48V in a 36v system

[cadstarsucks]

Thinking about it, I guess all the losses are resistive (some in the coil, some in the core) except for the loss due to friction which I would assume would be quite small.  So that would blow my "tens of watts at most" out of the water     But I have noticed that the actual current draw at both 36V and 48V is about the same (Peaks at around 30A on startup and then drops to around 20A during operation.) 

There is a metal bridge on the controller board leading to the neg. rail.  I assume that it is being used as a current sense resistor.  I haven't traced out that part of the circuit, but I am guessing that it leads back to an op-amp (I thought there was an LM356 on the board, but it may have been a LM358... It's hard to see the markings.) to cut back the duty cycle when the current gets over 20A.

Pete

LM358 would be an opamp.  I would have to see it to know the the thing is.  As to losses there are copper resistance losses, and magnetics losses in the form of eddy currents (normally not an issue) and hysteresis losses (which would show up at higher frequencies so at 60Hz should also not be an issue).

Dan

[myelectricbike]

At 320 RPM and 46 poles Golden sensors switch at 122.66 times per second per phase, however, their are 3 phases to consider and 2 directions of current flow per phase. Golden yokes are laminated of course to minimize Eddy currents. Surprised no one has yet mentioned Counter EMF.

However, again in relation to the topic copper conductors with smaller crossections represent greater electrical resistance and it is greater electrical resistance which results in the constraint imposed upon the HBS-36 not being suitable for use with 48 volt controller without upgrading either the power phase lead insulation or the power phase lead gage, still with the risk of thermal damage to the windings without upgrading them as well.

[cadstarsucks]

At 320 RPM and 46 poles Golden sensors switch at 122.66 times per second per phase, however, their are 3 phases to consider and 2 directions of current flow per phase. Golden yokes are laminated of course to minimize Eddy currents. Surprised no one has yet mentioned back EMF.

However, again in relation to the topic copper conductors with smaller crossections represent greater electrical resistance and it is greater electrical resistance which results in the constraint imposed upon the HBS-36 not being suitable for use with 48 volt controller without upgrading either the power phase lead insulation or the power phase lead gage, still with the risk of thermal damage to the windings without upgrading them as well.

Nice, a three phase adjustable HV drive would work then.  I have mentioned it indirectly previously: motor voltage is directly proportional to motor speed minus the IR drop ( current times resistance = voltage )

Scaling the motor voltage with motor speed over nameplate speed maintains the copper dissipation in safe limits while supplying rated torque at higher RPMs.

Dan

[myelectricbike]

Unfortunately Federal law prohibits ebike top speed of over 20 MPH, and modification is required to HBS-36 wiring to gain low end torque and acceleration to forestall thermal damage when 48 volts is applied.

However, PPL measurements consistently show an exponential increase in rotational losses verus motor speed and a linear increase in winding resistance per increase in rotaional speed at rated current.

[cadstarsucks]

Unfortunately Federal law prohibits ebike top speed of over 20 MPH, and modification is required to HBS-36 wiring to gain low end torque and acceleration to forestall thermal damage when 48 volts is applied.

Indeed unfortunate, unless you care to register as a motorcycle.

You can get more torque and acceleration if you reduce the rim and the rerate to bring the speed back up. 

You could, for instance get maximum torque by using the Golden 36V 500W motor on a 12" rim for the most stock torque at 11MPH.  Then, using a 72V rail and a special controller, bring the speed back up to the legal limit at around 1000W.

Dan

[myelectricbike]

The consumer market, unfortunately dictates wheel size and even though a smaller rim would allow higher RPM to be achieved faster during acceleration and reduce the duration of the load and wattage demand, the HBS-36 has 60c to 90c insulation which prohibits handling heavy or sustained loads with 48 volts, much less 72 volts, without wiring modification. Furthermore, if such modification makes an ebike motor capable of handling more than 750 watts then it can not longer be used.

[mustangman]

 The only was to change the federal law of course is through act of congress and a revision of the current law. The Federal law could look to California as an example of what the final version should look like. As far as the watt limit of 800, you could classify the motor for offroad use to get around the current regulations.

[Dalecv]

In Oregon electric bikes are limited to 20 MPH and motors to 1,000 watts. It is interesting in hearing that there is a federal law limiting electric bikes (what happened to state rights?). I have yet to see a federal TRAFFIC cop patrolling the highways around these parts to enforce any such laws.

[cadstarsucks]

The consumer market, unfortunately dictates wheel size and even though a smaller rim would allow higher RPM to be achieved faster during acceleration and reduce the duration of the load and wattage demand, the HBS-36 has 60c to 90c insulation which prohibits handling heavy or sustained loads with 48 volts, much less 72 volts, without wiring modification. Furthermore, if such modification makes an ebike motor capable of handling more than 750 watts then it can not longer be used.

Why do you insist on missing the point?  CONSUMER controllers would indeed cause a melt down, I am not denying this.  Wire temperature is related to CURRENT not POWER, were it not so they could not use ALUMINUM in high tension wires.

As an electronic DESIGN ENGINEER, I should know.  You, on the other hand have as yet, to my knowledge, admitted to being anything but a hobbyist.  As a further proof of my authenticity, my nick originates from the piece of crap that Puken (Zuken) Redac puts out known as Crapstar (Cadstar), which I am forced to use daily.

Dan

[myelectricbike]

Maximum current capability ratings are normally base on line voltage with maximum current ratings based on insulation temperature and ultimately wire size.

The reason you can use higher current at lower voltages is because wattage is a function of current times voltage. Thus wattage or power in the presence of changing voltage and current is used to rate wire capacity, still based on insulation temperature and ultimately wires size, i..e., wire diameter or crossection.

Thanks for the warning.

[cadstarsucks]

Maximum current capability ratings are normally base on line voltage with maximum current ratings based on insulation temperature and ultimately wire size.

The reason you can use higher current at lower voltages is because wattage is a function of current times voltage. Thus wattage or power in the presence of changing voltage or current is used to rate wire capacity, still based on insulation temperature and ultimately wires size, i..e., wire diameter or crossection.
 

Ummm...NO, you can NOT use higher currents.   The rotor resistance is constant, if we ignore the copper tempco, and the power dissipated in the winding resistance is the current squared times the resistance.

Dan

[myelectricbike]

In Oregon electric bikes are limited to 20 MPH and motors to 1,000 watts. It is interesting in hearing that there is a federal law limiting electric bikes (what happened to state rights?). I have yet to see a federal TRAFFIC cop patrolling the highways around these parts to enforce any such laws.

I was surprised to find that many bus drivers and cops know of the 20 MPH/750 watt limit. Shortly after stating in a conversation that I was experimenting with 48 volts and could do 30 MPH I fortunately spotted a cop at the far end of the quarter mile parking lot I normally use to check speed, in line with the diagonal traverse I regularly use. Since I had already done the speed check I was concentrating on conserving battery power and reserving it for hills on the return trip to carry my load. He smiled as I passed instead of cranking up and coming after me so the moral of the story is watch out for cops. Do all of your greater than 20 MPH or 750 Watts testing off-road or in a parking lot like me.

[myelectricbike]

Maximum current capability ratings are normally base on line voltage with maximum current ratings based on insulation temperature and ultimately wire size.

The reason you can use higher current at lower voltages is because wattage is a function of current times voltage. Thus wattage or power in the presence of changing voltage or current is used to rate wire capacity, still based on insulation temperature and ultimately wires size, i..e., wire diameter or crossection.
 

Ummm...NO, you can NOT use higher currents.   The rotor resistance is constant, if we ignore the copper tempco, and the power dissipated in the winding resistance is the current squared times the resistance.

Dan

I am referring to published wire current ratings for line voltage. Wire rated at 10 amps at 120 volts can carry 20 amps at 60 volts, in terms of insulation temperature and ultimately wire size because the wattage is the same. Ignoring the differences for AC then:

1,200 watts = 10 amps x 120 volts^[1]

...with the resistance of a conductor calculated as R= length of the conductor x electrical resistivity / cross sectional area.^[2]

With AC voltages the effective cross sectional area is reduced due to skin effect and is even lower for windings due to proximity effect.

Since 1,200 watts / 10 amps x 10 amps = 12 ohms and 120 volts² / 1,200 watts = 12 ohms and 60 volts² /12 ohms = 300 watts the following is correct:

300 watts is less than 1,200 watts such that the current can be raised by lowering the voltage to achieve the maximum current rating, since maximum current ratings are published for line voltage.

Since 300 watts, is only a quarter of the 1.200 watts derived rating at 120 volts and 12 ohms, it is possible to double the current when cutting the voltage in half to achieve the maximum wattage.

References:

¹Mathematics of electric power
²Resistance of a conductor

[pdonahue]

Maximum current capability ratings are normally base on line voltage with maximum current ratings based on insulation temperature and ultimately wire size.

The reason you can use higher current at lower voltages is because wattage is a function of current times voltage. Thus wattage or power in the presence of changing voltage or current is used to rate wire capacity, still based on insulation temperature and ultimately wires size, i..e., wire diameter or crossection.
 

Ummm...NO, you can NOT use higher currents.   The rotor resistance is constant, if we ignore the copper tempco, and the power dissipated in the winding resistance is the current squared times the resistance.

Dan

I am refering to published wire current ratings for line voltage. Wire rated at 10 amps at 120 volts can carry 20 amps at 60 volts, in terms of insulation temperature and ultimately wire size because the wattage is the same.

I'm no expert here, (though I do have an M.Eng. in Electrical Engineering) but the amp rating on a wire does not go up as the voltage comes down.  By that rational I should be able to run 1200A through it at 1V...  Not reasonable...  The wattage dissapated in a wire at 10 amps will be 1/4 of the power dissapated in a wire at 20 amps.  I believe that the piece of the puzzle you are missing here is that the actual voltage across the wire is not going from 120 to 60, but rather from some small value (x) to approximately some larger small value (2x).

Pete

[myelectricbike]

16 AWG wire is rated at 10 amps at 120 volts and can carry 1,200 watts. Reduce the voltage to 1 volt and 16 AWG can carry 1,200 amps because the derived wattage rating is not exceeded.