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Post by sparau »

please forgive my newbness :) and electrically technical stupidity (i am a computer programmer - not an electrician or an electronic engineer - my brother is but he took a well paid job in the UAE is no help - the bugger)

In my researching i have not come across the concept yet of a safety switch for an ev - ie. like the 1ms jobbies fitted to houses.

it seems to me that 400a @ 144v would hurt somewhat if something cut the main power feed and ground it to a part of the chassis making a partial circuit. i guess it would be unlikely as ? you would have to cut / connect both the + and - to a part of the chassis and bridge it but... just wondering.
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Post by acmotor »

sparau,
I am not certain I can extract the question out of that ?

A partial circuit is not a circuit and so is safe, partially, until something completes the circuit.

Are you thinking of earth leakage detectors as used on AC mains in houses ?
Yes, DC versions can be fitted to an EV.
The leakage current, particularly with wet wiring or motor, can be an issue though.

The best thing is to have no exposed terminals anywhere in an EV.
The voltage is less than the 240V mains lead draped across your feet right now !
(mind you that power source is connected to earth and so a fault can be detected)
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Post by sparau »

acmotor wrote: sparau,
I am not certain I can extract the question out of that ?


lol Image
acmotor wrote:A partial circuit is not a circuit and so is safe, partially, until something completes the circuit.


this is what i am thinking of - lets say the positive shorts out to the subframe for your engine - the negative shorts to the chassis - you lean over the side and touch the subframe - circuit complete.
acmotor wrote: Are you thinking of earth leakage detectors as used on AC mains in houses ?
Yes, DC versions can be fitted to an EV.


that is what i meant
acmotor wrote: The best thing is to have no exposed terminals anywhere in an EV.
The voltage is less than the 240V mains lead draped across your feet right now !


no exposed terminals doesnt discount a vehicle over rough roads after 50,000km of vibration... any shielding will wear with movement over time.

Isnt the voltage no more important than the current? isnt it the power as a whole that is the danger?

i suppose mostly speaking it is a moot point - if the chassis is connected to every metal object in the car it is 1 circuit in itself - if both the postiive and negative wear then they will arc and weld / melt themselves to oblivion in no time. and even during that process it should be no danger to touch the car as you would have significantly higher resistance than the metal you are touching.

please note: i could be very wrong Image Image Image
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Post by sparau »

if what i am saying above it true then best practice would be to make sure the ev is 1 circuit - ie. no rubber mounting engine / battery subframes.

in this case wouldnt zeva's mx5 conversion with the alloy subframe to hold the engine / battery pack end up cracking? the old idea - steel bends, alloy breaks? all chassis bend over big bumps and hard cornering (hence strut braces), wont a hard connected subframe of alloy break?
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Post by acmotor »

Voltage is also called potential. It comes first. The potential for current to flow. How much current flows is what will do you harm.
8mA is a nasty bite, 20mA (sustained)can kill.
Not much you say - you're right. 144V at 1A or 144V at 1000A is all the same when it comes to electrocution.
The physical damage that 1000A (at any voltage) can do is the other issue. It will blow a hole in the bodywork.

The body of the emotor should be connected to the chassis of the vehicle (bypassing the rubber engine mounts - as is done in an ICE).
Rubber mounting the motor or sub-frame is fine to control shock or vibration.

Don't mix the electrical and mechanical factors ??Image

Aluminium (welded in particular) can have fatigue / cracking issues if designed with minimal safety factor. (so can any material, some worse than others). Steel also has its failures.
Most aluminium work in an EV is rather overbuilt so this is less of an issue than with say an aircraft.

This is one of the reasons that NCOP14 calls for engineering assessment of conversions... So that potential problems can be spotted.

Conversions are likey to do a lot less km than ICEs at this stage and most likely to be city km so fatigue is probably a small issue compared with a 4WD in the bush. However your point re structural integrity is a good one. Image
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Post by acmotor »

sparau wrote:
i suppose mostly speaking it is a moot point - if the chassis is connected to every metal object in the car it is 1 circuit in itself - if both the postiive and negative wear then they will arc and weld / melt themselves to oblivion in no time. and even during that process it should be no danger to touch the car as you would have significantly higher resistance than the metal you are touching.


sparau,
You understand more than you realise. This very point is one I often try to get through to people.
Just add some fuses in your example and you will have more safety than most EVs with "isolated" battery packs. Image
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Post by Sparky Brother »





Just a quick one though. Do we interfere in some way with the dominant under NCOP safety features of the Safety equipment in the car which according to the document must be independent and able to perform when say a short cirquit between the windings and the frame of the motor occurs.

My question is is there any possbility having all the metal parts of the high voltage system grounded to the chassis to harm the safety system of the car? Sorry for the naive question but I`m still learning. I do agree that earthing is the ultimate protection. What I need is a logical expert explanation.
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Post by acmotor »

There is no problem complying with the NCOP14 requirement IMHO.
It requires the vehicles 12V system to be isolated from the traction battery so that hazards, headlights, horn etc still function. The assumption here being that the traction battery and traction system is going to be less reliable than the 12V system. Probably not a reality in a well built EV anyway.
NCOP14 does not ask for floating traction pack.
It does not ask for electrical isolation. The implication to me is functional isolation. You want proof ? the Doc. itself also accepts the 12V system being run off the first battery of the traction pack as is done in some conversions, but says that openning the traction battery contactor must leave the 12V system functional. This would be the case with the negative of the first battery grounded.
Personally I would never opt for this shared arrangement as it would likely result in battery unbalance and risk of over / reverse voltage in the 12V system if that first battery went O/C at a terminal or internally.
To me, the issue with NOT connecting the negative (or my prefernce, centre) of the traction battery to the chassis is that a single insulation failure will not go undetected - just waiting for you to touch something. Just ask an EV owner with a wet motor. But then NCOP14 requires that all electrical components are sealed against water and dust !! Image
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Post by Sparky Brother »

Thanks Tuarn I got the feeling I`m missing something but it`s all clear now.

Hm. I don`t like powering up the security system out of the main pack either so I`ll definitely opt for a separate service battery, all exposed metal parts of the traction system grounded to the chassis, very well protected electrical terminals preventing against earth leakage to occur and then some sort of an RCD protecting passengers and the ones outside from something more than the funky feeling of getting the belt.smileys/smiley18.gif

Ah. and I better don`t forget a Road Worthy Inspection on an EV one in a time when the car is for sell sounds more than irresponsible to me. Once a year should be a must with this sort of vehicles

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Post by acmotor »

That is a serious safety point you raise of pre-sale /annual inspection of converted EVs. It would be unpopular but a good safety move.
In WA we have no ICE annual inspections (yet - scary thought). It would perhaps not be equality to introduce them just for EVs. Your NSW/Vic situation may be different as annuals are already required ?
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Post by Johny »

Annuals not required in Victoria yet.
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Post by zeva »

acmotor wrote: To me, the issue with NOT connecting the negative (or my prefernce, centre) of the traction battery to the chassis is that a single insulation failure will not go undetected - just waiting for you to touch something. Just ask an EV owner with a wet motor. But then NCOP14 requires that all electrical components are sealed against water and dust !!


I'm of the opinion that we should have both physical and electrical isolation for the traction circuit in EVs..

Electrically, have the traction circuit isolated other than a ground leakage detector between it and the vehicle body. This way you usually won't get a zap when touching a single point in the traction circuit, but if a ground fault does occur, you'll know about it straight away via warning buzzer (or have it instantly open the main contactor if leakage current is above lethal levels for humans).

I'm also of the opinion that sealing all electrical components should be enforced - partly for water and dust, but equally to stop "average Joe" from getting zapped when he's poking around in the engine bay of the EV he just bought! (That is, of course, unless he ignores the mandatory electrical shock hazard signs on the electrical component boxes and opens them up himself..)

I was really impressed to see that Tuarn had done this (sealed electricals) with Red Suzi. It definitely adds an extra level of safety.
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Post by zeva »

acmotor wrote:
sparau wrote:
You understand more than you realise. This very point is one I often try to get through to people.
Just add some fuses in your example and you will have more safety than most EVs with "isolated" battery packs. Image


I'm not so sure I agree with this statement though. Ratings of fuses in EVs (even those tiny little 50A fuses you use in AC conversions Image ) are several orders of magnitude higher than lethal current levels for humans.. There's no way they'll save the aforementioned Average Joe from electrocution..
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Post by Johny »

acmotor's point was that the fuses allow the traction system to be grounded this providing repeatability in its behaviour and the fuses ensure that parts of the car body (or batteries) don't glow red-hot when there is a fault. The human protection still has to be totally insulator-guarded electrics. The problem with a ground fault system is that the fault (or human) may be the battery side of the main breaker. The fault system has to trigger on < 50mA which may well false trigger on DC systems with motor carbon dust build-up and be ignored (or disabled) by operators. It also becomes more complex for home-builders.
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Post by zeva »

Johny wrote: The problem with a ground fault system is that the fault (or human) may be the battery side of the main breaker.
Agreed, but similarly fuses won't protect from wiring faults "upstream" either. The best you can hope for is to have any safety devices (fuses/breakers/contactors) as close to the batteries as possible.
Johny wrote: The fault system has to trigger on < 50mA which may well false trigger on DC systems with motor carbon dust build-up and be ignored (or disabled) by operators.
Yes, it did occur to me that quiescent leakage might exceed lethal current for humans, making it harder to detect.. Perhaps it could be based on sudden changes in leakage current?

One way or another I think it would be useful to start exploring the idea, i.e get some leakage detectors into EVs and see how they go.
Johny wrote: It also becomes more complex for home-builders.
I think this is one factor we need to discount. While stricter safety standards may raise the required skill level for converting a car to electric, having just one person die of electrocution from an unsound EV would be incomparably bad, so must take priority. (Apart from the cost of human life, the oil companies would milk it for all its worth!)
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Post by Johny »

One immediate suggestion for DC conversions <= 144 VDC would be to ground the centre of the DC pack ensuring that there is no more than 72V with respect to ground at any point. Back that up with a clear understanding of keep +72 V physically far away as possible from -72 V so users would have a hard time touching both at once and it's all safer straight away. The centre ground could then be replaced by a ground fault system when available (or for experimentation).
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Post by zeva »

This debate on traction isolation has been bit of a contentious point for a while and has been discussed recently among the WAEVA safety committee - so it is something we'll have to come to some agreement on soon. In such cases I tend to defer to the collective wisdom of the experts on EVDL.org, so I posted the question there recently. The responses were fairly unanimous in favour of isolation. Here are some of their responses:

http://www.zeva.com.au/media/Isolation.pdf

Possibly the most significant comment, from Bill Dube: "If you make a regulation that requires that it is not isolated, none of the manufacturers will sell their car in Oz. It is a requirement that the traction wiring be isolated in most other countries."
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Post by acmotor »

Floating battery systems with one module of 200 or 300V without even the offering of leakage detection are so old school and give the owner a false sense of safety.
They go against Australian and European electrical standards that require protective earth and supply neutral connected to earth.
They will also give EVs a bad reputation with the public as people get electrocuted.

Centre grounded systems with breakup contactors to 72V or less and fuses at each battery pack location with automatic crash sensor activated contactor dropout and effectively insulated wiring, motor and terminals offer the best safety practice for the future of EVs.

OK, the wet DC motor people may not like the home truths.

You can post that on any forum you like and I will be interested to hear any informed and justified argument to the contrary.
Reasons such as "we have always done it that way" and "that would mean I need to make my motor waterproof" don't wash.

Tell Bill Dube that the regulation does not have to require that the traction system is not isolated, however it must not require that IT BE isolated as there are better, more reliable and more predicatable ways to make the system safe and these should be allowed, even encouraged for the future safety of EVs.

I am talking EV conversions.

Commercial EV manufacturers will go their own way and have to meet their own standards. If ADRs set higher standards then manufacturers will have to meet them.
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Post by zeva »

acmotor wrote: You can post that on any forum you like and I will be interested to hear any informed and justified argument to the contrary.

Here are the initial responses:

http://www.zeva.com.au/media/Isolation2.pdf

Disclaimer: To ensure I'm not involving any personal bias, I've included all responses offered.. So some of it is irrelevant waffle, but there are some good points made too.
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Post by acmotor »

Ian, you are welcome to pass this on....

Oh dear, all that response and not a single reason for electrical isolation.... and clearly missing the point of why mains electrical standards (not EV electrical ones) call for grounding / earthing. EV ones are still evolving and I hope in the safest direction.

I am entitled to my opinion on battery pack arrangement without character assassination. I am happy to debate the issues are you ?

Excuse me, I understand what double insulation is. BUT I cannot see it in EV conversions (I have several myself). So you use double insulated motors, controllers and contactors ? If we all did I would have less concern. Look closely and think about it.
Please show examples of the above that ARE double insulated. Beware any metal housed item that claims double insulation.

I do understand the best intention of electrically isolating the traction battery pack of a vehicle. My concern is that in practice it does not offer the best safety.

I will give 3 reasons for connecting the battery pack centre to the chassis of the vehicle.

Please address these points.

1) known situation.
If all electrically isolated packs included a monitoring system to warn the user or shut the pack down in the case of an insulation fault to chassis then I would have less concern. (and in the world of real safety, warn is not enough. Shutdown is required)
The problem with just electrically isolating is that you don't know where you stand and EV components are not DOUBLE INSULATED (except maybe the label on the welding cable !). So a single point (undetected) failure can make the system unsafe. The first insulation fault will go undetected and you then have a dangerous situation (typically without warning). A wet motor is a classic situation. Normally you could touch the battery pack !
With the centre of a battery pack connected to the vehicle, (can be via a suitable leakage detector) you have a know situation and any insulation failure will cause a shutdown or blow a fuse not a person. If electrically isolating the battery pack allows you to work with the leakage of a wet DC motor then I can understand that. Don't tell me it is safe though.

2) lower voltage.
For example, a 144 V pack centre grounded presents a potential of only 72V to the chassis of the vehicle (+72V and -72V). This is a safe voltage to handle. (try it before you suggest otherwise). 144V is not a safe voltage to handle and with a supposedly electrically isolated pack (as above), you may well be exposed to this full pack voltage between chassis and traction system.
Only if you can touch both the +ve and -ve terminals would you get 144V in a centre gounded system. So no worse than any system. (your terminals are insulated anyway, aren't they !) I hope the penny drops.

3) less electrical stress on motor winding insulation.
The main electrical stress to the enamel insulation on a motor's windings is from the voltage to ground / chassis / metal body of the motor in operation. If you have an electrically isolated battery pack then this voltage will be somewhere? between zero and full pack voltage. This is ignoring the potential of capacitive charge pumping (remember the PWM) producing additional voltage.
Now if the centre of the battery pack is grounded the MAXIMUM voltage across the winding insulation to motor body will be half the pack voltage.(and there is no chance of capacitive charge pumping as the system is not floating). If you can't picture this reduced voltage then ask more questions. It is not imaginary.
This is also an issue as many (most) DC motors are run at above their nameplate voltage so caring for the insulation is important.




Do consider also, that in the case of a vehicle collision, it will be almost certain that your electrical 'isolation' will be breached and that all you good intentions will be up in smoke. At least with a centre grounded pack and breakup contactors, fuses will blow and voltages will be lower.

The comment about false triggers with leakage detectors also was made when RCDs were introduced. They are now standard and mandatory (at least in Australia) and many more lives have been saved than lost by their introduction.

OK, so even if you can't see the world from this point of view, don't say an EV traction battery pack MUST be electrically isolated as it is not the only way to go.
If you need a must, then say leakage MUST be monitored and the pack automatically broken up into safe voltages if a fault occurs.

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Post by zeva »

I'll pass it on, but will also add my own thoughts now.
acmotor wrote:
Please address these points.

1) known situation.
If all electrically isolated packs included a monitoring system to warn the user or shut the pack down in the case of an insulation fault to chassis then I would have less concern. (and in the world of real safety, warn is not enough. Shutdown is required)
The problem with just electrically isolating is that you don't know where you stand and EV components are not DOUBLE INSULATED (except maybe the label on the welding cable !). So a single point (undetected) failure can make the system unsafe. The first insulation fault will go undetected and you then have a dangerous situation (typically without warning). A wet motor is a classic situation. Normally you could touch the battery pack !
With the centre of a battery pack connected to the vehicle, (can be via a suitable leakage detector) you have a know situation and any insulation failure will cause a shutdown or blow a fuse not a person. If electrically isolating the battery pack allows you to work with the leakage of a wet DC motor then I can understand that. Don't tell me it is safe though.
The amount of current required to start a fire under the right (wrong?) conditions, is far lower than the current required to blow the fuse(s) in a typical EV. Remember the resistor that started smoking at the meeting last night? What was that carrying, 5 amps? So I don't think a low impedance path between any part of the traction circuit and the vehicle body is sensible, due to the likelihood of other conductive paths developing over time (insulation faults etc).

But I think maybe we have found some common ground, as per the bit I highlighted above in bold.. I agree that the traction circuit SHOULD be tied to the vehicle body with an appropriate leakage detector. But better that it is a high impedance link, e.g 100Kohm, to make sure any current flow remains below lethal levels for humans.
acmotor wrote: 2) lower voltage.
For example, a 144 V pack centre grounded presents a potential of only 72V to the chassis of the vehicle (+72V and -72V). This is a safe voltage to handle. (try it before you suggest otherwise). 144V is not a safe voltage to handle and with a supposedly electrically isolated pack (as above), you may well be exposed to this full pack voltage between chassis and traction system.
Only if you can touch both the +ve and -ve terminals would you get 144V in a centre gounded system. So no worse than any system. (your terminals are insulated anyway, aren't they !) I hope the penny drops.
While this may be applicable for a 144V system, it is moot for higher system voltages. Most AC EVs have pack voltages well above 144V (you yourself have a 600V system, for example). Hence even half the pack has the potential for lethal current flow through a human.
acmotor wrote: 3) less electrical stress on motor winding insulation.
The main electrical stress to the enamel insulation on a motor's windings is from the voltage to ground / chassis / metal body of the motor in operation. If you have an electrically isolated battery pack then this voltage will be somewhere? between zero and full pack voltage. This is ignoring the potential of capacitive charge pumping (remember the PWM) producing additional voltage.
Now if the centre of the battery pack is grounded the MAXIMUM voltage across the winding insulation to motor body will be half the pack voltage.(and there is no chance of capacitive charge pumping as the system is not floating). If you can't picture this reduced voltage then ask more questions. It is not imaginary.
This is also an issue as many (most) DC motors are run at above their nameplate voltage so caring for the insulation is important.
If the motor housing is grounded to the middle of the pack via a low impedance connection (e.g a thick wire), and an insulation breakdown (or other conductive path) does develop in the motor (or elsewhere), current will flow. As mentioned earlier, this could easily be enough to start a fire before it blows any fuses.
acmotor wrote: OK, so even if you can't see the world from this point of view, don't say an EV traction battery pack MUST be electrically isolated as it is not the only way to go.
If you need a must, then say leakage MUST be monitored and the pack automatically broken up into safe voltages if a fault occurs.

I would say that is not an unreasonable thing, introducing mandatory leakage detectors, I'll back you on this. Likewise for mandatory inertia switches. And at least one contactor per battery box, so no current loops are possible when the contactors are open. And no exposed terminals with voltages above 32V (or whatever), i.e all exposed high voltage terminals should be sealed in appropriately labelled boxes.

My MX5 doesn't yet comply with all of the above, but I would still welcome the changes to NCOP for the sake of safety.
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Post by acmotor »

Ian,

Another post for you !

Unfortunately for the 100kohm suggestion this is simply too high a value as leakage in the order of 500ohm per volt (and lower is being asked for in the US now) often exists in practice. The unpredictability in an isolated system is that this background leakage can be from anywhere in the system to chassis.
Tell me, why are you afraid of low impedance leakage detection (aka effectively grounding) ? If this shuts the pack down, what is the problem. This has been accepted for years as best practice with mains power. Or do EVs run on different electrons ? The AC/DC power makes no difference to this safety function.
In reality you can have zero ohm to chassis from battery pack centre and just detect the current. If it exceeds some limit then shut the system down. If it false triggers then fix the system faults.

Ian, Please read what is in front of you !
I suggest leakage monitoring and battery pack voltage breakup. What more do you want ! Sorry, your response to item 2 is wasted in light of this.
Your MX5 has a 120V? system so it fits quite well with my example and I know you will add at least one more contactor now. Perhaps at the rear battery pack ?
Yes, my 600V system is a fair example of the newer generation of higher voltage AC EV systems. It is parlty why I am more concious than most of battery pack safety. My system is only 300V to chassis (the number that matters) and only 12 x 48V unconnected modules with 12 contactors and 4 fuses (one at each battery box location) plenty of redundancy - no single point failure. All my terminals are insulated or boxed. I am applying the best electrical practice for safety and leaving nothing to chance or single point failure.

Your concern about starting a fire is interesting. Are you implying that your EV is that unsafe ? Is there unsuitable fusing or other electrical protection ? I raised the point that in a collision your "isolation" is very likely to be lost and if your vehicle was only considered safe due to that wishful isolation and not other safety design such as fuses, leakage detection and battery pack breakup then you have a problem. If you just rely on isolation then a single point insulation failure can make the system dangerous.
No, the system will never be perfect, but it should be the best we can come up with.

It is all about safety.
When I run a wire, I think, how can I make it safe. What if the system shorts to ground here or here. What if... ? We should all do that and not just think we have made it safe 'cause someone somewhere said isolate the pack and it will all be tickety boo.

Still happy to debate. It is in our best interest.
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Post by acmotor »

Sorry, missed one point.

A motor's insulation is less likely to break down if the voltage across it is lower. Did you get that ?
If a motor's insulation breaks down then leakage detection to the centre of the battery pack (that shuts the battery system /controller down) may well save a fire or gross physical damage to the motor, providing the posibility of re-winding.

The same insulation breakdown in an electrically isolated system may well make the system leathal. But will you know before or after it gets you ?

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Post by zeva »

acmotor wrote: Tell me, why are you afraid of low impedance leakage detection (aka effectively grounding) ? If this shuts the pack down, what is the problem.
Firstly, there's plenty of energy in the input ripple capacitors of most motor controllers to kill a human (or even start a fire), and these are still in-circuit after the pack is isolated.

Secondly, surely the less current able to flow in a fault condition the better? Especially when we consider the possibility of a faulty leakage detector.

Can you justify to me why you would not maximise the impedance of a ground link? At least an impedance approaching the aforementioned 500ohm per volt (which is actually not so far off my 100Kohm guestimate for typical EV voltages).
acmotor wrote: This has been accepted for years as best practice with mains power. Or do EVs run on different electrons ?
No need to get facetious..
acmotor wrote: Your concern about starting a fire is interesting. Are you implying that your EV is that unsafe ?
Yes, it is potentially unsafe, but so is yours. (e.g lack of leakage detection in both cases)
acmotor wrote: Is there unsuitable fusing or other electrical protection ?
Correct. But the same goes for yours. And hence, arguably, every EV in Australia.
acmotor wrote: I raised the point that in a collision your "isolation" is very likely to be lost and if your vehicle was only considered safe due to that wishful isolation and not other safety design such as fuses, leakage detection and battery pack breakup then you have a problem.
I never implied a belief that isolation alone was sufficient. At this point we only disagree on the impedance of the ground link.
acmotor wrote: If you just rely on isolation then a single point insulation failure can make the system dangerous.
Dangerous how? 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.
Ian Hooper
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"Never doubt that the work of a small group of thoughtful, committed citizens can change the world." - Margaret Mead
http://www.zeva.com.au
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acmotor
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safety switches

Post by acmotor »

Great Ian,
You are thinking and addressing the points. I hope other forum goers appreciate the debate.

Motor controller capacitors - agreed, there is energy there (plenty in my controller !) However they are hardly in circuit. Have a look at your circuit and if it had blown a fuse(s) or contactor(s) had openned, just how non-circuit it actually is. If this were actually an issue then re-design would be required. It in no way justifies isolating the pack as all the uncertainties I have already mentioned still apply.
BTW my DC-DC runs off those capacitors and sucks them down (to the 12V system) in seconds to less than 60V before they lose the plot... controller then self discharges over the next few minutes (I guess most will do that anyway).
It is good that you consider these points. It may prompt you and others to re-arrange wiring, contactors and fuses to optimise safety. It may save your life or that of others.

The point of keeping the leakage detector impedance high I have already addressed. Perhaps if I also note that the 500ohm/V random leakage that may typically exist is just that - random. A leakage detection system to me will need to be an order of magnitude lower in impedance to be anywhere near reliable. e.g. the 240V 20mA RCD system that we all accept is 12kohm. Nothing more to say here.

Now you agree that fault conditions do occur and detection systems can be faulty. I guess you have come to the realisation that electrical isolation as a single point safety system can also be faulty. In the case of a collision, is very likey to become faulty.

Electrons, sorry about that. I needed to rattle your cage as it seemed you had gone to sleep. Image

I have no leakage detection fitted but as we both agree, it should be there.
I do have 4 fuses and 12 contactors. The fuses are fast semicondutor rated fuses of 75A. All fuses and terminals are enclosed (not just covered) The system design is that all components and wiring are rated to blow the fuses if required. My inertia shutoff and ES buttons (3x)are double wired to shut off the controller and break up the battery pack to 48V (open both ends) modules. Two of the fuses connect the + and - side of the centre of the battery pack to chassis. One or both of these will blow if any earth faults occur.
Batteries are enclosed in locked boxes. Once an ES is operated there is no more than 48V in this system (72 would be fine).
I have grounded to the chassis the centre of the battery pack so a single point failure WILL blow a fuse and shut the system down. This, along with best electrical installation practice (insulated / boxed terminals) does not completely replace the need for leakage detection, I would prefer both.

I consider there is suitable fusing and electrical installation standard in my system. At least I know where I stand. I am more likey to have a box of blow fuses than a fire. That is why wiring standards exist.
Human contact is by electrical safety standards excluded from live terminals.

Quote from Zeva:
Dangerous how? 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.

At least I don't have to answer that point - you did it for me ! Image

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 ?

Image
iMiEV MY12     110,230km in pure Electric and loving it !
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