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Two LB37's in a few months for a 36V to 48V upgrade - what's happening?

My son has a Schwinn S750 36V that we upgraded to a 48V using an LB37.  It worked great for a few months.  Then the LB37 failed and went to full mode and he crashed (it wasn't serious).  The throttle was damaged in the accident so we replaced it with a new one.  We bought another LB37 and installed it and connected it up.  It worked fine for a minute then started blowing 40A fuses.  Now when I power on the scooter it goes to run again telling me the LB37 has failed again.

What is going on here?  The motor is only a 750W.

I am not happy with this "no warranty" which means its all on you.  These things are $50 a pop.

I have attached pix of my install.  Straightforward.  You can see the previous LB37 wires spliced in.  FWIW, I know how to wire so these crimps are very solid.

Any advice, suggestions appreciated.  I don't want to put in another LB37 if it's just going to fail again.

(1.81 MB)
(1.55 MB)

Most likely the windings in the motor have burned through their insulation and are short circuiting which is putting too much of a load on the controller and causing it to fail.

The Watts rating of a brushed DC motor is the limit of Watts that the motor is rated for, and not the maximum Watts that it can draw from the controller. A 750 Watt motor can easily draw 1500 Watts of power if a load requiring that much power is placed on the motor and the controller attached to the motor can output 1500 Watts. Increasing the Voltage going to a DC motor will not increase the amount of Watts that the motor can handle. So if a 36 Volt motor is overvolted to 48 Volts, then the 48 Volt controller should be rated at 750 Watts. Using a 1000 Watt controller on a 750 Watt motor is a great way to hot rod it and get more power out of the motor, but will reduce the reliability and lifespan of the motor and controller.

If you replace the motor and controller with the same parts as before I would expect the same results. If you want the scooter to be reliable and don't want to keep pouring money into it, then I recommend converting it back to the stock 36 Volt 750 Watt parts. However if you want to modify it for more power and speed then I respect that and admire your ingenuity. My advise for modifying is to use the failure of parts as a guideline for what needs to be changed or improved when they are replaced. Eventually after a few component failures and improvements I think it is possible that an electric scooter modified for speed could be as or more reliable than a stock one.

Thanks very much!  My first thoughts were that the motor had lost windings but learned that it was quite rare for them to fail on a minor 12V increase but that's really the only explanation and the only common part left.  Is there a way to test the motor?

12 Volts is not too much of a Voltage increase however electric scooter motors can burn through their winding insulation even when ran at their listed Voltage if too much of a load is applied to them by going up too steep or too long of hills or going through sand or mud or any other condition which overloads the motor.

The only way I know of to test the motor is to take it apart and check the resistance of each winding. Most electric scooter motors are very difficult if not impossible to reassemble after taking them apart though. If the motor has burned coil insulation then it will usually have a burned electronics smell to it, although this smell may go away after a while if the motor has not been in use for a while.

Thanks for the continued help here.  I goofed, the stock motor is 1,000 W at 36V.  At 48 V it calcs out to be 1,777 Watts and 37 amps.  This clearly overloads the LB37.  I also put my nose right on the motor, near openings to the windings and couldn't smell even the slightest hint of burning.

Are there controllers available rated at 2,000 watts?

I see that you guys sell 1500 W, 48 V controllers with overcurrent protection.  Also, the exact motor I have is this one you sell with the rear wheel and gearbox attached for the Currie 1000: part MOT-EZRW1000

Controller: Item # SPD-481500

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