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Topic Title: Smart battery chargers
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Created On: 20 November 2013 05:02 PM
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 20 November 2013 05:02 PM
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Seen a lot about battery charging using pulse or step chargers and where speed is required these chargers clearly work well.

However where the battery is being used at the same time as being charged there are a few issues.

1) Either high voltage or voltage spikes which may effect equipment being used.

2) Equipment being used resulting in the battery being over charged as the thresh hold volts or amps which cause it to go to next stage is suppressed so it continues with a high charge rate after the 80% charged point has been reached.

By putting the load through the charger point 2) could be got around with the charger compensating for the load but my version of BS7671:2008 limits the voltage in a battery on charged in a caravan to 14 volt (A721.55.4.1) so to my mind battery chargers with higher voltages should only be used when the battery is not also being used.

I suppose a smart charger could be designed which swaps between two batteries one being charged and one being used but with main units can't really see the point as all that is required is a float charge as speed to re-charge not important.

However with solar panels and wind chargers finding a controller which does not have some boost feature seems hard to come by and speed of charging is important.

So thoughts please. Should one just say can't fit that it does not comply with A721.55.4.1 or is there a way to comply with A721.55.4.1 or does not complying with it really matter? It just seems that most solar panel controllers have either a ripple over 1.2 volt or a voltage over 14 volt so either way should not be fitted to caravans!
 20 November 2013 08:31 PM
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As regards regs compliance, I would not worry about the 14 volt limit too much ! treat it as 14 volts NOMINAL, not 14 volts absolute limit

A bit like the use of light switches marked "240 volts maximum" on UK mains supplies that are 230 volts nominal but up to 253 volts actual.

From a practical point of view, I would advise against the use of a mains powered smart or 3 step battery charger to charge a battery that is on load.
The load may be slightly overvolted, and the battery may be grossly overcharged.
In such circumstances a simple constant voltage float charger set to 13.8 volts is better.

In the case of a PV charge controller I would worry less, since firstly they are DESIGNED for off grid homes and the like in which current is likely used whilst the sun is shining, and secondly they cant cause long term overcharge as the sun does not shine 24/7
The better makes of PV charge controller work fine in off grid homes and should do just as well in a caravan.
 24 November 2013 10:16 AM
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I was rather surprised to hear Swift caravans have a step battery charger installed as standard. To my mind step battery chargers are used to charge batteries quickly where time is of the essence I would not have considered time to be so important when charging off the mains. However with motor movers caravan batteries get a lot more hammer than in the days of gas lights and foot operated water pumps so maybe I am wrong.

However unless one has a motor mover then likely within minutes of plugging in the charger will have gone into float stage so use of lights would likely be after this point so would not hold the charger into bulk and also the voltage was set at 14.4 not 14.8 so not too much of an over charge.

Today switch mode voltage control is common and likely most appliances where voltage is critical will have internal control which will cope with ripple and over voltage but older equipment may have problems especially with pulse and it is common to fit old car radios into caravans and with my IC290 transceiver 14.4 is over the tolerance given and pulse will likely do old things to the transmit which would be hard to see without very special equipment.

The stage charger is not so much a problem most have dip switches which can be set for old batteries at 13.8 volt or wet and gel batteries at 14.4 volt or fleece batteries at 14.8 volt at least the Waeco Mobitronic has those options so stage charging can be turned off. But the solar panel charger is more of a problem both MPPT (Maximum Power Point Tracking) and PWM (Pulse Width Modulation) controllers seem to output to the battery in either pulses or stage charging with no option to turn it off. And of course with a solar panel one does want to get in as much as one can while the sun is shining so really one done not want to turn it off. I note one PWM controller has three connections panel, battery, and lamp and I wonder if this is so when drawing current from the lamp connection it does not stop the controller going into float mode but trying to find info on the controllers is hard.

There is a problem where we buy a 12 volt TV in that it is designed to run from a switched mode power supply giving 12 volt not a battery at 13.8 volt and the same applies to 12 volt tungsten lamps specially the quartz halogen and running on 13.8 volts can damage them without upping to 14.4 or 14.8 volt.

To run from the battery I first use an inverter to lift to 230v simulated sin wave then back down to 12 volt which does seem rather a waste of power. I am sure there are 11 to 16 volt in and 12 volt out inverters I have seen similar units to run laptop off car battery but tend to be on the expensive side.

I tried to make a simple voltage regulator but although at 14.8 volts these will work at 12.4 when off charge they fail but at least I am aware and check what I am using but most people read 12 volt DC and say great I can run this off my 12 volt system 19% over voltage is rather pushing the limits 12% is bad enough.

So the regs give 11 to 14 volt that is quite a range without trying to squeeze in another 0.8 volt on top.

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