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Discussion Starter #1
I have a standard 100amp relay split charge system (50amp fuses/ very thick power cable) going to my 2 110ah leisure batteries which are wired in parallel.

With the engine off the combined voltage reading of the two batteries is around 12.8 volts at rest.
If i start the engine i get 14.1volts at the outgoing terminal on the 100a relay but the battery meter which is wired to the leisure batteries reads 13.5 volts, if I disconnect the second leisure battery the voltage rises to 13.9 volts with engine running.

What is this telling me ? when it was all first fitted, im sure I used to see 14+ volts at batteries with engine running.

If I disconnect the main earth cable from the leisure batteries and test with meter I get 14.1 volts, but as soon as its connected to batteries it drops to voltages shown above (im guessing beacuse it then has a load on it).
 

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Discussion Starter #3
They were both mains charged yesterday before we went camping (charged together as one bank) had stereoamp on for about 3 hours yesterday + compressor fridge and the voltage was down from 12.80 to 12.10 volts this morning. used to go down to that after about 3 days of stereo/fridge use.
Im mains charging them individually today, see if that makes any difference.
 

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Discussion Starter #5
Battery is fairly new and always kept on mains charger at home so pretty sure its ok.

when mains charger is connected, i get 14.5 volts at battery terminals and 14.5 volts on my lcd voltage display.
But for some reason when its the split charge charging, although I get 14.2 volts at split relay output its only 13.7 at battery, and im none the wiser as to why its not around the 14v mark :*

Surely the mains charger is kind of just mimicking what the split charge should be doing.
 

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The only way i can see you getting different readings at each end of a cable is (assuming the cable is not too thin and smoking hot :) ) a bad Connection / bad earth
 

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Discussion Starter #7 (Edited)
Will double check the earth connection to leisure battery, its deffo not the cable as the cable i used is the type found on heavy duty jump leads, proper thick cables.
also as mentioned earlier, if i remove the earth cable from battery and then put meter on live of battery and then black test probe on the loose earth lead i get the full 14.2v reading with engine running.

EDIT : just rigged up another earth cable from batt negative to bolt on body of van and made no difference at all, so not an earth problem.
doing my head in a bit now.
 

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You probably have increase internal resistance in the batteries as they are no longer brand new.

If you replaced them you could maybe achieve the readings you used to. Or if you replaced the split charge wiring with massive cable

You could try a heavy duty jump lead from positive on the start battery to positive on the leisure batteries and see what the readings are then.
 

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Essentially, It is heavy duty jump lead cable linking starter to leisure as i got the cable from a set of my dads jump leads which used to be used for lorries.
At 13.7 volts will the leisure battery be getting sufficient charge to keep them topped up ?
Yes but not as charged as they could be.

Your not gonna get it perfect without spending loads of cash either on new batteries or an alternator upgrade.
 

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If they are reading 12.8 at rest then they are fully charged (or one of them is). From this point they will stop drawing current from the alternator as the alternators regulator will slow down (confirmed by the 14+volts). If the voltage rises when you disconnect one battery then that battery has slightly different charge characteristics. I wouldn't worry about it until you see significant self discharge happening. It doesn't pay to get too "" about voltage readings, especially on digital panel meters.
 

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Discussion Starter #13
Thanks for that upsex , I left fridge on overnight and after 24 hours battery is down to 12.35 volts (have disconnected second battery for now)

Started engine tonight and now getting 13.8 volts at the split relay and 13.2 volts at batteries at back of van, these readings taken from a proper meter,not my panel meter.
 

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The 13.8 is about right but why are you losing 0.6 between the relay and the battery???? How long is the cable run and what CSA cable have you used?
 

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Discussion Starter #15 (Edited)
Cable run is around 4 meters and not sure on cable size, its the really thick size you find on proper heavy duty commercial jump leads. If I disconnect terminals from leisure. Battery and test leads I get the same voltage as at the split relay,it drops as soon as they are reconnected to battery. When first installed used to get same readings both ends.
 

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Cable run is around 4 meters and not sure on cable size, its the really thick size you find on proper heavy duty commercial jump leads. If I disconnect terminals from leisure. Battery and test leads I get the same voltage as at the split relay,it drops as soon as they are reconnected to battery. When first installed used to get same readings both ends.
You will get more voltage drop if the batteries are discharged due to the extra amperage needed to charge them, it will drop away when the batteries come back up
 

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You will get more voltage drop if the batteries are discharged due to the extra amperage needed to charge them, it will drop away when the batteries come back up
Sounds OK cable wise but there has to be a poor connection somewhere causing a high resistance.
 

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Discussion Starter #18 (Edited)
Ill check and clean the connections at the split relay and also where the live bolts to the fuseholders and see if that makes any difference.
Thanks.

EDIT : Problem solved, however im not sure I even did anything special, unbolted the terminals from the fuse holder nearest the leisure battery, checked fuse then refitted, started engine and was seeing 13.8v at the fuseholder and climbing slowly.
Then the engine note changed slightly as if some kind of relay had activated and it shot up to 14.2 volts T:
 

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Ill check and clean the connections at the split relay and also where the live bolts to the fuseholders and see if that makes any difference.
Thanks.

EDIT : Problem solved, however im not sure I even did anything special, unbolted the terminals from the fuse holder nearest the leisure battery, checked fuse then refitted, started engine and was seeing 13.8v at the fuseholder and climbing slowly.
Then the engine note changed slightly as if some kind of relay had activated and it shot up to 14.2 volts T:
That will be the glowplugs going off.glad its sorted
 

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Hi Where was the fuse holder mnearest the leisure batteries? I cant find any fuses from the back of the van where the batteries are loacted to the interior fuse box behind the drivers seat!:*
 
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