Battery charger regulation current v volts.

[ericmark]

In the past my battery chargers did have some current regulation, but in the main it was voltage, so on switch on the charger would bang out 35 amp, until the volts hit 14.8 volt when it would hold at that voltage until the current dropped to 3.5 amp at which point the volts dropped to 13.4 volts and it would be held at that voltage. There was also a timer so if it did not drop to 3.5 volt it would still reduce voltage after a set time, and there were some options with some types of lead acid you could select 14.4 volt instead of 14.8 volt.

So other that the start the output was voltage controlled.

However I have bought a stage charger where the current is regulated not the voltage.
Stage 1 it tests polarity.
Stage 2 0.8 amp pulse between 7.5 and 10.5 volt.
Stage 3 3.8 amp until voltage reaches 12.8 volt.
Stage 4 3 amp until voltage reaches 14.1 volt.
Stage 5 0.8 amp until voltage reaches 14.4 volt
Stage 6 0.1 amp until voltage drops to 12.6 volt
Stage 7 0.8 amp until voltage reaches 14.4 volt
So in real terms 4 stages starts at 3.8 amp then drops to 3 amp, then at what it considered as 80% charge drops to 0.8 amp and once fully charged maintains at 0.1 amp it will however cycle between stage 6 and 7 if the battery voltage drops.

I have tried recharging two completely discharged batteries, one very old 88 Ah and one nearly new 75 Ah in both cases I had to use another charger to get voltage over 7.5 volt and in both cases that resulted in missing the pulse stage, the 88 Ah was that sulphated that it dropped to the 3 amp stage nearly straight away, when the charging was interrupted and restarted it did spend one hour at 3.8 volt, it took 15 hours to reach the 80% charged stage, it never reached the fully charged stage even after 2 weeks on charge.

It was used to replace the 75 Ah in the caravan which was also found fully discharged and it worked the motor mover to get the caravan out so clearly the battery had been charged. Which I did not expect since it had been left for a year without charging.

The 75 Ah was far faster it was a new battery 2 months ago, the chart is from energy meter so first peak 12.30 to 1:30 is the other charger getting the voltage high enough for the charger to start working, the dip 2 Nov is where it dropped from 3.8 amp to 3 amp, and between 6 and 12 it dropped to 0.8 amp and 3 Nov dropped to 0.1 amp, not really nice curves energy meter software has done that.

However it did take from Wednesday to Friday to recharge the battery, however it does actually tell me when fully charged it's not look at ammeter and guess.

Clearly a very low charge rate, the whole idea of the old stage charger was to recharge batteries within a 8 hour shift patten so the fork lift or milk float was ready for next shift. The one I used was on a narrow boat so it needed to recharge batteries as quick as possible when we got a shore supply.

But question is do these really low output chargers actually look after the batteries better? Mine is a really cheap one from Lidi but some are rather expensive the Ctek seems to be the well know make.

Because current regulated and the voltage determines the stages not sure how high the first stage could go to, Ctek also do a 5 amp and 7 amp version and even one with 60 amp but as to how these work I don't know?

But it seems today we have a whole range of lead acid battery chargers using methods never considered when I trained as an auto electrician back in the 1970's I did worry a bit when it held the 88 Ah battery at 14.2 volts for such a long time, never quite reaching the 14.4 volt needed to drop it into final stage.

I would like to hear what other have to say about this new bred of lead acid battery chargers.

 

[SimonH2]

There's an element of "you get what you pay for" and there are "smart" chargers that will whack out far higher currents than that. Most use a combination of Constant Current (CC) and Constant Voltage (CV) - it tends to be CC initially to limit the load to what the charger is designed for, then CV until charging is complete, then a lower CV for maintenance.

Yours seems like a rather unusual charging regime and is nothing like anything I've seen before - does it by any chance cycle between stages 6 & 7 ? Looking at the figures, I think it's a case of making the circuits very simple - and hence cheap to manufacture. It only needs a small number of fixed currents - so no variable CC or CV circuits. So probably based on a very small processor, with on-off outputs to control the CC circuit, and a single voltage measuring circuit.

I think there are pros and cons both ways for high current vs low current charging. There's a lower limit below which the battery won't be charged, a higher (grey) limit where heating and/or gassing rate starts to be an issue, and in between it's a trade off between cost of charger and charge time - and for very large batteries, what your supply is capable of (c.f. discussions of the effect on the lecky network if everyone got a lecky car).

 

[ericmark]

I don't know what a "Smart Charger" is, I have worked on lead acid stage chargers with an output of 100A and 70 volt and be it a milk float, fork lift, mobility scooter or wheel chair the aim was the same, recharge the battery as quick as possible without damaging the battery.

However these chargers had one problem, to get it to latch into the final stage the current was monitored so if like on a narrow boat you are using the battery at the same time as charging it then it can over charge so we then got the pulse charger, again really high output, with narrow boats common for two 70A alternators to feed a pulse charger, it measures the voltage decay between the pulses and I suppose these complex devices would drop into the bracket of a "Smart Charger" there are some low output versions mainly for use with solar panels again whole idea is recharge the battery as fast as you can without damaging the battery.

However there is also a range of chargers with a maximum output of 3.8A or there about which are clearly not designed to recharge anything fast, likely the most well know is the CTek which has some really good reviews. At over £50 not cheap, however the MXS 3.8 is not limited to lead acid and the stages are very similar to the larger stage chargers in that the voltage is held static and the current varies once it reaches a point where the battery can't take maximum current. Even the 0.8A version of the CTek still regulates voltage.

With a good battery the Lidi charger has an advantage, it displays the battery voltage so in each of the stages you know how close it is to completing the stage, once in that third bar stage you can see how close to 14.4 volts at which point it goes into maintenance stage, I assume they consider at 0.1A the volts will drop, and once at 12.8 volt it returns to stage 6 (three bars) and will alternate between stage 6 and 7 (0.1A and 0.8A) however the question is what happens if the battery is not a good one?

The 75 Ah battery it charged A1 did what one expected, but the 88 Ah battery is rather old, and was removed from a vehicle as no good, but it still does sterling service in the caravan, this battery seems to be stuck on the 0.8A stage, it shows 14.3 volt so only just under the point when it goes into the final stage.

As to if 0.8A can damage a 88 Ah battery I would not think so, it is designed for 1.2 to 120 Ah with a manual selection above or below 14 Ah it will also charge 6 volt batteries 1.2 to 14 Ah and the main reason I bought it was to charge 7 to 20 Ah VRLA batteries, as the normal charger was too high of an output for small batteries used in chair lifts, and wheel chairs, and the dedicated charger will not charge batteries which have been standing for too long.

There is another cheap charger called a Maypole also 3.8A plus one called a Master Charger, both around £30 which more than the Lidi but still reasonable, but for £50 I can buy a 20A stage charger so the CTek to me is a silly price and a non starter. But other than the Lidi and the CTek the chargers don't say what they do, so not a clue if current regulated battery chargers are common or not with low power chargers.

Under 7.3 volt the Lidi charger thinks the battery is 6 volt, it will start charging at 3.7 volt it states "the appliance checks whether a fully charged 6 volt or a discharged 12 volt is present." I would love to know how? It seems if the battery does not raise from 7.3 to 7.5 volt in 90 seconds it considers it as faulty. I had to use the old battery charger to get battery over the threshold voltage, I could have used jump leads to do the same.