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AC/DC Motor Diferences

Number of messages: 37
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goncalosousa
Leiria, Portugal

Somebody knows the big diferences between AC and DC motors?
What is the inovation of AC electric motors?
Thank you and excuse my english (very bad) hehehe.

Posted 12 Sep 2005 07:44 PM

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paul_c
Quebec, Canada

In addition to Benny's and Fred's replies, the AC motor is totally enclosed and will resist to dust and humidity much better. Added to that is the fact that AC motors are unusally controled by high efficiency Transistor controlers (MOSFETS) which are energy misers. You can add that the controlers for AC motors are more versatile in the programing capabilities.

Posted 16 Sep 2005 07:10 AM

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Liftdoctor
Indiana, United States

There are a few drawbacks of an AC compared to a DC powered lift.   First, the AC motor controller will heat up faster and cut back the power to the motor if the lift truck is used to push loads or climb a lot of ramps.  The second thning is that the AC motors are new to lift trucks, at least in the US.  Replacement motors and motor controllers will be more expensive than convetional DC motors.  The third thing is the the power consuption of a AC truck is only about 3% less than a comparable DC truck.

The AC trucks I have seen do not have enclosed motors and Many DC motor trucks are now pwered by MOFSETS.

I can see a definate advantage to having an AC motor in an explosion proof truck.  All DC motors produce sparks at the brushes.   The AC motors do not.

I assume the above minor drawbacks of the AC motor powered lift trucks will be overcome and the AC motor will be much more common.

In the US, the common battery voltage is 36 or 48 volts.  Euerope is 72 to 80 volts.   The heat problem with the motor controller I mentioned may not be a factor in Europe.   I'm all for not having to replace those nasty black carbon brushes.

Modified 16 Sep 2005 09:59 AM
by poster.

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twetnysevnyrtec
Florida, United States

ac is an advantage,"less moving parts,less heat,heat is energy

Modified 28 Oct 2005 09:37 AM
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daniel_g
Flevoland, Netherlands

Some right and wrong comments in the above.

AC controllers do certainly run hotter than DC due to the amount of FETS that are being switched and the frequency that they are switched, both of which are substantially higher than DC units.

Power consumption is less than that of DC........The reason for the stated 3% is that AC machines are generally more powerful in terms of speed and torque compared to a DC units, so if an AC unit was de-rated the power saving would be higher.

AC power is superior to DC because the motors are more controllable, powerful and cheaper in the long run due to the reduction in parts, especially for the motors.....just think no looking at another raised comm bar from an operator bulldozing a load!

In Europe we are manufacturing 36V (For the US market), 48V, 72V (Not so much these days) and 80V units, and the technology has been used in Lift Trucks for 3 - 4 years here already.

Posted 13 Jan 2006 04:31 AM

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trainer
Indiana, United States

Toyota introduced AC drive to the US market in June 2000 to Class 1.

That would be 5 full years and some change......

NACCO - North American Coal corporation = NMHG = NACCO Material Handling Group = Hyster plus Yale

Introduced AC Class 1 Nov-Dec 2003

And the flip side
Crown...still using EV100 panel (giggle)

Posted 13 Jan 2006 05:14 AM

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mike_n
Alberta, Canada

There is 1 huge advantage to AC that no one has pointed out yet...
100% torque is availible 100% of the time.
The torque does not drop off as speed increases. You get higher loaded travel speeds without having to use huge inefficient motors.

The NACCO lineup was supposed to be 100% AC by Jan 06, but that's been pushed back till June 06.

All we have right now is the 3 and 4 wheel sit downs and the 3 wheel stand up (HSD)
We will also be transitioning over to Inmotion controls supposedly.

Our new AC narrow isle trucks look pretty, but I'll reserve judgement until they are actually running around.

Posted 24 Feb 2006 02:02 PM

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daniel_g
Flevoland, Netherlands

Good point there Mike.

We've been producing AC reachtrucks for 6 years now and not had too many problems and the same goes for the AC power pallet trucks we've had out there for a couple of years now..... so you've probably not got much to worry about.

Posted 25 Feb 2006 01:07 AM

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Scout
Alberta, Canada

It has been stated here that the AC motors have 100% torque 100% of the time, this is not very accurate, in fact the high voltage AC motors are great at producing torque but the low voltage motors have some serious issues. If you are bulldozing with AC motors you will have overheating problems especially in the lower voltages i.e. Power Jacks. The inverters will overheat and shut down. I would be very carefull when comparing AC technology to Advanced DC technology, I have witnessed two of the top Reach trucks one running on full AC and one running on full Advanced DC technology. The DC truck kicked the AC trucks butt. We used a police radar gun for speeds and the AC truck lost on just about everything. A company needs to be carefull before making this leap...Know the application and choose wisely.

Modified 25 Feb 2006 03:07 AM
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mike_n
Alberta, Canada

The low voltage jacks are still able to produce 100% torque at all RPMs.
The torque is a function of phase and so long as the phase is advanced far enough you get torque.

I can't argue about the low volts causing heat, however that'd be why companies like heinrich offer 48 volt jacks and 92-106 volt trucks.
Sadly NMHG is far far behind in this area, but we have recieved warnings about 96+ V units in the works.

In fact this is an area where ALL north american brands lag behind... but it's coming

BT's here in NA have been AC for a bunch of years, but they are simply rebadged heinrichs. I can attest to the speed, strength and durability of those reach trucks.

Abusing any electric truck will cause heat.
But I'd rather have a unit kick into thermal-cutback, then burn comms and brushes.

The Z series AC electrics from shyster are the fasteset, tourqeyest (sp?) units shyster has ever made. As long as you shut the 'economizer mode' off.(other wise they are real dogs :-) )

The shear number of wear items in a DC motored truck mean way more maintenance, period.

Every brand is AC or converting, so soon you won't have any choice.

It's just my humble opinion and I'm sorry if I offend.
I've worked on electric jacks, reaches, forklifts for 20 years, and the future IS ac.

Posted 27 Feb 2006 01:19 PM

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jamesss
Iowa, United States

Your statement about BT being a rebadged Jungheinrich is incorrect.

-------------------------
James S

Posted 3 Mar 2006 05:39 AM

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trainer
Indiana, United States

crown the king of electrics..(giggle)
use EV100

when will grandpa get some new teeth?

who knows..
some may say who cares....

Posted 5 Mar 2006 11:15 AM

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Liftdoctor
Indiana, United States

Trainer must be a Salesman for some barnd other than Crown and is trying to catch up.  Your name wouldn't be Paul would it?

Crown pickers, transistor.
Crown 3 wheel sit downs, transistor.
Crown pallet jacks, transistor.
These are all seperately excited motors for drive.
Crown reach trucks: AC or DC .  The price is the same. You pick AC or DC.
Crown turret truck: AC

The only Crowns that run EV100 is the RC and the FC.  And my Raymaond friend says thier AC controllers won't handle a freezer environment.
Ha!

Modified 9 Mar 2006 10:23 AM
by poster.

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trainer
Indiana, United States

I am not a salesperson....
My name is Trainer that could change...depends who is asking....
LOL

I was specifically talking about Class I, 3 and 4 wheel electrics....

Class II is another subject all together...

sorry if I had not specified class/model earlier

My fault... liftdoc

-------------------------
Trainer by day. Superhero by night. Brock Sampson is my hero!

Posted 9 Mar 2006 03:13 PM

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Liftdoctor
Indiana, United States

Trainer, no problem.   I have yet to see how the AC motors hold up. If they hold up better, great!
  The only high commutator bars I have ever seen from bulldozing are always on a 4 wheel sit down.  The reaches, pallet jacks, tuggers, will spin the tires.  The 3 wheel sit downs that have two drive motors just don't seem to raise a bar.  I suppose it is because the current is distributed to two motors.

My co worker and I saw a new Raymond pallet jack that was AC drive.  We both had the same thing on our mind: this is a sales gimmick in a pallet jack.  The brushes in the drive motor are so easy to change in a pallet jack that the savings in maintenance of having the AC motor is insignificant.  Most all DC drive trucks have seperately excited field windings now.  The motors run cooler, and there are no forward and reverse contactors.   There is also no need for a re-gen braking or field weakening contactor.   There are seperate transistors in the controller for the field and armature windings.  There is no fan on the controller running all the time like I see on most AC motor controllers.

This is an interesting discussion, but the guy who originally posted the question has not posted again.   Did we answer his question?

Modified 11 Mar 2006 11:58 AM
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jose_r
Nuevo leon, Mexico

Hi, We have 5 toyota´s 7FBEU18 and runs great with the AC drive, low maintenance, easy of service. Excelent units.
SOMEBODY hear something new about the new CLARK ECX with AC drive??

THank you

Posted 23 Apr 2006 01:04 AM

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etharp
North Carolina, United States

We just became the Clark dealer in the area i work in, and I have not had a chance to see some in harsh conditions with high hours and poor battery mantanance, but as far as driving, it seems every bit as nice as everyone else's A/C powered truck. not that much difference an operator would ever know.

Ww have had a little time now to consider A/C Tech in forklifts. at this point, I gotta say, the not having motor bursh and armature problems has lightened my workload some, and willl even more over time.

Posted 23 Sep 2006 11:48 PM

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DaveUK
BERKSHIRE, United Kingdom

Don’t know what everybody else thinks but 3 guys in this forum always seem to talk good sense and I always read their comments with interest, well done guys you make the forum.  They are: etharp, liftdoctor, and trainer.  I think it has all been said and everyone seems to favour AC drive.  In my humble opinion AC is best for Reach, Counterbalance and VNA. And SepEx is best for pallet jacks.
Only problem you will get with AC motors, is Encoder bearing failure.  The motors are “Asynchronous” 3-phase motors. Which means the Inverter logic needs the feed back from the encoder in the form of 2 channels 90 deg out of phase to detect direction and speed. This allows the Inverter to synchronise rotor speed and frequency to maintain the motor at its most efficient.  Think of it as the timing on an engine, as the RPM increase the vacuum advance moves the firing point more degrees before top dead centre.  Ac motors run with a slip value that varies with speed a torque…………………….Try disconnecting the encoder and test the result.  The motor will not run or run very slowly with a high frequency vibration and the current readings will be through the roof.  Don’t run ‘em for too long it could blow the inverter.
The bearings are tricky little buggers to replace and have to be fitted carefully to avoid damaging the encoder.  I usually warm ‘em up inside a plastic bag in warm water before fitting.  Anybody got another solution? Some of my colleagues emery the seating to make it slip on easy, but I always think this could cause problems in the future!

-------------------------
Who bravely dares must sometimes risk a fall.

Posted 27 Sep 2006 03:09 AM

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