NCOP 14 # 2.9 Chassis leakage

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Renard
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NCOP 14 # 2.9 Chassis leakage

Post by Renard » Wed, 11 May 2011, 22:52

I see from the new NCOP 14 in paragraph 2.9 that there should be "less than 20mA" leakage current from HAZV to "chassis or ELV components".

This current must be flowing between the +ve and -ve of the main battery terminals-- presumably via the chassis which must then have a definite potential with respect to the battery terminals.

One could detach the wiring from the terminals and megger across the wiring and chassis to check this current (or resistance to be precise.)

But I don't see how one could set up a "ground fault detection circuit or device" for continuous monitoring.
The chassis is not a ground in the same way as in ordinary AC wiring.

Could someone explain what the idea was here?
Renard

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NCOP 14 # 2.9 Chassis leakage

Post by CometBoy » Thu, 12 May 2011, 02:27

Hi Renard,

I think you will find it is not ” This current must be flowing between the +ve and -ve of the main battery terminals” but rather +ve or –ve to chassis....

The new standards read....

“Any HAZV traction battery system must be isolated from the chassis of the vehicle, and also from any auxiliary ELV components and wiring. Isolation must be designed such that there is a leakage current of less than 20 mA between any part of the HAZV system and either the chassis or ELV components in the vehicle, measured when the vehicle is at rest.

This requirement means that both the HAZV battery pack positive, and the HAZV battery pack negative, are to be floating relative to the chassis during normal operation, and both are to be treated as HAZV components.

A ground fault detection circuit or device may be used to identify that either the battery pack positive or battery pack negative have come into contact with the chassis or ELV part of the vehicle, and flag this as a fault to the driver or service technician.

Isolation should be checked manually before commencing any work or repairs on the HAZV circuits and any handbook or information prepared to assist the owner should make reference to this precaution.”


Renard your post is rather timely as I am just doing a service on my daily EV and part of that is checking the leakage resistance of the pack to chassis! For those of us using the older DC motor technology it is a fairly important check periodical as it indicates carbon (or other brush material) dust build up in the brush area of our motors. I also use a small infrared thermometers to check the temperature of the high current connections and terminations after a run during a service as well. I just have a couple 100K "tie down resistors" on the +ve and –ve pack ends and monitor via test points (so manual check only). Everyone on this forum will have a different view as to the best way to monitor leakage. Also DIY has covered this well a few years ago.

Cheers

Bruce

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NCOP 14 # 2.9 Chassis leakage

Post by Renard » Thu, 12 May 2011, 04:35

Cometboy,

My point was that current can't just flow to the chassis and stop there like a puddle; it has to flow from +ve to -ve.
Just it goes via the chassis. That is, there must be leakage from +ve to chassis and also from -ve to chassis.
Renard

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NCOP 14 # 2.9 Chassis leakage

Post by CometBoy » Thu, 12 May 2011, 05:15

Correct, from an electrical safety point of view, leakage to ground anywhere in an isolated system is not a dangerous situation on it own. But should a leakage path not be corrected and a failure occurs somewhere else over time then this has the potential (ha ha) to create an electrical safety issue.

IMHO Any single point earth leakage areas should be repaired ASAP.

The build up of brush dust has other problems as well but a different topic....

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NCOP 14 # 2.9 Chassis leakage

Post by evric » Thu, 12 May 2011, 06:34

I agree with Bruce,
But remember...
If, say, there is a severe leakage from the positive side of the HAZV to the chassis of the car(carbon buildup in motor), this is very dangerous if you, leaning across a bare body panel, touch the more negative side of the HAZV, you then make the other connection. Not a nice result.
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Last edited by evric on Wed, 11 May 2011, 20:35, edited 1 time in total.
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NCOP 14 # 2.9 Chassis leakage

Post by CometBoy » Thu, 12 May 2011, 13:25

Excellent example Eric.... Lots of scenarios can happen, let’s hope we don’t see any electrical paths being completed by us.

Some addition (common sense) thoughts are:

- Away have a “FULL” disconnect on your pack(s) and make sure this is used before undertaking any battery/cell maintenance. This is usually an Anderson style connector breaking + ve and – ve. I think such a connector (or other device) should be within visible range of the pack so you (and others) can see clearly if it is disconnected.

- The concept of breaking up packs into smaller lower voltage grouping that can be separately disconnected on higher voltage DIY EVs should be seriously considered during your design. With some form of fault leakage (manual or monitored) used on each group.

- Remember to insulate spanner etc on conductive tools when using then on pack maintenance.

- Think about the use of non contact tools for quick connection/terminal checks. Good IR temperature guns are relatively cheap and work so well in highlighting a potential problem. All you need to do is scan the pack and all the other high current connections after a good hard run and check for any unusual temperature hot spots.

- Always remember most accidents happen because of familiarization or we are in a hurry and choose to take short-cuts. Not a great idea when playing with large amounts of stored energy in our EVs.

Electrical safety consideration should not be understated and I’m happy to see them being addressed in the newer standards.

Bruce
Last edited by CometBoy on Thu, 12 May 2011, 03:35, edited 1 time in total.

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NCOP 14 # 2.9 Chassis leakage

Post by bga » Thu, 12 May 2011, 18:05

More what NCOP14 is about is not using the chassis for the traction power return, as the tail lights do. I think the concern was two-fold:
a) creating hot spots in the body and
b) getting 150 volts mixed up in the 12 volt supply, causing a fire.

If the traction power supply is isolated, then a single point grounding, say through wet brushes isn't going to cause anything catastrophic to happen.
The 20mA current was specified to make it relatively safe if a single terminal is accidentally touched by a careless owner or passer-by. You can still grab two terminals and give yourself a shock or melt a spanner - hence the covers.

Yes, the IR termperature gun is quick and accurate - a most useful addition to the tool kit. It's right up there with the DC current clamp meter.

NCOP-14 was deliberately written to not be prescriptive and only mentions that components in electrical circuits have to be appropriate, not that they have to be used within the manufacturer's reccomendations. It's up to the constructor and their engineer to ensure that the electrical design is fit for purpose.

AS3000 isn't very appropriate, it is an AC building wiring standard and doesn't consider vehicles, but has some useful information. UN ECE 100 is an electric vehicle standard which has almost no practical informatin in it, but does describe a procedure to test the traction power supply isolation; by alternately connecting resistors from the battery + and - to ground and measuring the voltage across the resistor.

An alternative to Anderson plugs is to have one or more links that are easily opened to disable the battery. Preferably not involvoing a spanner.

A convenient breaker would be the 'Big red Button', which can also be used as a battery disconnect.
Also, 12V 4WD battery isolators could be used if the design is appropriate for high sustained and peak traction currents and the creepage distances are sufficient to prevent arc-overs in the open state. I would expect that most 'heavy duty' types would be up to the current and isolation needed. They are not opened under load, so the DC break requirement is not applicable. (even small switches happily hold off about 300 volts)
I will definitely consider these in my 512 volt battery.

See the Red Suzi (evalbum) for an example of a vehicle with the battery isolated into 48 volt sections.

A way to look at the battery and its electrical energy is that it's like having a silent engine running at full speed while you're spannering the various parts. One slip and that spinning shaft (or propellerImage) is going to get you. In this case, the high current discharge.
Last edited by bga on Thu, 12 May 2011, 12:14, edited 1 time in total.
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NCOP 14 # 2.9 Chassis leakage

Post by weber » Tue, 17 Dec 2013, 04:22

See the posts on this topic in Weber and Coulomb's MX-5 build thread.
viewtopic.php?t=980&p=48143#p48143
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NCOP 14 # 2.9 Chassis leakage

Post by acmotor » Tue, 17 Dec 2013, 16:37

Isolation must be designed such that there is a leakage current of less than 20 mA between any part of the HAZV system and either the chassis or ELV components in the vehicle, measured when the vehicle is at rest.

Well red suzi complied with that Image All 48 modules were isolated when the ign was turned off even though pack centre was grounded when ign was on (actually ended up with a relay coil as the centre earth path that would shutdown pack in the case of earth fault, i.e. active monitoring). Perhaps that means that NCOP14 should clarify the 'at rest' statement ? to be ign on or off i.e. ready mode or shutdown. I could suggest that 'at rest' was ign off. Image and have complied.

I would like to see an active demonstratable insulation monitor as an NCOP requirement as I have long held the view that the ignorance is bliss logic of just isolating the pack is dangerous.
Like RCDs have a test funtion (button) there should be the same in DIY EVs.
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NCOP 14 # 2.9 Chassis leakage

Post by Richo » Tue, 17 Dec 2013, 20:52

Doesn't ambiguity work in your favour as you have suggested.

...And like RCDs no one will press it Image
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NCOP 14 # 2.9 Chassis leakage

Post by Stiive » Wed, 18 Dec 2013, 00:50

acmotor wrote: I would like to see an active demonstratable insulation monitor as an NCOP requirement


I use these:

http://www.bender.org/documents/IR155-0 ... 012830.pdf
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NCOP 14 # 2.9 Chassis leakage

Post by acmotor » Wed, 18 Dec 2013, 07:23

The 'button press' is to satisfy NCOP14 20mA leakage check. Otherwise the active monitoring does the work.

Yep, the insulation monitor equipment is out there and should be included in any build. It may be like seatbelts though. Smart for your own safety but probably needs legislation to make mandatory.

Yes Stiive, the bender unit datasheet makes intereting reading. Sounds like the self checking ground fault monitoring system in the Leaf and iMiEV.
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NCOP 14 # 2.9 Chassis leakage

Post by Bryce » Wed, 18 Dec 2013, 22:59

Also have used that one - also the Bender IR125Y. Both very easy to install - recommend the IR125 unit for easier DIY install.

CapTech (Capacitor technologies) who distribute them here in Oz are also rather helpful and designed a screen readout for us to use with the 150 unit.

Cheers
Bryce

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