# dual controllers



## aredxwrestler (Oct 10, 2011)

Instead of using 1 1000a controller can I use 2 500a controllers? Its a 144v pack AGM 205ah


----------



## DIYguy (Sep 18, 2008)

aredxwrestler said:


> Instead of using 1 1000a controller can I use 2 500a controllers? Its a 144v pack AGM 205ah


It think the short answer is; 
- with 2 motors yes (one each). 
- with one motor no.


----------



## aredxwrestler (Oct 10, 2011)

Yea that's what I was afraid of.


----------



## efan (Aug 27, 2009)

aredxwrestler said:


> Yea that's what I was afraid of.


2 DC controllers and one motor is possible, I know because I've seen it done (http://www.ohler.com/ev/spyder/history.html)...but I do not know what exactly it takes to make it work...and I am pretty sure you will have easier time just getting a more powerful controller


----------



## mechman600 (Oct 16, 2010)

I had an idea to use one controller to control the armature and another to control the field. In my head it allows two lower voltage controllers to make the motor act like a motor with twice the voltage of each controller. It was all dependent on armature windings and field windings having the same resistance. But, theory is one thing and reality is another. I posted this http://ecomodder.com/forum/279147-post19.html on Ecomodder.com and a member (Ryland) went into his garage and played around with a series wound motor and two 12V batteries and confirmed that this will not work. The motor would not start up on his own. Once spinning, it did keep going. I am no engineer, but I suspect that series wound motors rely on things like back-EMF to work properly, and if split up into separate circuits, they simply will not work.

Has anyone else tried this?


----------



## iti_uk (Oct 24, 2011)

mechman600 said:


> I had an idea to use one controller to control the armature and another to control the field. In my head it allows two lower voltage controllers to make the motor act like a motor with twice the voltage of each controller. It was all dependent on armature windings and field windings having the same resistance. But, theory is one thing and reality is another. I posted this http://ecomodder.com/forum/279147-post19.html on Ecomodder.com and a member (Ryland) went into his garage and played around with a series wound motor and two 12V batteries and confirmed that this will not work. The motor would not start up on his own. Once spinning, it did keep going. I am no engineer, but I suspect that series wound motors rely on things like back-EMF to work properly, and if split up into separate circuits, they simply will not work.
> 
> Has anyone else tried this?


Looking at the system from the armature's perspective, what's the difference between the field from the stator being created by permanent magnets and field coils? Maybe the field coils could be "throttled up" slightly ahead of the armature at low power levels, or stopped dropping below a certain level to allow the presence of a magnetic field for the armatures field to interact with...

Another way to look at it is "what is the difference in the nature of the current supplied in series with the armature and of that supplied by a seperate source?" The only thing that springs to mind would be possible current spikes due to shorting across the commutator of the armature as it spins...

Sort of convoluted and half-baked answer, but I wonder if it would make sense enough to try?

Chris


----------



## mechman600 (Oct 16, 2010)

iti_uk said:


> but I wonder if it would make sense enough to try?Chris


If you could somehow develop a way to control it properly, it would be worth it. Imagine two very cheap controllers, say 48V/650A, effectively acting like a 96V/650A system. As soon as controllers are >72V, they get expensive. Plus, pack voltage would only have to be 48V, so safer, and charging solutions would be cheaper. Unfortunately, coming up with a way to control it properly might offset costs savings.


----------



## EVfun (Mar 14, 2010)

2 controller with one for the field and the other for the armature won't gain much. The field is only a few volts even at full current. The overwhelming majority of the voltage is across the armature. Field power is only a few percent of the total motor power.

The only way that I know 2 controller have been used on a single motor involve splitting the field. In many series wound motors the 4 field windings are wired in series/parallel. By adding a 5th terminal to the motor you can run one controller through 2 field windings in series and then through the armature and back to first controller. The second controller runs through the other 2 field windings in series and through the armature and back to the second controller. The controllers are connected to each other where they are connected to the armature. The split fields are the inductors that allow the controllers to each regulate current without interfering with each other. I'm sure this is deep into warrantee void land.


----------



## Qer (May 7, 2008)

efan said:


> 2 DC controllers and one motor is possible, I know because I've seen it done (http://www.ohler.com/ev/spyder/history.html)...but I do not know what exactly it takes to make it work...and I am pretty sure you will have easier time just getting a more powerful controller


We considered making it possible to sync Solitons for more absurd current levels (yes, they have to be synced to make it reliable) but it turned out to be so complicated (especially if you want it to be fail safe too...) so we skipped it for a more traditional design; ie the Shiva.



EVfun said:


> The only way that I know 2 controller have been used on a single motor involve splitting the field. In many series wound motors the 4 field windings are wired in series/parallel.


Or you could buy one of the Kostovs where this is already done. 

http://kostov-motors.com/tractionmo...c)/seriesdcmotorsforelectricvehicles/k11250v/

However, since most of the voltage is over the armature the two controllers will probably still "see" each other despite powering two fields and thus probably have to be synchronized anyway, which kinda takes the point out of it.

I think I agree with efan here; a more powerful controller is easier. Or, if you have a high voltage controller, you could go for two motors in series with a low current controller and go for a pack voltage that's twice the suitable motor voltage.

That'd work too, although it's probably also not a cheap solution.


----------



## mechman600 (Oct 16, 2010)

EVfun said:


> The field is only a few volts even at full current. The overwhelming majority of the voltage is across the armature. Field power is only a few percent of the total motor power.


That's exactly what Ryland on Ecomodder.com found when he checked voltage drops for me when I had this idea. He hooked up a 12V battery to a small GE series wound motor and found the armature had a 11V drop across it and the field only had a 1V drop, or something to that effect. I wonder if is because of some weird back-EMF effect affecting the balance between the stator and field voltage drops. Or maybe they are quite simply different sized resistors.


----------



## major (Apr 4, 2008)

mechman600 said:


> That's exactly what Ryland on Ecomodder.com found when he checked voltage drops for me when I had this idea. He hooked up a 12V battery to a small GE series wound motor and found the armature had a 11V drop across it and the field only had a 1V drop, or something to that effect. I wonder if is because of some weird back-EMF effect affecting the balance between the stator and field voltage drops. Or maybe they are quite simply different sized resistors.


It is not weird, it is normal. At 12V no load with the armature spinning I would expect just a fraction of a volt across the field and nearly all of the 12V across the armature. 

The simplified equivalent circuit for the series wound motor consists of the field resistance, armature resistance and voltage source (back EMF). Although the armature and field resistance may be approximately equal the voltage drop across each is small compared to the back EMF when the motor is rotating at speed. And the sum of the armature resistance voltage drop and back EMF is what can be measured on the armature terminals on the motor. 

It is a fallacy to think that motor power is split equally between the armature and field. The only time that would be close to being true is at stall meaning zero RPM because there is no back EMF at zero RPM.

Regards,

major


----------



## mechman600 (Oct 16, 2010)

Crystal clear now. Thanks!


----------

