Battery charger voltage

[fxman]

I have a cheapo Lidl "smart" charger. It's so smart as to confuse the hell out of me. So I need help.

I was trying to revive a couple of dead/weak batteries. So I connected the charger up. After all night charging, I went from 10.x volts to 8.x volts. I measured the voltage across the battery poles while the charger was on and connected, and got 8.x volts. Shouldn't the charger be outputting greater than 12v? In other words, should I be seeing a larger reading than 8.x volts across the poles?

[mgv8]

Sound like your battery is gone, and cannot be recovered, or your charger is gone. My money in on battery.

[Benbay001]

Some of them refuse to try to charge a battery thats too low a voltage.
Try putting it on a power supply at a really low current.
(someone will correct me, im sure)

[fxman]

Even if the battery is gone, why would the charger output less than 12v?

Is it possible to measure the charger voltage by connecting a volt meter directly to it and nothing else? My gut tells me the charger output should be 12v+. But my gut could be wrong, hence my confusion.

[trickywoo]

Charger could be trying to desulfate and when you've measured it its in a discharge mode.

I'd leave it plugged in for a few days and see what happens. Obviously keep an eye on heat build up or over voltage in the meantime just in case.

[foxbody-87]

If the cell is goosed then the impedance will be very high, the charger will lack the ‘grunt’ to provide the requisite voltage (probably a good thing, as cells with high impedance can get rather hot).

[fxman]

Thanks for all your views. I am going with my gut and blaming the charger. It doesn't make any sense for the charger to have less than 12v regardless whether the battery is dead or not.

Over the years I had quite a bit of success bring batteries back from the dead and keeping them alive. For instance my 14 year old factory battery is still going strong and needs maintenance once a couple of years. I am trying fix up some batteries for my sister's car and running into some oddities. I don't think it's me.

I never needed to look at the charger before and hence unaware of its normal characteristics. But it cannot be right for the charger to output 8.x volts. The spec says 7.3v, 14.4v, and 14.7v in any case.

[motco]

foxbody-87 said:

If the cell is goosed then the impedance will be very high, the charger will lack the ‘grunt’ to provide the requisite voltage (probably a good thing, as cells with high impedance can get rather hot).

Exactly. It is current limited - by design or by accident. Measure the voltage off load (at the unconnected croc clips) and it will probably be too high because it gets dragged down by the load.

[fxman]

@foxbody-87

The charger is slightly warm. But the batteries are stone cold. My guess is lack of charger juice. But no way to know until I have a new charger.

[richard sails]

I suspect all these intelligent chargers will use the came chip and just use a slightly different looking case and display. I have several to keep quite a few batteries in good condition over winter and they all operate the same way.


If your charger is like my smart chargers it will have several modes. When connected to a battery it does not start charging immediately. The switch cycles between the different modes.

Off; not charging, reads the battery voltage only
Motorcycle; charges small batteries 1.2Ah to 14Ah uses a 0.8A charging current
Car; charges batteries 14Ah to 120Ah, uses a 3.8A charging current
Cold weather mode; For charging batteries 14Ah to 120Ah when temperatures are below 0 degrees

Once connected and a mode selected, the charger samples the battery voltage and then sets the charge program dependent upon the battery voltage:

If it sees more than 10.4 volts it knows the battery is a 12V battery and starts charging once you have selected motorbike, car or cold as above. Once the charger detects that the battery is fully charged it goes into trickle charge mode at reduced current.

Between 10.4 and 7.3 Volts the charger is not sure if the battery is a full charged 6V or a flat 12V battery. Once the mode button is pressed the charger waits for 90 seconds then attempts to recover the battery with pulse charging. Once 10.4V is reached the charger switches to normal charging mode as above. Again once the charger detects that the battery is fully charged it goes back into trickle charging using a much reduced current.

Between 3.8 and 7.3 volts it assumes the battery is a six volt battery and will only charge at 0.8A using something around 8V, actual voltage is controlled to a maximum by the current, i.e. It's the current that the charger controls not the voltage and does this buy varying the voltage across a limited range. This will not charge a 12V battery and sounds a bit like what your battery charger may be doing.

Below 3.8Volts the charger will not charge at all.

They are good for topping up and keeping a battery in good condition, however they are useless for completely flat batteries, I keep an old fashioned dumb charger for that purpose.

Hope this is useful.

Cheers

Edited by richard sails on Tuesday 17th April 18:47

Edited by richard sails on Tuesday 17th April 18:49

[fxman]

@richard sails

I never had to consider the problem before. Now that I have, I believe i have a good gut understanding of what is going on.

Electric current flows from high voltage to low voltage. So my batteries at 10.x volts were charging the charger at 8.x volts. Eventually the charger was fully "charged" and attained the same voltage as the batteries. What the charger gained, the batteries lost. I was reviving 2x 063 batteries in parallel.

Anyway, I am done with these smart chargers and ordered a not so smart £13.50 Streetwize charger from amazon that only has a full indicator and nothing else. I have my volt meter and don't need anything else. I am optimistic things will work out fine.

[AW10]

Why were you trying to charge 2 batteries in parallel?!

Did you ever try the charger on one battery at a time?

[Mr-B]

I think I have the same charger as you OP. I (stupidly) let a 2 year old battery go totally dead over the winter, tried connecting the charger and not much seemed to be happening. I have a very old jump starter pack which doesn't really work as a jump starter any more as it won't hold enough charge (but it will hold some not sure how much exactly) but I connected that to the battery along with the charger, left them all connected for a few minutes and it seemed to start charging, then removed the jump starter and the charger then carried on charging on its own. It took at good 24 or 48 hours to get it back to full charge and it now seems to be OK. Leaving on trickle mode seems to be keeping it at 14.X volts thankfully.

[fxman]

AW10 said:

Why were you trying to charge 2 batteries in parallel?!

Did you ever try the charger on one battery at a time?

Because I can, they are both dead, and makes no difference how it's done.

I even tried 3 parallel batteries at the same time, including the 14 year old working one in my car. That's just to get the charging going because the smart charger was too dumb to see the dead batteries.

[fxman]

Mr-B said:

Leaving on trickle mode seems to be keeping it at 14.X volts thankfully.

Good to have confirmation of the right volts. I was totally befuddled by the strange going-ons with the batteries that I was going to take them to the local recycle centre. Then the low volts got me thinking it wasn't the batteries at all. The charger still looked the business with all the lights seemingly doing the right things, all the while the charger was stealing amps from my batteries.

[AW10]

fxman said:

all the while the charger was stealing amps from my batteries.

Unscrew the bottom cover - you'll find them in there all lined up waiting for you.

On a more serious note what might well have been happening is that the stronger of the two batteries was charging the weaker one and so the displayed voltage dropped. No idea how the Lidl charger reacts when it's trying to charge the battery yet sees the apparent voltage drop rather than rise. At some point it might throw in the towel because what's its seeing makes no sense to it and/or thermal protection circuits kick in.

The charger only puts out 3.8 A at a maximum. Your two 063 batteries have a capacity of 45 Ah each. Theoretically if they were both dead the Lidl charger would take 90/3.8 = 24 hours to fully charge them both. Overnight may simply not have been long enough.

Can you post the voltages of the individual batteries? And try charging them 1 at a time?

[AW10]

Another question - the charger's display shows the voltage it’s measuring. Did this correspond to what your volt meter is seeing?

Edited by AW10 on Wednesday 18th April 10:59

[Mr2Mike]

As usual this is a user problem rather than a product issue.

[fxman]

@AW10

I have the old lidl charger. It has no display, just some lights.

Regardless of the battery volts. The charger volts must not be lower, or the battery will be charging the charger. This is the answer to the original question I asked. While connected to the charger and charging, the measurement across the battery posts should be >14v (at least for my charger). Connecting multiple batteries in parallel will have no impact on the measured voltage.


@Mr2Mike

You just stick with buying new batteries

[motco]

fxman said:

@AW10

I have the old lidl charger. It has no display, just some lights.

Regardless of the battery volts. The charger volts must not be lower, or the battery will be charging the charger. This is the answer to the original question I asked. While connected to the charger and charging, the measurement across the battery posts should be >14v (at least for my charger). Connecting multiple batteries in parallel will have no impact on the measured voltage.


@Mr2Mike

You just stick with buying new batteries

I'm afraid it will have an impact. As someone previously said, if the combined internal resistance of your batteries is such that the current drawn exceeds the charger's capacity, only two avenues lie ahead: shut down by overload protection, or voltage depression until the terminal voltage of the load rises. For the output to remain at >=14Vdc regardless of load you'd need a voltage source with unlimited current delivery.