Which Battery Monitor

[Euphonyx]

Hi Folks. Looking for some help again.

I want to fit a battery monitor. I have two 12v batteries and a 1-both-2 type switch. What monitor would suit best? I'm no electrical enginerr so the simpler the better. Thanks in advance

 

[JumbleDuck]

Hi Folks. Looking for some help again.

I want to fit a battery monitor. I have two 12v batteries and a 1-both-2 type switch. What monitor would suit best? I'm no electrical enginerr so the simpler the better. Thanks in advance

Simplest is a couple of cheap digital panel voltmeters ( a fiver each or so) from eBay. Most others involve more work fitting a shunt (small resistance near the battery; voltage across it measures the current). Some swear by Smartgauges which do everything from voltage and posh mathematics.

Are you going for obsessive "my battery is 75.696% charged" accuracy or a more relaxed "it's got a fair bit of oomph in it" indication?

 

[Aurai]

Hi

We have a "Smart Guage" which was a doddle to install. With hindsight, it appears that a decent voltage meter and a table printed off the Internet, does the job perfectly, can advise if either or both appeal.

Thank you

 

[VicS]

Hi Folks. Looking for some help again.

I want to fit a battery monitor. I have two 12v batteries and a 1-both-2 type switch. What monitor would suit best? I'm no electrical enginerr so the simpler the better. Thanks in advance

There is something in Jumbleducks suggestion to just use digital voltmeters but you do have to use them in the correct way, ie take the reading when the battery has rested with no charge or discharge for a minimum time and stick more or less to the same time. You cannot compare a reading taken an hour after coming off charge with one a day later for example.

If you want something inexpensive, sweet and simple and you are able to accept the limitations its the way to go.

If you want something more fancy and an instrument that attempt to tell you the % state of charge and display current and volts and is capable of "fully" monitoring one battery and giving a voltage reading of the other then the BM1 or BM2 may be for you.

BUT
they do need a system with a dedicated services battery, which will be fully monitored, and a dedicated starter battery. They may need a move away from the chop and change capability of a 1,2, both switch.

Some people like the simplicity of installation of the Smartgauge. Others are mystified as to how it can possibly do what it does do.
AFAIK the Smartgauge is a one battery instrument and that paralleling two with a 1, 2, both switch would confuse it.

 

[Anders_P42]

Victron BVM602 monitors two batteries, although simple volt monitoring on second one (usually starter batt).

http://www.victronenergy.com/battery-monitors/bmv-600s and bmv-602s/

Cost about £170.

Spec here

http://www.victronenergy.com/upload/documents/Datasheet-Battery-monitoring-EN.pdf

Anders

 

[Richard10002]

I narrowed it down to Smartguage or NASA BM2.

I chose the BM2 because it shows voltage, instantaneous amps in, or out, and cumulative amp hours. I can use my knowledge and judgement to work out how things are. It makes a stab at State of Charge, but it's not good at it - and it depends on you inputting the correct capacity of the bank, which is unknown.

If I didn't want to think about things, and was willing to trust the Smartguage, that's what I would have bought. Enough people seem to be happy that it's pretty close to correct.

 

[Stu Jackson]

Some people like the simplicity of installation of the Smartgauge. Others are mystified as to how it can possibly do what it does do.
AFAIK the Smartgauge is a one battery instrument and that paralleling two with a 1, 2, both switch would confuse it.

That's true. Except the only bank one needs be interested in is the house bank, 'cuz the start bank is always almost full.

This is a philosophical issue and I believe we Yanks have a different view, i.e., we charge house first, start second, whereas you choose to prioritize the start. But for simplicity, the Smartgauge can't be beat, but it is only good for one bank, and shouldn't be used or actually confused by a 1-2-B switch anyway. Use it to measure the house bank and you're done.

 

[longjohnsilver]

Victron BVM602 monitors two batteries, although simple volt monitoring on second one (usually starter batt).

http://www.victronenergy.com/battery-monitors/bmv-600s and bmv-602s/

Cost about £170.

Spec here

http://www.victronenergy.com/upload/documents/Datasheet-Battery-monitoring-EN.pdf

Anders

These are excellent, giving a constant indication of battery condition and showing amps in and out, as well as battery voltage and state of charge etc.

 

[sailinglegend420]

AFAIK the Smartgauge is a one battery instrument and that paralleling two with a 1, 2, both switch would confuse it.

it's interesting that maybe 75% of battery monitor installations are wrong, many because extra equipment has been installed afterwards which has bypassed the shunt. This can't happen with the SmartGauge which goes directly to the service battery so a 1,2,both switch can't confuse it. This applies also to battery monitors which must go directly to the battery. Probably 90% of Battery Monitors are programmed incorrectly which is one of the reasons they become more and more inaccurate as the batteries age. With the SmartGauge it becomes more and more accurate as it learns the battery dynamics.

Most battery monitors, including SmartGauge, measure at least two battery voltages. With a SmartGauge also buy a digital amp meter to keep an eye on charging and discharge currents.

 

[dslittle]

they do need a system with a dedicated services battery, which will be fully monitored, and a dedicated starter battery. They may need a move away from the chop and change capability of a 1,2, both switch.

Some people like the simplicity of installation of the Smartgauge. Others are mystified as to how it can possibly do what it does do.
AFAIK the Smartgauge is a one battery instrument and that paralleling two with a 1, 2, both switch would confuse it.

My Smartgauge will give me the volts on the domestic bank AND the starter battery. Simplicity itself to fit.

 

[MikeBz]

As others have said, if you're want an accurate state-of-charge measurement then it has to be a Smartgauge. I went for the BM1 over the Smartgauge because I wanted to see amps in/out as well as a rough state-of-charge. As it turns out the state-of-charge indicator on the BM1 is near to useless. With my new 200Ah of house batteries fully charged, it drops the displayed SoC from 100% to 80% after a few tens of minutes of a few amps being drawn, no matter how many times I reset it. I might save up for a Smartgauge as well.

 

[Richard10002]

As others have said, if you're want an accurate state-of-charge measurement then it has to be a Smartgauge. I went for the BM1 over the Smartgauge because I wanted to see amps in/out as well as a rough state-of-charge. As it turns out the state-of-charge indicator on the BM1 is near to useless. With my new 200Ah of house batteries fully charged, it drops the displayed SoC from 100% to 80% after a few tens of minutes of a few amps being drawn, no matter how many times I reset it. I might save up for a Smartgauge as well.

Your batteries won't be 200Ah even when new, and their capacity will drop over time. Try setting the capacity at 180Ah, and see how it looks. Then a bit of trial and error can get it close for some time.

My 330Ah bank is set in the BM2 at 150Ah, and SOC seems to be representative.

 

[dslittle]

Your batteries won't be 200Ah even when new, and their capacity will drop over time. Try setting the capacity at 180Ah, and see how it looks. Then a bit of trial and error can get it close for some time.

My 330Ah bank is set in the BM2 at 150Ah, and SOC seems to be representative.

As I said, I have a Smartgauge. I got it because (a) I am lazy and (b) I am easily confused by electrickery.

Whilst I have no doubt this works for you, and strongly believe in each to their own, I realy don't want to 'guess' an inaccurate number and then use that to determine the state of my battery bank. As has been said before the Smartgauge takes all of the guesswork out (if you believe/trust it - I personally do...)

 

[MikeBz]

Your batteries won't be 200Ah even when new, and their capacity will drop over time. Try setting the capacity at 180Ah, and see how it looks. Then a bit of trial and error can get it close for some time.

My 330Ah bank is set in the BM2 at 150Ah, and SOC seems to be representative.

Reducing the capacity setting in the BM is only going to make the SoC % drop faster. It takes about 3Ah of consumption to drop it by 20%, so from that you could deduce that it thinks the total capacity is about 15Ah. With 3-5A being drawn and the voltage stable at 12.8V it's clear to me that the SoC must be pretty close to 100%.

Anyway I can't really complain (even though I am) as I was warned by plenty of threads on the subject and made my decision!

 

[oldvarnish]

The state of batteries must be one of the most frequent topics here, and probably the least fully understood - certainly by me.

Assessing batteries is a hugely complex business, far beyond simply measuring the voltage across them. Complex mathematics are involved.

If you don't want to spend time getting to grips with the science, pay a bit more for a Smartguage and let it do the work for you - that's my choice.

 

[MikeBz]

Assessing batteries is a hugely complex business

Agreed.

... far beyond simply measuring the voltage across them.

And yet paradoxically, that is 'all' the Smartgauge does as in the only thing it measures is battery voltage. I'd love to know how it can tell the difference between the voltage dropping because I'm drawing 100A from a good battery vs. the voltage dropping at the same rate because I'm drawing 10A from a tired battery. It all seems too good to be true but there is plenty of good evidence that it really does work.

If you don't want to spend time getting to grips with the science, pay a bit more for a Smartguage and let it do the work for you - that's my choice.

Agreed, although it would always bug me that I just can't understand how it can possibly work from the amount of information it has.

 

[Robih]

Agreed, although it would always bug me that I just can't understand how it can possibly work from the amount of information it has.

Mike, I don't disagree with that but then I don't understand how this computer that I am typing this note in to works either!

 

[Euphonyx]

As I said, I have a Smartgauge. I got it because (a) I am lazy and (b) I am easily confused by electrickery.

Whilst I have no doubt this works for you, and strongly believe in each to their own, I realy don't want to 'guess' an inaccurate number and then use that to determine the state of my battery bank. As has been said before the Smartgauge takes all of the guesswork out (if you believe/trust it - I personally do...)

I'm with you on this.

Thanks, everyone, for the advice. The Smartguage seems to be the best option for me given my state of understanding.

 

[V1701]

..it's interesting that maybe 75% of battery monitor installations are wrong, many because extra equipment has been installed afterwards which has bypassed the shunt. Probably 90% of Battery Monitors are programmed incorrectly which is one of the reasons they become more and more inaccurate as the batteries age...

Can I ask on what evidence you are basing these claims?

I have 2 BM1s, one on my boat in Greece, one on my campervan here. The % state of charge is always a bit awry, as already said it will drop quickly after a relatively small load is applied but if you allow for this foible they provide very useful information. They are not that complicated to install, finding a position to mount the busbar close to one of the batteries in the bank to be monitored is probably the most awkward part of their installation...

 

[sailinglegend420]

Can I ask on what evidence you are basing these claims?....

See this thread for all the answers. Also my own experience in the Med over the last 7 years would suggest that 100% of boats with battery monitors that I have spoken to are either wired incorrectly or programmed incorrectly.

http://www.ybw.com/forums/showthrea...on-House-batts-necessary&highlight=SmartGauge