Want Opinions on Battery Monitors with SOH

[vermilye]

I ran a pair of lead acid batteries for 6 years without feeling the need for a drawdown test. After 6 years of use I was still not seeing faster depletion of available amp hours than when they were new. I suspect there was some loss after 6 years, but not enough for me to be concerned. That said, I did treat my batteries well. They never went below 60%, and then only a couple of times. They generally cycled from 80% to 95%-100%. daily.

If I was starting out with a set of batteries of unknown history, age, etc, I would either replace them or do a drawdown test before I headed out for an extended trip with them.

 

[MVA]

Pb-acid battery SOC (state of charge) can be estimated (roughly) by measuring the open circuit voltage or by measuring the density of the electrolyte with a hydrometer. In either case, one would have to wait ~3-4 hours for the electrolyte to equilibrate while the battery is open circuit (perhaps quite inconvenient). I would use the electrolyte density method (assuming it is flooded Pb-acid and not AGM) since I would also be able to detect variation across the cells, which would give me additional information on battery health.

A contributing factor to your design consideration is that Pb-acid batteries degrade very slowly (over years). Hence, having the battery fully charged and then measuring discharge with a coulomb counter (e.g., shunt) it a functional solution, assuming you can fully charge the battery with a few cycles. A secondary failure mode of Pb-acid batteries to consider (since you will be using it for medical devices) is the catastrophic failure of either a cell short or cell open circuit, thereby causing the complete failure of the battery or significant loss of voltage. I have had the former happen.

2 cents

 

[Tin]

Does anyone with Pb-acid batteries routinely run drawdown tests? This may be what I need to do rather than spend money on an SOH monitor but after reading this article, I am convinced knowing the true capacity is a big deal for Pb-acid and cannot be directly measured by a coulomb counter:

https://marinehowto.com/programming-a-battery-monitor/

Thanks again to all for the discussion and education.

Maybe I just need to get a coulomb counter and try to run a drawdown test... but maybe a better idea is just to buy new batteries and move on...

Mike

Ah now your starting to get it. There really is no such thing as a Health monitor, may be with exceptions of inductive/ impedance testers but even they have draw backs.
1. As others have suggested start with proper electrolyte levels
2. Fully charge your battery bank with a good quality multi charger.
3. When done let batteries rest for a couple hours.
4. Check each cell for proper voltage using a quality hydrometer. ( if a cell is bad, time for new batteries )
5. If cell are good do a draw down test.

Now you'll have a better understanding of your batteries condition.
Once you are confident your batteries are 100%, using a column counter is all you need. As you get use to your system, in time it will all come together.
It is then you will realize you need better battery chemistry, battery storage along with adequate means of replacing used AH.
Oh I almost forgot, you will also learn you need to redo your trailers electrical system wiring and component to achieve optimum performance. Now if all you are going to do is parking lot camping then disregard. good luck

 

[Shiny]

Thanks to all!

My conclusions:

1. I need to know what my "true" battery capacity currently is (health of my batteries) and I do not.

2. I need to know how much power I consume and how much I charge, regardless of capacity. Therefore I need a coulomb counter.

3. SOH monitors probably work great and are a good idea but unfortunately, those marketed do not provide access to the data I need to make informed decisions. A coulomb counter may not tell me if my batteries are degraded but it will tell me how much capacity I need and whether my charging system is up to replacing it.

So... I ordered a Thornwave monitor and shunt.

I will use it to assess the capacity of my batteries, either by a "controlled" drawdown test or by inference (ie indicated SOC vs AH consumed).

I can then decide if I need new batteries, bigger batteries, different batteries, and/or a more automated method to simplify monitoring, like an SOH product.

...............If I was starting out with a set of batteries of unknown history, age, etc, I would either replace them or do a drawdown test before I headed out for an extended trip with them.

This is the right advice and I need to step up and measure what I've got.

Pb-acid battery SOC (state of charge) can be estimated (roughly) by measuring the open circuit voltage or by measuring the density of the electrolyte with a hydrometer. In either case, one would have to wait ~3-4 hours for the electrolyte to equilibrate while the battery is open circuit (perhaps quite inconvenient). I would use the electrolyte density method (assuming it is flooded Pb-acid and not AGM) since I would also be able to detect variation across the cells, which would give me additional information on battery health.

A contributing factor to your design consideration is that Pb-acid batteries degrade very slowly (over years). Hence, having the battery fully charged and then measuring discharge with a coulomb counter (e.g., shunt) it a functional solution, assuming you can fully charge the battery with a few cycles. A secondary failure mode of Pb-acid batteries to consider (since you will be using it for medical devices) is the catastrophic failure of either a cell short or cell open circuit, thereby causing the complete failure of the battery or significant loss of voltage. I have had the former happen.

2 cents

Thanks. Good advice, and I reiterate my need to step up. As to medical devices, nobody dies if our CPAPs run out of power. We just wake up crabby and tired.

Ah now your starting to get it. There really is no such thing as a Health monitor, may be with exceptions of inductive/ impedance testers but even they have draw backs.
1. As others have suggested start with proper electrolyte levels
2. Fully charge your battery bank with a good quality multi charger.
3. When done let batteries rest for a couple hours.
4. Check each cell for proper voltage using a quality hydrometer. ( if a cell is bad, time for new batteries )
5. If cell are good do a draw down test.

Now you'll have a better understanding of your batteries condition.
Once you are confident your batteries are 100%, using a column counter is all you need. As you get use to your system, in time it will all come together.
It is then you will realize you need better battery chemistry, battery storage along with adequate means of replacing used AH.
Oh I almost forgot, you will also learn you need to redo your trailers electrical system wiring and component to achieve optimum performance. Now if all you are going to do is parking lot camping then disregard. good luck

Thank you! I do think the SOH monitors can do what they claim. I may also believe in fairies, but that's a different thread.

As to the advice on measuring, thank you. I double reiterate my need to step up.

And as to "mission creep", I get it. Hopefully we are close enough to parking lot campers to be happy with what we have and will learn to live within our electrical power means. If not, I don't think generators are evil. Just noisy.

So far, we are happy with the solar panels and with "real" data from a coulomb counter we'll be able to plan better and stress less.

Mike

 

[John in Santa Cruz]

I've never heard anyone calling an amp*hour meter a 'coulomb counter'. yes, I know, a coulomb is equivalent to an amp*second, but I've only ever seen coulombs used in a physics context, not in an electrical/electronics context.

if you accurately want to know your batteries capacity fully charge it, then put a load on it equivalent to its specified amp*hour rating divided by 20 for 10 hours, then let the battery rest an hour and use a hydrometer or the rest voltage and battery temperature against a suitable charge state scale for your type of battery (traditional flooded, maintenance free, and AGM all have slightly different voltages at a given charge state. If the battery holds its originally specified capacity, then it should be 50% discharged. if its more than 50% adjust the originally rated capacity by the difference.

say it was a 100AH battery, so you pull 5 amps off it for 10 hours, and now find its at 30% instead of the expected 50%, so 50AH is 70% of the batteries current capacity and not 50%. this would suggest its now an 70 amp*hour battery (50*.70*2).

 

[Shiny]

Thanks John

I never heard of it either, just saw it used on some of the "SOH monitor" blurbs online to describe the other type. What is a better term for the Victron style vs those that estimate SOH? AH loggers? Both the Balmar and Veratron use a shunt so it's not that simple.

And thanks for the measuring method summary. I'll have to buy a hygrometer. As others have said, it will help compare all the cells. Speaking of that, I think the Thornwave will let me monitor a second voltage which could flag an unbalance between my two 6V batteries.

 

[John in Santa Cruz]

Victron calls the BMVs and the SmartShunt battery monitors, seems good enough to me.

(compressor fridge cycling)

 

[BobG-ESC]

In response to this question: "Do you run drawdown tests to "calibrate" your monitor? My guess is the degradation mechanisms and resulting effect on capacity loss for LiFePO4 does not warrant it."


When I was running 5 AGM house batteries on a cruising sailboat, I ran a discharge curve when the batteries were new and then approximately every year after that to get idea of capacity. The discharge curves took a couple days to with readings 2 - 6 hours apart with much closer readings as the batteries approached 50% SOC. I only waited 2 minutes for batteries to stabilize with no load when taking voltage readings.


I also prepared charge curves.



I did these exercises because I ruined 5 AGMs by over charging them and did not want another expensive mistake.

 

[Shiny]

In response to this question: "Do you run drawdown tests to "calibrate" your monitor? My guess is the degradation mechanisms and resulting effect on capacity loss for LiFePO4 does not warrant it."


When I was running 5 AGM house batteries on a cruising sailboat, I ran a discharge curve when the batteries were new and then approximately every year after that to get idea of capacity. The discharge curves took a couple days to with readings 2 - 6 hours apart with much closer readings as the batteries approached 50% SOC. I only waited 2 minutes for batteries to stabilize with no load when taking voltage readings.


I also prepared charge curves.



I did these exercises because I ruined 5 AGMs by over charging them and did not want another expensive mistake.

Thanks BobG

What you did sounds like work but smart.

 

[Shiny]

I Binged "coulomb counter" and find it is a fairly common term.

Analog Devices uses this nomenclature to market a line of power management ICs:
https://www.analog.com/en/products/power-management/battery-management/coulomb-counter.html

Maxim is another IC manufacturer that describes it as "A feature or device that measures the accumulated energy added to and removed from a battery, allowing accurate estimates of battery charge level."

I speculate these ICs could be found in some of the monitors being discussed?

 

[Jack!]

Well.... I just learned the SmartShunt does not retain data and reportedly has a very short bluetooth range. I am now leaning toward the Thornwave device to provide the A, AH, V, and SOC data logs. It will cost more but the logging is worth it.

I'm using a Thornwave PowerMon5S. Choose it for the longer BT range as we want to be able to check power levels from the truck. I'm getting about 55ft of BT range. We have a 5.0, so our 4 Li batteries are only a little over 17' behind the truck, so that works well. Also, like the 3 years of data logging on the shunt. When we log onto the app it take a few seconds to load up the logged data. It took getting an initial full charge and then the SOC value kicked in.

We used the BlueSeas covered fuse holder to install this shunt. Wanted it protected, as we installed it as a "positive" shunt.
Works great, no complaints, does what we wanted.

 

[Shiny]

Hi Jack! Good to hear positive feedback and your idea for a shunt "insulator".

My Thornwave shunt and monitor arrived yesterday.

Our 5.0 is still covered as winter isn't over here but I can sneak in with help of zippers on a nice day. I hope to install before risk for snow is gone. I guess that's a good thing about parking it in the driveway!

Mike

 

[Shiny]

I apologize for the long rambling post but wanted to update after all the useful response.

I installed a Thornwave monitor and now have a few days experience.

Good news is our batteries seem "healthy enough" for now and I'm happy to have a couple "tools" that were missing from the GoPower metrics. Being able to measure current draw instead of just charging current is a big improvement. The AH "in and out" is another.

I ran a "capacity trial" by running light bulbs off the inverter as a load.

At dusk without sunlight, the voltage read 12.82 before I loaded with 89 W. The next morning, again with no charge current, the load had eaten 81 AH overnight. The voltage was down to 12.04 "loaded" but the Thornwave said the SOC was 64%. I thought this was a discrepency but when I removed the load, the voltage quickly recovered to 12.29, more consistent with the 64% value.

If our battery had zero degradation and we were measuring under "standard" conditions, 36% of 225 AH = 81 AH. This suggests the monitor is simply using the 225 AH I entered as the "advertised capacity" and reporting SOC as a proportion of this "assumed" capacity.

I still don't know the "actual" capacity but feel like 81 AH bringing the voltage to ~12.29 suggests our batteries have not lost a lot of capacity.

I still feel that an SOH monitor would be valuable as the Thornwave (and I assume other "coulomb counters") doesn't appear to estimate "true" capacity and the lack of a "static" voltage reading adds complexity. The Thornwave and others may have algorithms that modify the "assumed" or "user-input" capacity but it's not obvious to me yet. The ability to measure AH consumed is great, though.

So far so good and our solar panels have no trouble restoring full charge from ~80 AH during the day. I have seen the charge power reported as high as 320W which I think is amazing for sitting in my driveway in March without a fancy (MPPT) controller.

Mike

 

[Jack!]

We are using the Thornwave. Getting about 50 ft on the BT range which works well. Like the data retention. Thornwave gets the job done for our 4-BB 100ah bats. These bats likely have a longer "camping" life cycle than I do, so watch my state of health more than the batteries.

 

[Shiny]

Yes, the Thornwood BT range is impressive. I also like the data retention and easy download.

As to SOH monitors/estimators, I'm still holding out for someone with experience using one with FLA batteries. Anyone?

The attached chart is an example of what caught my attention and generated concern about lost capacity. It shows life (discharge cycles) vs depth of discharge.

I think it would be useful to install an isolation switch for the solar charge. As it sits, I can't flip a switch to isolate the GoPower controller from the battery. I think I could do this with a relay and control it with the Thornwood "Power ON/OFF" feature. They sell a solid state relay that would probably be easy to install. This would make it easier to let the battery "rest" for voltage checks without pulling the cover off the battery tub and removing connections.

 

[vermilye]

Yes, the Thornwood BT range is impressive. I also like the data retention and easy download.

As to SOH monitors/estimators, I'm still holding out for someone with experience using one with FLA batteries. Anyone?

The attached chart is an example of what caught my attention and generated concern about lost capacity. It shows life (discharge cycles) vs depth of discharge.

I think it would be useful to install an isolation switch for the solar charge. As it sits, I can't flip a switch to isolate the GoPower controller from the battery. I think I could do this with a relay and control it with the Thornwood "Power ON/OFF" feature. They sell a solid state relay that would probably be easy to install. This would make it easier to let the battery "rest" for voltage checks without pulling the cover off the battery tub and removing connections.

If you are going to disconnect the solar controller from the batteries, be sure you put the disconnect on the input side of the controller. GoPower, along with many solar controller manufacturers require connecting the controller to the battery before connecting the solar panels. It is possible to damage the controller if the solar panels are connected without the battery.

 

[BobG-ESC]

Here is an interesting thing. When I pull up the battery history it shows 27 cycles and 1 full discharge. The full discharge was last July when I checked the capacity of the battery. It is rated 170Ah. Although the history only shows 27 cycles, the batteries have been operating for many more cycles than that.

Except for the last few days I have not been on shore power since some time in December. The batteries have been in constant use and during the past few months they have been taking some pretty big hits from the air conditioner and electric teakettle. Charging has been from solar only.

Obviously there have been more than 27 cycles, some down to 20% SOC yet the Victron SmartShunt says 27 cycles. It looks to me that it somehow converts all the partial cycles to full cycle equivalents?

It doesn't really matter to me but is kinda interesting. I guess I can compare the cycles the shunt logs against the number of cycles the battery manufacturer claims and maybe know about how much life is left.

 

[cpaharley2008]

Your air conditioner is not battery powered, it is 120v only......

 

[Shiny]

If you are going to disconnect the solar controller from the batteries, be sure you put the disconnect on the input side of the controller. GoPower, along with many solar controller manufacturers require connecting the controller to the battery before connecting the solar panels. It is possible to damage the controller if the solar panels are connected without the battery.

Thank you! I am not jumping on this but will read the controller book before I do.

 

[BobG-ESC]

Yes, you are correct. It runs on the inverter.