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Help ! Cant Figure Out Why This Battery Cant be Charged.

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Patrick

Sun Jan 04 2015, 03:22AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

i have a gate opener on my parents property, it opens two large gates, via servos.

there is a control board, it does sensor logic, power sending as well as charging a local lead acid battery, 12v, 7Ah.
The incoming power is 18VAC, upto 2.2 amps (but really much less than 2.2A, always). the control board rectififies and regulates out to its pieces, and the battery.

Heres the problem:
the incoming 18VAC part works fine, the whole circuit board recives the correct voltages and the gates functions all work, they open and close and what not. BUT, it wont re-charge the lead acid. it take power out just fine, the big servos dont slow or stall. (they can draw 14 amps continuous to open the gates)

The new circuit board costs about $180, so id like to fix this one.

Next, Ive built a power supply that can charge the battery. and it generates a perfect charge voltage, and does charge the battery when the battery was connected (13.6VDC). The current is limited for safety.

But.... as soon as i plug the charger into the battery, then plug the controller into the battery, the voltage immediately gets pulled down to 12.6 or less, as the battery is depleted over several gate cycles each day. No matter what, i cant keep the battery above 12.6, or charging at all.

SO...im presuming the original charging circuit was damaged and now pulls voltage down preventing a charge at all.

I ask is there anything i can do? im trying to figure out if i can cut a trace or two, to disable the defective parts of the board.
I wonder if i can trick it into tolerating 13.6V with a resistor or zener, or something.

Andy

Sun Jan 04 2015, 03:32AM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874

Is it a sealed leadacid, normal the get charged at a lower than max, to stop gas beimg produced

Patrick

Sun Jan 04 2015, 03:37AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

right now im running it off a wet cell i can change the voltage easy.

im wondering if the orange NTC or PTC disc is bad?

I wonder if the onboard regulator sees my added "too much volrage" so cuts back to its normal 12 or so. ill check the cap tommarow.

Hazmatt_(The Underdog)

Sun Jan 04 2015, 05:40PM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

You might just need a new battery. They do go bad after a couple of years. Their charging efficiency drops as lead sulphate builds up on the plates and can no longer supply the surface area/current demanded of them. Look at de-sulphating your battery.

The battery is a 12V, but you need to add that extra 2.73V for the redox potential to reverse the chemical reaction in the battery, which is where the 14.73V comes from. But again, if the battery is too far gone, or in your case probably half way gone, then you'll probably need a new battery.

We're having to replace a lot of batteries, a hundred or so, in all the UPS's that are a couple of years old. They'll take a charge, but on a battery load test, they fail miserably, so it's time to get new ones in.

Patrick

Sun Jan 04 2015, 08:19PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

yeah i would adjust the voltage up or down as needed, its set for 13.6V now. the battery is about 17 days old (new), and works in every other load and smart charger. so its got to be good.

Hazmatt_(The Underdog)

Mon Jan 05 2015, 05:18AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

So its in the charger then. I didn't know because that wasn't in the post.
Batteries are sold already a year old, but that shouldn't be an issue.

Patrick

Mon Jan 05 2015, 08:08AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

if i just knew how to connect the charger when theres no load, then disconnect the charger when there is load, that would solve the problem.

Ash Small

Mon Jan 05 2015, 01:49PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Patrick wrote ...

if i just knew how to connect the charger when theres no load, then disconnect the charger when there is load, that would solve the problem.

The voltage drops as the battery discharges, just the same as the LiPo's you are used to.

I'd look at 'hacking' the voltage regulator from a Basch car alternator. These are a bolt on unit that bolts to the alternator, and has three wires, two connected to the brushes (one is an 'earth'), and a third, 'voltage sensor' wire . It senses when the voltage drops, and applies a voltage to the alternator to 'energize' it, and top up the battery.

Check out 'Automatic Voltage Regulator' here:

You then just need to devise a circuit that switches the charger on when you have an output from the 'exiter' output of the regulator.

You could probably devise a circuit that compares the battery voltage to the output from a voltage regulator IC, for example, and switches the charger on when the battery voltage drops below a pre-set voltage, but I'd probably try hacking the Bosch regulator myself.

There are other 12V alternator regulators you could use, but I've used the Bosch units myself, so that's why I'm suggesting them as a simple solutution. One connection to Earth, one to the +ve batter terminal, and an 'output voltage' you can use to 'trigger' the charger.

Bosch circuit diagram here:

EDIT: I'd probably connect a transistor across the 'brush' pins, and use the transistor to switch a relay to control the charger, but there are other configurations you could use.

Erlend^SE

Mon Jan 05 2015, 05:22PM

Registered Member #1565 Joined: Wed Jun 25 2008, 09:08PM
Location: Norway
Posts: 159

Try to find the charge regulator on the board.

Can the board be powered from mains without battery? What is the voltage on the connections for the battery when you do that?

Patrick

Mon Jan 05 2015, 08:49PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

the board runs off the 18VAC, at very few mA. the wall wart only really has the rating of 2.2A for the lead acid charger, and even thats overkill. so yes, the board can run off the wall wart for control logic, but not for those big motors, those need the lead-acid.

im just not sure if an external relay or transistor can cut in, and switch between the two circumstances.

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