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Old 01-26-2018, 06:28 PM   #21
Mooncarter
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Default Re: Is our Series Cart a practical application for Lithium Batteries?

Of course, I don't understand it. But JB knows this stuff!
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Old 01-27-2018, 12:49 AM   #22
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Default Re: Is our Series Cart a practical application for Lithium Batteries?

Quote:
Originally Posted by JohnnieB View Post
No aimed at me, but being a Techno-Nerd, I cannot resist answering this.
Thank you for that explanation .

So since motor amps can exceed battery amps, how does one go about properly selecting a controller when my peak battery current is 400 amps? I assume that controllers are rated based on "motor amps"?

I also wonder what your "green column" (difference between motor amps and battery amps) would look like in a maximum load (pedal to the metal) situation?
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Old 01-27-2018, 10:19 AM   #23
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Default Re: Is our Series Cart a practical application for Lithium Batteries?

I understand this is where a 'good' BMS comes into play.
It should restrict the flow to what is acceptable for the battery pack.
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Old 01-27-2018, 12:16 PM   #24
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Default Re: Is our Series Cart a practical application for Lithium Batteries?

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Originally Posted by ThreeCW View Post
Thank you for that explanation .

1. So since motor amps can exceed battery amps, how does one go about properly selecting a controller when my peak battery current is 400 amps? I assume that controllers are rated based on "motor amps"?

I also wonder what your "green column" (difference between motor amps and battery amps) would look like in a maximum load (pedal to the metal) situation?
1. Your assumption is correct and Controller selection is easy. Get an Alltrax SR controller.

The SR controllers are user programmable (laptop with USB cable) and you can set Max Battery Amps and Max Motor Amps independently. In a nutshell, you can set the battery amps to whatever the max draw for the battery pack is and still allow the motor to draw up to the limit set by the controllers amp rating. That allows you to obtain the maximum performance possible without sucking the guts out of the battery pack.

2. Maximum load and pedal to the metal aren't necessarily the same condition. The amount of current an electric motor can draw is determined by the RPM of the armature and the voltage applied. The are some other factors, but those are the biggies. For example a D&D ES-5-9 series motor fed by a 48V lead-acid battery pack is able to draw about 530A and produce about 80ft/lb of torque at 1000RPM, but can only draw about 50A and produce about 3ft/lb of torque at 4300RPM. The tricky part is that the voltage of a 48V lead-acid pack drops about 1.5V per 100A of current draw while corresponding voltage drop a 48V Lithium pack is far less, so higher amps would be seen at 1000RPM (something in the neighborhood is 640A) and the same motor would produce more torque at low RPM.

With the pedal on the metal the PWM output of the controller is at 100% duty-cycle and is effectively straight line DC, so there is no flywheel effect and Battery amps and Motor amps are equal. (See attached - from same data log as earlier example posted)

Since the amount of torque produced is determined and the number of amps flowing through the armature, max torque is not produced at 100% throttle.

The max armature amp draw I ever recorded with a ES-76-51 sepex motor and DCX500 controller was 504A while the battery current was 178A and the throttle was at 35%. Conversely, the highest battery current I recorded with the same setup was 391A at 100% throttle and 391A of armature current.
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File Type: jpg Battery vs Motor Amps WOT.jpg (281.2 KB, 0 views)
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Old 01-28-2018, 01:25 AM   #25
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Default Re: Is our Series Cart a practical application for Lithium Batteries?

It sounds you can be “double protected” to ensure that you stay within your Lithium battery discharge rating … with a good BMS and a properly programmed controller. I am starting to understand how this can all fit together now … thanks ScottyB and JohnnieB for your wise words . I would hate to see the “guts sucked out" of my future Lithium battery pack .

I was originally thinking that a 400 amp Alltrax SR controller would be sufficient to power my cart … but given JohnnieB’s post, I now understand that a 500 amp or even the 600 amp controller would be a better option. I would not want to be controller limited in my future carting operations given the 300 to 400 battery amps that I measured during my testing.

Now to find some suitably rated Lithium cells for a battery pack! Hopefully I can come up with an economically acceptable Lithium battery solution (willing to invest up to 2 times the cost of a lead acid pack given that I would expect twice the life out of Lithium).
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Old 01-28-2018, 08:37 AM   #26
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Default Re: Is our Series Cart a practical application for Lithium Batteries?

Quote:
Originally Posted by ThreeCW View Post
I was originally thinking that a 400 amp Alltrax SR controller would be sufficient to power my cart … but given JohnnieB’s post, I now understand that a 500 amp or even the 600 amp controller would be a better option. I would not want to be controller limited in my future carting operations given the 300 to 400 battery amps that I measured during my testing.
Overkill is underrated.

Advertised controller amp ratings are typically the 2-minute rating. Here is a chart showing Peak, 2-minute, 5-minute and Continuous values for SR controllers.

FWIW: I went from a DCX500 to a XCT400 because Alltrax hadn't released the XCT500 at the time and my data logs from the DCX500 showed my setup seldom exceeded the 460A peak of the XCT400 that was immediately available. Also, my tires are only 17" tall, so I have more torque at low RPMs than I can couple to the ground and having more low end torque would only cause the tires to spin more.
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File Type: jpg SR Specs.jpg (225.6 KB, 0 views)

Last edited by JohnnieB; 01-28-2018 at 08:38 AM.. Reason: forgot attachment
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Old 01-29-2018, 12:11 AM   #27
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Default Re: Is our Series Cart a practical application for Lithium Batteries?

I had some water leakage issues last year that disabled my Curtis Controller, so was planning to replace the original equipment Curtis with an Alltrax SR Controller. I resolved the water issues by drying out the controller and using some silicone caulking to seal it ... I have not experienced any problem since, but a replacement controller is still in my future plans. I would hate to have my Curtis controller go down on me again so I hope to be able to do a "proactive replacement" to an Alltrax SR sooner than later.

Getting back to Lithium batteries, if anyone can recommend any lithiums with at least a 3C continuous current rating I would appreciate it. The only ones that I have been able to find so far with this specification is the GBS cells which I am trying to source in Canada.
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Old 01-29-2018, 08:25 AM   #28
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Default Re: Is our Series Cart a practical application for Lithium Batteries?

I ended up with some LifePo4 100a 3C cells off of ebay.
They were new old stock.
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Old 10-23-2018, 12:07 PM   #29
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Default Re: Is our Series Cart a practical application for Lithium Batteries?

Quote:
Originally Posted by JohnnieB View Post
1. Your assumption is correct and Controller selection is easy. Get an Alltrax SR controller.
Help me out a bit here.

My AXE 4865 controller is programmable to a given extent. I pulled out my old Windows based laptop and fired it up. It still has the Alltrax software on it.

So, here's a pic from the Alltrax AXE Products webpage:



Is my assumption correct here, that if I set the "Max Output Current" to some given percentage (not sure what that would be) then the Alltrax Controller will control how many amps it will allow to draw from the battery pack?

Now, I am going to connect up the laptop while my existing LA T-105's are still installed and obtain some readings from that. I believe that will also provide me with a better understanding of the power need.

Dave
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Old 10-23-2018, 12:18 PM   #30
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Default Re: Is our Series Cart a practical application for Lithium Batteries?

Note:

Based upon further reading Alltrax documentation, if I understand the "Max Output Current %" adjustment, since my 48650 has a maximum output of 650amps, then (example only) if I set this option to 50%, the controller will limit maximum amp output to 325amps.

If I understand this correctly.

Dave
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