Battery Monitors

[STIG]

Firstly I would like to wish everyone a safe and Happy Christmas,

So I was thinking of treating le boat to a battery monitor, and am thinking about the nasa marine BM2, but on looking through t`internet I can see there are cheaper models. Now I know about you get what you pay for !!! but does anybody have any good/bad experiences with anything of this nature, and which one would be of most help.

Many thanks in advance 

[Richard10002]

I've got a BM2, a Smartgauge, and a Victron BMV712. 

 

The BM2 did all I wanted it to do and, apart from loving the Bluetooth control of the Victron, I would buy it again.

 

I wouldn't buy a Smartgauge again if you paid me!

 

I haven't considered anything cheaper, but have seen a Chinese monitor on Will Prowse YouTube channel,  which looked good, and which he liked - a bit like the BMV without the Bluetooth. 

[Tony Brooks]

22 minutes ago, STIG said:

Firstly I would like to wish everyone a safe and Happy Christmas,

So I was thinking of treating le boat to a battery monitor, and am thinking about the nasa marine BM2, but on looking through t`internet I can see there are cheaper models. Now I know about you get what you pay for !!! but does anybody have any good/bad experiences with anything of this nature, and which one would be of most help.

Many thanks in advance 

 

If you buy any monitor that basically counts amp hours please be aware that if fitted straight from the box without setting it up or if the user does not set it up properly and recalibrate it very regularly they all have a nasty habit of telling lies that actively encourage the destruction of your batteries. Some are better in this respect than others but all tend to be affected to some degree. The volts,amps and amp hours out reading swill be accurate, it is the % charged and Ah left that tend to be untrue so assess when fully charged by the tail current (1 to 2% of battery capacity) and the state of charge inferred from rested voltage. That way you can see just how far out the monitor reading has drifted.

 

I was more than happy to just use a decent digital ammeter and voltmeter (which you get with monitors) and managed to make a set of Exide leisure batteries last over six years until we sold the boat.

Edited December 20, 2021 by Tony Brooks

[GUMPY]

If you don't have solar then Smartgauge is about the best to tell you how your batteries are discharging. It will not tell you exactly how fully charged they are whilst you are charging it's within about 10%, however adding a simple ammeter will tell you when your batteries are pretty much fully charged.

[mrsmelly]

Ive had several different types. Forget the silly amp hour counter bit and they are good for checking tail current against voltage etc etc. The NASA is my favourite every time as it has a sensible display size and is waterproof. The display size means you can glance at it from a fair distance without the need of a grandchild to decipher it.

[Jen-in-Wellies]

Check the maximum current capacity of the shunt, if you are tempted by a cheapo monitor. Many seem to be rather limited and many common boat items, like an inverter of any size, will overload them. Remember that all current in, or out of the house batteries must go through the shunt, if it is to have even a chance of being accurate for a while. Will it cope with, say inverter running a heavy load, plus all your lights on and a water pump and shower drain pump running at the same time?

The usual name brand ones, like Victron and I think Nasa can.

[MtB]

23 minutes ago, Richard10002 said:

I've got a BM2, a Smartgauge, and a Victron BMV712. 

 

The Victron BMV712 has the best functionality AFAICS, but having one myself I find it has the most irritating drawback - the display is TINEEEEE.

 

Get a good look at one and see how small the main display is. Barely readable until you get close i.e. less than three feet away. And only then do you realise there is more, truly microscopic information on the screen which you can only see with ya glasses on and a torch! 

 

[nicknorman]

5 minutes ago, MtB said:

 

The Victron BMV712 has the best functionality AFAICS, but having one myself I find it has the most irritating drawback - the display is TINEEEEE.

 

Get a good look at one and see how small the main display is. Barely readable until you get close i.e. less than three feet away. And only then do you realise there is more, truly microscopic information on the screen which you can only see with ya glasses on and a torch! 

 

It’s true that the display is quite small. But I am unclear why you would want to walk up to it to read it, when it’s Bluetooth functionality means you can see everything you need to see (and more) from the comfort of your armchair, via your phone.

 

As Ah-counting monitor go, the BMV712 is very good IMO, not least because of its very low power consumption.

 

In my opinion the best setup for lead acid batteries is a combination of a Smartgauge, which gives an honest SoC during discharge, and a BMV712 which is good for monitoring charging. The combination allows a good idea of the health of the batteries (ie actual capacity as opposed to badged capacity).

Edited December 20, 2021 by nicknorman

[Bod]

33 minutes ago, Richard10002 said:

I've got a BM2, a Smartgauge, and a Victron BMV712. 

 

The BM2 did all I wanted it to do and, apart from loving the Bluetooth control of the Victron, I would buy it again.

 

I wouldn't buy a Smartgauge again if you paid me!

 

I haven't considered anything cheaper, but have seen a Chinese monitor on Will Prowse YouTube channel,  which looked good, and which he liked - a bit like the BMV without the Bluetooth. 

Why would you not have Smartgauge?

 

Bod

[MtB]

Just now, Bod said:

Why would you not have Smartgauge?

 

Bod

 

Because half the time, the display is lying.

[Bod]

1 minute ago, MtB said:

 

Because half the time, the display is lying.

Is this during charging?

 

Bod

[nicknorman]

Just now, MtB said:

 

Because half the time, the display is lying.

 

Same can be said for an Ah-counting display with anything other than brand new perfect condition batteries. In fact the Ah counter is worse because it lies all the time, except when the batteries have just been fully charged.

[MtB]

1 minute ago, nicknorman said:

 

Same can be said for an Ah-counting display with anything other than brand new perfect condition batteries. In fact the Ah counter is worse because it lies all the time, except when the batteries have just been fully charged.

 

WHAT??!!!!!

 

Even with my lithium irons?

 

😅

[MtB]

19 minutes ago, Bod said:

Is this during charging?

 

Bod

 

Yes.

 

Also lies during discharging if you draw a short straw like I did, and get palmed of with one incorrectly calibrated. And how would you know, until your batteries die? 

 

 

[nicknorman]

9 minutes ago, MtB said:

 

WHAT??!!!!!

 

Even with my lithium irons?

 

😅

Not so much with Li, because they have a much more stable and long lasting capacity. I think the OP was asking in relation to LA though, which tends to have a fickle and short-lived nominal capacity.

 

The only trouble is that with Li, one doesn’t tend to regularly fully charge and thus synchronise to 100%. Thus means that inevitable integration errors slowly build up. We’ve got a Mastervolt Ah-counting meter, and a BMV712. Shunts in series so they are measuring exactly the same current.

 

We leave the boat in the Marina at around 50%SoC connected to a charger whose voltage is set to that necessary to hold this SoC (around 13.18v). When I come back a month later, typically the Mastervolt has dropped to 40% whilst the BMV has risen to 60%. This despite following the procedure to zero the current measurement in the BMV 712.

 

What is really needed is a hybrid system that primarily uses Ah-counting, but in slow time that is tweaked slightly by an average (and accurate) battery voltage compensated for any current vs state of charge - in other words, a battery model of SoC vs no load voltage which is what the Smartgauge is - although unfortunately there is no Smartgauge for lithium batteries.

 

I have the capability to do that with my hardware (the BMS can modify the BMV712 SoC over Ve.direct) but I haven’t implemented the software yet.

[Bod]

10 minutes ago, MtB said:

 

Yes.

 

Also lies during discharging if you draw a short straw like I did, and get palmed of with one incorrectly calibrated. And how would you know, until your batteries die? 

 

 

I'm aware of your saga, and the advice you were given during it.

I'm sure that despite your unfortunate experience, many more batteries have been ruined by Amp-hour counting type monitors, than voltage measuring devices.

 

Bod.

Edited December 20, 2021 by Bod
to add last line.

[Tony Brooks]

In truth for overall simplicity the Smartguage is probably the best you can get as long as the factory calibrated it correctly AND the owner knows the display during charge and for a very short time afterwards is likely to be optimistic.

[IanD]

31 minutes ago, Tony Brooks said:

In truth for overall simplicity the Smartguage is probably the best you can get as long as the factory calibrated it correctly AND the owner knows the display during charge and for a very short time afterwards is likely to be optimistic.

 

IIRC there was a period quite a long time ago (8-10 years?) where some Smartgauges weren't being calibrated correctly (when manufacture/calibration switched from the designer to the current one?) and MtB got bitten, but after being identified this problem was fixed in subsequent units and has not happened since -- which would mean this is not a reason to avoid buying one today, as Tony says.

 

Unless somebody knows better... 😉

[Richard10002]

5 hours ago, MtB said:

 

The Victron BMV712 has the best functionality AFAICS, but having one myself I find it has the most irritating drawback - the display is TINEEEEE.

 

Get a good look at one and see how small the main display is. Barely readable until you get close i.e. less than three feet away. And only then do you realise there is more, truly microscopic information on the screen which you can only see with ya glasses on and a torch! 

 

Yes. My BMV unit is actually hidden away where I put it 2 years ago, always meaning to git it neatly somewhere I actually only use the Bluetooth info on my phone app, so have never needed the display.

[Richard10002]

5 hours ago, Bod said:

Why would you not have Smartgauge?

 

Bod

Having bought it, I felt as though I had been conned.

 

It merely shows a percentage which purports to be State of Charge. Thus, on its own there is a strong chance that you would use it like a petrol gauge, and assume your batteries are full when it says 100%.

 

As with all monitors, SOC is not to be trusted, and the Smartgauge manual actually states that it can only be trusted when discharging. Even the, I recall that the creator has been heard to ask why anybody would want to know their SOC if its over 80%, which suggests it can only be trusted when discharging below an SOC of 80%.

 

I would agree with Nick that, with a bit of fairly simple calculation, a Smartgauge and a NASA or a BMV, can help to establish actual capacity.

 

 

[Keeping Up]

Another vote for the Nasa BM2. It uses voltage to estimate SoC when discharging, and counts amp-hours when charging. Provided that you remember to reset the Ah counter to zero after charging and to regularly recalibrate the nominal capacity at least monthly (for example by setting it to show 100% when you know from the charge current that the batteries are genuinely fully charged) then it will actually give remarkably accurate displays of all parameters including SoC the whole time - as well as showing you what is the actual battery capacity. Add to that the ease of reading the display from a distance, it really is very good.

[blackrose]

I've got a BEP DC meter and a Smartgauge. Covers everything I need.

 

Edited December 20, 2021 by blackrose

[Bod]

40 minutes ago, Richard10002 said:

Having bought it, I felt as though I had been conned.

 

It merely shows a percentage which purports to be State of Charge. Thus, on its own there is a strong chance that you would use it like a petrol gauge, and assume your batteries are full when it says 100%.

 

As with all monitors, SOC is not to be trusted, and the Smartgauge manual actually states that it can only be trusted when discharging. Even the, I recall that the creator has been heard to ask why anybody would want to know their SOC if its over 80%, which suggests it can only be trusted when discharging below an SOC of 80%.

 

I would agree with Nick that, with a bit of fairly simple calculation, a Smartgauge and a NASA or a BMV, can help to establish actual capacity.

 

 

Yes, it shows a percentage of the State of Charge remaining in the battery.  It does not show how many amps are used, or left in the battery, or the actual capacity.  In that respect it could be used as a "petrol gauge" to a tank of unknown capacity.  (but it does have accurate volt meters)

As for the accuracy whilst charging, this is openly said in the instructions, albeit with out explaining the the reason, the Smartgauge see's the charging voltage, which is higher than the true battery voltage, which it needs to calculate the State of Charge.

 

Using the Smartgauge.

If the battery is slow to discharge, and slow to charge, the battery is in good condition.

Quick to discharge, quick to charge, battery is worn out, needs changing.

Slow to discharge, quick to charge, battery charger has the wrong setting or a fault.

Quick to discharge, slow to charge, too heavy load taken from battery.

 

Bod

 

 

 

[Tony Brooks]

6 minutes ago, Bod said:

snip

Quick to discharge, slow to charge, too heavy load taken from battery.

 

 

Or more likely a shorting cell or cells.

[Richard10002]

16 hours ago, Bod said:

As for the accuracy whilst charging, this is openly said in the instructions, albeit with out explaining the the reason

 

Hardly "openly said", when it is towards the end of the manual, long after you have handed over your money.

 

"PLEASE NOTE: SMARTGAUGE IS NOT ACCURATE WHEN CHARGING, AND SHOULD NOT BE RELIED ON DURING CHARGING" in the marketing material, on the box, and at the start of the instructions, would be a better example of "openly said".

 

The OP asked for some advice and experience. I fell for the marketing guff, and discovered it wasn't quite as it appeared. Not the only product this happens with, but this is the product I am talking about.

 

Equally, I would advise people not to buy anything from Curry's, or at least be wary of any information and advice received, but we aren't talking about that here.