Smoke came out of the reverse half of the H Bridge, then when we changed directions, smoke and sparks billowed out of the Forward half.:shade:
Naw, it's just a noisy circuit with a not so well triggered scope. Remember we are measuring across the motor with a load (driving a loco laying on it's side), so the collapsing BEMF field of the motor, and that little disc cap that Marklin put on the motor are causing the scope to trigger funny. :shade:
Folks, Here is some initial data. This is what we (Me, Mike and Rob) tested We ran a new 5 Pole motor in a Mikado with 1) DC 0-8V 2) DCC Voltage at the track set at 8.75V Step 1-28 (Decoder programmed for 28 Steps) 3) DCC Voltage at the track set at 16.06V (This was the Max Rob could go with his power supply) Step 1-28 Here is the graph showing the motor currents. On the left scale is the Current, Bottom DCC steps and top DC Volts and the corresponding graphs. You can see there is not much difference in current in DC and DCC. Also the speed is propotional to your current so if you have a DCC system you supply any recommended voltage you have for your DCC system and program your decoder so the max speed does not exceed your 8V DC speed then your stall current will also be the close to your DC stall current. Regarding Burning motors just check Jeff's post above. You can burn motor with DC and DCC if you stall and power it long enough. Another note on Dirty or or a heavily loaded motor you will notice that you will need to run it at a much higher speed step for normal speeds, you will see the same with DC, you will have to run it at much higher voltage for normal speeds. If you are a regular runner you will notice this and lube or clean the loco. If you run it at shows these at the few things you will notice first. So Bottom line if you are running DCC you will not burn the motor just because you have a higher voltage. I was planing to run the Mikado at 40V and reasonable speed for an hour and show no heating or burning but the amplifier I had did not respond to the PWM. If there is still doubts about burning motors I'll do it, if not it is not worth the time. The only precaution you will have to take is setting max loco speed, so you cannot accidentally run up the loco to max current when stalled. Kim
More waveforms seen at the motor In all the graph the the bottom wave is the zoomed in portion of the top wave Graph shows step 28 (Max Speed) All speeds are reversed so what you see on the graph is a negative voltage. The small portion of the PWM is when the DC voltage is OFF. The motor drive frequency is 50Hz DCC voltage set at 8.75V. The Scope scale is 2V per div. Same conditions as above but DCC voltage set at 16.06V, The Scope scale is 5V per division here. This is at Speed step 1 DCC V = 8.75 Speed Step 1 DCC Voltage at 16.06V All this graph show is you are pulsing the motor at track voltage - Decoder voltage drop Kim
Thanks Kim! So there you have it, data showing that as DCC Track Voltage goes up, the motor voltage also goes up, but the duty cycle goes down (pulses are shorter duration of time) so the motor receives approximately the same average power, and that power very closely matches what the motor would see from a pure DC source. Bottom line is, we really don't need to set our DCC track voltage lower under normal operation. It don't hurt, but for those concerned who did not add the diode bank voltage reducer, as long as you don't run your locos at full speed, you should be safe. I am still leaving my NCE systems set at the lowest voltage though.
Kim/Robert Real nice info. Now what you should do is set up a side business of curve matching for setting up MU's. Probably wouldn't work. The item of real interest here is that "high" voltage is not the problem that many had led us to believe. Thanks for running this experiment. From my viewpoint, it is pretty hard for me to believe a dinky little $25 chip can do this all so accurately.
