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Multi Charging Systems Connected To One Battery.


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#1 ericmark

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Posted 20 November 2013 - 01:46 AM

With the use of solar panels, and wind chargers the idea of having multi power sources all feeding same battery is something which is not so outrageous.

 

However with stage charging systems if a gust of wind raises the battery voltage for a short time it could reduce the charge from the solar panel as it erroneously makes it think the battery is charged so puts it in the last stage of float charging. We however can get controllers that take both wind charger and solar panel. HRDi.jpghowever these are limited to quite small outputs of around 10 amp so to connect for example a mains unit to them is not really an option. There are larger units. Some alternator charging systems are very complex AB1290_ProBat_alt-to-batt_charger_12v_90the unit shown will take two alternators and kids the alternators regulator that the battery still needs charging even when the battery has reached the float charge voltage however all well and good in a boat but hardly required in a caravan.

 

So with the exception of caravans with solar panels fitted from new where some form of stage charging is used how can we combine solar, wind and mains without one charging system upsetting the other?

 

More to the point how can it be done without costing an arm and a leg. The problems are that there are so many systems and clearly one size will not fit all. But to accept when on mains all other power sources are turned off it does seem a waste but again grid tie inverters on a caravan is not really an option.

 

Pre-stage chargers the float was higher at 13.8 volt but with stage chargers it drops down to around the 13.2 to 13.4 as float voltage clearly better for battery but only if the battery should be on float charge.

 

With small caravan not really worried if battery goes flat there are ways around the problem but big caravan with motor mover flat battery means can't get into back garden had to remove battery and charge before now and that's not fun with such a heavy battery.



#2 JTQ

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Posted 20 November 2013 - 07:27 AM

An interesting question but my initial reaction is one of doubting its optimised resolution would be cost effective.

 

With a multiple source charging system would you be particularly concerned that the individual regulators optimised the inputs at all times? For example if on EHU does it matter if you don't simultaneously get every last few extra amps the wind turbine or solar panel could give?

There is probably more an argument for optimising the solar and wind yields simultaneously as these are individually smaller inputs, but if throwing the cost to achieve it into the decision making then I doubt it. Let the solar do the bulk of the bright daytime work and the wind the night and dull daytime duties.

 

My two Morningstar solar controllers seem to operate independently on the very few occasions I have put out two panels; and as I recall things the maker claims they can operate independently though I suspect not both optimised.


Edited by JTQ, 20 November 2013 - 07:39 AM.


#3 BFM

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Posted 20 November 2013 - 07:38 AM

I agree with jtq. A battery is charged when it is charged, and each charging device senses when the voltage has reached what it 'considers' to be charged so its output drops. So if I am using solar and mains, one drops out before the other when the voltage is high enough. I conducted an experiment last summer to see how well charged the battery was just charged by the solar cell. I connected an intelligent charger up to see how much more it would add. It immediately switched to float maintenance mode, showing that the solar cell alone was doing a perfectly good job of keeping the battery adequately charged. If I reconnect the mains there is no drama; it too can measure the voltage so does nothing. I hypothesise that at night the mains charger will keep the 12v supplied and the battery charged, and during the day both solar and mains will do the same. I cannot see that adding or substituting a wind generator is going to be any more complicated.

 

I cannot see the point of a system that deliberately ignores the voltage and continues to try charging an already fully charged battery. This will simply boil off electrolyte.



#4 Paul_B

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Posted 20 November 2013 - 09:38 AM

I wouldn't think it likely that we with caravans would erect a wind turbine when on hook up, however like battery chargers there are good and poor in the controller world too,

JTQ has controllers which are from the top of the controller range and I would expect them to carry on charging the battery after the poorer type finished, they would fully charge the battery without any problems and much better than a lot of the so called staged mains chargers.

 

I've also put a few links on controllers in other posts but heres a good one, Why PWM



#5 ericmark

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Posted 20 November 2013 - 10:57 AM

The idea of stage charging is to cram into a battery as much power as one can in as short of time that you can. The first stage charger I came across was to charge a forklift battery here one had to fully charge the battery over night and only with a stage charger could this be done. With solar power it is reversed we want to charge over the day but same idea get as much power into battery in time available.

 

However the problem is with the forklift once on charger there was not any other input or output from the battery while on charge. But with our caravan we have both varying inputs and outputs from the battery at the same time. The standard way to move from bulk charge to float charge is to measure the current going into the battery but to do that the voltage must remain static and that’s not going to happen with a solar or wind charger. So another method has to be found. The following diagrams show how Sterling have tried to do this. See http://www.sterling-...tt-benefits.htm

 

voltage-curves-graph-sml.gifbank-current-curvegraph-sml.gif

So the idea is to switch off the charger for a few seconds and monitor the battery. But the only way this will work is if it's the only charger.

 

The only way I can see to charge to maximum is to have two batteries. If the charger charges one battery and the caravan uses the other battery then the old forklift charger idea would work. As the battery reaches float charge it would need to monitor the other battery and if not at float voltage swap batteries so one battery stage charged the other battery float charged batteries swapped either when stage charged battery about to go to float or float charged battery under 11 volt.

 

However with so many inputs and outputs from the single battery the only method we can use is the float charge and forget about stage chargers. This then raises the question what voltage to float at? We see this with cars and vans where instead of 13.2 volts a higher voltage is used with up to 14.2 volt selected. Its a compromise of course but floating at 13.8 volt will not really dry the battery out too much and will likely ensure it will not sulphate. 

 

So my thoughts are for caravans any smart charger are useless. When using the caravan they will not work and when in storage they are not required there is not a time constraint so not required. The idea of double battery is interesting but in real terms unlike the narrow boat there is a weight problem so can't really see it working.

 

So thoughts please. Although trained as an auto electrician then moved over to being a maintenance electrician then taking a degree in electrical and electronic engineering this is not so much technical, but more to do with how the caravan is used and stored I would therefore appreciate thoughts as I only really know how my caravans are used not how other peoples are used.



#6 ericmark

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Posted 20 November 2013 - 11:06 AM

As a PS yes read Paul B's link and it is interesting but it still has the same problem as any other smart system in that if you leave caravan for the day works great but use electric during the day and all those algorithms it talks about are messed up. Only if the charger can monitor how much power is used can it really work. Once a water pump, TV, radio, or any other item is switched on all this clever stuff is neutralised. 



#7 Paul_B

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Posted 20 November 2013 - 11:12 AM

The top solar controllers constantly monitor battery usage and temperature and charge accordingly  :)

 

They should be positioned close to the battery to allow this to work or use a remote sensor



#8 BFM

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Posted 20 November 2013 - 11:26 AM

My solar charger, which is fairly cheap and cheerful, cycles between charge and check several times a second.



#9 ericmark

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Posted 20 November 2013 - 03:43 PM

I have not reverse engineered a solar charger and have no intention of doing so one can only guess at what they do but unless it monitors drain on the battery it can't use battery voltage to trigger what it does as that voltage may be artificially low due to something be it TV, water pump, inverter as just can't see how they can work on a battery which is in use.

 

We had the same problem with the boat. A Waeco Mobitronic 925-012TC was fitted quite a good unit designed for up to 300 Ah of batteries with 25A output we were slightly over the ratting with 3 x 160 AH batteries on plugging into shore power it would pump in the 25A great but the current needed to drop to around 5 amp for it to go into float and watching TV would stop this happening. After set time either 4 or 8 hours according to dip switch settings it would time out and go to float but again the voltage had to drop to around 11.5 volt before it would restart cycle so it did over charge when one first plugged in if watching TV and it sat for 95% of the time in float charge mode even after the 3kW inverter had been used for washing machine which did discharge the batteries quite a bit.

 

Talking to other boat owners they were saying how batteries only lasted two years but these traction batteries should have been lasting at least 7 years used on milk floats we expected a 15 year life for same batteries. Clearly something very wrong but as to if over charging or under charging it was hard to tell. Charging voltage was selectable 13.8, 14.4 or 14.8 according to battery type but the main problem was unlike the milk float the battery was used and charged at the same time.

 

The solar controller is a very clever unit taking the power from the panel turning it into AC and transforming it up or down so as to present the panel with the best voltage to extract the most out of the panel that bit is very needed but with the output from the panel changing throughout the day unlike the mains charger using constant current and measuring volts on the battery is clearly not going to work. So as with the large alternator controllers it uses pulses and monitors battery volts off charge between pulses rather than on charge but just like the mains charger it relies on no load while charging. Items like the water pump don't run for long enough to be a problem but items like the TV can clearly result in over charging where the voltage is held low over a long time. I did find some controllers where the load was fed through the controller now with these yes it could work as the controller can compensate for the load as to if it does work is another question.

 

There is just one point solar panels do not have a massive output so even if they do over charge damage will be low. There is of course only one way to test. Measure battery state using a hydrometer or refraction meter and charge battery with different loads and see at what point it drops the charge rate. However how one would assess the charge rate with a mark/space ratio change I don't know? Clearly would need an oscilloscope and some very careful monitoring. In real terms if I was running a fleet of hire boats it may be worth the effort but for one caravan not a way. 

 

So as far as solar panels go we just have to have a reasonable sized battery which if it is over charged will likely survive and as far as main goes just no point in stage charging may as well just use a float charger and have done with it as in the main within 4 hours they are running at float voltage anyway.

 

However it is interesting to see how people are dealing with this and I must thank you all for your input. I have not seen battery temperature sensors for years. Ford tractors had them with a special ACR alternator but that is the only ones I have seen. To find used with solar panels is interesting but can't find who makes them. Links would be nice.


Edited by ericmark, 20 November 2013 - 03:47 PM.


#10 JTQ

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Posted 20 November 2013 - 04:31 PM

I don't buy into your statement that the idea of "stage" chargers "is to cram into a battery as much power as one can in as short of time that you can.".

If that was so then they would all be large capacity units peaking at what a battery could endure but they are not, some are 4.5%  of the AH rating.eg CTEK's MXS 5, a 5 amp unit for 110 Ah batteries.  Clearly there are stage chargers for rapid charging but that is by no means their sole function.

I suggest their purpose is to 100% charge a battery without overcharging it.

 

I also can't see an issue with a smart charger on an intermittently loaded battery either. As the load pulls down the voltage the smart charger, up to its current limits, will simply compensate with a contributory current to satisfy that load. Then after the event will reassess its position and take the right action. Schaudt, probably as good a maker of leisure vehicle chargers/controllers our side of the Atlantic as you could find, employed smart technology in building my Hymer's charger. I feel they would have thought out the logic and the benefits of them before building these very expensive units. 

 

On battery temperature sensors, my Morningstar solar controllers have a little bead sensor on the unit and these units have provision for remote sensing where they physically can't be positioned to sense battery compartment temperature themselves. I presume Morningstar resellers could provide you a remote sensor.


Edited by JTQ, 20 November 2013 - 04:40 PM.


#11 ericmark

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Posted 20 November 2013 - 05:19 PM

The more I read about "Smart" chargers the less they seem suitable for caravan use.

 

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 can't see how any of the smart chargers can comply. With pulse then voltage ripple exceeds 1.2 volt and with stage the voltage exceeds 14 volt either way it knocks them in the head for caravan use if the caravan is to comply with BS7671:2008. Using a CTEK to charge a motorcycle, wheelchair or golf trolley battery they are clearly very good and once you have one why not use it for other batteries but as to buying one with the idea of charging a caravan battery which to comply with regulations must be at least 40 AH not so sure really big enough.



#12 tictag

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Posted 20 November 2013 - 06:18 PM

An interesting challenge. It can’t be beyond the wit of man (or capitalism) to solve this – we’ve put robots on Mars!

 

The nub of the problem seems to be around integrating different supplies and voltages: maybe 14.4V from the towing electrics, 13.8V from a ‘van’s EHU power supply, something else from solar, generator, hydrogen fuel cell etc. Complicate this by consuming power at varying rates lowering any measured voltage. Lead-acid chemistry doesn’t help either because whilst a higher voltage is good sometimes, prolonged use can result in damage and, furthermore, there’s only a small couple of volts margin between a fully charged and fully discharged battery.

 

I wonder what would happen if we binned measuring battery voltage as an indicator of charge and instead went for specific gravity or pH? Stage charging from potentially multiple sources could be switched based on charge irrespective of terminal voltage or load on the battery.



#13 tictag

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Posted 20 November 2013 - 06:29 PM

I can't see how any of the smart chargers can comply. With pulse then voltage ripple exceeds 1.2 volt and with stage the voltage exceeds 14 volt either way it knocks them in the head for caravan use if the caravan is to comply with BS7671:2008.

 

I wonder if a pulse charging supply is actually considered 'variable DC' ;)



#14 tictag

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Posted 20 November 2013 - 06:59 PM

An integrated charger automatically switching multiple inputs based on set criteria (e.g. sufficient supply voltage, supply priority, mode of operation, time etc) would be something I’d buy.

 

Priority 1: Renewables. If the solar panels / wind turbine have a strong output, switch them in through the integrated MPPT controller.

Priority 2 EHU/Generator. No renewables but EHU? Automatically switch it in through the inbuilt dc power supply.

Priority 3 Towing Electrics. Towing electrics available? Automatically switch in directly to the battery via the habitation relay.

 

On the control panel you could manually override the automatic input source and a ‘boost’ button that switches the EHU/Generator power supply from float supply to smart charger that took additional inputs from my specific gravity sensor ;) and a current sensor to compensate for ancillary use.



#15 ericmark

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Posted 22 November 2013 - 09:52 PM

I do like the idea of a boost button so as standard it is float charged but user can select boost when time to charge is important. It would be rather easy to do charge current could hold on the boost latch and auto drop out as set current.

 

I have questioned the current normally set at 10% so with a 25A charger it will drop to float once charge current drops to 2.5A however in real terms it's the battery not the charger which should set the level so with a 110AH battery around 3A but with 40AH battery 1A I think the chargers should have dip switches to set charger to suit battery.

 

The priority system is all well and good where all three can provide the same power but if you have solar panels as a way to extend time when on a site with no huck-up then where there is huck-up then that would be priority one. Solar panels are heavy and the idea of having a roof full of solar panels which would then increase fuel consumption while towing does not really make sense it's a caravan not a narrow boat.

 

Towing power is also questionable with a car using standard split charging the solar panels may produce more than the car by time volt drop is considered. OK with a 12v to 12 v inverter like used to charge bow thruster batteries it will work far better than solar panels but how many people use them.

 

The priority would need to be dip switch controlled as set with the solar panel and car split charging type taken into consideration.

 

However back to the main problem who would decide priorities? I am sure that with a float charger both car and charger can supply the same battery together only when a stage charger is used is there a problem where back feed to the car could cause a problem with the engine management detecting over charging and taking what it thinks is appropriate action.

 

The real problem is the solar panels as to date I have not found any solar panel controller with simple float charge so as soon as the car is connected the solar panel must be switched off. So question is if the solar panel is integral with the caravan is there any point in charging from the car? Far safer to just have no connection to car so can't upset car engine management.

 

Clearly with a proper 12v to 12v inverter there can be no back feed to the car so you could use bow thruster type inverter but unless one is a real heavy user of 12 volt power this does seem a bit of over kill.

 

I also saw it as an interesting challenge and was surprised there were no reasonable priced commercial units. Talking to a fellow radio ham and he tells me he has a supplier of 3A anything in (zero to 24 volt) to 12 volt out switch mode units which are quite cheap but 3A is really a bit on small size. Next time I talk to him I must ask about using multi units as this would work OK with 6A that would be plenty. Three hours at 6A = 18AH and that should be enough to work water pump for a good few days and likely more than standard split charging would pump in.

 

Years ago I had a fleet of Library vehicles each one towing a trailer with batteries in trailer for lights. They had split charging but although on plug in we would measure a healthy 10 amp charge within 15 minutes this was down to 3 amp at that time 1970's there were no switch mode units to charge batteries and all attempts failed to put in enough charge. The only method that worked was to take a three phase tapping from the alternator and take it to two blocking diodes (one input unused) and from there to trailer and moving the tapping on RB440 CAV regulator to Hi. OK with this started at 30A (from 60A alternator) and dropped to 10 amp after 15 minutes which worked of sorts. However this was a steep learning curve and I realised how poor most split charging systems were. With the first boats I worked on also had problems the cables from the blocking diodes to batteries had to be exactly same length or it would burn out blocking diodes. Latter boat used two alternators one for each battery and still latter used the special Sterling inverter and today narrow boats can be charging aux batteries at 120A on first starting engine. But our caravans are still split charged today in the same way as they were in the 1970's in the main so in real terms very little charge gets into the battery.

 

To get a good charge from towing vehicle some thing like this $%28KGrHqUOKooE5j8Zw+jHBO,koiK2+g~~60_35 is required the plugs complying with BS AU 149a and BS AU 177a or BS EN ISO 11446 are really not man enough for 50A charge and although used on wagons I don't want a connector like that on my car thank you so with an integral solar panel on caravan I would not even try to charge from car.

 






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