tomjasz wrote: ↑
Dec 06, 2017 12:33 am
i have two MAC 10t motors and two EM3ev infineon 12FET IRFB4110 EM3ev Controllers (Black Case) and a CA3. Wondering what you would consider optimal power settings and battery voltage? I’m inept at using and interpreting the Grin chart. Learning but on z steep slope. Thank you.
The new Grin Simulator does 2WD natively so that will help you out.
Without knowing what you are trying to accomplish, it' really not possible to make and recommendations. Since you are using two identical motors with identical non-torque-throttle controllers, I'm guessing you are using identical wheels tires. That setup is inexpensive, super easy to set up, and always gives optimal efficiency when using a single throttle.
You will probably want to program down the controllers a bit - something like 35A battery current and maybe 70A phase current and zero block time (or as close as you can get). People do lots of crazy things with Macs, but impacts, jumps, starts on steep inclines with heavy loads, etc all tax the clutches so you need to hold back the phase amps and ramp your throttle with the CA to avoid eating a clutch.
The big thing will be you to figure out how much battery you can squeeze onto the frame. If you configure the two motors for 35A then they will want to pull a max of 70A so you would need a battery with a healthy C rate or else you will need to tone down the battery current in the controller/CA. A possible problem that you have is that you have 10T motors which have a low Kv and so need more voltage to go fast. As long as the bike is running in the controller-limited region of the curve (up hill, accelerating, etc) all motor winds perform the same so a Mac 8T would have the same torque as a Mac 10T - it's just that the 10T won't go as fast on the same voltage on the flat.
So - you need to figure out how fast you want to go to get your target battery voltage with the 10Ts. Then figure out what battery you can get/afford that will give you a healthy continuous discharge current. Divide that in two and that's the battery current limit (more or less) that you should use for your controllers - the CA uses an external shunt common to both controllers so that gets set to the full battery current. Macs like a phase-to-battery current ratio of about 2:1 for Infineons so set your phase current about twice your rated current in the controller. You can fiddle around with settings, but these rule-of-thumb numbers will work fine. So - as an example - if you get a battery with a constant discharge current of 60A, then you would set the CA to 60A max and the controllers to 30A 'rated' current (or a bit more - maybe 35A to get some headroom for fiddling with the CA) and set the controller phase current in the Infineons to about 2x the controller rated (battery) current or about 60A. Plug that stuff into the simulator and see what it will do.
So - as an example, if you get a 52V pack and want to climb a 10% grade you will see this:
This shows 24mph up a 10% grade without overheating with a power draw of about 1600W @ 84% efficiency. The controller is set to 35A/70A rated/phase Amps (max combined of 70A/140A) but we see that on this grade the bike is really only drawing 20A+20A = 40A. In fact, we see from the plots that we are out of the controller-limited range (to the right of the peak in the red line) and so the controller setting is not even in play at top speed on this hill. The controller-limited region comes into play under even heavier load like accelerating, but at the speed/load in this example it's really the motor that's limiting things. The same setup will hit about 28mph on the flat or go up a 15% incline at 22mph and eventually overheat in an hour (lonnnng hill). To make this work, you need a battery that can continuously discharge at those battery rates (say 40-50A) and you would crank the controller or CA back down to those levels (or maybe a bit higher so you can briefly accelerate before get down to the long haul).
If you go to a 72V battery on the same grade, you get this:
This is zipping up the 10% grade at 32mph and drawing about 46A from the pack. The bike should hit 37mph on the flat. But that's a pretty big pack if you are using Lion batteries.
Anyhow - hope there's enough stuff here so you can do your own What-Ifs depending on your specific terrain, loaded bike weight, funds, etc. Read my build thread - very similar to what you are contemplating.