What is the max acceptable voltage on a 72V D&D motor

[NCPW]

You could always charge the 10 modules to 4v/cell and get plenty of life out of them. You'd be running a 72v motor at a max of 80v.

I and many other members on here are running our 48v motors at or close to 58v without issue.

[JohnnieB]

Originally Posted by somfas

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

The “floating surface voltage” of the batteries is gone as soon as you put a load on them. Your 72 volt pack may read 74-76 after being charge but that will drop once the motor is powered up. Motor is ok to be used at 72 volt system, not 84 or 96.

I don't give 72V packs much thought, so these statements didn't immediately wave red flags at me. A floating surface charge would be above the normal 100% SoC voltage for a FLA battery pack. A fully charge 72V pack will be 76.4V for Trojan brand or 77.0V for US Battery brand. Right after being charged, the surface charge voltage of a 72V pack can be 90V or more.


Many people run 36V motors at 48V, which is 33.3% overvolting, but I have no idea how much overvolting a 72V can tolerate.

[scottyb]

With more volts comes less amps. Amps make heat and heat kills motors. Volts makes rpms and excessive rpms kill motors too... there is a fine line somewhere here. If I had a 72v motor I would sooner run it on 84 than 48. Keep us posted.

[JohnnieB]

Originally Posted by scottyb

With more volts comes less amps. Amps make heat and heat kills motors. Volts makes rpms and excessive rpms kill motors too... there is a fine line somewhere here. If I had a 72v motor I would sooner run it on 84 than 48. Keep us posted.

With more volts you use fewer amps to do the same amount of work, on the other hand, with higher volts the motor is capable of drawing more amps when spinning at the same RPM. That is why you get higher torque throughout the RPM spectrum when you up the voltage to the motor.

Electrically, DC motors are made up from several lengths of wire, a few carbon brushes and a copper commutator, none of which are particularity voltage sensitive. However, when you are upping the voltage and making the motor work harder, you are upping the amps and more amps generate more heat and heat kills motors, so there is a limit as to how much the voltage can be increased.

Going from a 77V fully charged FLA pack to a 83V Lithium pack is less than a 10% increase in voltage. (7.8% actually.)

More importantly, what is the max kW you can hit the motor with from a 72V FLA pack vs how many kW from a 83V lithium?

Originally Posted by somfas

I believe that the cells should charge to 4.15v max, 2 cells per module. So, 8.3v per module. 10 modules would be 83v max, and 9 modules would be 74.7v max. These are Nissan Leaf modules and I was advised by others on this forum to use 10 modules. My current battery pack (FLA) charges at 81.4 volts and the dash meter reads 78.9v now after being unplugged overnight. I have only run the Alltrax toolkit 1 time since I don't know what I am doing with it, and the volts it showed did not match up with my dash meter. It was relatively close, but lower than my dash meter.

Unless the solenoid contacts are closed, the toolkit battery voltage will be a bit less than what is seen on a dash mounted DVM.

[bronsonj]

Not to counter Johnnie... He's forgotten more about this than I'll ever know...

Consider he'll have nine 8V anchors he's getting rid of.. That'll trim the mass of the cart immensely and make the work load on the motor less.

Unless he's doing something stupid (like I am prone to do) then I would imagine he's going to be pulling less amps than before.

[JohnnieB]

Originally Posted by bronsonj

Not to counter Johnnie... He's forgotten more about this than I'll ever know...

Consider he'll have nine 8V anchors he's getting rid of.. That'll trim the mass of the cart immensely and make the work load on the motor less.

Unless he's doing something stupid (like I am prone to do) then I would imagine he's going to be pulling less amps than before.

No conflict, fewer amps needed with less load and going from FLA to LI is dropping the load by 400 lbs (6x12V) to 500 lbs (9x8V).

Conversely, the foot tends to get heavier as cart performance gets better. So with a much lighter cart and a little higher voltage, he might have the capability to pass more amps through the motor, but not the opportunity.

[bronsonj]

Originally Posted by JohnnieB

Conversely, the foot tends to get heavier as cart performance gets better. So with a much lighter cart and a little higher voltage, he might have the capability to pass more amps through the motor, but not the opportunity.

Yes... I never did a wheelie in a cart until I went Lithium, then I found wheelies to be very fun for the first few months. I've finally trimmed back the ramp rate to prevent that...

As to the OP, the most voltage sensitive part of a sepex cart is normally the controller. If your controller can handle over 92v then I'd go with an 11 pack of leaf cells (or equivalent Chevy Volt cells) charged to 4.15vpc max for a 91.3v pack max. As mentioned earlier, we overvolt 36v motors all the time at 48v and I'm overvolting my 48v motor with my 58v pack.

If you're worried about it, stick with a 10 pack of leaf cells for 83v. Another option is to trim back the max amps setting in your controller to avoid over taxing the motor and therefore causing too much heat. You may well find that at 83v or 92v with 4 or 5 hundred less pounds in the cart that you really don't need nearly as many amps.