back up to around 104.6 volts, which is how I know the battery has filled overnight, but the SOC will still read last nights figure say 61%?
It sounds like your battery monitor doesn't see the charge current at all. It might mean you have to thread a charger wire through its current sensor, or change where the charger connects (not directly to the pack, but somewhere earlier where the current sensor will see it).
5) As a hypothetical question has anyone experimented with Low Rolling Resistance tyres? Do they make a difference? How about thinner tyres and tyres pumped up high?
LRR tyres are usually a good idea. Higher tyre pressure certainly helps as well. Softer rides (from lower pressure tyres) cost range.
I would post a few pictures but I can't get them uploaded
Remember the maximum image file size is 100 KB. You may need to reduce their size to get the image file size below this limit.

Paul9 - Once upon a time...

Posted: Mon, 27 Jun 2011, 21:14
by woody
Welcome Paul!

There's an informal Sydney meetup at Terry Hills Tavern on July 12th, from 7:30, be good to see you there...
Paul9 wrote: How about thinner tyres and tyres pumped up high?
Pumping the tyres up does help, but there is a limit, and tradeoffs. The pressure in PSI = pounds per square inch. This means if you have 400 pounds weight on a tyre at 50PSI, your contact patch is approx 8 square inches, compared to 10 @ 40PSI, 12.5 sq. inches @ 32PSI. So you are trading contact patch (and probably grip) for efficiency gains.

I think tyre pressures beyond the tyre limit would be used by either insurance company to reject your claim, if you have a crash.

If you can find a recommendation on your tyre manufacturers site of 40PSI+ go for it though.

I know someone in Sydney who was running at 60PSI, but these were commercial / light truck tyres on a panel van.

Paul9 - Once upon a time...

Posted: Tue, 28 Jun 2011, 19:59
by Johny
Paul9 wrote:5) As a hypothetical question has anyone experimented with Low Rolling Resistance tyres? Do they make a difference? How about thinner tyres and tyres pumped up high?
Hi Paul. I have a set of Hancook Enfren 185/65R13H (http://www.hankooktyre.com.au/enfren/) tyres on order (well, about on order - it depends on D day). The reviews I read about them indicated that they were the first LRR tyres that the car mag tested that had the grip of "normal" tyres but were truly LRR. The 15k drive to my tyre dealer will be on my slightly tread bare Khumhos so I can note driving current etc. over the same path and compare when the LRRs are fitted. May be a couple of months (heard that before) though.

Edit: tread not thread (messed up my own pun)

Paul9 - Once upon a time...

Posted: Sat, 02 Jul 2011, 15:49
by Paul9
Thanks guys for the replies.

Thanks coulomb for your assistance - I was confused when my calculations were telling me that 5th gear gave me better performance than third (at a fuel cost/penalty of course!)
Woody, thanks for the invite to the Terry Hills get together. I have given the ev back to John to finish off so I wouldn't be able to bring it to the get together on the 12th. Maybe the get together after that?
Thanks Johny for the info on the Hancook tyres - I have already started checking on their specs.
Cheers
Paul

Paul9 - Once upon a time...

Posted: Sun, 17 Jul 2011, 20:14
by Paul9
Hi People

Further to Johny's last post about LLR tyres from Hancook, it appears from their website that the narrowest tyres they have are 175/60 whereas my Suzuki already has 165/70R13. It appears to me if I was to buy the thinnest (lowest rolling resistance) tyre from Hancook I would be increasing the rolling resistance rather than decreasing it (wider tyre = greater RR). I can buy 145/70R13 which are thinner but not LRR.

Would you know if it would be better to go 175/60's LRR or 145/70's which would not be LRR?

Thanks again
Paul

Paul9 - Once upon a time...

Posted: Mon, 18 Jul 2011, 02:37
by a4x4kiwi
Perhaps give the Hancook distributor a call and see if they have the rolling resistance data for both models.

Mal.

Paul9 - Once upon a time...

Posted: Fri, 14 Oct 2011, 01:26
by Paul9
Hi People,

Just an update - Sydney now has one more registered EV on our roads! Three trips to the RTA, complete with more paperwork than last years Hansard, and my Suzuki Swift is now registered and running really well!
Thanks to all who's advice got us there!
Cheers
Paul

Paul9 - Once upon a time...

Posted: Fri, 14 Oct 2011, 11:21
by EClubman
Congtrats!

Paul9 - Once upon a time...

Posted: Tue, 18 Oct 2011, 17:18
by woody
Hi Paul,
quick question - was your car engineered under the old system or has the new system come out?
cheers,
Woody

Paul9 - Once upon a time...

Posted: Tue, 18 Oct 2011, 19:38
by Paul9
Hi woody,

The car was engineered under the old system with a mechanical engineer's certificate but was registered on the 12th October which I THINK?? is after the cutover date (30th Sept).

Cheers
Paul

Paul9 - Once upon a time...

Posted: Tue, 18 Oct 2011, 19:43
by evric
Hi Paul,

Can we see some photos of the conversion please?

Eric

Paul9 - Once upon a time...

Posted: Tue, 18 Oct 2011, 23:22
by Paul9
Cant load pics due to the below error message. Sorry
Paul

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