Technical Battery Charger Voltage

I pulled an old battery charger off the shelf and tested it on a semi good battery. Not a 'smart' charger, just a 2 or 10 amp setting. Put a volt meter on the battery. It soon showed 16 volts. Left it overnight, showed 15 something in the morning. Amp gauge on the charger varied between 10 and 0, didn't pay a lot of attention. Took the charger off. No outside evidence of boiling, level still good. Sitting at 12.6 now.

Too much voltage?

 

Sounds about right. 12.6 is a fully charged battery.

 

I was taught many years ago to watch the current, when it drops to about half of the inital charge current, it's time to disconnect the charger.

There is no voltage regulation in old chargers, you have to regulate it yourself by keeping an eye on things. If the charger has a low maximum output current, just a few amps, then it takes a long time to cook a battery, fortunately. But the big chargers, can cause problems.

 

So true. I have an old charger from the 50s. Dad's when he had a Mobil station, big roll around thing with 6 and 12v capability. Has an 8 or 10 position switch to select voltage and rate. On 12v highest click it will go over 16 by a bit.

It had a mechanical timer that has failed and I can't find a replacement. Without the timer and on high it will destroy a smaller battery quickly. DAMHIKT.

 

Our $4000 super duper GM mandated smart charger will initially charge over 16 volts, and then taper off as the battery internal resistance lowers and it's charge increases. Batteries are complex chemical reactions lol. Here is everything you ever wanted to know....
http://www.chargingchargers.com/tutorials/12-volt-charger.html

 

My last "smart" charger decided that any and all batteries that I hooked it up to had a fault code come up. Code should have been deciphered as "dumb ass battery charger". I'm done with these pieces of shit and am currently on the hunt for a twenty year old charger that will work correctly forever.

 

I've never seen your charger but could something like this be adapted.

https://www.amazon.ca/Intermatic-FF12HC-12-Hour-Spring-Auto-Off/dp/B00062AUBQ

Phil

 

Thanks guys. Someone said 'batteries die in the summer but don't fall over until winter'. Mine are dropping like flies.

On a side note, lithium batteries have caught on big in the motorcycle world, not so much in cars. Weight of course is less of a factor in cars, but what about the almost endless duty cycle of lithium?

 

There are other problems with lithium batteries...they have to have built in monitoring and charging circuitry.

I'm still sticking with good old lead acid batteries for things that use a lot of current. Lithium is great for stuff that needs to be really portable, like my cell phone and laptop and whatnot.

Read some old automotive manuals about proper battery care, so you get an idea of what lead acid batteries want. The most important thing is to never let them sit around when they are discharged, they want to be fully charged all the time, so they won't sulfate and lose capacity. Although overcharging is also bad for them.

 

Yep!!
Found a nice one for 30 bucks.

 

Hey petejoe, That charger is perfect. Two settings 6v. and 12v. Straight 6 amps. You would have to back over it with your car to make it fail.

 

I recently took a battery out of a pickup that had not run in 5 years. It was 6 years old. It read 3 VDC. I removed the caps and put my Schauer 10-2 charger on it for 7 days on the 2 amp setting. When it checked 12v on its own I moved it to 10 amp and it finally started bubbling. The max reading with the charger on was 14.8. After 3 more days The electronic tester said it was 80% good and it could turnover the 460 in the pickup just fine. I feel I saved it from the dead....

 

I wonder how long it will crank an engine? Usually the reserve capacity on a battery like that is very low--it'll crank it for several seconds, but if the engine doesn't start up right away, it'll die.

 

You CAN get lucky with an old discharged battery by driving a bunch of amps into it quickly ( high amps , generate heat and hopefully break up some of the sulfatiob that’s happened on the plates) then switch to a FORMING CHARGE, low amps over a long time.
If it’s possible discharge the battery completely and do this procedure a couple - 3 times and you may be lucky and bring the battery back.

 

Years ago I made a desulfater off a youtube video, consisting of 110AC, a diode and a light bulb as I remember. Had some minor success but as Squirrel noted, the batteries that took a charge weakened quickly.

PicknPull sells recycled batteries cheap, with some kind of warranty. Anybody tried one? Just need something for my yard equipment.

 

WalMart has a one year warranty battery for around $50. First one I bought lasted 3 years, so I bought another to replace it. Can't hardly beat 3 years for $50.....

 

Have an old Sears 6 - 12 v.......stillcharging.....wish I could buy another.

 

Bump.

I still don't understand how chargers vary amperage. Always thought whatever was using the electricity determined the amperage draw. Like the water analogy, where the volts is the tank, the hose is the resistance and the faucet is the amperage.

So how does the charger vary amperage?

 

Flat tire & air pump is perhaps a better analogy to a flat battery & charger. As pressure (voltage) builds up in the tire (battery), the airflow rate (amperes) decreases. Jack E/NJ

 

I have one just like yours that I still use. Even after an occasional drop or fall it works great to this day. Maybe a little more bent up than yours though.

 

Thanks. Explains why chargers with meters typically taper off as the battery charges. So if you have a charger with a 20 amp setting, but your battery is not that weak, it will still have the 20 amp potential but may only be delivering less?

 

My timer is broken on my old battery charger so I found a outdoor Christmas light timer at a garage sale for a dollar. Had to tape up the sensor so it thought it was dark all the time but it works good.

 

From my days servicing large commercial battery systems, there was something wrong that could ruin lead acid batteries if the charge rate was higher than 2.45 vdc per cell. So for a 6 cell 12 v battery it would be 14.7 vdc. Higher than this for more than a short period will begin to ruin the battery.

 

I have a couple of the old style roll around battery chargers and I bought one of the new Smart chargers from Optima a few years ago because it supposedly not only charges but reconditions the battery. Like you I was disappointed when it gave a fault code and refused to do anything to depleted batteries. The other day it happened again, but in fooling with the Smart Charger I noticed that it also included a "Battery Maintain" function button. I pushed it and to my surprise the charger started charging. I left it on overnight and the next morning my battery was fully charged. Those of you who have Smart Chargers might want to see if yours contains a "Battery Maintain" feature and try it the next time you need to bring one back to life.

 

Little off the subject I always have a few battery ( tenders) going in the shop. I noticed that a tender will not charge up to max as a normal size charger will do. Not that that,s a bad thing ,just a observation. Check that yourself some time. gene

 

A "dumb" charger as sold for typical automotive use for the last 50 years or so were made with an iron core AC step down transformer and a DC rectifier.

They basically made some assumptions about the Ah rating of a car battery and sized the transformers current and voltage output to that. These types of chargers are unregulated. Remember a battery will accept just as much current as you give it.

So a "6 amp" charger pegs all 6 amps when connected to a dead or flat battery, and the voltage starts out low. The current tapers down as the battery slowly accepts the charge while the voltage slowly rises. The end state when battery is charged, the charger current is very low, maybe 1/10th of an amp, and the voltage is high, maybe 15 volts, at least in cold weather.

The voltage level is not regulated, but is limited somewhat by the transformer itself and the line voltage. In cold temperatures the internal resistance of the battery is high, and the voltage will not rise very high. In the summer I've seen these same units hit 17 volts pretty quickly.

Those $5 yard sale chargers are just about perfect, though. Fast enough to charge overnight, a good thorough deep charge, not so fast it starts melting or buckling plates. Slow and thorough charging is generally considered best for lead acid car batteries.

 

They are after all battery tenders, not really battery chargers. The one I have is only 0.75 amps. It would take days.. maybe a week or so to fully charge a large battery thoroughly.

They incorporate protection circuitry to automagically switch to float charge after maybe 8 or so hours. The idea behind that, is to prevent a battery just bubbling the electrolyte away for days at a time. As a battery starts to approach a full charge it starts outgassing pretty good, but if the charger doesn't have the ampere capability for the battery size it will be "stuck" there for a long long time. This is No Bueno.

 

Truck 64 ; Thanks for clarifying that for me. I even had a guy in town who sells batteries & chargers say all tenders will charge to maximum & hold it there. I have 4 tenders and they are all the same.They drop off before a full charge unlike a normal charger. Now I feel better.. I'm not losing it like my Wife says... Gene in Mn