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Sargent with built in split charge system.


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Does anybody have any experience of Sargent electrical units?


I’ve been investigating why my split charge is so slow and I think I’ve found the issue. It is using AWG10 size cables (very narrow) and also using the Sargent EC160 incorporated split charger which I’ve read is not very good.


I’m going to get someone to fit a DC/DC charger in its place but I’d like to check the wiring if someone knows.


Currently it has about 5 to 6 meters of AWG10 cable (+ and -) coming from the Vehicle battery into the back of the Sargent (labelled VB and GND) which then has another + cable going into the leisure batteries (LB) from the Sargent.


It also has a D+ signal cable going into the Sargent to let it know when the engine is running and when to split charge.


So, my thinking is remove the D+ signal wire and remove the 10AWG cables (VB and GND) going into the Sargent from the Vehicle battery.


Fit new AWG6 cables from the Vehicle battery to a DC/DC charger and then connect the DC/DC direct to the leisure battery.


The Sargent will still be connected to the leisure battery by the LB (leisure battery) cable that is already there and mentioned above.


Does this make sense and if anybody is using a Sargent without using it’s split charging facility, is this how it’s wired?


Thanks in advance.

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Wired in a Sterling 60A B2B. Ran new cables for it and installed a relay to disable 12V power to the Sargent from the split charging system. Found a engine on 12+ feed into the Sargent (EC450) - the D+ signal wire you reference. Everything works as it should - fridge on 12V, step retracting etc. Thought the system would work by just disconnecting the split charge relay permanently - what you are suggesting essentially I think but system would not power on hence the relay. There's a little bit of smarts in the EC system - you can power the leisure side of the van etc from the vehicle battery if you want and therefore the relay has it working perfectly. I also have a solar panel feeding via the EC440 and a battery master keeping the vehicle battery topped up so lots of back and forward but all works perfectly.


Sargent Manuals and circuit diagrams are here



I think the relay was this: https://www.12voltplanet.co.uk/mini-change-over-relay-12v-3040a-with-diode.html



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The OP is proposing to embark on what could be an expensive exercise, while the terminology that he uses suggests that his electrical knowledge is limited.


To the best of my knowledge, there is no such thing as a split charger. The "split charge relay", is just a relay that connects the vehicle and habitation batteries together, when the engine is running.


The use of AWG instead of the usual quoting of the cross sectional area (csa) of the cable only serves to

make the posting harder to follow, as it requires the use of a conversion table. 10 AWG = 5.26 sq mm, and 6 AWG = 13.30 sq mm.


To establish a reference point, I suggest that the OP measures the voltages at both vehicle and habitation battery terminals, when the engine is running and the habitation battery is partially discharged. It should be noted that in regard to charge current, small fractions of a volt are important.


While I agree that 5.26 sq mm (mm) cable is on the small size, the question also arises as to what amount of charge the OP is trying to replace in his habitation battery. If he could achieve a recommended maximum C/10 current of 10A into a 100 Ah battery that has been discharged to 50%, it would when allowing for the inefficiency of the battery, take about six hours of driving to replace.


As a first step, I suggest that he installs additional 16 sq mm (5 AWG) cables between the batteries. The cables should be routed via a point suitable for the future mounting of a B2B, bearing in need that such a B2B may need a habitation battery temperature sensor. At this location an additional split charge relay should be mounted and connected into the positive cable, which should also include 50A fuses close to each battery. If space allows the original 10 AWG cables could be left in situ without alteration.


As regards the new split charge relay I suggest a 120A rated item which will have low contact resistance. For an example see here. The lowest price that I found for such a relay was £6.24. This relay could be driven from the 12V fridge output of the Sargent unit.


I do not claim any originality for the above method of improving the habitation battery recharge rate. It was I believe, first suggested by the late Allan Evans. Allan claimed it made considerable improvment on his customers vehicles. I did not always agree with Allan, particularly in his assertion that when fitting a B2B, it was not necessary to disable the split charge relay.





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Alanb - 2021-10-13 4:24 PM


The OP is proposing to embark on what could be an expensive exercise, while the terminology that he uses suggests that his electrical knowledge is limited.



You are absolutely correct. I would not be doing it myself, I will be paying a pro to install for me. I'd just like to know what needs to be done to improve my knowledge.





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I don't know if the OP's van has - smart alternator, regen braking? If neither of these and a stable 14.4v is coming from alternator I would not fit B2B.


I found simply beefing up the wiring and a beefy split charge relay in accordance with the late Allan Evan's advice gave me 14.34v at leisure batteries. I used 25mm2 cable though 16mm2 was probably sufficient. I also fitted a relay to disable split charge in Sargent unit. See here




It worked very well at a fraction of the cost of B2B.


On the other hand if van HAS smart alt then B2B is required.

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