72v Lithium + Navitas - What is your voltage sag under load?

[fstop]

Just curious to see what folks that have Navitas 5KW motor / controller + a 72v LifePo4 battery are seeing in terms of voltage sag (at rest, no-load voltage -vs- under load voltage) when under full acceleration or at WOT? I'm curious to see what the variance here might be with different packs / cell types.

Helpful info would include tire diameter, gear ratio, cart type (4p, 6p, etc...) battery type / brand, current draw at time of voltage reading etc...

I'll add my own observations to start... Thanks to any contributors.

Battery: 72v LifePo4 (24 cell) generic China-sourced pack, 120ah cells
Cart: Onward 4P, 23" tires, 12.44 stock gears
Voltage / Current: 75.1v @180A load (WOT), 81v no load @ 100% SOC.

[Pat911]

Where are you measuring the battery voltage? Is it right at the battery terminals or is it what the Navitas is reporting? I ask because at 180A, wire, terminal and solenoid resistances are very significant.

The other important parameter to consider is ambient temperature as that will also significantly affect voltage sag.

[fstop]

Originally Posted by Pat911

Where are you measuring the battery voltage? Is it right at the battery terminals or is it what the Navitas is reporting? I ask because at 180A, wire, terminal and solenoid resistances are very significant.

The other important parameter to consider is ambient temperature as that will also significantly affect voltage sag.

Measuring at the battery terminals (shunt between terminal and controller, actually). Yes, Navitas is not that accurate. My shunt-based meter is within a tenth or so of my trusty Fluke 77 so it's very close.

Good point - approx. ambient temperature might be good to include - especially with winter coming on now. My prior example was at around 65f.

[Buttapollock1010]

Nice info. What kind of speed are u getting with 72v? Make the AC setup come to life? Think when my Trojans die I’m going 72v!

[reeseman44]

I build my own pack with high quality grade a cells, and a 500a Bluetooth bms. I have the silverwolf permanent magnet AC setup, which is supposedly more efficient than
And induction type AC motor. 100% soc is 80.4 after it it removed from charger for 12+ hrs. I see it go down to 76.5v at full acceleration. I have a 10" Lift and 27 inch auto radial tires on 15" wheels. I have hit a top speed of 47 mph on gps. That it definitely limited by torque and not rpm.
Out of pure curiosity, i am tempted to swap in the nav 5kw 600a and see the results.

[Buttapollock1010]

Nice numbers. I think 72v. Is my next step. Maybe I’llget brave and build my own if I get some free time.