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Old 08-05-2009, 11:40 AM   #2151 (permalink)
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Hey Don, that's exactly what Fran had just suggested to me about the throttle. He also said that it is often a problem when it goes below 0v. Hmm... The throttle pot is far away from the rest, and the wires are really long that could be picking up noise.

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Old 08-05-2009, 11:09 PM   #2152 (permalink)
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I will add the diodes to the next version controller board. The other way to cut out some of the interference is to make sure that you don't run low voltage signal wiring close and parallel to high voltage / current wiring.

If you need to cross a low current conductor over a high current conductor it should cross at 90 degrees. Also the low voltage wiring should be shielded with the shield connected to earth at both ends if possible.
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Old 08-06-2009, 09:22 AM   #2153 (permalink)
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Quote:
Originally Posted by KcElectricMan View Post
Since the idea of using a Atmega16 is being kicked around how about lets think about putting an H-Bridge into this so we can go in reverse without a transmission. Not everyone would need to build that part of the circuit if they only wanted forward rotation.
There are a couple problems with trying to reverse a series wound DC motor with an H-Bridge.

As current flows through the field windings it sets up a magnetic field. A second magnetic field is generated in the armature that is always in opposition to the first, because the armature current is switching direction from the action of the brushes. Because the field and the armature are connected in series, if you swap the direction of the current through the motor, you swap both the direction of both the field and the armature magnetic field and the result is a double negative. The motor continues to turn in the same direction. These motors are also known as Universal Motors as they can run on DC or on AC power.

A second problem with an H-bridge is that it requires more switching components (mosfets).

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An added benefit to this setup is the possibility to regen during breaking. Want to slow down? throw on the P- channel at a low rate. Kinda like a a Jake brake on a semi-tractor. Not full braking just a couple of hundred amps at the most.
I found an interesting study on series wound DC motors and regeneration. The author goes through the basics of series wound motors and used a half bridge with two contactors to achieve the reversing and regeneration functionality for a series wound DC motor. See pages 17-19 of:

http://eprints.usq.edu.au/501/1/DeanTHOMPSON-2005.pdf
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Old 08-06-2009, 10:11 AM   #2154 (permalink)
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Originally Posted by mcudogs View Post
I will add the diodes to the next version controller board. The other way to cut out some of the interference is to make sure that you don't run low voltage signal wiring close and parallel to high voltage / current wiring.
My potbox wiring does run pretty close to the motor loop wiring, but they don't cross and the two actually do run mostly perpendicular.

Could the diodes be added to the wiring on the potbox connectors (in these beta testing cases where the boards are complete already) and still be effective? They're easily accessible...

I switched back to 16 Mhz and it's working well, but I could add whatever components are required and see if I can get it to freeze up again. I don't miss the 8khz whine though. They have that rubberized asphalt stuff on the highways here in phoenix - virtually zero tire noise. Combine that with nearly zero motor noise and all you can hear is the whir of the vent fan. It's beautiful.
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Old 08-06-2009, 10:40 AM   #2155 (permalink)
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You are correct if you assume a series wound motor that is internally connected and only has 2 external terminal. That motor cannot be reversed simply by reversing the motor polarity at the external terminals.

For reversing to occur in a series or shunt wired motor you must have 4 external terminals. You reverse the series motor by reversing the field preferably. You reverse the shunt motor by reversing the shunt winding preferably. How can you tell the difference between a shunt or series motor when they both have 4 poles? The field on a shunt motor is only sized for providing the field current - much smaller the the armature current. A series motor must carry full current through both the field winding and the armature winding. Take some resistance measurement of the armature and the field windings of both types of motor that are similarly sized and you will immediately see the difference between the 2 of them.

The only Dc motor I can think of that can be reversed only having 2 wires leading to it is a specially prepared dc shunt motor that has its shunt winding internally fed from a diode bridge so that no matter which polarity you feed to the motor the diode directs the power to the shunt winding with the same polarity even though the power is switched going to the armature.

I know the simplified drawing I had a link too did not provide the complete picture. I will try to find my drawings from when I built an IGBT controller that was controlled by a 555 timer and was connected to 240v dc - 5 full size 48 volt forktruck battery packs. It had 16 - 300 amp Darlingtons set up in an H-bridge. It was used to power a 150 hp DC traction motor for switching trains inside of a Steel Mill I worked at.

It was not pretty, it was not ready to be driven on the street safely, in fact it was a bit scary - but it worked for 4 years that I know of and only failed one time taking out 4 IGBT's - they turned into slag.

But it did shift trains full of steel weighing hundreds of tons.
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Old 08-06-2009, 02:42 PM   #2156 (permalink)
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I don't currently have an EV but I am planning a conversion next summer and I was thinking that why not take advantage of the power steering pump that came with my "glider" in the first place. All I need is a motor to turn the pump.

Perhaps a motor like one from an electric lawn mower or some other motor.

Then I thought that it would be nice to reduce the power steering boost when running above a certain speed to avoid wasting energy....I need a controller.

I was thinking that a single mosfet/diode/cap stage would probably be enough for the power steering pump motor. The canev.com 12V systems have a peak 60A = 720W. At 120V that current is only 6A for the same power. That should nicely fit into a single mosfet/diode/cap stage.
What about a vacuum cleaner motor?
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Old 08-06-2009, 11:17 PM   #2157 (permalink)
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Most people who want to use power steering just use a main motor that has a front and rear shaft. The front shaft drives the transmission and the rear shaft drives the power steering pump / airconditioner etc.
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Old 08-07-2009, 09:55 AM   #2158 (permalink)
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Quote:
Originally Posted by jyanof View Post
My potbox wiring does run pretty close to the motor loop wiring, but they don't cross and the two actually do run mostly perpendicular.

Could the diodes be added to the wiring on the potbox connectors (in these beta testing cases where the boards are complete already) and still be effective? They're easily accessible...

I switched back to 16 Mhz and it's working well, but I could add whatever components are required and see if I can get it to freeze up again. I don't miss the 8khz whine though. They have that rubberized asphalt stuff on the highways here in phoenix - virtually zero tire noise. Combine that with nearly zero motor noise and all you can hear is the whir of the vent fan. It's beautiful.
The diodes have to be connected between pin 4 of J1 and gnd and +5v. There is no +5v or gnd on J1 so the only way would be to connect them on the pcb itself. R10 & R4 are connected to pin 4 J1 and are close to the edge of the board and probably the best place to connect the diodes.

I can send you the revised schematic by email if you like.
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Old 08-07-2009, 02:31 PM   #2159 (permalink)
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Originally Posted by mcudogs View Post
Most people who want to use power steering just use a main motor that has a front and rear shaft. The front shaft drives the transmission and the rear shaft drives the power steering pump / airconditioner etc.
Wouldn't that give maximum power steering at high speed when we really want it the other way around?
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Old 08-07-2009, 11:29 PM   #2160 (permalink)
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Originally Posted by mcudogs View Post
Also the low voltage wiring should be shielded with the shield connected to earth at both ends if possible.
This is incorrect, the shield should be connected to earth/frame at one end only (controller end that is). If there are multiple shielded cables they should if possible be connected to the same earth point.
The aim is to avoid earth loops.

In a similar way loops should be avoided in earth planes on printed circuit boards.


Last edited by squiggles; 08-07-2009 at 11:35 PM..
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