# Dc or ac your opinion



## evmetro (Apr 9, 2012)

I am not the most knowledgeable guy here, but I understand that you get more performance for less with dc. Maybe you could live without regen for a limited budget build, or step it up to an hpevs set up with a 1238 controller. These are not very expensive for ac.


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## Johnosu1 (Feb 27, 2013)

Thanks. For the reply for the regeneration with the dc I saw a couple of setups where they used a double ended dc motor and put a 12v clutch on the shaft to run a alernator on demand, that would make me happy. It just something mechanical to go wrong in my eyes tho. For the hpevs set up im not familiar with. And also I have found bits and pieces of open revolts ac controller. What happened with that? Thanks


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## dbeluscak (Mar 2, 2013)

I'm no expert here either, but I've been lurking for a while now. In my opinion, DC will be cheaper. Especially if you plan on building your own controller. AC is more efficient, also regen is more common. It all comes down to budget and your skill level. If you plan on doing the work yourself it's just a matter of range. 

Me personally, I am going to convert my 78 C10 with 1000vDC to power a 690 AC drive and motor. I already have the Vfd and it can run about any 3 phase motor. Regen is built in and with a 3 phase power supply it doubles as a charger. 

The battle between AC and DC still rages on. That's my 2 cents. I believe I'll leave it to the "experienced" experts from here. 

Best of luck in your upcoming project!


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## Ziggythewiz (May 16, 2010)

Regen nets most people under 10% greater range. If in 5 or 10 years an AC system costs only 10% more than the DC equivalent it'll make economic sense. By then the DC motor may need a little maintenance if you put heavy miles on it.


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## Sunking (Aug 10, 2009)

Pros use AC, Amateurs and most DIY's use DC because it is less expensive and less complicated.


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## Lauris_K (Feb 25, 2013)

Well if budget is limited and controller is being build by your own, unless you have good experience in building AC controllers I would say DC is your option. Other way - AC is best option, well in my personal opinion. Not only because of regeneration, but also efficiency, durability, power to weight ratio, wider rpm ratio with higher efficiency, maybe something else what I forgot.

Laurynas.


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## Bowser330 (Jun 15, 2008)

Ziggythewiz said:


> Regen nets most people under 10% greater range. If in 5 or 10 years an AC system costs only 10% more than the DC equivalent it'll make economic sense. By then the DC motor may need a little maintenance if you put heavy miles on it.


+1

In regards to maintenance, the modern brushes being used now last 80,000 miles before they need replacement and even that is not very expensive or involved, there are videos online to walk through it.

My recommendations would be to go with DC since its the best financially. I would save your mechanical regen ideas to when you save up more for your upgrades.

Motor: Pre-prepped EV forklift motors aren't cheap, Warp9 costs ~$1800..it will be cheaper to get a forklift motor from a junk yard and have a motor shop refurbish it (clean the inside and apply additional insulation, new brush holders, new brushes, clean the comm, kevlar banding, advance timing, etc.) for you, total cost ~900$?

Controller: Paul and Sabrina 144V 500A controller kit costs 600$, they are coming out with a 1000A version soon, not sure how much more it will cost...

Batteries: Even though Lead acid is cheaper in the short term, more expensive Lithium is a better investment. Calb CA "grey" cells can be purchased from certain sources for 1.25$/AH, so the 180AH cells will cost 225$. 144V will require 43 batteries or $9,700. 

~26kwh @ 300wh/mile = ~70 miles range @ 80% empty.
12.4lbs each x43 = 533lbs of battery weight

Total of three major components = $11,200
Still need:
Adapter motor-to-transmission
On-board charger
DC-to-DC converter
Cabling
Battery racks
etc.


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## Lauris_K (Feb 25, 2013)

10% with 70 miles range @80% DOD is +7 miles, and that is only on regen. That is useful when EV's count every extra mile. By the way I wonder have anyone did any real experiments on how milage differs on as possible close cars and diving situation with DC versus AC?


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## dladd (Jun 1, 2011)

Lauris_K said:


> 10% with 70 miles range @80% DOD is +7 miles, and that is only on regen. That is useful when EV's count every extra mile. By the way I wonder have anyone did any real experiments on how milage differs on as possible close cars and diving situation with DC versus AC?


it's not quite that simple though. Since the DC system is cheaper, you can buy a few more cells for less than the difference between AC and DC initial costs. So even with the added 10% efficiency of AC, you will still have more range with DC by virtue of the larger pack (which you bought with the money saved on DC initial purchase price). 

Anyway, big picture stuff it's pretty obvious that AC is 'better', that's why every single production EV out there is AC. But for the hobbiest, DC has it's advantages (cost and simplicity).


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## Bowser330 (Jun 15, 2008)

Lauris_K said:


> 10% with 70 miles range @80% DOD is +7 miles, and that is only on regen. That is useful when EV's count every extra mile. By the way I wonder have anyone did any real experiments on how milage differs on as possible close cars and diving situation with DC versus AC?


I haven't seen any comparisons but I have seen that the members with AC systems that have reported their efficiencies and the efficiencies aren't significantly better than members with DC systems.

Choosing a lighter donor car seems to be more beneficial than regen does...
I think EVTV.ME's rough formula is the "weight/10 = wh/mile", so 3000lb EV will get 300wh/mile, a 2500lb = 250wh/mile, etc.


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## Bowser330 (Jun 15, 2008)

dladd said:


> it's not quite that simple though. Since the DC system is cheaper, you can buy a few more cells for less than the difference between AC and DC initial costs. So even with the added 10% efficiency of AC, you will still have more range with DC by virtue of the larger pack (which you bought with the money saved on DC initial purchase price).
> 
> Anyway, big picture stuff it's pretty obvious that AC is 'better', that's why every single production EV out there is AC. But for the hobbiest, DC has it's advantages (cost and simplicity).


good points.

There aren't many members who wouldn't want an equally costing and equally powered AC system however for your first EV it might be a better idea to go DC.


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## Siwastaja (Aug 1, 2012)

Regen can give any significant savings only in some extreme cases such as very congested stop/go traffic and going up and down hills. Regen isn't there mainly because it would be so important, but simply because AC gives it automagically; disabling it would require extra effort in fact.

Difference in efficiency is also very small. Any properly built EV will be about 70% in total efficiency from wall socket to wheels, so what matters more is minimizing the physical losses after the wheels; aerodynamics and rolling resistance (car weight).

The reason I go for AC is because AC can be really cheaper *if* you DIY everything. Industrial AC motors waiting for either rewind or reconfiguration and a high-voltage drive system are abundant. Of course, forklift DC motors are also everywhere and it's somewhat easier to full-DIY a DC controller than an AC controller. For me, it's about going the better route just "because I can".


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## Bowser330 (Jun 15, 2008)

Siwastaja said:


> Regen can give any significant savings only in some extreme cases such as very congested stop/go traffic and going up and down hills. Regen isn't there mainly because it would be so important, but simply because AC gives it automagically; disabling it would require extra effort in fact.
> 
> Difference in efficiency is also very small. Any properly built EV will be about 70% in total efficiency from wall socket to wheels, so what matters more is minimizing the physical losses after the wheels; aerodynamics and rolling resistance (car weight).
> 
> The reason I go for AC is because AC can be really cheaper *if* you DIY everything. Industrial AC motors waiting for either rewind or reconfiguration and a high-voltage drive system are abundant. Of course, forklift DC motors are also everywhere and it's somewhat easier to full-DIY a DC controller than an AC controller. For me, it's about going the better route just "because I can".


I found one place that offers custom wound aluminum framed industrial motors, 75kw for 2000$ and 100kw for 3000$, not cheap, but also not extremely expensive...
http://www.customevperformance.com/c/4478065/1/motors.html

The only issue is finding an "affordable" inverter to use and customize the motor for it...currently there arent many offerings that are below 5-6K$

The DIY AC market would open up if more people would offer rewinding services for alum. frame AC motors and DIY AC inverters.

Once you build your AC inverter would you be open to sharing the knowledge to help others build their own as well? Maybe make a Youtube video series of the inverter construction in phases.


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## Siwastaja (Aug 1, 2012)

Bowser330 said:


> Once you build your AC inverter would you be open to sharing the knowledge to help others build their own as well? Maybe make a Youtube video series of the inverter construction in phases.


This is a general problem about publishing building instructions... If you want to give precise enough instructions to allow _anybody_ capable of soldering to build it, it will be an enormous task.

However, giving build instructions for those who kind of know what they are doing with electronics, would be relatively easy. They could also design their own inverter, but having clear instructions for one makes the job much more quick.

Yes, our plan is to go publish as much as possible, but not going to spend weeks to explain what an IGBT is. So, anybody who wants to build their own controllers or inverters, need to learn the basic lessons first.

BTW, from the "total DIY" viewpoint, AC is a lot safer; it's highly possible that a DC controller burns to full power on. This is not an issue with properly designed DC controllers that have appropriate safety systems. But a DIY AC drive simply cannot fail "on" if you are able to cut the power going to the_ microprocessor..._ An AC system also cannot produce _enormous _torque by accident - you need sophisticated control algorithm to do that. So if you consider planning proper safety systems, DC is not _that_ easy either. Both AC and DC share similar power stage design issues. The rest is "software" and algorithms and more about development time than parts exploding all over place all the time. That "parts exploding" step is similar for both AC and DC controller design.

So, for those who want to DIY their controller... If you don't care about your and others safety and want to get the car running as soon as possible with minimum effort, go for DC, it's the easiest. If you do care about the safety, either carefully design a proper DC drive, or choose AC to mess around with.

Of course, using any system that can provide any power to the wheels will need some safety considerations anyway.


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## Lauris_K (Feb 25, 2013)

Well for point that DC system is less complicated than AC I would say only if you are making controller by yourself, otherwise there is basically no difference, except one more wire to motor.

For price atm as special price there is still 75KW AC motor and controller system for 3750 Euro. and that is 144V system so won't be needed high voltage battery pack and complex BMS to balance it.

and for point that for price difference you can add extra cells to battery to gain back 10% of range, not sure about other countries law systems, but where I live car conversation can add up to 10% vehicle weight for it to be legit to register. and at this point you can not gain any extra range, but from system efficiency, either aero, weight, regeneration or other.


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## PStechPaul (May 1, 2012)

I am an advocate of AC systems, but there are pros and cons depending on certain details:

DC systems generally use lower voltage for fewer batteries and somewhat less shock hazard.
DC series wound motors have much higher low end torque so they may enable direct drive.
A DC motor controller is simpler and easier to design and build.
DC motors can overspeed and explode if unloaded and not adequately protected.
A failure (short) in a DC controller can cause a dangerous full-on condition.
AC induction motors can give better speed and torque control.
Standard industrial AC motors can be obtained very cheaply, and in a wider range of sizes and capabilities.
Standard VFDs are inexpensive and easily repaired or replaced, but may need special modification or programming to work properly for EVs.
Standard AC motors and VFDs need a high voltage battery pack.
AC induction motors are rugged, dependable, and need little maintenance.
ACIMs provide easy regeneration and dynamic braking.
There is a larger installed base of DC systems in the DIY community and thus more experience and support.
I am just comparing series wound DC machines with three phase AC induction motors, as these are the most common for full size EV conversions. BLDC motors and PMDC motors have their own pros and cons, and may be more suited for small vehicles such as bicycles. The ultimate EV motor may be the switched reluctance type, but they are not generally available to the hobbyist and DIYer. Much of the design decision process depends on the battery pack.


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## Bowser330 (Jun 15, 2008)

Lauris_K said:


> Well for point that DC system is less complicated than AC I would say only if you are making controller by yourself, otherwise there is basically no difference, except one more wire to motor.
> 
> For price atm as special price there is still 75KW AC motor and controller system for 3750 Euro. and that is 144V system so won't be needed high voltage battery pack and complex BMS to balance it.
> 
> and for point that for price difference you can add extra cells to battery to gain back 10% of range, not sure about other countries law systems, but where I live car conversation can add up to 10% vehicle weight for it to be legit to register. and at this point you can not gain any extra range, but from system efficiency, either aero, weight, regeneration or other.


I saw your previous posting where you advertise the AC motor and controller system for 3,750Euro ($4,837USD)

http://www.diyelectriccar.com/forums/showthread.php/jonelis-eu-ac-motor-controllers-bms-83832.html

The power chart of your system is linked below...(60kw & 155ftlbs)

http://www.diyelectriccar.com/forums/attachment.php?attachmentid=15648&d=1361829481

Unfortunately the system you offer is not that different from the AC systems that HPEVS has been offering...see the power chart of the AC-50 system below($4,500USD) 57kw & 120fltbs

http://hpevs.com/Site/power_graphs/...lt/650-amp/ac50 108 650 amp imperial peak.pdf


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## Ziggythewiz (May 16, 2010)

Siwastaja said:


> Both AC and DC share similar power stage design issues.


I think there's a little detail in there about 3 phase needing 3x the power components.


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## Hollie Maea (Dec 9, 2009)

PStechPaul said:


> DC series wound motors have much higher low end torque so they may enable direct drive.


I suspect that this is more of a function of the fact that series wound DC motors are cheap enough that some people have been willing to dump 2000+ Amps at them and see what happens.

It is true that AC motors in scalar control mode and even in open loop vector mode have quite bad low end torque. But an induction motor with properly tuned closed loop vector control, or better yet direct torque control, should be able to produce low end torque nearly as well as a series wound DC.

It's just that controllers that do that are super expensive. 

(I could be wrong, but based on my reading, this seems to be the case. Certainly Tesla doesn't have any trouble producing low end torque...)


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## Hollie Maea (Dec 9, 2009)

Ziggythewiz said:


> I think there's a little detail in there about 3 phase needing 3x the power components.


That's not exactly true. Yes, an AC controller requires three times as many power electronics components, but each one has to handle less power so they can be smaller for the same overall power.


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## PStechPaul (May 1, 2012)

I think there is a fundamental difference between ACIMs and DC series wound motors, with regard to torque. An ACIM has a certain locked rotor and breakaway torque such that it simply stalls and there is a low limit to the speed based on the slip frequency. You really can't get any more torque because the rotor magnetization depends on the relationship of the rotating field of the stator and the field which is induced in the rotor. I was looking at some motor specs and I saw some ACIMs with locked rotor torque about 2.5 to 3 times rated torque, while for others I saw as high as 6-7 times, which is similar to a series DC.

But a series DC motor has essentially no limit to the amount of current that can be dumped into it, and thus the magnetic field and torque, except for the relatively small series resistance of the windings, commutator, and brushes. There is no equivalent for an ACIM. 

A synchronous motor, however, may be thought able to produce more torque because the rotor is energized by means of brushes and slip rings. But synchronous machines are rather rare, and may be more prevalent in the form of large generators. Actually, from what I found, SMs typically have maximum torque of 150% to 200% of nominal, and they have no inherent start-up torque, so they are unsuitable for EV use:
http://www.hansen-motor.com/ac-synchronous-motors.php


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## Tesseract (Sep 27, 2008)

Hollie Maea said:


> That's not exactly true. Yes, an AC controller requires three times as many power electronics components, but each one has to handle less power so they can be smaller for the same overall power.


Again, not exactly true. First off, the switches in an inverter are utilized less than the switch in a DC drive because they must always be off for at least some fraction of each switching period.

Next, a significant fraction of the switch current rating (15-25%) is taken up by simply supplying the magnetizing current (Id) to an induction motor.

The long and the short of this is that you can make a 150-180kW inverter with three 600V/600A half bridge modules. That isn't smaller for the same power by any stretch of the definition.


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## Hollie Maea (Dec 9, 2009)

Tesseract said:


> Again, not exactly true. First off, the switches in an inverter are utilized less than the switch in a DC drive because they must always be off for at least some fraction of each switching period.
> 
> Next, a significant fraction of the switch current rating (15-25%) is taken up by simply supplying the magnetizing current (Id) to an induction motor.
> 
> The long and the short of this is that you can make a 150-180kW inverter with three 600V/600A half bridge modules. That isn't smaller for the same power by any stretch of the definition.


Thanks for the clarification. The point I was trying to make is that it doesn't require "three times as much" but maybe I am wrong on that too.


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## Johnosu1 (Feb 27, 2013)

This is what I love about this forum compared to others I am on, u guys are awesome I wasent thinking anybody would respond to the newbee lol . All this info is very helpfull I think I am going to go dc just for the simplisity and shoot for a ac system later on. I have some experience with vfds and control loops, I work at a ethanol plant and I do some of our work on our dcs so I will have some time to investigate the issue.but this does sound like one of those questions that will never be answered.


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## dbeluscak (Mar 2, 2013)

I agree 100% as being one of the "newbs" here. Everyone here is very good at helping out with what they know. Lots of experiences here, not a lot of BS opinions. I chose AC because I've got my controller already and motors are easy to come by. My hangup will be the initial cost of the battery pack. But by the time I'm at that stage, I'm hoping lithium well come down some in price. No matter how I get it done, 1000v isn't going to be cheap. Lead acid out of the question (unless I get them for free) due to weight/life cycle.


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## Qer (May 7, 2008)

Siwastaja said:


> BTW, from the "total DIY" viewpoint, AC is a lot safer; it's highly possible that a DC controller burns to full power on. This is not an issue with properly designed DC controllers that have appropriate safety systems. But a DIY AC drive simply cannot fail "on" if you are able to cut the power going to the_ microprocessor..._


I think I have to agree with this and would like to point out that it's generally a very bad idea to buy cheap contactors because no matter what system you choose you always want to be able to break the power. Even though an AC-system can't function if you cut the power to the micro processor it will still be bad if, for example, the throttle get stuck in a floored position and the microprocessor happily applies full throttle, just following orders.

Another possible solution is after a collision. If the wires gets damaged and you get a full short at the moment of impact you, again, want to be able to cut the power before your battery pack or something else bursts into fire.

Etc. And so on.

Generally speaking, no matter what motor/controller you have you want to be able to cut power in case something unforeseen happens. Even a very carefully designed system will have some kind of gotchas you didn't think of and when the pack suddenly dump all it's stored energy into a short or tries to propel your car into orbit you don't want the contactors to get welded shut. No matter AC or DC.

And about AC or DC? Meh. I think all relevant things about that has already been mentioned. Get something working, don't get stuck on details. An EV that runs is funnier than an EV that will, eventually, potentially, probably, likely, be the best since sliced bread. Maybe.


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## steven4601 (Nov 11, 2010)

Qer, an exceptionally great quote:

"An EV that runs is funnier than an EV that will"


Going to add it to my list of great quotes.


In the end, we're all EV enthousiasts, AC or DC, BMS or no BMS.


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## Ziggythewiz (May 16, 2010)

steven4601 said:


> Going to add it to my list of great quotes.


It's good to be remembered for more than just great pastries.


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## crackerjackz (Jun 26, 2009)

Qer said:


> And about AC or DC? Meh. I think all relevant things about that has already been mentioned. Get something working, don't get stuck on details. An EV that runs is funnier than an EV that will, eventually, potentially, probably, likely, be the best since sliced bread. Maybe.


 
have to agree I love this last phrase lol ... made me smile ...


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## Tesseract (Sep 27, 2008)

Hollie Maea said:


> That's not exactly true. Yes, an AC controller requires three times as many power electronics components, but each one has to handle less power so they can be smaller for the same overall power.


Continuing with the _not exactly true_ theme... You get less useful current from the switches in an inverter because they must be turned off for some percentage of time (typically a minimum of 15-30%, depending on modulation scheme). This typically results in a maximum output of 450A[rms] per phase using 600A IGBT half-bridge modules. (edit: I see I already made the same comment... oops...)

In the case of the induction motor, some of the output current is required to induce the field in the rotor, lopping off another 50-150A[rms] of useful (ie - torque-producing) current (the field excitation must be supplied by the controller for the series DC motor, as well, but in that case some of the output voltage is lost, instead of current).

Finally, while it is true that the power stage of the AC inverter cannot fail in such a way as to cause the motor to accelerate uncontrollably, it can fail in a way that shorts out the battery pack or causes the motor to brake with far more torque than would be available through regen alone (ie - "DC injection braking"). Arguing what is more dangerous - accelerating or decelerating suddenly - is kind of missing the point, as either failure mode could result in a Really Bad Day.

Disclaimer: I design the hardware for Evnetics, which currently only makes series DC motor controllers.


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## palmer_md (Jul 22, 2011)

Tesseract said:


> Disclaimer: I design the hardware for Evnetics, which currently only makes series DC motor controllers.


So when are we going to see the Soliton3 ?


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## Bowser330 (Jun 15, 2008)

Tesseract said:


> Disclaimer: I design the hardware for Evnetics, which _*currently*_ only makes series DC motor controllers.


Are we to expect something of the AC nature in the future? Or am i reading too far into it?


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## crackerjackz (Jun 26, 2009)

Bowser330 said:


> Are we to expect something of the AC nature in the future? Or am i reading too far into it?



Curtis controllers would be hard to beat. In every aspect ...


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## Bowser330 (Jun 15, 2008)

crackerjackz said:


> Curtis controllers would be hard to beat. In every aspect ...


The best AC Curtis is only rated at 144V and 500A, 72kw peak
EVWest has one for sale (stand alone) for $2,700
http://www.evwest.com/catalog/produ...ucts_id=230&osCsid=qhcf54io9lpfcq8vbp3dqhvs00

$2,700/72kw = $37.50 per kw output

Currently Evnetics makes the Soliton-1 that sells for ~$2,900 (EVWest) and its capable of 300kw or $9.66 per kw output

If Evnetics were to make a high power AC/BLDC controller, lets say 200kw for example, they could increase their price by 2.5X and still be on par with Curtis as far as price to power. 

$2900 x 2.5 = $7,250/200kw = $36.25 per kw output

Curtis is great and has really helped the AC/BLDC market by becoming popular, but the DIY market is still young in the AC/BLDC area...There is definitely room for more AC/BLDC products....

Disclaimer: I do not claim to know a single thing about the cost of materials needed to build a 200kw AC controller/inverter, I just believe that Evnetics wouldn't bother with an AC controller/inverter unless it was the high power variant.


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## palmer_md (Jul 22, 2011)

that may be part of the reason why we don't have a Soliton3. I don't know the pricing either, but I assume it would be nearly 3x and not 2x the cost to build. But at 3x, they are still competitive with what we have now at Rinehart and others. I suspect that Evnetics keeps an eye on how many controllers RMS sells and if they think the market is opening they might jump in, but right now the market for at $10k controller is pretty small. And for $10k you could just get a megawatt DC controller from Evnetics instead of a 200-300kW AC controller.


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## Tesseract (Sep 27, 2008)

palmer_md said:


> So when are we going to see the Soliton3 ?


Unknown. On the plus side, I put in the extra effort to make the hardware I designed for the locomotive drive system we developed last year adaptable for an inverter. On the minus side, that still leaves a big gaping hole called "software" to fill, and then there is the prospective market for such a beast, which needs to be considerably larger than the - at best - 10 DC controllers we sell per month. Now I seem to recall seeing a comment by Jack Rickard recently that he sells more Curtis/HPEVS systems than anything else (not surprising, given how much free advertising he gives them... ahem), but if he were to actually specify a number of sales, and that number was higher than, say, 20 systems per month, then I might reconsider my stance that there is simply not enough of a market to justify the development expense.




Bowser330 said:


> Are we to expect something of the AC nature in the future? Or am i reading too far into it?


You are reading too much into it, though see above.




crackerjackz said:


> Curtis controllers would be hard to beat. In every aspect ...


Correct. Curtis is also ~400x larger than us on gross revenue basis, so if they thought we were any threat at all they could easily squash us like the insignificant bugs that we are (or they could buy us out... ).




Bowser330 said:


> If Evnetics were to make a high power AC/BLDC controller, lets say 200kw for example, they could increase their price by 2.5X and still be on par with Curtis as far as price to power.


Without getting too deep into the details, to make an inverter using similar IGBTs as used in the Jr would cost approximately 2-2.5x more and still deliver the same maximum power of 150kW. However, the development effort - particularly for the software side of things - would be significantly more difficult than for the DC controllers (even if we kludged in off-the-shelf ACIM/BLDC motor control libraries) and, well, both me and the software engineer (Qer) like to be paid for our work.

In other words, we could only beat Curtis by 2x in power, but have at least 2x, but closer to 2.5x, the parts cost, and that doesn't even factor in the labor to develop/test this product. Sorry, but we can't really beat them at this particular game.


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## McRat (Jul 10, 2012)

Will brush motors be around in 25 years?

Companies that made buggy whips in 1890 are now gone.

Companies than made transportation support devices in 1890 are still around.


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## Tesseract (Sep 27, 2008)

McRat said:


> Will brush motors be around in 25 years?...


I don't know and, frankly, I don't care.


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## major (Apr 4, 2008)

McRat said:


> Will brush motors be around in 25 years?


I recall that same question 25 years ago


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## McRat (Jul 10, 2012)

major said:


> I recall that same question 25 years ago


With us it was paper blueprints. 

Let's just say we haven't bought a large format plotter in 15 years...


<--- greater than 90% paperless today.


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