Contactor coil diode.

Have you made or bought a converted vehicle if so this is for you
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aminorjourney
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Postby aminorjourney » Thu Aug 23, 2007 2:00 pm

For what it's worth John's diode photos are great! If you don't have the diode in then chances are the controller won't work (it goes into protection mode)

Chris, I think you'll need the diodes in parallel across the low current coil of the contactor. If you download a curtis manual it should explain it there :)
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EVguru
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Postby EVguru » Thu Aug 23, 2007 9:05 pm

If you don't have the diode in then chances are the controller won't work

I don't think the Curtis would be able to detect a missing diode. It's only a simple add on analogue card for the F/R contactor control. It obviously does detect a shorted contactor coil or freewheel diode though.

Does the 12v coil need one?


Yes, otherwise the ignition switch will eventually fail.

If the vehicle was to runaway due to a stuck throttle, failed controller etc. then you would be relying on this contactor to stop the vehicle. It's best therefore that it drops out smartly. A bi-directional transorb (or similar) in parallel with the coil would do the job.

Something like; http://uk.farnell.com/jsp/Semiconductor ... ku=9802185

If you do ever have a runaway, it will take you several seconds to remember the ignition switch. Having some kind of instinctive shutdown, like clutch and brake pedal together, might be a good idea.
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nino500
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Postby nino500 » Wed Sep 03, 2008 3:33 pm

Hi, I just tuned in to this thread.

I haven't started putting any electrics together yet but I know I'm going with 72 volts and I have a coice of Altrax axe or Curtis controllers.

I'd like to have a reliable failsafe in case of runaway/welded contactor situation. Would it be possible to have a mechanically seperated emergency contactor? Perhaps pulled open by hitting the clutch pedal (no actual clutch fitted so this would be its only use)

Another question about contactors: We all know that series motors can run several times over their rated voltage. What about contactor coils? If a system voltage was upped from 48 to 72 volts would the 48 volt contactors handle it or would this be suicide?

Cheers, Nino.

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Postby GregsGarage » Thu Sep 04, 2008 3:07 pm

nino500 wrote:I'd like to have a reliable failsafe in case of runaway/welded contactor situation. Would it be possible to have a mechanically seperated emergency contactor? Perhaps pulled open by hitting the clutch pedal (no actual clutch fitted so this would be its only use)


I have seen circuit breakers used with a remote panic button/lever inside the vehicle, operated by a cable. The trick is finding a suitable circuit breaker!

nino500 wrote:Another question about contactors: We all know that series motors can run several times over their rated voltage. What about contactor coils? If a system voltage was upped from 48 to 72 volts would the 48 volt contactors handle it or would this be suicide?

Cheers, Nino.


Motor ratings tend to reflect what the manufacturer was asked to supply rather than the capability of the motor. This does not apply to fuses, circuit breakers, wiring, switches, contactors etc. You must not exceed the manufactures ratings.

For a contactor there will be 2 voltage ratings, one for the coil that operates the contactor and the maximum voltage the contactor can break across the contacts. Make sure you are looking at the DC ratings, they will be much lower than the AC ratings. Since the coil and contacts are isolated from each other you can increase pack voltage to the maximum ratings of the contactor as long as you don't change the voltage to the coil. The coil voltage must match the voltage you are going to operate the coil with, normally 12 volts, but check this as it can be different for some controllers, My Kelly controller uses 24 volts so I have a seperate DC-DC convertor to operate the contactor and control side of the controller. I can then use any traction pack from 24v to 72v with this motor and controller without having to change anything. 8)
Greg Fordyce

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nino500
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Postby nino500 » Thu Sep 04, 2008 3:28 pm

Thanks Greg,

That confirms my gut feeling on the contactor point.

On the emergency stop side, I have a 126 which has cables operated by levers for choke and starter so I reckon either would do for an emergency stop. The clutch pedal would be more of an automatic reaction but if anybody else was driving they might accidentally hit the clutch as one does when driving an auto after a manual.

Nino.

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Postby GregsGarage » Thu Sep 04, 2008 7:09 pm

I am working on some battery boxes for my 126, some are going to be mounted were the fuel tank was and the space opposite. The heater hoses come out here, so I have been considering running a couple of cables where the heater hoses were (or actually still are at the moment) and connecting them to a Albright emergency disconnect switch. Not sure were it will go, but a big red button just says "hit me if it all goes pear shaped".
http://www.albright.co.uk/index.html
Greg Fordyce

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Postby GregsGarage » Thu Sep 04, 2008 7:19 pm

EVguru wrote:If the vehicle was to runaway due to a stuck throttle, failed controller etc. then you would be relying on this contactor to stop the vehicle. It's best therefore that it drops out smartly. A bi-directional transorb (or similar) in parallel with the coil would do the job.

Something like; http://uk.farnell.com/jsp/Semiconductor ... ku=9802185


Paul, would that be suitable for a 24 volt coil or would it be safer with something like this;

http://uk.farnell.com/9885498/semiconductors-discretes/product.us0?sku=stmicroelectronics-p6ke39ca

Thanks,
Greg Fordyce

Daewoo Matiz
http://www.evalbum.com/4191

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geekygrilli
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Postby geekygrilli » Thu Sep 04, 2008 7:57 pm

Hi Greg

I have a big red stop button on my dash for if things go wrong. Its quite obvious what its for, but it worries some passengers! My 2 year old daughter just wants to push it all the time!

Picture of button here, it is the Albright one and it works fine. It shuts off +ve to the controller. Not had to use it, yet.


http://www.batteryvehiclesociety.org.uk ... 67&start=0
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EVguru
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Postby EVguru » Fri Sep 05, 2008 3:37 pm

I really don't like the Big Red Button approach. It simply doesn't belong in a road car.

Having experienced a stuck throttle more than once over the years and having heard the experience of others, I seriously doubt if you would remember to use the BRB in an emergency. It takes far too many panic filled seconds to remember to reach for the ignition stwitch, a control you use every day.

Another reason for avoiding the BRB is that in many cases it requires bringing high voltage/current wiring into the cabin (the Fiat 126 is one exception).

Adding extra contactors is good. I always recommend two anyway, so the battery is fully isolated from the controller when the vehicle is off. I keep meaning to design an 'electronic circuit breaker' add on to latch off a contactor in the event of an overcurrent. This has the potential to be much faster than a fuse or conventional circuit breaker, both of which have a current/time curve, needing a large overcurrent to trip or blow fast.
Paul

http://www.compton.vispa.com/scirocco/
http://www.morini-mania.co.uk
http://www.compton.vispa.com/the_named

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geekygrilli
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Postby geekygrilli » Fri Sep 05, 2008 4:27 pm

I agree, Paul, the BRB is not in every day use, so can quite easily be forgotten about in a panic.

For many reasons I now wish I'd left the clutch in!


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