# Help!! BUS 24v-12v leisure battery charging??



## Barnesnz (Jul 18, 2010)

Hi all,

my name is sean barnett im a kiwi lad travelling around europe this summer with 7 other mates from home and im in spain now and having a few problems that i need to overcome if someone can explain

firstly now we are in a 1999 mercedes diesel 614d bus 4,200cc, i have installed a leisure battery setup off the 24v system, let me tell you what i have

a 220a/h leisure battery connected off the 1st of the 2 12v starter batterys  with a manual switch to disconnect when not driving, ive just bonded the earth of the leisure to the chasis rather than the battery, the starter batterys are connected in series to give 24v. off the leisure i have some 12v sounds being a 1600w amp 395w rms, 4x 6x9's. Then i have a 600w 1000w peak true sine wave inverter, off that I have 230v appliances of course, those being a 70w fridge, a 140w icemaker and 120w off fans.

Now what has happened so far is the ice maker and fridge when tryed to start would drop the inverter below 10v and would cut out, i thought the leisure battery needed more time to charge however not the case while in france we were driving along and the sounds started cutting out and the inverter with just the fans running, then the bus started cutting out then died and smelt a elec burning smell, alternator gone. Did I overload it? we now have a new 1 fitted and the leisure battery is still not charging, i need it to as am in europe for 3 months.

Now what i have since found out is that u cant charge 12v batterys or use 12v appliances of a 24v system by coming of the 1st battery?? ive heard that you need to get a 24v-12v dropper transformer, if this is the best way what type, Size etc?? or if there is a better suggestion out there, now also is my load to big in this case and if I get the leisure battery charging correctly and start putting full load on the alternator while driving do i risk frying it again, should i just get rid off the icemaker maybe??, possibly the amp too to reduce the load

ANY HELP ON THIS WOULD BE SO VERY MUCH APPRECIATED AS YOU CAN IMAGINE NOW ON THE ROAD TRYING TO FIX IT IS A PAIN ON MY TRIP, SHAME ONLY GOT THE BUS BACK 2 DAYS BEFORE LEAVING LONDON SO TEETHING PROBLEMS HAD TO BE FOUND OUT THE HARD WAY ON THE ROAD!!

HOPE SOMEONE OUT THER CAN HELP OR CAN GIVE ME A CONTACT ANYWRE THAT COULD EXPLAIN WHAT I NEED TO DO

Many thanks,
Sean Barnett and the rest of the boys


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## vwalan (Jul 18, 2010)

speak to an auto electric outlet or speak to gordon equipments limited 01255 555200 they do durite auto electical parts . as well as solar i use a durite24volt to 12 volt 20amp split charger part no.0-852-50  this charges a 12 volt batterywhile you are driving .but gives preferance to the 24 volt system . it as a float facility and works a treat .not cheap .but to me its the proper way to charge a 12 volt batt on a 24 v system . i then power other 12 batt from that one. i always have a fully charged 12v batt even though my truck is 12v . i keep a 12v under the rear passenger seat . ideal for jump starting cars etc.


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## Byronic (Jul 18, 2010)

your starter batteries are in SERIES not parallel to give 24v. A bit involved to carry out a proper job on the road but if you purchased another 12v lieisure battery then you could connect them in series, and then in turn connect them in series to your starters. Then take all your 12v requirements off 1 of the leisure batteries only.Every time you stop the engine and are using 12v appliances you will have to disconnect the 2 pairs of batts.( pull the leads off) or run the risk of flattening all 4. A 24v relay would be better way of disconnecting or heavy duty battery isolater switch. A 24v say 20amp dropper might be difficult to find, but in Spanish truck stops 3amp and 5amp droppers are often found you could join a few together.


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## vwalan (Jul 18, 2010)

durite do all thedroppers as well but in practicehaving had friends use droppers i find the proper charger much better. the dropper get very hot if used for charging and dont have the magic switching facility.


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## Tony Lee (Jul 19, 2010)

(Shakes head in disbelief!!!)

First things first - get rid of the icemaker. It is drawing 15 amps when running. Leave it until you are on 240V hookup.

Turn the volume down on the sound system.

Don't keep opening the fridge to get the beer out. Running off the inverter it will be dragging 10 amps out of the battery.

120W fans - another 15Amps

Disco ball lights, Jacuzzi pump - another ??? amps

A 600W inverter will be pushing to reliably start a 240V compressor so unless the battery is fully charged, the inverter may switch off due to inrush currents.

Best and quickest way out of your problem is to buy a 40amp 24V to 12V battery charger and keep the engine and habitation systems completely separate.  Big money though and it needs to be properly installed. Heavy cabling and fuses. It still won't provide enough power to run what you need to run if you want to camp out without hookups but at least it will save your engine electrical system PROVIDED the alternator will handle the load on an almost continuous basis.

And change your lifestyle

8 blokes in a motorhome
plus visitors


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## Barnesnz (Jul 19, 2010)

Thank u all very much for the help & advice I was definetly thinking the fridge & icemaker wer a bit much so def going to resort to those on campsite hook up. My 1 question is now if I get another leisure battery & connect it in series with my existing, wouldn't I then have to connect those to in PARALLEL with my starters for charging not series??? Then take my 12v appliances being sounds & inverter of the 1st battery? Also can I just use a cheaper car battery instead of buying another leisure? Will that do or will that then drain the leisure faster?? Wen parked up


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## Byronic (Jul 19, 2010)

yes of course the two sets of batts. would have to be connected in parallel to enable charging at 24v. perhaps I didn't make that clear in my post.Its best to match battery types and also amperages but I presume you're just after emergency fix? If so mismatched batts would work but you can't expect them to live as long. One advantage of having conventional batts is that in emergency you can swap them over with the starters, so don't buy too large as they won't fit under seat compartment. I thought kiws could fix anything with no.8 gauge fencing wire!!!


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## Tony Lee (Jul 19, 2010)

Barnesnz said:


> Thank u all very much for the help & advice I was definetly thinking the fridge & icemaker wer a bit much so def going to resort to those on campsite hook up. My 1 question is now if I get another leisure battery & connect it in series with my existing, wouldn't I then have to connect those to in PARALLEL with my starters for charging not series???
> YES
> Then take my 12v appliances being sounds & inverter of the 1st battery?
> NO, need to swap the two leisure batteries so they both get equal use or reconnect them in parallel while you are parked up
> ...



Doesn't matter if you connect two leisure batteries in series and then connect them in parallel with the starting batteries, you still can't drag all the 12v power form just one of those leisure batteries.
You would need to keep messing around drawing 12v power from each of the leisure batteries equally so they end up with roughly the same amount of charge when you reconnect them in series to connect in parallel with your starting batteries to charge them again.
A lot of messing around and the constant connecting and reconnecting of the batteries is very likely to result in something being connected the wrong way around.


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## Byronic (Jul 19, 2010)

ola Tony, all very true but what do you suggest as a tempary fix bearing in mind vans location other than finding local autoelectrician. (the leisure batts would tend to equalise out if left connected just need el cheapo isolator switch between both banks to prevent starters from being inadvertately drained)


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## Tony Lee (Jul 19, 2010)

Byronic said:


> ola Tony, all very true but what do you suggest as a tempary fix bearing in mind vans location other than finding local autoelectrician. (the leisure batts would tend to equalise out if left connected just need el cheapo isolator switch between both banks to prevent starters from being inadvertately drained)



--------------------------------------------

I understand your predicament. All that nice gear and nothing to power it with

Taking 12V power off the bottom battery in a series string is (sort of) OK if it is just a very small load. If you take all the current out of the bottom battery, you end up with the top battery totally full and the bottom battery empty. Trouble comes when you try to charge because a completely full battery doesn't take kindly to having lots of current pushed through it. It resists the current flow because there is no more chemical reaction left to allow the electrons through and any current you can get to flow just causes the electrolyte to "boil" off due to excessive gassing (or actual boiling in some cases).
Trouble is the bottom battery needs the current to get charged and it needs it at a certain rate and for a certain time. You can get the current to flow but only at the expense of wrecking the top battery.  Alternators hate such 'weird" loads and the other series string (starter batteries) won't like it either.

End result is if this is allowed to happen (maybe even once???) is the top battery way overcharged and the bottom battery way undercharged and an alternator that may well chuck a hissy-fit just to confuse the issue.. They can't equalise when off charge and the isolator opened either because the top battery is just sitting there with the positive terminal disconnected. Only way to equalise them is to completely disconnect the series string and move the top battery down (not literally) and put it in parallel with the bottom battery.

You have some pretty serious loads and running even just the fridge will seriously deplete the bottom battery over a day and once that happens, you will not be able to recover that battery by charging in series. You may get away with it for a while if you make sure you check water level but there is also the chance that having two series strings in parallel, one of which is seriously unbalanced, may cause problems with the good series string used for the engine.

Another poster suggested the solution and I also referred to it - but it is a real pain. That is charging the leisure batteries in series as you propose, but then completely disconnecting them from the engine batteries and reconfiguring them in parallel to deliver 12V equally from both batteries. Then reconnecting them in series to charge.  A real pain. You could do it conveniently using an isolator and jump-starter leads, but with such a temporary arrangement there is a real danger of one of the leads slipping off and shorting something to earth


A vanner equaliser is a device that works in your situation. It basically sits across the top battery and monitors the bottom battery voltage. If the bottom battery is dragged down, it takes charge from the top battery and pumps it into the bottom battery so they are always equally charged. sort of a special DC to DC charger. There are other methods as well but they all get expensive and do require a bit of engineering that may not be available in your area.

Back to your case.

If you are happy to minimise your power consumption and maybe swap the upper and lower  batteries  around every two or three days, you will be able to continue. 
The gloom and doom I am talking about doesn't happen with just one episode, but if one battery is dead flat and the other completely full, the rot will set in pretty quickly. Your alternator blowup and battery problems are likely the direct result and in the new setup you have 4 batteries and an alternator instead of two batteries and an alternator. Could get expensive..

Another solution you may be able to get going is to buy a 24V to 12V converter. A 20 amp model isn't all that expensive and you might be able to get one even larger. Then you could parallel charge the two sets of batteries via the isolating switch as you propose. The 24-12 converter would then sit across both leisure batteries and supply all your 12V loads.  Trouble is, while it will give you lighting, pumps and a bit of other gear  - whatever adds up to the current rating of the converter - It will not supply the bigger loads. Your sound system played at normal volume will be OK but supplying 600 watts to the inverter (50 amps) will not be possible.  If 20 amp converters are the biggest available, you could use two or three of them and feed separate parts of the 12V installation from each one. They are readily available and in Oz, even the auto-accessory shops sometimes sell them. Electronic component shops may also have them

I use this method on my 24V MCI. Most of my load is 24V (big inverter, pumps and such) but some is just not available in 24V - radio, stove ignitor, some lights - so they are fed via the converter.


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## Tony Lee (Jul 19, 2010)

Oh, of course a 24V 600W 240V inverter and a 20A 24V to 12V DC-DC converter would solve all of your problems - except for the sound system running at more than half volume, but I guess you could live with that.

Drawback is that 24V inverters may be hard to get.


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## Byronic (Jul 20, 2010)

I may be mistaken but it appears that you' re addressing your resolutions at myself but it's the KIWI lads that have the predicament!!!
I too have a van with 24v "main" circuitry and 12v "caravan" circuitry. My original electrical setup comprised a 24v/12v X 20 amp dropper. The dropper ran warm of course through ineffiency and eventually burnt out (I know.... it should have been 30 amps)
I then devised my own "bespoke" system viz.
a diagram is worth a 1000 words, but here goes
2x12v starter batteries
2x12v leisure batteries
60amp changeover 4 pole switch (1 pole as dash light indicator).
Briefly.. when engine is running and sw. is in position 1, batteries are all being charged, fridge is energised from 1 leisure via 24v relay . If sw. is in position 2 batteries are isolated. 12v supply is taken off same leisure battery. 2x80w solar panels charge via same battery.  I have tested with voltmeter and equalsation has been reasonable. I've used this system for 15 years the first batteries lasted 11 years. 
Incidently why no NZ on your itinery?


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## Tony Lee (Jul 20, 2010)

Yes, your setup has a good chance of success because you are using the top leisure battery as a "dummy" and using the bottom "working" battery for your modest loads AND using the solar panels to charge that same working bottom battery. At the end of the day - hopefully - the solar has done its job and when you hit the switch to connect to the engine charging system, the top dummy battery and the bottom working battery are both similarly charged.
Regardless of your success, dragging any load from just one of a series string is a chancy business.

The OPs case is vastly different. They have *humongous* 12V loads that would quickly flatten the working battery and no way of charging 12V except via a "sleeper" battery that is fully charged. They started out with the top battery connected to two bottom batteries, one of which - the leisure battery - would be flat when the manual switch was closed. That destroyed the system. Now they have two series strings, one of which is standard, the other consists of a sleeper battery and a flat working battery and they can't charge the working battery.

Lightening the electrical load considerably and an occasional swapping of the sleeper and working batteries would probably allow them to continue an albeit more subdued lifestyle.

If I had the problem on the side of the road, I would just use jumper cables to manually reconfigure the two leisure batteries from a series string for charging to a parallel setup for supplying the load - but this would not provide 12V while on the move (no music) - and is a bit too likely to result in batteries being connected backwards or leads falling off for me to recommend it to others.


NZ is not yet on my itinerary because it can safely wait until I'm too old and doddery to drive heavy RVs and then I can join an organised tour and get whisked around in a day or two of boring comfort.


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## Byronic (Jul 21, 2010)

I agree with your comments and certainly my loads on the batteriies are light compared to the o.p. I do have the advantages of low effeciency loss, no parts likely to overheat very few parts likely to malfunction (the changeover switch has millions of duty cycles) and simplicity so even I can fix,  which accounts for the main reason I cling on to a 20 year old MB 709d.
It pains me to hear of folks only regarding NZ as an adjunct to OZ, it 's by far the more interesting of the two countries!!


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## Tony Lee (Jul 21, 2010)

20 year old MB 709d.

Pretty young. My MCI is 32 years old and the OKA is 16 and not a bit of electronics in either of them - well, apart from all the stuff I've added of course, but none of that is mission critical. Having been stranded in the middle of Morocco because an arcing battery connection (hidden under the driver's seat) caused the system to scramble the security code, I know some of the disadvantages of modern EMSs

NZ really is on our list. Betty backpacked it a long long time ago and would also like to go back, but there are lots of places that are more difficult for us to get to - such as South America - and which really do require a higher level of fitness and good health and commitment than does NZ. NZ I can do in a wheelchair at a day's notice and no planning. Patagonia would be difficult.


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## Barnesnz (Jul 22, 2010)

First of all thanks very much for all the input, we are still in spain and weighing up what to do. Let me run u past what I was thinking.

Getting another 12v leisure battery of the same size connecting it in series with the other then those 2 in parallel with the starters for charging. Then buying a new 24v unsure what size really inverter. Doing away with the ice maker unless on site power. just running the fans and fridge whilst driving and while parked up without power for as long as the leisures permit?? Then getting rid of the amp and connecting the headunit to the bottom battery of the starters and connecting my speakers to the headunit, not as loud but cuts out the amp power usage. Or is it fine to stilll run the headunit and speakers from the bottom battery of the leisure setup?? And of course keep the 2 pole switch I have between the starters and the leisures.

Any advice on that thought would be great, we dont spending a little bit. Realising it will probably be quite a bit 

Many thanks
Sean Barnett


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## Byronic (Jul 22, 2010)

I guess your going to run most appliances off the inverter at 240v? The 24v inverter size needed would depend on the sum Wattage of all the items you are likely to be using at one time, plus a safety margin say 50%. Most inverters can take twice the max load at startup for a very short time. A reasonable spec. wouldbe;
500 WATTS OUTPUT with 1000WATT PEAK
SQUARE WAVE TYPE..... MUCH CHEAPER THAN TRUE SINE WAVE ( I run laptops, digatal TV with no probs off SQUARE WAVE)
Make sure cables from battery to inverter are sufficent cross section double up to make sure, usually inverter comes supplied with leads. 
As I've mentioned before Spanish truck fuel stops often stock 24v inverters camping type shops generally stick with 12v. 
Don't forget the battery isolator switch needs to be fairly beefy. I think Carrefour sell a 200 or 300 amp one cheap.


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## Byronic (Jul 22, 2010)

Soon as I posted my previous thread I realised that perhaps I should have interpretated your "24v inverter" as 24v-12v converter or voltage dropper.
Anyway the same princples apply, add up all the Wattages etc.and allow a margin. I reckon 20 amps to be minimum, they get expensive and hard to find in Spain if larger capacity. You can always connect them in parallel if only small ones available. NorAuto car accessory stores (in larger shopping complexes) have el cheapo ones about 5 amps, at least they did last year. If you're heading for Portugal FRANK WAGNER in ALJEZUR (Western Algarve) runs an alternative energy business, he stocks just about everything required.


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## Barnesnz (Jul 22, 2010)

Sounds all good then mate. Only going to run 70w fridge & 120w of fan all at 230v & only use icemaker on site power. What about the stereo? Come off the bottom of the leisure batterys or the starter batterys remembering I'm getting rid off the amp now. I'm thinking a 1500w inverter to give me plenty. Just matter of finding 1 in Spain. Will the alternator b ok with just yapping the headunit off the bottom battery as it is a small load? 

Thanks again for all ur speedy replys

Sean Barnett


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## vwalan (Jul 22, 2010)

you could keep your eyes open for a dutch man called bert he drives a daf truck with a drag trailer behind .he sells panelsinverters ,converters droppers etc .good man to talk to about these types of things. he,s usually about on the tourist way.


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## Barnesnz (Jul 22, 2010)

Also would have to go pure sine wave type in order to start fridge & fans easily. Correct??


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## Byronic (Jul 22, 2010)

You're talking almost domestic scale elecrical draw 200Watts is approx. 16Amps. Plus your "lighter loads" mama mia!!!! 
The fridge will be on say 50% duty cycle and the fan... who knows, but with  a nominal say 200Amps of battery power available and the inverter maybe 90% efficient with  its own cooling fan drawing power  then a couple of nights would be all you could expect.
The square wave inverters are usually a modified sine wave and will run your gear but you may need to quickly switch on off on....
As Alan in previous post suggests keep your eyes peeled for Bert the Dutchman his Daf truck is "very" distinctive when encamped it rises to 2 storeys and sides slideout, he retails all the requisite electrical gear.For a price he'll fit as well. There's always Frank Wagner on the Algarve as previus post


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## Byronic (Jul 22, 2010)

Assumed fridge to be 240v domestic compressor type, but if 3 way camping type then the boiler is on all the time. Even more power used.


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## Tony Lee (Jul 22, 2010)

Barnesnz said:


> Sounds all good then mate. Only going to run 70w fridge & 120w of fan all at 230v & only use icemaker on site power. What about the stereo? Come off the bottom of the leisure batterys or the starter batterys remembering I'm getting rid off the amp now. I'm thinking a 1500w inverter to give me plenty. Just matter of finding 1 in Spain. Will the alternator b ok with just yapping the headunit off the bottom battery as it is a small load?
> 
> Thanks again for all ur speedy replys
> 
> Sean Barnett




If you can find the 24VDC to 220VAC inverter, you will probably be able to also find a 24VDC to 12VDC converter at the same shop. That would then solve all your problems because all loads would be supplied from 24V and the batteries and alternator will thank you for it. If you get a 25Amp one, you might even be able to continue the process of damaging your hearing by using the main amplifier. If money is no object, get two - one for lights, pumps and other normal 12V loads and one for the music system.


(The DC - DC converters are cheaper than the inverters)


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## Tony Lee (Jul 22, 2010)

Barnesnz said:


> Also would have to go pure sine wave type in order to start fridge & fans easily. Correct??



Maybe not but it is true that any motor will run better from sinewave. Sometimes they run hotter and noisier off square wave but there is no easy way to predict.


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