How exactly does one measure resting voltage of a battery? Does the battery have to be disconnected from everything? Including the charge controller which does impose a small parasitic load? And can I ever be sure what the charge controller is doing, possibly it would be better to disconnect it? How about other milli-amp loads like a PWM dimmer that I put in my van, it draws about 7 ma when off...
resting voltage
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DC Fuse
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Good evening anm. How are you monitoring your battery now?
Consider looking into a Trimetric battery monitor.
This has a lot of features you'll enjoy so you know at all times amps in, amps out, state of charge,cumalative amp hrs. used, etc.
I would'nt be w/out mine - very good product!
Here's just one co. that sells them.
http://www.backwoodssolar.com/trimetric-22-awg-4-cond-wire
Consider looking into a Trimetric battery monitor.
This has a lot of features you'll enjoy so you know at all times amps in, amps out, state of charge,cumalative amp hrs. used, etc.
I would'nt be w/out mine - very good product!
Here's just one co. that sells them.
http://www.backwoodssolar.com/trimetric-22-awg-4-cond-wire
DC Fuse
Well-known member
Resting voltage is no draw whatsoever for hours.
DC current is elastic in that it can show both higher voltages and lower voltages at a meter than battery state of charge truly is.
The only way to get a true reading is a fully charged battery left alone for several hours.
Before i could afford a meter i just used a voltmeter dedicated to my batteries. That still showed me amps in and voltage.
https://vanlivingforum.com/showthread.php?tid=10349
DC current is elastic in that it can show both higher voltages and lower voltages at a meter than battery state of charge truly is.
The only way to get a true reading is a fully charged battery left alone for several hours.
Before i could afford a meter i just used a voltmeter dedicated to my batteries. That still showed me amps in and voltage.
https://vanlivingforum.com/showthread.php?tid=10349
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If you want 100% accuracy, It's my understanding you have to buy a fairly expensive meter with a shunt.
I don't need 100% accuracy, close is good enough for me!
For that all you need to do is turn off everything you can when you go to bed and the next day before the sun hits the panels look at the meter on the controller or use your voltmeter and check it. That number is plenty good enough for me.
During the day when power is going in and out the number will still be pretty close. If it's too low I go into conservation mode.
Bob
I don't need 100% accuracy, close is good enough for me!
For that all you need to do is turn off everything you can when you go to bed and the next day before the sun hits the panels look at the meter on the controller or use your voltmeter and check it. That number is plenty good enough for me.
During the day when power is going in and out the number will still be pretty close. If it's too low I go into conservation mode.
Bob
Zil
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I found this information. It is written to be understandable. Maybe it is.
http://www.batterystuff.com/kb/articles/battery-articles/battery-basics.html#6
http://www.batterystuff.com/kb/articles/battery-articles/battery-basics.html#6
Hey there @DC Fuse: I'm presently just using my digital multi-meter. A Trimetric would be nice but it's not within my budget right now...DC Fuse said:
that's a good idea, I hadn't even thought of keeping an eye on my starting battery...
@akrvbob: yes, that will be what I'll do too, at least for now. I usually can't sleep past dawn anyway, guess I'll just get up and check the batteries...akrvbob said:
@Zil: looks like some good info there, I'm going to bookmark it...Zil said:
I don't think that anyone has really answered my original question(s), whether the battery has to be disconnected from ALL loads including those tiny parasitic ones? before taking a resting voltage reading. I would think that milli-amp loads would not be any concern, if anything they may help the battery reach its resting voltage sooner, but that may be wishful thinking as much as anything...
Bela's Mom
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I believe that DC Fuse did answer your question when he said that resting voltage is no draw whatsoever for several hours.
Unless you use the methods that Sternwake recommends for checking voltages and capacity, ie, using a hydrometer, the best that you can do is to fully charge the battery, remove all loads for several hours, and then check it at the terminals.
I installed a switch between my charge controller and battery so that I could turn it off. Or I could pull the fuses but having a switch is easier for me. That way I can just use a ciggy plug in voltage meter to check my battery voltage.
Maybe you can install a switch to cut off your loads so that you don't have to disconnect things from the battery.[/align]
If you are wanting to check it without waiting several hours, you can try the method stated in the batterystuff link provided by Zil. A parasitic load will not help it get to resting voltage very quickly.
Unless you use the methods that Sternwake recommends for checking voltages and capacity, ie, using a hydrometer, the best that you can do is to fully charge the battery, remove all loads for several hours, and then check it at the terminals.
I installed a switch between my charge controller and battery so that I could turn it off. Or I could pull the fuses but having a switch is easier for me. That way I can just use a ciggy plug in voltage meter to check my battery voltage.
Maybe you can install a switch to cut off your loads so that you don't have to disconnect things from the battery.[/align]
If you are wanting to check it without waiting several hours, you can try the method stated in the batterystuff link provided by Zil. A parasitic load will not help it get to resting voltage very quickly.
SternWake
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The amount of rest needed for battery voltage to level off with all loads and charge sources removed, where it is truly representative of state of charge, can vary widely with many factors contributing.
Small parasitic loads generally are not too significant unless you have a DMM capable of 4 decimal places and you stress over the 2 last digits.
Surface charge after a charging source is removed generally screws up peoples estimation of SOC more so than time to rebound when removing loads.
Voltage settling to represent true state of charge will take different amounts of time between batteries and on the health of the battery, as well as between different makes of batteries, temperature, how big a load or charging source was, ect.
Moon phase, atmospheric pressure and the possible presence of Locusts too
Generally 2 to 3 hours is close enough, but the longer the better.
The more observations and the more tools one has to measure amps and volts, the better one is able to estimate state of charge, and notice degradation in battery performance as it accumulates cycles.
A battery monitor is a wonderful tool, but unless it is rezeroed when the battery is known to be absolutely fully charged, can throw off accuracy of them too, and they should not be considered 100% accurate even then.
Also the oft posted voltage/State of charge charts are not accurate for each and every battery. If your battery manufacturer posts such information, then that is the figure to use.
Trojan publishes expected Specific gravity readings along with voltage to represent state of charge, and this is confidence inspiring, as there is a lot of marketing mumbo jumbo literature written by people with little understanding of the product they are marketing. They like to use impressive words to inspire confidence.
Small parasitic loads generally are not too significant unless you have a DMM capable of 4 decimal places and you stress over the 2 last digits.
Surface charge after a charging source is removed generally screws up peoples estimation of SOC more so than time to rebound when removing loads.
Voltage settling to represent true state of charge will take different amounts of time between batteries and on the health of the battery, as well as between different makes of batteries, temperature, how big a load or charging source was, ect.
Moon phase, atmospheric pressure and the possible presence of Locusts too
Generally 2 to 3 hours is close enough, but the longer the better.
The more observations and the more tools one has to measure amps and volts, the better one is able to estimate state of charge, and notice degradation in battery performance as it accumulates cycles.
A battery monitor is a wonderful tool, but unless it is rezeroed when the battery is known to be absolutely fully charged, can throw off accuracy of them too, and they should not be considered 100% accurate even then.
Also the oft posted voltage/State of charge charts are not accurate for each and every battery. If your battery manufacturer posts such information, then that is the figure to use.
Trojan publishes expected Specific gravity readings along with voltage to represent state of charge, and this is confidence inspiring, as there is a lot of marketing mumbo jumbo literature written by people with little understanding of the product they are marketing. They like to use impressive words to inspire confidence.
Bela's Mom
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"Moon phase, atmospheric pressure and the possible presence of Locusts too "
You are too funny!
Thanks for always taking the time to share your battery knowledge!
"You are too funny!
Thanks for always taking the time to share your battery knowledge!
Zil
Well-known member
The use of a volt meter by itself is always just a close guess.
@Bela's Mom: I was just wanting some confirmation that a load of a few thousandths of an amp must be removed also, nobody specifically said so, they said 'loads' and I wouldn't normally count the charge controller as a 'load'.Bela said:
If it's that sensitive shouldn't there be a specification for the voltmeter? Voltmeters always have an resistance across the two leads that varies from manufacturer to manufacturer, which consequentially effects the circuit you are testing. Is there a recommended resistance or impedance for the meter?
Bela's Mom
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Sternwake has the best answers to your questions. My method is simple and not as accurate as it seems you want for your system.
I know that volt meters are not the most accurate to use; I used a digital multimeter at first but it became a hassle due to the location of my battery and when I compared the voltages between the multimeter and the plug-in voltmeter, they were the same. I don't have the money for the expensive monitors that others here use, which would probably be your best bet if you want to know the true condition of your battery at all times.
My four year old AGM is subjected to very high summer temperatures and that by itself can degrade batteries faster, so I just do the best I can at keeping it charged up and not allow it to sit in a discharged state.
By the way, your conversion is looking very, very nice!
I know that volt meters are not the most accurate to use; I used a digital multimeter at first but it became a hassle due to the location of my battery and when I compared the voltages between the multimeter and the plug-in voltmeter, they were the same. I don't have the money for the expensive monitors that others here use, which would probably be your best bet if you want to know the true condition of your battery at all times.
My four year old AGM is subjected to very high summer temperatures and that by itself can degrade batteries faster, so I just do the best I can at keeping it charged up and not allow it to sit in a discharged state.
By the way, your conversion is looking very, very nice!
@Bela's Mom: It's all new to me (relatively anyway) and there's so much I don't know, I'm trying to learn as much as I can, and make sure I don't overlook anything. I know what you mean, I can't afford the meter everyone recommends either, so I'll stick with my digital multi-meter.Bela said:
And thank you, I'm pretty pleased with my baby!
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You are way over thinking this thing. Yes, to get a 100% accurate you need to disconnect every possible draw. Do you have a really compelling need for 100% accuracy?
Turning everything off and checking in the morning should be accurate enough.
A good meter with a shunt will give you near 100% accuracy at nearly all times. But it will cost you some money and have a learning curve to install it. Is 100% accuracy worth it to you?
Volt meters are accurate if the battery is is being charged or discharged, but because of something called a float charge the battery itself is deceptive. The number it is giving off is wrong so the voltmeter is telling you what the battery is, but that is not the truth.
Bob
Turning everything off and checking in the morning should be accurate enough.
A good meter with a shunt will give you near 100% accuracy at nearly all times. But it will cost you some money and have a learning curve to install it. Is 100% accuracy worth it to you?
Volt meters are accurate if the battery is is being charged or discharged, but because of something called a float charge the battery itself is deceptive. The number it is giving off is wrong so the voltmeter is telling you what the battery is, but that is not the truth.
Bob
