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| miker Member Since: 13 Sep 2015 Location: Surrey Posts: 1763   
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The victron charger will do a more than adequate job
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1st Jul 2020 9:49pm |
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| JOE_130 Member Since: 26 Nov 2014 Location: Chelmsford Posts: 104 
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So you've got two charge sources in the 90.... if the solar controller has got a correct charge profile for the optimas (assuming they're agm?) then given enough direct sun and time it'll charge to 100%. If you have to rely on the split charge relay you won't get 100%, but for an agm in a defender the difference between a proper charge profile and the alternator voltage will be negligible. You certainly won't damage them even without the solar charger.
Only really need a strict charge profile for lithium. |
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3rd Jul 2020 8:34pm |
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| Badger110 Member Since: 06 Feb 2018 Location: South hams Posts: 1039 
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The MPPT will obviously supply power to the batteries via the panels, but it depends on the load you are putting on the batteries. More load beyond the input from the solar panel will drain the battery.
The benefits of a dc/dc charger are if you have a smart alternator that varies it's output when the vehicle is being driven or if you don't have a secondary input ( from panels or wind ), otherwise a standard VSR will suffice. |
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3rd Jul 2020 8:47pm |
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| Tompoole Member Since: 05 Jun 2011 Location: Bucks Posts: 827  
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Thanks people.
My concern is that when mppt is charging it will trigger relay and drag the starter battery down to aux battery level , as aux is running a fridge . I’ll run it for a bit but think I will swap out mppt and VSR for ctek dc dc . Cheers tom Have fun be happy |
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5th Jul 2020 5:10pm |
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| Badger110 Member Since: 06 Feb 2018 Location: South hams Posts: 1039
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To stop that, I placed one of these after the vsr before battery. Simple button press and you isolate the 2 batteries
https://www.amazon.co.uk/MagiDeal-20-100A-...B0745Z97QV |
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5th Jul 2020 6:36pm |
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| miker Member Since: 13 Sep 2015 Location: Surrey Posts: 1763
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If the voltage gets high enough to energise the VSR, then the aux battery is at a higher voltage than the starter, so will only be topping up the starter...
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5th Jul 2020 8:12pm |
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| Badger110 Member Since: 06 Feb 2018 Location: South hams Posts: 1039
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Not quite, it will equalise the batteries until the VSR closes
13.7v on the leisure and 12.4 on the starter, the relay opens from leisure side and equalises the 2 batteries to 13v. The relay will then close as the voltage on the leisure side drops below 13.7. Each time the relay opens, it leeches power from the leisure. At least that’s how I think it works and why I fitted a breaker after the VSR. |
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5th Jul 2020 9:15pm |
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| miker Member Since: 13 Sep 2015 Location: Surrey Posts: 1763
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So relay closed = batteries joined.
Relay opened = batteries isolated. When the relay activates (closes) the solar mmpt will charge both batteries, albeit more slowly than charging a single battery. It will open if the load applied is too high, and will keep the starter battery perfectly well charged to start the engine. If the whole bank is floating above 13v, it has no need to be isolated as it's all fully charged. The split charge has hysteresis, and if it's a victron split charge some level of intelligence. So the initial rush may well dip the voltage of the leisure slightly, but it will hold closed until the bank drops below 12.8v or so. They're designed to be installed in a way that enables loads on one side to not drain storage on the other, and for charging on one side to charge both once one side is sufficiently charged. |
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5th Jul 2020 9:25pm |
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| Badger110 Member Since: 06 Feb 2018 Location: South hams Posts: 1039
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Yes i see how that works, i was complicating things by incorrectly saying ' open ' meaning the relay has bridged the connection, when it's actually 'closed ' as you said.
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6th Jul 2020 8:10pm |
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| macfrank Member Since: 05 Nov 2015 Location: somewhere in the north Posts: 1076  
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Correct. However, despite hysteresis I noticed a cyclic closing and opening of the relay (NL split charge + CTEK charger, but should be similar with other VSRs). This could happen, if voltage difference between the batteries is rather high, say aux has 11,8V and starter 13,0V (just examples). When both batteries are connected, total voltage can be below hysteresis' lower threshold, so relay opens. Voltage then rises again above upper threshold, relay closes and so on. To avoid this, I added a switch to disable the split charge system. Also both batteries have their own CTEK connector, so I could charge either one separately, in case it gets deeply discharged. (though it never happened again, since I installed it 3 years ago  ) |
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7th Jul 2020 7:15pm |
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| miker Member Since: 13 Sep 2015 Location: Surrey Posts: 1763
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Definitely possible with a simple VSR, less likely/shouldn't happen with the algorithm in the Victron Cyrix range.
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7th Jul 2020 7:18pm |
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| macfrank Member Since: 05 Nov 2015 Location: somewhere in the north Posts: 1076
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Ah, interesting. Just read the datasheet. I seems to also watch a trend in voltage change, not just momentary values. That's better.
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7th Jul 2020 7:29pm |
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