However, over long cabling distances where voltages tend to drop and slew rates decrease, signal errors often occur. In a differential application, the host generates the original single-ended signal, which then goes to a differential transmitter. This transmitter creates the differential pair to be sent out over the cabling. With two signals generated, the receiver no longer references the voltage level to ground, but instead references the signals to each other.
This means that rather than looking for specific voltage levels, the receiver is always looking at the difference between the two signals. The differential receiver then reconstructs the pair of signals back into one single-ended signal that can be interpreted by the host device using the proper logic levels required by the host, Figure 3.
This type of interface also allows devices of differing voltage levels to operate together by way of communication between the differential transceivers. All this works together to overcome the signal degradation that would have occurred with a single-ended application over long cabling distances.
Signal degradation is not the only issue that arises over long cabling distances. The longer the cabling is within a system, the higher the chances that electrical noise and interference will make its way onto the cables and ultimately into the electrical system.
When noise couples onto cabling it shows up as voltages of varying magnitudes, but the benefit of using a balanced twisted pair cable is that the noise couples to the cable equally on each line. Because the differential receiver subtracts the signals from each other to get the reconstructed signal, it would ignore the noise shown equally on both wires, Figure 4.
The ability of the differential receiver to ignore voltages that are the same on both signal lines is referred to as common mode rejection. One of the other major physical layer benefits of RS is the signal voltage specification. RS does not require the use of a specific bus voltage, but instead specifies the minimum required differential voltage, which is the difference between the signal A and B voltages. This means that any RS device is able to receive the voltage range of -7 to 12 V, so an engineer can design the host system with any transmission voltage in that range.
This allows designers to create RS systems using their existing board voltages. With that being said, it is important to verify the product specifications to ensure that the device supports the full voltage range of the standard. However, they are also input tolerant between 0 and 12 V. This is especially important because as cable length increases, so does the voltage drop on the signal lines. RS is a duplex communication system in which multiple devices on the same bus can communicate in both directions.
In half-duplex, devices take turns using the same line where the host will assert control of the bus and send a command with all other devices listening. The intended recipient will listen for its address and then that device will assert control and respond back. It is connected to the RS differential transceiver that makes up the physical layer and converts the signals into the half-duplex differential format for use on the RS bus.
The host will then communicate with the RS through the UART, and it will tell the transceiver when to switch between transmit and receive. Slave devices will also use their UART in the same way. UART having dedicated transmit and receive lines allows it to operate as full-duplex, half-duplex, or even simplex, which means data only ever goes out or comes in on one line.
A UART interface is asynchronous which means that the communication does not include a clock. The host and slave devices must use their own internal clocks, and both devices must know at which clock-rate the data will be transmitted. This differs from a synchronous system such as Serial Peripheral Interface SPI where one of the signal lines contains a clock on which the listening device on the bus can capture data.
In addition, the UART generally has a normal format that most devices will use, but many options can be configured to change the norm. The idle state of UART is voltage high, so to begin transmission the UART uses a low pulse called a start bit, followed by 8 bits of data, and is completed with a high stop bit, Figure 8.
Immediately after the data leaves the transceiver, the host switches the mode of the transceiver to receive. When the slave is ready to respond, it transmits as the host did originally while the host now receives, Figure 9. The network layer deals with the actual communication between devices that occur on the RS bus. Because RS is mostly an electrical specification, the conversation could end here, but as it supports multi-drop, there is a need to address it in the OSI model.
There is no set specification for addressing the network layer, but the RS bus must be properly managed by a master to avoid bus collisions. Bus collisions occur when multiple devices attempt to communicate at once, which can be very harmful for the network.
When collisions occur, transmitters clash on both ends and effectively both create shorts. This causes each device to draw large amounts of current that could put the transceiver into thermal shutdown.
To avoid collisions, the master controls the bus and will make calls to individual devices. This is most often accomplished by having a command set that only specific devices recognize, or by having specific addresses for each device. The OSI model is not a set of rules but more of a model that helps engineers characterize systems. It appears to have regenerative braking.
However they warn that regenerative braking is not enough, and that you should also have mechanical braking. Looking closely at their web site, they offer a PM controller or a PM controller with regeneration. The serial number has this coded, and the one I bought does not have regeneration.
I thought I would chime in on this one, as I just completed my conversion of a four wheeler, using a Kelly Controls A controller.
I contacted Kelly directly, and inquired about ordering the correct controller for my motor. I have a used Elec-Trak field wound, seperately excited 36V motor. They recommended a particular controller and I ordered it. Well It did not work on the first try, and from the beginning Kelly said they would be willing to help develop a controller that would work with this motor. I contacted them, and they worked immediately on solving the problem.
They e-mailed programs for me to down load, and settings to try. After about a week, they sent me a tracking number and informed me a new controller was on the way with a modified field current and modified field saturation setting.
The second controller arrived in 3 days. I plugged it in and it worked right out of the box. So my first impression is excellent with Kelly. Their customer support was the greatest. The product seems to be very good. I took a risk with Kelly, as AllTrax has a controller already for this application. It seems the risk was well worth it. I hope too soon see a large vehicle controller v from Kelly. I am ready to convert a car, and I would order a Kelly Controller as my first choice.
Looking forward to checking out the new controller and seeing the elite up and running : Thank you for ordering it :. Just a point of information. I ran into a funny situation Dec. We were playing around with the 4-wheeler we converted using a Kelly Controller. When we first went to use it, The controller would not pull in the contactor. I thought it was a low voltage problem, but as it turns out, the Kelly controller won't energize the motor below 20 degrees C. After checking the error code, I realized that it was just too darn cold out about 5 degrees C.
I hope this controller produces the desired result. When setting the configuration of the new Kelly controller, I encountered something the people at Current told me nothing about. The last settings - after the controller temperature shutoff settings are something called "smooth setting" these settings include:. The defalut settings are "enable", 10, , , I strongly suspect the "low accel, low decel, hgh accel, high decel" settings will simply limit current to the set values, and the "inflection point" is the point at which the low and high sections converge.
Feel free to ask Fany C. I know about the inflection point from him. But knowing Kelly I am pretty sure they have not modified that waveforms in any way, the grwoling will simply reduced with less current, and thus acceleration will also be less I configured the controller settings per CuMoCo's recommendations.
I left smooth settings where they were. CuMoCo told me the the scooter would be quieter and have noticeably more starting torque - I noticed neither, in fact it was producing a bit of a "sputter" upon starting off.
I tried enabling the "noise reduction" setting. The result was less starting growl and less of that sputtering, but at the expense of a some starting torque. I then tried disabling the "smooth setting".
Oddly once disabled, re-enabling it did not bring back those five settings on the configuration window. I then took my third test ride - still no performance improvement - in fact it was probably a bit worse than the old controller. But at least the regen was working properly, and the old controller's annoying bbpppbbbpppbbbpppTT! But then - exactly coincident with hitting a moderate bump in the road, the controller stopped completely, aside from a some sputtering noises from the motor. No error flashes from the controller or BMS.
I smelled a slight whiff of something hot or burning. I was able to coast the scooter down hill most of the way home then a hell of a workout pushing the scooter uphill to the house. I regret not insisting that Current sell me the controller.
I suspect that Kelly, like so many Chinese manufacturers, probably practices lots of QC for products going to OEM's with a nice contract, but they sell crap to retail schmucks like me.
Time to put the malfunctioning - but at lest operable old controller back in. What are people's experience with Kelly's warranty service? Regarding Sevcon controllers, supposedly John, formerly at Current, was hoping to use Sevcon controllers in their scooters, but they would not return his phone calls or e-mails.
The hardware is upgraded also. We added the smooth control parameters in the user program. When you enable the smooth funtions,you will see five more parameters. You can adjust the low speed acceleration and decleration rate,and high speed acceleration and decleration rate in the user program. The inflection point is at the joint of low speed and high speed. But this new software version needs the new firmware and hardware to support. Sorry,it only can be useful on the new controllers which are produced after July.
Your controller can support this new functions. Usually you don't have to configure it if you think the current setting can drive the motor smoothly. Clear as mud. What does this physically mean? Deceleration and acceleration in any kind of motor vehicle is controlled by the human-operated throttle and brakes, what does it mean in the sense used here?
I suspect male because I talked to him on the phone, and the voice was lower than any female with regular hormone levels would have ;-. First of all, a Kelly controller will only save a newly programmed setting into it's memory if the controller is turned off and then on again after quitting the programming.
If you leave it on after quitting nothing will have changed yet. It is interesting that Fany talks of a "rate". It would imply that the new settings simply regulate how much time the controller takes to apply motor current in reaction to "throttle" changes. This is what I do manually to reduce mechanical wear and tear to the resin keeping the coil wires in place: When starting from standstill and I can help it I tend to apply the throttle very gently until the scooter begins to roll at more than walking pace, and then I apply whatever throttle setting I like.
This way the rough bangs of the block commutation do not cause such a groan when the motor is still very slow. When it speeds up a bit the inductivity begins to smoothen the current rise after commutation so the groaning is reduced. I suspect this is what these new settings do But be prepared to pay return shipping yourself, and they will send a replacement at their own cost. And my privately ordered controller was in no way lower qualty than the stock Kelly that was in my bike. I assume you may have some hall switch trouble in your motor, not necessarly a glitch in your new controller too.
Or it may be a loose elctrical connection if it quit on you after a bump? The controller was most definitely bad. The motor has two sets of hall sensors to provide a backup - and it malfunctioned with either set connected. All connections were re-checked and good.
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