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Unread 05-21-2013, 11:19 AM   #1
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Default A Tale of Six Batteries.

It was the best of times, it was the worst of times, it was the age of wisdom, it was the age of foolishness, it was the epoch of.......... Oops! Wrong story.

Based on the logo painted on the nose of my 2008 TXT PDS, I believe it came from a golf course in Arizona, where the climate is rough on batteries.
The date code on the cart is B0808 (Aug? - 2008 ) and the date code on the T-105 batteries is L9 (Dec-2009), so I suspect the first set of batteries only lasted about 18 months and the ones I received with it were the second set, and no more than about 18 months old when the cart found its way to my place in Jun-2011.

Other than tires with tread wear and slow leaks, the cart ran fine, but the the batteries wouldn't take a full charge, so I figured I'd be buying new batteries in the near future. However, having just bought the cart, my fun and games fund was low and I wanted to put off replacing the batteries until the next spring.

I knew better than to try any of the snake oil treatments, but also know from past experience with portable X-Ray machines and automated delivery systems (robotic carts), that repeatedly charging an already charged lead-acid battery will sometimes improve its storage capacity, so I thought I'd give it a try. After all, the batteries were destined to be trade-ins anyway.

Fortunately, while not taking a full charge, all six batteries in the pack were well matched. The spread between highest and lowest At-Rest voltage back then (and still is) <= 0.05V, so I didn't have to charge them separately to get the voltages in sync for series charging.

For the first few months, I used a Powerwise II, then I went to a Pro-Tech 3616 because it had float charging and when after it gave up the ghost, I got a DPI Accusense 36V charger, which is the best of both worlds.

When I started, they would only charge to a Soc of 85%, two months later they would got to 94%.
From that point on it was mostly being on float charge after the regular charge cycle ended rather than repeatedly initiating charges, but I still do it if they have been sitting more than a few days.
Anyway, Eight months after that, they were up to 98%
Yesterday, they were at 100%+, 25 hours after they came off float charging.
After documenting the voltages, I drove the cart 10.2 miles in PDS freedom mode to eliminate any voltage gains from regen braking.
An hour after I got back, they still had an 82% SoC, which is close to the max I could get them to take originally.
Basically, over the past two years, I gained about 10 miles of range just by judiciously charging my batteries.

Here are the Pack Voltages and SoC from my records.
Jun-2011 = 37.6V = 85%
Aug-2011 = 38.0V = 94%
Apr-2012 = 38.11V = 98%
May-2013 = 38.26V = 100%+

BTW - I questioned the last voltage also, but I verified it with three other DVMs.
Both the dash mount battery meter and two inexpensive handheld DVMs read 38.3V.
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Hopefully, in the next week or two, I'll be replacing the PDS controller with the DCX400PDS I already have and collect some data about what a more or less stock PDS cart (2Ga cable and 18.3" tires) will do with just an aftermarket controller/solenoid upgrade. (It currently does 19MPH in Freedom mode)
Then the six T-05 batteries will be replaced with seven Exide GC-145 batteries I already have, and collect data about the speed increase going from 36V to 42V.
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Unread 05-21-2013, 11:38 AM   #2
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Default Re: A Tale of Six Batteries.

JohnnieB
Can you add the charging frequencies to the post? Did you drive and then charge or sit idle and charge anyway. I would like to make a chart for charging my new 36V DCS setup?
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Unread 05-21-2013, 11:41 AM   #3
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Default Re: A Tale of Six Batteries.

help me out Johnny, new to this and trying to figure it all out (I do have an electronics background) I just bought an 88 36V EZgo 3 wheel. The batts are Interstate 6v (not sure Ah) and about 4 years old. When I got the cart home and initially charged it (Total Charge w/elapsed time dial) It only charged for about an hour. I was impatient so I jumped on it and tried it out. I ran it around for 15 minutes or so and noticed it was arcing real bad on the speed control board, wanting play around some more ran it for about another 5 mins and it was dead. The pack was reading around 26.65v, measured at the charging port. (sure they died out so bad due to the arcing). I parked it and charged it again.

This time it charged for aproximately 5.5 hours and measured 38.24v at the charging port.

I let it sit, 12 hours later came back and measured the pack as 37.21v (Measured each battery individually and all were within .04 of each other)

Drove it for around 1.5 hours up long slow grades a couple of steep hills against some good head winds with both the wife and I on it. (Ooops cleaned contacts to prevent arcing, still an issue but much less and not during this test ride) The voltage reads 35.81

The arcing started again and the pack dropped to 35.22v, so I stopped and charged it last night (according to the charger, elapsed time is 2 hours) Measured the V this morning it is 36.89

Here's where I need help, I know I need to replace the swipper arm contact and the speed control contact and am in the process of getting the parts.
1. What harm if any has been done to the batteries, or do they sound like they are doing OK?
2. The guy I bought it from said they sat without a charge for about 1 month, do they sound like they can be brought back? I feel like cycling is doing that.
3. Everyone talks about cycling to % but what voltage level for the pack does that equate too?
4. Is it 80% of SOC, and is SOC right off the charger or after rest?

Thanks for answering all my stupid questions, just seems these are salvagable for at least the next few months.
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Unread 05-21-2013, 12:06 PM   #4
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Default Re: A Tale of Six Batteries.

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Thanks for answering all my stupid questions
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Unread 05-21-2013, 12:13 PM   #5
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Default Re: A Tale of Six Batteries.

thats me
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Unread 05-21-2013, 12:58 PM   #6
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Default Re: A Tale of Six Batteries.

Quote:
Originally Posted by Springlake View Post
JohnnieB
Can you add the charging frequencies to the post? Did you drive and then charge or sit idle and charge anyway. I would like to make a chart for charging my new 36V DCS setup?
I Charged the cart after each use, no matter how slight and once or twice, sometimes as many as four or five times, a day I'd unplug the charger's plug from cart and plug it back in, initiating a new charge cycle.

After the first couple months, I backed off to initiating a new charge to once or twice a week, but still charged after each use, and still do. I got a charger that float charged for winter storage, but still initiated a regular charge cycle every week or two.
It (the ProTech) died the next spring, so I got a DPI and that is what I've used since.

With little exception, either my cart is being driven or the batteries are on charge or float charge.
One of the exceptions is when I let the batteries sit for a day to get an accurate At-Rest voltage to check the SoC.
Another one is when I know I'll be taking the cart out again within an hour or so and feel too lazy to walk between the garage and house, so I park it by the back porch.
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Unread 05-21-2013, 01:12 PM   #7
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Default Re: A Tale of Six Batteries.

ok ???? my turn for stupid question .. if charger shuts off after fully charging batteries and you unplug it and plug it back in , how can it turn back on if batteries are fully charged ? i understand the resting volts and surface charge ... but wont it overcharge batteries ?

jonnie please speak redneck so i understand
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Unread 05-21-2013, 01:20 PM   #8
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Default Re: A Tale of Six Batteries.

Quote:
Originally Posted by 3WheelDumbo View Post
1.What harm if any has been done to the batteries, or do they sound like they are doing OK?
2. The guy I bought it from said they sat without a charge for about 1 month, do they sound like they can be brought back? I feel like cycling is doing that.
3. Everyone talks about cycling to % but what voltage level for the pack does that equate too?
4. Is it 80% of SOC, and is SOC right off the charger or after rest?

Thanks for answering all my stupid questions, just seems these are salvagable for at least the next few months.
1. & 2. If the batteries were fully charged to start with, sitting for a month probably didn't hurt them.

Taking them down to 26.xx volts might have harmed them.

37.21 after 12 hour rest is only about 73% charged, If it improves, great, but only time will tell if they are doing okay.

3. The % is State of Charge (SoC) which is the opposite of Depth of Discharge. (SoC is the percentage of the batteries Amp-Hour rating that is left in the battery and DoD is the percent that was taken out)

4. Here is a chart correlating SoC with battery voltage.
Note: The voltages given are taken roughly 12 hours after the charger shuts off.

The batteries acquire a "Surface Charge" during charge and that has to be depleted before and accurate SoC can be estimated from the voltage.
Attached Images
File Type: jpg JohnnieB's SoC Chart.JPG (66.2 KB, 0 views)

Last edited by JohnnieB; 05-21-2013 at 01:22 PM.. Reason: Forgot to attach chart
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Unread 05-21-2013, 02:37 PM   #9
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Default Re: A Tale of Six Batteries.

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Originally Posted by crash test dummy View Post
ok ???? my turn for stupid question .. if charger shuts off after fully charging batteries and you unplug it and plug it back in , how can it turn back on if batteries are fully charged ? i understand the resting volts and surface charge ... but wont it overcharge batteries ?

jonnie please speak redneck so i understand
The charger shuts off when the on-charge voltage reaches about 45V and the pack voltage starts to rapidly decrease.
If you wait a couple hours or so after the charger shuts off, it will be down to about a volt or so above the at-rest voltage and the charger will hit them with the full amperage and taper off, until the on-charge voltage is once again up to about 45V.
If you don't wait very long after the charger turns off, the charger won't run very long.

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What is or isn't "Fully" charged is subject to interpretation, therefore "Overcharging" depends on how "Fully" charged is defined...
Technically, a lead-acid deep-cycle wet-cell is not "Fully" charged until the Specific Gravity of the electrolyte in a cell ceases to increase while a charging current is passing through that cell.
Open circuit terminal voltage tracks specific gravity (SG + 0.845 = Cell voltage), so it can be inferred that when a battery's (two or more cells) terminal voltage ceases to increase while a charging current is passing through it, it is fully charged.

Most, maybe all, of the older automatic golf cart battery chargers and many of the newer ones, simply look for a specific On-Charge voltage to terminate the charge, rather than using the far more complex change in voltage over time. The voltage picked (about 45V for a 36V charger) is less than "Fully" charged for most batteries, but close enough on average to adequately charge the batteries used in golf carts and the like, for nominal performance and longevity, while being low enough not to damage older and/or weaker batteries. (Hobson's Choice)

The SoC vs Voltage charts are based on empirical data using matured (broken in) batteries that were charged with typical golf cart battery chargers and rested. The 100% SoC voltage is the average voltage the batteries tested settled down to after 24 hours, rather than what is truly 100% SoC for a truly "Fully" charged battery.

All the charts I've seen are based on studies done by Trojan using Trojan batteries and that is why some brands of batteries don't line up at the top of the chart like most people think they ought to. It is also why my 3.5 year old batteries have an At-Rest voltage that is greater than the 100% SoC voltage listed.

To answer your question if I what I did was overcharging my batteries, I don't think so.
Unless you use a charger that continuously puts out a high constant current, say about 1/10th the AH rating of the battery, or more, there isn't much danger of actually overcharging the batteries since you would have to get the on-charge voltage above 2.8VPC (50.4V for a 36V battery pack) on a good battery and most of the chargers we have won't do that.

---------
Can a person with yellow skin (like in your avatar) have a red neck, or does it just look orange.
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Unread 05-21-2013, 03:39 PM   #10
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Default Re: A Tale of Six Batteries.

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Originally Posted by JohnnieB View Post
Can a person with yellow skin (like in your avatar) have a red neck, or does it just look orange.
do you wear a shinny tin foil hat like your avatar ? Touche
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