# split charge system



## flashingblade (Nov 2, 2008)

hi there. i know the basics but need some advice. i'm fitting a split charge system. i realise that the greater need of a battery, the greater the draw on the charging system (sorted by the regulator ). 
 suppose the van battery is full and the leisure batt is low, can i pressume it will draw as much as the altenator can supply ?
if so, this figure, in amps,  will be the rating of the altenator so i will need a relay with a value more than the altenator output. am i correct ?


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## lenny (Nov 2, 2008)

flashingblade said:


> hi there. i know the basics but need some advice. i'm fitting a split charge system. i realise that the greater need of a battery, the greater the draw on the charging system (sorted by the regulator ).
> suppose the van battery is full and the leisure batt is low, can i pressume it will draw as much as the altenator can supply ?
> if so, this figure, in amps,  will be the rating of the altenator so i will need a relay with a value more than the altenator output. am i correct ?



It,s no good asking me,Geoff


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## Deleted member 775 (Nov 2, 2008)

dont quote me as gospel as i know just enough on electrics to get by , but i think the relay will handle all charging needs to both batts automatically choosing which battery needs the most charge at the time. as for the amperage i would assume that a split charge relay suitable for a motor-home  will be able to handle whatever amperage your alternator pushes out, hope this is of some use to you. but if not i am sure some of our members who have self built will put you right .


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## jimmnlizz (Nov 2, 2008)

Hi Jeff, if you had mentioned this at Hayfield,  today, I could have shown you our set up on "Kwackers".  This is the web address where I bought it:-

http://www.brocott.co.uk/intelligent-self-switching-split-charge-relay-kit-12v-30amp-p-848.html?

I fitted one of these, a job that did not involve any crawling about,  back in August and it has done us proud with no foul ups at all.  There are no connections to your alternator and takes about ten mins to fit.  My sister said it could not be any good as it was a tenth of the price of the one that her husband fitted to their VW.   HA, I can buy another IF this goes wrong after the guarantee runs out!!!    JIM.


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## flashingblade (Nov 2, 2008)

*brocott*

hi jim. i have seen the brocott systems on ebay but i'm just trying to decide what rating of relay to buy, from an un-biased point of view. i don't want to buy a relay that could get frazzled by being asked to handle too many amps. it all starts to get a bit technical but not beyond me, i think!!
cheers


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## gary a (Nov 2, 2008)

*Split charge*

Hi am autospark,,mandrake is right ,,work away no probs,,,


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## messenger 2.5td (Nov 2, 2008)

*Split charging system*

Hi flashingblade Jims system sounds the easiest solution i remember getting the tour of his van back in august,Andy.


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## messenger 2.5td (Nov 2, 2008)

*Split charging system*

Going of the thread slightly anyone know how a second leisure battery can be connected to the first does it need a second relay,can they be connected positive to positive?Andy


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## Belgian (Nov 2, 2008)

flashingblade said:


> hi there. i know the basics but need some advice. i'm fitting a split charge system. i realise that the greater need of a battery, the greater the draw on the charging system (sorted by the regulator ).
> suppose the van battery is full and the leisure batt is low, can i pressume it will draw as much as the altenator can supply ?
> if so, this figure, in amps,  will be the rating of the altenator so i will need a relay with a value more than the altenator output. am i correct ?


A 'normal' relay will do,(should be good to handle 10A for a short while) The alternator gives a more or less steady Amps; charges first the startbatt. and then via the relay the leisure one. A flat battery draws only what the alternator can supply, no more.


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## Belgian (Nov 2, 2008)

messenger 2.5td said:


> Going of the thread slightly anyone know how a second leisure battery can be connected to the first does it need a second relay,can they be connected positive to positive?Andy



Best is, if the second battery is not of the same make, same output, same condition, to put a relay between them. Otherwise the weaker one will be sucking the other. A normal 3-point relay should do. You should connect the batteries parallel (+to+, -to-), not in serie:  you got 24V then


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## gary a (Nov 2, 2008)

*2nd batt*

Better fittin 2nd relay andy,,,,,,,


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## Deleted member 775 (Nov 2, 2008)

messenger 2.5td said:


> Going of the thread slightly anyone know how a second leisure battery can be connected to the first does it need a second relay,can they be connected positive to positive?Andy



this may help http://www.batteryminders.com/batterycharger/charging_multi_batteries.php  easier this way than try and rack my brains at my age


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## flashingblade (Nov 2, 2008)

*amps*

hi all. my dilema is - my altenator (without going outside in the cold ) will be rated around the 50-70 amps range. 
should the leisure battery flatten, would it draw all those amps until charged ? 
 if so, would i need a relay that could handle 70 amps ?


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## jimmnlizz (Nov 2, 2008)

I don't think so.  The Brocotts one is rated at 30amps but charges your starter battery first.  When that reaches 13.8 volts it switches over to your leisure battery until that reaches 13.8,  unless you are traveling at night, in the rain and its cold!  When your main van battery gets down to 12.4 volts it switches back from leisure to main and starts again.  So you can see, that it is continually switching back and forth between the batteries keeping them both charged, but concentrating on the main van battery as the priority.    JIM.


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## Deleted member 207 (Nov 3, 2008)

flashingblade said:


> hi all. my dilema is - my altenator (without going outside in the cold ) will be rated around the 50-70 amps range.
> should the leisure battery flatten, would it draw all those amps until charged ?
> if so, would i need a relay that could handle 70 amps ?



No, the battery wont (should n't) draw 70amps to recharge, but the leisure battery positive cable has to be fed off the starter battery positive cable via the relay, the relay is triggered by the + signal terminal on the alternator (same one as the Alt light on the dash uses). This is so the starter battery will float at 12V-14V and "pass on" any excess to the leisure battery. 

If you directly connect the leisure battery to the alternator (and use a relay to isolate the battery when the engine is not running), then its possible for the current draw to exceed a small 25Amp relay if you have other 12V items running at the same time as recharging the battery. Bosch supply a 75Amp relay, which should allow you to power a small town!! 

Usually wiring is the weaker part of the system, if you draw 75Amps then you need reasonably large cables - battery to starter motor sized.


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## Tony Lee (Nov 3, 2008)

Need to make sure that there is no way that the battery fed by that relay can be used to start the engine through the relay because the resulting current will be quite high.


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## jimmnlizz (Nov 3, 2008)

Hi Jeff, I told you on Saturday about the memory!!  I forgot to mention, in my previous post, that I thought that I had wired it up correctly, only two wires, what could go wrong??  We went up to Glentress Forest, for the northern meet, touring on the way.  the battery lasted a full 5 days..... so we had an early night!  The following day I found an earth terminal on the relay and decided to risk it and connect it up.  It worked a treat! From being totally flat to being fully charged, checked on a meter, took half an hour running down through the woods and onto the carpark in Peebles, and it was 13.6 volts. The alternator had managed to recharge the main battery and the leisure battery in half an hour!  So far so good, its been great ever since.  Fingers XXXXed!!!!  Just as a by the way, it is impossible for this set up to be able to start the engine. You would have to fit an extra battery cable, with a cut off switch in it, if you ever wanted to jump start the engine off the leisure battery. If you go this route don't forget to put same size earth cable in as well!!  JIM.


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## Timber (Nov 3, 2008)

*Split charge system*

With the basic split charge system the +ve terminal of the main and leisure batteries are connected together through a relay.  The relay is connected to the ignition circiut and closes when the ignition is switched on.  When the starter is activated it takes a very large current, causing the voltage in the ignition system to drop, and the relay will probably disconnect.  To make sure this happens, the earth connection on the relay can be connecter to the positive terminal on the starter motor. The starter motor have a very low resistance and will act as the earth.  When the starter is activated the "earth" on the relay rises to 12 volt and the relay drops out. Heavy duty cable should be used.

If the habitation battery is flat, some current may be taken from the starter battery until tyhe system stabilises.

It was the practice to fit fuses to the relay activating supply, but not to to fit one between the two batteries.  Every connection adds resistance to the circuit, and with high charging currents this can mean that the 2nd. battery never gets fully charged. Should you decide to fit one, a 50 amp fuse is needed to handle the initial surge of current, smaller fuses will have a short life. The fuse should be wired as close to the main battery as possible. It is essential to ensure that the wiring between the two batteries cannot under any circumstances touch the chassis.  Check that the insulation cannot be broken or scuffed.


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## jimmnlizz (Nov 3, 2008)

Unless, of course,  you have one of these:-  Intelligent Self Switching Split Charge Relay Kit 12V / 30Amp.   

http://www.brocott.co.uk/intelligent-self-switching-split-charge-relay-kit-12v-30amp-p-848.html?

     JIM.


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## flashingblade (Nov 3, 2008)

*sorted*

hi all. many thanks for all your advice, especially from Roger. i have spoken to a man who knows and in theory, a small (20/30amp) relay or the thin wiring could be overloaded, possibly resulting in a fire. i hope you all have your systems fused.  i am going down the route of a large relay and some thick wiring. over-engineering rules. i'm not knocking anyone else's system, just playing safe.
 if it burns, i will post the pictures !!


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## Tony Lee (Nov 4, 2008)

> The alternator had managed to recharge the main battery and the leisure battery in half an hour!



If that was after using the battery for 5 days, I doubt whether it would be anywhere near charged. 13.6V doesn't mean fully charged unless it first got to about 14.4V and then dropped back to float. Gel or AGM batteries are a little different, but still take a while to fully charge.



> i am going down the route of a large relay and some thick wiring. over-engineering rules. i


This is unlikely to be overengineering - merely good engineering. Using smallish cable for battery interconnects or supplying a three-way fridge results in excessive voltage drop (meaning anything over 0.5V) and this seriously reduces the efficiency of the fridge and means the battery will take hours to get anywhere near fully charged - or rather as fully charged as possible with a normal alternator and normal flooded-cell batteries.


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## Belgian (Nov 4, 2008)

*Golden advice !*



Tony Lee said:


> This is unlikely to be overengineering - merely good engineering. Using smallish cable for battery interconnects or supplying a three-way fridge results in excessive voltage drop (meaning anything over 0.5V) and this seriously reduces the efficiency of the fridge and means the battery will take hours to get anywhere near fully charged - or rather as fully charged as possible with a normal alternator and normal flooded-cell batteries.


This is a golden advice Tony Lee, thanks


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## wildman (Nov 5, 2008)

messenger 2.5td said:


> Going of the thread slightly anyone know how a second leisure battery can be connected to the first does it need a second relay,can they be connected positive to positive?Andy


They mus be connected posative to posative or you will end up with 24V battery. additional battery must be same size i.e. both 85 amp/hr or both 120 amp/hr if you mix them, 85 plus 120 you will end up with 2 x 85. It will always charge to the lower rate and no more.


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