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newworldorder avatar image
newworldorder asked

Need help with installing a BMV into a campervan

Hi everyone, I bought the Victron battery monitor. Reason I am here is because I have 2 6volt deep cycle batteries hooked up in series so 12volts. Then I have an inverter that is hooked up directly to my batteries. For setting up my monitor, do I have to have the negative terminal of the battery bank hooked to the shunt then carries on to ground, the red fuse is the power and that is connected to the positive on the battery bank. Do I have to have that connected to my inverter to or just hooked up to my battery. I have everything working but it says battery capacity 100%. The battery is almost at the 12.8 level where it will sync. So when it syncs will I then be able to see the draw on the device? Or should I see it now what is being used without it being synced to a full battery.


Thanks

BMV Battery Monitorbattery capacity
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4 Answers
Justin Cook - Bay Marine Supply USA avatar image
Justin Cook - Bay Marine Supply USA answered ·

@newworldorder, the only thing connected to the NEG side of your battery bank should be the "Battery" side of the shunt; all other chargers and load NEGs (including your inverter) need to be hooked up to the "Chargers and Loads" side of the shunt (sometimes only labeled "Loads"). The POS, obviously, still runs directly to the battery or to your POS busbar. Once you have your inverter NEG connected to the "Loads" side of the shunt, your BMV will be able to "see" the current out that it's drawing.

Also note that all charge source NEGs also need to go to the "Chargers and Loads" side of the shunt so that the BMV can also "see" the incoming current and update your SOC accordingly.

Make sure you correctly set your Ah capacity in the BMV. Your BMV will always start at 100% SOC when you first hook it up (you can turn this off, but it's a bit late for that) but will adjust itself after you have everything set correctly and connected correctly and it's had time to figure out what's going on in your battery bank. Basically, give it about a day once you have everything set.

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Thank you for your quick response!


I am new to this but I need to clarify something. Correct me if I am wrong .

The battery bank negative needs to be hooked up to the battery side of the shunt. The load side does that have to go to ground? In my case the chassis of the vehicle. And also on the load side I would put a wire going from load side to the inverter neg.

is that right?

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@newworldorder, correct, chassis ground connection must come off the "load" side of the shunt so that your BMV can "see" any loads you have connected directly to chassis ground; and, yes, your inverter NEG must connect to the "load" side of the shunt as well. If you have a bunch of loads/charge sources that are going to be running through the shunt, a common technique for connection (because you can only fit so many lugs onto the provided bolt) is to simply hook a NEG busbar to the "load" side of the shunt and then connect all your charge source negs, your load negs, and your chassis grounds to that NEG busbar.

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newworldorder avatar image newworldorder Justin Cook - Bay Marine Supply USA ♦ ·

What would you consider a charge source? The only thing that is charging my battery bank is 400 watts of solar at the moment.

I am going to post a pic of what I think it should be hooked up as.

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newworldorder avatar image
newworldorder answered ·

What would you consider a charge source? The only thing that is charging my battery bank is 400 watts of solar at the moment.

I am going to post a pic of what I think it should be hooked up as.



image.jpg (2.5 MiB)
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@newworldorder, so no... the NEG cable coming off your battery goes straight to the "battery" side of the shunt, not the NEG bus. The NEG bus gets attached to the "load" side of the shunt.

In re to charging sources, yes, your solar charger counts. The NEG lead from your solar charger also gets attached to the "load" side of the shunt, or to the NEG bus after you've connected it to the "load" side of the shunt.

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I've sort of whited-out the incorrect connections. Battery negative goes straight to battery side of the shunt. Everything else gets connected to the other side.

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newworldorder avatar image newworldorder Justin Cook - Bay Marine Supply USA ♦ ·

You sir are a god send. Seriously. I have been searching high and low for someone with the knowledge and know how. I really appreciate you taking your time to explain and to help me. I am sure I will be reaching out soon for more help.


Much love, Alberta Canada

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Hahaha glad to help, @newworldorder. The BMV hookup is pretty simple once you understand it, but it can be a chore getting there. I'm the technical support manager for a Victron/Sterling/Battle Born/Blue Sea/Bussman distributor in San Diego and the single most common call I receive about BMVs "malfunctioning" is due to people simply not grasping the everything else rule to these things, to whit: the only thing connected to the battery negative is the "battery" side of the shunt; everything else is connected to the other side of the shunt.

Once you get that "everything else" really truly means everything else, it's a breeze from there :)

Good luck with your system!

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newworldorder avatar image newworldorder Justin Cook - Bay Marine Supply USA ♦ ·

Ya that is extensive. It is great to know someone with such skill sets.


Another couple questions for you tho, so like I said before I converted a cargovan into a camper and I have 2 6volt deep cycle batteries in series. each with 190 amp hour. I was running a 900watt heater through my inverter and after I would say 6 min I was getting a low voltage alarm. Should I be able to run that heater for hours?


900watts /120 ac= 7.5 amps. So 190 amp hour bank /7.5 = a long time. Why is it giving me such a hard time

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(900 watts / 12 volts ) x 1.08 for (93% efficient for a victron inverter) = 81 amps from battery at a minimum. So max run time would be under one hour to 50% drained which is low as you would want to go to not kill the batteries. Also When AGM or flooded supply that high of an amp draw the total power (Ahs are decreased because they are rated for power draw over the course of 20 hours.)

You need to calculate the draw from the battery not just the amps in the 120v circuit as the power is coming from a 12v source. I made the same mistake when I first calculated my battery bank requirements. You also have to account for the loss from inverting the power from 12v to 120v through the inverter.

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Justin Cook - Bay Marine Supply USA avatar image
Justin Cook - Bay Marine Supply USA answered ·

@newworldorder, well if your 6v batteries are FLA or AGM, first you have to account for the fact that of your 190Ah capacity, only about half of that is usable... and that's brand-new. So, fully charged, your 190Ah capacity is actually around 90Ah usable. That is then substantially decreased by any age/usage on your batteries, plus any deep cycles of the batteries... every time they're discharged, you lose a little capacity off the top, meaning that you can't ever recharge them to the same level they were before... this is just the caveat of FLA and AGM batteries. They're cheap, but they're heavy and you can only really use half their capacity at most, and that capacity steadily decreases over time and usage.

The other thing to consider is that a heater is a resistive load, which actually consumes far more amperage than a capacitive load, so you're more likely than not seeing close to an 82-95A draw (at 12v) on your inverter running that heater... plus the draw of the inverter itself, which depending on the brand inverter you have can be surprisingly high. So, all that in mind, consider that you're drawing close to -if not in excess of- your total usable capacity (maybe even more if the batteries are old) just by turning that system on, so I'm actually not at all surprised that you're getting a low-voltage alarm right from the start.

As an example of this, I have a 1500w heater here on my test bench that I use for testing battery throughput; running it at full-bore, it consumes in excess of 184A when all is said and done, including the draw of the inverter itself - and that's with a Victron inverter, which has pretty much the highest efficiency rating of any on the market.

So, several ways you can get around this: First, possibly upgrade your inverter. If you're using an AIMS or a Xantrex or any of the knockoff brands, get rid of it and get a Victron or a Magnum.

Second, increase your battery capacity... the more Ah you have available, the less voltage drop you'll see when running your load, because the draw gets spread over your available Ah.

Third, change your battery chemistry if you can... LiFePO4's are expensive, but you can use 80% of your capacity without negative repercussion... and they'll last longer and deliver a lot more power upon demand (for instance, a Battle Born 100Ah battery will deliver a continuous 100A if you need it).

And, finally, the other thing that will help is to upsize your wiring from your battery to your inverter... the thicker (and more strands) the wire, the less resistance and the less voltage drop you'll see when running a load.

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nomadic-diesel avatar image
nomadic-diesel answered ·
@newworldorder Besides your solar panels other charge sources include 120v shore power (hard wired through an inverter/charger such as the Victron 2000) and charging off your alternator/starter battery with a battery to battery charger. A B2B will fast charge your camper batteries, BUT only while driving. Its advantages are charging the camper batteries at night and during heavy rain when the panels are least effective. Many rely solely on solar panels, but some add other means to charge them.
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