Help with DC motor wiring

Methinks you have a mystery wire you don't know about. Perhaps an extra shunt (or series) field directly connected?

...Jim Thompson

--
| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |

"The American Republic will endure until the day Congress
discovers that it can bribe the public with the public\'s money."

                 - Alexis de Tocqueville

That sounds like a seriously fun project. I want pics of the go kart too!

Presumably with scenario A you were running with the remnant magnetism giving an acceptable field strength and top speed. With B you probably had too high a field strength that resulted in the slow speed

- if you measured the current I expect it would have been lower than A.

For some reason by the time you tried C the remnant magnetism was too low to give reasonable running and the high-current tripped out then damaged the controller.

I think the best approach would be B but with a resistor in series with the field to adjust the top speed (maybe the 20 Ohm you originally miswired in A as a starting point).

kevin

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

Jim, there could be, I'm about to make a second forage into the motor and see if I can make a diagram of the motor.

Only wish I had taken more, and a good video before it died. Looks like three weeks to get the controller back from repair. Here's a picture.

Only wish I had taken more, and a good video before it died. Looks like three weeks to get the controller back from repair. Here's a picture.

Mike

Years ago I souped up a golf cart, for street use in Sun City, by shunting the (IIRC) series-wound field.

I used ordinary copper house wire for the shunt plus a starter relay to switch it in and out... head light dimmer button under the throttle pedal to control the starter relay ;-)

One of my uncles owned a golf cart place over there and sold hundreds with the modification.

Can you imagine 80+ year old little old ladies doing 27MPH screaming down the streets in golf carts ;-)

...Jim Thompson

--
| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
 I love to cook with wine     Sometimes I even put it in the food

picture.http://i395.photobucket.com/albums/pp37/Qmavam/gokartreduced.jpg

That looks sweet. Is it for a kid? I'm getting a sense of scale from the batteries that suggests that.

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

SNIP

Ok, I've disassembled the motor, it has four coils on the stator. Two of these (180* apart) have fine wire, (about) #23. The other two (on the opposite 180* apart) have (about) #15 wire. So yes, there is some mystery wire. I suspect the two coils of #23 wire is the Shunt field. The other two coils made with #15 wire are a bit strange, the have three different color varnished wires. ( possibly 3 paralleled coils?) The motor wire is sleaved and tied so I can't see any ends or connections. The motor has three motor connections coming out, labeled A2 and F2 (heavy wire) and F1 (smaller wire). F1 to F2 is 41 ohms, A2 and F2 is to close to zero for my meter to measure. Here is a picture of the motor plate.

I still don't have an understanding of my motor, the wire labels don't work logically for either type motor.

I think the motor is the 4 lead shunt type because of the lack of other connections (S1 and S2) Any help appreciated, Thanks, Mike

I fit in it just fine, thank you! It's a full size gokart, the guy I bought the original kart from is about

6'1". It started as a project to get my 14 yr old son building something instead of playing video games. Sigh, it was mostly a dad project, he only occasionally got involved, but hey I'm having fun! Here's another picture with my 17 yr old daughter coming in for a pit stop.

Mike

Or measure your current and adjust the sprocket on the motor.

At any rate, as you adjust the field current up in a DC motor like this the torque constant (which is the foot-lb/amp that the motor can put out) goes up. The torque constant _is_ the speed/voltage constant times some adjustment ratio, so as you increase the field current you not only give the motor more oomph you also make it want to go slower.

If it's rated for 28 volts I'd put a resistor in there to drop the shunt voltage to that figure, go with your wiring diagram B, and adjust the gearing ratio.

If you don't mind sticking your neck out a bit as far as motor life goes, consider yet another battery in there, with a 48V armature supply and a 28V field. 'Course, your controller should be up to the voltage and have the correct current limit...

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

I don't understand the point here? I have an amp meter on the kart, so I measure, at what current, at what load, and adjust the sprocket for what spec? My original goal was 25MPH at about 90% of the 2600rpm motor spec. However, I'm using 36 volts not the 28 volts the motor is spec'ed at. A neighbor checked my speed against has vehicle and reported almost 30 mph.

Interesting, so how do I incorporate that into a plan for fast acceleration and then high end speed? ( other than buy the proper controller :-)

I have a fixed 20 ohm resistor in series with a 50 ohm reostat to adjust the shunt current. I think I have some room for a taller gear, the current at full speed is well below motor spec. So I think I could load the motor some more with a lower sprocket ratio.

The original plan had a 48v battery pack, but my first attack on the local auto scrapyard only yielded 3 good batteries. Also I think it was good to start with a little less power, nothing got hot. The controller is rated for

48 volts and is safe to 60 volts. Correct current limit? hmm, the limit is fixed at 300 amps, a bit high for 62 amp motor.

Thanks, Mike

I don't know about it running on residual magnetism, we drove it 4 days with no change in performance until curiousity got the best of me and I started changing wires. In other words nothing changed until I changed it.

I don't recall having high current as I drove it, also it is fused well below the current limit of the controller.

Bigger sprocket = more cart speed per motor speed.

Bigger sprocket = more motor torque for any given cart condition.

More motor torque = more motor current.

So play with the gearing to make sure you're using all the motor has to give.

This is why I was suggesting a switchable resistor to the shunt -- give yourself high shunt current at low speeds, then (as an alternative to a mechanical gear change) give yourself lower shunt current at high speeds.

It'll kinda sorta act like a gear shift.

If you could adjust the current limit down you could let anyone jump in the thing and stomp on the throttle without worrying about smoking the motor. As it is, all someone has to do to burn up your nice motor is slowly bump the front wheels into a wall then floor the throttle (unless that just spins the rear tires).

(come to think of it that points out a safe gearing for the motor -- adjust the thing so it's pulling full current with the tires spinning. You'll be able to pull _more_ than full current if you hold it short of smoking the tires, but not for long before you've accelerated up to high speed).

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

That motor requires that the F1+F2 (field) be connected to a constant voltage source of the rated label..

If you apply less voltage than the rated max, the motor will have more RPM but less torque. More Field voltage up to it's max will give you more starting torque but less RMP's

SO, all isn't lost how ever, the "Series" field is there to offset the fields effect in the torque/speed window.

Most of the time series are configured for torque which means, when wired in series with the armature leads A1+A2+S1+S2 in CW direction will give you extra starting torque because the current that is exerted in the armature leads also goes through the "Series" leads which are in the Field. This increases the field for more torque and reduces RPM abilities.

So the trick is to reduce the fixed field voltage down a bit, like in the 75% range and use the series winding when the armature is exerting high currents which assumed is being generating from take offs and such.

When RPM's pick up and inertia loads are reduced, the current in the armature will also reduce along with the currents in the series field which in the end reduces the field current. Weaker field means more RPM's and thus, you have a motor with take off torque and speed compensation.

If you have a motor controller with a auto field weakening option, then don't use the series winding. allow the controller to do this for you while it controls the field.

"

Hi Jamie, I'm still don't know the layout of my motor, maybe you can help. I know it has four poles. Two of the poles have coils with many turns of # 23 wire, these are 180* apart. The two other poles have coils with less turns of #15 wire. These coils have three diffferent color wires. I suspect they're three coils in parallel, but no clues to confirm this. The motor has four brushes, two of them 180 degrres apart are electrically connected, and the other two are also 180 degrees apart and electrically connected. I have only three wires out of the motor. F2, A2 and F1 Here is the motor wiring plate ,

What does CPNS and IP stand for? Do you think my motor has these? Or do you think it has just a series and a shunt field? Are there any measurements I could make that would help me make a proper schematic? Could I put voltage on leads and the check magnteic fields? Thanks, Mike

[snip]

Motor theory suggests that a series field motor should not run at all with connections A or C. Some small amount of torque will be generated due to residual field pole magnetism, but nothing worth using.

Is it possible that the motor you have is compound wound? It might not be evident from an inspection of the wiring terminals, as the series field connection might not be brought out to the terminals.

--
Paul Hovnanian	paul@hovnanian.com
-----------------------------------------------------------------------
Have gnu, will travel.

This (the #15 wire) is most probably a compensation winding. Its not really a series field as in a compound motor, but it is there to correct for the field distortion when the motor runs at different speeds and/or under changing loads.

It may be possible to get such a motor to run as a series motor (it appears that you have done so) but this falls outside of its design specifications.

One thing to be careful about with series motors is overspeed in the event the mechanical load becomes disconnected.

Yes.

The best way to measure the low resistance circuit is to lock the rotor down, apply a volt or two across the A1, A2 terminals and measure the millovolt drops and polarity from point to point.

"CPNS" stands for "compensation".

Treat this as a shunt field motor.

--
Paul Hovnanian	paul@hovnanian.com
-----------------------------------------------------------------------
Have gnu, will travel.