CZal's Mazda Roadster (MX-5)

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Post by CZal » Sat, 09 Oct 2010, 06:16

Hi EV2Go, talk about quick response... I'm not the only one up at this time huh?!

I really don't want to dent the roadster's fun factor, so would like to accelerate pretty hard (actually veryy rarely but at least have it available), I've been thinking the acceleration will fall under the 10C 'impulse' discharge factor, while the continuous rating will have to keep me at speed?

The roadster will primarily be a commuter. I can't imagine ever doing more than 50km in a day... I still have the oil burner for camping trips...

We had a GoGreen thing on today in Melbourne and I managed to get into a Blade Electron (nice drive actually, interesting accelerator pedal controlled regen arrangement) Anyway in talking with Doug in the test drive he advised that they had 90Ah LiFePo4s in there and he estimated 100km range... Admittedly the Blade's got 192V and runs an Azure AC setup... but I'm thinking that the 60Ahs should give 40-50km in the lighter roadster....

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Post by CZal » Sat, 09 Oct 2010, 06:39

OK maybe 30-40km... still very acceptable in my scenario...

Also we need to fix the posting time... I've got a bit past 1:30am on my watch, but the post time will be about 10:30pm!

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Post by EV2Go » Sat, 09 Oct 2010, 06:45

The 10C is for like a split second, so you can't really rely on it at all. Even 3C is pushing these batteries a bit out of there comfort zone. So if you want reasonable performance I would be looking at the 90Ah to give you 270Amps.

I have driven a car similar to yours (the one I am basing the figure off) it's a convertable about the same weight, with the Netgain Impulse 9" (same motor except yours is 1 inch longer, similar performance, a few more Hp but next to nothing) and 45 * 90Ah Thunderskys.

Acceleration on the flat is nothing to write home about (probably around the same as an ICE) but the torque up hills was surprisingly good.

If I was only going 144v I would go the 90's but ultimately the decision is yours.

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Post by CZal » Sat, 09 Oct 2010, 06:59

Thanks heaps EV2Go,

That's the type of real world experience I'm looking for... Nothing worse than thinking I'm saving $2k only to find I've wasted $4k!

Just to confirm, the car you saw had a gearbox? It wasn't trying to accelerate using its final drive ratio...

Also does this mean I'm never going to get close to hitting the controller's 600A peak?

This is just to confirm (last ditch attempt style), looks like I have my answer :0)

Thanks again,
C.
Last edited by CZal on Fri, 08 Oct 2010, 20:00, edited 1 time in total.

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Post by EV2Go » Sat, 09 Oct 2010, 07:14

Yes it had a gearbox but no clutch, which makes quick gear changes non existant (and made it feel slower than it needed to). People will try tell you that you can get away without one, but I am definately not a fan of the no clutch theory.
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Post by weber » Sat, 09 Oct 2010, 14:23

Do not use 45 x 60 Ah lithiums in an MX-5. That would be a very dissapointing experience to drive and they would probably not last very long. As you probably know, we are putting 228 x 40 Ah in ours. That's equivalent to 45 x 200 Ah.
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Post by Electrocycle » Sat, 09 Oct 2010, 15:27

EV2Go wrote:I have driven a car similar to yours (the one I am basing the figure off) it's a convertable about the same weight, with the Netgain Impulse 9" (same motor except yours is 1 inch longer, similar performance, a few more Hp but next to nothing) and 45 * 90Ah Thunderskys.


How much range is it getting?
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Post by EV2Go » Sat, 09 Oct 2010, 15:39

I believe it's around the 70 mark at 80% DOD.

CZal I also recall hearing / seeing posted but I can't remember where, someone said that although they continue to deliver the Ah, they are less keen to deliver the full 3C sfter a while.
Last edited by EV2Go on Sat, 09 Oct 2010, 04:42, edited 1 time in total.

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Post by antiscab » Sun, 10 Oct 2010, 07:09

CZal wrote:
d. Constant discharge (real reason for this post)
Although I only have a 7km commute a big chunk of that is on the freeway so constant discharge is a concern.
TS batteries have a 3C constant discharge rating, which means that the 60s can put out 180A continuously. The controller can put out 200A constantly.


The definition of "constant" used in those data sheets is for 30 seconds.

0.3C is the continuous rated current - 20A for 60Ah cells and 30A for 90Ah cells.

now in the real world, everyone who has kept the cells below 0.8C continuous has had good service life.

I ran my first set of 40Ah cells at 55A continuous (1.4C), and I got ~500 cycles to 60% of original capacity.

7km is a relatively short commute, so the question is more,
how much minimum range do you need?
how far do you travel in a year?

a 60Ah pack would give you 25'000km and 90Ah 100'000km.
but if it takes you 5 years to do 25'000km, you may be better off with the 60Ah cells anyway.

Matt
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Post by EV2Go » Tue, 12 Oct 2010, 05:44

Hi Matt can you please explain how you came to those millage figures.

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Post by antiscab » Wed, 13 Oct 2010, 12:27

EV2Go wrote: Hi Matt can you please explain how you came to those millage figures.


The 25'000km number was an extrapolation from a few sources.

my old pack of 16 40Ah cells survived 500 cycles till capacity was 60% of original.
continuous discharge rate was 1.4C, with peaks of 5C.

anecdotally, the higher the continuous discharge rate the shorter the service life.

there was an extreme case where a pack was run at 2.3C continuous.
also TS cells, that pack lasted 80 cycles.

at the better end, Rod Dilkes 90Ah pack gets discharged at 0.8C continuous, and still has ~80% of original capacity after ~600 cycles.

the other bit of the puzzle is assumed wh/km.
I can't remember what number I assumed, but it will be different for everyone.
YMMV, you just won't know how much till you've built it.

getting a bigger pack does mean a longer service life, but as usual its a trade off with other factors.

that test was also on cells date 2007.
The newer cells seem more capable to faster discharge, so treat that as a worst case scenario.

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Post by EV2Go » Wed, 13 Oct 2010, 15:48

Those figures are alarmingly low aren't TS supposed to do >2000 cycles @ 80% DOD and > 3000 cycles @ 70% DOD, or is that only if you dicharge at 0.3C?

Anyway I don't want to highjack CZal thread but it is a concern if people are basing their economy of pack on these figures.
Last edited by EV2Go on Wed, 13 Oct 2010, 04:50, edited 1 time in total.

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Post by antiscab » Wed, 13 Oct 2010, 20:01

well my case was a bit extreme,

my discharges were 5C for 3 sec, then 1.4C until the battery was depleted, with the occasional 5C burst if I had to stop.
It was necessary, as 1.4C = 70kmh.

Most cars have a more gentle usage profile.
you might use ~1.4C to hold 100kmh, but you don't spend the entire packs service life doing 100kmh.

I'm repeating the experiment on my Vectrix, but with 60Ah cells this time.
at 110kmh (which I ride about 30% of the distance) I happen to use 1.4C (~85A) continuous.
100kmh is 1.1C or 65A continuous
it was a bit of a coincidence.

however, when im going slower, discharge rate is alot lower.

Most of the pack are 2010 cells, but I have included 3 x 2007 cells for reference.

the relationship between continuous discharge rate and service life seems kinda exponential.
this is all a bit anecdotal, and changes as the cells improve over the years.

generally try to size your pack so it takes an hour to take out 80% of the capacity at the speed you spend most of your time doing.

if this isn't possible due to a particular constraint (space, weight, money) then a different cell would be a good idea.
all IMO.

I highly recommend going for at least 45 x 90Ah cells.

Matt

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Post by EV2Go » Wed, 13 Oct 2010, 20:28

This would be a good topic to start a thread on... "Batteries the real life story". Problem is there are many people out there like myself that have little to no real life experience with EV batteries, and believe the marketing hype that they are handed by the battery manufactures (from lack of knowing better).

Of course the manufacturer puts in fine print 0.3C discharge but what does that really mean to the average punter that doesn't know what impact running at 3C will do.

Until you posted the few examples about how it reduces the service life I was blissfully ignorant of the fact that it would reduce the life cycles so dramatically.

So should you really be looking at different battery technologies then if the cost / cycles is too high?

It's an important topic and worthy of a tutorial or sticky, would be nice if the guys with the runs on the board educated those of us less educated.

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Post by antiscab » Thu, 14 Oct 2010, 10:32

EV2Go wrote:
So should you really be looking at different battery technologies then if the cost / cycles is too high?


Maybe,
in my case the lithium pack still lasted 5.5x longer than (in distance, 22'000km vs 4'000km) the lead acid pack it replaced ever did.

lead acid also doesn't like high continuous discharge rates, though some batteries are better equiped for it.

high rate cells like Headway, A123 or LifeBatt get tested at the higher rates for cycle life.

Its usually more cost effective just to get a bigger TS or CALB pack to get the power though so you have range aswell, unless it physically won't fit.

Matt
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Post by 7circle » Thu, 14 Oct 2010, 11:05

I'm shocked that this suggests Higher than 1C discharge rates reduce cycle life significantly.

How long often were the cells left below 2.2V or charged above 3.6V.

If you were depleting the cells without accurate BMS protection the characterised cycle life makes sense.

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Post by antiscab » Thu, 14 Oct 2010, 11:18

the cells were discharged below 2.2v twice, but were recharged immediately.

at the time, those two events had no immediate bearing on usable capacity.

the cells never went above 4v at the cell level, the BMS prevented that.
individual cells would end up above 3.6v, as the pack was charged to 3.65v pack average.

the capacity loss was on all cells, rather than just a few.

It will take me ~2 years to put the same number of cycles on the pack in my Vectrix. (similar continuous discharge rate)
The new pack only went into service 2 months ago.

I still need to sort out a capacity tester, so I can do a monthly capacity test.

Matt
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Post by 7circle » Fri, 15 Oct 2010, 06:15

If the Cells recovered to normal capacity after the deep discharge that makes sense.

The Upper voltages make sense.

So where you supprised they only lasted 500 Cycles after
"my discharges were 5C for 3 sec, then 1.4C until the battery was depleted, with the occasional 5C burst if I had to stop.
It was necessary, as 1.4C = 70kmh."

Sorry CZal for hijack ... Image

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Post by antiscab » Fri, 15 Oct 2010, 12:23

7circle wrote:
So where you supprised they only lasted 500 Cycles after
"my discharges were 5C for 3 sec, then 1.4C until the battery was depleted, with the occasional 5C burst if I had to stop.
It was necessary, as 1.4C = 70kmh."


Nope, not surprised.
I was running them at more than 4 x rated continuous discharge.

I was more interested in seeing how long they would last when being abused like that.

Now I'm interested if the newest generation of cells will last longer.

Matt
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Post by CZal » Fri, 15 Oct 2010, 17:26

Thanks to all for all the useful information,

I'm not concerned about any take over of threads. Batteries is the stage I'm up to in relation to this project so having this information here at this time is the right thing... (Obviously I'll have to learn how to bookmark the blog, as in weber and coloumb's!)

btw I'm deciding on batteries today... Will post once I've placed the big order :0)


C.

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Post by Mesuge » Mon, 18 Oct 2010, 10:54

All very good info, recommendations, and yet above it you have to take into account, how they related these 0.3C continuous discharges for 3-4k cycles etc. in the first place!?! Specifically, they mostly talk only about a single cell (not connected in string of larger batt. pack) in clean and temperature/humidity/vibration stable environment.

Well, the real world, daily EV application is something completely different, dirty elements, batteries charged and operated in series, often times in several subpacks of different capacity around the vehicle (bad). And all that sustained during very variable temp/hum/vibration conditions.. In other words, it's not only in the %DoD question.

In order to get some competetive operational costs per distance km/mi, the care of batteries is the supreme issue, unfortunately, many people don't get it, and lot of conversions end up with prematurely crippled performance, which sucks with these front loaded expenses.

No wonder, OEMs have been quite sceptical about the overall EV viability with current batt. technology because of this very issue. It could be done, but it's not easy. Look, how long it took, to get dozens of thousands km in somewaht reliable fashion from AGM/gel batteries, well the issue dragged for maybe more than a decade, and still to this date, mistakes could be made. Now we have the new technology lithium (and its many variations) and it's the same early mistakes all over again. While the good enough technology, larger module NiMH (plug&play) had been kicked out for dubious corporate reasons, but that's offtopic..
antiscab wrote: anecdotally, the higher the continuous discharge rate the shorter the service life.


Very true, this has been certainly addressed also in some "scientific/tech papers" on the topic. It's not easy to plan for say ~0.8-1.4C continuous, not only in terms of scaling up the pack, preparing budget, but also how to fit the sheer mass inside those often silly, build around ICE donors.
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Post by coulomb » Mon, 18 Oct 2010, 15:59

CZal wrote: I'll have to learn how to bookmark the blog, as in weber and coloumb's!

Great idea!

I've made a post on how it's done here.
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Post by weber » Tue, 19 Oct 2010, 16:16

Hi CZal. Sorry my earlier post in this thread was rather terse and dictatorial. I was running late for a job, but wanted to send off something quickly as I didn't want to see you making an expensive mistake. Thankfully others took the time to explain in detail.

I expect I am too late, but another option just occurred to me, and that is using 2 or 3 smaller cells in buddy pairs or triples (in parallel). e.g. 45 pairs of 60 Ah cells or 45 triples of 40 Ah cells.

Zeva (Ian Hooper) found in his excellent MX-5 conversion that he could not fit his 40 x 160 Ah cells in some of the locations he had hoped (e.g. the fuel-tank space behind the seats) because of their height. NevilleH has used triples of 40 Ah cells in his conversion (not an MX-5) and benefited from their lower height in being able to fit them more easily.

We were forced to use 40 Ah cells because of the high voltage we wanted for the industrial 3-phase VF drive. But even if we were using a lower voltage, we would still have needed to use the 40 Ah cells to be able to fit enough kilowatt-hours worth of cells, just to get the peak kilowatts we need to match the peak power to weight ratio of the original vehicle.

We were constantly struck by how many places we could just barely fit those 40 Ah cells. And of course if you were to go with 40 Ah pairs or triples we would be happy to share our battery rack designs.

If you haven't already I recommend you make a dummy cell out of cardboard, polystyrene or wood and try it in various places. But don't forget to add at least 15 mm to the width and 40 mm to the height to allow for the box or cage and the wiring.

The prime real-estate for batteries is closest to the centre of gravity horizontally and as low as possible vertically. In the MX-5 that's either side of the tailshaft and in the fuel-tank space between the rear subframe and the parcel-shelf.
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Post by CZal » Tue, 22 Feb 2011, 00:13

Hi all,

Back to posting after a long break, as always real life getting in the way of the ideal!

Image Ready to fit motor

Thanks to all who responded relating to the battery questions. (Weber, I'd much rather a terse email than a $5k mistake, thanks mate!)

Although I didn't need a lot of range, I did want enough power to keep the EV fun so decided on (and purchased) the 90Ah TS batteries. They've since come in and together with a consulting engineer we've started to fit them to the car.

Image Expensive little box!

I figured it was a good time to get an engineer in as there is little room in the Eunos and body cutting needed to occur. And rather than have the arguments later, I thought it best to start the compliance process now.

Initially I was going to put all 45 cells behind the seats (see pic below) but weight distribution concerns finally won through and we've decided to put 23 cells in back and 22 cells in the engine bay. This will keep the weight distribution (and funnily enough overall weight) almost identical to original spec, which I'm quite please with. This also means that the space we made for the second/lower row of batteries can now be used to house the charger and BMS and still leave more room in the boot than original!!

Image Image
There'll be a single row of Batteries in back and two rows in front



Have fitted the Warp9 to the car with provision for the P/S and Air/con to be included in the build.
Image Yeah baby! Waste some traction power!!

Next:
- VacPump for braking. Does anyone know if I can use a simple PVC pipe arrangement for the vac tank?
Image Like this??   Copyright Eugen. Hope it's ok I use this pic Eugen..

- Reverse Cycle air/con valve for heating

- DC-DC. Probably will initially charge the acc battery each night together with the traction pack and see how that goes...


Looking to really get moving now.. As always comments most welcome!!

CZal
Last edited by CZal on Mon, 21 Feb 2011, 13:31, edited 1 time in total.

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Post by CZal » Sun, 04 Nov 2012, 17:13

OK, another long break.... A long, long break. The car is moving along but so is life. So after a long sabbatical overseas and then coming home and getting married, the conversion continues Image

I've been working on the car and taking photos but not posting, so I'll try to break the posts down to the steps I took.

In this post, it's working out the control board and building.
As this is an R&D vehicle (and I love working on wood) I kept the control board pretty open and spaced apart.

Essentially I drew it out first:
Image

With the spacing, there's plenty of space to describe what each realy does:
Image

And then secure the bits and wire up:
Image

This bit was actually really simple thanks to EVWorks' wiring diagrams on their website. This control board later got bolted straight onto the front of the engine bay battery box.
(It shows the flow of the circuit logic pretty well but it's not ideal for a running car, the next time I build a board like this it will be compressed into a nice, safe lockable box)


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