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Old 09-10-2018, 01:11 AM   #1
tomgoldie
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Default Questions for TXT PDS Electronics Whiz

A few weeks back I described a problem I have with my cart wheels locking up when coasting downhill. I bought a Bluetooth multimeter to see if the over-voltage caused by regen braking was the culprit, but as the sampling rate is not quick enough to catch the instant protection is initiated and activation circuit is lost - though it does show steep drop-offs. (See attachment for graph)

So anyway, I'd appreciate any help anyone could offer with the following questions:

1) Is rollaway protection the same thing as the loss of the activation circuit, or are these separate functions?

2) Assuming my wheel lockup problem is caused by my SmartBattery lithium batteries' over-voltage protection being triggered by excess regen braking voltage, would adding a large capacitor help me not to lose the activation circuit?

3) How would regen braking/cart behavior be affected by working against a capacitor instead of a battery pack? Would there just be no braking due to falling current as capacitor voltage rises, or would/could it increase voltage so high that it would burn out my capacitor? I'm thinking something like this:

https://www.amazon.com/EZGO-Capacito.../dp/B007R0J8Y0
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Old 09-10-2018, 03:04 AM   #2
cgtech
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Default Re: Questions for TXT PDS Electronics Whiz

1- no, very different. In fact, rollaway commands the solenoid "on", not "off".


2- 20 millifarad (0.020 farad) is insignificant in the amount of power your dealing with. I feel that you would need whole farads, like more than 1 whole farad. 12v car stereo caps wouldn't work either, their voltage rating is too low.

3-. I feel that the bms controller would be satisfied as long as power had somewhere to go, and to the system as a whole, a large capacitor is just a "fast-reacting battery".

I am sorry to say, I don't think your batteries BMS is going to be compatible. Capacitors in the farad range and voltage range that might solve your issue are just not readily available. I think your best bet is a freedom chip to minimize regen, and never ever allowing the fully charged cart to reach top speed down the hill (where regen will kick in, no matter the chip). Tried just driving slow down the hill when first leaving the house fully charged? I also think these "runaway voltages" created when the batteries "just disappear" will eventually kill your controller too.
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Old 09-10-2018, 11:15 AM   #3
JohnnieB
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Default Re: Questions for TXT PDS Electronics Whiz

The steep voltage drop-offs seen on the graph is due to the motor (acting as a generator) being fed PWM (Pulse Width Modulated) DC rather than straight line DC.

When operating as a motor, the armature is fed from a set of MOSFETs that are switch on and off at about 18kHz. The pulsed DC output switches from 0V to battery pack voltage and the controller varies the duty cycle (how long the MOSFETs stay on each cycle) from 0% to 100% to regulate the amount of amps the armature can draw. If you measure the voltage applied to the armature with a DVM or VOM, you will read an average of the PWM DC voltage.

The same is true with the MOSFETs the feed the field windings, except max field current is only about 30A while armature current can be up to 300A with a stock PDS controller. I've never looked at the PWM fed to the field windings with an o'scope, so I don't know if the if the pulses are 0V to battery pack voltage, or 0V to something less than battery pack voltage, or if the PWM duty cycle only goes up to about 10%.

Anyways, the field winding are excited with PWM DC while in regen mode, so the output back to the battery is pulsed DC, hence the steep drop-offs. The wave shapes are not clean cut DC pulses because both the field and armature windings are inductors, which distort the leading and trailing edges of the pulses.

--------------
Personally, I'd install an Alltrax XCT48400 controller so I could adjust the amount of regen braking, or turn it off completely.
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Old 09-10-2018, 12:16 PM   #4
BobBoyce
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Default Re: Questions for TXT PDS Electronics Whiz

Quote:
Originally Posted by tomgoldie View Post
A few weeks back I described a problem I have with my cart wheels locking up when coasting downhill. I bought a Bluetooth multimeter to see if the over-voltage caused by regen braking was the culprit, but as the sampling rate is not quick enough to catch the instant protection is initiated and activation circuit is lost - though it does show steep drop-offs. (See attachment for graph)

So anyway, I'd appreciate any help anyone could offer with the following questions:

1) Is rollaway protection the same thing as the loss of the activation circuit, or are these separate functions?

2) Assuming my wheel lockup problem is caused by my SmartBattery lithium batteries' over-voltage protection being triggered by excess regen braking voltage, would adding a large capacitor help me not to lose the activation circuit?

3) How would regen braking/cart behavior be affected by working against a capacitor instead of a battery pack? Would there just be no braking due to falling current as capacitor voltage rises, or would/could it increase voltage so high that it would burn out my capacitor? I'm thinking something like this:

https://www.amazon.com/EZGO-Capacito.../dp/B007R0J8Y0
Those lithium batteries will not work. Each battery has internal fault monitoring that gets triggered by overcurrent and drops out the battery, and overvoltage that will drop out the battery. Another member here just went through the same thing a month or so ago. If you keep using this, it WILL corrupt the memory of your controller when it keeps cutting power to your controller suddenly.

He had to go to a lithium pack and return those lithium battery unit replacements.

Bob
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Old 09-10-2018, 10:10 PM   #5
tomgoldie
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Default Re: Questions for TXT PDS Electronics Whiz

Sorry everyone for the mess in replies. This is much harder on my phone.

Quote:
I think your best bet is a freedom chip to minimize regen, and never ever allowing the fully charged cart to reach top speed down the hill (where regen will kick in, no matter the chip). Tried just driving slow down the hill when first leaving the house fully charged? I also think these "runaway voltages" created when the batteries "just disappear" will eventually kill your controller too.
Bummer about the controller. I have the freedom chip. I am now betting the hesitation I am feeling just before lockup is the first bit of regen braking.
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Old 09-10-2018, 10:17 PM   #6
tomgoldie
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Default Re: Questions for TXT PDS Electronics Whiz

Quote:
Originally Posted by cgtech View Post
1- no, very different. In fact, rollaway commands the solenoid "on", not "off".
Thanks.


Quote:
Originally Posted by cgtech View Post
2- 20 millifarad (0.020 farad) is insignificant in the amount of power your dealing with. I feel that you would need whole farads, like more than 1 whole farad. 12v car stereo caps wouldn't work either, their voltage rating is too low.
I think the capital M in the capacitor in the liis MEGA (*10^6), no? And it's rated to 250V. If so, would it help - in your opinion?
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Old 09-10-2018, 10:30 PM   #7
tomgoldie
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Default Re: Questions for TXT PDS Electronics Whiz

Quote:
Originally Posted by JohnnieB View Post
The steep voltage drop-offs seen on the graph is due to the motor (acting as a generator) being fed PWM (Pulse Width Modulated) DC rather than straight line DC.

When operating as a motor, the armature is fed from a set of MOSFETs that are switch on and off at about 18kHz.completely.
It's hard to see on the picture, but the voltage reads are every half second. The ups and downs were coming from accelerator loads and regen braking. I don't think the sampling rate was quick enough to detect the cutout.

Quote:
Originally Posted by JohnnieB View Post
Personally, I'd install an Alltrax XCT48400 controller so I could adjust the amount of regen braking, or turn it off completely.
If my capacitor test doesn't work, the controller will likely be next - after I fry this one. Controllers and then new battery packs suggested by another would certainly work, but aren't in the budget :-(
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Old 09-10-2018, 10:46 PM   #8
tomgoldie
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Default Re: Questions for TXT PDS Electronics Whiz

Quote:
Originally Posted by BobBoyce View Post
Those lithium batteries will not work. Each battery has internal fault monitoring that gets triggered by overcurrent and drops out the battery, and overvoltage that will drop out the battery. Another member here just went through the same thing a month or so ago. If you keep using this, it WILL corrupt the memory of your controller when it keeps cutting power to your controller suddenly.

He had to go to a lithium pack and return those lithium battery unit replacements.

Bob
Did he consider or try a large capacitor, and did he consider a controller that could be programmed to stop regen braking? Given how long I've had these, there's no returning them - so a couple hundred for a controller beats a couple thousand for new Li ion batteries, any day :-)
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Old 09-11-2018, 02:57 AM   #9
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Default Re: Questions for TXT PDS Electronics Whiz

Quote:
Originally Posted by tomgoldie View Post
Did he consider or try a large capacitor, and did he consider a controller that could be programmed to stop regen braking? Given how long I've had these, there's no returning them - so a couple hundred for a controller beats a couple thousand for new Li ion batteries, any day :-)
Lithium packs for carts can be bought for hundreds these days. Under $700 for a 7 module Leaf pack if you shop around.

Controllers are no longer simple PWMs. They are microprocessor controlled.

A couple hundred for a controller... over and over again until the issue is resolved. Controllers have a specifc shutdown sequence, where the logic section is turned off while power remains applied at B+ and B- to allow a controlled shutdown. Data is moved from active memory to storage memory, then moved back upon powerup. If this sequence is interrupted by B+ going away before the sequence is complete, data loss or corruption occurs. Ultracaps would be hard pressed to supply the large currents required to maintain B+ voltage, plus the sequence (key off first, then at least 5 seconds of B+ maintained for the housekeeping) before the load sucks them flat! A battery shutdown kills the B+ before the sequence can begin.

What happens to your PC if you keep pulling the power plug from the wall instead of doing a proper shutdown? Modern controllers are computers.

Bob
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Old 09-11-2018, 11:09 AM   #10
cgtech
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Default Re: Questions for TXT PDS Electronics Whiz

Quote:
Originally Posted by tomgoldie View Post
Thanks.




I think the capital M in the capacitor in the liis MEGA (*10^6), no? And it's rated to 250V. If so, would it help - in your opinion?
If a one single farad cap for 12v is roughly 2.5" diameter, and 8" length, you can rest assured that a 1.5" diameter by 3" length cap at hundreds of volts is not millions of farads. And no, I don't think that cap will do anything at all for you..

Guy in picture is for scale.
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