Charging a battery at 11.9v

[proveitwithdata]

first time for everything. Neighbor wants me to charge up their vehicle that they rarely drive while they are on vacation. handed me a 1 amp 12v old school charger from yesteryear and said your good with cars....

I pop the hood, its got a panasonic battery with caps that cant be serviced with di, and is putting out 11.9v.

guide me here:

a) pop the caps, add water, and then hook it up to the charger
b) hook it up the charger for 24 hours and call it done

 

[GSCJR]

Connect the charger and forget about it.

 

[Mainia]

first time for everything. Neighbor wants me to charge up their vehicle that they rarely drive while they are on vacation. handed me a 1 amp 12v old school charger from yesteryear and said your good with cars....

I pop the hood, its got a panasonic battery with caps that cant be serviced with di, and is putting out 11.9v.

guide me here:

a) pop the caps, add water, and then hook it up to the charger
b) hook it up the charger for 24 hours and call it done

Panasonic battery.........is it a Toyota? My wife was able to get 9 years in Minnesota on her Panasonic battery. "Technically " you should fill the battery after a charge, but if low, just give it some expansion room. I guess if it is easy do it, but if you have to pry a plastic setup that was not meant to be opened...it's not your car the way I see it. Do you want the risk factor of damage? Our Panasonic has easy entry twist off caps. I would say B if it doesn't have easy twist off caps.

 

[JimPghPA]

If you leave an old school charger connected up to a battery too long there's a decent possibility you will overcharge the battery and damage it.

A good size car battery has about a 50 amp hour capacity.

I would shoot for anything between a quarter of a charge and 3/4 of a charge but preferably half a charge to 3/4 of a charge. When the voltage of the battery while on charge reaches 13.8 volts it's good enough to call it a day and disconnect.

Maybe hit it again with a charge something like every week to 10 days or so for another charge also.

 

[JimPghPA]

Overcharging will damage the battery.

It would be better off to charge it in a couple of short intervals such as maybe 6 hours or so ( actual amount of time not written in stone just anything like maybe a couple of hours to 8 hours or so), and then hit it again a day or two later for another 6 hours or so and repeat that until you see it coming up to 13.8 V while connected.

If you're like me and you forget about things it'd be a good idea to put some kind of a physical reminder someplace where you can't miss it so that you know to go back and disconnect the darn and thing after a while.

 

[JimPghPA]

Another problem that you may run into is that the old chargers were simply a Transformer and either one single diode or a push-pull double diode or a bridge. But the actual regulation of how fast they charged was simply the line voltage being stepped down by the transformer. Over the years line voltage in the United States has risen from what used to be 110 RMS to nowadays most places are somewhere around 125 v RMS and it's not unheard of to see 129 v rms.

The output of the old school transformer type setup will also increase the same percentage and can result in a old school type transformer charger that can easily overcharge a battery to the point that it ruins it because the output voltage will actually try to be too high because of this change in line voltage from decades ago.

So I would never leave a very old simple transformer diode charger permanently connected up because the line Voyage today is not what it used to be quite a few decades ago and those things will destroy a battery by trying to overcharge it.

There is even a slight Danger that an old school charger because it's trying to charge faster than it was originally designed for because the input voltage is higher could overheat to the point where it goes up in flames. So in a way it's a fire hazard. So one of the things you should be doing is placing it so that if it does go up in Flames it doesn't take anything with it.

 

[JimPghPA]

If you accidentally connect an old school charger backwards you'll destroy it.

 

[JimPghPA]

Is that enough information about old school battery chargers for you for a while, LOL.

 

[ripcord]

For the water, check it an make sure that each cell has enough water to at least barely cover the plates. If some are low, only add enough to just cover them.

11.9v is under 40% charged so it will take a long time to charge it with a 1 amp charger. I would put it on for 12 or so hours and come back and measure the voltage while it's charging. It should ideally spend at least a few hours at 14.4v or higher to get it close to full charge.

 

[JimPghPA]

14.4 V for a few hours is not going to hurt it. But 13.8 volts is enough to call it a day and disconnect for a week or so.

 

[JimPghPA]

Ripcord is right in that if you have to add water just bring it up enough so that it's over the plates and don't put any more than that in. And of course you have to use distilled water, not water with minerals in it.

 

[berniedd]

I had a Panasonic batt in my Honda. The caps can be removed with a little work. Add distilled water to just cover the tops of the plates if it is needed. I take it that you have a voltmeter because you mentioned it has 11.9 v open circuit voltage. That is a nearly dead battery. If it is truly an old school 1-ampere charger, it won't easily overcharge a 50 ampere-hour battery. I'd just hook it up, wait till the charging voltage reaches 13.7 volts at the battery terminals, wait 3 hours, then call it a day and remove the charger.

 

[Snagglefoot]

If it opens easily, take a look. If the water is below the plates, just tell your friend he neglected to keep it full, and now it’s done. You can do a Hail Mary by adding water and charging it to 13.8 V but that’s it. Why get involved with a guy who is trying to nickel and dime a situation but can still afford vacations. Tell him to buy a new battery and a new trickle charger.

 

[SC Maintenance]

I wouldn't mess with my neighbors battery. He asked you to perform a task. Be a good neighbor and perform the task - put the charger on as asked. You have a very good chance of breaking something it sounds either way, so follow the direction.

If you want to fix their battery, discuss it with them when they get home.

 

[Astro14]

You don’t have a smart charger of your own? I am happy to help out a neighbor, but this is a case where I would use a better tool.

 

[Number_35]

If you accidentally connect an old school charger backwards you'll destroy it.

I had a charger from the mid-'90s, and worried about connecting it backwards. I installed a green LED that would only light if the polarity was correct. I should have done a red one for reverse polarity also.

 

[Number_35]

Another problem that you may run into is that the old chargers were simply a Transformer and either one single diode or a push-pull double diode or a bridge. But the actual regulation of how fast they charged was simply the line voltage being stepped down by the transformer. Over the years line voltage in the United States has risen from what used to be 110 RMS to nowadays most places are somewhere around 125 v RMS and it's not unheard of to see 129 v rms.

The output of the old school transformer type setup will also increase the same percentage and can result in a old school type transformer charger that can easily overcharge a battery to the point that it ruins it because the output voltage will actually try to be too high because of this change in line voltage from decades ago.

So I would never leave a very old simple transformer diode charger permanently connected up because the line Voyage today is not what it used to be quite a few decades ago and those things will destroy a battery by trying to overcharge it.

There is even a slight Danger that an old school charger because it's trying to charge faster than it was originally designed for because the input voltage is higher could overheat to the point where it goes up in flames. So in a way it's a fire hazard. So one of the things you should be doing is placing it so that if it does go up in Flames it doesn't take anything with it.

That's good information, particularly about the output being directly proportional to line voltage (117 AC RMS in my house).

I suppose the next step up was to to put a Zener across the OP to clamp the voltage to c. 13.2 - 14.2 V.

 

[64bawagon]

You don’t have a smart charger of your own? I am happy to help out a neighbor, but this is a case where I would use a better tool.

My thoughts exactly. OP should tell the neighbor to pop for a NOCO genius 1A charger and put it on, plug it in and forget about it until they get home.

 

[eljefino]

This 11.9 volts sounds like after someone opened the door to pop the hood, and all the BCM controlled circuits came alive.

A full size battery is closer to 90 amp-hours, not 50.

I'd throw that charger on it, leave the hood on its safety catch, go to bed, and check it in the morning.

Batteries only lose water if they're overcharged, which you'll have to try hard to do with one single amp. It's internal resistance will go up as charged, so you won't be pushing a whole amp in when it's nearly full.

You just want this battery to not freeze (if applicable), and start the car when neighbor gets home. Shoot low.

 

[berniedd]

Just for the record, a battery's internal resistance goes up when it is in a discharged state; its internal resistance goes down when it is in a higher state of charge. That is why a charged battery can deliver more amperes (and more voltage) than a discharged battery. Resistance is the opposition to the flow of current.