[EVDL List]

Hi all,

I'm part of a group currently working towards updating the national
regulations for road-legal electric vehicles in Australia, and the
group's opinion is currently divided on the subject of whether the
power circuit should be isolated from the vehicle body.. So I'm hoping
to get some *technical* reasons for and against this from any experts
in the field!

Some people believe it should be isolated, because then you can't get
a shock from touching any one point in the power circuit and the
vehicle itself.

Others believe they should have a common ground so the potentials are
known, and so that there is a predictable voltage potential across the
insulation in the motor (i.e between the motor windings and the motor
housing).

I'm of the opinion that the power circuit should be isolated but
perhaps with a ground leakage detector between the power circuit and
the vehicle body, so you actually know if there is a ground fault in
the circuit.

Thoughts?

Ian Hooper
--
"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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[quote] Ian Hooper <xxx@xxx.xxx.au> wrote:
> Hi all,
>
> I'm part of a group currently working towards updating the national
> regulations for road-legal electric vehicles in Australia, and the
> group's opinion is currently divided on the subject of whether the
> power circuit should be isolated from the vehicle body.. So I'm hoping
> to get some *technical* reasons for and against this from any experts
> in the field!

First, on terminology - "Power circuit" is a bit ambiguous. With EVs,
it's more usual to say traction battery / traction power circuit.
"Power" might be confused with the mains power used to run the battery
charger.

> Some people believe it should be isolated, because then you can't get
> a shock from touching any one point in the power circuit and the
> vehicle itself.

Agreed. It avoids or mitigates several less obvious problems as well.

> Others believe they should have a common ground so the potentials are
> known, and so that there is a predictable voltage potential across the
> insulation in the motor (i.e between the motor windings and the motor
> housing).

It's not a good enough reason to counter the other reasons for keeping
it isolated, IMO.

Low-resistance paths will eventually develop, usually in the motor (on
a DC vehicle) while driving. If you've connected the pack to the
chassis elsewhere, this is likely to develop into high current faults
and which can damage the controller or motor.

With flooded batteries in a conversion vehicle, you also have the
problem of leakage between the pack and the chassis. Again, if you've
intentionally connected it at one point, you could well get "leakage"
from another battery to the chassis (or even insulation damage from a
cable rubbing or being crushed) : possibly a fire risk and at least it
will cause corrosion or balance problems.

There is also the problem of detecting such faults. If the pack is
connected to the chassis at some point, you can't automatically detect
a leakage current - the first you will know about it is when a serious
problem develops.

Finally, there's the issue that people expect high voltage battery
systems to be isolated, just because this is common practice in many
fields, not least electric vehicles. Doing it differently is a hazard
in itself, because people don't read warning labels..

> I'm of the opinion that the power circuit should be isolated but
> perhaps with a ground leakage detector between the power circuit and
> the vehicle body, so you actually know if there is a ground fault in
> the circuit.

The Peugeot/Citroen EVs are like this. I don't know if it needs to be
a requirement but it's definitely useful to alert you to a minor
problem (e.g. brush dust build up or water in a fuse holder) before it
becomes a major one.

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Ian,

I agree with you. It should be isolated, and a resistance to body it
a good idea. What type of circuitry are you thinking of?

Roger

[quote] Ian Hooper wrote:

>
> I'm of the opinion that the power circuit should be isolated but
> perhaps with a ground leakage detector between the power circuit and
> the vehicle body, so you actually know if there is a ground fault in
> the circuit.
>

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> > I'm part of a group currently working towards updating the national
> > regulations for road-legal electric vehicles in Australia, and the
> > group's opinion is currently divided on the subject of whether the
> > power circuit should be isolated from the vehicle body.. So I'm hoping
> > to get some *technical* reasons for and against this from any experts
> > in the field!

In my EV I have an isolated pack that developed a fault - a brush clip
came loose inside the DC motor that provided an intermittent connection
to the vehicle chassis. The other day I was standing on wet ground, I
touched an exposed nut on the rear battery rack, and received a shock.
Not sure if I was touching another part of the vehicle at the time.

I must admit the concept of "earth" or "ground" confuses me, for example
electrical systems that use 1 wire with earth return. I read some where
that a low impedance connection to the earth can be considered a supply
or sink of current. However I had assumed current must always flow in
loops.

So here is my question: if there is a connection between the pack and
vehicle chassis, does that mean that current can flow (via a person)
between the chassis and the earth?

Thanks,

David

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[quote]Bill Dube wrote:
> If you accidentally touch the traction wiring, and it is otherwise
> isolated, you will not get a shock at all, even if you touch the car
> body too. If the traction wiring is NOT isolated, the person that
> touches the traction wiring accidentally may not live to tell about it.

This brings up a question for me: I have a pack with a very small amount
of leakage between about the center of the pack (150 volts) and frame
ground. It's very low (2ma or so) but enough that it will rap my
knuckles if I touch one end of the pack.

So I don't. But I was wondering: If one put a resistor at the center of
the pack to frame ground to bleed off this charge, is that defeating the
purpose of a true isolated pack? If a ground fault did happen the
resistor would vaporize immediately or I could put a 150 volt 1a DC
rated 10k AIR fuse along with it.

It's a flooded NiCD pack, the controller will trip if there is more than
a 5ma leakage. But the 2ma is still annoying.

Chris

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Wouldn't the resistor actually act as a high impedance ground? I
think this type of fault protection would be a great safety addition
to any EV. I would tie it in to the main traction pack contactors.


[quote] Ian Hooper wrote:

> I don't know how ground fault detection is done "properly", but the
> sort of device which springs to mind would just have something like a
> 1K resistor in series with a current sensor, hooked up between the
> traction circuit ground and the car body.
>
> If a ground fault developed you would get (small) current flow through
> this link, which could be set up to signal an error/alarm/etc so you
> would know as soon as something is wrong. Or in more serious cases it
> could even open the main contactor automatically.
>
> Ian Hooper
> --
> "Never doubt that the work of a small group of thoughtful, committed
> citizens can change the world." - Margaret Mead
> http://www.zeva.com.au
>
> On 08/09/2008, at 10:24 PM, Roger Heuckeroth wrote:
>
>> Ian,
>>
>> I agree with you. It should be isolated, and a resistance to body it
>> a good idea. What type of circuitry are you thinking of?
>>
>> Roger
>>
>> On Sep 8, 2008, at 2:52 AM, Ian Hooper wrote:
>>
>>>
>>> I'm of the opinion that the power circuit should be isolated but
>>> perhaps with a ground leakage detector between the power circuit and
>>> the vehicle body, so you actually know if there is a ground fault in
>>> the circuit.
>>>
>>
>> _______________________________________________
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>>
>>
>
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[quote]Chris Zach wrote:
> I have a pack with a very small amount of leakage between about the
> center of the pack (150 volts) and frame ground. It's very low (2ma
> or so)

2ma isn't "very low". It's enough to kill under the wrong circumstances.
The leakage limit for medical electronics is 0.5ma, which is considered
low enough to be safe even for invalids or children, or conditions like
wet skin.

The usual 5ma limit is considered the most you can allow under normal
conditions (a normal healthy person, able to move himself quickly out of
contact, skin not wet, etc.). Your 2ma is most of the way there.

So, I would find the cause of this 2ma leakage, and fix it if possible.
It might be electrolyte on the battery tops, carbon dust in the motor, a
failed component somewhere, etc.

Besides safety, there's another reason to fix it. This DC leakage
current will cause corrosion at the terminals or body parts it is
flowing between. The battery terminal and/or chassis mounting point will
rot away over time.

> If one put a resistor at the center of the pack to frame ground to
> bleed off this charge, is that defeating the purpose of a true
> isolated pack? If a ground fault did happen the resistor would
> vaporize immediately or I could put a 150 volt 1a DC rated 10k
> AIR fuse along with it.

A large value resistor between pack and ground (100k or more) is
relatively common. This value is high enough so you can't get a deadly
current through it (100k is 1ma with a 100v pack). But it's low enough
to bleed off any static charge or minor leakage currents.

Systems that have this resistor also usually sense the voltage across it
(or current in it) to detect ground faults. If such a fault is detected,
it shuts down the system. The resistor isn't usually connected in just
one place in the pack; there's one at each end, or one that gets
switched alternately to each end. That way it detects a ground fault no
matter where it occurs in the pack.
--
Ring the bells that still can ring
Forget the perfect offering
There is a crack in everything
That's how the light gets in -- Leonard Cohen
--
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart_at_earthlink.net

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Ask him what makes grounded safer than ungrounded.

His main argument seems to be that houses require the supply neutral
to be connected to earth ground.

However, the EV regulations of other countries seem much more
applicable to EVs than house grounding. The chassis of the vehicle
cannot serve the same purpose of earth ground; it doesn't have the
same electrical properties.

Yes, breakup contactors, multiple fuses, crash sensors, and proper
insulation will make an EV safer. But isolation (in addition to these
other safety features) will also reduce the negative consequences of
problems.

He is framing the question as isolation or other safety measures,
while in reality they are not mutually exclusive.

-Morgan LaMoore

[quote] Ian Hooper <xxx@xxx.xxx.au> wrote:
> Sorry to dig up an old thread, but I shared everyone's comments
> regarding isolation with our EV safety committee, and here's the
> response from main proponent for non-isolated traction circuits. (He
> has a habit of fighting hard for his beliefs!) I welcome any further
> comment:
>
> ----------
>
> 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.
>
> ----------
>
> Ian Hooper
> --
> "Never doubt that the work of a small group of thoughtful, committed
> citizens can change the world." - Margaret Mead
> http://www.zeva.com.au
>
> On 08/09/2008, at 2:52 PM, Ian Hooper wrote:
>
>> Hi all,
>>
>> I'm part of a group currently working towards updating the national
>> regulations for road-legal electric vehicles in Australia, and the
>> group's opinion is currently divided on the subject of whether the
>> power circuit should be isolated from the vehicle body.. So I'm hoping
>> to get some *technical* reasons for and against this from any experts
>> in the field!
>>
>> Some people believe it should be isolated, because then you can't get
>> a shock from touching any one point in the power circuit and the
>> vehicle itself.
>>
>> Others believe they should have a common ground so the potentials are
>> known, and so that there is a predictable voltage potential across the
>> insulation in the motor (i.e between the motor windings and the motor
>> housing).
>>
>> I'm of the opinion that the power circuit should be isolated but
>> perhaps with a ground leakage detector between the power circuit and
>> the vehicle body, so you actually know if there is a ground fault in
>> the circuit.
>>
>> Thoughts?
>>
>> Ian Hooper
>> --
>> "Never doubt that the work of a small group of thoughtful, committed
>> citizens can change the world." - Margaret Mead
>> http://www.zeva.com.au
>>
>> _______________________________________________
>> General EVDL support: http://evdl.org/help/
>> Usage guidelines: http://evdl.org/help/index.html#conv
>> Archives: http://evdl.org/archive/
>> Subscription options: http://lists.sjsu.edu/mailman/listinfo/ev
>>
>>
>
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>

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> 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.
>
It appears this is essentially going into the debate of whether double
insulated or grounding is better for safety. The differences are
covered here:
http://en.wikipedia.org/wiki/Appliance_classes

It seems EVDL members are pretty much in the double insulated camp,
while this EV safety committee member thinks that grounding is just as
good or better, and believes the regulations should allow either route.

If one uses the grounded pack design, a GFCI is going to be critical in
making the design safe, and to shut things down if leaks develop. (A
note on GFCI's: I recall that US spec GFCI's have a much lower trigger
threshold than European GFCI's...say 5 ma vs 20 ma or so. This may
increase safety at the risk of higher false positives (mis triggers)
(some equipment is not recommended to be run on GFCI circuits because an
unnoticed erroneous triggering is likely worse than allowing the leakage
to take place. e.g. data center equipment, freezers.)

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Oh dear.

Well, it strikes me that he provides no reasoning as to why a center
grounded system with the protection he mentions would provide better
protection than an insulated battery pack. He counters none of the arguments
made by people on this list. He just states that it is safer, tears down a
straw man argument, attacks DC motor people, etc.

This is probably a waste of my time but, more comments below

[quote] Ian Hooper <xxx@xxx.xxx.au> wrote:

> Sorry to dig up an old thread, but I shared everyone's comments
> regarding isolation with our EV safety committee, and here's the
> response from main proponent for non-isolated traction circuits. (He
> has a habit of fighting hard for his beliefs!) I welcome any further
> comment:
>
> ----------
>
> 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.


Isolated battery packs does not prevent leakage detection.


>
> They go against Australian and European electrical standards that
> require protective earth and supply neutral connected to earth.


All high voltage EV standards I'm aware of calls for isolated battery pack.
Can he provide us with what specific standard he's referring to?


>
> They will also give EVs a bad reputation with the public as people get
> electrocuted.
>

Care to provide an example of people having been electrocuted by an EV
because of its isolated battery pack?


>
> 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.
>

All of those things are good measure commonly used in EVs, except, the
center ground for reasons already discussed.



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

ad hominem

>
>
> 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.
>

strawman


>
> 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.
>

Commercial EV manufacturers follow SAE standards j1772, j1773,j2344,j2289.



>
> ----------
>
> Ian Hooper
> --
> "Never doubt that the work of a small group of thoughtful, committed
> citizens can change the world." - Margaret Mead
> http://www.zeva.com.au
>
> On 08/09/2008, at 2:52 PM, Ian Hooper wrote:
>
> > Hi all,
> >
> > I'm part of a group currently working towards updating the national
> > regulations for road-legal electric vehicles in Australia, and the
> > group's opinion is currently divided on the subject of whether the
> > power circuit should be isolated from the vehicle body.. So I'm hoping
> > to get some *technical* reasons for and against this from any experts
> > in the field!
> >
> > Some people believe it should be isolated, because then you can't get
> > a shock from touching any one point in the power circuit and the
> > vehicle itself.
> >
> > Others believe they should have a common ground so the potentials are
> > known, and so that there is a predictable voltage potential across the
> > insulation in the motor (i.e between the motor windings and the motor
> > housing).
> >
> > I'm of the opinion that the power circuit should be isolated but
> > perhaps with a ground leakage detector between the power circuit and
> > the vehicle body, so you actually know if there is a ground fault in
> > the circuit.
> >
> > Thoughts?
> >
> > Ian Hooper
> > --
> > "Never doubt that the work of a small group of thoughtful, committed
> > citizens can change the world." - Margaret Mead
> > http://www.zeva.com.au
> >
> > _______________________________________________
> > General EVDL support: http://evdl.org/help/
> > Usage guidelines: http://evdl.org/help/index.html#conv
> > Archives: http://evdl.org/archive/
> > Subscription options: http://lists.sjsu.edu/mailman/listinfo/ev
> >
> >
>
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>
>


--
www.electric-lemon.com
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