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Old 08-10-2020, 10:31 AM   #21
Sergio
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Default Re: Best lithium setup for Navitas 600/5kw?

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Originally Posted by dougrobling View Post
I have installed 3 sets of Navitas 5kw sets here in my neighborhood. Two have 72V Lithium Iron Phosphate batteries and are VERY NOTICABLY faster and more powerful than the same exact setup and settings as the 48V Lead Acid set-up. The only difference in the programming is that I set the two lithium sets with a current draw limit of 200A and the L/A set with a limit of 300A. That should make the wattage availability to all carts the same, but as I said earlier, there is still a noticeable difference,
I ran them all up the same (steep) hill here and the Lead acid accelerates quickly to about 18mph and then continues to slowly increase speed up to about 22 while still climbing (I set it's limit to 30) The Lithium carts accelerate quickly all the way up the hill to about 35mph (Their limit is set at 40)

That is likely more related to the loss in weight of Lead vs Lithium than the voltage itself, DC carts behave the same when you remove the weight as it increases the HP/Weight ration.


Does anyone in your neighborhood have the same controller/motor combo running on a 50v+ Lithium setup to compare?
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Old 08-12-2020, 07:34 AM   #22
fstop
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Default Re: Best lithium setup for Navitas 600/5kw?

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Originally Posted by Sergio View Post
That is likely more related to the loss in weight of Lead vs Lithium than the voltage itself, DC carts behave the same when you remove the weight as it increases the HP/Weight ration.


Does anyone in your neighborhood have the same controller/motor combo running on a 50v+ Lithium setup to compare?
I'll let him give you his 72v info directly, but IIRC he's mentioned here on several occasions that his 72v cart is able to make +/- 50mph on flat ground if the speed is unlimited in the app / controller.

He and I have the same cart / drive system (he has 22" tires, mine are 22.5", and he has a Curtis Cab on one of his - otherwise same gears, motor, controller etc...), but I have only a 52v battery - my speeds are correspondingly less at only 38mph on flat ground.

This indicates that there is a major difference in performance potential with this motor / controller between a 72v input -vs- a 52v input.

You've mentioned that input voltage should not make much difference on an AC motor / controller - and I wouldn't disagree with any principals behind it or doubt your reasoning, but the reality - for whatever reason, and, again, probably best asked of Navitas - is that adding 20v to the input voltage makes a major difference in top speed. I would assume acceleration potential would also increase, but that may not be the case. I think acceleration rate is limited in the controller (by parameters not available in the "dealer" app), and may already be "maxing out" with the 52v setups on flat ground. Uphill acceleration and speed-keeping would likely be superior on the 72v as the 52v cart would likely begin to be current / voltage starved on an incline, and not be limited by the FW, but by electrical deficiency. This is conjecture on my part, however.
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Old 08-12-2020, 07:51 AM   #23
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Default Re: Best lithium setup for Navitas 600/5kw?

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.
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Old 08-12-2020, 08:15 AM   #24
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Default Re: Best lithium setup for Navitas 600/5kw?

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Originally Posted by Sergio View Post
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.
And you could be right, but that is contrary to what the manufacturer of the controller / motor is saying.

It would be interesting to see current drawn from the battery data from Doug on his 72v setup.

I can say on mine, it has no problem delivering ~230 amps during acceleration.

It will draw more than this on hills, and for a longer time as you go up that incline.

I'll say I haven't pushed experimenting with this because I'm not wanting to stress my equipment for no reason, but the point is that it can supply at least 250 amps for 5+ seconds based on my brief experiments, w/out issue or BMS shutoff.

WOT current draw is right at about 145A. So apparently the motor / controller has more current available from the battery system but is not utilizing it for some reason. That reason may be what Navitas could tell you - I'm not claiming to know.
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Old 08-12-2020, 05:55 PM   #25
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Default Re: Best lithium setup for Navitas 600/5kw?

fstop, I am not doubting you have seen faster or experienced yourself faster cart speeds with the 72v setups, I guess I have a more focused interest in understanding the factors involved for that increase
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Old 08-12-2020, 07:29 PM   #26
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Default Re: Best lithium setup for Navitas 600/5kw?

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fstop, I am not doubting you have seen faster or experienced yourself faster cart speeds with the 72v setups, I guess I have a more focused interest in understanding the factors involved for that increase
Yeah - I'd be curious to know myself, even if I didn't understand in detail all the technical reasons for it.

I suspect there could be logic in the controller that is limiting it in some way, maybe because of liability (a lot less users with 72v, but could still demonstrate the power of the system w/out so much liability exposure?). Or maybe it has to do with component durability within the controller, and 72v system could operate with less current through the controller and they'd have a lower failure rate / longer product life?

Both total guesses.
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Old 08-21-2020, 10:33 AM   #27
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Default Re: Best lithium setup for Navitas 600/5kw?

All great questions. If no one has answers by the next time I chat with Navitas I'll inquire. I need to call them on some issues anyway. Overall they have great support and are very willing to answer questions.
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Old 08-21-2020, 12:53 PM   #28
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Default Re: Best lithium setup for Navitas 600/5kw?

The actual question if You want to ask them is:

Quote:
Assuming Your battery pack has enough current discharge to provide the nominal voltage needed under load to prevent a "slip" on the AC motor, is there any speed increase (quantify if possible) by going to a higher voltage pack?

If You can post their answer or any comments they have it would be nice to understand the capabilities of the Navitas AC Controller.

I see from other threads that Navitas is adding a lot more configuration parameters to deal with different lithium battery packs and BMS limitations.
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Old 08-21-2020, 01:06 PM   #29
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Default Re: Best lithium setup for Navitas 600/5kw?

Directy from Navitas tech when asked about the benefits of going to 72V:

Good rule of thumb… (Voltage = Speed) – (Amps = Torque)

In the end, I will problably not do a 72V 18S battery setup but go for a more standard 48V setup as I am fine with 30mph top speed. (Navitas says 35 mph is to expect with 48V). Torque is more important to me.
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Old 08-21-2020, 01:36 PM   #30
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Default Re: Best lithium setup for Navitas 600/5kw?

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Originally Posted by Sampras1977 View Post

Good rule of thumb… (Voltage = Speed) – (Amps = Torque)
Yes, when talking about DC carts but this discussion is about 3 phase AC systems.
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