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Discussion Starter #1
I am having a time getting a full charge into my pack.

1. When you gas a pack to help the batteries last longer
and charge better, does it turn the acid a little gray?

2. A 10 hour charge still only brings up the pack 3/4 full.
72 volt, 20 amp charger. It tapers off as the pack
charges up, as most chargers that I have used, do.

3. What is a good voltage for charging a 72 volt pack?

4. Anyone else having this problem?
 

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Answers:

1) Yes, the distribution of bubbles caused by heavy charging will tend to cause sediment in the bottom of the battery to be stirred up. I haven't heard anything that indicates that this is an abnormal condition or that the presence of cloudy electrolyte is a problem. It might be a sign that the batteries are old and have sluffed a lot of active material off of the plates.

2) Most chargers will taper down the charge rate as the battery fills simply because the battery's terminal voltage is rising, presenting a smaller load on the charger.

3) Consult your battery manufacturer, but a 72 volt pack would bulk charge at 86.4 volts, float at 81.6, and equalize upwards of 90.

4) What makes you think you have a problem? Are you not getting sufficient range from your battery pack? Have you checked to see that you don't have a single cell or battery that is failing? Have you checked the individual cells/battery blocks with a volt meter after loading and during charging to see if the voltages match up? What do the specific gravities of each cell look like?

More details might help us give you an accurate diagnosis.
 

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Discussion Starter #3 (Edited)
#1 The pack is not old and 2 of the batteries have less than 200 miles on them.

#4 The range is OK for now, but when colder weather gets here, I want to have a full charge to work with.
I bought a new hydrometer and even with the temp adjustment, I only get a little over 3/4 charge on each battery.
I put the new Vector charger on one of the new batteries and it ran for the full length charge and showed "fully charged" when done.
A check with the hydrometer still shows 3/4 charge.
The same test on an older battery had the very same results.
I find no bad cells on any of the 6 batteries.
A battery load test shows 12.3 volts before and after.
The load test is in the good range.

If I put the 72volt charger on just 5 of the batteries, I get some gasing and discolor of the acid, but still none that show a full charge.
I am thinking of adding another new battery and hooking it up in parallel, to one near it in the pack.
It wouldn't add voltage, but amps might be of help.
Anyone had good results with that?
 

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A few things to consider:

Mating up batteries of different ages and/or life cycle conditions isn't really advisable, but if you are having fairly even battery voltages under load testing, you might want to overlook that for now. The alternative is buying an entire new battery pack and starting from scratch. Probably worth running a mix-n-match pack until you really need to replace them as a unit.

You are saying that your battery charger is indicating "charged", but what voltage is it considering the job finished? Are you able to read the charge current going into the batteries during the charge cycle? As a rule, you can expect to return 20% more ampere-hours to a discharged battery than you took out. Is your charger failing to provide sufficient voltage and/or current to complete the absorb cycle of the charge? You can hammer 75-80% of the ampere-hours back in fairly fast, but the last 25% or so will be returned slowly as the chemistry of the battery changes less quickly as the electrolyte reaches the charged state.

Here's a copy-and-paste from an article I wrote for a New Zealand magazine several years ago:

Mr. Sharkey said:
Multiple stage charging is the best and most economical way to fill up batteries. Three stages are usually preferred, bulk, absorption, and float.

Bulk charging is done to return 75% of the energy removed from the battery quickly. Amperage is kept as high as the battery and charging source will allow, usually equal to a value of 10-20% of the batteries ampere-hour capacity ( a 220 ampere-hour battery would be charged at 22 to 44 amps, expressed as C10 or C5. The equation for determining this value is Capacity divided by charging current determines time to charge fully [C value] 220/5=44=C5) When the battery voltage reaches approximately 2.41 volts per cell (14.5 volts for a 12 volt battery), absorption stage is initiated.

In absorption stage, the current into the battery is limited to hold the terminal voltage at a pre-set value just below it's gassing voltage, usually 14.5-14.6 volts, for a specified period of time, from half an hour to several hours, depending on the specifications of the battery manufacturer. During this time, the battery is allowed to slowly absorb approximately 20% of the electricity being returned in the charging process. At the end of the given time, the float stage is initiated.

Float charging is a condition in which the battery is held at a specified voltage that is well below it's gassing point, but high enough that the remaining 5% of capacity can be returned. Typical float voltage for a 12 volt lead acid battery might be 13.1 volts. A battery can be left on float charge indefinitely without damage or excessive water loss.
It could be that your charger isn't set up to fully deliver the absorbition cycle. Either that or your hydrometer is whack or your battery chemistry is different than you anticipate and the specific gravity differs from the standard you're expecting.

About the only way to tell if the batteries are really fully charged is to run a full cycle load test, measuring the Ah removed with a calibrated accumulating instrument, then recharge, tallying the Ah returned.

You still have some detective work to do, something is giving you false indications, the charger, the hydrometer, or your batteries. If the cells are gassing, then they are pretty well full, so I'd tend to rule that one out.
 

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Discussion Starter #5
I got my new voltmeter from Ian and it shows that my charger is doing a better job than I thought.

Althought it doesn't "gas" the pack, it does put it up to 86 volts when charged for 3 hours @ 20 amps, on a DOD of 25%.

All of the batteries are working better now, after being recharged over the last 100 miles, 2 charges per day.
I thought I might have had feedback from the pack to the charger, so I put a heavy diode in the line on the + cable of the charger.
It got hot during the next charge, so I took it out.

It has been running fine now for a couple weeks.
 
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