Measuring State of Charge (SOC) at almost full troubles

[rgleason]

(--Following your suggestion John)


One task/problem is to figure out when the batteries have finally reached 100% SOC and that is not always readily apparent due to issues I have with various meters and SG.


Measuring both Specific Gravity and Link10 volts/amps (has a shunt with all connectors recently cleaned and tightened) is difficult at higher states of charge.

1. SPECIFIC GRAVITY: When measuring specific gravity with normal glass float with bulb you pull in battery electrolite several times, to adjust so the bulb is truly floating, and then release the bulb, the float will go down a little. You push the bulb just a little and the bulb with rise a little. So what is the best technique to get the right readings? There is quite a range there.
2. LINK10 & SHUNT: With the Link10 as the battery gets fuller toward 100%SOC the number of amps going in jumps around quite a bit, probably due to the field current being adjusted and the battery rejecting and accepting charge. I try to average those readings.
3. CLAMP METER: When using the Uni T Clamp on meter, clamped at the battery I find that the amps are higher than what the Link10 reads (although I have very recently cleaned and tightened all sensor and cable connections), and it also jumps around such that I cannot determine if the batteries are at the Trojan recommended

• Float= Constant Current 1%-3% of C20 as voltage increases, for 225ah this is 2.25a to 6.75a

• and the clamping meter shows about that range jumping around. So how the devil do I determine 100%SOC? Will it ever go down to just showing 1 amp?

Both my measuring and reading skills need to improve I think. Heck I have a hard time seeing the numbers on the float bulb!


I guess measurement of Voltage to check for 100% SOC is not as good because of issues like:
A. Was it recently charged up and has a residual higher voltage,
B. Has it been resting (24hr)? etc.
C. What have house loads done to it since it was recently charged up?

[Bleemus]

You need a decent but not expensive ammeter with a shunt. I threw my SG bulb away long ago.

[john61ct]

You just need an ammeter on the bank, not expensive.

Cheap AH-counter can help with avoiding discharging too far.

And the Link was never that accurate, most have been tossed long ago.

modern BMs like SmartGauge or 712-BMV are better but of course pricey.

[rgleason]

I like the link10, but I guess it is not that accurate. It was a replacement for a Cruising Solutions E-Meter one of the first devices that used peukart number for the battery to calculate, but I guess the Link10 is getting old now too, compared to current technology.

Victron BMV-712 $206
Looks pretty good, might fit the link10 hole. I suppose the BMV-702 would also do the job.

Smartgauge $284
This stuff is starting to get expensive, it the computation worth it? --within %5 accuracy on SOC? Is it better than 712?

DC 0-120V 0-100A Volt Amp Ah Power Capacity Percent Battery Monitor
This does much what the Link10 does, is it really any better? $29
If it is, I'll get one until I get the Victron, but what do I do about having two shunts?


I haven't found an answer about the jumping up and down of amps that I see during charging with all my measurement sensors except SG. I believe this is normal, so what do these devices do differently? Just average it?

"In order to use voltage as a measure of a battery’s SOC, however, the battery must be rested — with no charge source and no loads — for at least eight hours, a condition that’s neither routine nor practical aboard any cruising vessel.... alternative way to measure SOC that provides much more information than the humble voltmeter: Enter the amp-hour meter."

[rgleason]

Rod explained the smartmeter advantage here
Boy this can get expensive, using the lastest and greatest.

[a64pilot]

Originally Posted by rgleason

Rod explained the smartmeter advantage here
Boy this can get expensive, using the lastest and greatest.

It can, and isn’t always necessary. It is entirely possible to spend money that you will never recoup, you have to decide if you want to.
Also it’s pretty well known that the Smart Gauge isn’t particularly accurate during charging, so it’s not the instrument to use to determine fully charged.
A good ammeter isn’t that expensive, and can tell you very accurately when your fully charged

[rgleason]

A good ammeter isn’t that expensive, and can tell you very accurately when your fully charged

The link10 is also an ammeter, it has a shunt.

[john61ct]

Yes, having both SmartGauge (best for SoC) and BMV (AH counting) many say overkill, I say great if you have $ and like lots of info.

Specific gravity requires resting just like voltage.

Trailing amps is the cheapest and canonical for 100% SoC, benchmark / reset the rest off that.

For those on a budget just that plus any AH counter is "good enough" IMO.

So from that POV, use just the Link 10 **if** you think its ammeter is good.

If unsure then $50-100 on a second one to compare? Or borrow / hire a Fluke once in a while if Link can be calibrated?

[lateral]

"for 225ah this is 2.25a to 6.75a"---There is your answer.

Obsessing that I'm 99.99999% full is a waste of my boat maintenance time.

On Smart gauge, if you want one cheaper.
http://jgtech.com/monitors.htm

I bought one & sold it without installing as I intend to have wind generation as well.
Not enough time for the SG to sort its self out. And charging/discharging Amps tells me more.
I don't dispute they are a good device in the right setup.
Prefer a shunt, & a hall sensor. (Chinese)

I find Balmar equipment out of my budget and have found other industry alternators, regulators, DM's without the marine markup and of similar performance more suitable
especially in terms of having complete backup, "drop in" replacements.
Horses for courses.
Similarly in sailing electronics.

[rgleason]

1. Trailing amps is the cheapest and canonical for 100% SoC, benchmark / reset the rest off that.
2. For those on a budget just that plus any AH counter is "good enough" IMO.
3. Then $50-100 on a second one to compare? Or borrow / hire a Fluke

Yes, I will get a second AH counter for comparison to the Link10
How about DC 0-120V 0-100A Volt Amp Ah Power Capacity Percent Battery Monitor Watt Meter 50A-1000A Shunt (0-120.0V,0-50.0A)
for $30.

The only problem I see, is it has a shut, and I don't think this shunt is very good for our system. Anyway, I shouldn't have two shunts in series should I? Its problematical, two shunts in series will screw up the Link10 measurement of amps and AH. (Also I can change the Battery AH on the Link10 so the peukert calc is done differently, the Link10 also resets itself if there is a change in capacity after a drawdown of more than .2C and then full recharge, the battery AH are reset, is that what you mean by adjust?

Another counter AH which I could get would be
MICTUNING DC 6.5-100V 0-100A LCD Digital Display Ammeter Voltmeter Multimeter Volt Watt Power Energy Meter Blue with 100A/75mV Shunt
for $17
But it would have the same issue of two shunts in a row.

I also have the Uni T UR203 Clamp Meter

Also I think I am going to stop by Harbor Freight and get a 12v/6v Battery Load Tester (are these devices ok? IE do they actually work properly?)

I will load test when I first get to the boat, then get to a dock and charge watching "tailing amps" and then and equalize (maybe 3x's). Then load test again.

Depending on what I find out, I will then get the new batteries. This will be much easier to do next time!

[rgleason]

I think I found a reference to the "adjustment" of the Link10 that John refers to, but it is for Victron AH meters.

1. CEF Charge Efficiency Factor (Victron)
2. Reset SOC State of Charge (Victron - button to push when batts are fully charged)
3. Peukert Number = (This is what I have on the Link10)
4. AH = (This is what I have on the Link 10, I can adjust this down)
5. Also the Link10 automatically adjusts when there is a drop of I think .2C and then resets at the highest charge when brought back up. Also if you are adding more amps it will reset at the higher level.

Measuring "Trailing Amps" (various quotes):

1. For those who strive to regularly get their expensive banks back to 100% Full, trailing amps is really the only accurate measure, and not at all difficult.
2. Then adjustable charge sources can be calibrated so Absorb Hold Time can be adjusted until this is automatically handled most of the time.
3. Those who just shrug and accept the conventional "cruisers don't get to Full" will say this is overkill, and likely need to replace their bank a bit (or a lot) more frequently ---That works only if you "just charge" in an ideal world and have no load running while charging. Otherwise tail current is a myth.
4. Tail current, measured going into the battery (not exiting the charger), should work well as long as the loads in play don't exceed the capacity of the charger. So the key, in a Victron scenario, is whether the BMV communicates with the charger to indicate the "real" battery current.
5. For all the trouble we go to to try to figure out whether we have 60% vs 50% SOC, we dont' seem to spend much time trying to figure out whether our chargers are doing the right thing by our batteries. That seems to me to be a misallocation of attention and effort.Your boat your call.

Another good way to check the battery condition is "resting voltage" but that has to be without solar on it and after resting for 12-24 hrs. (or put a .05c load on it for a short while after charging to remove the surface current on the plates) which might be useful. It will give some idea of SOC and the health of the battery and confirm that there are no shorts, however only a 20hr load test will give the actual capacity.
See this good sticky post


Applying a load and measuring to determine capacity as described here by Cal40John

C = (measured test Amp-hours)/(1-decimalSOC)
I put a 9 amp load for one hour, so 9 amp-hrs consumed. If I read a voltage at the end of that period of say 12.63, which my state of charge chart (not presented in this thread) says is a state of charge of 95%, then C=9/(1-0.95) = 180 amp-hour capacity at full charge. In this case my battery is still as new.

[Stu Jackson]

Originally Posted by rgleason

I think I found a reference to the "adjustment" of the Link10 that John refers to, but it is for Victron AH meters.

1. CEF Charge Efficiency Factor (Victron)
2. Reset SOC State of Charge (Victron - button to push when batts are fully charged)
3. Peukert Number = (This is what I have on the Link10)
4. AH = (This is what I have on the Link 10, I can adjust this down)
5. Also the Link10 automatically adjusts when there is a drop of I think .2C and then resets at the highest charge when brought back up. Also if you are adding more amps it will reset at the higher level.

Measuring "Trailing Amps" (various quotes):>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>

rg,


IIRC, I posted my "Gotcha" topic on one of your earlier discussions about this issue.


I think you are overthinking this issue, and had recommended to you a week or two ago to just consider slowing down and absorbing (pun intended!) the material you have before you now. I'm an engineer, and back in the mid-90s when coulomb counters first came out, it took (even me...geez, humble, huh?) a while to figure it all out.


In your case, for example, you are now considering a second unit to compare to your Link 10. IIRC, one of the critical issues in navigation has always been that if you have two sources of information, and they are different, which one do you trust? It is a classic issue, and a reality. I also think you've hit the nail on the head about two shunts. The reason folks may not have had immediate reaction to that idea is that I know of no one who has tried it in the past decade or two, doesn't mean it hasn't happened, or that maybe the guy who did it doesn't read CF, or is sailing today, or Maine Sail hasn't tried it yet!


I believe the reality is this: for years and years, sailors got along running their battery banks between 50% and 85%, and made it there and back again. In fact, Maine Sail has mentioned this is his writeup about coulomb counters, hasn't he? Then the counters came into the picture. People then mistakenly felt they were fuel gauges and didn't learn how to set them up and calibrate and regularly reset them, again Maine Sail came to the rescue and I wrote my Gotcha article. We learned about shunts, that going to float is not full, and that, as Johnct and Maine Sail have repeatedly stressed that full is 1-2% (pick YOUR number) AT ABSORBTION VOLTAGE (so simply recycle/restart your charging source when the amps IN get very low for your bank size to actually SEE when FULL occurs).



Then folks started adding wind and solar and the mantra subtly but importantly shifted from the 50-85% TO how do I keep them, in some cases, completely topped up? "I'm completely full by noon with my solar (after a 60ah load all night long from the fridge and lights)." Ever heard that one?!? Some people end up chasing their own tails to keep their banks at 100% which is impossible, but others have realized that with proper care a bank can last longer, but never indefinitely. sailboy1 has noted many times that batteries are a consumable item. Then comes along the Smart Gauge and Maine Sail's fine writeup about that particular item, and the CC vs SG discussions. Dockhead has written fervently about his experiences with both CCs and the SG. If you haven't read it, you should consider finding it here.


My experience, rg, is with over a decade of my Link 2000, spending hours with the manual, my boat and the Link, and reading everything I could about how they work, I understand what it is telling me, and how it works. It is a RELATIVE instrument. For example, I have written many times about battery acceptance: "What goes OUT of your house bank becomes easy to learn from the Energy Budget previously discussed and posted. It's what goes back IN that most people are missing, and relates to the state of charge of your house bank in a very direct manner." Regardless of how you use your boat, this is true. I am a coastal cruiser who does a lot of anchoring out, no solar, a 100ah daily energy budget, a nominal 400 ah wet cell 12V house bank with a small reserve bank, on a 1-2-B switch with the AO to the house bank and a combiner - just a basic bare bones system, but one most folks have been using thanks to Maine Sail's contributions.


So, before you invest in more telemetry, you might consider just taking a deep breath and "cooling your heels" for a bit and let some more soak in. Ever tried to loosen a stubborn nut, you go away for a break, come back, and BINGO it's free? Magic? Hardly.


Good luck.


PS - re: amps jumping around. Does your Link 10 have an option for instantaneous OR averaged amps? My Link 2000 does. It can do instantaneous (0 sec.) or 8, 16 & 32 sec). Makes a difference to what's on the screen.

[john61ct]

Originally Posted by rgleason

I think I am going to stop by Harbor Freight and get a 12v/6v Battery Load Tester (are these devices ok? IE do they actually work properly?)

No, pretty useless.

See MS BM howto for a proper 20-hour load test.

Practice on the old bank, then do a benchmark after the commissioning process of the new one, maybe after breaking in period is done.

As for shunts, multiple BMs can run off the same one, but maybe only one that can be calibrated?

[rgleason]

Making Your Battery Monitor More Accurate
Installing a Battery Moniter

[john61ct]

Yep, those are canon.

You probably already saw the SmartGauge review as well.