Strange Battery Question

Rangerdaniel

Ok gonna try to make this short. 36 volt 95 Medalist with 605 Trojans that are 12 months old. I have posted a few times on the board and you guys have helped a ton.

I had issues with getting my batteries up to 100% (using scottybs digital voltmeter).

Well I wasnt using the cart a lot, not a lot of discharge. However, I was constantly charging it. Then, I moved and have been using the cart more, and looks like the batteries are improving.

Last week when I took the cart to the new house on a FULL CHARGE it read 37.2 and dropped pretty quickly while i was driving it around the new neighborhood. By the end of my ride batteries were reading about 60% (I never let it get that low but didnt have a choice bc i had to get back to the house). I was a little bit irritated about it bc I have put a lot of work into the batteries and assumed they were dying....

Then I plugged it up, and unlike the previous times it actually charged for a pretty long time (lot longer than before). On Saturday morning after charging it read 38.1.

Since then i have run it a few times and charged it as well. it is reading btn 38.1-38.2.

Does this seem normal?

BGW

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crash test dummy

try these

http://www.buggiesgonewild.com/elect...ery-guide.html
http://www.buggiesgonewild.com/elect...-readings.html





mine charge to 44.3 then drops to 38.7

bigstik40

Remember, those voltages are after 6-12 hrs rest after charger shuts off. You will get higher readings if you check them sooner. RAY

P.S. - I have fairly new (6 months old) Trojan T-105's and they settle out at 38.6 volts after proper rest

JohnnieB

If you were having troubles getting the batteries to charge to 100%, the batteries were sitting in a partially discharged state and the amorphous (soft) lead sulfate that remained on (in) the plates from not being fully charged turned into crystalline (Hard) lead sulfate. In other words, your batteries aged (sulfated the plates) more than a year in that 12 months, even though you were charging them regularly, as they should be.
Fortunately, increased usage (deeper discharges) and recharging appears to be reversing the process somewhat.

However, the root cause of the problem may still exist. That being the charger you used and the resistance in the charging loop.

What charger are you using?
What is the on-charge voltage when charger shuts off automatically?
Is the on-charge battery pack voltage at red and black wires on the charger's control board, identical to the on charge voltage at the battery pack's main positive and negative terminals?

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A deep-cycle lead-acid wet-cell battery isn't "Fully" charged until the specific gravity of the electrolyte ceases to increase when a charging current is passing through the cells. The open circuit voltage tracks the specific gravity (SG +0.845), so it may also be used to determine when a battery is fully charged.

The better battery chargers (not necessarily the more expensive ones) monitor the the rise in the on-charge voltage and terminates the charge when the on-charge voltage ceases to rise, or at least ceases to increase more than a few Milli-volts over a predetermined time interval. However, most golf cart battery chargers simply shut off when the on-charge voltage reaches a predetermined value, typically in the 44V-46V range for a 36V charger.

Since Trojan batteries dominated the golf cart battery field for many years, the 44V-46V charger cut-off range for Trojan batteries is used be most golf cart chargers and is not necessarily the optimal charger cut-off voltage range for all batteries. (IE: US battery and Exide batteries need to be taken to a higher voltage to be "fully" charged, if a fixed voltage cut-off is used.)

However, you have Trojan T-605 batteries, so the 44V-46V range should suffice and if the on-charge voltage, as measured at the main battery pack terminals is less than about 45V and the individual on-charge battery voltages are not reaching 7.5V before charger shuts off, there is something wrong with the charger, or the charging loop.

If you have one of the ferroresonant transformer type chargers, (Case about a cubic foot, weighs about 20-30 pounds and hums like a bad florescent light fixture), by-pass the relay and let the batteries charge for about 12 hours, drive the cart until the pack is down to about 70% SoC and then do it again. Then discharge and charge for another 12 hours.

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I use a charger that uses dV/dT to terminate the regular charge cycle, then goes into a float charge mode when it terminates, and has different charge profiles for different battery brands. And doesn't cost all that much.

Rangerdaniel

Thank you for the help. That actually makes a lot of sence.

I am using the erroresonant charger.

The voltage when the charger shuts off is around 38.0-38.1. 24 hours later it is near 37.7

I am gonna check the wires / colors.

How can I bypass the relay?

JohnnieB

Different control board but the bypassing the relay is same.

Be careful, the big capacitor will bite you even when charger isn't plugged in.

Charger shutting off at 38.0-38.1 volts is way too low and your batteries are only getting charged to 85% SoC. (37.7V after 24 hours rest)

Attached Images

Relay - Jumper.JPG (55.8 KB, 0 views)

Rangerdaniel

Well to clarify. When it is first plugged up it is well above 38.1 or so. I am not sure about the exact reading when it turns off. You mean i am at the cart getting a reading when it turns off?

The 38.1 - 38.0 is shortly after it is has been off for a little while (maybe an hour).

If it is reading 38.1 or so when it immediately turns off are you saying I have either a charger or some type of resistance in the charging loop?

What is the best way to check resistance in the charging loop?

JohnnieB

Let them charge overnight, then start a new charge the next AM and monitor the on-charge voltage at the main terminals of the battery pack. Recharging without being discharged should reach the cut-off voltage in just a few minutes. Ought to be about 45V, or higher.


Anything less than about 12 hours of rest time after the charger shuts off automatically, isn't going to give a very accurate indication of the State of Charge. A reading of about 38V an hour after the charge shuts off, is a low reading, but doesn't correspond directly to SoC because it is still part of the surface charge that lead-acid batteries acquire while being charged.

Without disconnecting everything, the resistance of the charge loop cannot be measured with an Ohmmeter because there is a power source in it (the battery pack) that will burn out the Ohmmeter if it is attached.

The easiest way to check is measure the on-charge battery pack voltage at the main terminals and at the red and black wire on the control board. If they are not IDENTICAL, there is excessive resistance in the charging loop.

crash test dummy

how do you discharge capacitor ?

JohnnieB

I got shot down the last time I said how I do it.

The recommended way is a using a resistor and insulated jumper wires.