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?

[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.

[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.

[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.

[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.

[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.

[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

[fxman]

motco said:

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.

Fair point. Let me modify the rule then:

Voltage measurement across the battery posts when not connected to charger must be lower than after connecting the live charger for the charging to be effective.

Examples:

Battery voltage 12.0v. After connecting charger: 12.2v. Charging is effective.
Battery voltage 12.0v. After connecting charger: 14.7v. Charging is effective.
Battery voltage 12.0v. After connecting charger: 10.0v. Charging is ineffective.
Battery voltage 12.0v. After connecting charger: 12.0v. Charging is ineffective.

[fxman]

motco said:

Quite so. But do you know: a) open circuit charger voltage, b)open circuit battery voltage, c)terminal voltage on charge - one battery only. Once connected the charger and battery will show the same voltage, obviously, and that will rise over time providing current is flowing into the battery and the battery is healthy but low on charge.

Well, I am shallow and content with the bare minimum I need to know.

I do know now with 100% certainty that after charging all night a 10v battery and attaining a final voltage of 8v indicates a knackered charger.

[fxman]

richard sails said:

What are the voltages of the batteries BEFORE you connect the charger, if much less than 11V you will probably find it difficult to charge using your intelligent charger. In that case use a dumb charger to get them up to a reasonable state of charge first.

The technique to trick the rather dumb intelligent chargers is to connect a good battery to the bad. Once the charging starts, or some time after, the good battery can be taken off.

The batteries were 4v. Since the charger sometimes worked, the batteries were taken beyond 10v. Now the charger can reliable charge at 8v, and that's where the batteries ended up.

[fxman]

AW10 said:

Before you condemn the charger to an early grave what happens if you connect it to a known good battery?

Donno. But I can't afford to have my working battery to be at 8v. So I won't even try.

The germans over-engineer their stuff. Hopefully, the cheap chinese made replacement will work better. I should have it in the next couple of days.

Don't worry, you will hear the end of the story. Should be a happy ending unless my luck gets me a DOA charger.

[fxman]

E-bmw said:

TBH it is a case of horses for courses.

If you understand how batteries & chargers work a "dumb" charger is fine & I heave done with them for years & will do for many more.

Having said that, not everyone does as per the whole conversation above.

A "smart" charger will only charge what it thinks will take a charge based on certain logical criteria & so for many they are also fine.

I am sure of 2 things: both the 'smart' charger and the maintenance-free batteries are designed to sell more batteries. The smart charger will tell people their batteries are gone when in fact a non-smart charger could bring them back. The battery sellers couldn't ask for a better profit making tool. For the more aware, even the completely dead batteries could be bought back if there is access to the individual cells. So now they glue the battery shut and tell you they are doing it for your good. But, not really. They'd rather you didn't bring them back.

[fxman]

AW10 said:

Ah, give it a go for 5 minutes with your voltmeter attached.

I suspect you are trying to do my battery an injury! I am sitting quite comfortably at my computer. You wouldn't want me to move now would you? trust me, or rather trust my gut, it's right.

[fxman]

GreenV8S said:

I'm not at all convinced about that. Deep discharging these wet car batteries is very bad for them and will distort the plates, sometimes even to the extent that they form ain internal short. Even if you manage to get all cells to take a charge afterwards, in my experience the battery is never as good afterwards. Being able to put current through an individual cell doesn't address the fact that the cell is stuffed.

May be true in some cases. Mostly it's not. The prime killer is sulfation. It's is not reversible electrically, but possible chemically. This is why they glue the batteries shut now, to block off the route of salvation..

[fxman]

AW10 said:

No, my guess is that your charger is fine and that your batteries are https://imgur.com/gallery/ghCzIyf

Ok, we'll see in a couple of days with the new charger.

The game plan: revive 2x 063 batteries. One is 2-3 months old that's gone through a single cycle of complete discharge owing to a parasitic draw. The other is 8+ years old with maintainable cells. It sat for 6+ month and completely discharged with one cell completely dead (0v) but revived chemically. Both batteries were 4.x volts.

[fxman]

The chinese charger is in. The difference is immediately apparent. While connected and charging, the measurement across the posts is 12.5v. With the charger not connected, the measurement is 5.5v. These measurements are for the batteries connected in parallel.

People betting on the original charger being good have lost their money. As for whether the batteries are bad or not, I am fairly certain of being able to revive the maintainable old battery back to full health. I am not so sure of the non-maintainable new battery. But, because it is new, there is a reasonable chance of it coming back alive. If not, I'll try destructive disassembly of the cover to see if I can gain access to the cells. If I have cell access, I am back in business.

I am now right off the cheap german crap. I bought various other lidl car gadgets in the past and they have all failed with very little use. I am suspicious of their stuff being "designed" to fail rather than bad manufacturing. From now on, the chinese get my money.

[fxman]

GreenV8S said:

I expect you'll find the 'cheap German crap' was made in China. And I think you'll find the problems you have are the result of it being cheap, not the country that made it.

The lidl charger definitely says german at the back. The chinese charger doesn't say anything at all. But one can just tell it's made cheaply and where it came from. I wouldn't hesitate to say the german one is pro-class in terms of quality of impression. But it's crap-class in terms of effectiveness.

Anyway, the non-maintainable new battery appeared to have been revived. Since I don't have a load-tester, I have no way to know for sure. But my gut says it's servicible if I were to put it back in a car.

The 8 year old battery, appears to have 2 weak cells. I'll continue to work on that. I can hear that battery bubbling when connected to the chinese charger.

[fxman]

Ok, here's the end of the story.

The non-maintainable battery was completely revived. Full marks to the dumb chinese charger. It can reach places where "smart" chargers can't go. My friends, it's not cheap that's the deciding factor, but to know.

All the cells in the maintainable battery have been revived to perfection. But, it was a complete failure. Polarity in 2 cells were completely reversed. These cells may have been like that since the beginning. But the idea they could be like that was so alien to me that I was blind to them even if I did see them. The battery now has 4v = 2v + 2v + 2v + 2v - 2v - 2v. Based on my searches, this may be fixable by completely discharging the battery and then recharge.

I am working at my limit now. So I may well dispose of the battery should I become tired of the play. Neither battery is needed for anything. I am doing them purely for fun and to re-validate my battery cell revival method. The re-validation was a success, and I am very confident of keeping the unrelated 14 year old battery in my car going indefinitely until I run out of chemical supplies.

Edited by fxman on Sunday 22 April 12:59

[fxman]

Found a quick solution for discharging the battery by connecting a 120cm and 80cm pc case fans to the battery. Will run until 0v.

Edited by fxman on Sunday 22 April 13:40