# Controller closer to battery or to motor



## major (Apr 4, 2008)

For the distances encountered on an EV I doubt it is terribly important, but I think nearer the motor is better. Three motor leads vs two battery and motor current is higher.


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## stealthhack (Aug 18, 2011)

major said:


> For the distances encountered on an EV I doubt it is terribly important, but I think nearer the motor is better. Three motor leads vs two battery and motor current is higher.


It's quite the opposite:
you have 10kW that are equal transferred thru 3 wires so are about 3,33kW per phase but if you transfer the same amount of energy with 2 wires in a DC system there is a difference in the losses in favour of the 3 phase system.


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## major (Apr 4, 2008)

stealthhack said:


> It's quite the opposite:
> you have 10kW that are equal transferred thru 3 wires so are about 3,33kW per phase but if you transfer the same amount of energy with 2 wires in a DC system there is a difference in the losses in favour of the 3 phase system.


I'm not sure what you're talking about, but I know the RMS phase current is higher than the DC input current for ACIM motor drives for almost all, if not all, cases and I suspect it is also for PMSM. It is the current which determines the size of the cable. So you should use larger diameter motor cables. And you need 3 motor cables opposed to two battery cables. That tells me you'll save copper by locating the inverter closer to the motor.

Want proof? See: http://hpevs.com/Site/images/torque...44 volt 500 amp imperial continuous TE NF.pdf Compare the DC current to the RMS current (which is the motor phase current).


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## stealthhack (Aug 18, 2011)

major said:


> I'm not sure what you're talking about, but I know the RMS phase current is higher than the DC input current for ACIM motor drives for almost all, if not all, cases and I suspect it is also for PMSM. It is the current which determines the size of the cable. So you should use larger diameter motor cables. And you need 3 motor cables opposed to two battery cables. That tells me you'll save copper by locating the inverter closer to the motor.
> 
> Want proof? See: http://hpevs.com/Site/images/torque...44 volt 500 amp imperial continuous TE NF.pdf Compare the DC current to the RMS current (which is the motor phase current).


Yep BUT that RMS current is for the 3 phases(combined), so from the graph you can see that this motor needs 175Arms from 3 phases(175/3 = 58,3Arms per phase) to produce 18hp.
for Example: one single phase motor @230V nominal will need 19Arms ot make 4kw at the shaft, but one 3 phase motor will need 19/3= 6,33Arms per phase to make the same work at the shaft.
http://myelectrical.com/notes/entryid/8/three-phase-power-simple-calculations


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## major (Apr 4, 2008)

stealthhack said:


> Yep BUT that RMS current is for the 3 phases(combined), so from the graph you can see that this motor needs 175Arms from 3 phases(175/3 = 58,3Arms per phase) to produce 18hp.
> for Example: one single phase motor @230V nominal will need 19Arms ot make 4kw at the shaft, but one 3 phase motor will need 19/3= 6,33Arms per phase to make the same work at the shaft.
> http://myelectrical.com/notes/entryid/8/three-phase-power-simple-calculations


The operative equation from your reference is: 









The term pf is always less than 1 and V_LL is always less than V_DC, so I_RMS (phase) is almost always, if not always greater than I_DC. At low speed, phase current can be significantly larger than battery current.


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## stealthhack (Aug 18, 2011)

Very helpful, thanks!


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## major (Apr 4, 2008)

stealthhack said:


> Yep BUT that RMS current is for the 3 phases(combined), so from the graph you can see that this motor needs 175Arms from 3 phases(175/3 = 58,3Arms per phase) to produce 18hp.


Ref: http://hpevs.com/Site/images/torque...44 volt 500 amp imperial continuous TE NF.pdf 

The "RMS Current" indicated on that graph is the motor phase current which is measured with a current sensor on each of the 3 cables from the inverter to the motor. It is the current in each wire.


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## dougingraham (Jul 26, 2011)

stealthhack said:


> From some time ago i'm collecting the parts for AC electric conversion, and one question come in my mind:
> Is it more effective to move the controller closer to the main battery(where DC cables will be shorter thus less sag from the cable), or the standart way far from battery and closer to the AC motor(controller in engine compartment and battery in trunk)?
> I'm asking because i know than AC power is more susceptible to travel long distances with less loss than DC power!
> My setup will be with AC24LS motor, 50mm2 cables, and SEVCON gen 4 550A(working voltg 50-100V) controller.
> Thans in advance!


If you look at this from a controller manufacturer standpoint you want the controller right on top of the battery. This would allow them to reduce the size of the capacitors.

If you look at it from the standpoint of electrical losses the loop to the motor is the most important because the currents are higher there than on the battery side. With your 550A limit I would use 1/0 size cable everywhere. it is heavy enough to handle your average currents and light enough to be easy to work with and not cost too much. The losses in the cable will not be significant. If your current was 1000A I would suggest 2/0 cable. For currents beyond that every wire run needs to be carefully considered.


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## dtbaker (Jan 5, 2008)

with properly sized cables, the loss should be negligible.... compared to the need to dump heat from the controller. THAT is easier to do from the motor bay with fluid circ pump and little radiator/core with good airflow.


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## stealthhack (Aug 18, 2011)

PStechPaul said:


> I have been looking into Litz wire for a DC-DC transformer I am building that will operate at 50-100 kHz or so, and it does seem that the skin effect is quite significant. Here is some theory:
> http://newenglandwire.com/products/litz-and-formed-cables/theory
> 
> According to my calculations, #1/0 cable at 350 CM/Amp is good for 300 amps, and has a DC resistance of 100 uOhms/foot. So 10 feet of cable would have a loss of 90 watts at 300 amps. However, the AC resistance at 20 kHz is 12.4 times that, so it may be very significant (1100 kW). However, that is just the carrier frequency and the effective waveform will usually be less than 200 Hz, at which the cable has about 1.24 times that at DC, and the losses will be 112 watts.
> ...


The cable for motor-controller connection is already purchased and it is 50mm2(approx #1/0 in AWG system). wich is good for all day city driving and some overloading such as 500Arms thru him(for short periods).
I have i more 35mm2 purchased long ago but it's from welding machine, can i make parallel cables on each phase something like 50mm2 + 35mm2 on a phase and would 50mm2 only be enough for 44KW of power to the motor.
Thanks in advance.


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## gunnarhs (Apr 24, 2012)

stealthhack said:


> From some time ago i'm collecting the parts for AC electric conversion, and one question come in my mind:
> Is it more effective to move the controller closer to the main battery(where DC cables will be shorter thus less sag from the cable), or the standart way far from battery and closer to the AC motor(controller in engine compartment and battery in trunk)?
> I'm asking because i know than AC power is more susceptible to travel long distances with less loss than DC power!
> My setup will be with AC24LS motor, 50mm2 cables, and SEVCON gen 4 550A(working voltg 50-100V) controller.
> Thans in advance!


For an electric vehicle this is no question that the controller should be located near the motor. Major and others here described the main part of the problem regarding the (resistive) loss and higher currents motor-side.
The only thing I want to clarify better is that when looking at an EV you (usually) always have the full voltage battery side of the controller. On the motor side you have usually average 50% of the (modulatet battery) voltage during a (city) driving circle at nominal power. 
As Power P = UI is about the same in and out of controller (minus up to 10% losses) this means that you have most of the time higher currents motor side. This applies both to DC and AC but is easier to verify in a DC system.
In addition to that 3 Phase AC-systems have more EMI than DC (usually), affecting other systems in the vehicle. Therefore it is better not do have them distributed over the whole vehicle.


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## grip911 (Dec 14, 2011)

i `ve seen a lot of builds where guys have mounted their controllers (inverters) right on top of the motor. If you do this make sure you use very good shielding if your encoder wires or any other sensors are close to the main motor cables. you will get interference if you don`t.( been there, done that.)


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## dtbaker (Jan 5, 2008)

don't skimp on main traction pack cable. go with the fine strand orange jacketted 2/0 welding cable.... negligible resistance at normal loads. 

as I said before, the PRIMARY concern locating the controller is to prevent overheating. So, you probably do not want to install directly over the outlet fan of the motor or in an enclosed trunk... you want to put in somewhere it gets airflow, and you have easy access to plumb fluid cooling hose/radiator if you plan to run more than 200amps for very long.


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