Should a car battery charger produce more than 15v

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rustypigeon

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My truck has not run for a couple of months so I decided to charge the battery. My multimeter showed 12.2v before I started charging. I left the multimeter connected while charging. When I hooked up the charger, it went to about 14.5 volts and climbed up to 15.5 volts after about 2 minutes on the charger. This seemed a bit high to me and I didn't want it to go any higher so I unhooked it.

My charger is an old Sears 6 amp model that I bought for $5 at a garage sale a few years ago. It appears to be made in the 1970's based on the brown paint scheme.

Shouldn't battery chargers stay below 15v? I was thinking more like 14.4v during the charge cycle would be more normal. Is it time to buy a new charger?
 
Seems a bit much. How many amps did it indicate?

Those buzz boxes aren't too bright but usually perform all right, as the battery stabilizes things.

I would try the charger on a different vehicle before condemning it.
 
I have a year old Schumacher 2-6 and 10 Amp Battery Charger and have had it read into the low 15 volt range charging as well. It didn't stay that way for the duration of the charge though. The voltage later was in the lower 14s. I was alarmed as well till the voltage tapered off. It is a smart charger.
 
No it should not go that high but most all of the cheaper chargers do. The voltage should not go anywhere into the 15s.

It's a trick the cheap chargers use to charge faster at the expense of battery life. The higher voltage is abusive to the cells.

A good charger should not exceed 14.6-14.7v. My pro Logix charger usually is right around 14.6v max
 
Originally Posted By: 901Memphis
No it should not go that high but most all of the cheaper chargers do. The voltage should not go anywhere into the 15s.

It's a trick the cheap chargers use to charge faster at the expense of battery life. The higher voltage is abusive to the cells.

A good charger should not exceed 14.6-14.7v. My pro Logix charger usually is right around 14.6v max


Terrible statement. The higher the voltage the higher the current. Cheap chargers only source a few amps so the voltage is lower.

V=i*r

If the charging voltage is that high, it means the resistance of the battery is higher now. Typical of an old sulfated battery.
 
It was normal for old fashioned chargers that are simply a transformer and diodes to have an unregulated output and normal for the voltage to rise as charge current falls. In fact they usually went higher than that on open circuit. You did the right thing monitoring the voltage and normally you should disconnect and stop charging at 14.6 volts. 15.5 volts if not for too long will do no harm to a wet cell battery but could more quickly damage a valve regulated type like an AGM if it vented off and lost electrolyte.

The reason why the voltage of an unregulated charger rises so high is because of an effect called transformer regulation. The voltage output of any transformer and that includes the big ones that supply your home, have a voltage output that varies with load. The better quality ones don't vary as much but all are affected. Electrical distribution transformers have multiple secondary winding connections or taps as they are called and these days big transformers have automatic tap changing to respond to load changes.

Modern battery chargers get around the inherent poor regulation of transformers by limiting and controlling the voltage electronically.
 
In the 1970's the RMS Voltage supplied to most homes in the United States was 112 to 117 Volts, and your 1970's charger consisting of a transformer and diode(s) was designed to produce the proper output voltage when an input Voltage of 112 to 117 Volts RMS was supplied to it.

Now days the RMS Voltage supplied to most homes is 124 to 129 Volts RMS. Your 1970's charger will have the output Voltage increase because the transformer in will produce a higher output Voltage when the higher input Voltage is applied to it.
 
Originally Posted By: JimPghPA
In the 1970's the RMS Voltage supplied to most homes in the United States was 112 to 117 Volts, and your 1970's charger consisting of a transformer and diode(s) was designed to produce the proper output voltage when an input Voltage of 112 to 117 Volts RMS was supplied to it.

Now days the RMS Voltage supplied to most homes is 124 to 129 Volts RMS. Your 1970's charger will have the output Voltage increase because the transformer in will produce a higher output Voltage when the higher input Voltage is applied to it.


Well that makes it even worse on top of the transformer regulation effect.

In the UK our voltage has technically reduced from 240V to 230V in order to harmonize with Europe. We met them half way as theirs went up from 220V to 230V.

Just curious, Why did voltage rise in the US ?
 
actually this is good unless you leave it cook for a week.
gives the battery an equalization charge.reverses some sulfation.
if you have a vehicle that sits a lot this will extend battery life.
the fact that you started at 12.2 and quickly got to 15.5 tells me that battery is worn out or badly sulfated.
let it run 8 hours and see if it helps.
 
Doesn't internal resistance of a charging battery go up as it becomes more charged? So voltage goes up at battery terminals? Think voltage divider circuit equivalent.
 
Originally Posted By: JimPghPA
In the 1970's the RMS Voltage supplied to most homes in the United States was 112 to 117 Volts, and your 1970's charger consisting of a transformer and diode(s) was designed to produce the proper output voltage when an input Voltage of 112 to 117 Volts RMS was supplied to it.

Now days the RMS Voltage supplied to most homes is 124 to 129 Volts RMS. Your 1970's charger will have the output Voltage increase because the transformer in will produce a higher output Voltage when the higher input Voltage is applied to it.


Link please!
 
Originally Posted By: barryh

Just curious, Why did voltage rise in the US ?


The power companies did this so that there was less electrical loss between the power station and your home. The higher the voltage, the less loss there is. With higher voltage, they can also use smaller electrical wires.
If you think this causes problems with an old battery charger, try running vintage '50s audio tube amps on 129 volts when it was designed for 110.
 
Internal resistance goes down significantly with increasing state of charge both because of the battery chemistry and possibly in addition because of the increase in battery temperature.

A fully charged battery is in the position of being able to provide the highest cranking amps because it's in the state of lowest internal resistance. Like wise a warm battery vs a cold battery.

Voltage regulators usually have a negative temperature coefficient to reduce charge voltage and therefore current as temperature increases. It's rarer to find that compensation built into a battery charger but some of the modern ones do have that feature
 
Originally Posted By: Kruse
Originally Posted By: barryh

Just curious, Why did voltage rise in the US ?


The power companies did this so that there was less electrical loss between the power station and your home. The higher the voltage, the less loss there is. With higher voltage, they can also use smaller electrical wires. ...
That would make sense for transmission lines, but not why they can't drop it to the nominal 120V at the last transformer.

The voltage here is usually around 124V. I believe they do that simply to increase our power consumption, to increase their income.
 
Originally Posted By: 901Memphis
A good charger should not exceed 14.6-14.7v. My pro Logix charger usually is right around 14.6v max

My Pro Logix charges at 14.8V pretty much all the time.
 
Charging voltage is based upon impedance.

Vcharge=Vopencircuit+I*R

So within reason to force some current I it will need some over potential to do it.

The colder it gets, the more likely a voltage regulator may allow higher over potentials..

Of course higher voltages also means more electrolysis of water and possibly more hydrogen gassing and corrosion.

Everything has a trade.

High 14s are fine. Beyond that I'd suspect a multimeter calibration issue first, then investigate closer.
 
I use a DC power supply and set at 15.8V to charge.
But that's bcuz I want to do equalizing charge on my batteries.
 
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