Battery bank voltages not what I expected. (New/Old batteries.)

[Timxyz]

Hello,

I'm working on a Club car for my father-in-law. The car was supposed to be having charging problems which simply turned out to be a defective battery condition meter.
I'm going over everything mostly to learn how the electrical system operates so that I might be able to help him in the future.

I fully charged the car and let it rest for 24 hours so that the batteries would stabilize.

The battery bank is 48v with four trojan 12v flooded batteries. Two of the batteries are old (5+ years) and two are newer (a year or two.)

While measuring battery voltages I came across two things that I didn't expect:

1.) All of the battery voltages were close to 12.78 volts. This is fully charged if I'm not mistaken.

2.) All battery voltages are within a couple of hundredths of a volt compared to each other. The four battery voltages were 12.78v, 12.78v, 12.75v and 12.75v. The total (measured) voltage was 51.0v

Since two of the batteries were much older, I expected to find all of the batteries to be pulled down to something less than a full charge. I also expected to find more voltage variation between batteries.

Would someone be able to explain to me why the voltages are so close? Is there some sort of equalization when charging to the voltage of the worst battery? Could someone also explain how the batteries seem to be in top condition when some are so old? I was always under the impression that it wasn't a good idea to mix old and new batteries.

These readings were not taken under a load....I plan to read each battery while going up a hill to see how they operate while working under load.

Edit.) I forgot to add that I do have a hydrometer but really dislike using it. I have to shake and tap it to get all of the bubbles off of the indicator. It's no fun. I dislike messing around with acid and would rather use a meter wherever I can.

Sorry for the lengthy post.
Thanks in advance for anyone who could educate me on this.

Regards,
Tim

[aintgotthis]

There is a lot of difference between volts and amps. The battery can have 12 volts but not be able to hold a load. You will see that with older batteries that only show up when under load for a period of time. The charger does have a float to it at the end of it's cycle to try to even the voltage.

The problem with mixing old and new batteries is that you will never have a new pack. Putting a new battery in with old batteries is very hard on the new one because it is doing most of the work. By the time another battery craps out, your new one is not new anymore. It is a bad cycle. I know batteries are expensive but when we put in a new battery, we put them all in.

[ThreeCW]

Originally Posted by Timxyz

These readings were not taken under a load....I plan to read each battery while going up a hill to see how they operate while working under load.

Load testing is a good plan. It will be interesting to see how the load tests of the newer vs. old batteries compare.

Perhaps your "old batteries" have been very well maintained and thus many not be showing their age (voltage wise anyway) ??

[Timxyz]

Originally Posted by aintgotthis

There is a lot of difference between volts and amps. The battery can have 12 volts but not be able to hold a load. You will see that with older batteries that only show up when under load for a period of time. The charger does have a float to it at the end of it's cycle to try to even the voltage.
.

Thank you for that, I hate to ask even more questions, but now I wonder if the charts that show the percent of charge according to the voltage will show a fully charged battery that might have half of the capacity? I always assumed (from looking at charts) that a battery with less capacity wouldn't charge up to the full voltage and that you could tell how good the battery was from the final charge voltage. It sounds like I might be wrong about this.

I'm sure that you're right about replacing all of the batteries. Do you ever save older batteries to try to match up with older battery banks? It probably would be hard to match them I guess.

Originally Posted by ThreeCW

Load testing is a good plan. It will be interesting to see how the load tests of the newer vs. old batteries compare.

Perhaps your "old batteries" have been very well maintained and thus many not be showing their age (voltage wise anyway) ??

Thank you. I think that my father-in-law is very good at charging after each use and probably keeps a good eye on the water levels.....I'd probably run the cart for days without charging.

I'll post my results when I get them I wish I could monitor all the batteries at once but I don't have enough resources to do that.

Take care. Thank you both for your time.

[aintgotthis]

For people that have a limited amount to spend, we usually recommend a used battery If they only need one which we sell for $20-$75.

We have had carts that have one bad battery so we throw in a used one and load test them again. Usually we end up getting another five or ten minutes capacity before another one drops below voltage. Patching together a battery pack is exactly that. A patch. Don't get me wrong, it works but it will never be 100%.

[NoleFan4Ever]

Originally Posted by aintgotthis

For people that have a limited amount to spend, we usually recommend a used battery If they only need one which we sell for $20-$75.

Bump! (It is an interim to help get you by and works appropriately)

[ThreeCW]

Originally Posted by Timxyz

I think that my father-in-law is very good at charging after each use and probably keeps a good eye on the water levels.....I'd probably run the cart for days without charging.

I'll post my results when I get them I wish I could monitor all the batteries at once but I don't have enough resources to do that.

Being 5 years old means that your father in law must be looking after the batteries reasonably well (or very well depending on the load test results)

Most people load test their carts on a hill at a fairly aggressive speed / pedal position. Hook up your multi-meter to the entire pack first for the initial load test. Then repeat the test for each individual battery.

Here is a photo of a meter probe set up which can make load testing easier to accomplish:

IMG_7799.jpg

[Fairtax4me]

Resting Voltage is only half the story.
You can have a battery that shows low voltage, but still holds plenty of capacity.
You can also have a battery that shows perfect or even above normal voltage, yet holds almost no capacity. The oy way to determine that is with a battery capacitance tester, or by doing a capacity load test by driving the cart and seeing how quickly the voltage drops when the pack is under load.

To answer part of your original question. Yes, the last phase of the charge sequence, also called the “finish phase” is designed partly to help equalize the voltage between cells. There is also what’s sometimes referred to as an equalization charge, which holds the pack at a high voltage for an extended time to help equalize the voltage between cells.
Basically, it’s running a second charge cycle immediately after the first cycle finishes. Since the pack is already fully charged at that point, the charge control will quickly move through the bulk charge and absorption phases to the finish phase where it will then stay for a certain amount of time depending on several factors. Regardless of how it’s done, holding the pack voltage at an elevated level with a low level charge current for a period of time helps bring the cells to near equal voltage. There can certainly be a capacity difference even if the voltage is equal.
Load testing each individual battery and checking at rest voltages after driving the cart for a while will show you which batteries are not holding as much capacity.
Even if some batteries are older than others, if they are somewhat properly cared for there May not be a major differenence in capacity solely due to age.

[Timxyz]

Hi.

I've done the load test, but before I post what I found I just want to thank each of you for every comment and every bit of advice. Every suggestion and the picture of the test probe (I made one just like it by the way.) was greatly appreciated. Everyone here seems to go out of their way to help out. Thank you everyone.

Just sending an update on my load test.

I found out that the hill that I intended to use is too short and not steep enough (40 degrees, maybe?) to really tell anything. Each battery started out at (no load) with around 12.8 volts and pulled down loaded to 11.8 volts and then I was at the top of the hill. I'm ready to call the car good and send it back to my father-in-law after the new battery meter comes.

One bad thing that I found out this weekend... My father-in-law added water to the batteries before I came. Apparently they were really low. He added tap water and worse, it was after the water conditioner. I told him that he should use distilled water. It's a little too late I guess.

I hope that I'm not wearing out my welcome around here... I was going to make a new post asking about this.

Thank you all again.
Have a good day.
Regards,
Tim

[ThreeCW]

It looks like your have a reasonably health battery pack based on the static voltages and the "under load" voltages.

Perhaps your father in law lives in a area with low water solids ... I would have expected that 5 years of adding "high total dissolved solids" tap water would be detrimental to the battery health. Adding tap water is better than NOT adding any water, but distilled water is certainly the best practice.

It is nice that you are able to help him out with his cart.

Happy Carting