Upgraded the Cycle Analyst today to the large screen model. Very nice!
The shunt setting from the old CA didn't work by about a factor of two. Recalibrated, need to re-test. My usual ammeters aren't helping here due to the different connectors and high voltage. So I'm calibrating to the recharge amp-hours on the Cellpro 10S. Not the best, but good for now.
Next task may be to set the controller parameters and get regen going.
Thinking about setting the battery and phase current limits in the controller. I don't subscribe to the "2.5 times" or whatever factor rule. There are too many potential issues here that can make those factors wrong, even dangerous. Ignoring this can lead to overheating and smoke.Factors affecting Safe Current Limits:Battery Current Limit Factors
* Cell Current (factoring for parallel)(Turnigy 25C 10AH, 250A optimistically)
* Cell cables and connectors (2x #12, 2x 4mm bullets in parallel)
* Battery Cables and Connectors (#6, SB50)
* Controller cables and traces and shunt (#12)
I suspect the battery current limit for this setup is the controller wiring and traces. A #12 wire, type TW, single wire in open air, 86 degrees ambient, wire no more than 140 degrees F, with single layer plastic insulation, is rated at 30 amps.
So perhaps 30 battery amps is a good current limit unless the controller's input wiring is upgraded:
* #10 would be 40 amps (NEC ratings)
* #8 would be 60 amps
* #6 would be 80 ampsOther Battery Current Limit Factors (not equipment protection)
* Enforcing a power input limit for the motor
* Enforcing a power limit for range extension
It is better to use the Cycle Analyst for this since you can easily reprogram it in the field. On the other hand, for some applications like a power limited bike for kids or newbies, perhaps the controller is the right place to do it. In my case 20A for 1500W is about right.Phase Current Limit Factors
* FETs, accounting for parallelism (2 each 4110's in this 12 FET)
* Controller phase wires, traces and connectors (#12) (#12, PowerPole 30's)
* Motor wires cables, coil wires (#14?)
* Adjustment for 3 conductors (1.5x)
* Motor magnetic saturation
The motor saturation is hopefully the limit here. But we also have to worry about the #14 wires. To the first order I'll ignore the traces, hopefully they aren't the weak link yet. If the motor wires are really #14 the rating from the NEC, for single conductor open air, ambient 86F, wire less than 140F as before, is 25 phase amps. May need to beef up those phase wires!
The 30 amp PowerPole connectors in the phase leads, with #14 wires will have a temperature rise of 40C at 29 amps. So they are just better than the #14 wire itself.
Since three wires are used for phase current, and only two at a time carry current so the heating is reduced. This allows a 1.5x improvement over the wire's rating for current. So this would be 25*1.5 or 38 amps.Magnetic Saturation
Justin's measurements for the torque vs current knee are here:http://endless-sphere.com/forums/viewto ... =2&t=14494
It shows a drop in the torque to current ratio of 40% above this point:
70 n-m torque
9C 7x9 (9 turn) motor
50*9 = 450 amp-turns at the knee
With my 10 turn motor that would be 45 amps. Going above this phase current is quite inefficient, so we don't want to do that.
So the wiring is the limit at just under 40 phase amps. I'll have to measure the wires and confirm that.
If I upgrade the phase wiring and connectors the next limit is the motor saturation at just under 50 phase amps.
Regarding the FET limits, we have a 12 FET so there are two FETs in parallel in each phase. The TO220 package limit is generally considered to be 75 amps, and the paralleling derating factor is 50% of the additional FET for balance, so we only credit half of the second FET and 75 * 1.5 amps. Now we also have the 1.5 factor from using two phase wires at a time, which is another 1.5 so 75 * 1.5 * 1.5. Then half the time we are using the alternate set of hi side vs low side fets, so that gives another factor of 2 in heat dissipation so 75 * 1.5 * 1.5 * 2 which is about 300 amps IF the one FET can really handle 75 amps. If we want to run the FET conservatively we would take 80% of that, or 240 amps. If we want to be ultra conservative it would be half of that or 150 amps. A close inspection of the FET data sheet is indicated to see if further derating is needed. But since we already have a 50 amp saturation limit we can assume the FETs are not the problem here.
So to be absolutely reliable use 40 amps. To take minor risks with the connectors and cable use 50 amps. Going beyond 50 amps is a significant waste of energy and will cause a great deal of motor heating. If this is not enough torque, look into dual hubmotors or driving through reduction.
On the Regen, I need to set that for 75V max. Seem to recall there is a problem with high voltage regen, not sure where that happens. Have to do more searching. Thanks for any tips here!