voltage drop, batteries under load.

[DaveGood]

Nicknorman,

 

If monitoring voltage alone, and peforming repeated calculations on that single piece of data , is sufficient to give an accurate reading of SOC, (which is what Smartbauge does).

 

Why does monitoring voltage and amps and temperature and voltage drop when under load give a less accurate or misleading result? Why does more information and greater knowledge lead to a worse outcome?

 

 

 

DaveGood

[gbclive]

Slightly at a tangent, has anyone fitted a Merlin DataCell II? This is effectively a Smartgauge Mk2, as well as using custom algorithms on voltage and voltage change over time, it also uses a shunt ammeter to properly measure current too.

No, but it's a tad over £1,000!

[DaveGood]

By,eck

 

The smartgauge gives a state of charge reading under dynamic load, so for that matter does your volt meter, your rev counter, and your temperature gauge.

 

Which ones do you not trust when under "dynamic load", all, some, none?

 

DaveGood

Edited March 30, 2015 by DaveGood

[Paul C]

Nicknorman,

 

If monitoring voltage alone, and peforming repeated calculations on that single piece of data , is sufficient to give an accurate reading of SOC, (which is what Smartbauge does).

 

Why does monitoring voltage and amps and temperature and voltage drop when under load give a less accurate or misleading result? Why does more information and greater knowledge lead to a worse outcome?

 

 

 

DaveGood

 

Because of sampling rate - one of the keys to its success is the fact that it reads changes to voltage constantly. By all means if a machine measured the voltage, amps, temperature too it would be better - see previous post regarding Merlin DataCell II.

[DaveGood]

I agree with you PaulC, and with Nicknorman.

 

What I don't understand is why one of the most basic parameters of battery performance, voltage drop when under load, is regarded as a taboo subject, dangerous to bring up, and absolutely noone had any idea what the answer is.

 

Not one person has come here, or on other forums I've posted to with an answer. But there have been plenty of people who, while, not knowing the answer themselves, have told me it's

pointless to know and seem offended I asked.

DaveGood

[nicknorman]

Not one person has come here, or on other forums I've posted to with an answer.

 

 

Perhaps that should tell you something about the question?

 

 

What I don't understand is why one of the most basic parameters of battery performance, voltage drop when under load, is regarded as a taboo subject, dangerous to bring up, and absolutely noone had any idea what the answer is.

 

But there have been plenty of people who, while, not knowing the answer themselves, have told me it's

pointless to know and seem offended I asked.

 

 

No, not taboo, not dangerous and no-one is offended. But yes, pointless and we have no idea what the answer is because it is a non-question that doesn't have an answer.

[Paul C]

I agree with you PaulC, and with Nicknorman.

 

What I don't understand is why one of the most basic parameters of battery performance, voltage drop when under load, is regarded as a taboo subject, dangerous to bring up, and absolutely noone had any idea what the answer is.

 

Not one person has come here, or on other forums I've posted to with an answer. But there have been plenty of people who, while, not knowing the answer themselves, have told me it's

pointless to know and seem offended I asked.

DaveGood

 

Its not dangerous/taboo, its just that its not really been considered because its inaccurate. Its a bit like me asking someone to predict the fuel economy of my car and giving its length and average speed. Yes there's a correlation - a very rough one - but I'd expect everyone to come back and say "you can't really predict fuel economy from those two variables alone".

[DaveGood]

If voltage drop under load is an inaccurate measure of battery SOC why believe the Merlin II or Smartgauge are accurate?

 

They both take their main reference for judging battery SOC from the battery voltage whether under load or not.

 

The arguement that you can take one or at most, two, parameters of any physical system and by subjecting that parameter to intense scrutiny over a long period of time you will gain a full understanding of the health of that system is a flawed one.

 

I can monitor your blood pressure and your temperature second by second, it wouldn't tell me you were blind.

 

All, I've done, here and other forums, is ask if anyone had any info on what voltage drop is normal for x amps applied to y battery bank.

 

I've met with little but ignorance and disapproval.

 

DaveGood

[GUMPY]

The arguement that you can take one or at most, two, parameters of any physical system and by subjecting that parameter to intense scrutiny over a long period of time you will gain a full understanding of the health of that system is a flawed one.

 

If it is flawed then please explain just how the origional smartgauge is so accurate?

SG only looks at voltage and possibly time as well so no more than two parameters and yet in the past 10 years there is still not a more accurate method of measuring SOC.

If you believe that you can "cobble together" (your words) a system that is as accurate then good luck to you, even beter if it tells me the battery bank total capacity which SG doesn't, Ill volunteer to be a tester in 5 years when you have a prototype working, just as I did for Gibbo.

 

ETA

I can give you a pretty good approximation of the SOC of rested batteries with just a voltmeter accurate to 2 decimal places.

Edited March 30, 2015 by Loddon

[Naughty Cal]

 

Known variables: voltage reading of battery, load currently applied could be used to predict state of charge.

As can reading the volt meter and ammeter.

 

I personally don't see what any extra information would add.

[DaveGood]

Loddon, Naughty Cal,

 

Do either of you know how much fuel your engine will use on half power for eight hours? I bet you do, and if you don't it'll take you less then ten minutes online to find out what your engine should burn in that time.

 

My question is the same, but applied to batteries.

 

This is stuff we all should know.

 

DaveGood

[Naughty Cal]

Loddon, Naughty Cal,

 

Do either of you know how much fuel your engine will use on half power for eight hours? I bet you do, and if you don't it'll take you less then ten minutes online to find out what your engine should burn in that time.

 

My question is the same, but applied to batteries.

 

This is stuff we all should know.

 

DaveGood

More than the tank holds.

 

Although I'm not sure what that has to do with batteries!

[DaveGood]

Loddon,

 

I know, or, not having one myself, accept from the evidence of others, that it is highly accurate, also highly expensive, there are useful solar panel systems out there that cost less.

 

And I know there are many people on this forum who are not sure where to find the price of another two bags of coal to carry them through April, never mind be in a position to buy either a PV system or smartgauge.

 

If I can work out a rough, rule of thumb method that will allow them to better manage their battery bank, without cost to them ,I will do so, but I'm getting no help here.

 

DaveGood

Edited March 30, 2015 by DaveGood

[GUMPY]

Loddon, Naughty Cal,

 

Do either of you know how much fuel your engine will use on half power for eight hours? I bet you do, and if you don't it'll take you less then ten minutes online to find out what your engine should burn in that time.

 

My question is the same, but applied to batteries.

 

This is stuff we all should know.

 

DaveGood

Half power what's that?

with 50hp available in a NB I rarely get that high

Actually like SOC its not really something I care about as I know that I have enough batteries to last a day or so without recharging, and I have to deal with electrical crap for a living so its not something I constantly check on.

System design is a far more important thing than SOC since if a system is designed well it will meet the users needs without having to worry about SOC/voltage drop or any parameters at all

[GUMPY]

If I can work out a rough, rule of thumb method that will allow them to better manage their battery bank, without cost to them ,I will do so, but I'm getting no help here.

Roughly

with no load and at least 2hrs after charging.

12.7v fully charged

12.6v 90%

12.5v 80%

12.4v 70%

12.3v 60%

12.2v 50%

 

Just a voltmeter connected direct to the batteries will give you this info.

Edited March 30, 2015 by Loddon

[Naughty Cal]

Roughly

with no load and at least 2hrs after charging.

12.7v fully charged

12.55 80%

12.45 70%

12.35 60%

12.25v 50%

 

Just a voltmeter connected direct to the batteries will give you this info.

And that is as simple as it needs to be.

[bizzard]

Nor me. I have only one 110 amp service battery, well, I have another, but it's usually switched out. At the moment my lovely little voltmeter with the blue digital digits is reading 12.6v, if I turn a tap on, now this can be important, If I remember I turn a tap on before switching the pump on and off before turning the tap off, this saves load on the battery by not starting and stopping the pump under load-pressure. The pumps certainly last much longer too by not being left dormant under pressure.

Anyhow, erm, forgotten where I was now. Yes, The wee voltmeter is reading 12.6v, I open a tap and switch the pump on, the voltage drops to 12.4v, turn the pump off and the voltmeter providing it wasn't on the verge of dropping to 12.5v when I started the pump returns to 12.6v, if however the reading was on the verge of dropping to 12.5v before switching the pump on it might remain at 12.5v. So I reckon the amount the voltage drops when a known load is released upon a new or nearly new battery is X amount depending on what load and the drop will increase as the battery gets older with weaker cells rather than because of the state of charge.

Hope this helps.

Edited March 30, 2015 by bizzard

[GUMPY]

And that is as simple as it needs to be.

Figures adjusted although to be honest its not difficult.

[DaveGood]

Good info Loddon, thank you,

 

But now consider the case of livesboards who, for whatever reason, cannot shut down thier electrical systems for two hours, this time of year.

 

I've met some.

 

DaveGood

[GUMPY]

Good info Loddon, thank you,

 

But now consider the case of livesboards who, for whatever reason, cannot shut down thier electrical systems for two hours, this time of year.

 

I've met some.

 

DaveGood

As usual on this forum you read what you thought I said not what I did

I didn't say shut down the system for 2 hours I said shut it down whilst taking the measurements......

Easiest to take the measurements first thing in the morning or when you get home from work it only takes seconds to look at the meyer.

Oh and as for livaboards I have been one for 25years so do have a vague idea of what's going on.

Edited March 30, 2015 by Loddon

[DaveGood]

Everything helps buzzard.

 

DaveGood

[Phil Ambrose]

Slightly at a tangent, has anyone fitted a Merlin DataCell II? This is effectively a Smartgauge Mk2, as well as using custom algorithms on voltage and voltage change over time, it also uses a shunt ammeter to properly measure current too.

I use a Merlin Power Gauge Lite, shunt based (500amp) and tells me the voltage on domestic bank, starter, amps in and out plus amp/hrs used and percentage remaining

Phil

[bizzard]

At this time of year when you wouldn't need electric fridges on, a few hours with the system shut down shouldn't be any problem at. Just fill a few pots and kettle with water beforehand to heat on the gas for the usual things. Laptops should work on their battery ect.

[nicknorman]

All, I've done, here and other forums, is ask if anyone had any info on what voltage drop is normal for x amps applied to y battery bank.

I've met with little but ignorance and disapproval.

DaveGood

I've tried to explain the issues to you, patiently and repetitively, but you are intransigent and now somewhat rude. I'm out.

[Iain_S]

I use a Merlin Power Gauge Lite, shunt based (500amp) and tells me the voltage on domestic bank, starter, amps in and out plus amp/hrs used and percentage remaining

Phil

 

We've got one of these on Kelpie. Good for voltage and amp hours used, but the percentage reading is calculated by (Amp.Hours out/Battery capacity) x 100, so fairly useless, as we haven't any idea what the battery capacity actually is. Nominal value is 440AH, but old batteries ,so a lot less than this now.

The Amp.Hours used figure is a bit suspect after a partial charge, as well, as it appears to be calculated on the basis that 1AH out equals 1.25AH in. (default setting).

 

Quite a good instrument, but would ideally be complimented by a Smartgauge, as the combination would give more information than could be gleaned from either on it's own.

 

Iain