Monitoring Battery Discharge

[john61ct]

Originally Posted by GrowleyMonster

The "SmartGuage" battery monitor looks like a great piece of gear but to get the full benefit of it you need to take the time to program it properly. You will I think need your Peukert coefficient or else your capacity at 20hr disch rate and your reserve or else capacity at some other discharge rate.

True for AH counter type BMs but Merlin SmartGauge is an exception, both more accurate and more user friendly.

Balmar SG200 combines both types, but still very new

[EngNate]

Originally Posted by EngNate

OP said "out and about for a few nights". It's not a cheap solution, but a DCM-100 battery monitor and an SMS-100 text module from Maretron would provide the ability to text in and receive a status message that includes battery voltage. Unfortunately, state of charge cannot be obtained this way, however, with a Maretron display alerts can be setup for any monitored parameter and be sent by sms. Quite a bit higher on the $ scale you can get full remote monitoring on a mobile device - it requires the N2K View PC software to configure screens for the device, as well as the IP Gateway and internet connection.

Forgot to include: If there is no display or N2K View on PC in the system then a USB or IP gateway is needed to configure the modules with the (free) N2K Analyzer software.

[dmkkeng]

Originally Posted by Cheechako

Many devices have a built in voltmeter now days. VHF, Depth Sounder, GPS etc. My experience with "amp counters" has not been pleasant, easy or reliable. Your's may be better. In the end, what you need to know is simple.
For the KISS minded:

I had a similar experience, my solar system was indicating 100% SOC however actual charge was significantly lower. I have since changed some of the settings on my solar controller however as a back up I developed a voltage chart similar to yours for reference going forward. The chart information is based on loading the batteries and at each .1vdc drop checking the specific gravity of the batteries and comparing this with the manufacturers (Rolls 6V Batteries) information for battery charge level. The chart I came up with is as follows;

(vdc) (%)
11.9 44
12.0 50
12.1 56
12.2 63
12.3 69
12.4 75
12.5 81
12.6 88
12.7 94
12.8 100

At 12.1vdc I fire up my generator and charge the batteries for 4-6 hours to get the batteries back to the 80%+ range.

[john61ct]

Those correspondences will change over time, but since you are being conservative to start with, seems like a good setup.

[lateral]

Originally Posted by GrowleyMonster

FLA batteries?


Determining state of charge by checking battery voltage is most accurate when the batts have been resting for 24 hours, or at least 12 hours. If you are discharging batteries then your voltage reading will be down a bit more than the resting voltage. Heavier discharge, more down. Light discharge, less down. The good news though, is that means you will apparently have less juice than you actually do. So you won't be toasting your batteries. If you calculate that your batteries are at say 50%, they might actually be at 55% or 60% but they won't be 40% or 30%. You can also check Specific Gravity, but remember to correct SG higher by .004 for each ten degrees (fahrenheit, of course) above 80f. Vice versa for cooler than 80f.



There are cheap monitors all over fleabay and amazon that will display system voltage, discharge amps, watts, and watt/hours used. These cheap (under $20 including shunt) monitors do not typically give you percentage state of charge but you will know the SOC fairly close by the watt/hours discharged since last reset. They don't reset automatically... you have to do it yourself. Push a button.


The "SmartGuage" battery monitor looks like a great piece of gear but to get the full benefit of it you need to take the time to program it properly. You will I think need your Peukert coefficient or else your capacity at 20hr disch rate and your reserve or else capacity at some other discharge rate. You can discover this yourself, actually. Set it up right, and this gadget will give you a fairly accurate picture of where you are in your batteries' discharge cycle.


There are also "dumb guage" bar graph displays that work like the gas guage on your car, about as accurate as the monitor I mentioned above that gives all the data.



Another tactic is to have two separate banks. Run on one for 24 hours. Check the offline bank's voltage and SG, take readings twice, three times if the first two dont agree. Record your observations and switch banks. Every 24 hours check the bank that has rested and then bring it online.



Resting means no load. It also means no charging. Charge while it is online.


There are disadvantages to having split banks but at low discharge currents it is small potatoes. Some zealots will go to war with you over this, but it's your boat. There are also obvious advantages to a split bank. Put them in parallel with an Off/A/B/Both switch, when you need lots of juice for starting an engine or whatevah.

According to Balmar for the SG200 you do not have to do a current capacity test, rather just program in the manufacturers (new) capacity and it will work it out over several cycles.
Neither do you program in Peukerts, just type of bat.
Easy install.

[GrowleyMonster]

Originally Posted by lateral

According to Balmar for the SG200 you do not have to do a current capacity test, rather just program in the manufacturers (new) capacity and it will work it out over several cycles.
Neither do you program in Peukerts, just type of bat.
Easy install.

Sounds nice. I assume it works for different voltages? For instance, a 48v propulsion bank?

[Wood]

^^^ Yes it works up to 48v but must be disconnected from system for equalization at those voltages.

[witzgall]

For equalization of a 48v system, you just have to remove the fuses on the SG200 power line.

For a similar reason, the SG200 may not be suitable for charging a 48v system in arctic conditions, if temperature-compensated charging is used.

Chris

Originally Posted by Wood

^^^ Yes it works up to 48v but must be disconnected from system for equalization at those voltages.

[john61ct]

batteries should be equalized as individual units

also helps to spot the outlier problems before they fail

[GrowleyMonster]

Originally Posted by john61ct

batteries should be equalized as individual units

also helps to spot the outlier problems before they fail

Indeed. I prefer to equalize my batteries (6v) individually, and use a manual charging system (Variac, welder rectifier, and appropriate metering). But it is nice to know that the SG200 can handle routine monitoring of a 48v bank without preprogramming. I just might get one for my electric boat.

[smac999]

Originally Posted by dmkkeng

I had a similar experience, my solar system was indicating 100% SOC however actual charge was significantly lower. I have since changed some of the settings on my solar controller however as a back up I developed a voltage chart similar to yours for reference going forward. The chart information is based on loading the batteries and at each .1vdc drop checking the specific gravity of the batteries and comparing this with the manufacturers (Rolls 6V Batteries) information for battery charge level. The chart I came up with is as follows;

(vdc) (%)
11.9 44
12.0 50
12.1 56
12.2 63
12.3 69
12.4 75
12.5 81
12.6 88
12.7 94
12.8 100

At 12.1vdc I fire up my generator and charge the batteries for 4-6 hours to get the batteries back to the 80%+ range.

you shouldn't need 4-6 hours to get from 56% to 80%. your charger is way too small and you would be saving a lot of fuel and noise with a bigger one.

should take 1-2 hours

what is your bank size, charger size, and gen size?

[Adelie]

I disagree. Charger might be a little small. 3hr or so sounds right.
Somewhere between 65-75% battery will become voltage limited, amps will taper as voltage is held constant. That’s the absorption phase, bigger charger does nothing to speed up the process.

Bigger charger only helps during bulk charging and from 50% it’s only going to shave 15-45min from total time.

[john61ct]

If you actually want to get to 100% Full, no matter how powerful the charge source the last 5-10% can take another 3-4 hours.

Needed at least a few times a week if you want good longevity

[ayates]

Can anyone was has an SG-200 shunt tell me the distance between the two mounting holes?




Thanks,


Allan.