 | Home > In Car Electronics > B2B Charger or Relay? |
 
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| 8619simon Member Since: 04 Nov 2016 Location: North Wales Posts: 247   
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A DC to DC charger is always going to be more efficient than a simple voltage sensitive relay and it will ensure your AGM batteries are charged properly and to 100%. The Australians do 12volt systems very well and there are plenty of good Australian YouTube content creators that go into the pro's and con's, Ronny Dahl, Andrew St Pierre Wight etc.
The Victron systems you have indicated are good but you need to choose the right model. As far as I understand it the 24 in the model relates to a 24 v system. So a 24 / 12 is a Dc to DC charger designed to work with a 24v input from the alternator and charge a 12V auxiliary battery. The 12 / 12 models work with a 12v alternator and charge a 12v auxiliary - this would be the standard in most Defenders. The more amps you can put into the battery will increase the speed of recharge so the 12/12-30A is going to charge your battery quicker than the 12/12-18A model. I was in a similar position in our camper van a while ago having run Relay split charge systems for quite a few years. I swapped over to a Renology Dc to DC charge system and it is way more efficient. The battery charges quicker so replenishes on shorter drives and also keeps it in better overall condition. They are a bit more expensive but worth it in my view. |
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7th Nov 2021 9:59pm |
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| felixp Member Since: 29 Oct 2020 Location: Bavaria Posts: 39 
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Thanks for the quick reply!
Ah yeah didn't even realize it said 24, I was so overwhelmed by all the options 
I will be going with the "Victron Orion-Tr Smart 12/12-18A (220W) DC DC" then. Seems to be the best option. Question regarding the battery setup in the Defender. Would you still go with two AGM Batteries or could I mix and keep using my normal wet battery as the starter battery? |
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7th Nov 2021 10:21pm |
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| jimbo55 Member Since: 15 Jul 2020 Location: Midlands Posts: 399 
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Don’t bother with a relay, get a proper battery to battery charger, most of them now charge at the correct voltages and rates to suit the AGM batteries and not just whatever the alternator puts out. I went with the CTEK d250se and 120s recently and they work very well and I can have it all installed in the batery box with my 2 odyssey batteries.
Simply split charge were really helpful when I rang up and discussed the positives and negatives of the CTEK and the victron options and I was able to buy a full kit with all the cables, connectors etc. In one to save having to buy from a load of different places |
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8th Nov 2021 8:30am |
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| Cupboard Member Since: 21 Mar 2014 Location: Suffolk Posts: 2971 
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An 80Ah battery is smaller than the standard Puma battery. The standard is a 019 sized battery and you can just (with a bit of fiddling) fit two in the battery box.
There's really not a lot of point in fitting a DC-DC charger in a Defender. In some applications they can help, but in most cases when a vehicle has a relatively dumb alternator they don't. Take the Ctek, it's limited to 20A, or the Orion at 18A. You'll spend most of the charge cycle sat at the current limit, not actually getting any benefit from a voltage boost. I use a Victron Cyrix CT 230A and have seen charge currents of about 45A in to my second battery, and it stays at currents higher than most DC-DC chargers can manage until 90-95% charged. The alternator puts out a fairly steady 14.4V which is a perfectly sensible voltage to charge and lead acid batteries at. It is correct to say that an AGM battery can charge faster (and get hotter) using a slightly higher voltage, however that's only relevant if your charge isn't current limited. Ctek will sell you an extra to their charger called the Smartpass which is basically a slightly clever voltage sensitive relay that bypasses the DC-DC charger for the bulk of the charge cycle. Where a DC-Dc charger makes a lot of sense is if you've got a trailer with thin wires feeding it, or you need to limit the charge going in to a battery to stop it overloading an alternator. It doesn't sound like that's relevant to you. Sticking to a relay, you have the advantage of assistance when winching, assistance when running an air compressor (mine is fed from the second battery so I can use it whilst parked but if the engine's running it performs better fed from the alternator) or you can jump start yourself. The final thing to consider is if you actually need any sort of split charge at all. A lead acid battery's cranking amps don't really drop much until you get below 50% state of charge. A lead acid battery last a lot longer (number of cycles) if you don't discharge it too far. Even deep discharge batteries (we're not talking about caravan batteries here, they're just cheap starter batteries with a different sticker) have their lives significantly shortened by being drained, and 50% is usually the maximum recommended discharge level. That all being said, if you had two batteries connected in full time parallel you get both improved starting and improved camping performance and the system is simpler. Add in a battery state of charge meter with some sort of low voltage disconnect (which you have the budget for if you're not wasting it on a DC-DC charger) and you've got a very robust system. It's how trucks do it, they don't have camping batteries for powering the fridge and night heater but run multiple large batteries in series (for 24V) and parallel (for increase capacity). |
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8th Nov 2021 5:08pm |
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| Fooknose Member Since: 11 Apr 2021 Location: Sheffield Posts: 10 
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Thks, interesting read. I found my 2014 110 dead. CTEK charger had turned itself off and would not connect. Presumed battery died. Relay switch does nothing when pressed, including no increase on the voltage of the starter battery. Presume this is all normal and my new battery will sort it all? My new defender could not start the car on HD jump leads, although a friends BMW did. Does make me wonder whether the AGM batt will actually help me with a low starter batt when the time comes? Does it have enough power? TIA.
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14th Aug 2024 4:27pm |
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| jst Member Since: 14 Jan 2008 Location: Taunton Posts: 8050  
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I run a split charge relay, blue sea ony 130 and a drive vsr on my 110. Numax batteries, 31xvf or 27xvfs and works well for me. Victor solar controller with 150w means 6 days no engine start had samensetup two years or so now works well. No dc to do for me. Cheers
James 110 2012 XS Utility 130 2011 M57 bespoke Camper 90 2010 Hardtop 90 M57 1988 Hardtop |
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16th Aug 2024 2:25pm |
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