Lead acid battery testers?

[robinbanks]

Yet since then, it seems to have almost fully recovered - stands for weeks unused, and still cranks it over just fine

Is have said that was more likely to be a connection fault elsewhere, bad Earth etc

 

[Harry Bloomfield]

Is have said that was more likely to be a connection fault elsewhere, bad Earth etc

No, absolutely not. The battery voltage was way down below 9v, and connected to my charger, the charger did not recognise it. The only way to get it to begin charging, was to parallel it with a good battery. I was unable to find any reason for it to be flat, I even suspected the alternator, of not charging, but that proved fine, and no parasitic discharges

 

[ericmark]

The only way to get it to begin charging, was to parallel it with a good battery.

Did that, and it seems cell gone short circuit in bad battery, result two discharged batteries.

 

[JohnW2]

Did that, and it seems cell gone short circuit in bad battery, result two discharged batteries.

If (as I think is being said) a charger won't charge because the battery voltage is too low, is not the 'solution' to initially put one or two ('good') 2V cells in series with it, until the battery's voltage rises (if it ever does!) to a figure that the charger 'recognises'?

 

[Harry Bloomfield]

If (as I think is being said) a charger won't charge because the battery voltage is too low, is not the 'solution' to initially put one or two ('good') 2V cells in series with it, until the battery's voltage rises (if it ever does!) to a figure that the charger 'recognises'?

Where are you going to source a couple of lead acid cells from, to do that? A second 12v battery, is easy to source, and simple to connect - it just needs a minute or two, to get the flat battery up to voltage, and taking a charge.

 

[JohnW2]

Where are you going to source a couple of lead acid cells from, to do that?

On a shelf in my cellar
However, they are readily available in "D-cell" format.

A second 12v battery, is easy to source, and simple to connect - it just needs a minute or two, to get the flat battery up to voltage, and taking a charge.

Fair enough, but even that will presumably fail if, as in eric's example, the flat battery has a S/C cell, or is otherwise unchargeable.

I suppose the simplest way of all (which is probably what I would do) would be to initially use a totally 'dumb' (aka 'old fashioned') charger for a little while.

 

[ericmark]

In my case, I am using my charger, as the firms charger is a large unwieldy thing, of this design, not the one shown, but taking it up/down steps is not easy. So my little Lidi charger, is far easier to carry, and once set, often a week before I look at it again.

So I had an approximant 35 Ah battery in parallel with an approximant 110 Ah battery, and the pair were down to 10 volts, and the 110 Ah reasonably sure OK as used to start a generator, but my charger had over the last week lost power, so was not charging this morning.

Bit of a pain, as the 110 Ah battery I had wanted to swap for another battery, but now another week before I can swap it.

However the main thing I have realised, is lead acid batteries take a long time to charge. A lithium battery can be fully charged in 1.5 hours, but not a lead acid, even if only just discharged, looking at 10 hours with a stage charger to recharge, and if been discharged for some time, likely looking at 10 days. It is pointless having a battery charger able to deliver 25 amp, as within 15 minutes, it is down to 1 amp.

 

[Harry Bloomfield]

I suppose the simplest way of all (which is probably what I would do) would be to initially use a totally 'dumb' (aka 'old fashioned') charger for a little while.

Yep, that would work, or a fixed voltage charger.

 

[JohnW2]

Yep, that would work, or a fixed voltage charger.

Indeed - that's what I meant by "a totally 'dumb' (aka 'old fashioned') charger"

 

[Harry Bloomfield]

Indeed - that's what I meant by "a totally 'dumb' (aka 'old fashioned') charger"

Totally dumb, in my book, is a transformer, and a rectifier only - absolutely no control, and a battery killer, unless closely supervised. A fixed voltage output, depending on the voltage, wouldn't do any damage to a battery, if left connected longer term.

 

[ericmark]

A fixed voltage output

It would depend on what that fixed voltage is? The standard stage charger starts with a fixed current, the maximum the charger can deliver. This then changes to a fixed voltage often for a 12 volt lead acid around 14.8 volts, until the current drops to around 4 amp, depending on battery size, and then a fixed voltage of around 12.8 volts.

Car alternators often had a fixed voltage of 13.8 volts, with a car with heavy use on the electrics that could rise to 14.4 volts, the idea is the battery will never be charged for long enough to cause damage.

Canal boats run for longer, but also tend to use the battery more with engine not running, so a pulse charger is used, where the speed of voltage decay is used to work out charge rate, the problem is the battery may be used while on charge, where with a fork lift, mobility scooter, golf trolley, the battery is either used or charged, never both at the same time.

Today the engine management works out what is required, I know when the battery is not fully charged, as the stop/start stops working. I noted the warrantee on a vehicle battery was often 2 years or more, unless fitted to a Taxi, when it dropped to 6 months. Buses and Milk tankers used nickel iron batteries, 24 volt needed 20 cells not 12 cells as with lead acid. And these were really heavy. And all seemed to be reversed, store discharged no charged as with lead acid. And the SG did not alter between charged and discharged.

The CAV 208 alternator actually had current regulation, with a resistor connected between the M1 and M2 terminals on the regulator, plus often a ammeter. Still called the regulator a 440 but the Hi, Med, Low was replaced with M1 and M2. And that alternator was darn heavy, 60 amp output at tick over.

 

[Harry Bloomfield]

It would depend on what that fixed voltage is?

That is why I qualified that with - A fixed voltage output, depending on the voltage,'

'The standard stage charger starts with a fixed current, the maximum the charger can deliver. This then changes to a fixed voltage often for a 12 volt lead acid around 14.8 volts, until the current drops to around 4 amp, depending on battery size, and then a fixed voltage of around 12.8 volts.'

Eric, we were discussing 'dumb chargers'..

 

[JohnW2]

Totally dumb, in my book, is a transformer, and a rectifier only - absolutely no control, and a battery killer, unless closely supervised.

Indeed - and that's all any of us had for decades, wasn't it (and I still have some )? In the application I'm talking about it would be 'closely supervised', since it would (if it was going to work at all) only have to be used for a short time (probably measured in minutes) to get the battery voltage high enough for a new-fanged charger being able to take over.

A fixed voltage output, depending on the voltage, wouldn't do any damage to a battery, if left connected longer term.

I'm not sure what distinction you're making here, oor what sort of thing you're talking about - "a transformer and rectifier only" is surely gives an essentially "fixed voltage output", doesn't it ?

 

[ericmark]

Years ago we had very poor quality transformers, where a load would cause the voltage to drop, and a 14 volt RMS transformer would produce 19.8 volt peak to peak, a drop of 1.2 volt across a pair of silicon diodes, but the whole idea was to equalise the cells, and once charged they would be topped up with deionised water.

The dynamo was set to an open circuit voltage of 16 volt, with a two bobbin regulator, and in general we did not look after lead acid batteries.

The sealed for life battery changed all that, I would have been about 20 year old when they came out, so the dumb charger as you call them, stopped being used around 1972. Except for very low outputs, around 1 amp, we have needed some form of regulation. Some were rather simple, with a timer, but the Zenor diode was the common way to stop over charging.


I note

for the same battery charger

one does question if fully automatic why and not cheap, at £38 for a 5.6 amp battery charger, which states it has a sealed mode! It seems Halfords don't have a clue about what they are selling. The do this one for £30

so why would anyone buy this load of rubbish?

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[JohnW2]

Years ago we had very poor quality transformers, where a load would cause the voltage to drop, and a 14 volt RMS transformer would produce 19.8 volt peak to peak, a drop of 1.2 volt across a pair of silicon diodes

At least a couple of the ones I still have pre-dated silicon diodes, at least in applications like this, instead having (massive, with fins) "metal-oxide" rectifiers