series wound dc motors

[islandlodger]

HI mr electrical boffin
I HAVE 2 SERIES WOUND DC MOTORS THAT WERE SUPPLIED TO ME AS 24hp CONTINUOUS, AT 72VOLTS, 36hp PEAK. WHEN I CHECK THE INTERNET ALL I FIND IS THAT THESE MOTORS CAN BE ONLY 10/12hp.
ANYONE HAVE KNOWLEDGE OF DC MOTORS?
WOULD BE GREAT TO FIND THE TRUE hp AND TO KICK THE SELLER'S BUTT.
CHEERS
ISLANDLODGER.
islandlodger@yahoo.com

[CDK]

Power is voltage times current. Since you state only voltage, nobody can tell you the power rating without additional information.
For the power range you are talking about, series wound motors are unusual because they have no stable rpm. With insufficient load they reach suicidal speed.

[lazeyjack]

thats dragging abt 250 amps, where will thejuice come from? to run?

[islandlodger]

HI ALL
CAN YOU TELL ME WHAT IS THE PEAK AND CONTINUOUS HP RATING FROM THIS DOCUMENT? PLEASE, IF YOU CAN, PERHAPS YOU CAN TELL ME HOW.
THESE MOTORS WERE PART OF AN ELECTRIC MOTOR SYSTEM FOR A CAT. THE USE OF 12x6VOLT DEEP CYCLE BATTERIES OF 225A/HR PER MOTOR, POTENTIOMETERS, ALLTRAX CONTROLLERS, WERE THE SYSTEM.
THE MOTORS ARE FROM DD MOTORSYSTEMS NEW YORK USA,
MODEL# ES67A-29. THEY REFUSE TO COMMIT THEMSELVES TO ANY RATING. THEIR ATTITUDE IS THAT I MUST GET THE INFO FROM THEIR DEALER IN MY COUNTRY. I RESIDE IN THAILAND. THE AGENT'S ARE CLUB CART ASIA IN SUNNY PATTAYA. THEY SUPPLIEDTHE DOCUMENT. THE DIRECTORS OF THE COMPANY ARE MR.MARK FORTUNE (SOUTH AFRICA) AND A MR ROLAND BECKER (AUSTRALIAN) (A SUFFERER OF ACCUTE VERBAL INCONTINENCE)
THE ORIGIN POWER WAS TO BE 36HP DIESEL OUTBOARDS - BUT THE NOISE!!
THE BOAT DID NOT PERFORM:- 6.8KNOTS AS AGAINST ABOUT 20KNOTS.
I SEE THAT WEB SITES ALL STATE THAT THIS MOTOR IS ONLY 12 HP @ 72VOLTS, WHICH WOULD PROBABLY ACCOUNT FOR THE LOW SPEED.
ANY HELP WILL BE BE GREATLY APPRECIATED.
CONTRACT DOCUMENTS CLEARLY STATE:- 24HP AND 36HP PEAK.
THE CATAMARAN WAS BUILT BY ***** ********** - SEE POST -
LOW PRICE CATAMARANS
CHEERS
ISLAND LODGER

[Rick Willoughby]

Firstly I would like to draw your attention to item 19 here:
http://www.101emailetiquettetips.com/

Not a particular issue for me but some people may feel you are screaming at them.

OK - Now for the motor. It is rated at 12HP on 72V, say 200A. You will find this aligns well with its peak efficiency of 83% just before this power output. To get this power continuously it should be in a well-ventillated location and less than 40C ambient temperature.

The test data indicates it can cope with 388A. On 72V this is giving 23HP. The peak power you will be able to get will depend on the controller current limit and the gearing in conjunction with the prop pitch.

Running the motor well above 12HP (200A) for more than a few minutes will fry it. Many of the motors have in-built thermistors that can be wired into the controller to cut power should the temperature rise dangerously.

The motor is capable of running up to 144V. So you could expect a continuous rating around 24HP at this voltage. Problem is that the brushes will not last too long. Also if the motor is allowed to freewheel it will likely throw itself to pieces.

So you need to check if the controller is rated to 144V. If it can take this then initial trials could be done by putting the two battery banks in series to get the 144V.

You could expect to get about 20 minutes running from the batteries at 24HP per motor with the existing batteries. If you double the batteries they will run for maybe 1 hour but the speed will drop because of the extra weight. I hope you did not expect to go very far.

The thing that matters is the current. You should not exceed 200A for more than a few minutes. The sort of time to get on the plane and then ease off. Increasing the voltage will give more power for the same current but comes at the cost of shorter bearing life and brush life so maintenance costs go up. These are duty dependent so you just need to see if they are adequate for your needs.

Rick W.

[islandlodger]

Thanks Rick
Sorry i'm new to this. but i'm learning too!!
The info was very informative -
the controllers were only 72v.
I will put my thinking cap on and my special boots for kicking.
cheers
island lodger

[Rick Willoughby]

Originally Posted by islandlodger

Thanks Rick
Sorry i'm new to this. but i'm learning too!!
The info was very informative -
the controllers were only 72v.
I will put my thinking cap on and my special boots for kicking.
cheers
island lodger

An important item to measure is the current. If the motors are not propped correctly then they may not be developing anything like 12HP.

If you provide some detail on the hull (shape and displacement), props and gearing if any then it would be possible to do some calculations.

Measuring motor current should be a pre-requisite of the installation. Do you know what current is achieved at full throttle. Also check motor voltage. The controller may have an internal control limit. Most of the controllers have programmable settings. Silly part about this is that most require a computer coms port for setting so are not compatible with computers today.

Rick W