Hey guys, Just about to start wiring up motors for my Iowa-class, and while I have the wiring diagram for MAG-type setups, I am using an ESC instead and wanted to see if that wiring diagram is the way to go (with ESC in place of the MAG switches and resistor) or if there is a different, more efficient, and also safer way to go about it.
I tend to favor a parallel motor setup when using two motors on a single ESC. In the parallel circuit, both motors get full circuit voltage. If one motor dies, the second motor will continue to operate. The Richelieu used this setup for years without any problems.
Which means that the motors don't share any wiring at all, but receive current straight from the ESC? the diagram I have must be a series diagram; for counter-rotation, the port motor sends its negative to the starboard's positive, and the port motor is the one that receives the power.
Well I have heard from some that running the motor in reverse all the time is not the best thing to do for them. But, neither is the enviroment they run in too. I would have to think that it doesn't matter either. I am also curious how the ESC would care.
Two motors wired in series will share the available voltage. For instance, with a 6 volt battery, each motor would use 3 volts. If the motors are perfectly matched, both motors will turn the same rpm at 3 volts (not 6 volts). Variables such as prop shaft resistance or dissimilar motors will cause one motor to work harder and draw more power away from the second motor in the circuit. So what happens is one motor is doing more work (load) on a finite voltage shared between two motors. That can lead to the harder working motor to fail or wear out earlier than the second motor. Not to mention if one motor does burn out, then the second motor will stop working also. This is all very layman by the way. There are far more variables that effect both types of circuits.
As for running a motor in reverse ... If the motor is designed for one direction by having it's timing advanced and fixed off of neutral timing, then running it backwards may indeed cause extra wear on the brushes/commutator and draw more amps. Frankly, I do not know if the standard 540 or 550 size motors we use have advanced timing. Even so, it will take time to wear it out if it was running in reverse.
I was being coy, Mike... I have breathed more DC motor dust than most people will in their lifetimes Not that I enjoyed it. But cleaning a 13-ton DC motor from the inside twice a month for several years will give you new perspectives on them. Don't get me started on the control circuitry Any DC motor with the customary commutator setup can adjust its timing, in theory. How hard or easy it is depends on the motor. The cheapies I've gotten from Johnson can be modified to adjust their timing, but if you aren't heavy on DC motors, I advise to leave well enough alone. If you have a performance 550-size motor with adjustable brush rigging, many of them come with instructions on adjusting timing. Be warned, if you go too far, you will greatly increase brush wear, and can if you go far enough do some light welding After all, the whole thing is designed from the factory to ensure that commutation takes place in the 'neutral plane', where no (or minimal) current is flowing thru the brushes. On tiny lil commutators like our motors, you're going to have some undesirable current flow thru the brushes regardless, but not enough to kill the motors. Why some motors get the heaves if you run them backwards is that the manufacturer (working under a unidirectional specification) sets the timing advanced in that direction, so that as the motor speeds up, the shift of the neutral plane with the increased armature current will move into a better position. When you spin the same motor backwards, the neutral plane rotates AWAY from where you want it (no free lunch, right?). This eats up the brushes due to arcing and sparking from commutating outside the neutral plane. While I agree with Mike on most things, I have to respectfully disagree with his statement about motor voltages in series. Two motors in series will share the same current, which is proportional to their summed resistance(and summed CEMFs) versus the voltage applied. If one bogs down, its CEMF goes down, and thus the total resistance goes down, increasing the overall current seen by both motors. Two motors in parallel will see the same voltage, but the current that each motor draws will be affected by it's own resistance plus CEMF. The motor that is more bogged down will slow, reducing its CEMF, thus increasing current (to that motor only), which increases speed until the CEMF + resistance of that motor equals that of the other motor in parallel. Summary: Motors in series = get the same current, motors in parallel = get the same voltage. If anyone really wants to jump in and tell me I'm wrong (could be!), be prepared to school me in Kirchoff's Voltage Law and Kirchoff's Current Law. Those unfamiliar with these, can check Wikipedia or call Gascan, who is currently attending Nuclear EM A-school taking Basic Electricity, and should be a heavy toad on these things.
Firstly, can't thank you guys enough for all the input. Sounds like for these Johnson 550s that I have, running them in parallel from the ESC will be the best option, so that in the worst case, I will always (ideally) have at least one functional motor to push the Iowa-class monstrosity (now so very close to getting in the water!) around. If I were doing a MAG-type throttle assembly, I might go with what the series diagram gave me, but the idea of variable throttle is just too good to pass up.
Just remember that if you have two motors in parallel on one ESC that if one stops entirely, it will pull more current than the operating motor, reducing the current to the operating one. Series is okay, if one gets mossed and stops, its resistance will go down, and actually increase current to the operating motor (because total system resistance goes down and therefore the total current goes up). Win! Lest I sound too smart, I will step up and admit that I drew those drawings on the MWCI How-To site. The parallel arrangement will be corrected to series Not sure what I was thinking when I drew them
