Burned up my first motor

[Boy Scout]

Burned up this motor in no time.
I’ve got another I can bolt in, but would like to know what I did wrong, before I toast another.

Basic numbers:
Motor: 72v 3000w
Battery: 72v 3000w 50a
Sprockets: front 10 tooth rear 53 tooth #40
Weight: approx 330lbs

 

[E-HP]

It looks like the phase wires melted, but the windings don't look so bad. What happened?

 

[SafeDiscDancing]

72 volts to get to 4900 rpm means a kV of 68.

So at 10 volts you spin at 680 rpm.

10 tooth to 53 tooth means 5.3 reduction.

Then 10 volts translates to 128 rpm at the rear wheel.

By the time you reach about 40 volts your speed would be something like 30 mph I would guess.

The bottom line... and what should be intuitively obvious... is you need much lower gearing.

Switch to a #219 chain and sprocket and go 84 tooth on the rear and 12 tooth up front to get 7 for reduction.

 

[amberwolf]

gearing appears to be too high as noted above.

also, what controller are you using? (not listed in your post, but visible in the pics as a pretty large metal box) the controller is what limits power to the motor (not the battery). if the controller is allowing more current to the motor than it should have in the circumstances you're using it under, the motor can easily cook.

what are the circumstances you're using the system under, and your riding style, speed, etc? knowing those may help determine how much power you actually need, to find out if the system is even powerful enough to do what you want without damage.

 

[Chalo]

I told you low motor RPM was key. Now you have learned why.

I think you'd have been much better off with the same number of Wh of battery capacity at a much lower voltage.

 

[calab]

Would anyone really, honestly put that heat job into the cooked motor category and allow Boy Scout into the Cooked Motor Club?
- Windings look fine, take the phase wires off and resolder new phase wires on, you will need a 60w iron to dump enough heat into the windings. Also remember to slip on some heavy duty heat shrink before you button it up, I almost forgot slipping heat shrink onto my battery wires doing the connector tonight, luckily I remembered this time. Also lucky I had bought some thicker heat shrink suitable for 10awg. I had an unexplained spark reconnecting my split battery after a charge a couple days ago, still dont know what happened. Had lots of light, in a bit of a hurry but not rushed. Luckily I had enough juice to get home, with a detour to the closest transit. I am using XT90's with a series adapter, a split male off the bullet wouldnt have done nothing bc it has its own separated housing. Maybe a hose clamp was biting into a cable, but I dont see no scrapes. Also lucky I can reuse some old XT90's and not use my good ones, I have a pile of XT60 but I prefer XT90 for my big fat fingers. I really do need to stock up on some cheap XT90's from Hobbyking, and some silicone wire in 12awg and 10awg.

 

[Boy Scout]

The controller & motor where mated by the manufacturer, so pretty sure they are compatible.

Where can I find sprockets & chains ?

Got a motor sprocket here to mate to the wheel sprocket
http://electricscooterparts.com/
But don’t see those reccomended gearing options.

 

[Chalo]

The controller & motor where mated by the manufacturer, so pretty sure they are compatible.

The gearing ratio and load are well outside the manufacturer's control, so maybe start there with your failure analysis.

The rated motor RPM times your gear reduction equal about 925 RPM. Is that the speed you were running at? I'm guessing not.

 

[calab]

You are on the right track with scooter parts, I believe the gears come in various shanks like a D-shank to slip onto the spinning shaft, or a Slip-Lock thingy, even seen a star shaped. You best get the low down on the gearing for your bike for what speed you want. Small drive motor gear to big wheel gear = slower but more torque. To much maths for me, not my game with brushless hub motors.

 

[SafeDiscDancing]

#219 Go Kart Chains

Very small pitch to allow high gear reduction ratios and very strong because they use them on 15 horsepower go karts.

You can buy the rear sprockets on eBay for $20.

It's the front sprocket that is more difficult... usually involving some adapting.

You can buy #35 sized front sprockets for nothing and then grind them down. (what I do)

 

[Boy Scout]

Looks like I can get front 10 rear 70, and still get the mathematical 7:1 gear reduction of the 12 to 84 suggested earlier in this thread.

How do I figure the difference in rpm with a 10 front rather than a 12 ?

 

[DogDipstick]

Always best to have staggered chain teeth. This way no teeth and links will ever repeat the same contact, upon RPM, they will revolve and contact the next link... or tooth. The wear on the chain/sprocket will be much less.

I would go 14T front or 15T front. A wider ration. Divide the first number by the last, and you get the ration. A 330 lb bike is not trivial.

10/53 = 0.188

14/53 = 0.264

This is a 28.787878% change in gearing.

As is, you are asking alot of that 10T sprocket. I doubt a 70T sprocket would fit there. To much diameter. You should have the power to move that 14T/53T.

The gear ratio is calculated by dividing the angular or rotational speed of the output shaft by the angular speed of the input shaft. It can also be calculated by dividing the total driving gear’s teeth by the total driven gear’s teeth.

 

[99t4]

Looks like I can get front 10 rear 70, and still get the mathematical 7:1 gear reduction of the 12 to 84 suggested earlier in this thread.

10T can be problematical as there are not enough teeth engaged to keep the chain from jumping. Just because they sell them does not mean it is a good idea.

 

[SafeDiscDancing]

I get away with an 11t to 100t... the 100 tooth sprockets are rare.

14t to 98t gets you 7 to 1 reduction.

One thing... anything below 12t and you need a roller AFTER the power runs past the front sprocket to keep the chain wrapped tightly.

Smaller sprockets will skip if you don't add a roller.

More teeth are better than less.

On my newest creation I'll be attempting a 10t to 94t... but might need to go to 11t if it does not work well.

A 100t #219 Sprocket has a diameter of 10".



A bunch of attempts, options and failures as well as one never worked on.

 

[Boy Scout]

I’ve got a double D output shaft, so I’m much more limited on front options

 

[SafeDiscDancing]

I’ve got a double D output shaft, so I’m much more limited on front options

https://thebigbearingstore.com/12-tooth-sprocket-for-35-roller-chain/

What I do is search around for something that works as a solid base and is cheap.

Maybe find something that easily can be mounted on your existing shaft.

Then just start very carefully grinding it from it's #35 size to the #219 size... it's not much to take off and it's very easy to take too much off and ruin what you are working on.

Anyway... your choices are:

1) Gear the motor down in one big step... a reduction of 7 as a minimum using #219 chain.

2) Do a two stage reduction.

...when you think like that the work of grinding doesn't seem so bad.

 

[DogDipstick]

What you are saying, Mr Chalo, is :

The rated motor RPM times your gear reduction equal about 925 RPM.

: is that it would be better to have a lower voltage for a lower top speed rpm.... So as to not load the motor so much with its rpm range it wants to shoot for at speed? Lower voltage but keep the wH capacity? Run that?

Switch to a #219 chain and sprocket and go 84 tooth on the rear and 12 tooth up front to get 7 for reduction.

..and you are saying switch to 219 for the chain wrap, ability to get a few more teeth on the front and same time get enough teeth in the rear for that 7:1 and more teeth the same package: Given the restrictions of the larger chain, available sprockets that will fit?

12 inch tire, 10T front, 53T rear, (72v) 4900rpm, is 33mph. As is, overheating.

Put a 70T in place of the 53T and you get a 24mph. 14T-98T in #219 would give the same 24mph.

https://www.bmikarts.com/Go-Kart-Gear-Ratio-Speed-Calculator




.....is this correct? .. and a combo of those two would be best?

... and I was wrong above:? My suggestion would in fact load the motor more: Wrong way for a ratio change the OP needs.

 

[SafeDiscDancing]

https://cart.electricscooterparts.com/10-tooth-sprocket-with-10mm-x-8-5mm-double-d-bore-for-35-chain

Basically you cannot go lower than about 10 teeth on ANY chain without having serious troubles.

Having a shorter pitch means more teeth everywhere.

More teeth opens the door to more gear reduction.

To get a motor to run at adequate speed you need a minimum of 1-to-7 and it's better closer to 1-to-9 reduction.

#219 is pretty much the only way to do it.

I have over 10,000 miles on a setup with 11t to 100t using a #219 chain.

What fried his motor was having only a 1-to-5.3 reduction which was way off.

Another source:

https://www.ebay.com/itm/-35-Chain-Sprocket-9T-40T-tooth-Pitch-9-575mm-3-8-for-35-06B-Roller-Chain/183828102307?hash=item2acd023ca3:g:0AMAAOSwN7Bc55MF&pageci=227ee34c-9e17-4449-95d4-bfa3fc15f4a3&redirect=mobile

 

[SafeDiscDancing]

Put a 70T in place of the 53T and you get a 24mph. 14T-98T in #219 would give the same 24mph.

Actually if the 70T would fit on his bike yeah... great idea.

Do they sell them that big?

What outside diameter would that be?

My guess is it will be bigger than 10" because that's what a 100t #219 turns out to be.

But heck yeah... I'm sorry I didn't think of that.

--------------------

https://cart.electricscooterparts.com/72-tooth-sprocket-for-40-41-and-420-chain-with-g1-mounting-pattern

A bit pricy at $84 but maybe he can shop around to find a lower price.

Given he has already invested in this direction it's probably cheaper and easier to go to 72 teeth.

Outside diameter just under 12".

 

[Boy Scout]

Universal sprocket adapter
https://www.gopowersports.com/universal-sprocket-adapter-8-wheels/

Rear sprocket up to 85t
https://www.gopowersports.com/split-sprockets-35/

Are there any videos on how to grind #35 ? Due to the limited options for the front, and frame+my fat butt=330lbs might stick with #35

 

[SafeDiscDancing]

Are there any videos on how to grind #35 ?

https://cart.electricscooterparts.com/80-tooth-sprocket-for-40-41-and-420-chain-with-g1-mounting-pattern

80 Tooth Sprocket for #40, #41, and #420 Chain

Made from Aircraft-Grade Tempered (Hardened) Aluminum Alloy
For #40, #41, and #420 Chain
80 Teeth
G1 Mounting Pattern
13" OD
2" ID
2.875" Bolt Circle Diameter
Four 3/8" ID Bolt Holes

...just buy that.

Save yourself a lot of work.

Just double check what a 13" sprocket will look like on that tire. (it's going to be near the lower edge of your tire)

Check clearances all around.

The #219 are really useful for getting high reduction, but you can do "good enough" at #40.