battery and charger questions/ issues

[3ftover]

Thanks. I tried some of the diagnostic stuff but no beep unless I did something wrong. No beep in reverse either. Think the beeper is broke.

[JohnnieB]

The device used for as a Beeper (Sonalert) seldom fail, so is most likely disconnected.

It's attached to the left side of the passenger side glove box. The two pop rivets you can see inside the glove box hold the mounting bracket.
Unless you've got long, skinny arms with a couple extra joints, you have to remove the panel Keyswitch and F/R switch are on to get to it.

[3ftover]

Can a battery read 6.37 volts but not be fully charged? I hooked up a 6v charger and it shows charging at full 6 amps.

[3ftover]

So I hooked a 6v charger to one of the batteries and after two hours this is what it reads....It woulds seem to me it is not charged. Yes?

[JohnnieB]

In general terms, at 6.37V after a 6v cart battery has been neither charge nor discharged for about 12 hours, it is typically considered to be charged to 100% of it's current (at the present time) storage capacity.

The fact that the picture of the ammeter on the charger shows 5 Amps of current flow, simply means the open circuit voltage of the charger is higher than the open circuit on-charge voltage of the battery. When current flows through the charger, the output voltage decreases in proportion to the current flow and at the instant the picture was taken, it required 5 Amps of current flow to reduce the charger's output voltage enough to equal the battery's on-charge voltage at that moment.

The questions are: What is the on-charge voltage of the battery and is the charger designed for Car batteries (SLI) or Golf Cart batteries (Deep Cycle)?

Technically, a lead-acid wet cell isn't "Fully" charged until the Specific Gravity of the electrolyte ceases to rise while a charging current is passing through it.
Since the on-charge open circuit voltage increases as the SG of the electrolyte increases, it too ceases to increase when the cell is fully charged.

However, the internal resistance of the cell also influences the on-charge open circuit voltage of the cell, so the on-charge open circuit voltage of a new cell that is "Fully" charged is different from a properly broken in cell, which is different from an older cell, which is different from an abused or improperly maintained cell. In addition, no two cells are exactly the same when they come off the assemble line and no two cells age exactly the same.

Fortunately, the variances in on-charge open circuit voltages between cells, which are slight if the cells are similar in age and have received similar number of charge/discharge cycles and similar routine maintenance throughout their lifespan to date, lessen as the cells rest after being charged, regardless if they were "Fully" charged or not.

After about 12 hours rest after having a charging current passed through it, the average at-rest open circuit voltage of an average cell that has been charged up to an on-charge open circuit voltage between 2.45V and 2.79V after being light to moderately discharged about 100 times will be approximately 2.122V. There are three 2V cells in a 6V battery, so that average at-rest open circuit voltage of an average 6V battery will be 6.366V.

Equally as fortunate, the at-rest open circuit voltage (after about 12 hours) linearly correlates to the percentage of the maximum capacity of electrical energy that is chemically stored in the cells. Since 2.166V is the average at-rest voltage the average cell settles to, it is assigned 100% State of Charge and each 0.02V (approximate) reduction in at-rest open circuit voltage is a 10% reduction in amount of energy stored.

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Beg or borrow, but don't steal, a known good 36V cart battery charger and see if it works normally on your battery pack.

If you cannot obtain a known good charger, use you 6V car battery charger to charge each 6V battery until the on-charge voltage equals 7.5V.
If none will reach 7.5V, they should all reach the same max voltage.
If one, or more, don't they are bad.

If they all do, try the QE on the pack. (Without discharging any of the batteries)
If it doesn't progress to a solid a Green LED, it is bad.

[3ftover]

Thanks JB. A lot of technical info there. I have asked and will continue to ask to borrow a charger. The few I have found don't have the same connection as me. I sort of did what u said last night but probably could have let them charge with the car chargers longer. Charged with QE overnight and woke up to still blinking. For fear of overcharging I unplugged this morning. It was still blinking. I can say I stayed up late and watched the voltage climb to about 41.6 around 10:30. Set my alram for 2am and it was at 42v. This morning at 5am it sropped to 41.8. That is when I unplugged. I am going to try once more but I do feel the charger is broke. Also it only blinks what I think is the short blink which would indicate the batteries are less than 80%. True or not I don't know. Last note. With the QE or the car charger the batteries seem to peg out at 6.8 to 6.9. I have seen one go over 7v and the new one definitely does. But for the most part they are all in the same range.

[JohnnieB]

Yeah, battery stuff can get pretty technical, but as long as you keep them as fully charged as possible, the technical stuff more or less takes care of itself.

While it is true that batteries can be damaged by overcharging them, it is difficult to overcharge them with consumer grade chargers, unless you use a 12V charger on a 6V battery, or something similar.


I'm not 100% sure because none of the batteries, including the rebuilt one, are getting up to the 7.3 or so volts needed to shut off the QE automatically, but I think the QE is bad.

[crash51730]

I think I have a similar problem possibly. Older batteries 08 Trojans. This thread has taught me a lot about batteries. It seems like I have two batteries that are lower voltages than the rest. They also happen to be the ones the old radio was hooked to. I don't mean to thread hijack. Am I correct in assuming that a 6 volt battery should top off at about 7.5 volts and then level down to 6.3-6.4 volts? It seems as though my charger works fine but hours after the charger shuts off, pack voltage drops to 37-37.5 volts. Also I wanted to double check I understood something correctly. Is it true you can charge 2 batteries with a 12 volt charger and not unhook the whole pack? Thanks again.

[JohnnieB]

It is directly related, so not much of a hijack.

More amp-hours are drawn out of the two batteries used to power the radio (or lights, or other 12V stuff), so their at-rest voltage will be slightly lower than the rest. Because they are charged in series, and the charger shuts off when the pack voltage reaches a predetermined point, the same same charging current passes through them for the same amount of time. The net result is that they are slightly less charged and the rest of the batteries in the pack are slightly more charged. Then they start out the next discharge/recharge cycle slightly less charged and if the 12V accessories are used during that cycle, the imbalance gets worse than it was on the preceding cycle.

Because a more deeply discharged battery charges faster for a given charging current, the downward spiral levels out with the batteries being used for accessories just a few 1/10's of a volt less than the rest. Otherwise, you would end up with six dead batteries, two dead from undercharging and four dead from overcharging.
(More than likely, the charger would stop turning on before it got to that point.)

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A good 2V cell can go up to about 2.79V, which is about 8.37V for a 6V battery, or about 50.22 for 36V battery pack.
Most 36V golf cart chargers automatically shut off in the 44 to 46 volt range, so so the maximum on-charge voltage for a 6V battery is typically from about 7.33V to about 7.66V.

If you are using a manual charger, 7.5V is a good target value for a 6V lead-acid wet cell deep cycle battery.
That will level off to an at-rest voltage of about 6.37V per 6V battery, or about 38.2V for a 36V battery pack.

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With a 37V to 37.5V pack voltage, your pack is only storing about 75% to 80% of it rated storage capacity.
However, I suspect you've got four batteries in the 85% range and two in the 70% range.

Check the individual battery voltages, both after they have rested 12 hours after being charged and again 5-10 minutes after the cart has been driven for a few miles.

In both instances, the difference between the highest and lowest battery voltage should be 0.1V or less. (It won't be since you tap the pack for your 12V accessories.)

The weaker batteries will drop more than the others.
Basically the voltage spread should be pretty close to the same before and after use.

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Yes, you can charge individual batteries using a 6V charger or pairs of batteries using a 12V charger, without disconnecting the battery pack's interconnecting cables.

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Charge up the two batteries yu use for accessories until their at-rest voltage is close to the rest of the pack. Taking the up to about 15V with a 12V charger before charging the whole pack with a 36V charge a couple of times will probably get them pretty close.

As for then only charging up o about 80% or so, once they are all in the same ball park with the at-rest voltage, charge them repeatedly with little or no discharging between charge cycles.

With any luck, you might gain about 10%, or so, storage capacity.

Be sure to keep an eye on the fluid level. Use distilled water only.

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BTW: Get a 36v to 12V reducer or install a separate 12V battery to run the accessories and your main pack will last longer.

[simple man]

Originally Posted by 3ftover

Thanks JB. A lot of technical info there. I have asked and will continue to ask to borrow a charger. The few I have found don't have the same connection as me. I sort of did what u said last night but probably could have let them charge with the car chargers longer. Charged with QE overnight and woke up to still blinking. For fear of overcharging I unplugged this morning. It was still blinking. I can say I stayed up late and watched the voltage climb to about 41.6 around 10:30. Set my alram for 2am and it was at 42v. This morning at 5am it sropped to 41.8. That is when I unplugged. I am going to try once more but I do feel the charger is broke. Also it only blinks what I think is the short blink which would indicate the batteries are less than 80%. True or not I don't know. Last note. With the QE or the car charger the batteries seem to peg out at 6.8 to 6.9. I have seen one go over 7v and the new one definitely does. But for the most part they are all in the same range.

I have had this too! Found out it was simply an appliance dropping the ac voltage. Hot water tank goes on and drops the input voltage of the charger, so naturally the output will decrease also! This used to bother me too, until a friend suggested what it might be! Check your ac outlet with a meter sometime. You will be amazed at how much it varies!