*** New Tool - Data Plotter

[safe]

Data Plotter

Don't you hate it how you can look up a motor and they give you a few data points but DON'T tell you what you really want to know like how much resistance the motor has?

Well now you can and for only $14.95 plus shipping and handling... no wait... actually it's FREE!!!

Okay, well the market/interest for this is small, but it's a useful tool for anyone like myself that is trying to make an accurate comparison of different motors. All you do is plug in the motor data points into a spreadsheet and then you can see how it shows up on the charts. You then carefully try out different values for the resistance and others and you arrive at what's really going on.

I think they "pad" the efficiency numbers a little because they always tend to be a percentage or two higher than makes any sense based on the data.

Overall the data can be fit pretty closely...

 

[safe]

So these are the charts that you use to plot the data points. You can see where the data points show up relative to the curves that the main parameters define... it's the curves that you adjust... so it's a "curve fitting" action that you have to perform.

 

[safe]

Downloadable File Needs Conversion

Not that anyone really needs this tool, but if there is some poor innocent person that does wouldn't it be great if they could have it converted from the old "works" format into the newer ".xls" format?

If there is a person with a heart of gold that could do that for me I'm sure you will get a reward in heaven...

(Note: During the conversion process you will likely lose the charts, so just rebuild them yourself... it's pretty easy to do if you know how to use a spreadsheet)

 

[knightmb]

What were they using to convert it to Excel format? My Excel can't open it to convert

Thought about Open Office? It's free

 

[safe]

What were they using to convert it to Excel format? My Excel can't open it to convert

Thought about Open Office? It's free

I had a power supply go out on my existing computer a few days ago and managed to get a new one (used) for $20. As long as this old computer keeps going I want to keep it alive. Eventually I'll buy all new stuff and when I do I'll upgrade everything. (I've backed up everything I need)

Let's see if there are any requests for the tool... if not (since it solves a very narrow problem that most people wouldn't care about) then we will have saved the effort of converting it.

 

[Dalecv]

Only a 173 KB File, why compress it? Did you save file as shown here? http://office.microsoft.com/en-us/excel/HA010448771033.aspx

 

[xyster]

Probably no accident Safe's spreadsheets never work for anyone else. He obviously doesn't want us to know the equations are all BS, and the graphs are just connect-the-dot pics.

 

[TylerDurden]

Probably no accident Safe's spreadsheets never work for anyone else. He obviously doesn't want us to know the equations are all BS, and the graphs are just connect-the-dot pics.

The equations he has are ok... he's just missing a bunch more that should be in there.

 

[safe]

It might turn out that there is no one that actually wants the tool anyway, so if that's true then the conversion is not necessary.

I've been examining the entire line of products that Unite produces and will eventually publish an "exhaustive" list of the resistance values for their motors.

Some interesting results so far:

The 1200 watt MY1020 has a much higher resistance than the 1000 watt MY1020 motor. (0.3 ohms verses 0.2 ohms) I own both of these motors and the real world experience matches this data. (I use the 1000 watt now)

If you have a choice between their higher and lower voltage motors the LOWER voltage one tends to have better (lower) resistance numbers. Basically they seem to allow much higher resistance values in the higher voltage "because they can get away with it". You basically lose any advantage of overvolting going from the lower volt version to the higher.

Some motors are clearly better than others...

 

[dirty_d]

the lower resistance of the lower voltage motor isn't an advantage it works out just the same as the high resistance of the higher voltage one, the 48V motor has more windings of thinner wire, so with less amperage you get the same torque, more windings means more back-emf so at 48V you get the same rpms as at 36V, you get the same heat in both.

 

[safe]

...more windings means more back-emf.

You mean more voltage means more backemf... there's no relationship between resistance and back-emf. Strictly speaking it's the permanent magnets that define the backemf, that's why the Inductance motor was such a revolution in thought you can effectively vary the backemf dynamically.

Unite seems to use higher resistance wire for the higher voltage motor probably so that it will survive the higher heat that the standard (BCL) PWM controller produces at low rpms. If some really smart person wanted to overvolt a lower voltage motor with less resistance and then put MCL on it to cut the heat then you really do get a better result that way. :wink:

My observation was more about my own intentions to "trick out" a small motor. The lower voltage, lower resistance motor would be the better choice for "tricking out" than the higher voltage, higher resistance one.

If run at the specified voltage the result is roughly the same for both motors... (so in that you are correct)

 

[dirty_d]

You mean more voltage means more backemf...

no, for two given motors rotating at the same rpm with the same magnets the one with more windings will have a higher back-emf voltage. more windings in the same sized motor means more resistance.

 

[safe]

You mean more voltage means more backemf...

no, for two given motors rotating at the same rpm with the same magnets the one with more windings will have a higher back-emf voltage. more windings in the same sized motor means more resistance.

BackEmf is probably the easiest thing to calculate:

BackEmf = VoltageConstant * ( RPM / RadiansSecConstant )

RadiansSecConstant = 9.54957822696164

VoltageConstant = Voltage / MaximumRpm

So as you can see there is no effect of the resistance directly. Basically a higher resistance value translates into a lower efficiency, but a better ability to absorb heat. A motor that has a very low resistance can potentially mean that it can't handle the heat very well. This isn't always true... the PMG 132 is a pancake style motor that only has a resistance of 0.025 ohms, but seems to do very well handling the heat. So it's a trade off... the lower voltage motor can afford to take more chances with heat, so they can afford to wire it in a more "fragile" manner. The higher voltage motor running with the typical BCL controller produces a lot more heat and so the overall wiring is made stronger and this ends up translating to higher resistance.

For example:

I own the 1200 watt Unite and the 1000 watt Unite motors. They both run fine in my bike, but the 1000 watt has a resistance of 0.2 ohms while the 1200 watt has a resistance of 0.3 ohms. I can ride the 1200 watt motor all day long at 36 volts (how my bike is wired) and it doesn't even begin to get warm. On my 1000 watt motor I do gain heat and by the end of a ride my motor is just getting to the point of being hot... like 125 degrees or so. The 1200 watt motor has higher resistance, but it seems to be able to handle heat much better. The 1200 watt motor is actually designed for 48 volts so it can take a lot more heat if I tried using it at it's recommended voltage.

The two motors are nearly identical as far as size and weight.

The data was confirmed by actual road testing on my bike and the spreadsheets came up extremely accurate.

 

[safe]

Testers Needed!!!

Could someone try downloading this and see which of the versions I'm able to save you can then open and still get the charts with it? The Windows 4.5a version is the natural one on my computer and that seems to be what is creating all the problems...

I'm kind of hoping that the Windows 3.0 Version works perfectly and then I'll from now on be able to upload stuff without any problems.


Note: I moved the download to the next page...

 

[xyster]

Testers Needed!!!

Could someone try downloading this and see which of the versions I'm able to save you can then open and still get the charts with it?

Like I'm going to just trust that your spreadsheets aren't contaminated with some virus designed to turn my computer into your spreadsheet-spitting slave machine...

 

[safe]

Like I'm going to just trust that your spreadsheets aren't contaminated with some virus designed to turn my computer into your spreadsheet-spitting slave machine...

They don't make that many viruses anymore for Windows 98. I added all the usual Windows Update packages and the machine is behind a router and I have a firewall too. I don't permit my email attachments to be automatically opened either. Since I've been running the machine this last year I've had a pretty uneventful time with it. (other than having a power supply fail a week ago... I found a used one to replace it for $20)

The main reason I want the files tested is that in the future if I upload a chart I will be able to also upload the supporting spreadsheet so if there is any controversy about accuracy then people will be able to verify it's correctness independently.

It's all part of progessing to better ways of passing data back and forth... 8)

So again... someone please download this zip file and tell me which versions work for you and which don't. I want to see what is the easiest file format that I can convert things too so that as many people are happy as possible...

 

[dirty_d]

So as you can see there is no effect of the resistance directly. Basically a higher resistance value translates into a lower efficiency, but a better ability to absorb heat.

wrong, allow me to explain fully, you were comparing two different motors by the way.

take these two motors the MY1020 1000W 36V and 48V http://www.cn-dcmotor.com/productShows.asp?ArticleID=276

36V model
no-load speed: 3700rpm(387.5 rad/s)
rated rpm: 3000rpm(314.2 rad/s)
rated current: 35.6A

K = 36.0 / 387.5 = .093
back-emf at 3000rpm = .093 * 314.2 = 29.2V
winding resistance = (36.0 - 29.2) / 35.6 = .191ohms
heat dissipation at rated load = (35.6 * 35.6) * .191 = 242.1W

48V model
no-load speed: 3700rpm(387.5 rad/s)
rated rpm: 3000rpm(314.2 rad/s)
rated current: 26.7A

K = 48.0 / 387.5 = .124
back-emf at 3000rpm = .124 * 314.2 = 39V
winding resistance = (48.0 - 39) / 26.7 = .337ohms
heat dissipation at rated load = (26.7 * 26.7) * .337 = 240.2W

as you can see they both put out 1000W at their rated load an both dissipate the same amount of heat so both have equal efficiency.

 

[safe]

...so both have equal efficiency.

They end up being equal if run at their normal voltage.

But if you take the 36V motor and boost the voltage to 48V then it's lower resistance produces a better result than the motor that normally runs at 48V. So in that sense the 36V motor is "better" than the 48V motor. Now the only question becomes how well each motor responds to 48V heat. The 36V motor might NOT handle the heat as well based on it's physical design. This becomes the rationale for choosing the 48V motor. But, if you did something like forced air cooling or MCL (which actually should be called "Armature Current Limiting" ACL... oops!... based on how the controller industry uses the terminology) you could get all the "good stuff" of the low resistance and not have to worry about overheating.

My guess is that a low resistance motor is harder to make heat tolerant. (but it can be done)

Try it. Take the 36V motor you just looked at and increase the voltage to 48V and see the numbers you get...

 

[dirty_d]

yes boosting the 36V motors voltage by 33% will make it more powerful than the stock 48V motor, but boosting the 48V motors voltage by 33% yields the same result.

 

[safe]

yes boosting the 36V motors voltage by 33% will make it more powerful than the stock 48V motor, but boosting the 48V motors voltage by 33% yields the same result.

But that wasn't the question.

The question was:

"If you are going to be creating a 48V bike and have the choice of the 36V or the 48V motor which one do you choose?"

 

[fechter]

If you run a 36v motor at 48v, the rpm will be higher. This will increase windage and core losses. The max efficiency will likely be a bit lower at 48v.

 

[safe]

If you run a 36v motor at 48v, the rpm will be higher. This will increase windage and core losses. The max efficiency will likely be a bit lower at 48v.

Possibly.

It would depend on the rate at which those losses rise with increasing rpms. Since those are normally not significant until the rpms rise to very high levels I'd tend to think the extra losses are not as significant as the benefits of a lower base resistance.

We're talking about going from 3350 rpm to 4467 rpm.... so the maximum speed is still within numbers that are not extreme.

If we were talking about 6000+ rpm then I'd agree, but not 4500 rpm.

There are brushed motors that normally operate at 6880 rpms, so the brushes should be okay within the range we are talking about. The PMG 080 for example:

 

[safe]

36V MY1020 1000 Watt

The 36V and the 48V "stock" motors produce the same output so we can lump them together under that label.

Taking the 36V motor and increasing the voltage to 48V while keeping the controller limit constant at 40 amps produces this chart.

Even if some of the other losses increase slightly the net gain in power of about 400 watts at peak is a huge increase.

Higher resistance contributes to higher losses... so picking the motor with the lower resistance value "should" be the better choice in most cases.

Note: The values in the chart include the 95% controller efficiency and a 93% powertrain efficiency, so the initial values were a little higher. I would think that this is likely what you would actually see in real life. This is my own bikes motor after all so I have a lot of real world experience with it. (though I have not tried overvolting it, so I'm tempted )

If I simply added an extra 12V to my existing bike (possibly with something like LiFePO4) and switched to a 48V controller my bike should be able to get up into the 45 mph range on the flat (with real ease) and on the downhill I'd expect speeds nearing 60 mph...

 

[vanilla ice]

Do it man. Don't forget to post some vids.

I have a 36v my1020 500w I want to try bumping up to 48v, maybe more.

 

[safe]

I have a 36v my1020 500w I want to try bumping up to 48v, maybe more.

The 36V 500w motor should go to 48V very well.

Beyond 48V and I'd start to worry about things like overheating, in fact, the ideal thing would be to use the armature current limiting idea (if possible) to guard against that.

You have to be sensible about the idea of heat increases... they are real if you are going to stick with the standard controllers. (but it's only going to develop as a problem while running at lower rpms)

The Unite motors aren't exactly what you can call "Big Iron" like the mighty 5304 hub motor with it's built in 25lb heat sink! :lol:

I get 0.34 ohms as your motors resistance.

Your MY1020 500 Watt 36 Volt motor is overvolted in this chart with all the same efficiency losses factored in as previously: