Why do some caravans come with stage chargers?

Aug 11, 2018
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I am talking about from the 230 volt hook up, I can see why you use a DC to DC stage charger when towing, that is very different, one we would hope nothing 12 volt is being used while being charged, and two there is a limited time so you want to charge as quick as you can.

I know the stage charger does not comply with BS7671:2008 as the voltage is too high, 14 volt is the upper limit, this likely also means pulse chargers are out, however when you have solar panels then likely as when towing, I can see how time is important, so can see why pulse charging is done with solar panels and wind chargers.

But it seems many caravans still have stage chargers working off the mains, again can see why with a narrow boat, when you moor at the Pub you want a fast charge, but why have stage chargers for caravans from the mains hook up? Even if touring, you are likely connected to mains for more than 8 hours so no real need for a fast charge.

There are two major problems with the stage charger, one is higher voltage 14.8 volt will reduce tungsten bulb life, and two is the current is monitored so it knows when to drop into float mode, so any current draw can cause it to stick in bulk mode and over charge the battery. The 35A charger we had on the narrow boat switched to float when charge rate dropped to around 4 amp, switch on a few lamps, and it will only come out of float mode when it times out.

Now I can't see why manufacturers would fit stage chargers which they know do not comply with BS7671:2008 unless there was some benefit. So there must be a reason, but what is that reason?
 
Mar 14, 2005
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Hello Eric,

I will first say I am not familiar with the detail requirements of BS7671:2008 and despite a quick Google search I have not found any specifics for 12V systems. If you could point to the relevant details that would be helpful.

How it would specifically apply to charging of Lead Acid touring caravan batteries, I am not sure, but I will make one observation, it is highly likely the standard will have been revised since 2008, but whether that would affect its provisions for 12V dc systems I don't know.

Multi-stage battery charging is widely accepted as the best way to keep a battery well charged, and to maximise its life, some such dedicated systems also include battery recovery programmes to rejuvenation tired batteries. Many such systems are manufactured in the EU including the UK, so I would suspect that such designs would have to be compliant with the relevant regulations including CE and BS7671 at what ever stage was in place at the time of manufacture.

So I doubt there are any systems fitted to UK caravans that would not comply with the regulations.

Since I started caravanning (Late 1950's) we have seen the increased use of appliances that need 12V dc power, and that means the demands on batteries have generally increased, (though in recent times the increased use of LED lighting has reduced the long term loads). Consequently the need for effective battery charging has become more important, so the 1970's standards of PSU's only producing 13.8V have given way to smart chargers, that monitor voltage and current, and then decide on the best type of charging to build the charge in the battery.

Importantly, the chargers should look at the state of the battery and set the appropriate charge mode, so long term connection to mains should not be detrimental to the battery.

One of the reasons the peak voltage limit in caravans was set at 13.8V was becasue many of the chargers that were traditionally fitted prior to the limit was imposed were very basic transformers and rectifiers, with no voltage regulation. Such chargers may have had an RMS voltage of 14V which was needed to provide a reasonable charging current, it did mean the peak voltage from the rectifier would be around 19V7 at rated current, but under lower current demands the voltage could rise to 22V or more.

As the battery reaches full charge, the current demand drops, which allowed the peak voltages to rise, and I know from practical experience it was enough to destroy a battery that had been left on charge for a number of months.

The modern multistage chargers should only use pulses to test the state of the battery before deciding how to address the battery, and unlike the old unregulated chargers should not continue to cook the battery. they should reduce charge current to a trickle when the battery reaches its maintenance (long term)state. Some manufacturers of multi-stage dedicated chargers claim their systems can be left connected to a battery indefinitely, what I can't tell you is if the caravan chargers also have these characteristics, you would need to check the specifications of the charger in your caravan.
 
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The regulations state:-
A721.55.4.1 Generators and transformer/rectifier unit
If a supply is obtained from a generator or from a low voltage supply via a transformer/rectifier unit, the extra-low.
voltage at the output terminals of the supply unit should be maintained between 11 V minimum and 14 V maximum with applied loads varying from 0.5 A minimum up to the maximum rated load of the supply unit. Over the same load range, alternating voltage ripple should not exceed 1.2 V peak to peak.

I do realise there are units designed to charge miss used batteries, and there are special stage chargers such as the one sold from time to time by Lidi and the Ctek 3.8A which would never replace the built in caravan charger but are able through multi-stage charging to bring miss treated batteries back to life.

However in a maintained system with a 35A float charger set to 13.6 to 13.8 volt the battery does nothing, other than maybe smooth the supply where switch mode regulation is used. The caravan is positioned with a motor mover, then within 15 minutes it is float charged for at least 12 hours when only a small part of its capacity is used.

I first came across the problem with a narrow boat, and to be fair often with a narrow boat rapid recharge is required, but the standard stage charger normally has 3 stages.
1) As much output as the charger can give.
2) Holding the voltage at 14.4 or 14.8 volt depending on battery type.
3) Once the current drops to a set limit, normally around 4 amp reduce the voltage to around 13.6 volt which it will try to maintain until either switched off, or the voltage falls to 11.8 volt (that can vary) when it restarts the stage charging.

There is often a safety timer, either 4 or 8 hours, once stage 2 is obtained, it starts to time out. So the time held at 14.8 volt is limited. With a bank of three 160 Ah batteries on a boat you would think a 35A charger is rather small, and would not damage batteries, however it was found they needed topping up rather frequent, OK not helped being in the engine compartment, but the main problem was the central heating circulation pump, this used nearly the same as the current needed to put the charger into float stage, so every time the power tripped the batteries would be charged at 14.8 volt for 8 hours, until the timer cut in.

Once we found out what was going on, we found there was a switch which turned off the stage charging and turned it into a float charger, once this was set to float, tungsten bulbs lasted longer and the battery did not need topping up any where near as frequent.

My caravan is float charged, but when looking at other caravans it seems they often have stage chargers fitted, now for the DC to DC charger car to caravan I can see why you need a stage charger, and with solar panels I can see why you have a pulse charger.

But I simply can't see why the mains powered charger is a stage charger, OK there may be a special circumstance where the caravan is parked outside the house with power connected and once unloaded it is taken to a storage place where there is no power, but this must be rare, however it seems many caravans are fitted as standard with stage chargers. The question is why?

With the exception of the specials like the CTek, the stage charger gives the battery a lot more stress to a float charger, however, fork lift, milk float, mobility scooter to name but some want to recharge the battery fast, but there is no real need for this speed with a caravan, they can be simply float charged.

I am sure I have missed something, but just can't see what.
 
Nov 16, 2015
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ericmark said:
I am talking about from the 230 volt hook up, I can see why you use a DC to DC stage charger when towing, that is very different, one we would hope nothing 12 volt is being used while being charged, and two there is a limited time so you want to charge as quick as you can.

I know the stage charger does not comply with BS7671:2008 as the voltage is too high, 14 volt is the upper limit, this likely also means pulse chargers are out, however when you have solar panels then likely as when towing, I can see how time is important, so can see why pulse charging is done with solar panels and wind chargers.

But it seems many caravans still have stage chargers working off the mains, again can see why with a narrow boat, when you moor at the Pub you want a fast charge, but why have stage chargers for caravans from the mains hook up? Even if touring, you are likely connected to mains for more than 8 hours so no real need for a fast charge.

There are two major problems with the stage charger, one is higher voltage 14.8 volt will reduce tungsten bulb life, and two is the current is monitored so it knows when to drop into float mode, so any current draw can cause it to stick in bulk mode and over charge the battery. The 35A charger we had on the narrow boat switched to float when charge rate dropped to around 4 amp, switch on a few lamps, and it will only come out of float mode when it times out.

Now I can't see why manufacturers would fit stage chargers which they know do not comply with BS7671:2008 unless there was some benefit. So there must be a reason, but what is that reason?

Because they do, !!! Ask the manufacturers.
 
Nov 16, 2015
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ericmark said:
The regulations state:-
A721.55.4.1 Generators and transformer/rectifier unit
If a supply is obtained from a generator or from a low voltage supply via a transformer/rectifier unit, the extra-low.
voltage at the output terminals of the supply unit should be maintained between 11 V minimum and 14 V maximum with applied loads varying from 0.5 A minimum up to the maximum rated load of the supply unit. Over the same load range, alternating voltage ripple should not exceed 1.2 V peak to peak.

I do realise there are units designed to charge miss used batteries, and there are special stage chargers such as the one sold from time to time by Lidi and the Ctek 3.8A which would never replace the built in caravan charger but are able through multi-stage charging to bring miss treated batteries back to life.

However in a maintained system with a 35A float charger set to 13.6 to 13.8 volt the battery does nothing, other than maybe smooth the supply where switch mode regulation is used. The caravan is positioned with a motor mover, then within 15 minutes it is float charged for at least 12 hours when only a small part of its capacity is used.

I first came across the problem with a narrow boat, and to be fair often with a narrow boat rapid recharge is required, but the standard stage charger normally has 3 stages.
1) As much output as the charger can give.
2) Holding the voltage at 14.4 or 14.8 volt depending on battery type.
3) Once the current drops to a set limit, normally around 4 amp reduce the voltage to around 13.6 volt which it will try to maintain until either switched off, or the voltage falls to 11.8 volt (that can vary) when it restarts the stage charging.

There is often a safety timer, either 4 or 8 hours, once stage 2 is obtained, it starts to time out. So the time held at 14.8 volt is limited. With a bank of three 160 Ah batteries on a boat you would think a 35A charger is rather small, and would not damage batteries, however it was found they needed topping up rather frequent, OK not helped being in the engine compartment, but the main problem was the central heating circulation pump, this used nearly the same as the current needed to put the charger into float stage, so every time the power tripped the batteries would be charged at 14.8 volt for 8 hours, until the timer cut in.

Once we found out what was going on, we found there was a switch which turned off the stage charging and turned it into a float charger, once this was set to float, tungsten bulbs lasted longer and the battery did not need topping up any where near as frequent.

My caravan is float charged, but when looking at other caravans it seems they often have stage chargers fitted, now for the DC to DC charger car to caravan I can see why you need a stage charger, and with solar panels I can see why you have a pulse charger.

But I simply can't see why the mains powered charger is a stage charger, OK there may be a special circumstance where the caravan is parked outside the house with power connected and once unloaded it is taken to a storage place where there is no power, but this must be rare, however it seems many caravans are fitted as standard with stage chargers. The question is why?

With the exception of the specials like the CTek, the stage charger gives the battery a lot more stress to a float charger, however, fork lift, milk float, mobility scooter to name but some want to recharge the battery fast, but there is no real need for this speed with a caravan, they can be simply float charged.

I am sure I have missed something, but just can't see what.

Erik, it looks like your answering your own Questions, in a very long winded way, Which caravan do you have?
And it is quite often for folk to unload the caravan, have it on mains hookup at home, clean it out return to storage remove all power, I have not been out for two months unfortunately and my battery when I checked two days ago was still at 12.7 volts. . I think you are over complicating yourself. And maybe not enjoying your caravanning, as much as you could.
Hutch
 
Nov 11, 2009
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I’m having some difficulty understanding what the objective of this thread is all about. Even messing about for a while in black cylindrical objects we didn’t discuss their batteries in such depth.
I’ve never really had a problem with the onboard performance of my caravan batteries. During periods I’m storage the battery was removed and kept linked to a CTEK unit. This present van purports to have stage charging so now it’s kept at home the battery gets a periodic supply from the home mains generally as part of bringing the fridge down to temperature. So I don’t plan to go looking for problems where none exist as far as my battery is concerned.
 
Mar 14, 2005
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ericmark said:
The regulations state:-
A721.55.4.1 Generators and transformer/rectifier unit
If a supply is obtained from a generator or from a low voltage supply via a transformer/rectifier unit, the extra-low.
voltage at the output terminals of the supply unit should be maintained between 11 V minimum and 14 V maximum with applied loads varying from 0.5 A minimum up to the maximum rated load of the supply unit. Over the same load range, alternating voltage ripple should not exceed 1.2 V peak to peak. .......I am sure I have missed something, but just can't see what.

This is quote is strangely specific, and I wonder why it refers to ELV output of 11 to 14V! after all there are many different ELV voltages for appliances, 5 V USB, 9V for many guitar pedals, 12V for a number of wireless devices, , 19V for many laptops, 24V 36V for power tools, so I suspect you may have miss-understood the area of concern covered by the regulations, and its my suspicion it refers to the special supplies relating to most domestic and probably commercial LED lighting PSUs.

I also think your experience of a a marine installation may have given you the wrong expectation of what the charger in a caravan is capable of. Just becasue you cant see a particular usage pattern that might require a multistage charger, does not mean there isn't one

It's my expectation that the MS chargers are likely to prolong the life of a caravan battery, more so than the previous 13.8V constant charge systems. I'm pretty certain there is nothing to be unduly to be worried about,
 
Aug 11, 2018
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The regulation quoted is from the caravan section, so does not relate to drills etc. I am not worried, just interested, my caravan battery is now kept on charge 24/7 and the caravan is used at home as my wife's craft studio.

Not talking about small Ctek chargers, and like, but the large charger if doing what it should will charge battery to around 90% charged will bulk charge, then drops to float for last 10% so it only speeds you charge when battery is less than 90% charged anyway, so 99% of the time stage charging is not used.

I was never taught about the modern smart charger, when I went to collage to learn auto electrics they did not exist. In fact regulated chargers of any kind were rare, the whole idea of having a battery on charge for a very long time was rather a specialist field, GPO clearly did, now Open Reach, and stand-by generators, but nothing in the home.

Today completely different, alarm panels, stair lifts, emergency lights all keep the battery charged 24/7 and we now have the VRLA battery which would be wrecked by the old chargers.

I realised my training was lacking, I put some VRLA batteries to charge and used an energy monitor on the supply to charger, this allowed me to see how the charger, in this case the Lidi charger, actually charged the battery. The Lidi charger has 5 charging rates 3.8A, 3A, 0.8A 0.1A and zero, the first two once complete it will not auto return to, the last three is will alternate between them.

First eye opener was how a sulphated battery charged, I had always thought this was a gradual recovery, however this is not the case, it can sit for weeks, even months, seeming as if nothing is happening, then over 24 hours it will except the bulk of the charge. The second was how long it takes to complete the charge cycle, the little 7 Ah VRLA batteries I was playing with would take most of the charge within 24 hours, but it took a week to put the last little bit into the battery at which the charger switched completely to zero charge rate until voltage drops to 12.8 and switching charger off/on within an hour again charger at zero charge rate. In the past I would have taken batteries off charge once the charge rate had dropped, I never thought it would take so long to get the last little bit into the battery.

So in the grand scheme of things, it takes around 6 hours to recharge a battery to 90% from completely discharged using stage charging, and 12 hours to same point using float charging, but both take the same time, around a week to put that last 10% in the battery, so all in all the stage charger is 4% faster.

So to get that 4% faster, it reduces bulb life and often stresses the battery, so looking at the over all picture, one wondered if it is done to increase after sale maintenance charges on the caravan, as I just can't see the advantage of stage charging with a caravan, only the disadvantages. OK fork lifts, milk floats, mobility scooter, but not charging caravans from the mains.

As yet found no real good reason other than to sell more bulbs and batteries.
 
May 24, 2014
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I too think you are overcomplicating and overthinking things. The caravans will have been made to various standards and regulations. The manufactuers will have batteries (no pun intended) of lawyers that check everything legal and using electrical specialists to help comply with the standards. Its the sort of thing my daughter does but with chemicals.

As Hutch says, enjoy your caravanning, you will achieve no more than a headache thinking like this.

On a lighter note, if I ever meet you, I wont ask you the time in case you take my watch to bits. :cheer:
 
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Oh I would, I love reverse engineering. Thank you all, the BS7671:2008 is not law, although it can be used in a court of law, so electricians tend to treat it as law.

I have not had a new caravan in a long time, so although I know stage chargers are fitted, it could be they are switched to float as standard, and the ones I have seen have been switched to stage charging by the owners?

It could be as simple as so many stage chargers are made, they are actually cheaper than float chargers.
 
May 24, 2014
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The battery charger is the least of your problems in the caravan world. As the venerable Mr Clarkson would say "Remember, they were built by minkies".

Bits missing, screws dropping out, furniture coming away from the walls, damp, and so on and so forth. Thats a modern caravan.
 
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Thingy said:
.....The battery charger is the least of your problems in the caravan world....

Mmm ! It was the main problem for me when it burnt out in France , I could have handled a couple of screws falling out here and there ! :eek:hmy:
 
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Craigyoung said:
Thingy said:
.....The battery charger is the least of your problems in the caravan world....

Mmm ! It was the main problem for me when it burnt out in France , I could have handled a couple of screws falling out here and there ! :eek:hmy:

At least when my power unit failed it was only a round trip of 140 miles to get a new one, always carry a spare one now, as lots of other Spare things, left the spare Jocky wheel at home though.
 
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Same here , if we tour uk we are under warranty but if we're going overseas European touring I always carry the spare charger now that we had in the Bailey's from France ! And give it to our friends when they go to France to .
 
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Yes I have a Lidi Charger left in caravan just in case. OK it would not work that well, but it would get me out of a hole.

Supply to charger failed in Forest of Dean (RCD would not hold in) we tried to find a replacement, we tried all sorts of shops, and gave up, so went to pick up Milk in Lidi and there was a bin full of them.

Got back to caravan tried switching on power, and this time nothing tripped, got home tried the insulation tester to locate fault, what ever it had been, now gone, can't find any fault.
 
May 24, 2014
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Surely the easiest thing to carry for emergency would be a CTEk charger?

Here

The perfect universal 12V charger

Larger battery performance

The MXS 7.0 is perfect for charging the larger batteries that you find in RVs, boats caravans and cars.

The MXS 7.0 is a fully automatic 8-step charger that delivers 7A to 12V batteries from 14-150Ah and is also suitable for maintenance charging up to 225Ah. It includes battery diagnosis to establish whether your battery can receive and retain a charge, a special Recond mode for restoring and reconditioning stratified and deeply discharged batteries, a winter program for charging in cold weather and an AGM battery option. The MXS 7.0 can even be used as a power supply source for 12V equipment up to 7A.

Fully automatic ‘connect and forget’ charging
AGM, Normal and Recond programs
Charges batteries up to 150Ah
Power supply for 12V equipment up to 7A
5-year warranty
 
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The XS - 7000 is a really good charger, at a really good price, it is a stage charger, the main point is it has no buttons that need pressing, it auto gives the battery what it needs up to 7 amp, there is also a 25 amp version.

However the MSX - 7 has like the Lidi charger a mode button, it is designed to charge a battery that is not being used, not to maintain a battery while in use.

For £14 the Lidi charger will charge at 3.8A which is enough to keep one going when for what ever reason the built in charger fails. But like the MSX range of CTek chargers it is not designed to maintain a caravan battery.

The XS25000 is over £500 and the XS7000 is over £100 that is just a tad more expensive than the Lidi at £14.
 
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ericmark said:
...However the MSX - 7 has like the Lidi charger a mode button, it is designed to charge a battery that is not being used, not to maintain a battery while in use..

I hadn't considered the point you make so I have done some research. I have been unable to verify the statement above, In a number of the instruction books for the Ctek models it does refer to maintenance charging, but it does not warn against using power from a battery with the charger connected, which if it were dangerous or detrimental to the charger of the battery I am pretty certain it would say. From a practical perspective,Ctek claim their products are short circuit and wrong polarity protected and will also detect if they're connected to a battery of the wrong generic voltage. That is pretty comprehensive protection, and suggests they're not going to be phased if some charge is depleted by using the battery.

Ctek do recommend the MXS 5.0 for 110Ah batteries, but that would still be a potential 120Ah charge current over 24 hours so they probably would be sufficient to more than maintain a caravan battery for the duration of any holiday.
 
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I don't have the Ctek MSX - 7 only the Lidi cheap copy, but wonder why if the MSX - 7 is OK to charge a battery while being used do they also market the XS - 7000?

If like the Lidi then when you connect it to the battery all it does is show the battery voltage, well in fact the Ctek MSX - 7 does not even do that, it has no display to show voltage, and if leads are wrong way around show a warning light.

It just sits there doing nothing, until the user confirms all OK and presses the mode button. Only then will it start to charge. The XS - 7000 however will start charging as soon as connected to battery and mains, it does not require the user to press any buttons.

I don't have the Ctek MSX - 7 I can only read the instructions, however the cheap Lidi charger is designed so if self discharge results in battery voltage dropping below 12.8 volt it will re-start charging at 0.8A. However nothing in the instructions makes me think if 0.8A is not enough it would return to 3A or 3.8A settings, although not tested.

Clearly using the battery will be unlikely to damage the charger, but if it will not auto return to a high amp charge rate, then in essence all you have is a 0.8A charger with the Lidi version, which is hardly likely to maintain a battery.

That does not mean I don't like the chargers, I think they are great, and carry one as an emergency charger, no big sweat in the evening when I turn on lights pressing the mode button to re-select 3.8A charge rate. However I would not continue using it, I would replace or repair the original charging system.

I have nothing against the Ctek XS - 25000 I am sure it is a really good charger, however I also think it is a rather expensive charger so would simply not want to pay that much. And the Ctek XS - 7000 is a bit too small for a caravan with all 12 volt lighting.
 

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