Measuring State of Charge (SOC) at almost full troubles

[rgleason]

Stu, Regarding Link10 gotcha

I assume this happened awhile ago, and it raises an issue with my install. Got to get the Battery loads on the other side of the shunt (-) (Including solar?)

[QUOTE]The charging current has tapered down to about 13A with 20Ah still to go with the charging voltage at 14.4V. Now one of the refrigeration units turns on drawing 5A. This causes the battery charge current to drop below the 2% threshold and after 6 minutes the Link 20 thinks the batteries are fully charged because the charge voltage is over 13.2V, the charge current is below 2% or 9.2A, and these conditions have been met for 6 minutes. Then to make matters worse, the recharge efficiency factor is recalculated to a higher value (ex. 0.97 vs 0.95) so the at the next charge cycle the Link 20 thinks that the batteries require fewer input AH for the used AH. This is not true of course, but it makes the under-charge condition worse.[/QUOTE]

What are you charging with? Shorepower or Alternator? Why aren't they capable of carrying the Ref at 5 amps and keeping the battery charging up at where it should be? Presumably the batts are close to full. I won't second guess, because you know this better than me, but where was your alternator regulator sensing? Also I assume your shorepower charger is adequate amperage and sensing from the right places?

[Stu Jackson]

Originally Posted by rgleason

What are you charging with? Shorepower or Alternator? Why aren't they capable of carrying the Ref at 5 amps and keeping the battery charging up at where it should be? Presumably the batts are close to full. I won't second guess, because you know this better than me, but where was your alternator regulator sensing? Also I assume your shorepower charger is adequate amperage and sensing from the right places?

rg,


My shorepower charger is part of my Freedom 15 I/C, 75A, it's huge.


It doesn't matter. Alternator OR shorepower.


THE POINT is that CCs use NET amperage. Really...that's all.


Get your head around the fact that defaults are just that, and WHY Rich and I said what we did.


Then read it again.


Then get a good night's sleep and do it again the next day.


I am serious.


Maine Sail wrote it up a little differently, but essentially says the same thing.



My alternator sense wire is at the house bank.

Why aren't they capable of carrying the Ref at 5 amps and keeping the battery charging up at where it should be?

It IS. If the bank is full and the fridge is off and the charging rate is 2 amps, when the fridge kicks on the charging rate goes up for a very short period of time and then drops back down to 2 because the fridge load is being carried by the bank which is full and the load is a pass through.


Try it yourself.



As I've said, you need some time to literally play around with your existing instruments before you go buy new ones.

[rgleason]

So, the alt or charger is taking the additional load of the refridge, but that is not measured at the shunt on the neg near the batter. The drop you've noticed is from the discontinuity of loads when the refridg kicks on and the alt/charger has not caught up to the drop in voltage/current?

-- I guess I read this stuff again tomorrow.


I just called Steve, the guy at UsaBatterysales.com, to see about ordering T-105 and what the warrantee was (18 months) and he suggested that I should be exercising the batteries two or three times a month during the winter. rather than just charging them up. He suggested a couple of incandescent lamps and discharge the battery for a couple of hours, then recharge to kick the sulfates off. I haven't done this during the winter. I'm going to see if I can't recover these guys I guess.

[john61ct]

No, when not in use just keep them regularly topped up to 100% Full.

Assuming they've gone through the commissioning process, which should be done right away when you buy.

It is very rare for retailers to employ people with much in-depth knowledge. Just the fact most just sit on the shelf for months in inventory says a lot. . .

Best to rely on the maker's documentation, engineers and tech support, straight from the horse's mouth.

If a company doesn't make such quality resources easily accessible to their customers, a great reason to avoid buying their products.

[john61ct]

And find a local dealer, shipping costs usually wreck the value proposition with such a heavy product category.

[rgleason]

OK I understand John, about the Manuf. Specs and winter exercise,, reasonable points.

Also, I just picked the T105 up at Northeast Battery in Providence last time, which is a very busy place and I don't think many batteries hang around there.

[Stu Jackson]

[QUOTE=rgleason;2665381]Stu, Regarding Link10 gotcha

I assume this happened awhile ago, and it raises an issue with my install. Got to get the Battery loads on the other side of the shunt (-) (Including solar?)

The charging current has tapered down to about 13A with 20Ah still to go with the charging voltage at 14.4V. Now one of the refrigeration units turns on drawing 5A. This causes the battery charge current to drop below the 2% threshold and after 6 minutes the Link 20 thinks the batteries are fully charged because the charge voltage is over 13.2V, the charge current is below 2% or 9.2A, and these conditions have been met for 6 minutes. Then to make matters worse, the recharge efficiency factor is recalculated to a higher value (ex. 0.97 vs 0.95) so the at the next charge cycle the Link 20 thinks that the batteries require fewer input AH for the used AH. This is not true of course, but it makes the under-charge condition worse.[/QUOTE

]

What are you charging with? Shorepower or Alternator? Why aren't they capable of carrying the Ref at 5 amps and keeping the battery charging up at where it should be? Presumably the batts are close to full. I won't second guess, because you know this better than me, but where was your alternator regulator sensing? Also I assume your shorepower charger is adequate amperage and sensing from the right places?

rg,


I was thinking about this again late last night. You sure keep me thinkin'.



It could well be that you may be confusing the operation of the ALGORITHM in the battery monitor with the load and "response" of a charging source when additional load is being placed on the bank while charging.


The entire purpose of the Gotcha discussion was to detail how the ALGORITHM in the battery monitor could lead to premature float. For automatic systems as well as if using the algorithm and montior to do so manually.


It is truly a numbers "game" if you start with the factory default values of 13.2 and 2%.


Maine Sail call it "premature floatulation." Same thing. Same warning.


The key to the Gotcha is as written:



The fix for this gotcha is to set the Link 20 parameters to 15v and 1%. These parameters are not ever going to be met, so that means that the Link 20 will never think the batteries are fully charged until the AH used are fully counted down to zero. Also set the recharge efficiency factor to manual of 0.94 instead of the automatic setting of 0.95. This will stop the automatic recalculation and fix the recharge efficiency to be 0.94.


Some Link units do not allow the auto CEF to be changed. Doesn't matter if you "fix" the V and %. Indeed, you can fix only ONE of those two.


And, as we keep repeating, fully charged is 1-2% AT ABSORBTION VOLTAGE.


If you're down to float voltage, just turn the charger off and then on again and watch the amperage.


So, please note that this has nothing to do with the small changes in charging amps when a load is applied. It is ONLY for determining whether you are FULL or not and to void premature float, manually or automatically.

[rgleason]

Stu, thanks for persisting. I believe I understand how to fix it. That is clear.
I am still trying to understand the underlying events, not so much the algorithm in the Link10 which I understand.
1. Charging current down to 13a -20ah 14.4v
2. Refrig Unit turns on, drawing 5.2a
3. Charging current drops to below 9.2a (2%x450ah approx) at 13.2v
4. This condition continues for 6 minutes.
5. Link10 declares batteries full and reset CEF higher.
6. Screws up future Link20 calcs, & prematurely predicts SOC and misinforms operator.
7. Since the Link10 is not connected to the charging device it does not cause premature float, as stated. I causes the operator to think the battery is full when it is not.

I have run Ozefridge with a big evaporator reservoir drawing 4.8-5.2 amps at the same time as charging my batteries using a Balmar 90-65amp alternator and ARS-5 regulator. I haven't specifically noted a big change in the amps when I switch on or off the link10, but perhaps I've forgotten about this.

This spring I also connected my Guest 10amp charger to the batteries and ran a number of 5 hour tests on the refrig, to adjust it for optimal operation during the summer. With this small a charger, I think there was a difference shown in the Link10 amperage, between when the refrig was on or not. My focus was on the refridge operation.

Currents and Regulator response
However I believe that given a good charging power source and sense wires, that any drop in voltage at the battery due to the refrig being turned on, will result in an increase in field current to the alternator and consequently an commensurate increase in current going to the two loads (batteries 13a + refrig 5.2a).

Link10/20
What does the Link 10/20 Battery monitoring see?
1. Shunt is near Bat (-)
2. Link sense wires are on both sides of the shunt.
3. Where does the Alt (-) go? Straight to the House (-)? or is it connected to the shunts side away from the battery? It must be if the Link is going to able to sense the Alternator's current and volts, which it does.
4. Presumably the Alt + goes straight to the battery
5. So what is happening in this sensor circuit to the current?
-Alt is adding current / amps and if the Alt (-) is at the correct side of the shunt the Link sensing wires will see that.
-Refridge is drawing down 5.2a and that would be picked up by the Link sensing wires.
So, yes there would be a reduction in the current sensed by the Link 10/20 when the refridge is turned on, if the alternator black wire is attached to the correct side of the shunt. Otherwise if the connection is direct to the bat (-) the Link 10/20 will not see the alternator current.


I guess I should reset the LINK pronto and reprogram the settings with a lesser bat capacity, which is just a guess. As you would say, I might have been Gotcha.

[Stu Jackson]

-Refridge is drawing down 5.2a and that would be picked up by the Link sensing wires.
So, yes there would be a reduction in the current sensed by the Link 10/20 when the refridge is turned on, if the alternator black wire is attached to the correct side of the shunt. Otherwise if the connection is direct to the bat (-) the Link 10/20 will not see the alternator current.

and I earlier wrote

...the small changes in charging amps when a load is applied...

rg,


When the bank is at PSOC, there WILL be a change in NET charge when the fridge kicks on. In re-reading this thread again this morning, I realized that in the all my posts I had only considered what happens when the bank is FULL, and kept saying there wouldn't be a change in net amps. Sorry about that. If so, the Gotcha wouldn't come into play, right?



Your last post and some earlier ones seem to indicate that you may not be sure if your wiring is correct. AO to house bank seems you DO know (for sure?). The shunt is easy: only ONE (-) wire from the battery bank, everything else on the other side to the engine block. Alternators are either case grounded to the engine or have their (-) wire brought right back to the engine close-by; rarely would the expense of running a (-) conductor back to a set of batteries be incurred. So take a look, but I don't think you have an issue there. If you see the charging from the alternator on the Link, wouldn't that indicate the wiring is OK? Turn the fridge off with the bank at PSOC (not full), run the engine up and read the Link.

[Stu Jackson]

Originally Posted by rgleason

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I guess I should reset the LINK pronto and reprogram the settings with a lesser bat capacity, which is just a guess. >>>>>>>>>>>>>>>>

I was with you all the way to here. WTF??? Where did "...lesser bat capacity..." come from?

[curtis742]

Reading this thread gave me a headache. You guys must be engineers or something because you are over thinking all of this.
Just buy a cheap Chinese digital volt meter and mount it where you can see it easily. On a 12V system shut the battery switch and hav a beer. Then look at the meter. 12.7v is a full charge, 12.1v is 50% charge which should not be exceeded. Batteries will, over time, sulfate steadily decreasing capacity until the batteries no longer are useful. Employing a desulfater will extend battery life beyond the normal 5-6 year lifespan. Constantly worrying about algorithms and charge / discharge ratios and counters is silly. Relax and have a beer. If your charging voltage is 14.5 v, it works. If the battery voltage is above 12.5 when the sun goes down have another beer. If the able conditions are below the stated values replace the batteries or repair the charging system and have another beer. Relax and go sailing and avoid succumbing to developing mental disorders associated with higher level math. In the end it doesn't matter, things either work or they don't.

[john61ct]

In other words you don't think this whole topic is worth the trouble.

Best to just ignore the thread?

Like jumping into a technical thread on designing custom 12V icebox conversions and saying "just buy an Engel portable"

[Stu Jackson]

Originally Posted by curtis742

>>>>>>>>>>>>
>>>>>>>>>>>>>>
You guys must be engineers or something

>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>

Some of us are actually both.


And do enjoy sharing information on how things work.


And then there's this:


Loaded Battery Voltage vs. SOC - AGM Lead Acid Battery by Maine Sail --- why using battery voltage as an indicator of battery SOC is something that requires thought & understanding.

http://forums.sailboatowners.com/index.php?threads/loaded-battery-voltage-vs-soc-agm-lead-acid-battery.176854/

[john61ct]

Another good snippet

http://www.sailnet.com/forums/showth.../topics/298137

[noelex 77]

Curtis, a side effect of poor battery management is horror of horrors, warm beer!

I am sure with this new revelation you will now understand the concern about details such as charging algorithms and realise that this type of thread is far more important than more trivial subjects such as how to survive a storm.

Real men do not concern themselves with minor matters such as storms providing the beer is cold .