Series Vs Parallel

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woody
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Series Vs Parallel

Post by woody »

In either case reversing is just swapping A2 + B1.

There are double-ended contactors which are double pole both ends. e.g. Albright SW121.

Cafe Electric has a diagram for two motors series/parallel and reverse, but that's not the whole picture.

Can the Australian Distributor for your controller help you out? :-D

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Johny
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Post by Johny »

What is the winding layout of this motor?
Are their 2 field windings?
Are the field windings the same or is one a series and one a parallel?
It would help a lot if you could show us the connections.
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Post by EV2Go »

I didn't make the rules, I just graphically represented what Mr Kostov said Image

If it is simple as switching B1 & A2 why does it show different connections for series?, is that only true for 4 connection motors?

Not overly concerned with the interconnecting wires they are cheap, I guess I am looking to reduce the MOST amount of contactors to keep price and voltage consumption down.

Image
Last edited by EV2Go on Sat, 22 Jan 2011, 04:25, edited 1 time in total.
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Post by EV2Go »

woody wrote: In either case reversing is just swapping A2 + B1.

There are double-ended contactors which are double pole both ends. e.g. Albright SW121.

Cafe Electric has a diagram for two motors series/parallel and reverse, but that's not the whole picture.

Can the Australian Distributor for your controller help you out? :-D

cheers,
Woody
Currently the Soliton1 doesn't have series / parallel switching (told it's coming) but isn't this more a motor issue than a controller?
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Post by Johny »

EV2Go wrote:Currently the Soliton1 doesn't have series / parallel switching (told it's coming) but isn't this more a motor issue than a controller?
Yes.
I'm trying to make sense of the diagram...
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Post by Johny »

Ok. These are series or parallel FIELD modes.
In parallel you get more torque and less speed. Series field connection gets you more speed due to field weakening.
Now it depends on what max motor RPM you want.

This is still a series motor isn't it? In that the field(s) still go in series with the armature?
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Post by EV2Go »

Anthony just gave me a call and we were just talking about it. From my limited understanding it would appear that it is just series and parallel field switching on the motor.

Really doesn't matter whether I have it in series or parallel. I figure I am going to have so much torque off the line that I am going to have to limit the current ramp rate anyway.

I probably won't need any more top end revs either... I will be doing ~100kph@2500rpm, so that works out to 200kph@5000rpm with a few revs to go.

Figuring I am going to have an abundance of torque, I may as well configure it for parallel and give me more top end power.
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Post by Johny »

It does matter a little bit. More field current at low speeds will be slightly more efficient (if Kostov have done it right - which they have). I.E. The motor will draw less current for a given torque at same RPM in parallel field mode.

If you put the parallel and series data they gave on a graph and calculate current you should see it at say 4000 RPM.
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Post by EV2Go »

Can you give me an example I am having a bit of trouble understanding their graph.
Last edited by EV2Go on Wed, 21 Apr 2010, 13:55, edited 1 time in total.
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Post by EV2Go »

Just went through the exercise of seeing how much work would be involved to do series / parallel.

Only 1 more contactor than Parallel CCW & CW

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Post by Johny »

What battery voltage are you going to have?
It looks like series only helps with voltage above 212 VDC and RPM above about 4800.
Haven't had much access to home computer tonight...
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Post by EV2Go »

Current plans are for 288v. Not sure how often it will see 4800rpm unless it hit 190kph at the drags. Not sure how fast it will accelerate but I'm guessing it might be more like 130kph.
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Post by Johny »

If it wasn't that you are drag racing it, it really isn't worth the extra trouble. You gain about 2kW above 3800 RPM by going to series.
I would imagine that low down would lose something similar in series.
So switch from parallel to series somewhere between 3400 and 3700.
really is a bit of a guess though.
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Post by coulomb »

[ Edit: oops, seems I skipped a lot of posts... ]
Johny wrote: This is still a series motor isn't it? In that the field(s) still go in series with the armature?

Yes, the diagram says "excitation: serial".
Last edited by coulomb on Wed, 21 Apr 2010, 19:25, edited 1 time in total.
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Post by coulomb »

Johny wrote: In parallel you get more torque and less speed. Series field connection gets you more speed due to field weakening.
Yes, but interestingly, not twice the torque as I'd expect.

The diagram shows another (fifth!) field winding in series with the armature. Maybe this has turns on both pole pairs, and has many more turns than the other "D" field windings. Maybe this is done so that if you wire the other fields incorrectly, the motor doesn't blow up.

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Post by Johny »

Ahhh - I haven't been scrolling the diagram - I see the circuit now!Image
The Kostov is emerging as interestingly different to the other DC Motor offerings. Somebody has put some thought into this one.
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Post by Squiggles »

My guess is that the fifth winding actually represents the interpoles.
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Post by Squiggles »

Johny wrote:
The Kostov is emerging as interestingly different to the other DC Motor offerings. Somebody has put some thought into this one.


On paper Kostov motors seem to be superior to several other offerings and reasonably priced.
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Post by Speedily »

EV2Go wrote: Anthony just gave me a call and we were just talking about it. From my limited understanding it would appear that it is just series and parallel field switching on the motor.

Really doesn't matter whether I have it in series or parallel. I figure I am going to have so much torque off the line that I am going to have to limit the current ramp rate anyway.

I probably won't need any more top end revs either... I will be doing ~100kph@2500rpm, so that works out to 200kph@5000rpm with a few revs to go.

Figuring I am going to have an abundance of torque, I may as well configure it for parallel and give me more top end power.


Maybe go with parallel and later on try series and if it goes better then it's worth the cost of the contactors Image
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Post by Squiggles »

This is a bit off topic, and I am sure there will be a train spotter out there that corrects me.
The old Sydney electric trains used to have two motors in a drive car.
The controller was manual and operated through contactors.
Four positions, Notch 1 - Notch 3 then Weak Field.

I gather it went something like
Notch 1 - everything in series
Notch 2 - fields in parallel motors in series
Notch 3 - Fields in parallel motors in parallel
Weak Field - What it says, somehow field strength was reduced.

The point is there was some good reason for having such an arrangement. High torque low speed in Notch 1 to low torque high speed in weak field.
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Post by Plamenator »

Hello,
Anthony send me a mail for this thread.
As I work for Kostov Motors, I hope the below explanation will be of some use.

Series/parallel field switching (SFS/PFS) refers to the way the stator windings are connected. It really gives you two motors in one.
SFS yields 210A/45kW/77NM/5600rpm@250V while PFS gives 250A/40kW/72Nm/5400rpm@192V.
To see the difference more clearly you can think about it like:
SFS: 210A/77Nm/4300rpm@192V
PFS: 250A/72Nm/5400rpm@192V (PFS exactly replicates the performance of K11" 192V).
We consider 6000rpm to be the threshold for continuous rpm hence SFS gives you the opportunity to increase voltage to 250V. Problem is not arcing as the motors have interpoles but centrifugal force which will tear the collector appart if used systematically above 6000-7000rpm.
In SFS all 4 stator coils are connected in series to each other and can handle 210A for 60min.
In PFS the 4 coils are grouped in 2 pairs (connected in parallel within the pair) which pairs in turn are in series. This is equivalent to having double the copper cross-section hence the amps increase from 210 to 250A.
The "5th winding" are indeed the interpoles.

You may ask which mode is better?
For racing I would think that PFM is better with a battery nominal of 210-220V. It just handles overload better. Of course battery can be with 250-260V nominal but make sure you have an rpm sensor to cut-off above 6000-6200rpm (6000rpm is scary fast btw).
For city driving I would go for SFM as it is gentler on the battery.
Really this is up to users to determine.
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Post by antiscab »

wow,

Welcome Plamenator :)

it is always good to have representatives of EV part manufacturers joining the forums :)

how much torque will that motor give at 2500rpm if its wired in series and 1000A is applied?
what would its voltage be at that operating condition?

thanks,
Matt
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Post by EV2Go »

Thanks Plamen, is there a reason why PFS is rated at a lower voltage?

You say you would use parallel for drag racing yet it has lower Kw output figures (approx 71Kw vs 94Kw) when rated at 192v vs 250v for series.

Could PFS be sucessfully run at 250v?

Last edited by EV2Go on Sat, 22 Jan 2011, 04:32, edited 1 time in total.
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Post by Plamenator »

Not that I encourage you to go to 1000A, but anyway we have:

210A   77Nm (nominal-from performance curve)
500A   215Nm (from performance curve)
1000A 600NM (extrapolation from 215/77 ratio)

RPM should be ROUGHLY around 2000 (?) assuming a 250-260V of battery nominal. Voltage is irrelevant to torque.

The above is an educated guess of course.
You can probably get more peak torque out of PFM as it needs more amps to zorch than SFM Image
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Post by Plamenator »

PFM is at lower voltage because at 250V, PFM will result in 7000rpm which we do not regard as safe.
During racing you have such overload that even at 250V, your rpm will be much less than even 5000.
Therefore you can probably use PFM for racing with much higher voltage - of course an rpm sensor fail safe is encouraged.
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