Energy Monitors and true battery state question

[sailorboy1]

The thing with my house bank that has always annoyed me is that the voltage in the morning with a load of the radio and refrigerator and with -30 AH out has always seemed real low. The BM says the batteries are 90+% SOC but the voltage suggests they are 70%. If I just used voltage I would be freaking out all the time and starting engine/generator to charge them.

[Kenomac]

Hello,

This Magnetrinic DCC 4000 battery monitoring system is 13 years old, is there a good reason to replace it? I will be adding 500w of solar shortly.

Ken

[Maine Sail]

Originally Posted by sailorboy1

The thing with my house bank that has always annoyed me is that the voltage in the morning with a load of the radio and refrigerator and with -30 AH out has always seemed real low. The BM says the batteries are 90+% SOC but the voltage suggests they are 70%. If I just used voltage I would be freaking out all the time and starting engine/generator to charge them.

Most likely cause is very, very common and it's a fibbing Ah counter. This results from being incorrectly programmed and improperly calibrated and not routinely reset to a known full state.

[sailorboy1]

Originally Posted by Maine Sail

Most likely cause is very, very common and it's a fibbing Ah counter. This results from being incorrectly programmed and improperly calibrated and not routinely reset to a known full state.

This is the standard answer. But I've gone though all this the past years and am pretty convinced I have the unit programmed correctly for the batteries in use (some of the values were supplied by you). I also am sure my batteries are getting fully charged. They are on solar and are getting charged at 14.6V absorption that I used to hold for an hour and now am holding for 4 hours, or till the solar controller only puts out 2 amps at the 14.6V (460AH bank of 4 6V batteries). The solar controller log says they did the full 4 hours 5 times last week because since the refrigerator is on the output doesn't get down to 2 amps unless it cycles off. I also charged them and equalized them last month till they accepted less than 1 amp.

The other night I got to the boat just as the sun was going down and the batteries were at 12.7V at -2AH with the solar snoozing. But as normal the next morning they were at -30 AH and reading 12.3V with a -5 amp discharge occurring.

They have acted this way since new for that amount of discharge and load. They just seem to have a larger than I would expect voltage drop under fairly small loads.

[Maine Sail]

Originally Posted by sailorboy1

The other night I got to the boat just as the sun was going down and the batteries were at 12.7V at -2AH with the solar snoozing. But as normal the next morning they were at -30 AH and reading 12.3V with a -5 amp discharge occurring.

I feel like we've been through this before but....?

Where is the voltage sense/measurement point tied into the system? Have you confirmed this voltage with an accurate DVM measured at the battery terminals?

12.3V is a quite low loaded voltage for a 5A load (.01C discharge rate) -30Ah down (only 6.5% of assumed face value capacity used) on a 460Ah bank. Discharging at that low a rate actually serves to put you at a higher SOC than 93.5% due to Peukert...

Your discharge rate is only .01C & this is considerably less than the 20 hour discharge rate so the voltage should be higher than 12.3V, if the batteries have the capacity you believe they do.

I'll share an actual measured voltage from a T105 bank at 90% SOC under the 20 hour discharge rate. This discharge rate is approx 4X your discharge rate.

At 90% SOC & 76F, while discharging a slightly used T105 bank (two T105's in series that had tested at 209.2Ah's) on my test bench, was at 12.54V at 90% SOC under a constant load load of 11.25A. The equivalent load at 90% SOC on your bank would be 23A. This is why I suggest that your battery monitor may be fibbing or the batteries simply no longer have the same or similar capacity to what is programmed..

While this graph is not accurate for all batteries your bank should be fairly close.

To figure out the C/XX just divide your Ah capacity by the number..

460Ah / 100 = 4.6A = C/100 Discharge Rate
460Ah / 20 = 23A = C/20 Discharge Rate

Your discharge rate, at 5A, is closest to C/100 so at 90% SOC you should be pretty close to the chart..

[sailorboy1]

Originally Posted by Maine Sail

Where is the voltage sense/measurement point tied into the system? Have you confirmed this voltage with an accurate DVM measured at the battery terminals?

Measured at the battery by the BM and the panel volt meter and a hand held at the battery all agree. Been that way since day 1.

[poiu]

Originally Posted by Kenomac

Hello,

This Magnetrinic DCC 4000 battery monitoring system is 13 years old, is there a good reason to replace it? I will be adding 500w of solar shortly.

Ken

I've got them too. I've even got the hand written breaker switch label

I think it's fine. I don't think the latest kit is much different. If you don't do it already, just cross check the amp counter with a volt reading now ideally first thing in the morning when there is no load to make sure the counter has not got out of step. Use a chart like the one in the last post to estimate charge level. Dockhead made the point and I agree it is pretty good way to measure capacity.
Worth also checking each cell now and then to try to catch a failing one before it drags the bank down.

I do the same with my lithium batteries, just the curve is 3 x flatter and a different shape.

[smac999]

Originally Posted by sailorboy1

The thing with my house bank that has always annoyed me is that the voltage in the morning with a load of the radio and refrigerator and with -30 AH out has always seemed real low. The BM says the batteries are 90+% SOC but the voltage suggests they are 70%. If I just used voltage I would be freaking out all the time and starting engine/generator to charge them.

your batteries are probably weak. do a C20 test. and when you get your answer, program the meter to the new AH specs. make as spread sheet of time vs voltage. try to plug the boat in for 24 hours before you do it to make sure you are charged.

the last 3 C20 tests I did the agms lasted less then an hour... one was 1200ah and one was 2400ah. big bills and unhappy owners.

[Zanshin]

Thanks for all the useful information on the matter. I've been monitoring my power consumption (and charging) for a while - using an Arduino that stores data every 30 seconds to a SD-Card; this gets data from the Xantrex LinkPro (using their communication protocol) and from sensors that I have on my solar panel MPPT outputs and from the genset/engine. In addition, I had a GPS chip and a humidity/temperature/pressure sensor that I threw in for good measure

Attached are some charts for the past 37 days of data showing the discrepancy between the Amps displayed and the actual Watts consumed/generated. The curves for my general consumption and for solar charging show little difference when taken separately, but the overall difference is about 10% when I use a nominal 24V voltage for the house bank. When I change that nominal voltage to 25.46V I get an average 0% difference between measured and actual amps, which is what I used for the bottom chart.

click on the image above for a larger chart

click on the image above for a larger chart

[poiu]

Originally Posted by Zanshin

Thanks for all the useful information on the matter. I've been monitoring my power consumption (and charging) for a while - using an Arduino that stores data every 30 seconds to a SD-Card; this gets data from the Xantrex LinkPro (using their communication protocol) and from sensors that I have on my solar panel MPPT outputs and from the genset/engine. In addition, I had a GPS chip and a humidity/temperature/pressure sensor that I threw in for good measure

Attached are some charts for the past 37 days of data showing the discrepancy between the Amps displayed and the actual Watts consumed/generated. The curves for my general consumption and for solar charging show little difference when taken separately, but the overall difference is about 10% when I use a nominal 24V voltage for the house bank. When I change that nominal voltage to 25.46V I get an average 0% difference between measured and actual amps, which is what I used for the bottom chart.


click on the image above to get a full-sized graph

How many daily amps or watt/hrs do you get out of your 750A panels? Looks like maybe 2.4kWHr as a guess. That would be 3.2 x your nominal capacity, which would be a little low. From the drop off in the evening it looks like you are getting more shading at that time. Maybe through the day too a bit.

[Zanshin]

poiu - the dropoff on the solar panels is due to the battery bank getting filled up during the course of the day and the MPPT controllers switch from "bulk" to "absorption"; so they could put out more power and that would make the distribution more standard.
I didn't post all of the data, but my 750 watt panels (6 Solbian 125W panels, each with its own Genasun MPPT controller) produce power 9 1/2 hours a day and generate 77Ah daily (so about 2kWHr). I have some losses in the connectors going through the hull which I am going to replace, and will also shorten some of the cable runs to reduce losses.

[Maine Sail]

Originally Posted by Zanshin

click on the image above for a larger chart

The one thing that jumps out at me is the lack of attained absorption level voltage.. Your solar is rarely even getting to absorption levels, likely still in bulk, and your engine alt is not even breaking 27.7V or (13.85V as a 12V equivalent). Unless you have GEL batteries set for 14.1V this type of behavior will be pretty damaging over time to the batteries. The peak voltages I see look to be about 14.25V and driven by the generator yet solar averages are barely breaking 13.5V. With this type of cycling your batteries really need a solid 4-6+ hours per day at absorption voltage to attain 100% SOC. For GEL type batteries this would be 14.1V-14.3V (manufacturer dependent), for AGM batteries 14.4V to 14.7V (manufacturer dependent) and for deep cycle flooded such as Trojan 14.7V - 14.8V.

[Zanshin]

Yes, the %SOC shown on the chart is from the Xantrex LinkPro and certainly don't show the true state of the batteries. The batteries are sealed Vetus SMF batteries, and although I've written to the manufacturer (a couple of times) to get detailed charging information I've gotten absolutely nothing back, except that 14.4V should be the maximum bulk voltage but they haven't told me their absorption or float voltages. I can adjust the Victron charger, which runs off the generator, to output that voltage, but cannot adjust the alternator on the engine. Likewise the Genasun MPPT controllers have a fixed maximum bulk output of 28.4V but, even though I used a large diameter cable for the short distance from the controllers to the main power bus bar, I think that there are some voltage losses there which I need to find.

[Maine Sail]

Originally Posted by Zanshin

Yes, the %SOC shown on the chart is from the Xantrex LinkPro and certainly don't show the true state of the batteries. The batteries are sealed Vetus SMF batteries, and although I've written to the manufacturer (a couple of times) to get detailed charging information I've gotten absolutely nothing back, except that 14.4V should be the maximum bulk voltage but they haven't told me their absorption or float voltages. I can adjust the Victron charger, which runs off the generator, to output that voltage, but cannot adjust the alternator on the engine. Likewise the Genasun MPPT controllers have a fixed maximum bulk output of 28.4V but, even though I used a large diameter cable for the short distance from the controllers to the main power bus bar, I think that there are some voltage losses there which I need to find.

The Vetus SMF range are sealed "maintenance free" flooded batteries. You are going to be looking at a min absorption of around 14.4V but probably higher for optimal health. I am just curious why you chose the Vetus SMF when the store walking distance from Nanny Cay (where I last saw your boat on the hard) sells Trojan & other known quality brands?

[Zanshin]

I was in St. Martin when I bought those batteries last year from Budget Marine. My thinking at the time, as I'd just installed the solar panels, was that I would rarely, if ever, go below 75% SOC and didn't require anything beyond a simple maintenance free battery. So far I don't drain the batteries far, but as you noted, I don't get them to truly 100% yet, either.