Best lithium setup for Navitas 600/5kw?

[Danimal1228]

Segio, Did you ever get an answer on the higher voltage question? Im in the same boat. With the AC Navitas I want to know if there is any advantage to going higher voltage, other than lowering current draw.

[Sergio]

I never did and while I agree on the lower current advantage on the higher voltage setup, it also increases the cost of every component like the controller, solenoid, reducer, etc.

Since the 3 phase AC induction motor controls speed by varying the driver frequency, I am curious to know if the Navitas Controller does anything different to increase the speed when powered by the higher voltage.

[morvolts2]

Has anyone put a freq meter on the motor on 72v vs 48?
Perhaps the increase in voltage(which should increase the available wattage)
allows the controller to increase the frequency?

[Pat911]

Originally Posted by Sergio

If You have a 52v pack with inadequate capacity to provide the current needed, then either increasing the capacity of the exist 52v pack or using a pack of the same capacity but higher voltage would increase the speed.

The point I keep trying to get across is the speed increase is not related to the voltage as in DC systems, but it could be because your existing pack just cannot deliver the current needed for the load demand.

Hi Sergio,

I found this chart on the Navitas website. It provides operational data for their 5kW motor.



As it shows, the peak power is just over 7.5kW and it is produced just under 1000rpm. The chart doesn’t differentiate between 48v or 72v controller input voltage. If the motor/controller combination performance is improved at 72v, it could be that the controller allows a faster increase in output frequency, and hence acceleration under 72v conditions.

A theory could be that the controller is throttling back acceleration at 48v to limit the peak battery current, as opposed to the pack not being able to deliver the required current. If the peak battery current is the same at 72v as it is at 48v, the resultant acceleration at 48v would be less than at 72v.

What are your thoughts on this theory?

Cheers
Pat.

[morvolts2]

it looks like the controller is limiting the voltage to 34v, which doesnt make sense if the higher voltage is available.
Higher voltage(given that components are rated for it) is always the best choice for performance and efficiency

[fstop]

I can tell you, having had a 51v lithium pack for the last year or so, and just recently switching to a very similar pack with 72v, that performance is increased substantially. Radically is probably not too strong a word. It's a big difference.

I can go back through some of my older data (with the 51v pack) from the controller and see if anything related to frequency is apparent. I don't think I ever checked it while driving though, but I might be able to get a static comparison.

Edit: Went back and looked at some older data, and not sure it is even useful, but see below.

Parameter "Rated Vrms" was 40 in both the older 51v configuration, and the current 72v one.

Parameter "Rated Frequency" was and is still 78.

[Pat911]

Morvolts2, that is the motor data sheet. The motor is rated at 34v and so the controller MUST keep it at or below 34v to prevent motor overheating and eventual burnout.

Remember, we are talking about a VFD (Variable Frequency Drive) motor here. It’s supply voltage doesn’t govern its speed, the supply frequency does. And torque can be increased by increasing the rate of change of the frequency signal. The faster that frequency increases the faster it will accelerate. Current draw will increase accordingly.

@fstop, is there a parameter relating to maximum current, especially on the supply side or frequency rate of change (or acceleration limit)?

Cheers
Pat.

[fstop]

Originally Posted by Pat911

Morvolts2, that is the motor data sheet. The motor is rated at 34v and so the controller MUST keep it at or below 34v to prevent motor overheating and eventual burnout.

Remember, we are talking about a VFD (Variable Frequency Drive) motor here. It’s supply voltage doesn’t govern its speed, the supply frequency does. And torque can be increased by increasing the rate of change of the frequency signal. The faster that frequency increases the faster it will accelerate. Current draw will increase accordingly.

@fstop, is there a parameter relating to maximum current, especially on the supply side or frequency rate of change (or acceleration limit)?

Cheers
Pat.

There is a max. acceleration rate parameter, but it doesn't have any effect on top speed, (and not a tremendous one on acceleration in my experience).

I believe there is a current parameter in there, but IIRC it looks like a multiplier, not an amp figure, and I'm pretty sure that figure also is the same since I changed to a 72v configuration. I think it was .8 or .9 IIRC.

[Pat911]

Fstop,

I have to agree with Sergio here, the higher input voltage SHOULD have nothing to do with top speed. You can see from the chart above that the motor supply voltage remains the same from about 900rpm up. Can you see your motor rpm at top speed and do you have that same data for when you were running the lower voltage pack?

Cheers
Pat.

[fstop]

Originally Posted by Pat911

Fstop,

I have to agree with Sergio here, the higher input voltage SHOULD have nothing to do with top speed. You can see from the chart above that the motor supply voltage remains the same from about 900rpm up. Can you see your motor rpm at top speed and do you have that same data for when you were running the lower voltage pack?

Cheers
Pat.

I wouldn't disagree with you or Sergio on this point. Awhile back some appeared to question the legitimacy of the speeds recorded with higher input voltages because it didn't seem like it would matter, and I would only reiterate that that is a very real thing - period.

As to "how" that is happening, given you and Sergio's apparent familiarity with AC / VFD drive systems, I have no clue - my expertise is way below your pay grades in this area.

As to RPMs, before my setup would max out around 7K, and now it's around 8500. So a major difference. But in terms of subjective difference, it's the acceleration that really is just night and day -vs- 51v.

I'll say on an input voltage sag percentage, under full acceleration, my 51v pack and the current 72v one "sagged" about the same - which is not much IMO - around 6% max worst case under the hardest part of the acceleration load.

So there's that, but I'll have to leave it to you guys to figure out HOW it is doing it, but there is no question it is doing it. It's not just me - others have shared basically the same experience.