Battery charge current vs voltage?

[Maine Sail]

Different ways

There are many ways to skin the cat. My monitor is set to more accurately represent a full charge on my system. My charge % is set to 1% as that is more closely representative of the acceptance my bank has at near full (98-100%). 2% acceptance still takes a few hours of charging before my bank is accepting closer to 1% acceptance.

Setting up the monitor parameters depends upon your "system". I think there is a LOT of misunderstanding out there when it comes to batteries, charging, acceptance, CEF, Peukert and monitors in general. For me I don't accept the 2% built in "charged" parameter as 100% because it is not on my bank.

Even though I have tweaked my monitor to best work with my system I still manually re-calibrate at least once per week.

One thing that also happens is that most chargers won't "float" with a load applied. My chargers float, on my bank at full charge, is under 2 amps. Any load of more than 2 amps, and sometimes even less, takes me right out of float.

Of course this all depends on your charger and the "load" but a fridge kicking on can quickly move your charger out of float voltage and put it back into delivering an absorption voltage. Most meters properly set up will not re-set until %/time/volts are achieved for longer than five minutes. With loads running, while charging, you may never re-set because multiple parameters are required..

In my case, with my charging system, it is 1%/13.4V/5 minutes. On alternator it will not re-set as I am unwilling to run my engine for 8+ hours to achieve this so get it back to about 85-90% SOC then I manually re-set when the solar panel has had time to sufficiently top off the bank when it is showing about 1% acceptance.

As sailors we need to get every amp hour out of our cruising banks. Setting up your monitor to leave precious ah's on the table can lead to deeper discharges which can ultimately shorten battery life. 2% acceptance on my bank is not fully charged.

This is an example of a 200 ah bank when used cruising on the hook with only an alternator.

SOC = state of charge
DOD = depth of discharge

Total Bank Capacity = 200 ah
DOD to 50% SOC = 100 ah
Max alt recharge = 80%
Usable Ah's = 60Ah

200 Ah @80 SOC = 160 Ah's

160 usable @80% SOC to a 50% DOD (100 Ah's) leaves 60 usable Ah's before you hit a 50% DOD..


Total usable Ah's, when cruising and charging off the alt, from a 200 Ah bank = 60 Amp Hours !!!

To me every counted Ah counts and leaving mine at 2% acceptance was not something I was happy with..

In this scenario, which is actually quite accurate, you only really have 30% of the capacity of your entire bank to use when out cruising and only charging off the alternator.

Sadly in a situation like this a monitor will only count amps because it would take hours and hours and hours to ever hit float and totally re-charge the bank for an automatic re-set. Furthermore if your alt is single stage regulated you'll need to change the volt parameters too as it will never hit 13.4v, 13.6v, 13.7v etc. as the regulator does not have a "float" setting..

In short slapping in battery monitor and expecting it to "work accurately" is not really a plan that will result in the performance you'd like to see. There are LOTS of variables to more accurate battery monitor performance and all of them need to be considered..

 

[Sybaris]

Maine Sail,

Yes I totally agree with you. In your case you have done proper testing and decided that 1% is better in your case and although the automatic synchronization does take place sometimes you also do it manually. You have all angles covered.

My only point as I have stated several times is that I don't think it helps to disable the automatic synchronization in a Freedom/Link combination, and if you do so you should certainly make sure you do a manual synchronization on a regular basis, which I hope Mitiempo makes this clear to his clients.

This is what I wrote in my summary:

FACT: If you disable the Charged Parameters and want stop your amp meter from accumulating and increased error over time you will have to do a manual synchronization at intervals of your own choosing.

The case of using a Freedom/Link combination is slightly different than yours as they are built for each other specifically and I can only hope that the Xantrex engineers have run extensive tests over the years and would not advice quite clearly against changing those values if doing so was beneficial.

I my case I never get even close to 50%, but I am fortunate to have a large battery bank and very good solar panels. I also do a manual synchronisation for time to time (although I am not as regular as you), and when the CEF value has fallen for a period of 6 months or so (which it has now by the way) I run the Equalization program to freshen up the batteries.

Cheers,
Per

 

[Conachair]

Conachair
The meter reads "full" when the voltage drops not when it goes up. During charge voltage starts high and ends up at float level (13.7). It has to see a drop to float voltage and less than 5 amps to declare full. The voltage is not the big issue anyway, it's the amps in. When your fridge starts the net amps can drop below 5 and this combined with float voltage causes the meter to declare full when it still has a way to go.
Brian

Ah, your meter works differently from mine then, the bep I have resets when the voltage and amps are both high. Doesn't matter if it's coming from engine, solar/wind or mains. How does your charger know when to go to float?

 

[Maine Sail]

Ah, your meter works differently from mine then, the bep I have resets when the voltage and amps are both high.

If the amps are high the batteries are not charged. Batteries decline in acceptance rates as they near full charge. Most meters are programmed to reset when the batteries reach less than 2% acceptance of the banks total programmed size. Re-setting to "full" would be quite inaccurate when the "amps are high".

Doesn't matter if it's coming from engine, solar/wind or mains. How does your charger know when to go to float?

Your batteries don't care where the charge comes from, acceptance is acceptance. Most wet cells can accept 20-25% of their 20 hour rate when dead. The acceptance rates decline rapidly from about 80% to 100% SOC until they are accepting very little amps. In my case near 100% they are accepting equal to or less than 1% of the 20 hour Ah rating..

If your batteries are still accepting "high amps" they are not charged. You may want to do a closer inspection of the set up parameters on your BEP....

 

[exfinnsailor]

We use the fridge method

When the fridge will not start its time to switch the engine on .. Or find a marina .. When the fridge switches on and the lights don't dim you can turn the engine off ..

 

[Allan]

As I understand it, to fit a battery monitor you must have a shunt between all charging sources and the batteries. Does this reduce the charging, particularly from low power sources like wind turbines and solar panels?
Allan

 

[mitiempo]

Allan
No, it will not reduce the charging voltage. The shunt is installed in the negative line close to the battery to be monitored. The two big lugs on top carry the current and the small screws are where the sense wires go. The shunt has to be the first stop for the negative wire from the battery so it sees everything. For every amp that leaves or enters the battery a very small amount of current goes to the meter through the sense wires. In the case of the one shown 50 millivolts for 500 amps.

 

[Conachair]

If the amps are high the batteries are not charged. .

Typo, I meant low amps. Under 5a.

 

[mitiempo]

ConaChair
Voltage has to drop as well - on any charger and is required by any battery. The charger will start charging at 12 volts quickly rising to 14.4 volts at maximum charger current - this is the bulk charge. The acceptance stage is at 14.4 volts with a falling current. Float is about 13.5 volts give or take a bit with lower current dropping to less than 2% of bank size. As Maine Sail states his bank accepts 1% or less of the bank's 20 hour rating when near a full charge.
So if your voltage dropped when the fridge came on it would still stay on float and if the amperage was at or below the 2% setting for the required period of minutes (5) the meter would consider the battery full and reset.
You ask how my charger knows when to go to float. When the batteries acceptance rate drops below 2% of bank size float starts. The problem we have discussed at length is that this is the beginning of float but not yet a fully charged battery. By adjusting the meter it will not call "Full" ahead of time. On a large bank of say 400 AH this "false full" could be 30 to 40 amps less than full. This last 10% or so of charge goes in very slowly. On your 200 AH bank it could be 20 amps shy of full. By changing the 2% to 1% the full will be stated by the meter when the battery bank is a lot closer to full.
Because the last stage of charge takes so long it is not worth trying to get it if using the engine's alternator to charge. If plugged in using the shorepower charger or using solar or wind chargers the batteries will get fully charged, although this can take from 4 hours to as long as 7 or 8 hours.

 

[Allan]

Allan
No, it will not reduce the charging voltage. The shunt is installed in the negative line close to the battery to be monitored. The two big lugs on top carry the current and the small screws are where the sense wires go. The shunt has to be the first stop for the negative wire from the battery so it sees everything. For every amp that leaves or enters the battery a very small amount of current goes to the meter through the sense wires. In the case of the one shown 50 millivolts for 500 amps.

I am not sure how many amps my wind turbine produces, less than five, I would guess. That would mean less than 0.5millivolts, would the monitor pick that up?
Allan

 

[mitiempo]

Allan
You made a math mistake I think. The output has to be over battery voltage to charge, in other words over from 12 to about 14 volts depending on battery state of charge. According to the Rutland chart (I believe you have a Rutland) at 15 knots you should generate about 4 amps and yes the shunt will have no problem measuring this if it gets to the battery. To give you an idea of how accurate the shunt is I installed a monitor on a friends boat. Then we graphed all his power using items - every individual light, pump, etc. We saw how many amps some lights were using and he purchased some LED bulbs and after installing the LEds we rechecked them. It had no problem measuring .1 amps out. That's one tenth of an amp.
Here's the chart for the Rutland - 12 volts on the left side.

 

[Stu Jackson]

Gentlemen,

Maine Sail was kind enough to suggest I join you here. I look forward to learning more about boating from participating with you. I have a small stash of PBO's in my library, having purchased them whenever I was visiting the UK over the years.

I have reviewed this particular topic. Per, it simply appears that you are confusing the synchronization with the Link's statement of premature float if the Gotcha is not corrected.

The long "Gotcha" topic on our C34 Forum Main Message Board covers both synchronization and "declaration of full" in Replies #2 & 3.

The issue is not whether Maine Sail has done his own testing or not, or whether your charger is a Xantrex or a Freedom with its connection to the Link.

The fact is that the Link WILL show premature full because of the MATH LOGIC inside THE ALGORITHM.

Reply #3 in the C34 Gotcha topic discusses this simple math:

400 amp hour house bank
2% is 8.4 amps
Fridge load is 4.9 amps
8.4 minus 4.9 = 3.5 which is less than 2%
Battery acceptance reduces input charging amperage to 13.2 or 13.4 V

The "charging current" is "really" 8.4 AMPS until the fridge "KICKS IN" at which point the "charging current" doesn't actually change, BUT the Link algorithm is dealing with the NET current being read on the display, which is 3.5 amps.

Since the A is less than 2% AND AT THE SAME TIME the V is at or above the 13.2 or 13.4, the Link says the bank is full when it is not, as described in detail in the topic.

This is a simple "either and/or" mathematical statement that any basic computer 101 course, from as long ago and as way way back as the old FORTRAN days: IF and WHEN the parameters are met, the trigger is pulled and the banks are "declared" full when they are not.

And further, synchronization WILL occur and has nothing to do with this. As Reply #2 (in our C34 Message Board topic) questions, Ken brings up this very issue. Synchronization is when the Link resets to full, so the Gotcha concept doesn't affect the synchronization, it just stops premature declaration of full batteries. Synchronization is simple, read the Link instruction manual.

I am sorry that there appear to be misunderstandings of the Link "Gothca" concept, and confusion with synchronization - they are two separate, but related, things.

I have seen it at work in real life. We have a Freedom 15, circa 1998 model with it's own 1/0 wiring, but no echo charger. We were "forced" to address the issue of how to charge a house bank and a reserve bank with a single output shorepower source well before most people even heard of combiners, because most people had multiple output shorepower chargers.

I immediately removed the old isolators the PO had installed. The Freedom I/C went in in 1998, but I maintain that I set a world's record for procrastination by not installing the Link until eight years later.

I learned about acceptance the hard way, and prepared this topic for our C34 skippers and forum registrants, Battery Acceptance: http://c34.org/bbs/index.php/topic,4787.0.html The first post reflects the underlying concern, as expressed as well by Rick when he prompted the "Gotcha" syndrome.

Once I made the Gotcha change, the Link does NOT prematurely kick the Freedom into float, and fully charges the house bank within a reasonable time.

Please remember, as clearly explained in the Gotcha topic:

Rich is not saying it will never show full, he's saying that the concept is to avoid showing "full" prematurely when they are not, because the way the "guts" of the Link works, it WILL eventually and correctly show full when the ah are counted down to zero. This is based on the kWHr calculation within the algorithm. By simply changing the full parameters will assure that the bank is actually full, and not before then.

Implementing the Gotcha recommendations will simply avoid chronically undercharging your house bank. We believe that is a good thing to avoid, whether you have a Freedom I/C or any other kind of charger.

 

[Stu Jackson]

The Link GOTCHA

Brian understands. Per, synchronization has nothing to do with the dangers of declaring a bank full prematurely. Actually, all of your points have been discussed and addressed in Brian's links to my acceptance and Gotcha topics.

The math is simple: when a 4.9 amp fridge comes on it can be well less than 2% of the 360 to 400 ah house bank. Please, don't just "trust me" on this one, do the math. In fact, the math WAS done in the Link Gotcha topic that Brian linked.

So many people think in terms of full banks going to empty, when the appropriate approach has to be starting with a depleted bank and trying to most effectively charge same.

All of Per's objections were discussed at length in the "Gotcha" topic. I've read this topic over again a few times and I just don't understand the "objections." Why is anyone arguing about this?

It's not the original programmer's ideas that are being questioned at all. Indeed, their programming is just fine, all we're pointing out is that the DEFAULT is something that UNLESS YOU UNDERSTAND, could serve to bite you where it hurts the most: trying to get a bank charged properly without prematurely declaring a bank full and undercharging a house bank.

What's not to like about the programming?

What is not understood about a default value? Heck, it's gotta be something, so choose one!

What's the "argument?" None is required. A lack of understanding of the basic thesis is not a valid cause for disagreement.

Please remember, in other discussions about Link 2000s, that there are other default values that REQUIRE understanding for proper setup.

For instance, the F11 function (Battery Used for Control) on a Link 2000 defaults to two equal house banks, a popular electrical design some decades ago.

This default is required to be changed if you have a different system. The old two equal bank electrical battery system design has been changed to the newer "preferred" system with the largest house bank and a separate small reserve bank. This requires that on the Link 2000 the F11 default value be changed. If you don't, the wrong bank will be used to make charging decisions. We are not saying the default value, in that case, is wrong, merely that it needs to be changed.

That's simply called Programming 101.

If you do not modify the % to less than any percent that your system will need for it to work for YOU, the Link will prematurely declare the bank full, and if you have a Freedom I/C controlled by the Link, it'll switch to float too soon.

There is no "damage" done other than this: if you stayed plugged in it'll take a looong time to fully charge your bank because it'll kick out of absorption to float much too soon if you have a Freedom I/C; if you like to unplug you will be fooled into staying plugged in too long; if you manually operate your charger based on what the Link is saying, you'll chronically undercharge your bank.

This is what Rich pointed out to us and which we've simply passed along to help you avoid that problem.

 

[mitiempo]

Stu
Welcome to the forum.

 

[Stu Jackson]

Thanks, Brian. We live in San Francisco, but are now in Cowichan Bay on the Island visiting my wife's parents.

Nice to be here, and to have learned about this forum.