Battery Monitor query.

[Revolvor]

I have a question relating to Battery Monitors, such as the NASA Marine BM1.

When I fitted an extra leisure battery and solar panels to my MH, I also fitted a CTEK Battery Sense Monitor. This is connected to the batteries via Bluetooth and gives a basic indication of battery charge state.

I would like to upgrade to a more sophisticated Battery Monitor, such as a BM1 but have a query over the display – specifically the bar-chart showing battery capacity. What exactly does that mean? I know one should only use 50% of a Lead Acid Battery’s capacity, but does that mean the bar-chart should not go below 50%?

Also, when the display says “XX Hours to discharge”, is that to fully discharge it, or just to get down to 50% Capacity?

Thanks, John

 

[Deneb]

I don't know what the BM1 does, but the Victron BMV displays the percentage SOC in relation to the total battery capacity programmed in its settings.

So if you have two 100Ah batteries and set the capacity as 200Ah, 50% SOC on the display means that it calculates the remaining capacity to be 100Ah.

But the discharge floor can also be set to whatever you desire. So if you set the discharge floor to 50%, the time to go averaging period (how long you can sustain the current draw from the battery) is based on the discharge floor that has been set, i.e. how long it will take for the battery to reach 50% SOC.

So assuming the settings above, if it reports 80% SOC and an averaging period of 100 hours, you have 80% of the original 200Ah capacity available, and at the current discharge rate you can run for 100 hours before reaching 50% SOC.

The time to go display varies according to current draw at any given time, but you can configure the averaging period between 0 and 12 minutes to adjust the window over which the average is calculated. If you set it at zero, the estimate will fluctuate instantly with every change in current draw. Set at 12 minutes, it will change more slowly and the switching on of a fridge compressor for instance, won't cause a sudden severe recalculation. As the compressor in my fridge normally only runs for a maximum of about 10 minutes at a time, a 12 minute averaging period means that the time to go stays more consistent with the likely "life" of the battery leading to better accuracy at any given time you check the display.

 

[cbrookson]

Just to add to the comprehensive reply above: Victron now do a smart shunt, you can read it using Bluetooth and the Victron App. I've not used it, but it looks just as good as my BMV (which is tucked under a bench seat in the Hymer anyway!). You just connect it in to the battery bank and it will measure the current and voltage, as well as history. It will monitor Voltage on the Vehicle Battery as well. Means you leave out the display ...

I just check it with Bluetooth from the house to see if all is working well! It might suit you for monitoring, you can add displays but that sounds like overkill. The price does seem to about the same as the BMV though, but is each much easier to install ...

Cheers

 

[Deneb]

Or the BMV-712 which can connect via bluetooth and smartphone but also has the display, which I find far easier when I'm in the van and just want a quick glance to see what's what, and don't have to keep finding my phone and waiting while the app starts up and log in.

But I may be a dinosaur!

 

[Pausim]

My BMV display is in the battery compartment and I haven’t looked at it since doing the initial battery settings. I use the bluetooth app for everything else.

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[Richard n Ann]

but does that mean the bar-chart should not go below 50%?

Yes

 

[Richard n Ann]

is that to fully discharge it

Yes

 

[Revolvor]

Thanks to all for your helpful comments/suggestions and answers to my questions. I am pretty sure now that a monitor will be of benefit. Now I just need to make a decision regarding the brand, and whether to have a permanent display, or just rely on Bluetooth to my phone. I can see benefits/disadvantages with both methods.

 

[XxAnthxX]

I went for the Victron Smartshunt for the simplicity of the install.

it can be viewed on my phone (iOS) or on my van radio head unit (Android).

Download the VictronConnect app and select demo library and select the smart shunt (or one of the BMV’s) and have a look at a simulation of the info and parameters available, see if it would suit your requirements.

 

[Pausim]

Another vote for the Victron, it can be set up with proper parameters for all types of battery. Unlike some battery monitors it doesn’t come up with impossible readings of 105% because it hasn’t worked out that most batteries are only 95% efficient when charging.

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[the1andonly]

If you want something without spending an arm and a leg
Coulomb counting amps in and out %soc a bit simpler than the big brands



https://rover.ebay.com/rover/1/710-...0001&campid=5338547443&icep_item=373310462883

 

[mitzimad]

If you want something without spending an arm and a leg
Coulomb counting amps in and out %soc a bit simpler than the big brands



https://rover.ebay.com/rover/1/710-...0001&campid=5338547443&icep_item=373310462883

Does the victron do anything more than this one?

 

[Deneb]

Does the victron do anything more than this one?

Difficult to know without seeing a manual for the eBay item (if one exists). But leaving aside the networking facilities of Victron equipment, my gut feeling is yes. The numerous settings on the Victron monitors allows you to fine tune the device to your individual setup, increasing the accuracy of the information you get from it.

It looks from the eBay listing that item simply has basic realtime current/voltage/capacity display. With the Victron correctly configured, you also have time-to-go to your discharge floor, high/low voltage alarms and associated triggers for connected devices, history, real-time monitoring graphs via the phone app, ability to resync the batteries to full charge manually on the device (if you have the separate display model) and/or the phone app, monitoring of vehicle battery voltage/multiple habitation batteries midpoint voltage/habitation battery temperature (one of those three items dependent on programming and wiring etc.

You can find the manuals for the different Victron monitors on their website. Might be worth having a read of those for the models you are contemplating, to help make up your mind.

 

[XxAnthxX]

Does the victron do anything more than this one?

As I previously mentioned

Download the VictronConnect app and select demo library and select the smart shunt (or one of the BMV’s) and have a look at a simulation of the info and parameters available, see if it would suit your requirements.

The Victron units do seem to have almost infinite control/setup configurations and are software upgradable but If you don’t need any of the other features the eBay alternative might just be a perfect solution for you. I’m not sure if the reduced capacity of the shunt itself on the eBay alternative might cause you an issue with your setup?

Victron SmartShunt: easy install, networked, all-in-one battery monitor

I've found Victron's BMV battery monitors to be simple, reliable, and easy to understand. Now, the new SmartShunt combines the BMV's shunt and electronics into a single unit barely larger than the regular shunt with Bluetooth and Victron's VE.Direct networking built-in. In my testing, the...

panbo.com

To be honest the Victron Smartshunt does way more than I currently need, but my reason for choosing the Victron unit was the bluetooth.....I didn’t want to cut holes for or mount external displays.

 

[Pausim]

Does the victron do anything more than this one?

Yes, accuracy. A simple coulomb counter will give you an idea of where your battery stands but not as accurately. If you take 50Ah out of your battery it takes more than 50Ah to charge it back to where it was. There is the basic charging efficiency and on top of this the Peukerts exponent needs to be taken into account. If you use 50Ah at a slow rate of 5A (for 10 hours) it takes less out of the battery than taking 50Ah at 50A (for 1 hour). Peukerts exponent is used to calculate this. The Victron has settings for charging efficiency and Peukerts. If you don’t allow for these factors the the readings drift away over time until the information is way off target. The Victron also automatically synchronises itself when the battery is fully charged by monitoring the voltage and the drop off in charging current, to stop it drifting.

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[Diabalo]

If you want something without spending an arm and a leg
Coulomb counting amps in and out %soc a bit simpler than the big brands



https://rover.ebay.com/rover/1/710-...0001&campid=5338547443&icep_item=373310462883

I have one of these fitted and it does the Job just search for battery monitor on YouTube there are several vids for the above unit. I cant comment on the Victron equivalent.

 

[Stealaway]

Thanks to all for your helpful comments/suggestions and answers to my questions. I am pretty sure now that a monitor will be of benefit. Now I just need to make a decision regarding the brand, and whether to have a permanent display, or just rely on Bluetooth to my phone. I can see benefits/disadvantages with both methods.

What am I missing?
I have a £4.99 Ebay digital voltmeter.

Hopefully during the day I can get as much charge as necessary into the leisure batteries via the B2B or my solar panels.
In the evening I glance at the voltmeter occasionally while watching TV.
When and if it drops to 12.2 volts I turn the TV off.

Simples! What more information do I need?

 

[Deneb]

What am I missing?
I have a £4.99 Ebay digital voltmeter.

Hopefully during the day I can get as much charge as necessary into the leisure batteries via the B2B or my solar panels.
In the evening I glance at the voltmeter occasionally while watching TV.
When and if it drops to 12.2 volts I turn the TV off.

Simples! What more information do I need?

Maybe none if you're happy with that.

If you're regularly off grid for extended periods, knowing with a greater degree of certainty what you can take from or put in to your batteries might assume more importance.

12.2 volts under load gives you no real idea of the SOC of your batteries. Nor does 14.4 volts when the sun is out. In either case, they could be near as or fully charged, or much below that.

A fuly charged battery may drop to an indicated 12.2v with a load on it, such as a compressor fridge. It will gradually return to its true resting voltage when the load is removed. You need to wait several hours after removing all loads and charge from your battery to determine its true resting voltage, and hence a guestimate of its true SOC. A properly calibrated battery monitor can do that instantly, even when its being charged or under load.

 

[two]

I cannot remember the details for the NASA but am pretty sure that I set the theoretical capacity of the battery bank (170Ah) and it showed how much was remaining so I had to keep it above 50%. I could have entered half of that (85Ah) and then regarded the bar chart as 'available capacity left to use'. Your choice of unit may be influenced by the style of other displays in use. The Nasa has a large square format. Victron is small and round. Victron stores much more information, if you are prepared to delve into the history (easier with a smart phone).

 

[berni109]

Like most things in life u get what u pay for.
If u want the all singing all dancing state of the art battery monitor go for it and get your wallet out.
On my last van I fitted a juntec vat-xxxx which cost about £20 from our Chinese friends. I did everything I wanted and I never even scratched the surface of its functionality.
Just bought another for the new van because it's so easy to fit as a basic unit but I might have considered the round one mentioned above as connecting it up looks simple as well.
As two said above set the capacity to 50% of the battery bank so the remaining available capacity is what's represented by the display graphic.
Once its setup how often are you going to look at it anyway once the initial novelty has passed.

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