Some "don'ts" for EV building

Technical discussion on converting internal combustion to electric
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Some "don'ts" for EV building

Post by Salty9 » Wed, 22 May 2013, 07:01

Don't expect to recoup your EV investment by selling the vehicle
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Post by acmotor » Wed, 22 May 2013, 07:34

Salty9 wrote: Don't expect to recoup your EV investment by selling the vehicle


That's a good one !
maybe even..

Don't expect to be able to sell your EV.
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Post by jonescg » Wed, 22 May 2013, 17:10

Never apply an economic argument to EV conversions and expect it to come out in your favour

In life, we do all sorts of stuff that gives us great joy yet costs us money. Have we ever applied an economic justification for having kids? For pursuing a PhD? No. So why should your EV be any different? Sure the daily running costs of your EV might be lower, but be honest; the initial cost is astronomically high. The reality is that ALL cars/bikes/boats will cost you money every single day you have them, whether you use them or not. Petrol, electric or otherwise, they will never provide a positive return. So don't expect them to 'break even'.

Have you ever had that conversation with your wife/friend/bank manager (who all may be the same person) - you know: "$40,000 for a conversion? You could have bought a ___ for that kind of money!"

Of course you could have. You could have also given it all to charity. You could have invested in the stock market. You could have pissed it up against a wall. But you didn't - you wanted an electric vehicle that you put together yourself. And the challenge it presented is in itself the reward.

I've heard similar dilemmas with solar PV - "How long until it's paid itself off" is a futile exercise. Someone has to pay for it - whether it's you paying upfront or the taxpayer paying for a subsidy, nothing is free, or going to become free in the future.

Summary: Never attempt to justify your EV conversion using only economic arguments. Because you will end up not doing an EV conversion.
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Post by Richo » Fri, 31 May 2013, 03:47

Dont measure your battery terminals with calipers or a steel ruler

I've heard it's shocking Image

Seriously Image
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Post by BigMouse » Fri, 31 May 2013, 03:50

Richo wrote:Dont measure your battery terminals with calipers or a steel ruler

I've heard it's shocking Image

Seriously Image


You know, that's a really valid point! I very nearly did exactly this. Luckily, my brain worked faster than my hands did and I grabbed a plastic ruler instead. It could have been a very "derp" moment.

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Post by bladecar » Fri, 31 May 2013, 11:59

Hi Jonescg,

Yes, yes and yes.

And, you know, you can't really apply an economic argument to buying most of the other vehicles on the road.

Owners of particular makes know which parts are likely to supply the car's manufacturers with much of their income (as opposed to the cost of the vehicle). E.g., the Toyota Camry: Disk pads can last 100 000 kms and when you take your car to a repair shop and say, I want new disk pads, they say "We have to replace your disks as well, they "may" be under tolerance".   So, when you have a background where you machined the sh*t out of front disks (especially if they were lease cars and because they warped, or squeaked (and because it was expected), you might say: "Put disk pads on, Do Not replace the disks."

And I just have to mention the $800 to $1000 ignition "keys" that you "will" have to replace, for whatever reason, sooner or later. These $800 keys are there to protect you against "theft".

When you look at the maintenance costs for many cars out there (and the 10 year "You still have one of those" concept), electric cars are a nice alternative, especially if you can build it, modify it, upgrade it (yes, really upgrade it) yourself.   Wish I could.

Planet heating, global warming, poisoning the air, where does all that sludgy oil go (or too much of it). Why do motors run when standing still? Smell the exhaust.

Watch the petrol/diesel cars accelerate away from the lights and see the brake lights come on just in time to stop at the next set of lights. And they have to put more nasty stuff into the tank to be able to drive like that, they have to pay for it. There is a better way if you start to casually think about it.

Get on your bike or miss some of this. Build your electric car or you'll never wonder what those mechanical noises are, all around you, but not you... and the more you listen to it, the less you can ignore it.

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Post by Richo » Fri, 31 May 2013, 20:41

bladecar wrote:Watch the petrol/diesel cars accelerate away from the lights and see the brake lights come on just in time to stop at the next set of lights.
The ones to watch are the cars that have the brake lights on all the time. Image
Yep my jeep gets really SH*^ economy doing 100kph down the freeway - and for some reason the brakes only last 2000km.
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Post by Bryce » Sat, 01 Jun 2013, 17:07

Use slip-on numbers to identify all new 12V control wiring

Ditto on the record all wiring as you go. Add this tip and it becomes even easier to trouble shoot the inevitable 'senior moments' that occur over the time of the build (like connecting to a N/O contact instead of N/C).

That reminds me of another related tip: see next post :)

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Post by Bryce » Sat, 01 Jun 2013, 17:12

Don't turn on all the new systems at once. Test them one at a time.

Tempting as it may be to 'switch on the car and drive' when the last connection is made. DON'T DO IT!

Spend the time and test all your circuits one at a time. (By leaving all other fuses out except the circuit you are testing).Saves blown fuses, blown components and runaway cars that way.

Included in this tip is put the driven wheels off the ground before testing the drive circuits: a reversed throttle pot connection is easy to do!

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Post by coulomb » Mon, 17 Feb 2014, 05:17

Don't reuse the existing wiring loom for critical analogue signals, like the pedal signal.

You don't know where that loom has been. Or more to the point, where it's still going. It's possible that noise pick-up from a bunch of unused "special-ground" cables was contributing to our jerky accelerator problem. If this indeed was the source of the problem, in our case it took a long time to track down, because it seemed to be intermittent.
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Post by coulomb » Mon, 17 Feb 2014, 05:32

Don't put a very heavy battery (say over 30% of the original donor's weight) in a convertible or other donor with lower than usual stiffness.
For example, 327 kg of LiFePO4 battery, plus very roughly 60 kg of battery boxes, plus contactors and cables, into an MX-5 convertible. It creaks noticeably when creeping around a carpark or driveway, and has disturbing torsional (twisting) motion with road unevenness. The lack of roof in a convertible makes a bigger difference than you might expect.

It's not a fatal problem, but if you have a lower weight option with this type of donor, this is one reason to favour the lower weight option.
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Post by weber » Wed, 19 Feb 2014, 17:58

coulomb wrote:Don't put a very heavy battery (say over 30% of the original donor's weight) in a convertible or other donor with lower than usual stiffness.
I agree with your general point, but in our specific case ...
... MX-5 convertible ... has disturbing torsional (twisting) motion with road unevenness.
... I think this is misleading. You make it sound as though it's winding up like a piece of licorice. What it does is shudder at the rear if one rear wheel hits a bump or pothole. The shudder apparently consists of undamped torsional oscillations, as evidenced by the fact that if both rear wheels hit a bump together it does not occur.

This problem occurs even with standard MX-5's (although not as bad) and so solutions are readily available, such as this butterfly brace from Flyin' Miata.

Image
Last edited by weber on Wed, 19 Feb 2014, 07:14, edited 1 time in total.
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Post by jonescg » Wed, 19 Feb 2014, 18:26

I'm going to put a roll cage in the CRX when it comes time to convert it, for exactly this reason. I'm removing some folded metal in the chassis, so I'd feel better about replacing that with a skeleton of some kind.
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Post by weber » Wed, 19 Feb 2014, 19:06

Here are the measured results of a Brisbane company installing a roll cage of their own design in an MX-5.

Image

It looks way over-the-top to me (no pun intended).
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Post by Johny » Wed, 19 Feb 2014, 19:29

That looks like a few kilograms of extra mass to accelerate and brake.
I like the butterfly brace a lot more - even a simple crossmember under there would help IMO.

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Post by weber » Wed, 19 Feb 2014, 19:53

coulomb wrote:Don't reuse the existing wiring loom for critical analogue signals, like the pedal signal.

You don't know where that loom has been. Or more to the point, where it's still going. It's possible that noise pick-up from a bunch of unused "special-ground" cables was contributing to our jerky accelerator problem. If this indeed was the source of the problem, in our case it took a long time to track down, because it seemed to be intermittent.

It didn't just seem to be intermittent, it clearly was intermittent, spending hours to days in one state or the other. Readers can find more detail in the four posts beginning here: viewtopic.php?title=weber-and-coulombs- ... 472#p49472.

This time, I don't even agree with your general point. I think it's absolutely fine to reuse wires (or coaxial cables) in the existing wiring loom for critical analog signals if you know they were used for critical analog signals before, which is exactly what we did. And it is working fine now.

Of course, you need a diagram of the existing wiring loom, in which case you know exactly where it's been and where it's going. What we did wrong was to ignore what the diagram was trying to tell us, namely that the BLK-LGN net went to lots of places other than the two we were using it at (throttle sensor and ECU). Or rather, we failed to heed the following advice ...
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Post by weber » Wed, 19 Feb 2014, 19:53

Don't forget to separately insulate all unused connectors or wire ends in the wiring loom including ground lugs and ground wire ends.

Since ground wires are at chassis potential it's tempting to think it won't matter if they come in contact with the chassis or other such ground wires, particularly when they used to be connected to the chassis anyway.

But when it comes to analog signals, there should be one and only one point of connection to the chassis (in our case, via the 12V power connection to our EVCU (which is like an ECU, but for an EV)). Also, these signal grounds should form a star or tree. If there is a loop anywhere, it will act like the short-circuited secondary of a transformer and will have voltages and currents induced in it by stray magnetic fields from the motor and its cables, and battery cables. This will add lots of noise to the signal.

[Edit: Changed to a "don't"]
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Post by poprock » Wed, 19 Feb 2014, 21:45

Consult state regulations before even pulling the ICE. For my Sirion I made a nice battery box in the spare wheel well, sealed & ventilated to atmosphere. Battery weight was 100kg. I downloaded the NSW VRSS sheet (july 2013)which discourages extra weight behind the rear axle;handling issues may be caused. To me it is no different to carrying a similar load in the hatch space but to eliminate a possible cause for rejection I then made a box fitted in place of the fuel tank using the original mounting bolts. After I had that sorted out I then discovered the Electric Echo Journal blog. (Toyota's version of the Sirion). So even after much research there will still be unavoidable " shoulda dones " Image

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Post by weber » Thu, 11 Jun 2015, 23:10

What's wrong with this picture (fuse, cable, bolted lugs)?

This was supplied by a battery manufacturer. Both connections were bolted the same. I have taken one apart so you can see the detail.

Image
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Post by acmotor » Thu, 11 Jun 2015, 23:35

Well... The cable lug should be in direct contact with the fuse. The flat washer and spring washer should be copper at best then plated steel or stainless as lesser options and be under the nut as a mechanical restraint and the working current should not have its primary path through the washers, nut or bolt.
There is an issue with the bolt/slot size not allowing best surface area contact, but then a 250A fuse on 35mm sq cable would not be 100% duty cycle intended anyway.
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Post by 4Springs » Thu, 11 Jun 2015, 23:41

Maybe the washer is the bit that is supposed to melt at 250A? Would be "slow blow" I reckon. Image

Are those nuts and washers painted? Image
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Post by weber » Fri, 12 Jun 2015, 00:49

That's a very polite analysis acmotor. The most polite words I could manage, on realising what they had done, were "Jesus wept!". Image

I would have said a 250 A fuse on 35 mm^2 cable was utterly pointless, unless perhaps it had silicone or fibreglass insulation. The cable doesn't show a temperature rating or insulation type, unless they're only given among the Chinese characters.

One other problem, which you sort of mentioned, but in a different way -- M8 studs used to bolt a fuse with 10 mm slots. But as you imply, all the problems other than the washers-in-the-joint can be considered to be due to the too-big-fuse.

Hee hee. "Fusible-washers". They would need to blow at around 125 A continuous to protect the presumably-PVC insulation on the 35 mm^2 cable, but somehow I don't think they would have much luck breaking an arc at 250 Vdc, which is what this was intended for.

I measured the connection that's still bolted, at around 0.08 ohms. Doesn't sound like much does it. But at 125 A, P = I^2 * R = 125 * 125 * 0.08 = 1250 watts! [Edit: At 250 A, 5 kW!]
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Post by weber » Fri, 12 Jun 2015, 01:24

Yes, the nut and spring washer are in fact painted. Multimeter says no conductivity until you go for spots where the paint has flaked off. The flat washer however appears to have a black oxide or black zinc chromate finish which is mildly conductive.

Possibly even the putting of the washers where they did was a response to the too-big-fuse, as in,

"Look at that huge gap between the fuse slot and that skinny stud. The cable lug will just fall into it! We'd better bridge it with a nice big mudguard washer. Now where should we put the spring washer? Well, we've always put it on top of the flat washer in the past. ... Now the lug and the nut. There, that looks good."

BTW, conductivity of steel is less than 1/8th that of copper, stainless 1/40th, paint 1/infinityth. But that's not a problem when you put them where they are supposed to go. Washers are mechanical components, not electrical. I presume the reason acmotor favours copper washers is not for their conductivity, but to minimise dissimilar-metals corrosion issues.

[Edit: Replaced "spring washer is" with "nut and spring washer are".]
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Post by jonescg » Fri, 12 Jun 2015, 01:46

I would have answered your question with "everything". Image
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Post by acmotor » Fri, 12 Jun 2015, 03:19

Yes, a little knowledge can be the problem. Maybe the parts selector or assembler decided that a 250A fuse must be twice as good as a 125A fuse ! ..... And that corrosion may be an issue so let's paint the plain steel washers. Then the assembler comes along and as weber says.. Let's fill that gap ..... Oh and we usually put the spring washer over the flat washer and so on.
It is like that old mistake... Solder tinning a stranded cable end then putting it in a screw terminal ! Seems like a good idea but more understanding and you realise it is dumb. The solder creeps, the terminal loosens and overheats or becomes intermittent.
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