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



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Unread 05-01-2015, 07:40 AM   #11
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Default Re: New EZGO owner with some questions on charging and parts

Something isn't quite adding up, if each battery was at least 6.8 the pack voltage would have been 40.8v or above. It sounds like the batteries are on the decline and may not last much longer, but from my experience with a past cart, I had some batteries that only held 37.8 volts after a charge and they worked fine for my needs for a long time before I sold the cart. Just keep nursing them and don't run them down too low and there may be plenty of useful life left in them.
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Unread 05-01-2015, 08:02 AM   #12
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Default Re: New EZGO owner with some questions on charging and parts

Quote:
Originally Posted by Bmatlock00 View Post
Something isn't quite adding up, if each battery was at least 6.8 the pack voltage would have been 40.8v or above. It sounds like the batteries are on the decline and may not last much longer, but from my experience with a past cart, I had some batteries that only held 37.8 volts after a charge and they worked fine for my needs for a long time before I sold the cart. Just keep nursing them and don't run them down too low and there may be plenty of useful life left in them.
Awesome, Thanks. I just checked them again when I woke up and the pack is at 37.8.
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Unread 05-01-2015, 10:11 AM   #13
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Default Re: New EZGO owner with some questions on charging and parts

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Originally Posted by FLmedic View Post
Awesome, Thanks. I just checked them again when I woke up and the pack is at 37.8.
An at-rest voltage of 37.8V is a SoC (State of Charge) of only 88%.
The temperature corrected specific gravity of the electrolyte should be reading about 1.255, what are you getting?

If you add 0.845 to the SG, you get what the cell voltage should read. There are 18 cells in a 36V pack so, you can get a rough estimated of what the pack voltage ought to read, which should verify your voltmeter accuracy.

-----------
If your Powerwise charge is the one in the attached picture, it does not float charge.

When it first comes on, it should be putting out about 17A-20A.
When it shuts off, the pack voltage should be in the 44V to 46V range.
Otherwise, the charger may not be fully charging the batteries.

-------------
If your voltmeter and charger check out, and your batteries are truly only charging the 88% SoC, some improvement might be obtained by charging them back-to-back several times.

The batteries that came with my cart would only charge to 85% and I got them up to 98% by charging the living daylights out of them. It took a couple months.
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Unread 05-01-2015, 09:28 PM   #14
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Default Re: New EZGO owner with some questions on charging and parts

Understood. I just installed a DVM from Scottyb so I should be able to track it more closely.

When I checked the SG all of the cells read in the good range. The hydrometer doesn't have specific numbers. It is like the one attached. In fact they were all very high in the good range.

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Unread 05-02-2015, 09:15 AM   #15
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Default Re: New EZGO owner with some questions on charging and parts

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Originally Posted by FLmedic View Post
.............When I checked the SG all of the cells read in the good range. The hydrometer doesn't have specific numbers. It is like the one attached. In fact they were all very high in the good range............
The hydrometer in the picture does have some SG numbers. There are pretty big jumps between numbers, so the resolution isn't very good, but with a pack voltage of 37.9V, the average voltage of each of the eighteen cells in a 36V pack would be about 2.1V, which ought to have a SG of about 1.255 and that would be at the upper end of the "Fair" range rather than "very high in the good", so either the voltmeter reading is off or the hydrometer reading is off.

The tricky part about using a hydrometer like the one pictured, is that there is a "Fluid Level" line that it has to be precisely filled to. If filled above or below the line, the reading is wrong.
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Unread 05-02-2015, 11:10 AM   #16
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Default Re: New EZGO owner with some questions on charging and parts

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Originally Posted by JohnnieB View Post
The hydrometer in the picture does have some SG numbers. There are pretty big jumps between numbers, so the resolution isn't very good, but with a pack voltage of 37.9V, the average voltage of each of the eighteen cells in a 36V pack would be about 2.1V, which ought to have a SG of about 1.255 and that would be at the upper end of the "Fair" range rather than "very high in the good", so either the voltmeter reading is off or the hydrometer reading is off.

The tricky part about using a hydrometer like the one pictured, is that there is a "Fluid Level" line that it has to be precisely filled to. If filled above or below the line, the reading is wrong.
Ok I will attempt to check again tomorrow morning when I get hom efrom work then. Thanks for all the help!
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Unread 05-04-2015, 07:18 PM   #17
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Default Re: New EZGO owner with some questions on charging and parts

So I finished up the install on my Carts Unlimited DVM and I am now able to track voltage alot better. My question is I see 50% is 36.3v and I have read everything that says DO NOT GO UNDER THAT.. But is that at rest or while driving. On a flat road with the pedal pinned I get down to 35.5v and around 13mph. Should I be worried???

My resting volts are now around 38.3 I believe so it looks like my charging routine is helping with battery health.
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Unread 05-05-2015, 10:06 AM   #18
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Default Re: New EZGO owner with some questions on charging and parts

The "Do not go under 50% SoC" rule of thumb, is the At-Rest voltage.
The 35.5V you saw while driving was an Under-Load voltage.

The DVM battery meter displays what the pack voltage is at the moment, so it is up to the person viewing it to decipher what it means.

1. On-Charge voltage: Voltage while the charger is charging the batteries. With the charger you have, it starts out at whatever the pack voltage is when the charger was connected up somewhere in the 44V to 46V range.


2. Under-Load voltage: When amps are being drawn from a lead-acid battery battery, the battery voltage decreases. The more amps drawn, the greater the decrease.

When battery manufacturers do non-destructive testing on their products they only load them down to 1.75VPC (Volts per Cell), which is 31.5V for a 36Vpack.

Physical damage to the plates start occurring at about 1.5VPC, which is 27.0V for a 36V pack.


3. At-Rest voltage: The pack voltage as read about 12 hours after the charger shuts off, or about half an hour after the cart stops being driven.

When the charger shuts off, the pack voltage is at the peak On-Charge voltage (~45V) and if the voltage is read too soon after the charge shuts off, the voltage will be artificially high.

The voltage drops quickly under load, but recovers slowly, so pack voltage reading made too soon after the cart stops will be artificially low.

Fortunately, most of the recovery takes place in the first few minutes, so when out and about and you want to estimate the SoC to figure out if it is time to head towards wherever the battery charger is, a 5 to 10 minute rest is usually sufficient. The SoC estimate will be on the low side, but that is the safe side.
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Unread 05-05-2015, 01:17 PM   #19
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I am going to laminate this and put it on my windshield.. Great information buddy. Will definitely need to share with my wife.
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