Contactor orientation

Technical discussion on converting internal combustion to electric
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Contactor orientation

Post by Taxman » Fri, 29 Nov 2013, 00:47

Hey guys,

So I'm wading through the mind swamp that is the circuit for my motorbike conversion. I've just noticed that my main contactor has a positive mark on one terminal. It'll be on the positive line, so does that mean I need to connect the battery +ve to the blank side of the contactor, then the +ve side of the contactor on to the manual contactor, which incidently also has a + mark on one side.

Why would it matter which way a contactor is wired? It's just a lump of copper across two lumps of copper, right?

Also, does it matter which way the shunt is orientated? These are all pretty basic questions, I know, but it's one of those things, where you're sure until you have to actually put it together.


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Contactor orientation

Post by jonescg » Fri, 29 Nov 2013, 01:35

Contactor - yes. There are small magnets which "blow out" the DC arc which is formed, especially when opening under load (even a small one). The direction of the current flow will determine how effective the "blow" will be from the magnetic field. If I'm not mistaken, the terminal marked + goes to the highest potential side of the circuit (that is, the positive terminal of the battery).

The shunt doesn't matter, but what does matter is the wiring to the current sensor. It records a tiny voltage drop which is proportional to the current flow. That voltage difference will be either positive or negative, depending on the way you wire it up.

Good luck with it!

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Contactor orientation

Post by Taxman » Fri, 29 Nov 2013, 02:09

Awesome, thanks!

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Post by BigMouse » Fri, 29 Nov 2013, 03:34

I've often wondered, on AC conversions, what happens if you need to open the contactor during regen. The potential would be reversed.

I suppose the controller would drop out as it senses a rising DC bus voltage within the controller and extinguish the arc. Regen can't occur due to shorted IGBTs (with an induction motor) either since commutation is required. I suppose it's relatively safe.

If not, there'd be a need for dual contactors installed with opposing polarity. Maybe on PMAC/BLDC/IPM this could be something to consider?

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Post by coulomb » Fri, 29 Nov 2013, 13:47

BigMouse wrote: I've often wondered, on AC conversions, what happens if you need to open the contactor during regen. The potential would be reversed.

I've wondered too. Especially since if something goes wrong and you reach for the kill switch, you've probably taken your foot off the pedal, and might be mashing the brakes, either or both of which will induce regen.

Regen current is less than maximum drive current, of course, so it's not too bad. But regen could still be 40-60% of maximum drive current, so that's quite significant.

In the case of our MX-5, we turn off the contactors through the keyswitch. So the controller will get a zero torque command eventually, but it might take a few milliseconds to come through. It's possible the arc may not extinguish until that command comes through, which may damage the contacts. But at least it should be pretty much instantaneous as far as the driver is concerned.
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Post by Johny » Fri, 29 Nov 2013, 14:32

In the Vogue there in an opto isolator that kills gate drive in the controller (Inhibit input) when the 12V is dropped to the main contactors.
Image
I also use this input to stop the controller alerts sounding when ignition is turned off (which causes BMS monitor alerts when the 12V enable disappears) while the controller caps are discharging.

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Contactor orientation

Post by Taxman » Fri, 29 Nov 2013, 14:51

Awesome info guys,

I've been looking for circuit examples, and some have the 12v loop that fires up the main contactor going through the throttle microswitch. So that means that the contactor is opening every time you take your hand off the throttle. Do I want the contactor to be opening and closing all the time like that? Or would that be alright if I have a precharge resistor and suppression diode on the contactor? I was just thinking it would shorten the life of the contactor or controller.



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Post by Johny » Fri, 29 Nov 2013, 15:01

Personally I would not be opening and closing the contactor with the throttle Aux. switch. Use the switch to somehow ensure that the throttle is all the way off (say - short the controller throttle input). Do this using separate wiring so it's a safeguard should the throttle pot wiring ground be disconnected.
There may be another input on the controller for this purpose.

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Post by acmotor » Fri, 29 Nov 2013, 16:43

Considering the considerable capacitor bank in the VFD (controller)....

At the actual instant when the contactor opens between battery and VFD DC bus, the voltage across the contacts is zero, so no arc. This increases rapidly as the DC bus goes up or down depending on what is going on in the VFD, edit: but dv/dt limited by caps. Either way the VFD handles its DC bus safely.

So no issue for the contactor.... unless there is a major short in the VFD and then the contactor (assuming kilovac or similar with mag w/o) is already in the correct polarity.   

Red suzi had the main contactor (12 x simple 48VDC contact relays in series, one on each battery module) on a time delay (approx 100ms) produced by a 2mF capacitor and series diode across the coil of a feeding relay that came from ign switch and Estop circuit. The feeding relay aux contact performed an instannt coast of the VFD and 100ms later the contactor openned. This ensured that the VFD had let go and VFD DC bus was at the same resting potential as the battery bank (assuming no catastrophyic fault existed) before the relays openned.
In fact, this circuit worked in test with just one 48VDC relay in all sorts of induced shutown tests.... not recommended to use one low V relay only, but proved the point.
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Post by 4Springs » Wed, 08 Jan 2014, 20:40

jonescg wrote:If I'm not mistaken, the terminal marked + goes to the highest potential side of the circuit (that is, the positive terminal of the battery).

The positive terminal of the battery, so the negative terminal of the nearest cell?
I'm putting my contactors back in again now. Last time I didn't pay attention to the orientation, but since I read this thread I'd like to get it right this time. The contactor I'm looking at is in the middle of the battery, so it is between two cells. If I understand correctly what jonescg has said, then I treat the contactor as if it is another cell. So from cell 24 +ve to contactor -ve, then contactor +ve to cell 25 -ve.
Is this correct?


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Post by Johny » Wed, 08 Jan 2014, 20:48

No, that's exactly the opposite of what jonescq said.
Imagine you place a voltmeter across the contactors open contacts.
Whichever terminal measures MORE positive should be the + terminal.


Last edited by Johny on Wed, 08 Jan 2014, 09:49, edited 1 time in total.

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Post by jonescg » Wed, 08 Jan 2014, 20:50

From EV Source:
"Note on A1/A2 connections: due to the magnetic blowouts, it is important that the connection is made with polarity observed. Current flows into A2 (+), and out of A1 (-)"

Conventional current or actual current? Image
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Post by Johny » Wed, 08 Jan 2014, 21:00

jonescg wrote:Conventional current or actual current? Image
Yes, it's a bit confusing to indicate current direction.
See little plus signs on the EV200 contactor main terminals in this diagram.
Image
Last edited by Johny on Wed, 08 Jan 2014, 10:03, edited 1 time in total.

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Post by jonescg » Wed, 08 Jan 2014, 21:16

Hmm, just checking my race bike's power layout and I think I have them in backwards. You'd think Gigavac would have made it clear with a single diagram...
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Post by Johny » Wed, 08 Jan 2014, 21:23

Someone should verify my understanding of this as well before everyone changes everything.
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Post by zeva » Wed, 08 Jan 2014, 21:32

Yep I'm pretty sure Johny is correct, and the quote from EV Source (for conventional current).

+ (Kilovac) or A2 (Gigavac) should be the anode, where conventional current flows in.
- (Kilovac) or A1 (Gigavac) should be the cathode, where conventional current flows out.

I kinda wish they just labelled them "A" and "K" instead.. would be more intuitive.
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Post by acmotor » Thu, 09 Jan 2014, 00:40

Holding a kilovac EV200AAANA in my hand now it clearly has +A1   and   -A2 (right terminal) cast into the plastic, as also noted on the data sheet. (Not what Ian suggested ?)
I connect +A1 to the battery + terminal.   The battery + terminal is the most + potential in the system. Except with regen but then regen should not be occurring if the relay is being opened.

I agree with Johny's diagram.

Note this polarity only effects the magnetic wipeout function on opening and relay will break either way round and you would only know there was a problem if it were breaking high currents (hundreds of amps at hundreds of volts). You could use one for years an never know there was an orientation issue until you needed it to work under stress.

Edit: still getting it right.
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Post by zeva » Thu, 09 Jan 2014, 01:03

Gosh, how confusing. I thought the Kilovacs were marked with + and - and the Gigavacs A2 and A1. So the Kilovacs have +A1 and -A2.. And the Gigavacs appear to have -A1 and +A2:

http://www.greegoo.cn/UploadFilesother/ ... sion-1.jpg

One would be forgiven for getting confused. But I think we're in agreement: whichever one says + gets connected to B+.
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Post by acmotor » Thu, 09 Jan 2014, 01:28

Yep. Good advice Ian.
Look for + and connect it to plus.        ( not like cells in series )
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Post by coulomb » Thu, 09 Jan 2014, 01:58

jonescg wrote: Conventional current or actual current? Image


It's always conventional current (positive to negative), but the smiley face says you probably knew that already. Just for total clarity, then.

I also note that the polarity sensitivity means you have to choose between drive current and regen current, assuming the vehicle has regen. You would obviously connect it for drive current, as indicated above, positive of the pack to positive on the contactor. But this means that if you have to panic open in a heavy regen situation, the magnets will be working against you. (E.g. when the crash sensor opens the main contactor(s) in an actual crash.) And in a panic situation, it's actually likely that your foot will be planted to the brake pedal, which will likely cause maximum regen. Regen current is always less than maximum drive current, but in some designs, it can be say 40-60% as much.

In the MX-5, we largely ignore this problem. (When the Driver Control Unit detects the crash sensor, however, it does go to "off" mode, so there is no drive or regen current.)

So that's one reason for using non polarised contactors in an AC conversion. But the choices in affordable contactors that handle high voltage are quite low.
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Post by coulomb » Thu, 09 Jan 2014, 02:06

zeva wrote: I kinda wish they just labelled them "A" and "K" instead.. would be more intuitive.

Oh, please no Image It does my head in how they call anode and cathode the opposite in polarity on batteries compared to LEDs.

I'm sure that there is a good reason for it.

I think the A1 and A2 are irrelevant labels, just take heed of the + and -.
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Post by jonescg » Thu, 09 Jan 2014, 15:29

From Gigavac:

"Hi Chris,

The contactor should be oriented so the flow of current through the contactor is from +(A2) to –(A1). In this case the battery should be hooked to the A2 or + terminal and the load hooked to the A1 or - terminal.   

http://www.gigavac.com/apps/direction.html

Please let me know if you have further questions.

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Post by acmotor » Thu, 09 Jan 2014, 16:35

So kilovac and gigavac can't get their act together on A1 and A2

That is as bad as menekes vs J1772.      Can't we have a standard ?

At least we have the answer to the relays.... Read the + on the relay.
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Post by DavidC » Thu, 09 Jan 2014, 23:24

The A 1 and A 2 markings are usually on the coil of a contactor and with dc current we are usually worried about the flow thru the contacts.

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Post by Johny » Fri, 10 Jan 2014, 14:23

Not in this case David. You can just see the A1 marking on the EV200 in this picture.
Image

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