Ways to reverse Series DC Motor -100% FWD 30% RVRS

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Ways to reverse Series DC Motor -100% FWD 30% RVRS

Post by Johny »

EV2Go wrote: What about a Gigavac GX14 or GX16 for forward motion and some piddly little thing for reverse?
Good idea. Even better if you can limit the current while in reverse. You could also parallel the forward contactors for higher current with careful cable layout.

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Ways to reverse Series DC Motor -100% FWD 30% RVRS

Post by bga »

It would be *necessary* to limit the current in reverse. Condider flooring the throttle:
The motor current goes to maximum (~1000A), this overwhelms the reversing supply so that the field becomes positive and the vehicle moves forward. Also, the field voltage will be limited by (reverse) conduction in the flyback diodes of the reversing supply, toasting it.

EVWORKS use and sell the nanfeng reversers, I know that they torture the things in their EVs and have had no problems with them.

For those concerned about high current, a quad of heavy (GX16?) contactors could be used for this purpose, but would be much more expensive than the chinese reverser.

Two reversers could be used in parallel, although the XG16 approach would be cleaner at that stage.
The 4 contactors could be arranged like the diodes in a full wave bridge, making the links/wiring easy.
Some interlocks would be needed, like throttle and relay sequencing.

The modular reversers default to 'forward' with no coils energised, whereas a quad would have to energise two coils at any time.

... back to my AC drive implementationImage
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Ways to reverse Series DC Motor -100% FWD 30% RVRS

Post by EV2Go »

Just thinking out loud... but if the cotroller already has a contactor built in that is normally open (NO) and you add a reversing conctactor that is normally closed (NC) that would reduce the current draw right?

Since if the reversing contactor is NC it requires no voltage to hold it closed?

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Ways to reverse Series DC Motor -100% FWD 30% RVRS

Post by 7circle »

If the Forward current is 1000A and the reverse current is 250A,
then 1:4 ratio of the same contactor would be needed.
Sharing current is very hard to equalise.

Image

The contacts can be jammed closed, so many contactors have Low rated Auxillary Contacts for feedback.

The built in Contactor is shown in the top left of the blue box representing the SOLITON1 Motor Controller. The power to pullin the contacts is low for some types, like the GIGAVAC's

The amount of contactors needed to make this work is why I thought there could be a simpler circuit that could give reverse at 1/4 of main current.

Also the maintenance of all those contactors looks difficult when they wear. The ALLBRIGHT and NANFENG can have the contacts replaced.
The GIGAVAC are sealed so would need to be replaced when they start to over heat or fail.

The GX14 350AMP with AUX NO/NC
gigavac site wrote:Contact Resistance
     Max @ rated carry current     .4 mohms
     Typical @ rated carry current .15 to .3 mohms
The GIGAVAC site has contact resistance for the GX16 600Amp
gigavac site wrote:Contact Resistance
     Max @ rated carry current     .3 mohms
     Typical @ rated carry current .11 to .2 mohms
     

If a performance EV is using Batteries that are rated with high C rates and capable of discharging 1000A at 250V, their DC internal resistance is going to be low. (Per cell 3.2-2.2V/1000A = 1mOhm per Cell x 80 = 80mOhm for the pack)

So 80mOhm for the battery compared to 2x 0.4mOhm for the top and bottom contacts. And with 4 in parallel that's reduced to 2 x 0.16mOhm.

I am impressed with the minimal resistance of the contacts.

But there are so many points for failure for the forward motion.
Building a mechanical support frame and wiring will be complicated too. The GX14 is available in a NC version this would reduce coil power in forward drive mode.

Adding a second reverse motor is also complicated.

The REVERSE MODE DC/DC is only enabled for reverse, but it is more complicated. The SOLITON1 has the features to include it but not as a standard implementation.

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Ways to reverse Series DC Motor -100% FWD 30% RVRS

Post by EV2Go »

Sorry I think I got that wrong way around...

The Soliton1 contactor is normally open so no current passes while the controller isn't powered up.

If the GX16 forward controller was normally closed it wouldn't draw any current (or maybe less).

if the GX12 or GX14 reversing contactor was normally open it wouldn't draw any current (or maybe less).

Since reverse would be used say 1/10,000 of the operational life it would rarely be used and would be the only time when the GX16 was open and the GX12-14 was closed.

Image

The controller could switch the contactors the same time it switches the current.

Image
Last edited by EV2Go on Thu, 21 Oct 2010, 21:26, edited 1 time in total.

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Ways to reverse Series DC Motor -100% FWD 30% RVRS

Post by 7circle »

Thats sound like good use of Normally Closed contactors to save power loss in the Coils.

Problem is I can't find the GX16 in a Normally closed version.
GIGAVC TABLE

Any idea on costs of the
GX12
GX14
GXNC14
GX16

Also it is good to now when the contactor is OFF before turning on the reverse contactor ON. These are the Auxiliary (AUX) contacts and can be made to be closed in the ACTIVE Coil Energised state or in the NORMAL Coil de-energised state.

Problem is only some GIGAVAC contactors have the AUX contacts available when the COIL is de-energised indicating the main contacts are not jammed/seized/welded closed.


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Ways to reverse Series DC Motor -100% FWD 30% RVRS

Post by bga »

From the EVWorks website:
    GX14 (2 models $195, $239) Not sure of the differences
    GX16 $545
    Nanfeng 400A reverser $185.

You'd definitely not want to use more GX16's than necessary.

I wouldn't be too worried about putting 1000A through a 400A rated contactor. Most of these things are conservatively rated like industrial switchgear is.
They are probably good for several times the rated curent for a few seconds, long enough to burn some rubber and get the battery to sag noticeably.

Whats the worst that can happen? The field gets shorted out or goes open and the car doesn't go anywhere then the foot is put down.

With the money saved on the cheap contactor, the spare can be quickly installed.Image

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Ways to reverse Series DC Motor -100% FWD 30% RVRS

Post by EV2Go »

7circle wrote: Thats sound like good use of Normally Closed contactors to save power loss in the Coils.

Problem is I can't find the GX16 in a Normally closed version.
GIGAVC TABLE

Any idea on costs of the
GX12
GX14
GXNC14
GX16

Also it is good to now when the contactor is OFF before turning on the reverse contactor ON. These are the Auxiliary (AUX) contacts and can be made to be closed in the ACTIVE Coil Energised state or in the NORMAL Coil de-energised state.

Problem is only some GIGAVAC contactors have the AUX contacts available when the COIL is de-energised indicating the main contacts are not jammed/seized/welded closed.


I think a GXNC14 (350A continuous) and a GX11 (150A) or GX12 (225A) would suffice. Only problem is fashioning it into a reversing contactor like the Nanfeng
bga wrote: From the EVWorks website:
    GX14 (2 models $195, $239) Not sure of the differences
    GX16 $545
    Nanfeng 400A reverser $185.

You'd definitely not want to use more GX16's than necessary.

I wouldn't be too worried about putting 1000A through a 400A rated contactor. Most of these things are conservatively rated like industrial switchgear is.
They are probably good for several times the rated curent for a few seconds, long enough to burn some rubber and get the battery to sag noticeably.

Whats the worst that can happen? The field gets shorted out or goes open and the car doesn't go anywhere then the foot is put down.

With the money saved on the cheap contactor, the spare can be quickly installed.Image


The price difference is the aux sensing to see if the circuit is open / closed.

Well plans are not to exceed the motor rating 500A by too significant amount say ~600A, so I think the 350A GXNC14 would do the job.
Last edited by EV2Go on Fri, 22 Oct 2010, 16:52, edited 1 time in total.

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Ways to reverse Series DC Motor -100% FWD 30% RVRS

Post by 7circle »

The AUX relay feedback is not relay needed as BGA mentioned as the motor, controller, or batteries wont be damaged as long as the motor controller can limit the current.

BUT.. if contactors a bypassing the FIELD winding the driver may keep a huge current passing in the motor as the motor is not making the vehicle move because it cant' generate Torque. So the health of the wiring, motor and contactors could be jeopardised. So the AUX contacts used to inhibit the overload would be valuable.

The NANFENG DPDT has the interlock built-in. [Edit - Opps - They don't Edit 2! - Oops they do if supply is from top to bottom.] But if they are paralleled that interlock is redundant. But 2 in parallel would cope better with 400A continuous.

So if you where satisfied with ~600A through the motor for forward and used two GX14 for forward and two for reverse that's 4x $195 = $800

Looking at the GXNC14 data spec this contactor is right on the limit of coping with 600Amps.

The contacts have macx temp rating of
225degC intermittent and
175degC continuous

And from that they have a 10 second rating of 710A for a 50degC Ambient.
A continuous rating of 400A for a 50degC Ambient.

Its all right on the edge of failure. So if the components are selected as such be prepared for regular replacements.

This doesn't make sense to me personally, that's why I thought a different approach could be found.

The FIELD reversal with negative potential with a
1000W 3.3V supply,
1mH 400A filter
a 4A relay and FUSE
a 400A contactor
would be worth considering.

[Edit - Opps - They don't (NANFENG DPDT allows a bypass short)]
[Edit 3 - Oops they do if supply is from top to bottom not left to right.
Image
Sorry fro my brain lapse, I had considered this previously]

[EDIT - NANFENG do have some bigger DPDT ZJQ6XXP DC contactor
Last edited by 7circle on Sun, 24 Oct 2010, 11:10, edited 1 time in total.

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Post by 7circle »

bga wrote: From the EVWorks website:
    GX14 (2 models $195, $239) Not sure of the differences
    GX16 $545
    Nanfeng 400A reverser $185.

You'd definitely not want to use more GX16's than necessary.

I wouldn't be too worried about putting 1000A through a 400A rated contactor. Most of these things are conservatively rated like industrial switchgear is.
They are probably good for several times the rated curent for a few seconds, long enough to burn some rubber and get the battery to sag noticeably.

Whats the worst that can happen? The field gets shorted out or goes open and the car doesn't go anywhere then the foot is put down.

With the money saved on the cheap contactor, the spare can be quickly installed.Image


The NANFENG DPDT reversing contactor has a 400A rating based on 4x Ie for 5 seconds. I assume Ie is the 100A rating mentioned in the INFO-PAGE in the same cell

You mention "the car doesn't go anywhere when the foot is put down."
this make me think that the 100% throttle is pushing max controller current into the ROTOR because the contactors are bypassing the current. (Ah thats why they but the reversing on the Rotor so the Commutator doesn't get damaged when the Contactor jams up)

But how long will the driver keep putting the big currents through by-pass. Not realising the wiring and is getting overheated.

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Post by EV2Go »

Why would I need 2 * GX14 for reverse I don't need 600A for reverse?

Or is it a case of the forward and reverse must match.

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Post by Tritium_James »

Maybe I'm confused here, but when you guys talk about 30% in reverse, don't you really mean 30% speed? I think you're going to still need 100% current because otherwise you won't be able to reverse up hills, gutters, etc.

So this would mean any contactors and other bits in the motor connections are going to have to be rated to full motor current, for both directions. I don't think there's any free lunch...

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Post by EV2Go »

Not looking for a free lunch, perhaps my limited understanding is causing confusion.

I figure 250v - 600A forward and say 50V - 100A in reverse (it's only a trike) so I figured you would use lower rated contactors in reverse.

If the motor only sees 50v because of the reverse limiter in the controller, that has to effect current doesn't it?
Last edited by EV2Go on Sun, 24 Oct 2010, 08:46, edited 1 time in total.

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Post by Tritium_James »

EV2Go wrote:I figure 250v - 600A forward and say 50V - 100A in reverse (it's only a trike) so I figured you would use lower rated contactors in reverse.
Oh, OK. Yes, that's probably OK then. For a car, I think you'd want to design it for full torque in reverse too, otherwise you might get stuck in a parking spot where you have to reverse it out uphill or something.
EV2Go wrote:If the motor only sees 50v because of the reverse limiter in the controller, that has to effect current doesn't it?
No. Since at stall (eg reversing up a hill out of a tight parking spot) there is no back-EMF from the motor (because it is at zero speed, or close to it), the controller can quite easily develop full current from only a few volts, maybe up to 10's of volts depending on the resistance of the motor, brushes, wiring, contactors and controller itself. A more efficient system will be able to develop full current at a lower voltage.

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Post by 7circle »

EV2Go wrote: Why would I need 2 * GX14 for reverse I don't need 600A for reverse?

Or is it a case of the forward and reverse must match.


No they don't need to match. It may be cheaper to keep them the same though.
If you can source a quote, its just a pain that they
GX16 @ $545
GXNC14 ???
GX14 @ $195 or 245 with AUX NO SPST economiser
GX12
GX11

So estimating prices and looking at the combinations:
2FWD GX16 @$545 and 2RVS GX16 @$545 would be about $2200
2FWD GX16 @$545 and 2RVS GX14 @$195 would be about $1480

6FWD GX14 @$195 and 2RVS GX14 @195 would be abount $1560
4FWD GX14 @$195 and 2RVS GX14 @$195 would be about $1170

As these contactors are not for emergency disconnect and switch with NO current (normally) they could be constructed in many ways.
So there are many options. A mechanical gear lever could move metal plates to make a Big DPDT Switch would work. But the design would take alot of knowledge and effort to get right so it will be safe, reliable, efficient and affordable.

(OR ditch the DPDT and use the isolated power supply to reverse the FIELD)

Its always a bit of a battle to consider best theoretical and best economically.

I still haven't got the Kf and Kr factors for the Kostov 11" Motor.
Or worked out the thermal dissapations factors of the Field and Rotor.
So its general knowledge approach as normal to nous it out.

For the SOLITON1 controlling the 11" KOSOTOV from a high power 250Vdc Battery.
KOSTOV Torque Curves for Different Connections

Trying to estimate the Power/Torque needs:
Forward Target
- 300A Continuous Field and Rotor
- 600A 10 min Field and Rotor
- 1000A peaks for 20 Seconds
- Vout 100% of Vbat

Reverse Target (Field Current opposite to Rotor)
- Vout: 30% of Vbat (~ 85Vdc) to limit speed
- (Slow throttle response would be good too, with such power on tap)
- I_Field Continuous of 150A Continous Field, and I_Rotor 150A

Working out the variation of Field and Rotor Current with the FIELD PSU is complicated.

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Post by EV2Go »

If I really needed to resort to that many contactors I would seriously have to consider a mechanical reverse and do away with all of the contactors (except the one in the controller of course).

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Post by Electrocycle »

what's wrong with a single contactor reversing the field (or armature) connections?
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Post by 7circle »

EV2Go wrote: If I really needed to resort to that many contactors I would seriously have to consider a mechanical reverse and do away with all of the contactors (except the one in the controller of course).


Yes those high current Gigavacs aren't cheap.

So how much would a reverse gear box cost. It would mean you loose direct forward drive, it has to pass a gear ratio, unless the differential had a change over , but no likely in 90deg Dif. Sounds like the problem of adding contactors to get reverse.
Electrocycle wrote: what's wrong with a single contactor reversing the field (or armature) connections?


How would you get reverse with a single contactor.
I assume you mean a single coil moving the DPDT contacts.

The NANFENG use two coils and are two separate SPDT only rated to less than 250A continuous. The spec does say they are tested for 1000Vac for 1 Min, so I assume this means a 1000V to Chassis and coil. To maintain isolation on such a frame it would be important to keep dust away that could allow leakage paths. A battery pack getting up over 300V charged, is a worry, I'm worried at over 48V.

I would like to know how Ian Hooper's MX-5 has travelled using the NANFENG for connection to the Armature/Rotor. The battery back is 40 cells so 160Vdc max.
You can see the NANFENG close to the front motor hear:
http://zeva.com.au/conversion_blog/larg ... 010845.JPG
The EVALBUM has it with a 200V 750A controller.
There is no dust or splash protection I can see in the pics.
It would be good to hear an update to the blog, as the 5000kM mark would show up any obvious issues.

It would be helpful to know the voltage drop from the Controller to Armature/Rotor via one side of the reversing contactor, when current is up near 500A or more. You could then double this (or better measure it) for the other side to get power loss.

The NONCHN YUEQING NANFENG www.kingnan.com website spec info appears very generic and repetitive between products, which makes me feel its not accurate for the product it is displaying. Tried the google translation of the Chinese language page too.

Using two parallel NANFENG's could get the current up, and the extra bus bar links could help with heat-dissipation. 2x $185 is $370.

Remember power loss is I²R so going from 400A to 800A is 4 times the power loss even with out positive temperature co-efficient rises.

I hope this is helpful to some people, I'm also interested in CONTACTORs or relays for Series / Parallel or Star / Delta connection changes, which considers similar issues.

Building a mechanical switch with a stack of high current vacuum contactors could be interesting, if the contacts are cheap.

Its a bit hard to compare contactors used for supply to controllers as they only supply max current when the controller is out putting max power.
The motor side gets huge currents from standstill to max power, as the current relates to torque.

I bolded the important issue above of knowing the losses of the reversing contactor as when your accelerating at low speeds this contributes a larger proportion of losses than at high speeds.

IF the Voltage drop on either side is 5V then the power loss at 600A is 6kW. That's a lot to loose, when a direct link it would be a 100th that.
I'm thinking the 40mV/100A per contact is not realistic one the whole reversing contactor and cable package is installed.

I hope I'm wrong.

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Post by EV2Go »

Couple of ways I can see this happening.

First and probably easiest would be like the pic below.

have a high torque starter (~3hp) directly in front of the motor and leave a bit of aux shaft sticking out. As the starter turns it throws the bendix out. Put some kind of soft 1 way coupling on both the motor and the starter.

Second way is leave a bit of aux shaft and fit a flexplate to it and mount the starter parallel to the Kostov.

The first way has no parasitic losses on the motor because once you take your finger off the reversing button the bendix retracts and the starter is totally disengaged (other than the weight of a small rubbery coupling). Second way adds the weight of the flexplate.

Third drive it off the output shaft. Nowhere near as easy as I wanted to do a direct coupling to the diff.

Image

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Post by 7circle »

EV2Go wrote: Couple of ways I can see this happening.

First and probably easiest would be like the pic below.

have a high torque starter (~3hp) directly in front of the motor and leave a bit of aux shaft sticking out. As the starter turns it throws the bendix out. Put some kind of soft 1 way coupling on both the motor and the starter.

Second way is leave a bit of aux shaft and fit a flexplate to it and mount the starter parallel to the Kostov.

The first way has no parasitic losses on the motor because once you take your finger off the reversing button the bendix retracts and the starter is totally disengaged (other than the weight of a small rubbery coupling). Second way adds the weight of the flexplate.

Third drive it off the output shaft. Nowhere near as easy as I wanted to do a direct coupling to the diff.

Image


Would you just use a push button to operate the starter?
So if it was 2.2kW Electrical (it may be alot more) 2.2kW/12V = 183A
Tried to get specs on the MAX for torque and 12V RPM at no load.

So you might push it a few times to inch back slowly.
Will it drive it over curbs?
or up small hills?

What limitations would you see this having?
Cost to get it to work?

With direct pressure to DC motor shaft with no reduction gear ratio, torque will be much less than if it normally goes on the edge of the flywheel.

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Post by EV2Go »

Don't know if you have ever tried it, or needed to try it, but a very long time ago I was stuck (can't remember the reason maybe out of fuel) and I couldn't push the car (HQ Panel Van) by myself because of the slight incline or the road surface. So I just put it in first and cranked the key and it moved it well enough to get it off the road maybe 10 feet or so.

That was on just a standard Holden starter motor, not a high torque monster like these. So in my particular case I think a starter would do the job adequately.

Bearing in mind though that is a gear reduction on the flywheel, on the reverse gear ratio and a diff ratio.

Maybe I would need a flexplate to make its life easier.

Cost maybe ~$400 give or take and depending on the starter, some are as cheap as US$120.

If I put the button on the handlebars (as I would as part of the controls) I could get my fat bum off the trike and that would save 85-90kgs it had to push.
Last edited by EV2Go on Mon, 25 Oct 2010, 12:40, edited 1 time in total.

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Post by EV2Go »

Just looking at the specs of that cheapy I posted a picture of ($124)

Maximum Recommended Compression Ratio 10.0:1
Gear Reduction Ratio 3.75:1
Mounting Block Material Billet aluminum
Quantity Sold individually.
Notes This starter is designed for stock, low compression applications using stock timing advance curves .

With their gear-reduction drives, heavy-duty Powermaster PowerMax starters really crank out the power--160 ft.-lbs. of torque. So, they can handle engines with moderate compression ratios.

160ft-lb would be enough wouldn't it?

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Post by EV2Go »

Ok here is a wild and wacky idea that is totally left of field...

1)     What if I put an electric clutch off an A/C unit on the front of the motor (seen this done and we have discussed this before).
2)     Run a fan belt or direct connect through coupling to a generator, this provides the regen I would have liked to use under deceleration. Which recovers some (albeit little) power, also helps brake pad and rotor wear.
3)     Reverse the generator somehow to make it act as a motor for reverse...

Extra distance / less power – Win
Extra braking / less wear – Win
Reverse at minimal cost – Win
Compact design - Win

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Post by Johny »

How about one of those 5-10kW BLDC motor/controller combinations.
Not usually enough power for more than a small bike but plenty for your application and regen. comes for free. The BLDC controller and A/C clutch are powered up by first small application of rear brake lever. Have to find one that will handle 250VDC though.

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Post by EV2Go »

Or a button on the hand controls / better yet triggers off a 0v reading from the throttle and a button for reverse. That way neither regen or reverse could be activated whilst throttle above zero.
Last edited by EV2Go on Wed, 27 Oct 2010, 06:03, edited 1 time in total.

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