 | Home > In Car Electronics > Victron BMV 712 smart battery monitor |
 
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| kmac Member Since: 07 Oct 2009 Location: Middlesex Posts: 1294   
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Since not many here are using the Victron and after much online reading about coulomb counters, I went for a Merlin Smart Gauge battery monitor instead. May eventually get the Victron as well.
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28th Jul 2021 9:51pm |
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| Matt110 Member Since: 29 Jun 2014 Location: UK Posts: 673
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Sorry, didn't see your first post.
For completeness of thread and to help if you decide to get one... Yes they're excellent. The simplest ones have a single shunt and monitor on the earth side of your second battery. They measure current flow out of the battery and calculate the ah consumed, giving you a pretty reliable battery percentage state of charge especially if you're only using fairly low currents. They do time left to go to flat (50% state of charge assumption = flat). I have one fitted, it's very reliable and really handy when you are wild camping for more than one night to know what your battery is doing with a fridge running or similar. The more expensive ones can then do a voltage only measurement on the starter battery too, or you can use that sensor as a midpoint measurement of a twin bank of batteries, which tells you if one or other of the batteries is dropping or failing. If it does so it'll knacker the other ones in the bank too. It also does charge in the other direction, so you'll see the current flowing back into the batteries once the engine is running. A puma at idle with no consumers running will put about 60a back into the battery. So you can then watch it charge and turn the vehicle off when done. The Bluetooth functionality is meant to be good but mine doesn't have that. I was OK with just a gauge. Hope that helps. |
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28th Jul 2021 9:58pm |
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| kmac Member Since: 07 Oct 2009 Location: Middlesex Posts: 1294
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Thanks Matt - have my eye on the BMV 712 which has both Bluetooth and voltage sensor for the starter battery (or any other second battery not part of the auxiliary battery bank).
I know the chap on here who has just installed the Redarc Redvision system used to have a BMV 712 and sold it for £50 - wish I had seen that post in time. |
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29th Jul 2021 11:36am |
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| Badger110 Member Since: 06 Feb 2018 Location: South hams Posts: 1025 
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I bought this one from Amazon
Battery Monitor 12v which does the same job but it's not bluetooth...although why you need bluetooth when it shows what you need to know on the display is beyond me 
Less than £50 and mine's been faultless for a few years now. |
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29th Jul 2021 6:28pm |
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| kmac Member Since: 07 Oct 2009 Location: Middlesex Posts: 1294
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Yeah saw this also. Agree bluetooth is a gimmick as there is a display.
Just settled on Victron as my dual battery VSR is a Victron Cyrix Saying that the green display of yours goes better with the Defender displays |
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29th Jul 2021 9:41pm |
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| Cupboard Member Since: 21 Mar 2014 Location: Suffolk Posts: 2971 
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I have a BMV 712. It's good. I'd do it again.
They also have some simpler options like the SmartShunt that might be worth considering. Also if you have a solar charge controller you might find that has enough functionality built in already. My current system has a Victron split charge relay, BMV712 and a Victron solar charge controller. I'm not a particular Victron fanboy but they make good stuff that works. A big limitation with all of this sort of thing is they have no way of knowing if your battery is knackered. You might have used 10Ah out of it, it's reading 90% but actually the battery is old and dead. The other thing that I think is worth considering is not using split charge and just running both batteries (they should be identical) in parallel. Use a battery monitor and low voltage disconnect as a safety net. The reason you'd want to do it is the same reason that heavy trucks do it. A battery keeps most of its cranking amps until it drops below about 50% state of charge. A battery lasts long the less you cycle it - disproportionately so. If you're regularly completely draining a battery it will only have a handful of cycles, if you only ever take 25% out it will last years. 50% is usually the tradeoff people make between longevity and carrying around too many unused batteries. You can look up battery datasheets if you like. So if you've got space for 2* 100Ah, 800CCA batteries (which you do have in a Defender and that's approximately the specs of a 019 battery) then you have a choice. Split charge, have 800 cranking amps from your starter battery and 50 usable amp hours from your camping battery - or - full time parallel (with a low voltage disconnect as a safety net), 1600CCA and 100Ah usable camping capacity in an overall simpler system. That's not how I've done it at the moment but next time I change batteries it's what I will be doing. These are graphs from a couple of different brands of AGM batteries, flooded batteries tend to be cheaper but less tolerant.  Click image to enlarge Click image to enlarge |
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4th Aug 2021 8:39pm |
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