Charging different Ah batteries.

[Marsupial]

Float is a voltage, not a current and depending on what batteries you have the temperature, the state they're in book you read it varies from 13.2 to 14.4 volts. You wont harm them with a 3.5amp charger UNLESS the voltage is high.

 

[Plevier]

Houleaux said 13V, never as high as 14V. Data for my Trojan T105s says self-discharge approx. 0.6% (varies with temp. of course) and float charge at 13.2V, 1%-3% of C/20.

So for 220Ah batteries, that puts self-discharge around 1.3A and float at 2.2A-6.6A. A steady 3.5A sounds reasonable on that basis. Of course OP hasn't said anything about make and type of battery.

He did mention "if I left it running for 24 hours or so". I can't see a couple of days at 13V, 3.5A float causing any damage to flooded deep-cycle batteries.

Perhaps Houleaux can give more information about the batteries (sealed, etc.)

I don't dispute what you say in your case.
However the T105 is an unusual battery by today's norms, it uses a traditional lead antimony alloy (rather than the now normal lead low antimony plus selenium or lead calcium) to help achieve good cycle life (and high temperature tolerance) at the expense of higher self discharge rate and float current for a market where these don't matter - floor cleaning machines with frequent recharging. That's why an unusually low float voltage is specified too. The float current will increase with antimony migration over the life of the battery, the 3% is probably to cover that with safety. The 1% would be for a new one.
I'm not knocking it, it's a good way of achieving the objective if you don't mind the downsides, but it's out of fashion. All the emphasis now is on maintenance free which requires low gassing and no (or rare) equalisation charging and hence low float current even at high float/recharge voltages. Vehicle alternators now tend to be set at 14 or 14.2V where they used to be 13.8V.
As the OP said he has two 110Ah leisure batteries I have assumed they will be typical modern style ones, either calcium or low antimony, and this is born out by his now saying one is maintenance free.
These should show much lower float current than a battery like the T105 at any voltage below about 14V at which it will start to rise.
Typical figures at 13.5V are well under 0.5% C20 (and for AGM as low as 0.1% C20).
I can't copy and paste it but there is a graph agreeing my values at fig 9 in this research paper http://www.telepower.com.au/INT95e.PDF

So I can't explain the OP's high float current (unless the batteries are knackered which he hasn't indicated).
If he leaves it on for longer maybe the current will reduce.

 

[Plevier]

Float is a voltage, not a current and depending on what batteries you have the temperature, the state they're in book you read it varies from 13.2 to 14.4 volts. You wont harm them with a 3.5amp charger UNLESS the voltage is high.

The float voltage is not a random choice.
The main determinants are the alloy used for the plate grids and the fully charged specific gravity of the electrolyte.
I haven't personally come across anything needing 14.4V float, for most batteries that would be a respectable recharge voltage although of course you can go higher. Offhand the highest specified float I can think of is 13.8V. (Vehicle alternators are regarded as recharge not float - they aren't continuous.)
As you say, it should be temperature corrected too.

 

[pvb]

It isn't 'necessary' but possibly still worthwhile.

My findings are in agreement with Mawm's - post 117.

My Sterling regulator senses the boat battery and therefore cannot maintain the engine battery at the float voltage of 13.6 whilst doing its job and charging the boat battery to 14.9v.

One solution would be to use a maintenance-free starter battery - these tend to have a higher tolerance to elevated charge voltages.

Just to correct a common misconception; the Sterling alternator regulator can't produce a "float voltage of 13.6". It can increase the alternator voltage, but can't decrease it. The lowest voltage a Sterling alternator regulator can produce is the voltage set by the alternator's integral regulator - typically 14.0 to 14.4v.

 

[Houleaux]

Thanks to you all for your considered opinions.

So I can't explain the OP's high float current (unless the batteries are knackered which he hasn't indicated).
If he leaves it on for longer maybe the current will reduce.

The batteries don't show any obvious signs of being knackered but, to be fair, they're not worked very hard. The BM1, which I take with a pinch of salt, will show 100% capacity after an overnight charge but, once the charger is unplugged, this soon drops to 80% without any significant current draw. Running the engine (which has a Sterling regulator) from this starting point will show a charging voltage of 14.4V but only single figure Amp charging rate, which suggests to me that the batteries must be nearly fully charged.

Whilst I can't really justify the expense of a decent marine charger, perhaps I'll swap my old relic for the Lidl one and see if that (eventually) drops down to a trickle charge!

Thanks again.

Rob

 

[Houleaux]

Oh sod it! This looks better than the Lidl one! http://www.ctekchargers.co.uk/ctek-m200.php?gclid=CJr2lvGK5bQCFSTLtAod9X8AVQ

Any views / opinions on better alternatives?

 

[ianj99]

One solution would be to use a maintenance-free starter battery - these tend to have a higher tolerance to elevated charge voltages.

Just to correct a common misconception; the Sterling alternator regulator can't produce a "float voltage of 13.6". It can increase the alternator voltage, but can't decrease it. The lowest voltage a Sterling alternator regulator can produce is the voltage set by the alternator's integral regulator - typically 14.0 to 14.4v.

Not in my case as the alternator regulator has been removed - I forgot that most owners will leave the existing reg in place in which case, you are correct. My Sterling therefore has full control of the charging and yes it does work, and did work also with the original 40amp alternator when the the old external Lucas CAV regulator (type 440 I think) was removed.

 

[Plevier]

Thanks to you all for your considered opinions.

The batteries don't show any obvious signs of being knackered but, to be fair, they're not worked very hard. The BM1, which I take with a pinch of salt, will show 100% capacity after an overnight charge but, once the charger is unplugged, this soon drops to 80% without any significant current draw. Running the engine (which has a Sterling regulator) from this starting point will show a charging voltage of 14.4V but only single figure Amp charging rate, which suggests to me that the batteries must be nearly fully charged.

Whilst I can't really justify the expense of a decent marine charger, perhaps I'll swap my old relic for the Lidl one and see if that (eventually) drops down to a trickle charge!

Thanks again.

Rob

Well this all gets more complicated as you trickle more information out! I suspect your batteries are not in the best of health but I don't know how you calibrate the BM1 and whether that is working right. You could do a test discharge with light bulbs to draw about 5A, one battery at a time, won't be accurate but will give you some idea of what your battery capacity really is.
You could find one battery is OK but the other has a shorted cell, that would show up as high float current but poor capacity. Happened to me last year, I've thrown one out and assume the other is on its last legs too, no point replacing just one. What open circuit voltage do the two show when isolated and stood for a few hours after charge?
If they are fully charged and in a decent state then presumably the Sterling should quickly drop back to your alternator voltage - but what is that set at? Is it an old 13.8V system or a newish 14V or 14.2V?
I've got one of the Lidl chargers, it's handy but I don't think adequate for a step forward for you, as you say the CTek looks much better and decent value. Really though you should be looking at a 25A but that will cost more. Normal recommendation is to have at least 10% of capacity available as charging current.

 

[VicS]

Oh sod it! This looks better than the Lidl one! http://www.ctekchargers.co.uk/ctek-m200.php?gclid=CJr2lvGK5bQCFSTLtAod9X8AVQ

Any views / opinions on better alternatives?

From what I have read on here the Ctek chargers are ones to judge others against.

Want a cheap charger low output charger ... Buy Lidl's or Aldi's one

Want to pay more for a better one buy a Ctek one.

The one you have linked to is a 15 amp one so not in the same category as the 3.8 amp Lidl one

Comparable Cteks are the M45 marine charger or the MSX 3.6 Both significantly more expensive than the Lidl one.

I'd buy the Lidl one if I wanted a cheap maintenance charger for use at home.

Id consider a Ctek one if I wanted a compact charger for the boat.

You might also like to consider that one of the comics (PBO IIRC) voted one of the Ring Smartcharge + range as best buy not long ago

 

[wotayottie]

The lowest voltage a Sterling alternator regulator can produce is the voltage set by the alternator's integral regulator - typically 14.0 to 14.4v.

OK but I thought that the engine alternator regulator dropped the voltage back to a float at 13.4 or whatever ie is two stage and not simply regulating the max voltage. Never got myself organised to measure the voltage and check on this - does anyone know for sure?

If it is single stage then does it make sense to disconnect the internal alternator regulator when an external sterling type one is connected?

 

[Marsupial]

The float voltage is not a random choice.
The main determinants are the alloy used for the plate grids and the fully charged specific gravity of the electrolyte.
I haven't personally come across anything needing 14.4V float, for most batteries that would be a respectable recharge voltage although of course you can go higher. Offhand the highest specified float I can think of is 13.8V. (Vehicle alternators are regarded as recharge not float - they aren't continuous.)
As you say, it should be temperature corrected too.

No it's not random but SOME sources (christec) quote 14.4 for lead calcium at 20deg C others 13.8 yet others 13.2 BUT the condition of the battery is all - and unless we take it apart we don't really know that.

A low float voltage (according to some) will encourage sulphation, too high and the electrolyte will gas, the skill is to set the float voltage to that just below the gassing voltage. The trouble is without charging on a bench with lots of test gear we don't really know what the gassing voltage is, also we don't know the internal resistance or the actual capacity and with modern batteries we have no way of knowing the SG of the electrolyte.

So we end up in an unhappy place where battery charging even with "smart" chargers is an informed guess.

However, the point I am making is that float "charge" is a voltage not a current and most battery chargers will not maintain they're full charging current capability at float voltage so a 3.5 amp charger will hardly show any current at all at float what ever that may set to.

 

[ianj99]

OK but I thought that the engine alternator regulator dropped the voltage back to a float at 13.4 or whatever ie is two stage and not simply regulating the max voltage. Never got myself organised to measure the voltage and check on this - does anyone know for sure?

In the past, standard automotive alternators regulate at about 13.6 -13.8v ie float volts which is why a car and most marine engine batteries never exceed about 85% charge. They are not 2 stage regulators so if they were designed to charge at much over 14v, there is a risk of gassing on a long journey.

More modern vehicles may have more sophisticated systems and there is usually a connection for the engine ecu as well.
I'm not sure whether this is for charging control (doubtful) or just there as an 'emergency shut down' feature to prevent an excessively high voltage from a faulty regulator killing the vehicle electronics.

 

[pvb]

OK but I thought that the engine alternator regulator dropped the voltage back to a float at 13.4 or whatever ie is two stage and not simply regulating the max voltage. Never got myself organised to measure the voltage and check on this - does anyone know for sure?

If it is single stage then does it make sense to disconnect the internal alternator regulator when an external sterling type one is connected?

Internal regulators just have one voltage setting. If you want a "smart" regulator to drop back to float, you need to disable the internal regulator. However, the downside of doing that is that if your "smart" regulator fails, there's no charge at all.

 

[ianj99]

So we end up in an unhappy place where battery charging even with "smart" chargers is an informed guess.

Further compounded by the condition (age and past charging regimes) and also battery temperature. Cold batteries require a significantly higher absorption charging voltage.

However, smart chargers do a pretty good job especially when there is no load on the battery - ie where they can accurately measure the voltage during the rest phase to determine the state of charge.
I am surprised that smart chargers do no have a usb port through which the age, capacity and battery type, could be supplied.

 

[ianj99]

Internal regulators just have one voltage setting. If you want a "smart" regulator to drop back to float, you need to disable the internal regulator. However, the downside of doing that is that if your "smart" regulator fails, there's no charge at all.

Modern electronics are very reliable and it wouldn't be rocket science to rig up a switch fitted near the alternator to reconnect the internal reg.

 

[pvb]

Modern electronics are very reliable and it wouldn't be rocket science to rig up a switch fitted near the alternator to reconnect the internal reg.

Of course. The point I was making was that people need to consider the potential consequences before they start messing about with their alternators.

 

[ianj99]

Internal regulators just have one voltage setting. If you want a "smart" regulator to drop back to float, you need to disable the internal regulator. However, the downside of doing that is that if your "smart" regulator fails, there's no charge at all.

Why do you think that alternators are charging at more than float voltage (give or a take a bit at the alternator output to allow for voltage drops)?

Its because they charge at this that engine batteries are undercharged and automotive electronics & lighting are designed to run at float voltage.

If they charged at a much higher voltage, there would be no real need for smart charges because batteries would reach a much higher state of charge and also increse risk of gassing / water loss.

I have a device called a Scangauge connected to my car's diagnostic socket. It can display any 4 engine parameters eg ign timing, throttle position and when set to display volts, this alternated between 13.9 and 14 - ie 13.95v. Switching on the headlights cause a momentary drop to 12.7. Exactly as I expected. (car is a 2010 DS3)

 

[Houleaux]

Well this all gets more complicated as you trickle more information out! I suspect your batteries are not in the best of health but I don't know how you calibrate the BM1 and whether that is working right. You could do a test discharge with light bulbs to draw about 5A, one battery at a time, won't be accurate but will give you some idea of what your battery capacity really is.
You could find one battery is OK but the other has a shorted cell, that would show up as high float current but poor capacity. Happened to me last year, I've thrown one out and assume the other is on its last legs too, no point replacing just one. What open circuit voltage do the two show when isolated and stood for a few hours after charge?
If they are fully charged and in a decent state then presumably the Sterling should quickly drop back to your alternator voltage - but what is that set at? Is it an old 13.8V system or a newish 14V or 14.2V?
I've got one of the Lidl chargers, it's handy but I don't think adequate for a step forward for you, as you say the CTek looks much better and decent value. Really though you should be looking at a 25A but that will cost more. Normal recommendation is to have at least 10% of capacity available as charging current.

I awoke in the middle of the night to the smell of boiling batteries in August 2010 with the BM1 reading 11.8V and the good old charger still sticking in its 3.5A! I immediately shut off the charger, but both batteries were quite hot to the touch - not good! In the morning the voltage had dropped further and the batteries were completely flat. One was older than the other so I replaced that and started the engine on it. I then switched to both and the good old aternator threw 50A (its max rated output) at the batteries for a while, after which all seemed ok - although I suspect the remaining "old" battery had suffered as a consequence. I used this pair for about a year before replacing the older one (a sealed battery) because I couldn't see any colour in the inspection window (too little electrolyte left?) and the BM1 seemed to suggest that the combined capacity of the batteries wasn't what it should have been. So my batteries have had a chequered past(!) - I should really have done what you did and replace them both... Maybe the first of the new batteries has been damaged by association with the severely discharged one?

I'm not at the boat and I can't remember exactly what the voltage of the batteries is after they've been standing following a charge. Somewhere around 12.2V to 12.4V I think, but I may be wrong. The last time I put a tester on each battery individually they read about the same. My alternator regulator is set at 13.8V, not the higher voltage of newer ones.

A 25A charger? I'm sure you're right! The trouble is, I can so easily get talked into spending cash....!! I'm off to have a look at what's available - just to look you understand!!

 

[Houleaux]

You might also like to consider that one of the comics (PBO IIRC) voted one of the Ring Smartcharge + range as best buy not long ago

Thanks. I'll have a look at those too.

 

[Plevier]

No it's not random but SOME sources (christec) quote 14.4 for lead calcium at 20deg C others 13.8 yet others 13.2 BUT the condition of the battery is all - and unless we take it apart we don't really know that.

A low float voltage (according to some) will encourage sulphation, too high and the electrolyte will gas, the skill is to set the float voltage to that just below the gassing voltage. The trouble is without charging on a bench with lots of test gear we don't really know what the gassing voltage is, also we don't know the internal resistance or the actual capacity and with modern batteries we have no way of knowing the SG of the electrolyte.

So we end up in an unhappy place where battery charging even with "smart" chargers is an informed guess.

However, the point I am making is that float "charge" is a voltage not a current and most battery chargers will not maintain they're full charging current capability at float voltage so a 3.5 amp charger will hardly show any current at all at float what ever that may set to.

Yes I have a Cristec charger that offers that crazy voltage too, but have you ever seen a battery manufacturer specify a float that high?
Too low a float voltage will indirectly encourage sulphation by letting state of charge decline. The starting point is that at 25 degrees C, open cct voltage = s.g. + 0.85V. So with typical traditional battery s.g. of 1.25, OCV=2.10V. The minimum to maintain charge is this +0.1V so that's 2.20V i.e. 13.2V for a 12V battery. The minimum recharge voltage is another 0.1V so 13.8V for a 12V battery.
Those values are still widely used and were appropriate for batteries made with lead-antimony alloy containing 8-10% antimony (the Sb is added for strength, stiffness and castability, pure lead is unusable for traditional construction). These batteries would lose water even at those voltages, increasingly through life, and would corrode rapidly at higher voltages.
I'm an elec eng not a metallurgist or chemist and my time in the battery industry was on applications not fundamentals so forgive me if this is a bit wrong, but I believe the problem is that the high Sb content precipitated at grain boundaries forming local cells that gassed and corroded. Also Sb from the +ve plates would dissolve and re-deposit on the -ve plates forming even more vigorous gassing spots, hence the increase in gassing through life.
Most lead-antimony batteries now have gone to 1.5-1.8% Sb plus a trace of selenium which I think is a grain refiner. This retains the Sb in solid solution greatly reducing the gassing and corrosion and eliminating the Sb migration. This has allowed the use of higher voltages, in turn allowing higher s.g which is now typically 1.28 needing a minimum float of 13.4V. (Not all good news - cycle life isn't as good, so deep cycle batteries e.g. the Trojan mentioned earlier tend still to be high Sb). Low antimony batteries can be "maintenance free" although the small print will normally prohibit fast charging.
Lead-calcium came in as another alternative to reduce gassing, it gasses abut 50-75% as much as low antimony. These like about 0.05vpc higher so a min float of say 13.7V. You can go higher but 14.4V is too high.

So that's the logic of the different figures you see (and I haven't covered gel, AGM or pure lead, all of which have their quirks!)

You don't want to juggle the float voltage according to the condition of the battery. The original float voltage is fine until the battery is kaput.

I don't know any charger that deliberately limits its current capacity at float voltage as you suggest. It doesn't need to. Float current is small, it doesn't need limiting.