Triple Rewind of Unite 500W Motor

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I've been using these:

http://cgi.ebay.com/300-Pcs-NiCd-Su...photoQQcmdZViewItemQQ_trksidZp1742.m153.l1262

It comes to $1.28 each. (they are rated at 10C, so they can handle some abuse)

I place them in PVC tubes with springs on the ends and that way there is no soldering. About 1%-5% of the cells are going to go bad over time so you need to be able to swap out the bad cells. I did that recently and it took me 15 minutes to identify the bad cell and replace it. A soldered pack can be a real hassle to unsolder then resolder. Also, spring loaded cells never can get loose soldered connections because of riding shocks and vibrations. I've found that solderless is a completely flawless way to do it. (the RC people do a lot of solderless tube stuff)

Anyway... that's a whole other project that I'm into...

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Overvolting does the same thing as these rewinds. The whole point of doing this would be to PROVE that a simple rewind could deliver performance levels that were much higher. So my advice would be to stick to the stock configuration all the way around and just change one variable... the motor windings.

So just stay totally stock except the rewind.
 
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Rewind etc.

:cool:Stacking the batteries that way is a pretty neat trick,flexible too, you could put them alongside the frame tubes,I don't care really what it looks like,but don't like all that weight in the rear,thanks.
 
I use pre-1982 copper pennies as battery cell conductors. All I do is take a wire, spread out the little strands around the penny and then solder it. After that I sand it smooth with a belt sander to make a very high quality conductor to the battery cells. You will need to remove the cell's wrapping plastic too... if you don't the plastic can get in the way and prevent the tube from working properly.

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...but you could save a lot of time just buying something like this:

https://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=7639

The whole point of this should be to test the Rewind on a STOCK bike... you really should start off with the Stock batteries and avoid getting into this battery upgrade process. (new batteries will skew the results)

What I want to see is a 100% Stock WalMart bike being given only the Rewind and then measure the results.

From the "scientific perspective" changing too many variables makes any improvement less clear.

You should approach this as a "tutuorial for newbies" to ebikes that want an upgrade path without spending money.

Stock Batteries
Stock Controller
Rewind the Motor


...that's what I want to see. :cool:
 

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We Need A Volunteer

duivendyk, if you can buy a WalMart bike and do a Rewinding Upgrade that would be great, but if not we need to find a volunteer to do it.

So the call is out: "We need a volunteer".

Let's get everyone talking about this and even spreading the word around to anyone that would do it or anyone that might presently own an inexpensive ebike and wants to see their performance doubled.

Most of these cheap ebikes are upgradable.

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Note: My Rewind has turned out to be a complete success (1400 watts of power from a 500 watt motor) and I'm nearing 500 miles on it without problems.
 
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This rewind business has paid off for your particular operation,running at high speed high rpm,where over-volted motors tend to perform well.I am interested in the WM/currie,but as you may realise by now,I take my equations and calculate things out,whatever I predicted so far has been substantiated by your tests.So I decided to run some calcs.based on a 24 V ,20 amp motor with a armature resistance of 0.24 Ohms with a nl speed of 3200 rpm and then do a theoretical "rewind" for 3/4 the # of turns increasing the nl. speed to 4250 rpm,and reducing the resistance to (3/4)^ (^=squared)or or 0.56x0.24=.135 Ohm .Wether you can do better than that with multiple winds resistancewise is moot,anybody's guess as far as I'm concerned.
If we assume input volts&current (24V,20 A) we can compute the back emf,in the original case the armature drop is 20x 0.24= 4.8 V leaving 19.2V for the back emf,so the armature loss is 20x4.8= 96 Watts and the efficiency is (480- 96)/480= 80%(this disregards core loss).
OK ,so far so good now the rewound motor.We will first take the same input situation, 24V, 20 Amp and find out armature drop which is 0.135x 20=2.7 Volt,.the back emf is 21.3 and the efficiency is 21.3/24=89% a 9% improvement.This amounts to reducing the loss from 96 to 54 Watts,a 44 % reduction.Halleluja !!
Regrettably there is a snake lurking in the grass,this improvement can ONLY be realized if the motor is allowed to develop it's power at the higher rpm and lower torque it is now running at,that is about a 4/3 increase in gearing ratio is required.I will illustrate this next:
the motor has now 0.75 of the original # of turns and needs run at 1,333x 3200 =4250 rpm nl. to provide the reqd. back emf. The 20Amp motorspeed turns out to be 3800 rpm (it used to be 2560 rpm).The motor torque computes to 75% of the original value.
OK, so what if we used the controller to reduce the voltage to the motor,to get the same torque as before, that requires 4/3 x 20= 26.6 Amps,so the armature voltage drop increases to 0.135x 26.6=3.6 V.If we assume that the controller is 100% efficient we can figure our the output voltage to the motor, it is (20/26.8)x 24=17.9V. So the back emf becomes, 17.9- 3.6=15.3 V and the motor speed (15.3/24)x 4250=2700 rpm.The speed of the original motor under 20Amp load was (19.2/24)x 3200=2600 rpm.The armature loss is 3.6x26.8=96.5 Watts and the efficiency is (480-96.5)/480=80%
EXACTLY what we got with the initial unmodified motor.However the controller efficiency for a stepdown from 24 to 18V is certainly lower than straight through.If we assume a 2% differential, the input power would be 490 W and the eficiency would be (48/49)x 80=78%
The upshot of all these calculations is that in all likelyhood it is an excercise in futility to rewind any motor unless the concomitant changes in rpm&torque are allowed for,the transmission ratio from motor to driven wheel HAS to be modified to make it possible to realize the POTENTIAL improvement in efficiency which as I have proven can be substantial.So it makes no sense to rewind a Currie motor, unless the appropriate mechanical changes can be made.Sorry about that,this is the way the cookie crumbles.
If you want to get more power and efficiency it's easier to just up the voltage say to 32 or 36V, than to rewind.My calculations show that at 32V the eff. goes up to 90%.Of course the speeds must change by the voltage ratios (33 and 50%) or to 4250, resp. 4800 rpm
 
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If you want to get more power and efficiency it's easier to just up the voltage say to 32 or 36V, than to rewind.


Which is exactly what alot have done as per i mentioned my last post if i recall correctly :)

I have taken a break from my CNC mill construction as the 20 AWG wire i order arrived. I have pulled the motor from my trike LUCKY i did too (will post pics later tonight) the insulation was lifted on all the bends and is now a blackend colour. Safe ...you also posted paaages back that the Unite 1000watt is wound with AWG20 wire stock its not, i have measured the wire from mine it is DEFINITELY thinner than AWG20 its AWG22.. I suggest you get digital verniers matey ;-)

I would also NOT recommend the average Joe go out and re-wind one of these motors if one is under the assumption its a 'quick' affair ITS NOT, I like the DIY approach myself but i'm LOATHING this rewinding business and i havent even started the rewind, has taken me best part of 2 hours to get the original wire off, granted alot of the insulation was melted together so the wires couldn't be un-wound. It took over half an hour just to remove the fiber glass strips only ONE slid out the rest were glued and had to be cut and pried out ... I have just painted the first coat of black heat resistant paint on the motor when this dries i shall start the rewind process. I will do a double rewind as per Frank suggested he would try if he did it again(although he suggested AWG21 NOT AWG20) this will be a nice comparison between this motor and Franks single wind when it arrives later in the week, no graphs with 'guessing' how it will perform i will bolt it in and try them both.

Shall be back with pictures later tonight/tomorrow.

KiM
 
So I decided to run some calcs.based on a 24 V ,20 amp motor

I'm going to stop you right there.

Redo everything using a 30 amp current limit.
101188.gif height=100 width=100

http://tncscooters.com/product.php?sku=101188

This 24 volt controller has 3 connectors.

Rated Voltage 24 Volts.
Max Current 30 Amps.
Usable Motors: Up to 500 Watts.

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I've said it before and I'll repeat it again... they tend to run these motors "too rich" and you gain the advantage by exploiting that knowledge.

24V * 30A = 720W input * 80% = 576W peak power output

Rated power is less at 450 watts.

:D A 20 amp current limit is more appropriate for a 250 watt motor.

We are actually talking about one of these on the WalMart bikes:

http://www.monsterscooterparts.com/24v45moupkit.html

yhst-92821211804676_2049_103846172 hegiht=100 width=100
 
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I would also NOT recommend the average Joe go out and re-wind one of these motors if one is under the assumption its a 'quick' affair ITS NOT, I like the DIY approach myself but i'm LOATHING this rewinding business and i havent even started the rewind, has taken me best part of 2 hours to get the original wire off, granted alot of the insulation was melted together so the wires couldn't be un-wound.

I agree.

This is why a volunteer for the WalMart bike idea might be hard to find because the type of person that buys those tends to be new to ebiking and not all that devoted to it yet.

What is really needed is for one of us "ebike addicts" to commit to doing it to prove to others that performance increases are possible.

Rewinding is a true "stealth upgrade".

And the best thing is you get the extra power without needing to replace anything else, all you are really doing is changing a motor that runs too "rich" to one that runs "lean".

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I have to repeat....

My 500 watt motor has been reliably producing 1400 watts of output power without overheating for nearly 500 miles now. This has clearly been a successful upgrade.
 
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Finished the rewind im too knackered to bother with pics tonight and still have two mates over having a few Jacks will resize the pics and up them tomorrow. I took HEAPS of pics haha... I still have to apply the epoxy, and upgrade the wiring on the brush plate re-assemble and re-set the timing. As is the motor is rewound 2x11 the end plate vent holes have been ENLARGED and additional holes added ...Back tomorrow off for another JDs & coke and a slice of pizza before the two larackins finish it off haha..

KiM

p.s you must have nanna hands if you can't complete a rewind in one whack to safe toughen up LOL :p
 
p.s you must have nanna hands if you can't complete a rewind in one whack to safe toughen up LOL :p

Just wait until you are nearly 50. :unsure: (I'm starting to develop some early stages of arthritis, my mother has it so bad she can barely move her fingers now, but she's in her late 70's)

But you used 21 AWG. I found that the 22 AWG was painful and the 20 AWG was not so bad and it does depend a lot on how tight you wind things.

11x2=22 21 AWG

That sounds like it will work well. Should be strong and run cool. :cool:

(mine was the same configuration, but 20 AWG)

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P.S: I'm impressed at your speed in completing this. Your feelings will change once you get the motor running. There's something incredibly scary about rewinding because it seems so complicated, but once you've done it you know what you are doing and it's not scary anymore.
 
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