Smart Gauge vs Nasa BM-1

[Robin2]

 

What a bizarre statement.

 

I just want it to tell me the facts with real amp-hours, not fuzzy ones adjusted by some factor.

 

By the way did you see the bit I added to my previous post while you were replying to it?

[Gibbo]

However I am very curious.

 

Why does the amp-hour counter go so far adrift so quickly?

 

 

Many reasons:-

 

The charge efficiency varies depending upon the SOC.

 

The charge efficiency varies depending upon the previous discharge current.

 

Peukert's equation is a very rough, empirical, approximation that does indeed affect the actual power removed as opposed to simply the run time until the voltage collapses (as some people think).

 

Given a fixed shunt that has to be able to measure up to (say) 500 amps, in an electrically noisy environment such as a boat or vehicle, it is nigh on impossible to also measure down to (say) 0.1 amp on the same shunt with good repeatability and accuracy (look at the voltage you're trying to measure across the shunt).

 

Many loads/chargers are not pure DC but are actually a DC signal with AC superimposed on them. This is incredibly difficult to accurately integrate. Especially at the price people are prepared to pay for the device.

 

 

What are you using as a standard against which it is drifting?

 

 

That's easy, just run an amp hour counter for a few days discharging and recharging but never fully recharge. Then fully recharge, and see how far out the amp hour counter is.

 

Is there a consistent error that could be compensated for?

 

Afraid not, if there was someone would have done it.

 

I just want it to tell me the facts with real amp-hours, not fuzzy ones adjusted by some factor.

 

Make the following assumption:-

 

The actual charge efficiency of the battery bank is 90%.

 

Then do this:-

 

You discharge a 200ahr bank by 100ahrs.

 

You recharge by 100ahrs.

 

The meter says the batteries are full.

 

The batteries are actually at -10ahrs. They are 95% full.

 

Do this 5 times and the batteries are at 75% SOC, but the amp hour counter says they are full.

 

That's one way they run adrift.

[smileypete]

That's not charge efficiency. That's everything about them. It's been covered many many times before but there are two main problems with amp hour counters:-

 

1. They can't work at all if they don't know the battery capacity. In the real world, they won't know it because batteries lose capacity as they age and the amp hour counter does not know this. That's the first problem that stops them working.

That should be covered in the user manual. (the BM-1 manual does)

 

2. It's all very well saying "You have to make sure you fully recharge to reset the meter". In the real world that rarely happens. It's just a fact of life. It's simply the way it is. Under those circumstances they fail again because they run adrift. Charge efficiency compensated or not makes no difference, well it does, it helps, but it doesn't cure it.

As long as it uses compensation to under-read amp hours available or SoC it shouldn't be a huge problem.

 

If not then compensation can be added externally in the way I proposed.

 

Edit: Anyone used an amp-hour counter and experienced this problem? If so which make/model was it?

 

cheers,

Pete.

Edited March 4, 2011 by smileypete

[nb Innisfree]

I came across this prob when I started cruising a few years ago, tried guessing the ever decreasing batt capacity and feeding it in to our BMV 501 but really it was just a guessing game. I used to use the 2% of batt capacity to estimate when they were fully charged but as that also relied on accurately estimating batt capacity I was just going round in circles, 2% isn't really fully charged anyway. As I said earlier the best you can hope for when off grid and using power on a daily basis is to do a weekly 8+hour absorption, even then you lose out eventually. Batts are doomed whichever way you look at it.

Edited March 4, 2011 by nb Innisfree

[Naughty Cal]

I came across this prob when I started cruising a few years ago, tried guessing the ever decreasing batt capacity and feeding it in to our BMV 501 but really it was just a guessing game. I used to use the 2% of batt capacity to estimate when they were fully charged but as that also relied on accurately estimating batt capacity I was just going round in circles, 2% isn't really fully charged anyway. As I said earlier the best you can hope for when off grid and using power on a daily basis is to do a weekly 8+hour absorption, even then you lose out eventually. Batts are doomed whichever way you look at it.

 

Batteries are a consumable item. Whichever way you charge them they will need replacing at some point

[nb Innisfree]

Remember Smartgauge only guesses the state of charge, that's all, it doesn't know, but it guesses better than anything else and that guess is accurate enough to be of practical use.

[nb Innisfree]

Batteries are a consumable item. Whichever way you charge them they will need replacing at some point

 

Yeah I know but when they arrive all shiny and new you can't help falling for them...

[Naughty Cal]

Yeah I know but when they arrive all shiny and new you can't help falling for them...

 

Strange boy

[Chalky]

Just been to the boat. Left the tunnel light on by accident and the battery reads 0.6V.

Don't need a meter to tell me it's new battery time! My intelligent charger doesn't even recognise that there's a battery attached.

[Gibbo]

Remember Smartgauge only guesses the state of charge, that's all, it doesn't know, but it guesses better than anything else and that guess is accurate enough to be of practical use.

 

That's actually a rather good way of putting it.

 

The reality is that monitoring batteries is not an exact science... As much as people want it to be an exact science, as much as people expect it to be an exact science, as much as many armchair experts know it is an exact science, the reality is that it isn't. And that's an absolute fact. It's a difficult fact to accept, and it takes a long time for this unfortunate fact to sink in, but nevertheless, it is indeed a fact.

 

It's no good making loads of highly accurate measurements on something then hoping to predict the future from the result of those measurements if the basic idea is flawed, and that's the problem amp hour counters are up against.

 

Another reality is that, no matter how much a small minority try to fight it, SmartGauge does it better

 

Just been to the boat. Left the tunnel light on by accident and the battery reads 0.6V.

Don't need a meter to tell me it's new battery time! My intelligent charger doesn't even recognise that there's a battery attached.

 

Depends how long it's been like that for. It's certainly worth giving it a charge and crossing your fingers.

[FadeToScarlet]

Strange boy

 

What can I say, he clearly felt a spark.