# 12VDC to 240VDC

Discussion in 'The Projects Forum' started by CircuitZord, Aug 3, 2014.

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1. ### CircuitZord Thread Starter Member

Oct 8, 2012
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I plan to run a 3-phase PMSM motor which requires roughly 230VAC to operate.

My 12VDC source is an automotive battery, and I need to step up the 12VDC to over 200VDC before I use a 3 phase inverter.

I am a little confused as to how I should go about doing this. There are plenty of 12VDC to 240VAC single phase inverters on the market, but I can't find a whole lot of information regards to a boost converter setup to such a high voltage from 12V. Is this possible?

All the boost converter IC's I have seen only seem to suggest a max Vout of 80V from 12V.

Any sort of guidance is appreciated here.

Feb 19, 2010
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3. ### CircuitZord Thread Starter Member

Oct 8, 2012
59
2
Yea, I did see that earlier, but seeing the 555 timer there made me think running that kind of system off an automotive battery drawing a not-so-minor amount of current powering a 3-phase motor will probably lead to some reliability problems.

Looking in to some LLC resonant converters now, as I think that will probably be more heavy-duty.

Still open to any suggestions

4. ### shortbus AAC Fanatic!

Sep 30, 2009
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Don't quite understand you reasons for that? All the 555 is doing is giving output for the switching, it's not handling any of the high current or voltage.

5. ### wayneh Expert

Sep 9, 2010
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You don't need to build your own inverter, although that circuit will work. As noted, the big currents are thru the power transistors, not the 555. If you need DC, just rectify what comes out of the commercial product.

6. ### Papabravo Expert

Feb 24, 2006
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Like many people, you fail to grasp the implications of such a power conversion scheme. The basic design calculation starts with a simple idea: Power out will always be less (sometimes much less) than power in. Let us take the simple example of converting 12VDC to 200VDC. Let us say we want 746 Watts (1 Horsepower) from this process.

746 Watts / 200 VDC = 3.73 Amperes, so far so good. Let us say that the conversion process is 75% efficient.

746 Watts / .75 ≈ 1 killowatt of input power.

1 kilowatt / 12V = 83.3 Amperes.

Now you begin to see the problem. That is a great deal of current to be playing around with. It will drain an automotive battery very quickly. A typical 100 Wh battery will be gone in less than 6 minutes. As the battery discharges and the voltage drops the converter's demand for current will increase to maintain a constant power level. A deep cycle marine battery might last a bit longer, but there you have it.

Now add in the inefficiency of the inverter and your power requirement for current out of the 12V battery just shot up into the stratosphere.

Instead of me trying to guess what you're thinking about, why don't you tell us what your actual requirements are because they sure don't look feasible to me.

Last edited: Aug 18, 2014
CircuitZord and MikeML like this.
7. ### CircuitZord Thread Starter Member

Oct 8, 2012
59
2

Haha, thanks!

I will admit that this lingering in the back of my mind, but I didn't give much thought to it.

OK...for the bigger picture. I'm working on an electric power steering system (EPS), traditionally these systems have used brushed DC motors, but over time these wear out. So the improvements are that a lot of them are using 3 phase brushless motors.

Within the brushless motors, there is BLDC and PMSM. Similar, but the PMSM is driven by sinusoidal currents, what this means is better position control and less torque ripple. Pretty much what is needed for a high quality EPS system.

Now, the reason I didn't consider too much about the current drawing from the battery is because I assumed that it will always be charging from the alternator and rectifier.

Now most 3 phase PMSM motors I have been able to find that are compact, small and <5kg are 230VAC motors. Looking at some general estimates about torques generated at the steering wheel for a car, it appears roughly 20Nm at the most is required to turn the wheel (with no assistance) at a standstill (0 km/h)

So I'm guessing the motor to assist will need to generate at most 15Nm.

I haven't been able to find 3-phase motors at lower operating voltages that can supply this kind of torque without some kind of gear reduction.

Any help appreciated!

8. ### alfacliff Well-Known Member

Dec 13, 2013
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if torque is a problem, why not use a gear train to allow the motor tu run at higher rpm, and the gear train output slower at higher torque? direct drive will always be most torque from motor.

9. ### tcmtech Distinguished Member

Nov 4, 2013
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If you are needing low volt high torque motor stepper motors are what you should be looking for.

As far as the brush wear out reasoning I am not buying it. Any decent quality and properly sized DC servo would far outlast any power steering system of any vehicle.

10. ### CircuitZord Thread Starter Member

Oct 8, 2012
59
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Tcmtech, brush wear, better torque, position control and response time is the reason most of the industry is moving to 3 phase brushless motors in EPS systems if not already most major manufacturers have.

There are still EPS manufacturers that use brushed motors, improved systems etc. but part of the reason brushed motors were used in the first place was because of the wide proliferation of them in industry, they were much cheaper and of course much easier to control.

Stepper motors was also a consideration, however this has inherent torque ripple which is harder to compensate for. It's possible but requires more complicated algorithms. Torque ripple is a problem because this will feedback through the steering column and can be felt at the steering wheel.

11. ### tcmtech Distinguished Member

Nov 4, 2013
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I wouldn't know. The only power steering systems I work with are hydraulics based.

As far as low voltage high torque goes if steppers are not your thing then brushless servos are the next in line.

12. ### Wendy Moderator

Mar 24, 2008
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The owners of All About Circuits has elected not to host discussions of automotive electrical system modifications/enhancements due to safety concerns, the potential of legal ramifications and the possible circumvention of vehicle regulations at the state and federal level.

This thread is against the AAC forum rules, Chapter 6, as seen here: