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Electric EZGO Electric EZ GO Marathon, Medalist, TXT and RXV.



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Old 09-11-2021, 12:03 PM   #1
JRaf
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Default Batteries, charger, a long confessionary tale...

Long story, hope you’ll be patient with me. A neighbor gave me a 1993 EZGO Marathon. It had flat tires, dents, ripped up seats, and it hadn’t run in… years? I fixed up the worst dents, the seats, fixed or replaced wheels and tires, cleaned up the wiring, and pulled the batteries, old interstates that were dry, swollen, truly horrific.
He also handed over the original charger, a dusty, spider-webbed non-functioning “Total Charge III”. I cleaned that up, put in a new board, new diodes, and a new capacitor. I tried to save the old batteries slowly with an automobile charger, finally getting one or two batteries to hold voltage. I could even get the motor to turn and the cart to roll a few feet before they died.
Now I'm never going to use this cart a lot. I will never leave my property or the immediate environs. I don't play golf. I plan on using the cart every day but I'll never put more than ten minutes of pedal time on it. It has a bed in the back, useful for hauling tools and trash and stuff.
So... I went out and bought three 12v marine batteries, installed them and the cart ran! I’m not breaking any speed records but I could get around the rancho, drag feed and hay out to my back pasture and parts and tools to my constantly-needs-service old tractor and collection of terrible cars. I could even (for a day or two) go up and down my long, hilly driveway.
But then I tried to charge the batteries and something happened. I plugged in the old EZGO anvil, the ammeter went up to around 16 amp (actually more like 18 on my clamp on meter) and the charger hummed purposefully. I measured the charger voltage coming into the pack at around 44 volts. After an hour or so the amps would drop down to 7, then 5 then 2, then almost nothing and the charger would stop.
I let the pack sit overnight and in the morning the pack voltage was sitting nicely at 38.5 and the (3) batteries seemed to be in balance. But the cart had no mojo. It ran fine on flat ground but wouldn’t go up hills. Huh.
I checked everything, swapped out and cleaned terminals and wires, cleaned and went through all the electrics. I repeatedly recharged the batteries. And I could get it to work intermittently. But if I charged the pack and let the cart rest overnight I would get the same symptoms, runs okay but dies on hills, re-charge, runs okay, but I had to keep the cart on the charger every few hours, even though the batteries would measure fine at rest.
I searched for other problems, unattached every wire, taking the batteries completely out of the circuit after a fresh charge. I went through the wiring, replaced the solenoid, checked the F/R switch, even backed off the brakes to check for drag. I checked for parasitic drain and found nothing.
I also played with the charger some more, shorted the wires so it wouldn’t turn off. But would run for a few minutes or half an hour at full amperage, then the amps would come down slowly, and it would hum but barely put out any charge at all.
But it all seemed obvious right? It had to be the cheap marine batteries.
I gave up on that experiment and finally bought 6 new six-volt batteries (Centennials designed and built by US Batteries). They are new, right off the pallet, manufactured August 2021, and they all measured 6.45v sitting in the back of my car.
I installed them in the cart, knowing that I had solved the problem. I drove up my hill from my barn to the shed where the charger lives. All fine but I want to treat them right, so I put the cart on the charger. And it hummed and the ammeter popped right up to seventeen volts and ran for a few hours, same pattern, gradually dropping down and turning off. I let them rest overnight and the charge held at 38.7.
I drove down the hill and couldn’t get back up.
I charged them once more. The charge lasted an hour and I had the same problem again. They measure fine but the cart won’t climb the hill.
I’m currently charging the batteries with an auto charger which runs for a while (it’s only charging at 3 or 4 amps) and then I’m going to leave them alone... because I now believe that while the marine batteries were the wrong thing that I probably killed them... by under-charging or over-charging and I don't want to do it again.
Bu which is it? The old charger checks out with every test I can find… should I just give in (again) and spend money on a modern charger?
More importantly, will that solve the problem?
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Old 09-11-2021, 01:28 PM   #2
JohnnieB
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Default Re: Batteries, charger, a long confessionary tale...

Problem may not have been marine batteries or TC-III charger. Might be high amp cables, F/R switch contacts or solenoid contacts.

Is any cable, connection or contact getting hot after trying to go uphill?

What drive type. Resistor or controller?

What is the AH of the 6V batteries?

What does battery pack voltage drop to trying to go uphill?

What do the individual battery voltages drop to trying to go uphill?

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Battery charging: Batteries ought to be charged prior to first use and after each use.

Too late for the first part, but need to be put on charge after each use. Or at least put on overnight charge after being used that day.

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Charger: US Battery brand batteries need a higher finish voltage the Trojan batteries and the TC-III is designed for Trojan batteries. It typically shuts off in the 44V to 46V range while US Battery brand batteries need 45V or higher, so some, but not all TC-III's will work with US Battery products.

A Modern chargers that uses dV/dT (Change in Voltage over Change in Time) technology charge until the rate the voltage increase meets specific criteria and eliminates that issue.

------------

Bottom line:
1. A13 or 14 high amp cables need to by 4Ga or thicker.
2. There should be zero voltage drop across the solenoid's contacts.
3. There should be zero voltage drop across the F/R switch's contacts.
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Old 09-11-2021, 03:23 PM   #3
JRaf
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Default Re: Batteries, charger, a long confessionary tale...

Thanks JohnnyB. I don't have a great reason for not doing so but I haven't measured the voltage drop on the pack or the individual batteries, but I'll try and do that today.
It's a controller cart, the 6v batteries are 200ah.
I'll go through the F/R switch again but it's very clean and microswitches are all fully functional according to my meters.
I haven't looked for hotspots anywhere I'll do that as well.
As I recall the amps coming off the TCIII got higher than 44v when it was connected to the cart. Maybe 46.8? I didn't write it down unfortunately. I have a handful of meters, they all measure a little differently.
The battery cables are in good shape, all 4ga. The cables coming from and to the controller, the F/R switch, and the charger are all 2ga. I haven't noticed excess heat but I'll check.
I've installed two new solenoids and the cart's behavior is the same but I'll take measurements looking for v drop there and at the F/R as well. If it means anything, doesn't matter what direction I'm going the "voltage drop" (if that's what it is) appears.
In my defense I only drove the cart 50 yards up the hill after installing the batteries to get to the charger, then gave it a full charge.
I'm a little reluctant to do too much testing since I'm obviously doing something wrong but I'll clamp some meters on the terminals and measure the sag.
Thanks, this must get old for you.
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Old 09-11-2021, 04:15 PM   #4
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Default Re: Batteries, charger, a long confessionary tale...

If one of your meters has a Min/Max function, let it do the work for you.

Just connect it and run the cart, the look at the numbers after the fact.

I've used it to get the max voltage reached during a charge cycle and getting minimum voltage under load for battery pack and individual batteries as well as max motor temperature and max motor RPM. (DMM has Temp and RPM functions)
--------------------

The batteries appear to have been pretty well charged when you got them, so driving 50 yards before putting on charge didn't hurt them much if any. The reason for the charge before first use rule of thumb is that sometime new batteries have set for a long time and are 50% or less charged when you get them. Human nature more or less dictates flooring the cart to see what it'll do with new batteries and if the batteries are that low, it is pretty easy to drop the voltage down to 1.5VPC (Volts per Cell) or less and physically damage the plates. (Not everybody checks the battery voltage before installing them like you did.)

-----------
The symptoms point to either the battery pack dropping more in voltage than it ought to, or the voltage stays within the normal range at the battery pack, but it's not getting to the motor.

Excessive resistance in a cable, connection or contact generates heat, so a non-contact (IR) thermometer comes in handy looking for hot spots.
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Old 09-11-2021, 05:24 PM   #5
JRaf
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Default Re: Batteries, charger, a long confessionary tale...

Wow, thanks so much. Yeah, I have a meter with a high low toggle. Never knew what that was for.
Sorry for all the words but my results so far:
I charged the batteries with the auto charger (not the TCIII). I think it hit a max of about 4 amps… so I don’t know how charged the batteries actually are (not very judging by the results).
Pack voltage reads 38.6 at rest. I hook up clips and drive down and up hill. The voltage dips down just below 37 on flat surface. When I hit the hill it drops down below 36. I’m foot to the floor now. Pack voltage flashes below 35, then starts coming back up even as the cart is slowing and coming to a stop. As cart stops it’s at almost 37 volts.
I Fred Flintstone the rest of the way up and cart stays just around 37. I park. Pack voltage drifts back up to 38.5.
Some of the wires running to the F/R switch are warm to the touch. (I reported those as 2ga, they’re not, they’re skinnier, probably 4 gauge) The battery wires are all cool.
I do notice that the resistor across the big terminals on the solenoid is warm to the touch.
I move the meter onto the number one battery (nearest the positive leg of the charger). Resting voltage is 6.45. Going up the hill the voltage drops to a low of 6.0 but even as the cart stops the battery rises to around 6.2 volts. The wires from the F/R switch to the controller and solenoid are warm again. Nothing else. And battery voltage is resting at 6.45.
I try all the other batteries with similar results. Everything is within a tenth of a volt.
I’m a little confused about what to measure and where on the solenoid and F/R switch. But I’ll go back through the Marathon troubleshooting manual and go through those (unloaded) tests again.
The interesting thing is that though the cart and pack are running at low voltage and with disappointing results (stopping on hills), the pack doesn’t seem to be losing voltage or amperage as I run it. It FEELS as though it’s undercharged. (But wouldn’t an overcharged battery feel undercharged as well?)
I still haven’t hooked back up the TCIII. I really don’t want to destroy these batteries. Then again, perhaps I’ll destroy them by failing to get them up to some better state of charge.
I'll run more tests and I'll hook up the meter as you suggested and get some more details on the voltage/amperage charging/time curve with the TCIII.
Thanks again.
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Old 09-11-2021, 05:45 PM   #6
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Default Re: Batteries, charger, a long confessionary tale...

I would measure the voltage drop across the F/R switch and from the solenoid to the motor, your warm wires could be caused by a poor connection in the F/R switch or where the wires connect to it.

As for the pack voltage, I would measure from the pack negative (at the end of the string of batteries) to positive on the 3rd battery (should be 19.3V at rest if the whole pack is at 38.6V), then from negative on the 4th battery to positive on the 6th battery.
That should let you see which half of the pack is causing the voltage loss.

Aaron Z
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Old 09-11-2021, 06:11 PM   #7
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Default Re: Batteries, charger, a long confessionary tale...

The batteries seem to be responding about normally for being new 200AH batteries. A new battery only has about 75% of its rated storage capacity until it has a couple dozen charge cycles under its belt, so your are running something akin to a 150AH pack.

Since it is a Marathon with a pot box throttle that has set for a while, and nothing is getting really hot, it might be the throttle isn't opening fully.

Pull the black and white wires off the controller and measure the Ohms between the loose wires. Ought to be about 0Ω with pedal up and about 5000Ω with pedal down. (Up to about 300Ω pedal up and about 6000Ω is okay - but anything over 7000Ω shuts off the controller.)
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Old 09-11-2021, 07:32 PM   #8
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Default Re: Batteries, charger, a long confessionary tale...

I got interrupted while typing and sent the last post before it was finished.

The is little chance of overcharging the new batteries with the TC-III. Only issue with it is that it might be shutting off before the on-charge voltage reaches 45V or above.

Use it for an overnight charge tonight. If it is still running in the morning, let is run if the amps are down to about 8A or less. The first charge for new batteries sometimes takes 20 hours or more, but yours were pretty well charged, so it probably won't be on in the morning.

Deep-Cycle Lead-Acid Wet-Cell batteries are not fully charged until the SG (Specific Gravity) of the electrolyte ceases to rise while there is a charging current passing through it. Battery voltage track SG, so it can be inferred the battery isn't fully charged until the on-charge voltage ceases to rise while on charge. Modern charges that use dV/dT technology don't shut off until the voltage stops rising and can reach up to about 8.37V for a 6V battery, or about 50.2V for a 36V battery pack, but most batteries don't go that high.

Here is a SoC chart for US Battery.
Attached Images
File Type: jpg USB SoC 36-42-48V.jpg (176.8 KB, 0 views)
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Old 09-12-2021, 11:17 AM   #9
JRaf
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Default Re: Batteries, charger, a long confessionary tale...

Okay. I charged the batteries with the TCIII last evening. These were the results:
0:00 - resting pack voltage is at 38.67. I plug in the cart. Amperage immediately goes up to 18.1ah, charging voltage to 41.09v
5:00 minutes in we’re at 17.5amps, voltage has risen to 41.72v.
10:00 15.7a, 42.55v.
20:00 7.3a, 44.5v
30:00 3.8a , 44.78v
40:00 3.6a , 44.87v
60:00 3.2a , 44.89v
At right around 70 minutes the amperage was around 3.1, the voltage was 44.9, and the charger turned off. The pack voltage immediately dropped; two minutes after the charger quit the pack is down to 40.5v. After twenty minutes it’s 39.8. After twelve hours the pack is resting at 38.65v.
So according to this particular meter (it’s a Chinese clamp on meter, which I believe to be fairly accurate) the pack voltage never quite got to 45 volts.
This is the first time I’ve actually measured the way the TCIII uses amperage to drive up the voltage to the desired level. I imagine that if the batteries were in a very weak state, the amperage would have stayed at a higher level for longer before tapering off and slowly approaching that “not quite” 45 volts. (And for these particular batteries that might not be quite as high as I’d hope to get.)
A couple of more observations:
The TCIII is probably working as well as it can under the circumstances. It efficiently brought the pack voltage up to the required number without burning anything up. (If I hadn’t been cheap or stubborn and just gone out and bought some Trojan batteries everything might be fine. I suppose there’s a lesson to be learned there.)
Unfortunately I think that ship has sailed. So the fault right now might be in the battery design or the break-in period on the battery pack. But I think a more modern, somewhat addressable charger is in order. The Lester Summit II seems about the best out there. Is that correct? (Also, for my own volition is there a “state of charge” chart for Trojan or similar batteries? I’d like to compare it to the US Batteries version.)
Beyond that, I’m still curious. The board I put in the TCIII is just a generic board I bought on ebay that fits a number of these EZGO chargers that rely on a massive old transformer (I will admit to an affection for this old tech). But there IS a little potentiometer on the board. I wonder what it does? Might it control the “finishing” voltage?
Similarly, what would happen if I changed the big capacitor in the circuit to one of some different measure? The one that’s in my TCIII right now is the original old rusty one that seemed to deliver slightly lower pack voltage and I thought that would be a little safer than the new replacement which is the same value (20MFD, 370vac). The new one seemed to deliver a little more voltage when measured out of circuit, though that deviation may have been caused by a meter I no longer use. I also have another cap that’s somewhat different value (which I purchased by mistake). I worry that by changing cap values I’d be changing the shape of the DC voltage as it passes through the diodes. There, I’ve hit the limits of my electronic knowledge.
But… changing the cap value is also a little counter to my understanding of the charger’s mechanism. It’s the circuit board that’s actually measuring the pack voltage and controlling the amperage, right? If the cap delivered higher voltage than the board “thought” was suitable it would still cut it off around 45 volts right?
At some point I will short the two power wires on the board and see if I can drive the finish voltage a little higher. I don’t think the results will change because the board is still in-circuit, reading the pack voltage and reducing amperage as it sees fit.
Finally, I’ll also go back through this thread and try and finish all the other measurements I didn’t complete last night.
Again, thanks JohnnyB (and others) for your extraordinary help. I’m not an engineer, not close, but I actually understand almost all of the stuff you say. Your patience and kindness is much appreciated.
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Old 09-12-2021, 12:36 PM   #10
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Default Re: Batteries, charger, a long confessionary tale...

The control board in the TC-III (and all the other ferroresonant transformer type chargers) is a semi-smart switch whose function is limited to turning the charger on and off. The battery pack voltage energizes the relay on the control board and the AC voltage from the power cord is applied to the ferroresonant transformer's primary, starting the charging process.

The on-charge voltage will then rise until it reaches 45V +/- 1V, at which point the control board's circuitry will de-energize the relay, removing AC power from the ferroresonant transformer's primary and terminating the charge cycle.

If the on-charge voltage does not climb to 45V +/- 1V within a preset period of time (typically 16 hours), then a timer on the control board causes the relay to de-energize, terminating the cycle.

------------

The charge profile is built into the ferroresonant transformer and boost capacitor. The battery pack determines the on-charge voltage and on-charge voltage determines the amps via saturation of the ferroresonant transformer's core.

The ferroresonant transformer and boost capacitor form a resonate circuit that saturates the transform core limiting the max amps to about 20A when the on-charge voltage is below about 42V and to progressively fewer and fewer amps as the on-charge voltage increases up to the 45V cutoff value.

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The ferroresonant transformer and boost capacitor are a matched set.

To determine if transfromer and capacitor are good and are properly matched, bypass the relay on the control board so the charge will turn on when charger isn't plugged into cart.

WARNING: There is high voltage (Up to about 500VAC) on the capacitor. Be careful!!!!!!


Measure the AC voltage between the wires attached to the diodes on the heat sink with and without the capacitor connected to the transformer.

Without the capacitor, you should get 60VAC +/- 5VAC.
With the capacitor, you should get 90VAC +/- 7VAC.

-------------

I've attached some stuff that you might find useful.
Attached Images
File Type: jpg Charge curve.JPG (33.2 KB, 0 views)
File Type: jpg Transformer-Capacitor test - Text-1.jpg (367.7 KB, 0 views)
File Type: jpg Transformer-Capacitor test.JPG (66.2 KB, 0 views)
File Type: jpg SoC vs Voltage - Trojan Battery.JPG (56.9 KB, 0 views)
Attached Files
File Type: pdf Total Charge III Parts and service-1.pdf (3.28 MB, 0 views)
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