Differences in motor magnets?

[emaayan]

hi..

i've heard that there several different types for motor magnets and that would effect motor performance. like ferrite vs ceramic, is that true?

 

[parajared]

You bet.
Magnets are rated in a couple of ways; gauss and heat resistance. Most of the motors out there produce the same amount of gauss, but not all the motors resist the same amount of heat. Running your motor as hot as you can get away with is the name of the game in hot rodding electric motors and some magnets die off as low as 120 celcius.

 

[major]

i've heard that there several different types for motor magnets and that would effect motor performance. like ferrite vs ceramic, is that true?

Yep, it is true.

There are four classes of modern commercialized magnets, each based on their material composition. Within each class is a family of grades with their own magnetic properties. These general classes are:

Neodymium Iron Boron

Samarium Cobalt

Ceramic

Alnico

Ref: http://www.magnetsales.com/design/DesignG.htm

BTW, ceramic and ferrite most often refer to the same class of magnets.

 

[emaayan]

so why is it that mac motor has a black magnet, and bmc motor has a "grey" magnet?

 

[bearing]

Probably coated with black epoxy vs. nickel.

 

[fechter]

Nearly all magnets used in bike motors these days are NdFeB rare earth magnets. These are virtually immune to being demagnetized by high currents in the windings. They will lose their magnetizm if overheated though, and they come in a variety of temperature ratings. These are generally the strongest magnets for their size.

Cobalt-Samarium magnets are weaker, but can tolerate much higher temperatures.

Ceramic magnets can take high temperatures, but are easily demagnetized if the motor current goes too high. I've done this to a few. They are also weaker than the other types for a given size, so are usually quite thick in a motor.

NdFeB magnets are suceptible to corrosion, so must be coated with something. Nickel plating is common, as is epoxy.

 

[emaayan]

and yet the bmc motor is stronger the the mac, see , this whole thing started when i noticed that i can go faster with a bmc motor then with a mac motor, more over, using a 9 fet controller with a bmc motor produced a wavy sound, i could sense it hard trouble pushing the bike, all this didn't happen with a 40 amp 12 fet controller.

em3ev said , it might be that the bmc motor is "harder" to drive, which i understand until i was told that it was a stronger magnet, and that black magnets are ferite and weaker while ceramic magnets are stronger.

this is the black magnet next to mac motor (ignore the mystery crack, i have a new magnet without)

and this is the grey magnet next to bmc

the bmc motor go 25% faster (and louder) then mac motor.

 

[fechter]

The BMC motor uses NdFeB magnets, not ceramic. It is a single ring magnetized with 16 poles.

There may be differences in the strength though. Overheating the motor could weaken them too.

A weaker magnet will cause the motor to run faster at no-load, but have less torque.

I've always had problems with the hall timing on those motors though. I think some of the controllers specifically made for them compensate for the timing, but if you try using a 'regular' controller, you may run into problems with the timing. Check the no-load running current. You could try swapping controllers to see if that makes a difference too.

Some of the newer ones have the hall sensors located differently (cutouts in the teeth) vs. having them located in the middle of the slot. This puts the timing back to neutral and allows most standard controllers to work properly.

 

[DAND214]

My BMC is slower and weaker than my MAC?
Not the same pole count and or wind. BMC costs more but rather sure the magnets are the same type.

Dan

 

[emaayan]

the no-load running currrent is about 5 amp, both controllers are infineons, don't know if that's a regular controller , the bmc controller which came with it, looked like this after 30 minute ride

 

[fechter]

Yikes! blown capacitors. Not good.

Mine runs close to 5A @48v no load with an analog Crystalyte controller. I think this is really higher than it should be, but the best you can do without some kind of timing shift. Yes, the Infineon is a normal type controller. I think the dedicated BMC controllers have some kind of timing shift.

You might try measuring the no-load / full speed rpm of both motors. If they have the same number of windings, they should run at the same speed. If the magnets are different, the speed will be different.

Another test is to un-power things and short all the phase wires together, then turn the motor shaft and feel how much resistance you get. If the magnets are toast, the resistance will be less.

 

[emaayan]

i have no idea how to measure RPM, i do know then when on a table, using just a slight throttle movement makes the BMC jumps up and almost bitch slam me, while the mac is a lot more relaxed.

 

[fechter]

If it was installed on the bike, you could possibly use a bike speedometer on the driven wheel. Otherwise something like a photo tach or a mulitmeter that reads frequency (Hz) on one of the hall signals would work. I realize not everybody has cool toys like these.

You might get some idea just from the pitch of the motor at full speed.

 

[emaayan]

when on the bike , i to speeds of 50 kph vs 40 or less on with the mac. that's for sure, the motor sounds louder also.

 

[fechter]

I think they have identical windings, so I'd guess the magnets got weak on the MAC. Any chance it was severely overheated at some point in the past?

 

[emaayan]

i find extremely unlikely considering it's a brand new mac motor, directly from the factory BUT if you look closely at wingdings both motors , it would seem the bmc's are thicker..

 

[DAND214]

i find extremely unlikely considering it's a brand new mac motor, directly from the factory BUT if you look closely at wingdings both motors , it would seem the bmc's are thicker..

Heavier windings? Then they are not the same!

Dan

 

[emaayan]

you tell me..
on the left we have the mac , on the right the BMC..

 

[Hillhater]

That photo of the windings answers all your original questions !!

and yet the bmc motor is stronger the the mac, see , this whole thing started when i noticed that i can go faster with a bmc motor then with a mac motor,
the bmc motor go 25% faster (and louder) then mac motor.

 

[emaayan]

So the windings are what makes the motor harder to drive? If I wanted to specify to MAC to use these type of windings how would describe it?

 

[major]

So the windings are what makes the motor harder to drive? If I wanted to specify to MAC to use these type of windings how would describe it?

The number of turns in the coil and wire diameter determine the relationship between voltage and RPM and between torque and current. Along with the magnet strength and motor size/shape, you get a particular motor design. The manufacturer is unlikely to alter that design at your request. But the winding is specified in turns/coil (T/c) and wire diameter or cross sectional area. The coils are sometimes wound with multiple strands of wire in parallel instead of larger wire. The way the coils are connected together in groups also enters into the equation. So a simple look or count of the wires on the coil may be deceiving.

 

[gwhy!1]

So the windings are what makes the motor harder to drive? If I wanted to specify to MAC to use these type of windings how would describe it?

The number of turns in the coil and wire diameter determine the relationship between voltage and RPM and between torque and current. Along with the magnet strength and motor size/shape, you get a particular motor design. The manufacturer is unlikely to alter that design at your request. But the winding is specified in turns/coil (T/c) and wire diameter or cross sectional area. The coils are sometimes wound with multiple strands of wire in parallel instead of larger wire. The way the coils are connected together in groups also enters into the equation. So a simple look or count of the wires on the coil may be deceiving.

Where is the best place to buy one of these motors ? , and what are typical prices ? .Thanks.