safety switches

Post by **sparau** » Fri, 19 Sep 2008, 19:53

zeva wrote:Electrically, a single point insulation failure would be almost identical to a deliberate ground link at some arbitrary potential. So, dangerous perhaps because it's unknown. Hence the need for a leakage detector.

makes sense to me. although the idea of halving the voltage seems good too (although half 190 would still be dangerous from what i am reading).

@ACMOTOR - sry how do you split up the battery packs? at some point they are all going serial to get your 600v - so how does the 48v pack idea work?

Post by **sparau** » Fri, 19 Sep 2008, 20:01

Does this sum it up?

So with leakage detector on both systems

isolated pluses
- temporary short wont start fire as nowhere to complete circuit
isolated -ive
- short could go unnoticed on 1 or other leads if the leakage detector fails, then any unshielded connector could kill

grounded pluses
- half voltage
- on failure of leakage detector any short will be very noticable by the welding or blowing holes in chassis or blowing of fuse.
grounded -ives
- any connector at any time is live 1/2 full pack (still ouch)

Post by **Sparky Brother** » Fri, 19 Sep 2008, 22:31

OK Guys. what I have to say here is I greatly appreciate all positions in this particular debate as I and not only am finding it crucial for the future of the EVs over the Dino juice cars. It is more than obvious that it won`t be easy to get agreed on certain type of protection. Which is more important though is that a common path will be found for the good of all.

Now. I don`t think I had a good chance to introduce my self in the very beginning so I`ll be brief.

I am a 40 years old Air conditioning Technician in the middle of my mature aged apprenticeship in Electro Technology so I am currently doing my daily job and studying in the same time.

Today I sat one of the never endind exams namely in cirquit development which I take very seriously so I decided to print out this debate on paper and asked my teacher if he wouldn`t mind while I`m doing my exam to check out what we are after and give some honest opinion.

OK I handed out my papers expecting him to share his opinion on this such important issue. What got me in a real shock was the answer "What do you guyis need this sh... for?" I managed to keep my temper down explaning very politely all our points of view plus the one that due to our addiction to the Fossil Fuels we managed to corner ourselves into situation where we`ve got no choice but to kiss Oil rich nations asses and he is the one who keeps us company in it!

I wouldn`t waste my time in re-telling the whole conversation, just the end: "Stay away of that!" he said!

All right! If this is the opinion of one TAFE teacher (and to be honest I shared my interest in EV conversions with the same degree of success with other two) who labels him self as extremely knowledgeable in the Electro Technology Area what is really the future of the Electrical Vehicles at all!?? I mean who the hell will be teaching all those who will be required to service the EV fleet because Tomorrow is Today! No one could refuze the fact that almost every big car manufacturer has got their fully Plug in EV ready for mass production

Gosh this guy really got me out of my skin today. This however made me believe I am on the right track!smileys/smiley20.gif I simply do not understand why those who get paid to make us understand the Electricity is nothing related to VooDoo Magic are sh*tting themselves when it comes to take the bone out of the Dino nations mouth!!!???

Post by **a4x4kiwi** » Fri, 19 Sep 2008, 23:45

Hi Sparky,

Interesting experience, Reminds me of the conversations the guy at Coffs Harbor had with local auto electricians. If I start a new thread, can you give your thoughts on reverse cycle aircon please?

Thanks, Mal.

Post by **Sparky Brother** » Sat, 20 Sep 2008, 00:05

As for the reversed cycle A/C no problem. I actually was the first to read your thread on this topic about a month and a half or so and was actively restraining my self not to start thinking of this.smileys/smiley4.gif

Go ahead! Open the thread. Let`s see what will pop up!

Post by **a4x4kiwi** » Sat, 20 Sep 2008, 00:30

done

Post by **zeva** » Sat, 20 Sep 2008, 02:41

It kind of feels like we're flogging a dead horse now so I'll keep this post brief, then will probably let everything sink in for a while.. And perhaps it's time for others to share their thoughts!?

So firstly, it feels like this remains unanswered:

zeva wrote:Can you justify to me why you would not maximise the impedance of a ground link?

Last chance to convince me for a while so make it good

And secondly to just let you know where I stand WRT your list:

acmotor wrote: OK, so do we agree on any/all of these ?
1. Leakage detection from the centre of the pack ?
2. I suggest max 50ohm per volt impedance ?
3. This includes the option to hard connect ?
4. Fuses and contactors at each battery box (part of pack) location ?
5. Contactors (if not already covered in above) to break the pack up into <=72V (nominal) modules ?
6. Battery pack breakup to be a valid alternative to the single mechanical ES button ? (I threw this one in as it should be considered at some stage)
7. An inertia sensor 360deg(?) to automatically break battery pack up via above contactors ?

1. Yes.
2. I don't want to start quoting numbers until I have actually tested typical quiescent leakage in some EVs, other than to suggest the higher the impedance the better.
3. An emphatic no!
4. Yes.
5. Would recommend but not mandate.
6. Yes.
7. Yes.

Post by **acmotor** » Sat, 20 Sep 2008, 07:37

I don't have to justify current best practice electrical standards !

Earth leakage detectors are well established.

The answer to your question - uncertainty. You understand that already.
Perhaps your answer lays in the opposite question ?

I will leave you to do some tests on your dead horse. Maybe you can produce a leakage detector you can trust at 100kohm !

Perhaps the suggestion should read...
"electrically isolated battery packs are only permitted with the inclusion of effective leakage detection and automatic pack shutdown "
That one would be hard to oppose if you believe in safety !

The wet motor brigade will probably still object !

Read again #3 the OPTION to hard connect (no mandate either way)
I hope that after reading this thread that people will think twice about blindly asking for electrically isolated packs alone and not involving a full suite of electrical safety features.

I make it 4.75 out of 7
Not bad given the ultra negative vibes from around the globe to start with !

Did you post all this on US forum ? How are they shaping up ?

The times, they are a chan...g..ing ! (never could sing)

Post by **acmotor** » Sat, 20 Sep 2008, 07:49

Just wondering..
If you agree with 4 then given that 5 will be most likey be complied with as a result, then why resist a very safe move for the EV world ?

To clarify further...
A zebra battery, or similar sealed module, would not come under this rule, you understand why.
Individual cell / battery constructions such as the MX5 or red suzi would come under this rule. For obvious safety.

Post by **Lowly** » Sat, 20 Sep 2008, 18:38

Thanks to those who are putting a lot of thought into this, standards are not much fun.

After going through all the posts here and on the EVDL following the thread that Ian wrote, I thought it time to add my thoughts.

I think that an important starting point with this is to determine the safest solution and then decide what compromises we are willing to make to that solution for ease of installation.

My feeling is that the safest option is to have an isolated traction battery pack with leakage detection. It would also be best to have all terminals insulated so they are not possible to touch.

Different people obviously have preferences as to what compromises they are willing to take - ie have exposed terminals, not isolate the system.

I cannot accept that it is best to have a hard connection and effectively make the voltage potentials the "worst case scenario" just to "know where you stand" (or even half the worst case scenario). It would be far safer to isolate the battery pack but to deal with all terminals as if they were at a high voltage potential (and insulate them).

I have not reached the wiring stage for my vehicle so am probably not qualified to speak about how hard the two challenges of

1. isolation with leakage detection
2. no exposed terminals

are to implement, however I think that if compromises are made to the standards for ease of installation then a good risk analysis/ justification needs to be done as to why this compromise is okay.

Regards

Greg

Post by **acmotor** » Sat, 20 Sep 2008, 19:34

Greg, Thanks for stepping in.
Your point re preferences is important and I think our NCOP guidelines need to accomodate these preferences as there is more than one way to skin a cat. Mandating one option at the exclusion of others and then not even enforcing existing requirements leaves safety the loser.

Let me chew over the status quo and leave advancements for a moment...

Compliance with existing NCOP14 seems to be non existant in some areas so it is hard to move to a higher safety standard.

Greg, non insulated terminals are not an option at any time in any way under the existing regs. There is no compromise available here so you don't have to worry about making that choice !

Please Guys don't make this simply an electrically ground / isolate debate. I only put that one in to show that electrical isolation is not the only option and there are VALID arguments for and against, however neither is safer and I would prefer NCOP14 to suggest / require some of the other safety points 1-7 listed above.

Back to NCOP14....

NCOP14 sect. 2.6 'Controls' says the master switch must isolate all electrical connections to the power source.
To me, this askes for a dual pole switch breaking both +ve and -ve from the battery pack not just one or the other. i.e the word used is 'all'.
(Personally I would never bring both into the same switch anyway)
This is not what people are doing now, so is this compliance ?

NCOP14 2.7 .... ' All electrical control apparatus, the motor and major ventillation system components must be effectively sealed or otherwise resistant to water and dust ingress.'

I see non compliance.

'All electrical installation work must be designed and executed in accordance with acceptable codes and standards. All power unit wiring and connections must be insulated (double insulated if appropriate) and provided with adequate mechanical protection.'

I see non compliance.

On the topic of electrical insulation / isolation...

Births, deaths and insulation failure. They are all realities of life.
EVs must be tollerant by design, as best can be, of insulation failure.
Consider your electrical system. Imagine insulation failure at any point. How will it cope ? How safe will it be ? Will it shut down ?

There seems to be general support for leakage detectors.

Once you get a leakage detection, what are you going to do with the information.
Manually ?
Automatically ?
One battery line (+ve ?)
Both batter lines ?
All available contactors ?
What will be the reset options ?

Post by **Goombi** » Sun, 21 Sep 2008, 00:36

Hi
Would 2 phase cirquit braker (250 amp) do as a cut out switch? can be used as automatic cut out or manual. There are options as used by Crown Forklifts . Anderson high voltage coupling with a manual pull out handle,brakes the connection( both cables). however,all high voltage cables and switches must be outside the cabin other then cables running from batteries under the vehicle ) One more question.. where would one place high amp fuses? on both cables or just one and how can they be isolated from possible short with a body?If burn out fuses were to be insulated in case of short the whole insulation will burn!!! Cirquit braker would be the most accceptable and most practical. Is there such a thing for DC?

Post by **acmotor** » Sun, 21 Sep 2008, 02:58

Zeva do some high current DC circuit breakers. They can also be used as cutout switch.
Fuses or circuit breakers are fine. (in preference to melting cables)
NCOP14 only seems to require one fuse but does ask for good electrical practice so there does need to be more than one in most installations.
Particularly when batteries are located around the vehicle.

Fuses should be mounted in manufacturer's fuse blocks or housed in water / dust proof boxes as per NCOP14.

Goombi,
Traction system wiring CAN be inside the passenger area if it is located in rigid protective housing. See NCOP14
Have you got a copy ? The link is NCOP14

More on NCOP14...

" All electrical control apparatus for the traction circuit should be designed on fail-safe principles; i.e. the failure of any individual component within the traction circuit should stop the motor. "

Oh well, that rules out electrically isolated traction battery packs.
The single failure of insulation does not stop the motor !

Clearly, the failure of insulation needs to be monitored for (leakage detection or similar)

Post by **Lowly** » Sun, 21 Sep 2008, 17:17

acmotor,

I guess there are some things the I need to put more thought into. How for instance to you double insulate battery terminals? Are there off the shelf solutions? I guess that putting all the batteries in a suitable box may be some sort of solution but I guess that the box will then need to meet the relevant standards.

Regards

Greg

Post by **acmotor** » Mon, 22 Sep 2008, 02:31

Greg,
Good question re double insulation.

IMHO The double insulation in an EV is from electrical components to chassis or human contact.
To me, the principle of double insualtion means two types or levels of electrical insulation in series. (possibly-probably different)
At least one level should require tools (screwdriver / spanner) to remove or open. A warning label should advise a person that an electrical shock hazard exists if they remove such cover.

The idea being that if one level fails the other still provides insulation and thus safety.

Double insulated cable (wire) would have two separate plastic jackets between wire and human contact. An extention cord is an example. Figure 8 cable is only single insulated and relies on earth leakage detection for the second level of safety.
A single insulated wire inside a plastic conduit could be considered to be double insulated.

Double insulated battery terminals (insulated from human contact that is !) could be considered to exist if the terminal is covered individually with insulating material (like the 12V terminals in modern cars) and then a cover placed over the whole battery pack. (or the pack be in a box that is either lined with or made of insulating material.)

Double insulation is not a must under NCOP14 but single insulation is.
BTW the bonnet is not insulation although it provides some factor of access limiting in normal operation.

Most single insulated (e.g. kettle), or metal bodied (e.g.electric motors), or access cover without insulated terminal (washing machine), type equipment must be earthed and operated with an earth leakage detector under modern electrical standards.

There is also the factor of heat resistance of the levels of insulation.
These go all the way from say 85deg C to flame proof.
The choice here is related to the expected operating temperature and if possible the temperature under fault conditions before fuse blow or other shutdown.

Insulation after water ingress is another factor to consider.
Either block water access or make insulation properties not water affected.

Insulation after dust (conductive - possibly combined with water)collects is another issue. IP55 or better ratings should be considered.

The other factor for EVs is the question of insulation still existing after a collision or battery failure.
Not much is mandated in this area as yet other than battery physical mounting g forces.
The commercial EV manufacurers of the future will have to do a lot of design and crash testing to establish and meet some realistic safety standards. (hopefully not the commercial approach that was taken with the fuel tank of the Ford Pinto ! )

Post by **acmotor** » Mon, 22 Sep 2008, 02:39

I should have noted that I consider double insulation of the traction system in an EV to be, in reality, almost impossible.
Some components can (and should) be double insulated (wiring), others like the motor, AC or DC are much harder to deal with.

Post by **sparau** » Mon, 22 Sep 2008, 18:48

Point to keep in mind perhaps is that when talking of standards you need to consider what the body is made of.

i mean with a carbon fibre chassis / shell the traction circuit is obviously going to be isolated anyway.

btw - this sounds the best option - i mean there are physically many more hurdles to getting yourself electrocuted with a cf body

It seems to me the only parts of a car which could short would be suspension / subframe that has the driveshafts and the steering column.

Post by **acmotor** » Mon, 22 Sep 2008, 19:20

Yet another angle !
I guess I am thinking of EV conversions.
Not much chance of a non conductive chassis / body there !

Post by **Lowly** » Wed, 24 Sep 2008, 19:39

Been having some more thought about the double insulation discussion above. This is getting a bit off topic (maybe it is time that we had a forum section dedicated to safety and regulations?)

It is probably helpful to distinguish between

1. insulation that is required to ensure no shorts (ie when attached to a chassis rail) and
2. insulation that is required to stop people touching conducting elements.

As acmotor suggested there are some connections (such as motors) that are difficult to ensure double insulation. The risk here I think fits into category (1). As such is there an argument for the use of interlocks on the bonnet or other compartments?

Regards

Greg

Post by **Rob M** » Wed, 24 Sep 2008, 21:25

The suggestion of an on going discussion on safety issues and regulations would be useful at the moment. The safety committee (which I am currently chairing) is currently looking at the NCOP guidlines with the view to having some input in the next revision (November this year) I can post a copy of the relevant guidlines to invite comments if members feel that would be helpful.
The topic on insulation above would be only a small part of the guidlines.
I had a meeting with DPI vehicle safety yesterday and the impression I got is that they would welcome feedback.
Topics mentioned were:
1.Clear and strong indications that the vehicle is electric.
2.Clear and concise instructions available to emergency personnel.
3.MSDS for battery chemicals in the event of spillage.
4.clearly labelled and conveniently located mechanically operated safety switch to disconnectect the traction pack from all electrical equipment.
5. Proper restraint of battery pack/s
6.Maintainance of original crumple zone
7.Guidlines on not only vehicle mass but weight distribution as well.
8.ADR's be conformed with.
9.Approval in principle must be obtained prior to commencement of any modification to a licensed vehicle.
They are going to confer with Dept of Energy on electrical requirements.

Post by **acmotor** » Thu, 25 Sep 2008, 05:24

I've copied Rob's post to an new topic in Electric vehicle conversions.

"NCOP14 regulations, safety and revision"

Rob deserves a new thread !

This thread can continue on topic with safety switches.