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 7circle » Tue, 12 Oct 2010, 21:05

Adding Contractors/Relays to reverse motors adds losses, complexity,
The reversing of vehicles is slow speed so power needed is small.

Also the traction Pack is usually isolated from the 12V Axillary supply.
Using this supply to drive the motor as a "Shunt Field Motor" would drive the currents in opposite directions than normal forward drive current from the Motor Controller.

Image

The Soliton1 DC Motor Controller has only two terminals for motor connection.

So adding an isolated adjustable current source for reverse would keep the main drive very efficient and reliable as it doesn't have contactors or other switching devices absorbing losses in the 1000A path.

So to reverse the Main Contactor is disabled and the connections across the field is enabled and the throttle adjusts the current into the motor. it could be kept old school with just resistive current limit from a 12V power supply. And just a pulsed ON/OFF. Or a DC/DC with current control could be used. Say the DC/DC used to Charge the Aux Battery switched over to power the reverse when needed.

Any comments?


[Edit - Added tot he Topic Description "-100%FWD 30% RVRS"]
Last edited by 7circle on Tue, 19 Oct 2010, 19:21, edited 1 time in total.

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

Post by 7circle » Tue, 12 Oct 2010, 21:37

I'm collecting my thoughts already.

Shunt will have limited stall torrge due most of the current going through the rotor and the required field current for low RPM torque will be negligible. Image

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

Post by 7circle » Tue, 12 Oct 2010, 23:28

The Sepeately Excited (SEPEX) approach would be better.

Image

The dotted orange current would charge the DC Bus cap to 12V max.
If the CAP has 100V it can't discharge via the Power FET/IGBT due the intrinsic diode.

The dotted green current is limited by the voltage of the Field.
If the field voltage is larger (by ~0.7V) then the current stays in the rotor only.

ISOLATION: Does the AUX battery need to be isolated from the Motro Controller?
If it does then the investment in extra 12V output DC/DC could be acceptable if they can be switched between charging the AUX circuit or reverse function by relays. A 1000W 300V/12V Charger could be split to 3 x 330W DC/DC's.

At least the 2 x 1000A contactors for Reversal are eliminated. And their losses.

Assuming you need 5Km/h and 1000kg up 30deg Hill
P= 1000 x 9.8 x Sin30 x 5/3.6 = 6.8kW

That's heaps, too steep, 10deg is 1.1kW @ 5km/h
That's still large so of the speed was crawl at 1km/h and 10deg
power is 5th at 220W.

So if Motor gives 100km/h from 240V at no load
5km/h needs about 20th of 240 or 12V. (Current P/V=220W/12V=~19A)

Efficency is dependent on the current control method.

So matching the current for the Rotor and Field is motor specific.
Might be worth looking at the Kostov parameters to get current estimates.

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

Post by EV2Go » Wed, 13 Oct 2010, 01:23

I have absolutely no idea what your talking about but it looks interesting Image(I tell a lie I actually follow it ever so slightly)

I don't understand the full workings of what you've drawn, but conceptually it makes sense to use a lessor power source for the limited reversing functionality and bypassing losses in the main power circuit.

It's brilliant, now let's see if you can make it work. Image

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

Post by EV2Go » Wed, 13 Oct 2010, 02:22

An idea just came to me along the same lines as what your trying to do...

What if you used a second controller? When the igniton key is turned of the controller is disconnected, no power flows from the controller to the motor.

Now if you had both controllers powered by a single On-Off-On switch that way both controllers couldn't be powered at the same time.

Not sure if it would try push power back up the other controller, but at least that's the basis of the idea.
Last edited by EV2Go on Tue, 12 Oct 2010, 15:24, edited 1 time in total.

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

Post by 7circle » Wed, 13 Oct 2010, 07:11

Yeah, The second controller would need to be a SepEx type but of lower power rating (lower cost) than the main Power Controller.

Comparing to contactors when all contactor changes occur with no current.
To Reverse a 300A/250V motor with contactors would take
2 Large 300Adc 1000A Surge, 12Vdc Coil (2 x $200) ?? Maybe less.
(est. 40mV drop per 100A per contact => 200A@160mV=32V plus extra wiring)
And the smaller contactors for reverse power:
2 Medium 50Adc 100A Surge, 12Vdc Coil (2 x $20) ??

So if you could use the AUX 12V Charging system, you get more value out of it. Two 250V/12V@13A (150W) DC/DC PSU's (2 x $100)

Kostov 11" Motor Feild resistance looks like 0.025Ohm in parallel
and Motor Rotor resistance looks like 0.75ohm, so... [Edit thats 0.075ohm from graphs not real measurement, my measurements may be off due to saturation]
Looks like less than 3V is required. So a 3.6 to 5V at 100A (500W) DC/DC with current ref would kick it.

Looks also like a single supply would work with a Contactor across the Controller Motor Terminals to short out the Flyback Diode to eliminate the power loss of (0.85 *100A = 85W).

Image

So I reckon a power supply with Vout:0-4V/100A from Input: 200V-400V would be very handy to charge up or test Large LiFePO4 Cells.

Mean Well PSU's from PRocon Website has a SP-480 for $270 or a RSP-1000.
These would need to have remote signal Pulsed to Throttle to get variation. Not so tidy.

Plenty of other sources for PSU with 5Vmax : 0-100A current regulation

Any way I'm still more for AC motors so I'm not sure if I get much more value out of looking into this.

[Edit thats 0.075ohm from graphs not real measurement, my measurements may be off due to saturation]
Last edited by 7circle on Fri, 29 Oct 2010, 17:45, edited 1 time in total.

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

Post by EV2Go » Wed, 13 Oct 2010, 07:28

Andrew had an excellent suggestion of something he had seen, and that was to use a starter motor to back up. Most are a couple of HP enough to do the tiny bit of reversing we're talking.

But I definately like the train of thought and where you're going with this.
Last edited by EV2Go on Tue, 12 Oct 2010, 20:29, edited 1 time in total.

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

Post by Speedily » Wed, 13 Oct 2010, 21:45

i'm thinking small starter motor for reversing up just with a contactor run it on 12V

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

Post by EV2Go » Wed, 13 Oct 2010, 21:57

Far simpler but where to put it... I'm fairly limited on spots it could put it as would you be. Andrew mentioned seeing it run on the brake rotor but not sure how that would go down with the engineer. Not a great deal of room between motor and diff. The only place I can think to put it would be on the fan end of the motor.

Could put some kind of dog clutch or lug setup on the rotor end and when the bendix on the starter motor threw it forward it would then egaged at the end of its travel. Problem is it would be direct drive and no gear reduction.

Another option would be take the bendix out of the starter motor place a air cond pulley setup on either the starter motor or the motor so it is only engaged during movement.

Edit: Actually you might be right because you could put the starter parallel to your motors and run a flywheel.
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Ways to reverse Series DC Motor -100% FWD 30% RVRS

Post by Speedily » Wed, 13 Oct 2010, 22:27

It will be at the back of the car with the battery for it, i plan on removing it when i dont need it. about 20kgs





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

Post by EV2Go » Wed, 13 Oct 2010, 22:32

Yeah that would be as easy as to run off the main drive shaft at the back... but what happens if you stage too deep and cant get back behind the line?

Still thinking 7Circles idea has merrit.

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

Post by Speedily » Thu, 14 Oct 2010, 01:46

The days i dont have someone to help me run the car i put the motor on

You could run a 2nd motor with your setup and it will work well.

Use a dog clutch off the drive shaft

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

Post by Richo » Thu, 14 Oct 2010, 03:06

A 3-phase bridge would do it.
4 are arranged in a H-Bridge and 2 in a half bridge.
Also the BEMF would be half now.
So those running a 144V system would now only need 72V.
Some fat mosfets could do synchronous rectification and give you reverse.
But it does sound expensive considering some dc controllers only have 1 switiching device not 6.
I think this setup would still need one main contactor.

The PWM to each switching device needs to be synchronised.
On low duty cycles, such as reversing, if the pulse is staggered it may cause stuttering on the motor.
This is why two seperate controllers would not be the best setup.
So the short answer is NO but the long answer is YES.
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Ways to reverse Series DC Motor -100% FWD 30% RVRS

Post by EV2Go » Thu, 14 Oct 2010, 04:35

Would it make any difference to the equation if the motor voltage could be turned right down in reverse?

Image

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Post by Richo » Thu, 14 Oct 2010, 04:44

It would but I don't see a practical way of doing that.
If the voltage is lower the duty cycle will be higher.
So the offset on unsyncronised PWM will only be minor.
So the short answer is NO but the long answer is YES.
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Ways to reverse Series DC Motor -100% FWD 30% RVRS

Post by 7circle » Thu, 14 Oct 2010, 07:50

Just got new power supply for my PC...
Was in a bad state noisey dying fan and with my soldered short across a dead PTC with room fan blowing on it to keep it cool. Image Not good.
Ah peice again and less worries of crashes.

Back to topic..
The Voltage settings in the Soliton configuration software for "reverse" are only useful if you have the 2 big and 2 small contactors for reversing the Field current wrt to the Rotor current.

My idea is to make the Soliton/Motor setup run efficiently with just the Pos and Neg to the motor (with parallel fields in series with rotor)

When driver selects reverse buy switch, the Soliton Controller is set to IDLE with confirmation back from Soliton it wont run. Then a 3 pole contactor is pulled in. The three wires are conneted to Field and Rotor as per picture:
Image

The independent Power supplies feed currents through the Field (see below:85A) and The throttle adjusts the Rotor voltage (See below: up to 55V or max current of 5A to get reverse).

I still haven't worked out the 11" Kostov Motor Torque Constant wrt to the Feild Current to know how the Armature Voltage will increase with RPM.

I'm thinking 5V on the rotor even with 100A in the field will not give a very high reverse speed.

I'm trying to select Power supplies with Output voltages that can be used for multiple purposes. So 4 x 3V3 gives 13.3V in series.
So 1 3V3 for Field and 3 x 3V3 for Rotor could be a good combo.
Or 1 3V3 for Field and 1 x 10V (12V trimmed back)

My theory of SepEX DC motors is wanting. Here goes..

11" Kostov 192 Parallel Curve

Pmech is BEMF x Rotor Current
P= T x W (W: rad/sec)
BEMF = Pmech/Irotor = 40.4kW/250A = 161.6V

Rotor BEMF is proportional to RPM and Field Current

BEMF = If x Kv x W

If 50 km/h is 2000 RPM (150Km/h is 6000 RPM)
then 5 km/h is 200 RPM (x 2PI/60 = 0.1047)
            is 21 rad/Sec

Kv = 161.6V/(250A x 21) (for Parallel Field)
   = 0.03078 (V/(A.rad/Sec))

1/Kt = Kv V/(Rad/Sec)

BEMF = If x Kv x W

BEMF = 100A x 0.03078 x 21 = 64.64V

64V is heaps more than 10V..... Image or ealier 3.3V on rotor.

So for 200W of mech power it needs 3A in Rotor.

The Power In is Pfield + Protor
Pfield = 2.5V x 100A = 250W
Protor = BEMF x I + IR
       = 64 x 3 + 3 x 0.075
       = 200 + 0.225 = 200W

Eff = Pmech / (Pfield + Protor)
     = 200 / (250 + 200) = 44%

Eff is very bad but it is not used often.

Balancing the Field and Rotor PSU's to get a good combination.

So if Field PSU is 3V3 with 85A current limit
Field will be 85A x 0.025 = 2.125V

Rotor BEMF at 200RPM = 85A x 0.03078 x 21 = 55V
So PMech of 200W needs 3.6A

I was thinking of using an Elcon Charger as it has variable current adustment, but I don't think will run at low voltages, it makes an Alarm for low Battery. If this could be disabled over CAN/Serial Port it could be a goer.

So Field PSU of 3V3 / 85A like SP-480-3.3 Procon @ $270

And Rotor PSU of 48V / 5A (240W) with 0-115% Voltage adjustment is needed for speed control to 200RPM (~ 5km/h)
So a SPV-300-48 has Voltage Adjustment 20% to 110% and 6.25A Max
Procon @ $160 for SPV-300-48.

With a bit of stiction in the drive/wheels would suit a 20% startup.
With 1000kg momentum to shift appears to make sense.

I hope my grey matter is sparkling tonight and figured this correctly.
Any comments?


@ EV2GO : What cost have you allocated for the Contactors for Reversing?


After reading through this I just realised the Rotor PSU is redundant as the Soliton can be used for this. Image Image Image

Sketch of circuit looks much better.
The 3V3 Supply reverses the polarity of the field.

So the Soliton Parameters can be used by limiting the reverse voltage to say 64V.

Need draw up another circuit to explain current flows.
Need big filter to protect 3V3 from Soliton 300V PWM Signal.

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

Post by 7circle » Thu, 14 Oct 2010, 10:05

I thought filter looks costly and hang on when the Soliton is running is a 300V PWM source at 8kHz (i think switching freq is about 8KHz)

So the power to reverse the Field can be leached from the Soliton Drive.

So here's a sketch.
Image

This needs a
- 10A Relay
- Transformer Fast Toroidal Turns 100:10(300VA ??? 300W) 100A Secondary. 10A Primary, Freq 8KHz
- Diode Bridge 600V, 100A
- 100A relay for secondary. As need to isolate for forward motion
- Perhaps a 10A Fuse the primary side.

Looks simple enough.
Apart from 3Vrms through Diode Bridge (3V - (2x 0.7V) = 1.6V)
Lots of Losses.
Maybe a tapped Secondary of 3V+3V with just two 50A Diodes. 3V-0.7V=2.3V (50A Germanium Shotchky Diodes with 0.3V drop might be affordable 3V-0.3V=2.7V)

Also need to think about the Rotor Reactance causing huge voltage.
- Current continuity for the inductance will be maintained by the diode, so looks okay.

So it will leach power and force the Rotor Voltage to be higher than the PWM Average from the Controller. Only by 2.5V for 100A in Field.

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

Post by 7circle » Thu, 14 Oct 2010, 10:53

Added the Tapped Transformer and Secondary Relay Contacts
And a Primary Fuse.

So with the Soliton Driving its FET with 8KHz at (25% Duty) 0.25x240V=60V
the Primary is has 240V for 25% and 0.7V 75% of 0.125mSec.

When the throttle is just on.
Duty is say 5%. So 240V for 5% and 0.7 for 95% of 0.125mSec

Image

But I'm wondering if it could be made for less than a Chinese built SMPS 3V3 85A for $270. And you can use the PSU when you want to charge up you spare Li-Ion cells.

Any way see what comments percale up. ImageIt may just be a clown of an Idea

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

Post by bga » Thu, 14 Oct 2010, 16:17

Hi All,

Have I missed something here?

Series motors (or shunt motors like AC drills) always turn the same direction regardless of applied voltage.

All these schemes are making 3-phase AC sound easy Image
It's not the end of the world, but I can see it from here.

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Post by Johny » Thu, 14 Oct 2010, 16:21

Your are correct - when the fields and armatures are fixed in series or parallel.
They are attempting to come up with a viable scheme to reverse the field polarity (for low speed reversing) without involving high-current contactors.

Edit: Added parallel
Last edited by Johny on Thu, 14 Oct 2010, 05:21, edited 1 time in total.

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

Post by 7circle » Thu, 14 Oct 2010, 20:31

bga wrote: ...Series motors (or shunt motors like AC drills) always turn the same direction regardless of applied voltage.
...

Johny wrote: Your are correct - when the fields and armatures are fixed in series or parallel.
They are attempting to come up with a viable scheme to reverse the field polarity (for low speed reversing) without involving high-current contactors.

Edit: Added parallel


Another Circuit with just the $270 85A 3V3 PSU to try and make the concept look simpler.

Does this help?

Image


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

Post by EV2Go » Thu, 14 Oct 2010, 21:02

Sorry for the delay trying to sort out a freight issue.
Richo wrote: I think this setup would still need one main contactor.
The Soliton1 has a beefy built in contactor
7circle wrote: When driver selects reverse buy switch, the Soliton Controller is set to IDLE with confirmation back from Soliton it wont run.
@ EV2GO : What cost have you allocated for the Contactors for Reversing?
I thought filter looks costly and hang on when the Soliton is running is a 300V PWM source at 8kHz (i think switching freq is about 8KHz)
The controller has 3 input and 3 outputs so perhaps there is something on the controller that might be of use.
Would image several hundred $300-$400 maybe sightly more.
Has an option for both 8KHz & 14KHz

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Post by Speedily » Thu, 14 Oct 2010, 21:16

I still think a small motor and a battery is the way to go with your setup EV2GO

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Post by bga » Thu, 14 Oct 2010, 21:28

I couldn't interest you in one of these reversing contactors?


It's not the end of the world, but I can see it from here.

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Post by EV2Go » Thu, 14 Oct 2010, 21:39

Speedily wrote: I still think a small motor and a battery is the way to go with your setup EV2GO

It's just a theorectical discussion to see if it is possible, to see if they can manage to come up with something worth trying.

If the experts agree that it is plausable then I would contact EVNetics to make sure it would cause no damage to the controller.

Otherwise I am going with a reversing contactor rather than mechanical.
bga wrote: I couldn't interest you in one of these reversing contactors?

I believe the whole concept is to do away with the reversing contactor to maximise the main controller power.
Last edited by EV2Go on Thu, 14 Oct 2010, 10:44, edited 1 time in total.

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