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Electric Motorkhana and khanacross car

Posted: Mon, 19 Oct 2015, 19:49
by galderdi
Hi,

Some of the Brisbane guys might remember me from a meeting a few months back. I am building an electric motorkhana and khanacross car from the ground upImage

The car is bigger than a traditional motorkhana car because I wanted to have two seats plus I want to also compete in Khanacross so I want more structure around me in case of a mishap (mishaps are very unlikely in motorkhana but are a risk in Khanacross)

I am still on track for the car to be complete by Christmas and entered for its first event late Jan or Early Feb 2016.

It is running 144V through a Curtis controller on to an Advanced DC 9 inch motor.
I think I have most of it under control but just a couple of quick questions regarding safety:

The scenario is for some unforseen reason the insulation fails on the high voltage power and the power is transmitted to the chassis.

To protect the occupants from electric shock am I better off-
A) Connecting the earth side of the high voltage to the chassis and relying on the fuse blowing before the occupants happen to touch the chassis or
B) not connecting the high voltage to the chassis at all and then having a relay connected to the chassis that would trip if it sensed any significant volatage thus disconnecting the high voltage crcuit.

Is it possible to complete the circuit through a person from the chassis to the ground we walk on? Or is it only possible to complete the circuit through to the -ve of the battery pack?

What have other people done to protect the occupants?

Electric Motorkhana and khanacross car

Posted: Mon, 19 Oct 2015, 19:58
by galderdi
Here are a couple of more recent pics:

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Electric Motorkhana and khanacross car

Posted: Mon, 19 Oct 2015, 20:12
by Jeff Owen
This looks like a good show and tell item for the meeting this Wednesday night. If you don't already have a trailer, I am sure we can find one.

Jeff Owen

Electric Motorkhana and khanacross car

Posted: Mon, 19 Oct 2015, 20:37
by galderdi
This Wednesday might be a little premature. The car isn't powered yet so it would be a pain to get it on the trailer.

And more importantly I need to disassemble the whole thing so I can flip it over and complete some welds underneath. Not to mention tidy some of the ugly welds I've already done :-)

Realistically I can't see it being ready for that sort of thing until the December meeting (if you have a December meeting)

But I will try to come along with some photos this Wednesday.

Electric Motorkhana and khanacross car

Posted: Tue, 20 Oct 2015, 03:47
by coulomb
galderdi wrote: To protect the occupants from electric shock am I better off-
A) Connecting the earth side of the high voltage to the chassis and relying on the fuse blowing before the occupants happen to touch the chassis or
B) not connecting the high voltage to the chassis at all and then having a relay connected to the chassis that would trip if it sensed any significant voltage thus disconnecting the high voltage crcuit.
NCOP14 requires B:

viewtopic.php?title=ncop-14-29-chassis-leakage&t=2619

If you connect one end of the pack to the chassis, then almost any accidental connection from a cable to chassis will result in an arc, heat, bright light, UV light, metal snot, and probably a blown fuse and loss of traction. An accidental touch of the other end of the pack will result in a nasty shock, perhaps death.

By contrast, if you get one such failure with an isolated system, there is none of this, and the vehicle continues to work. An accidental touch to either end (before the insulation failure), then there is likely only a very slight shock, almost certainly not fatal. The insulation monitoring system should detect the fault (perhaps only at next start), and should issue a warning. If you ignore the warning, then the next accidental connection will likely result in the arc and all the attendant excitement, and any accidental touch will result in the painful shock. But then you will be stupid for having ignored the warning.
What have other people done to protect the occupants?

Mexy, our red MX-5, with a 720 V pack, has a fully floating pack as required, and there is an insulation monitoring capability built into a part of our battery monitoring system. There are two "IMUs" (Insulation Monitoring Units), one for each half of the pack. That was mainly because we started off with the two half-packs in parallel (360 V), and wanted to switch to both half packs in series (720 V, as it now stands). All the IMUs do is switch a 100kR 7W resistor in series with an opto-isolator between one end of the pack and ground. The opto isolator effectively measures the current; if there is enough current to make the phototransistor conduct, then the test has failed. You always need two tests (so two resistors, relays, and optos in our case), because no matter where you do the test, if the leakage / short happens to be there, you won't detect it. The test position is a sort of blind spot for the insulation tester. So you test one end of the pack, disconnect, then test the other end. This all takes a fraction of a second, and is built into the delay whenever the key-switch comes on.

viewtopic.php?title=weber-and-coulombs- ... 111#p48111

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[ Edit: I forgot, this capability is also built into our latest BMS master, which we call a BMU (Battery Master Unit). ]

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Electric Motorkhana and khanacross car

Posted: Tue, 20 Oct 2015, 11:39
by galderdi
Excellent. Thanks for the reply and info. I will take a closer look.

Electric Motorkhana and khanacross car

Posted: Wed, 21 Oct 2015, 12:10
by galderdi
Can I buy one of the isolation monitoring systems or similar?
I'm not really in a position to construct my own.
I thought about attaching a dual pole circuit braeker. With one pole attached to the chassis so if it receives a zap from the high voltage it would trip that pole and also the second pole which would trip the main contactor thus removing the part of the circuit with the fault.

Electric Motorkhana and khanacross car

Posted: Tue, 27 Oct 2015, 12:01
by galderdi
This weekend just past I swapped the old steering rack for a fast ratio MR2 rack. It took a lot of modification but I am happy with the result. I then moved on to the last piece of firewall and fitting the pedals. I had to mount the master cylinder in a central position because the right suspension blocked the traditional position. That meant running a linkage from the brake pedal over the top of the steering and clutch to the new position of the master cylinder. Again a lot of fabrication was required but I am happy with the result.

Then last night I wired up a dial to control the available power. The dial has 10 positions roughly from 10% through to 100%. This will be useful for wet weather, testing, loading the car on the trailer and when I let other people drive it.

Electric Motorkhana and khanacross car

Posted: Mon, 21 Dec 2015, 18:56
by galderdi
I am still on track for the first 2016 motorkhana for Feb 7th.

All I need to do is:
•     Swapping the rear hubs and upgrading the rear springs to handle the weight
•     Brakes all round
•     Panels and dash
•     Belts
•     Another set of batteries
•     And a handful of other minor items

I estimate another 4 days effort and then some tweaks / adjustments

Electric Motorkhana and khanacross car

Posted: Mon, 21 Dec 2015, 19:14
by Rusdy
galderdi wrote: Can I buy one of the isolation monitoring systems or similar?
I'm not really in a position to construct my own.


There are several product already in the market for this (Line Insulation Monitor). One that my company use is this one: Bender LIM unit. Specific to EV is this one: LIM unit for EV

There is alarm and trip setting, and maybe can be connected to your automatic disconnection switch, if required.

The 'bender' unit is pretty expensive (industrial rating), but you may find cheaper one if you google around.

Electric Motorkhana and khanacross car

Posted: Tue, 22 Dec 2015, 19:21
by galderdi
Thanks Rusdy