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Just came across a new draft document for EV conversions on the LVVTA website. Submissions are open until 31-march-2011.

Please give the document a read and get your comments in!

http://lvvta.proboards.com/index.cgi?board=docs&action=display&thread=135
It all looks reasonable except for the following items:

Instrumentation

2.4(1) The instrumentation of an electrically‐powered low volume vehicle must provide
to the driver, a clear visual indication of:

(d) in the case of a vehicle fitted with an electric vacuum pump, a loss of vacuum that may result in a loss or reduction of braking performance;

(f) the occurrence of a ground fault (isolation failure), accompanied by an
audible warning.
So I need a vacuum gauge hooked up to a warning light? and wtf?

Accelerator

2.4(2) An electrically‐powered low volume vehicle must have an accelerator pedal, and
an associated control mechanism for the control of the electrical motor and circuitry, incorporating a fail‐safe design.
"A single potentiometer type mechanism is not acceptable as a means of compliance with 2.4(2)."
Are they implying we need some sort of dual pot setup with redundancy or failover? I don't know how to pass this one.

Anyone else submitted feedback to this document?

Pete.
 

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Discussion Starter · #3 ·
It all looks reasonable except for the following items:



So I need a vacuum gauge hooked up to a warning light? and wtf?

I think a vac pressure switch would do. Just need a tee in the line to the vac pump and a simple SMC vacuum switch. This statement is also inconsistent with the braking assist paragraph, which mentions vacuum and air. What about an air pressure failure? Neither paragraph mentions any other type of brake assist i.e. hydraulic.
I think the whole paragraph should be less specific and simply require a braking assistance failure warning.

Are they implying we need some sort of dual pot setup with redundancy or failover? I don't know how to pass this one.

I would hope that hall effect pedals would be OK as they are (supposedly) failsafe. I think the comment is in reference to pot boxes specifically as they can wear a "spot" on the most commonly used throttle position.
The discussion document covers the need for redundancy

Anyone else submitted feedback to this document?

Pete.
I actually have the greatest resistance to the warning sitcker on the bumper! In my opinion it signals that my vehicle is somehow unsafe and inherently dangerous.

Will petrol cars need to have a "flammable" sticker attached - I think not.

Something else that kind of slips in - how do you detect whether a ventilation fan is working or not? I did find some Omron resistive flow sensors on RSnewzealand but they start at 120 bucks and go up from there.
 

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Vacuum failure shouldnt be too bad as it is just a low pressure switch on the vacuum reservoir.

The single pot throttle always worried me a little as it is a basic weak point in the system. Dual pots with one that say increases in voltage the more the pedal is pressed and the other that decreases could be compared to determine if the throttle pot has failed. I can understand what they are trying to do this this piece but it could be made clearer on what they are looking for with regards to "failsafe".

I too am a little annoyed with the need for EV warning stickers. As it has been said it makes an EV sound more dangerous than an ICE car which is completely wrong. Most high voltage stuff needs warnings on it anyway doesnt it?

One good point from this I see if the removal for the need to vent batteries if they dont produce gases during charging. It might still be required to keep them cool during charging though. With regards to ventalation fans brushless DC fans are theoretically spark proof so could be used. If the large 120mm computer BLDC fans are used some of them have a tachometer wire coming from them so the PC knows if it fails. This or something similar could be used in an EV ventalation system.

Ryan Gibbs
 

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I completely agree with the thoughts on the label too.
I know someone who got around it with their last conversion by pointing out that hybrids don't have some fancy sign that turns on and off depending on if they're running on electric or not!
 

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Discussion Starter · #6 ·
Something else to watch out for is that all cars from 1992 on will have to comply with the new requirements. I would hope that all owners of registered ev will be contactd but wjat this means in terms of compliance costs is not clear.

In the building industry they have documents outlining "acceptable solutions". Perhaps we will need to develop ansimilar document for EV converters too. As far as anything goes, we should at least demand consistency between OEM vehicles and our conversions. Much of the stuff in the draft standard is following this approach (and sort of assumes scratch build rather than conversion) so that is particularly why I disagree with the bumber sticker requirement.

I personally welcome the new document even if some might roll their eyes and complain about the costs or complexity of compliance. The last thing we want is for these vehicles to be considered dangerous, or worse still - BANNED.
 

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Thanks Nick
I have written asking for a couple of minor changes and answered their questionnaire

What I sent

Dear Linda,

I would like to comment on the
LVV Standard 75‐00(00) Electric and Hybrid Vehicles (Original version/Draft # 5)

I am a chartered engineer and a member of IPENZ,
More cogently I am most of the way through building myself a scratch built electric car; I have been following the current standards and the New Zealand Hobby Car Technical Manual

Yours Sincerely

Eur. Ing. Duncan Cairncross BSc. DMS. C.Eng. FIMechE. MIPENZ. MFEANI.

From the Draft

2.2(5)
(c) is designed to protect the wiring and electrical components of the electrical drive from over‐current and damage, with at least 20% overload capacity; and
(d) has no more over‐load capacity than is necessary, in order to protect the electrical wiring and components of the electrical drive from damage;
This is actually not possible, by the time a suitable fuse has blown or breaker has tripped the “electrical components” will be toast, the fuse or breaker can stop the incident but will not be able to save the controller and motor.

2.4(1)
(f) the occurrence of a ground fault (isolation failure), accompanied by an audible warning.
With a brushed DC motor a ground fault warning mechanism will be very unreliable and not useful.

2.4(2)
An electrically‐powered low volume vehicle must have an accelerator pedal, and an associated control mechanism for the control of the electrical motor and circuitry, incorporating a fail‐safe design.
Would a circuit that would only permit the controller to be engaged when a separate switch on the throttle was closed in addition to the throttle potentiometer meet this condition?

2.4(3)
The transmission of an electrically‐powered low volume vehicle must incorporate an operative inhibitor switch that will, in the case of an electric reversing switch being fitted, prevent reverse from being inadvertently engaged during forward motion.
Would a circuit that would only permit the reversing contactor to be engaged when the brakes were applied meet this condition?

General
There is an assumption in the draft that an electric car will be heavier than an IC engine car, this is certainly true for a car using lead acid batteries but less certain for a car using lithium batteries.
 

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From the Questionnaire - part one

Q3 2.2(1)(e) Mechanical master switch
Should a mechanical master switch be mandated to disconnect batteries and can it be in battery box if non–venting type batteries are used?
I am using Alderson connectors to disconnect my batteries into partial packs
– is this a “mechanical switch”?


Q4 2.2(3) High voltage
UNECE regulations designate high voltage as 60V DC and 25V AC. Australia requires orange cabling for any voltages over 32V. FIA set the limit at 42V and 50V depending on vehicle type. What should the figure be set at?
I would recommend setting it at the lower of the two levels 42v DC and 25v AC

Q5 2.2(5)(b) Over‐current device
Can an over‐current device be in a battery pack?
In the case of a lead acid battery that would be a bad idea as an explosive gas mix may be present, for all other chemistries an overcurrent device should be as close to the batteries as possible so inside the pack would be ok.


Q6 2.3(1) Battery restraint
What is a sensible acceleration level to apply to battery restraint in directions other than forward?
The 2.5G in the draft standard is a good number – should also apply to vertical acceleration

Q7 2.3(2) Battery compartment sealing
Should drip tubes or a catch tray be allowed as an alternative to a fully sealed battery compartment?
I don’t understand what is being fixed here?

Q8 2.3(4) Battery compartment venting
Is venting of a battery compartment required when batteries are discharging, or only when charging or during regenerative braking?
Only when being charged or during regenerative braking – only for lead acid batteries

Q9 2.4(1)(f) Ground fault detection
Should a manual ground fault detection system be mandatory?
No – with a brushed DC motor ground fault detection will be very unreliable

Q10 2.4(2) Accelerator design
Fail‐safe accelerator design – it is assumed that a single potentiometer is not sufficient and a twin potentiometer should be used.
Existing motor controllers do not have the facility to use twin potentiometers, a better system would be to use the throttle potentiometer (or hall-effect unit) in series with a micro-switch on the throttle lever then both would need to be activated to allow current to the motor.
Additionally the controller should not be able to be switched on (initial switch on) unless the throttle is at zero or the micro-switch is open

Q11 2.4(3) Transmission
Should the trans have an inhibitor to prevent motor energisation whilst in gear, for auto and manual transmissions?
I assume this means initial switch on of the controller –
This would be very difficult for a modifier to do
A switch on the accelerator as above or a switch on the brake would be much easier to do, would give equal or better protection and is similar to the starter inhibitor on the clutch on some IC vehicles.
The vehicle I am building is direct drive with no clutch – there is no way to mechanically disconnect the drive

Q12 2.6(1) High voltage warning labels
Should high voltage stickers on bumpers be mandatory?
Warning is needed “under the hood” or anywhere where the high voltage can be encountered,
Is external warning really needed?


Q13 ‐‐‐‐ Current switches
The FIA specifies the following requirement:
"In order to prevent contact melting of the general circuit breaker its [I²t] (ampere square seconds characteristics, representing heat energy dissipated on the breaker contacts during switching) must be sufficient to guarantee proper operation of the circuit breaker, even under surge current conditions, in particular those occurring
during the connection of the traction battery to the power bus."
Should we include a similar requirement?
In normal operation contactors should never have to make or break under load,
Contactors should be capable of making and breaking the currents required –however they should not be required to have a long life under these conditions. Tens of operations to failure not thousands

even under surge current conditions, in particular those occurring during the connection of the traction battery to the power bus
This would be an indication of very poor design – the power pack should be connected to the controller through a resister until the capacitors have charged to the pack voltage and only then should the main contactor pull in. (PreCharge)

Q14 ‐‐‐‐ Insulation resistance testing
Should Insulation resistance testing (from UNECE 100) be mandated?
Certifiers will need to use a specialist meter to do this (also see FIA requirements in Q15).
For the foreseeable future brushed DC motors will be the most commonly used motors, these have inherent leakage due to carbon dust
This makes mandatory testing useless


Q15 ‐‐‐‐‐ Insulation resistance testing
The FIA specifies the following requirement:
“Every part of the electrical equipment must have a minimum insulation resistance between all live components and earth.
‐ For equipment with up to 300 volt to earth, the insulation resistance must reach the following value: 250 k Ohms.
‐ For equipment with more than 300 volts to earth, the insulation resistance must reach the following value: 500 k Ohms.
The measurement of the insulation resistance must be carried out using a d.c. voltage of at least 100 volts.”
Should we include a similar requirement?
As above this is useless with brushed DC motors

Q16 ‐‐‐‐ Insulation performance
The FIA specifies the following requirement:
“All electrically live parts must be protected against accidental contact. Insulating material not having sufficient mechanical resistance, i.e. paint coating, enamel, oxides, fibre coatings (soaked or not) or insulating tapes are not accepted.”
Should we include a similar requirement?
This is seems to be sensible but on closer examination is silly there are lots of parts inside their compartments that cannot be properly insulated
It must be clear that this does not include parts that are safely inside their compartments otherwise we will have issues with battery terminals and motor terminals and all of the bits inside my controller.
If you open the hood or battery box there will be “hot” parts in there unless you have disconnected the battery pack – as you should if working there
If you open up a main circuit board on a building you will find a plastic protector plate and underneath lots of un-insulated parts
Also needs to be expanded so that I can use taped on plastic tubes for instance
 

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Questionnaire part 2

Q17 ‐‐‐‐ Voltage across capacitors
The FIA specifies the following requirement:
“Voltage across capacitors belonging to the power circuit should fall below 65 volts within 5 seconds after the general‐circuit breaker is opened or the over current trips of the traction battery are blown.”
Should we include a similar requirement?
This is almost a sensible requirement
BUT in order to implement this on a converted vehicle a resister would need to be permanently connected across the input to the controller.
(This is because it must operate when any of the failures occur not just when the controller shuts down)
My controller has 16 off 820uF capacitors – to drop from 200v to 65v in 5 seconds would require 350mAmps
This would draw 70 watts continuously from my battery pack and require a resister capable of operating at 70 watts continuous.
If it is in place to ensure that safety personnel are not exposed to high voltages in the controller a longer time interval would make more sense.
100 seconds would be a sensible time and would reduce the requirements by a factor of 20.


Q18 ‐‐‐‐ Battery units
The FIA specifies the following requirements:
“Many different chemistries for Li‐Ion cells are on the market. They are not at all the same. They all have different safety requirements. Therefore, the BSE must, in general, be appropriate for the battery chemistry, as recommended by the cell manufacturer. For Lithium‐Ion (Lithium Polymer) batteries prone to thermal runaway it is strictly prohibited to remove or modify the monitoring and safety electronics delivered by the manufacturer with each cell (or module). For Lithium‐Ion (Lithium Polymer) batteries, only batteries equipped with an exclusive voltage monitoring and protective system to prevent overcharging and under‐voltage at each battery cell shall be approved. Furthermore, temperature control of the Lithium battery cells must be foreseen in the Battery Management System to prevent thermal runaway during overload or battery failure. A separate and redundant surveillance unit in the storage system should monitor the cell voltage and temperatures to shut the system
down at a single cell malfunction. The assembly of the battery cells in a battery pack must be carried out by a manufacturer with the appropriate technology. The specification of the battery pack, modules and cells, as well
as a document from the said manufacturer attesting to the safety of the produced battery pack, must be verified.”
Should we include similar requirements?
This is overkill –
Battery technology marches on, I can currently buy Lithium Polymer cells that would need massive abuse to fail in this manner, I won’t be using them because they are too expensive but they should not be banned by a blanket statement like this.
Also the best battery management systems currently available are hobby level systems
If I was using these cells I would expect to have to provide some sort of a fire shield for charging

Q19 ‐‐‐‐ ‘Live light’ for battery cover
The FIA specifies the following requirement:
“The Safe/Live Signage must be activated jointly by both the Driver Master Switch (DMS) and the General Circuit Breaker (GCB). If the Power Circuit is switched on (condition to drive the vehicle) by both the DMS and the GCB, the Power Circuit will be energised and turn to Live condition. Two redundant RED lights symbolising “danger high voltage” must be activated on the dashboard, as well as one red tail light to clearly show that it could be life threatening to work on the Power Circuit. If the Power Circuit is switched off by the DMS and/or the GCB, the Power Circuit will be de‐energised and discharged (no voltage on Live components). Both red dashboard lights and the red tail light will be switched off to clearly show that the Power Circuit is dead and it is now safe to work on the vehicle.”
Should we include a similar requirement?
This is silly – you don’t have a red light to say your motor is running on an IC car when in most modern cars you can’t hear the motor idling
The external light is even worse – it doesn’t help even when the light is off it is not safe to work on the vehicle unless you know exactly what you are doing

Q20 ‐‐‐‐ Power circuitry
The FIA specifies the following requirement:
“It is strongly recommended to use power circuitry as shown in the diagram using two “High Voltage Relays” or a single “High Voltage Relay” with two separate contacts for both traction battery polarities. A single relay with only
one breaking contact is not recommended.”
Should we include a similar requirement or recommendation?
This is a sensible requirement and should be recommended


Duncan Cairncross
 

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Hi

Dan here, from the Low Volume Vehicle Technical Association. We are an incorporated society set up to meet the needs of those wanting and needing to modify vehicles. In the early 90s government standards were introduced which effectively prohibited modifications that may affect safety. LVVTA was set up by enthusiast groups (including the Constructors Car Club) to ensure vehicles could still be modified, by working with the Ministry of Transport (and now NZTA) to create regulations that allow modifications while retaining a satisfactory level of safety. Safety must be our highest priority, but we also aim to provide practical standards to work to.

Thanks for taking the time to respond to the draft electric vehicle standard. I don't profess to be an expert on electric vehicles and especially the areas of electronics and high voltage, so any feedback is good for us to understand this type of modification better.

I'd like to make it clear that no requirements are set in stone so there will be changes made following the consultation. Submissions should be as per the instructions on our website, but one point that has been raised I would like to have further feedback on here as I get the feeling it may be slightly contentious... :rolleyes:

The suggestion to use hazard warning labels was carried over from the 1997 construction forms. The rationale is that externally the vehicle may look like a standard petrol/diesel driven model and so some indication of the modifications may be useful to emergency services.

This seems more important to me as the voltage used is ever increasing. The batteries may be well isolated but if the vehicle is involved in a big crash this may not be the case - if it were a petrol vehicle, everyone would know how to treat the vehicle, but as an electric vehicle the rules are different.

So instead of external labels, what measures can be mandated so that the likelihood of danger from the batteries contacting the metal vehicle structure is minimised? Do we already have enough in place?

The latest draft Australian guidelines (NCOP14) state that the battery compartments must be labelled but external vehicle labels are not mentioned so maybe they have resolved this.

Dan
 

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Hi Dan

External Hazard warning labels

I am ambivalent about these, in a crash they may not be seen by rescue personnel anyway

The risks are not that high - if sufficient damage has occurred to short to the frame you have probably blown every fuse in the system.
I will be fitting a fuse and disconnecter (manual) in the middle of my pack, I can't think of a situation where the frame could be live without blowing the fuse

Saying that if I need to stick or paint some warning labels on the car - then so be it
The only worry is if I have to stick a label on the "bumper" - and I don't have a bumper!
 

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Clause 2.3(6)(e) states that force ventilation of battery compartment must "operates by extracting gas from the battery compartments, and not by blowing in air which could leak out of the compartment"
and clause 2.3(6)(j) "has an inlet opening external to the vehicle." the notes state that this inlet should be placed where the local pressure is likely to be higher than atmospheric pressure.
These two requirements seem incongruent with each other. Is it OK to use positive pressure to move air through the compartment or not?

I have built my compartment with the fan blowing air into the compartment and I would rather not have to redesign it and rebuild it. If the sealing of the compartment is excellent and wont leak I don’t see a problem with the way I have built it. By putting the fan on the inlet any hydrogen or corrosive vapors generated do not pass through the fan. Even though the fan I have is a 12v brushless DC fan and shouldn't generate any electrical spark I cannot guarantee that it will not building up a static charge and so would still rather not have it within the mixture of gasses generated by the batteries. By blowing air in rather than extracting it I was able to place the vents at the top of the compartment and vents could be properly sized to prevent any restriction to flow hence the pressure differential between the inside and the outside of the compartment will be low hence even if the seal became compromised leakage would be low. By having the fan blow into the compartment the fan turbulence will assist with mixing of the hydrogen with the air while an extractor would leave dead zones of still air where higher concentrations of hydrogen could remain. Turbulence would be down stream of an extractor in its ducting. Once you start dictating solutions you stifle innovation. Regulations should mandate desired end results and leave methods of achieving those results as guidelines.

Quote; - “Hydrogen mixed with air is flammable over a wide range of concentration; 4 to 75% by volume, and readily ignited by common sources of ignition such as electrical sparks or small flames. Near optimal or stoichiometric mixtures of hydrogen and air are so sensitive to ignition that initiation of combustion can be caused by miniscule friction or static discharges and hence, for practical purposes can be considered to occur spontaneously.” Stoichiometric mixture is 29.5% hydrogen by volume in air.

The small volumes of hydrogen generated by the batteries and the volume of air moved by the fan should prevent combustible concentrations developing let alone stoichiometric mixtures. Most hydrogen would probably be generated during an equalization charge. The Diffusion Coefficient of hydrogen in air is high (0.61 at 20°C). This should result in a low concentration differential between the bottom of the compartment and the top and a natural loss of hydrogen out an open vent even without forced ventilation (highly unlikely to be sufficient though).
 

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Here is some more information which will give an idea of when hydrogen will be generated and how much.

Quote;- “Still very rare, but more common are hydrogen explosions. Hydrogen is only generated when the battery is overcharged, and this is only when the charge voltage across a cell is above what they call the "gassing voltage." Hydrogen cannot be generated if the voltage is lower than the gassing voltage. This is temperature dependent (see the link above), but at room temperature it is 14.34V for a 12 volt cell. There is a possibility for a tiny bit of hydrogen generated at the end of charge because the 6 cells are jockeying for the last bit of charge. A weaker cell will charge last, and since it has lower resistance the voltage across it will be lower than across the other cells, which have stopped charging. This causes higher voltage to appear across the full cells, and this higher voltage can sometimes be above the gassing voltage. This gas is often recombined, especially in sealed lead acid batteries, but sometimes it can escape, especially in flooded lead acid batteries.

Charge in a well ventilated area.

In order to explode the hydrogen must be over 4% by volume of the air it is mixed with. For example, if you were overcharging at a rate of 30 amps and had a battery box with the air volume of 20 inches cubed (50 cm cubed) you could get an explosive mixture in 8 minutes. To fill a 10 x 10 x 8 foot room with 4% hydrogen at a 30 amp overcharge rate would take 24 hours.
Overcharge rates are typically less than 1 amp, so you can see that it doesn't take much ventilation to keep you in the safe zone.”

http://www.powerstream.com/how-to-use-a-battery-charger.htm

An article on ventilation of battery rooms.

http://www.battcon.com/PapersFinal2002/VaccaroPaper2002.pdf

It is apparent to me that a small amount of leakage (such as a single digit percentage of volume vented) from a battery compartment into the vehicle interior would not have material effect on the safety of people or property within the duration of a typical overnight charge.
Note;- In the experiment that the largest concentration difference they noted was 7% from the top to the bottom of a drum that is 52cm tall i.e. Somewhere around 1.85% hydrogen at the top of the drum and around 1.72% at the bottom. This repaid diffusion of hydrogen into the air reduces the need to top vent the compartment. Most compartments won’t be 52cm tall and hence will see even lower concentration differentials.
 

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The requirement for forced exhaust during charging (and discharging, and for some time afterwards) shouldn't be a surprise - it's there in the current (1997) rules as well...

Unless I've misinterpreted something (which is not beyond the realms of possibility :))...
 

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The requirement for forced exhaust during charging (and discharging, and for some time afterwards) shouldn't be a surprise - it's there in the current (1997) rules as well...

Unless I've misinterpreted something (which is not beyond the realms of possibility :))...
I don't disagree with the requirement for forced ventilation of enclosed battery compartments I am disagreeing with the requirement that it be by extractor fan only.

Hydrogen can be extremely dangerous in enclosed spaces while being fairly benign in open spaces. To understand the risks it is necessary to understand how hydrogen will behave and at what rate it is likely to be generated. That way sensible rules can be created to deal with the real risks not the ones that we imagine might exist. In the absence of knowing, solutions tend to be massively over engineered and have redundant elements to them.

For instance I had wondered if hydrogen would accumulate at the top of the compartment forming a much higher concentration there and reaching a combustible mixture faster at the top. The high diffusion rate of hydrogen in air and the low observed deviations in hydrogen concentrations in the experimental data answered that question. The amount of hydrogen likely to be generated is unfortunately illusive. Here is an extract from an article on submarine batteries

"The open-circuit hydrogen-evolution rate per Ah of rated capacity for new cells is between 0.00636 and 0.105 cm3 hˉ Ahˉ at STP at 20–50 °C, respectively. For old cells, a> three-fold increase is observed; the evolution rate ranges from 0.0237 to 0.361 cm3 hˉ Ahˉ at STP at 20–50 °C, respectively. On float-charge, using an uncompensated float voltage, the hydrogen-evolution rate of new cells is between 0.0166 and 0.241 cm3 hˉ Ahˉ at STP at 20–50 °C, respectively. For old cells, the rates increase to 0.0298–0.903 cm3 hˉ Ahˉ at STP at 20–50 °C, respectively."

Using the last evolution rates applied to my rear battery pack of 5 off 130Ah batteries and a vehicle interior volume of 2492 liter or about 2500000 cm it would take between 28 hr's at 50°C and 5 weeks at 20°C to create a combustible mixture of 4% assuming no diffusion of hydrogen out the vehicles vents. So even if the pack was open to the vehicles interior a combustible mixture wouldn't eventuate within the 8 hour charge period even at very high ambient temperatures. Unfortunately this data is for float charge rates and not my particular batteries. The battery compartment would reach combustible concentrations much more quickly without forced ventilation but certainly not within the three minute post charge purge stipulated.
 

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Thanks to everyone who took the time to make submissions - all of them very detailed and extremely useful.

I have been away the last two weeks conducting certifier training so I will go through all of the feedback in the coming weeks.

Regards
Dan
 

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Discussion Starter · #18 ·
Thanks for keeping us up to date.

Any thoughts on how long it might take to finalise and release the Standard? I realise that you might have quite a few comments to process and I don't expect it will be in the next couple of weeks.

Will there be a draft v2 or are we straight to "release" from here?

Cheers
 

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Next week I need to lock myself away in a quiet room for a couple of days to go through all of the submissions and make changes to the draft document.

Once that's done I will get it reviewed internally and with NZTA, then most likely put the new draft back out for further comment in May, just to those who responded the first time around.

The final document then gets tidied up for a final proofing and presentation to NZTA to sign off. Publication happens at the next update of our technical manuals. As we make three or four updates a year that won't take too long (in comparison to Land Transport Rules anyway!).

Dan
 

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Methods of detecting fan failure in battery compartment forced ventilation system.
Modes of failure;-
1) Fan motor goes open circuit.
2) Fan becomes jammed, bearings seized or obstacle obstructing fan rotation.
3) Brushless or electronically commutated motor electronics failure.
4) Failure in post purge (delayed off) circuit.
5) Fan power supply failure (blown fuse, broken wire, bad connection).

Some fans are equipped with a pulse generator generating pulses per revolution. This could be used to detect fan rotation. I'm not sure what kind of circuit would be needed to convert this into a warning light signal. (Light goes off above X number of pulses per second). The other way would be motor amps illuminating the warning light above and below the normal amperage draw range.

Since the fan would only be active during charging (or only be providing a safety function during charging at the end of the charging cycle) putting such a warning light on the dash board might be redundant i.e. No one is in the driver’s seat to see it while the car is charging. The car is in all likelihood going to be shut in the garage all on its lonesome with no one around to see or hear any sort of warning device should the fan fail mid charge. Built in redundancy is likely a much beter option for dealing with this safety concern i.e. two or more fans on distinctly separate circuits. This does multiply costs and a completely duplicate system is not practical, both circuits would for instance be feed from the one accessory battery supplied from the one DC/DC converter (which does sort of give redundancy of supply i.e. battery or DC/DC) and be feed through the one wiring loom. It would however be better than the warning light that no one sees until it’s too late.
 
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