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Old 04-14-2012, 02:45 PM   #1
bigstik40
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Default Battery voltage & sp. gravity ok but low capacity

I'm looking for some more help understanding batteries. I have been in the process of "mothering" a set of 4 year old Trojan T-105's. I have been charging daily and really don't discharge them that deeply (not a golfer). Individual voltages and specific gravity are in the 90% + area. Recently, I had one battery drop out on me under load. I replaced that battery with a good used battery similarly aged. Today, I find another battery (ironically in the same position) acting the same. After only a few miles, this battery voltage went to under 1 volt at full speed. I brought the cart home and checked specific gravity on this battery. All 3 cells have 3 balls floating + one almost floating (I know, I know, get a real hydrometer - but mine just broke, so). Two days ago I ran voltages and sp. gr. and this battery after full charge and 12 hrs + rest was 6.36 v and 1270 sp. gr. (before hydrometer broke). So by the measurements this battery looks good but capacity is low. What gives ?? Another dead player?? I'm starting to think the only really good test for batteries is a load test!! Thanks - RAY
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Old 04-14-2012, 05:05 PM   #2
scottyb
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Default Re: Battery voltage & sp. gravity ok but low capacity

Bigstik40,
As they say the proof is in the pudding
Actually I don't know what that means but the loadtest is the mother of all performance evaluation when it comes to wet cell golf cart batteries.
Specific gravity tests have to be evaluated on a cell by cell basis. I use a refractometer for spectrum analysis, most people think that's overboard but, I have been fooled before. When evaluating cells a difference of say 15 points indicates a problem or, at least, a potential problem. Also battery to battery should be fairly even. Say +/- 20 points.
Remember since we use the battery within the top 50% of it's capacity any battery that comes up to 75% has lost 50% of it's useful range.

Bottom line is the load test is king.
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Old 04-14-2012, 08:59 PM   #3
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Default Re: Battery voltage & sp. gravity ok but low capacity

Thanks, Scotty. Most of the threads here place a lot of emphasis on voltage measurements, but now I see that will only indicate state of charge and not how long they will last.
You can have a 225 AH battery that is down to 50 AH show up as good, but in actuality it really is only a good 50 AH battery. Is there some quick way to determine how good/bad a batteries capacity is?? (Maybe that is the load test ) I guess monitoring your on board meter under power can tell you something (after the fact) - yes/no. Still learning here!! Can the length of time batteries take to charge tell anything?? Thanks - RAY

Last edited by bigstik40; 04-14-2012 at 09:02 PM.. Reason: correction
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Old 04-15-2012, 05:00 AM   #4
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Default Re: Battery voltage & sp. gravity ok but low capacity

If you have a DMM, you can hook it up to individual batteries and see what each one does as you climb a hill. Real world load testing.
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Old 04-15-2012, 06:07 AM   #5
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Default Re: Battery voltage & sp. gravity ok but low capacity

Quote:
Originally Posted by scottyb View Post
Actually I don't know what that means but the loadtest is the mother of all performance evaluation when it comes to wet cell golf cart batteries.
Do you need a specific unit for 8V?
Any idea of an inexpensive unit to recommend?

Quote:
Specific gravity tests have to be evaluated on a cell by cell basis. I use a refractometer for spectrum analysis,
I have one for my fish tank, what are the test results you're looking for and what do they mean?
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Old 04-15-2012, 07:48 AM   #6
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Default Re: Battery voltage & sp. gravity ok but low capacity

Ray,

I knew a lot about batteries in general until I bought a cart and discovered how much I didn't know about flooded lead-acid cells.
I'm still learning too, but maybe I can shed some light on a few things.

The only practical way to find out how much energy is stored in a battery is to empty it.
The most accurate way of measuring the energy that was stored in a battery is dumping it into a purely resistive load and measuring the heat generated (Calorimetry).
Discharging at a constant current and measuring time gives a close approximation if you stop the discharge before the battery is too weak to supply the constant current rate and extrapolate.
Both of these methods require precision equipment and take several hours to conduct.

The "Load Testers" sold at auto stores are voltmeters with a resistor across the leads and essentially measure the internal resistance of the battery rather than storage capacity.
Monitoring battery voltage with a DVM while driving provides more accurate information since the actual load is being used.

A lot of emphasis is placed on voltage because it is relatively easy to measure and most people can use a voltmeter.
Terminal voltage cannot tell you how much chemical energy is stored in a battery since the voltage is the same as long as the number of cells in the battery is the same.
A fully charged flooded lead-acid cell will measure approximately 2.37V whether it is the size of a beer can or a bath tub.
Voltage will tell you whether your charger is working or not, if your batteries are taking and/or holding a charge, but won't tell you run-time (Storage capacity)

Specific Gravity and voltage are more or less tied together, but SG is harder to measure and less understood by most people.
Basically, it tells you how many of the sulfate ions have been returned to the electrolyte during recharging.
Problem is, you don't generally know how many were there to start with, or how many have been lost due to spillage.
No sulfate ions are actually lost during the discharge/recharge process, but some become permanently bonded to the plates.
You loose water through electrolysis, but that is all.
If you measure SG when the electrolyte level is just covering the plates, it will read higher than it will if the electrolyte is at the prescribed level.
If the cells are filled too high, some of the electrolyte will bubble out during gassing (electrolysis of the water) and sulfate ions will be lost.
When the lost electrolyte (diluted sulfuric acid) is replaced with pure water, the SG becomes lower.
To use SG meaningfully, you must measure it when the batteries are new, and subsequently refer back to that value to determine battery health.
It is, however, a good tool for comparing the cells in the same battery since they most likely started the same and were subjected to the same conditions.

One way to visualize the diminishing battery storage capacity as it ages is to think of it as a water bucket.
When the bucket is new, the top is a perfect circle, the bottom is flat and the sides are smooth.
There is a line at the top that says "1 Gal.", but you aren't sure it is accurate.
The sides are tapered, so just calculation the volume of a cylinder won't work and you've misplaced you solid geometry handbook, so you "Borrow" a measuring cup from the kitchen.
Sure enough, it holds exactly 16 cups of water even though it wasn't "Made in USA".
After hauling countless buckets of water to the house from the spring, the top of bucket is no longer a perfect circle, the bottom isn't exactly flat and the tapered sides have some dents and dings.
You can still fill it to the line marked "1 Gal.", but does it still hold 16 cups of water?
You'll have to "Borrow" the measuring cup again to find out.

Batteries age (Sulfated plates) just like water buckets collect dents and dings.
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Old 04-15-2012, 08:26 AM   #7
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Default Re: Battery voltage & sp. gravity ok but low capacity

The refractometer is just an advanced tool to measure specific gravity of the battery electrolyte solution.
Battery electrolyte is a mixture of 64% Water and 36% Sulfuric Acid.
A Specific gravity reading of 1.270 is 100% charged, 1.190 is 50% charged. 50% is the depletion limit recommended by major manufactures.
The lead acid battery is made up of plates suspended in the electrolyte solution which causes a chemical reaction that produce electrons. When you test a battery with a hydrometer you are measuring the amount of sulfuric acid in the electrolyte.
If your reading is low, that means the chemistry that makes electrons is lacking.
When you discharge a battery the sulfur is stuck to the batteries positive plates and when you recharge the battery the sulfur returns to the electrolyte.
As a battery ages (or is damaged) this exchange of electrons becomes less effective. The result is some of the sulfur is permanently bonded to the lead plates, commonly referred to as sulfated. This is the common death of all wet cell batteries.
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Old 04-15-2012, 08:28 AM   #8
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Question Re: Battery voltage & sp. gravity ok but low capacity

Just bought a cart last week, 6 8V Trojans, they take a charge and the cart runs.

But there are no date stickers on them, should I just keep running with them until they die or what should can I do to see how much life may be left?

this cart was used daily on a farm before I bought it so it hasn't been sitting doing nothing.

A friend suggested emptying them and put new acid in?

Or take some fluid out with a baster and ad Epsom salt and distilled water.
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Old 04-15-2012, 08:32 AM   #9
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Default Re: Battery voltage & sp. gravity ok but low capacity

Quote:
Originally Posted by scottyb View Post
The refractometer is just an advanced tool to measure specific gravity of the battery electrolyte solution.
Battery electrolyte is a mixture of 64% Water and 36% Sulfuric Acid.
A Specific gravity reading of 1.270 is 100% charged, 1.190 is 50% charged. 50% is the depletion limit recommended by major manufactures.

commonly referred to as sulfated. This is the common death of all wet cell batteries.
Ok so the refractometer is just measuring it more accurately than a float type hydrometer.

what about using de-sulfating chemicals?
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Old 04-15-2012, 08:41 AM   #10
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Default Re: Battery voltage & sp. gravity ok but low capacity

HA ha, the bucket to the well analogy They say one day the bottom will drop out.

Most shops have a battery bank discharge machine. Mine is made by Lester and discharges 36 and 48v packs at a rate comparable to average cart operation. Several aspects are recorded during the test which can show the useful state of the pack, mainly available run time. The test can be done is in as little as 20 minutes on a bad pack or over 100 minutes on a very good pack.
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