Side discussions moved from "What a battery monitor may not tell you"

[booster]

Originally Posted by RossWilliams

You also might want to take a look at this Rolls Battery description of voltage readings . Its chart has a voltage of 11.04 under load at 75% discharged. At 50% discharge the voltage is 11.58. Those are under load, not resting voltages.

You also might want to read this discussion of the confusion that under load and resting/open voltages can create in determining the actual state of the battery.

You can understand why manufacturers use idiot lights, given how complicated is to get a precise and accurate state of charge from batteries where that is a constantly moving target.

You have just described why you don't use voltage for SOC or AH down measurements, as there are too many qualifiers, with load being a big one, as is temperature, battery age, etc. A monitor gets rid of all that stuff and measures directly and can very accurately know when the batteries are fully charged by looking at the amps going into the batteries.

[GeorgeRa]

Originally Posted by RossWilliams

………………..You can understand why manufacturers use idiot lights, ………………….

Yes, I can - they are cheap. But they look good, they are bright, often red, some folks can enjoy starring at them looking for wisdom which could come or not.

[booster]

Originally Posted by GeorgeRa

Yes, I can - they are cheap. But they look good, they are bright, often red, some folks can enjoy starring at them looking for wisdom which could come or not.

Ah yes, perception vs reality in consumer stuff certainly is in play here, along with the low price of the lights.


Very similar to any digital gauge, measuring tool, meter, whatever that displays XX.XXXX but is only accurate to XX.X. Unexperienced users will insist that if it displays on the digital panel it has to be valid and accurate. We had this issue with process equipment and gauging all the time in the places I worked. Lots of displays that had the non valid digits taped over.

[Bud]

Originally Posted by booster

Ah yes, perception vs reality in consumer stuff certainly is in play here, along with the low price of the lights.


Very similar to any digital gauge, measuring tool, meter, whatever that displays XX.XXXX but is only accurate to XX.X. Unexperienced users will insist that if it displays on the digital panel it has to be valid and accurate. We had this issue with process equipment and gauging all the time in the places I worked. Lots of displays that had the non valid digits taped over.

"Unexperienced users"

BINGO booster. That explains a lot. If new B's owners had received the appropriate education and training the lights could have been kind of ok especially pre agm's. Explains a lot about our culture. Better would be battery voltage meters that I use effectively. Years ago I knew what the lights might have meant, but was not sure with different light boxes out there. Later I knew the voltage required to have each light flicker off and on, not the last one. Heck if I can recall at the moment what those voltages are, but it was kind of fun/interesting finding out. The Key is the 'Want To' about what 11.789 volts means under what load. That can be learned as you know over time and without risking a 10% SOC.

I found that interestingly enough my application, how I use the B is about as good as it gets with my Walmart batteries, dumb charger, poor inefficient cabling for the second battery, over charging with the alternator,............... This is by coincidence, I sure didn't plan it that way.

I arrive home with a full charge, then a Battery Tender at about 13.1. I do drive off with a full charge or near full charge, but too lazy to stop the original, stock alternator charging. I boondock about half the time always getting a full charge at least every 7-10 discharges. With shore power and dumb charger at about 13.5-6 volts, the alternator provides the full charge when I drive off. If too short a drive (unlikely), it won't be the next time.

Prior to these new 2 batteries, I hardly ever thought about battery maintenance stuff. My 61 Beetle battery may never have been watered, and not with any distilled water.

I don't like fooling with the watering, but very little is required. With my present application, again, it hardly gets any better. I can't run the microwave, but the little I use it virtually no one is bothered, offended with 5 less than 10 minutes of the LOUD onan. Well, I guess there is the threat of how long will it, the LOUD onan will last.

I may move to a new B, I'll probably choose the 'best' way concerning battery stuff. But key again is understanding and using it. booster you are very good at explain this stuff, along with some others. That is not imo, fact. Thanks all.

Bud

[RossWilliams]

But key again is understanding and using it.

That is precisely correct. And the ability to misuse out of ignorance a complex battery monitor that promises you an accurate state of charge under all conditions is very high. You need to understand that the manufacturers AH rating may not apply to a brand new battery and will almost certainly be wrong for an older battery. You need to understand that if your monitor doesn't have a temperature control that accurately captures the temperature of the batteries, it cannot give you an accurate state of charge. You certainly need to understand that amps in/amps out by itself is highly misleading.

I suspect there are a lot of people out there with battery monitors who don't know any of those things. And they think that if their battery is rated at 200AH, they are safe as long as its amp count says haven't used more than 160.

Some people here have described the idea that AGM batteries shouldn't be taken below 50% as a "myth". In one sense they are right, occasionally taking your battery down close to 80% is not going to wreck the battery. What they don't say, is that there is no way to actually know whether you are at 80% or 90% or 70%. And the older your battery is, the more wear it has had the more likely it is that your measurement of state of charge will tell you that you are at 70% and you are closer to 90%.

The danger is the illusion of precision in an environment that is inherently imprecise.

[avanti]

Originally Posted by booster

Ah yes, perception vs reality in consumer stuff certainly is in play here, along with the low price of the lights.


Very similar to any digital gauge, measuring tool, meter, whatever that displays XX.XXXX but is only accurate to XX.X. Unexperienced users will insist that if it displays on the digital panel it has to be valid and accurate. We had this issue with process equipment and gauging all the time in the places I worked. Lots of displays that had the non valid digits taped over.

Brings to mind the temperature needle on many cars that are programmed to always point to the center of the "normal" range as long as the temperature is anywhere within the normal range. Don't want to panic anyone by showing the temperature rising when going up a hill.

[booster]

Of course with all this, the lights still work off voltage, so you also have aging issues that cause voltage to be incorrect in relation to charge.


A damaged or worn battery with reduced capacity will very often still charge to 12.7v, so is it full, or how full.


A reduced capacity battery may not be able to charge to 12.7v but still have more capacity than the one above.


And the list goes on.


Even if you put all of Ross's worries about dumb users into play, if you have a monitor it will count ah of use and if you or it reset to 100% when you are or even think you are full, it will count spot on from there.


With the lights and reduced capacity you have no idea how much power you have or could use, or even a way to find out. Full light to empty light for a 100ah battery could be 100ah or 10ah but all you have is a % of that unkown number, so not very useful.


Does Ross realize that unless he has a balancer on his system, he will have half his batteries at a different SOC than the other half, nearly all the time. Which ones are the lights measuring?

[GeorgeRa]

I have Bluesea small OLED voltmeter and house <> chassis batteries current gauges located in the very visible place from inside or outside. They are giving me a quick assessment of current activity.

SOC is displayed on the ME-MRC50 visible from the driver side of the sofa rear.

All gauges have their specific benefits, SOC is obvious, voltmeter for quick assessment of what is going on, and the current gauge primarily set for alternator to house charging indicated by the positive sign.

On my 1977 VW Westfalia I had to install additional battery to be able to run LPG heater and used a small analog voltmeter with reduced scale, if I recall it was 8-14 or 16V. My first trailer in 1987 had dummy LED indicators, I quickly replaced them with a shunt-based ammeter. My first battery monitor was LINK -10 in the early nineties.

[booster]

Originally Posted by peteco

Booster: hang in there, don't let the "odd poster" influence your posting.

One question: will a charger on float at 13.5v (my present Triplite) eventually fully charge a battery?

I dredged this post back up as an "operator error" gave me an "opportunity" to run a test of this on our wet cell starting battery (6 month old Interstate 24DC marine starting battery w cell. I forgot to unplug the GPS when we returned from out latest short trip so starting battery got very low, not dead, though.


I ran a charge cycle on the coach batteries with the separator closes so the starting battery also so it. When done and rested after the charge and 3days of float, the battery checked at 12.8v with no loads. I checked the specific gravity and it was at 1235, which is not near full for even these batteries which tend to max out at 1260 tops in most cases. So the charge and float were certainly short of charge.


I then ran 4 charge cycles, with mini equalize with tiny Ctek 7 amp charger. This would put absorption voltage on for while ans also a short equalize voltage. After 4 cycles, the voltage checked 12.8 rested andthe specific gravity was checking 1255, so very close to what would be full charge on it, if not at full charge.


The conclusion looks like it would be that short charge and float would not get this wet cell full within 3-4 days, but putting the higher charge voltages on it did quite quickly. Of particular note to me was that it checked 12.8v after both checkpoints, rested, even though one checkpoint was short of full charge and one was very close to or fully charged. Another reference point that would indicate voltage is not a good indicator of a full battery by itself, which many of us have seen before.


It does appear that the full absorption voltage to fully charged is necessary to get the battery completely full reliably.

[eric1514]

Interesting. Sometimes I would come back from a trip and plug my van in. I have a PD charger/converter with a remote pendant. It would select "boost" mode which is 14.4 volts vs. "normal" mode (13.6) or "storage" mode (13.2). I figured since I wasn't going to use the van for a few day, I would be nice to the batteries and just force the charger into storage mode. Now I gather, that I should start at boost and let the charger do it's thing.

[booster]

Originally Posted by eric1514

Interesting. Sometimes I would come back from a trip and plug my van in. I have a PD charger/converter with a remote pendant. It would select "boost" mode which is 14.4 volts vs. "normal" mode (13.6) or "storage" mode (13.2). I figured since I wasn't going to use the van for a few day, I would be nice to the batteries and just force the charger into storage mode. Now I gather, that I should start at boost and let the charger do it's thing.

I think in your case, which mode you choose would depend on how full the batteries were from the drive, which on most newer vans is in the low 14s or higher for voltage. If it has seen 14.3v all day, best to go to float, if was a short drive and batteries were low when you started, the full charge.


If you have a battery monitor, you would just put it into full charge mode and look at the charging amps. If they are indicating that the batteries are full, force it to float. Quite a few folks use a monitor with a PD charger to manually get very accurate charging, but it is a bit of PITA to do sometimes.

[eric1514]

Originally Posted by booster

I think in your case, which mode you choose would depend on how full the batteries were from the drive, which on most newer vans is in the low 14s or higher for voltage. If it has seen 14.3v all day, best to go to float, if was a short drive and batteries were low when you started, the full charge.


If you have a battery monitor, you would just put it into full charge mode and look at the charging amps. If they are indicating that the batteries are full, force it to float. Quite a few folks use a monitor with a PD charger to manually get very accurate charging, but it is a bit of PITA to do sometimes.

I do have a Trimetric but silly me, I never thought to use it that way. In fact when I plug in at home I turn the display off. I've been using it primarily to check on how much battery I have left after a couple of days of boondocking, keeping an eye on my fridge and solar.

[booster]

Originally Posted by eric1514

I do have a Trimetric but silly me, I never thought to use it that way. In fact when I plug in at home I turn the display off. I've been using it primarily to check on how much battery I have left after a couple of days of boondocking, keeping an eye on my fridge and solar.

Once you get used to taking a look at the charging amps once in a while, you will get a pretty feel for how long the batteries still need to charge, as that is fairly consistent when watching amps for most circumstances.


Markopolo has probably been doing the monitor/PD charger routine longer than most so he may pop in with some pointers of the best ways to do it.

[markopolo]

Have you set the charged light indicator voltage and amps yet? That's critical as it resets the Ah counter. The SOC reading will get less and less accurate the longer it goes without getting the batteries fully charged and resetting the counter.

I chose 14.3V and 1A or less as the criteria for my setup. There would be minimal persistent loads on mine, probably just the propane detector and a very low amp draw relay. My PD unit didn't seem to be able to meet 14.4V & 1A or less. 14.4V & 2A or less might be an alternative.

I have approx 400Ah of batteries in the van but very light use for the past three years as I've been using other RV's for accommodation. Almost 400 nights in those other RV's over the last three years. The van is currently used only in support of hobbies and running errands etc. so lights, fan & pump - very light use.

[eric1514]

Originally Posted by markopolo

Have you set the charged light indicator voltage and amps yet? That's critical as it resets the Ah counter. The SOC reading will get less and less accurate the longer it goes without getting the batteries fully charged and resetting the counter.

I chose 14.3V and 1A or less as the criteria for my setup. There would be minimal persistent loads on mine, probably just the propane detector and a very low amp draw relay. My PD unit didn't seem to be able to meet 14.4V & 1A or less. 14.4V & 2A or less might be an alternative.

I have approx 400Ah of batteries in the van but very light use for the past three years as I've been using other RV's for accommodation. Almost 400 nights in those other RV's over the last three years. The van is currently used only in support of hobbies and running errands etc. so lights, fan & pump - very light use.

I set the voltage as 14.3 and the amps at 2. I have 210Ah. I suspect the charged light comes on too early but that's just a hunch.

[booster]

Originally Posted by eric1514

I set the voltage as 14.3 and the amps at 2. I have 210Ah. I suspect the charged light comes on too early but that's just a hunch.

That is about 1% of capacity, so not all that bad, depending on the batteries. If wet cells, it would be on low end and hard to get to on some batteries. For Lifeline AGM it would be a bit higher than the .5% they recommend. Best to check with the manufacturer to see what they recommend and then double check by watching the charging as it nears the top end. Set the amps lower than you will get to and keep triggering the 14.3v until the change in amps gets very small. A decent way to do it is to discharge the batteries to 50% and then recharge while watching. Most batteries will be in the 8+ hours to get to a good transition amp reading. Once you get to 10 hours I think going further is more harm than good to the battery, and you would add a few tenths of an amp to the reading at that point and use that for your setting.


At 2 amps you are not way off and likely to the slight undercharge side. With that setting if it is a bit early, at least you are getting good monitor reset to 100% calibration so your discharge SOC readings will be accurate.

[markopolo]

Probably a bit too early as previously mentioned. You could try 14.4V & 2A easily enough.

It's been a long time since I looked at current flow when the PD unit is in Boost mode so I can't help much with what Booster was getting at earlier.

PD units have that automatic periodic boost feature which actually might get the batteries full even with the early forced transition to normal or float modes.

Edit: I deleted some stuff as it was not accurate. For anyone who read it, I had the batteries disconnected from the PD charger since last Monday. I just remembered when I saw zero amps in or out on the Trimetric.

[eric1514]

The P2 setting for amps is really a percentage number so when I say I have the monitor set for 2, it really means 2% of my 210Ah which is actually around 4 amps. That was the default recommendation from Bogart. Sorry for the confusion. I think I'll change that to 1%.

[booster]

Originally Posted by eric1514

The P2 setting for amps is really a percentage number so when I say I have the monitor set for 2, it really means 2% of my 210Ah which is actually around 4 amps. That was the default recommendation from Bogart. Sorry for the confusion. I think I'll change that to 1%.

Good idea to try and then just put in boost to see if it gets there in a reasonable length of time so you get a reset without severe overcharging. I think it will be quite safe and if anything a bit early but not much.

[markopolo]

I forgot that the newer Trimetric P2 setting is for % of Ah. On mine you just enter the actual amps you want.

TM-2025: P2 is a value in amperes (1A to 100A)
TM-2030: P2 % of Ah rating