Smart Battery chargers with caravans (Including Solar)

[ericmark]

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!

 

[paulc2]

What kind of battery is being charged? Eg open cell lead acid, maintenance free, Calcium, AGM, etc

What kind of "12V" electrical devices can't cope with eg 14.8V charging voltage?

Equipment being used during charging does NOT result in the battery being overcharged, at least on the better chargers. Also, some have a battery temperature monitor, which pretty much ensures no overcharging since it will shut off with high battery temp.

 

[ericmark]

What kind of battery is being charged? Eg open cell lead acid, maintenance free, Calcium, AGM, etc

Lead acid but the regulations do not say which type of lead acid. I know the charger on the boat could be configured for type of battery and there is an option with dip switches to limit to 13.8 volt but using that option it is simply a float charger there is not "smart" function

What kind of "12V" electrical devices can't cope with eg 14.8V charging voltage?

I know my IC 290 radio is limited to 14 volt where the FT 290R has a 9 to 16 volt range but that's not the point it is not me who has set the limits it's the IET/BSi with BS7671:2008 regulation A721.55.4.1 which sets the limits.

Equipment being used during charging does NOT result in the battery being overcharged, at least on the better chargers. Also, some have a battery temperature monitor, which pretty much ensures no overcharging since it will shut off with high battery temp.

The set charger used on the boat was configurable but set for Fleece batteries at 14.8 volt it could be set for a time of 4 (wet) or 8 (Gel and fleece) hours so if the charger for any reason failed to drop into the third stage it would still after 8 hours drop to float although this function could be switched off however using the current trigger the current needed to drop to 2.5 amp clearly where any appliance draws 2.5 amp (10% of full charging current) then it would only drop into float if the timers time expires. So it will hold the battery at 14.8 volts well past the 80% charged when it should drop into float mode.

Not used the pulse type but again the charger looks at the off charge voltage between pulses so likely that too would malfunction where there is a load on the battery but this is only assumed can't state it as fact. As to better charger the WAECO MOBITRONIC 925-024TB at around £200 new I would have considered as one of the better chargers. The Sterling ProDigital is similar spec but does have the option of fitting temperature senders to close it down should something go wrong. However these are really designed for boats not caravans and most boats will have at least two banks of batteries one which will be engine start and will never be stage charged so sensitive equipment can be connected to a bank which is not stage charged.

The boat we had the aux batteries were three 160 AH traction batteries and 25A for so much capacity was not really that much but in a caravan the battery may only be 40AH and with these small batteries it would be easy to buckle the plates.

Since solar panels are not low voltage they do not come under the A721.55.4.1 restriction and it would seem these also once a day go into an equalising charge mode which could upset some equipment but I see nothing to say batteries charged from solar panels should not be used while being charged.

 

[paulc2]

Sounds like the radio isn't suitable for a caravan and the battery charger isn't as smart as it should be.

 

[ericmark]

The Icom IC290 transceiver was built pre-1980 well before any stage chargers were used for anything other than milk floats and fork lifts and in both cases these do not use battery while on charge. The Icom 290 was given as an example of items which are limited to 13.8 volt which has been accepted for many years as the float charge voltage used to maintain 12 volt lead acid batteries. BS7671 seems to have taken this fact on board when it limited the voltage available to appliances on a 12 volt system to 14 volt.

With most caravans once it is connected to mains it will stay connected for long enough to fully charge a battery with a float charge and there is very little need for any smart charger running of the mains.

However solar and wind is another thing and we want to store all we can while the power is available but this does not line up with the using of the power. Ideal would be two batteries and have one in use and one being charged but weight is a problem also as far as I can work out as yet nothing on the market to allow auto swapping of batteries.

There is no reason why a twin battery charger can't be used boats often have float charge to one battery bank and stage charge to other bank but a narrow boat often has rows of bricks to weight the boat and adding extra batteries just means removing same weight of bricks.

 

[paulc2]

What kind of solar controller are you using, or are you simply connecting it direct to battery? My solar controller does 3 stage charging (bulk, absorption, float) and is MPPT.

You could charge one battery while another is charging and swap them over every now and again but its inefficient (Peurket effect) and just means a bunch of switching (in heavy cable - which isn't cheap) so more connectors to go bad and more £££ in cables and bits. Thus, you never really see well designed electrical systems with it. The reason a boat has 2 banks is so the domestic one can run down and the engine starter battery is split to ensure it remains as fully charged as possible for its job. Bow thruster battery (bank) is sometimes found because with the potentially 140 ft of cable distance to serve a bow thruster, the voltage drop/size of cable to overcome it would be horrendous!