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Electric EZGO Electric EZ GO Marathon, Medalist, TXT and RXV. |
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09-10-2018, 01:11 AM | #1 |
Not Yet Wild
Join Date: Aug 2018
Posts: 17
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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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09-10-2018, 03:04 AM | #2 |
Over This Interview Is...
Join Date: Jun 2012
Location: AZ
Posts: 17,449
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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. |
09-10-2018, 11:15 AM | #3 |
Techno-Nerd
Join Date: Jun 2011
Location: West Virginia
Posts: 19,654
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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. |
09-10-2018, 12:16 PM | #4 | |
Gone Insane
Join Date: Oct 2015
Location: TN/NC/GA Tri-state area
Posts: 3,952
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Re: Questions for TXT PDS Electronics Whiz
Quote:
He had to go to a lithium pack and return those lithium battery unit replacements. Bob |
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09-10-2018, 10:10 PM | #5 | |
Not Yet Wild
Join Date: Aug 2018
Posts: 17
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Re: Questions for TXT PDS Electronics Whiz
Sorry everyone for the mess in replies. This is much harder on my phone.
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09-10-2018, 10:17 PM | #6 | |
Not Yet Wild
Join Date: Aug 2018
Posts: 17
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Re: Questions for TXT PDS Electronics Whiz
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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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09-10-2018, 10:30 PM | #7 | |
Not Yet Wild
Join Date: Aug 2018
Posts: 17
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Re: Questions for TXT PDS Electronics Whiz
Quote:
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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09-10-2018, 10:46 PM | #8 | |
Not Yet Wild
Join Date: Aug 2018
Posts: 17
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Re: Questions for TXT PDS Electronics Whiz
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09-11-2018, 02:57 AM | #9 | |
Gone Insane
Join Date: Oct 2015
Location: TN/NC/GA Tri-state area
Posts: 3,952
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Re: Questions for TXT PDS Electronics Whiz
Quote:
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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09-11-2018, 11:09 AM | #10 | |
Over This Interview Is...
Join Date: Jun 2012
Location: AZ
Posts: 17,449
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Re: Questions for TXT PDS Electronics Whiz
Quote:
Guy in picture is for scale. |
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