Jump to content

BMV, Smartgauge, ammeter....


Wittenham

Featured Posts

1 minute ago, nicknorman said:

Pointing it out is fine. If you didn’t, I would! But comparing it to a doorstop isn’t quite the same thing. We knew what you were talking about, but it could have misled the OP.

 

 

Yes I apologise for that. It was a joke but I know lots of people are terribly sensitive about criticism of Smartgauges. 

 

It would actually make a terrible doorstop. Far too light. 

 

  • Haha 1
Link to comment
Share on other sites

2 minutes ago, Tony Brooks said:

Could not find a 50mm round one to fit a hole any cheaper.

Ah, mines just a little square one.   You could have bought a square hole to fit the £3 square one.

Link to comment
Share on other sites

The BMV is good at showing amps flowing, can give an idea of amp hours used (but you have to have the correct peukert value) but can be usefull. It can also give an idea of when the battery is charged ie 0 amp hours, but that requires the correct efficiency being set. The SOC requires the correct battery capacity to be set.  Since all these settings vary with battery age and temperature etc they are at best guestimates, of amp hours used and SOC.  I use one though and find it usefull for amps and volts and approximate amp hours. By comparing amp hours and the Smartgauge percentage I get a fair idea of battery life and can see the slow decline in capacity (8% in 3 years so far) AGM batteries.  I also have an ammeter in the alternator lead and a voltmeter, both with big displays which I can see from the steering position so I know when volts are 14.3+ and amps less than 4 the batteries are full.

  • Greenie 1
Link to comment
Share on other sites

54 minutes ago, Detling said:

 It can also give an idea of when the battery is charged ie 0 amp hours, but that requires the correct efficiency being set.

I think it gives you more than an 'idea' when the battery bank is full.

The tail current at 14.3V+ tells you what you need to know. Ok you need to have an 'idea' of capacity but you can still be way out on that and still know where you are with tail current. On a 600Ahr bank, I knew I was full when the tail current was down around 6-8A at that charging voltage and I could reset the gauge. Even if the efficiency was set way off, you would still know it was full.

There is enough info on here to have a go at getting all the settings other than capacity pretty near right.

Link to comment
Share on other sites

20 minutes ago, Dr Bob said:

There is enough info on here to have a go at getting all the settings other than capacity pretty near right.

 

And that, as Nick pointed out earlier, is where a Smartgauge in conjunction with a BMV is really good for establishing the actual capacity. 

  • Horror 1
Link to comment
Share on other sites

19 minutes ago, Mike the Boilerman said:

 

And that, as Nick pointed out earlier, is where a Smartgauge in conjunction with a BMV is really good for establishing the actual capacity. 

OMG, MtB needs therapy. He has actually said something nice about  SG! 

1 hour ago, Detling said:

The BMV is good at showing amps flowing, can give an idea of amp hours used (but you have to have the correct peukert value) but can be usefull. It can also give an idea of when the battery is charged ie 0 amp hours, but that requires the correct efficiency being set. The SOC requires the correct battery capacity to be set.  Since all these settings vary with battery age and temperature etc they are at best guestimates, of amp hours used and SOC.  I use one though and find it usefull for amps and volts and approximate amp hours. By comparing amp hours and the Smartgauge percentage I get a fair idea of battery life and can see the slow decline in capacity (8% in 3 years so far) AGM batteries.  I also have an ammeter in the alternator lead and a voltmeter, both with big displays which I can see from the steering position so I know when volts are 14.3+ and amps less than 4 the batteries are full.

Peukert is not relevant to amp hours used nor SoC. It is only relevant to “time to run to flat at the present discharge rate” which is not usually a useful parameter.

 

I think the later BMV gauges automatically set the charge efficiency factor.

Link to comment
Share on other sites

as always, thanks for the helpful - and entertaining - answers.  My conclusions are:

 

- keep the SG

- give away the ammeter

- RTFM for both devices

- despite being a volume purchaser, MtB probably does not get a Christmas card from the SG company

 

 

  • Greenie 1
Link to comment
Share on other sites

3 hours ago, Tony Brooks said:

I wish I was as happy with my £30 digital Chinese voltmeter. I am sure it reads between 0.2 and 0.3 volts low. Not much good when assessing state of charge but at least wrong on the fail safe side of things.

The one I have is a dual voltmeter/ammeter. It is about 0.1V low on voltage readings, and about 0.5A out on current (again low.) For the cost I can't complain. I did have a similar gauge that was just a votlmeter but this was less accurate.

Link to comment
Share on other sites

  • 2 weeks later...
On 06/06/2019 at 13:19, nicknorman said:

OMG, MtB needs therapy. He has actually said something nice about  SG! 

Peukert is not relevant to amp hours used nor SoC. It is only relevant to “time to run to flat at the present discharge rate” which is not usually a useful parameter.

 

I think the later BMV gauges automatically set the charge efficiency factor.

I'd agree that Peukert Factor is not relevant to Consumed Ah however changing the Peukert factor has an immediate effect on the SoC reading. My BMV is currently showing an SoC of 90% ( PF set at 1.25) changing the PF to 1.1 changes the SoC reading to 82% and changing it to 1.4 changes the SoC to 95%. This seems counter intuitive as me sketchy understanding of Peukert Factor is that the higher the factor the greater the discharge at higher loads, a perfect battery having a PF of 1, I'd therefore expect that a higher PF would show a lower SoC.  The time Remaining is infinite as the solar is ensuring a positive charge. Do we have any mathematical/physics geniuses who can explain this in English? 

Link to comment
Share on other sites

1 hour ago, grahame r said:

This seems counter intuitive...

Not really. The BMV is looking at Ah going into the battery to replace the Ah taken out. If it reckoned the battery was at 50% after discharging a battery having a Peukert Exponent of 1.4 then it’ll actually be less discharged than if you took a battery with a PE of 1.1 down to 50%. Therefore the Ah that you’ve put in will result in a higher SoC reading. Remember that charge efficiency has nothing to do with Peukert. 

 

Edited by WotEver
Changed Ah for % to save Nick’s hair.
Link to comment
Share on other sites

28 minutes ago, WotEver said:

Not really. The BMV is looking at Ah going into the battery to replace the Ah taken out. If you’ve used 100Ah from a battery having a Peukert Exponent of 1.4 then it’ll actually be less discharged than if you took that 100Ah out of a battery with a PE of 1.1. Therefore the 80Ah that you’ve put in will result in a higher SoC. remember that charge efficiency has nothing to do with Peukert. 

No, 100AH is 100AH regardless of peukert or how fast you discharged it. The SoC is the same. Please don’t make me go through it all yet again, I might start crying!

1 hour ago, grahame r said:

I'd agree that Peukert Factor is not relevant to Consumed Ah however changing the Peukert factor has an immediate effect on the SoC reading. My BMV is currently showing an SoC of 90% ( PF set at 1.25) changing the PF to 1.1 changes the SoC reading to 82% and changing it to 1.4 changes the SoC to 95%. This seems counter intuitive as me sketchy understanding of Peukert Factor is that the higher the factor the greater the discharge at higher loads, a perfect battery having a PF of 1, I'd therefore expect that a higher PF would show a lower SoC.  The time Remaining is infinite as the solar is ensuring a positive charge. Do we have any mathematical/physics geniuses who can explain this in English? 

In that case the BMV’s SoC algorithm is faulty (ie wrongly designed). Probably explains why BMV SoC readings are not known for their accuracy! Peukert should have no impact on SoC. It certainly doesn’t on my properly-designed mastervolt AH counting device (Mastershunt). 

Edited by nicknorman
Link to comment
Share on other sites

29 minutes ago, nicknorman said:

Please don’t make me go through it all yet again, I might start crying!

But you always get it wrong :P

32 minutes ago, nicknorman said:

In that case the BMV’s SoC algorithm is faulty (ie wrongly designed)

Well, we already know it is because it’s so wildly inaccurate, but see my amended post for an explanation. 

Link to comment
Share on other sites

On 06/06/2019 at 01:27, Mike the Boilerman said:

 

Yes. Two are shyte, one is accurate. 

 

Checked with a DVM tested for accuracy against another DVM checked for accuracy against a university instrument calibrated to something accurate.

 

That should do, shouldn't it? 

 

 

I've been meaning to ask this for months and months ( and no, I don't want to get into a debate.) Why don't you re-calibrate the inaccurate ones using your wizzo ones as a datum?

Link to comment
Share on other sites

9 minutes ago, Slim said:

I've been meaning to ask this for months and months ( and no, I don't want to get into a debate.) Why don't you re-calibrate the inaccurate ones using your wizzo ones as a datum?

:D:clapping:?

Link to comment
Share on other sites

53 minutes ago, Slim said:

I've been meaning to ask this for months and months ( and no, I don't want to get into a debate.) Why don't you re-calibrate the inaccurate ones using your wizzo ones as a datum?

 

I have done, silly!

 

The point remains though, and all I am ever saying is that a Smartgauge can't be trusted 'straight from the box' in my personal experience, much to the annoyance of you Smartgauge evangelists.

 

 

Link to comment
Share on other sites

3 hours ago, Slim said:

I've been meaning to ask this for months and months ( and no, I don't want to get into a debate.) Why don't you re-calibrate the inaccurate ones using your wizzo ones as a datum?

How does one go about re-calibrating a Smart Gauge?

Link to comment
Share on other sites

1 hour ago, grahame r said:

How does one go about re-calibrating a Smart Gauge?

 

27 minutes ago, gbclive said:

Plus 1 for this, pretty please?

Firstly, why do you think your Smartgauges need recalibrating? They should only be recalibrated if they actually need it.

Edited by nicknorman
Link to comment
Share on other sites

I didn't say I wanted to re-calibrate it, I had read MtBs previous comments and checked my Smartgauge which was reading about 0.3V low. I contacted Smartgauge and they replaced it without quibble, the replacement being correct. I am, however, curious to know if there are any secret ways of affecting the SG readings as claimed by MtB and others, just a naturally curious mind.   

Link to comment
Share on other sites

7 hours ago, grahame r said:

I didn't say I wanted to re-calibrate it, I had read MtBs previous comments and checked my Smartgauge which was reading about 0.3V low. I contacted Smartgauge and they replaced it without quibble, the replacement being correct. I am, however, curious to know if there are any secret ways of affecting the SG readings as claimed by MtB and others, just a naturally curious mind.   

If you have a naturally curious mind, then why not get a BMV which gives you voltage plus Amps and Amp hours used. Far more info to get your brain around? 

Link to comment
Share on other sites

7 hours ago, grahame r said:

I didn't say I wanted to re-calibrate it, I had read MtBs previous comments and checked my Smartgauge which was reading about 0.3V low. I contacted Smartgauge and they replaced it without quibble, the replacement being correct. I am, however, curious to know if there are any secret ways of affecting the SG readings as claimed by MtB and others, just a naturally curious mind.   

Yes there is a secret way to adjust the voltage reading. Since SG only measures voltage, once that is measured correctly the SG will be accurate.

4 minutes ago, Dr Bob said:

If you have a naturally curious mind, then why not get a BMV which gives you voltage plus Amps and Amp hours used. Far more info to get your brain around? 

Why not indeed! Perhaps because the BMV doesn’t calculate SoC directly, it merely derives it from AH out and a presumption about battery capacity which is usually wrong.

  • Happy 1
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.