Question about battry charge levels

Anything electric, AC or DC

Question about battry charge levels

Postby cracker39 » Fri May 26, 2006 10:23 am

In the chart below (from The 12volt Side of Life (Part 1)), The fully charged voltage is 12.6 and the 0% charge is 10.5 volts. How did they arrive at 10.5 as being 0%? What is the formula for this? My battery is 13.6 volts when fully charged. I presume that for my battery, 10.5 would not be the correct voltage for 0%I need to know the formula so I can create a chart specifically for my battery. I am running a test now to monitor the voltage drop while using lights and fan on just 12 volts with the shore power off. Help, Please.

[list=]http://www.tnttt.com/gallery/image.php?image_id=8856[/list]
Dale

Sometimes I pretend to be normal. But, that gets boring...so I go back to being me.

Squidget Pop Top Build Pages http://www.thesquidget.com/ptbuild/ptbuild.html

Squidget and Pop Top Plans Info and Photos: http://www.TheSquidget.com
User avatar
cracker39
3000 Club
3000 Club
 
Posts: 3069
Images: 233
Joined: Thu Jun 30, 2005 2:18 pm
Location: Lake Alfred, Florida, USA

Postby cracker39 » Fri May 26, 2006 10:23 am

oops...
Image
Dale

Sometimes I pretend to be normal. But, that gets boring...so I go back to being me.

Squidget Pop Top Build Pages http://www.thesquidget.com/ptbuild/ptbuild.html

Squidget and Pop Top Plans Info and Photos: http://www.TheSquidget.com
User avatar
cracker39
3000 Club
3000 Club
 
Posts: 3069
Images: 233
Joined: Thu Jun 30, 2005 2:18 pm
Location: Lake Alfred, Florida, USA

Postby Q » Fri May 26, 2006 11:43 am

The 12.6 volts for a fully charged battery is "resting voltage". That means that if you fully charge your battery then let it set for several hours you should read 12.6 volts. The same applies to the 10.5 volts for zero charge.

Q
User avatar
Q
Teardrop Master
 
Posts: 282
Joined: Wed Jan 05, 2005 12:59 pm
Location: Bend
Top

Postby cracker39 » Fri May 26, 2006 11:52 am

Thanks. I turned off the lights and fan, put the shore power back on for a while and the voltage stabilized again at 13.5. I turned off the shore power and the volt meter dropped to 13.2. I'll let it sit for 2 or 3 hours to see what it reads then. That's when I'll restart my test. I'll leave the fan and lights of for about 3 hours, turn them off, let it stabilize for a few hours and recheck the voltage. Then, I'll resume the test in the morning for a few more hours, and repeat the rest and check steps. I'll do this until it reaches 50% capacity and see how many hours of usage it took to get there. The fan is probably drawing about twice what the two light bulbs are drawing, so I can figure out how much amperage I can use before It will get down to 50%.
Dale

Sometimes I pretend to be normal. But, that gets boring...so I go back to being me.

Squidget Pop Top Build Pages http://www.thesquidget.com/ptbuild/ptbuild.html

Squidget and Pop Top Plans Info and Photos: http://www.TheSquidget.com
User avatar
cracker39
3000 Club
3000 Club
 
Posts: 3069
Images: 233
Joined: Thu Jun 30, 2005 2:18 pm
Location: Lake Alfred, Florida, USA
Top

Postby Melvin » Fri May 26, 2006 1:16 pm

Keep in mind that unless you got a $100+ Fluke or something your meter is unlikely to be rated tighter than +-5%.

Also even if you are using an accurate meter the voltage reading is going to vary with temperature.
Commandant Louis Joseph Lahure has a singular distinction in military history - he defeated a navy on horseback. Occupying Holland in January 1795, the French continental army learned that the mighty Dutch navy had been frozen into the ice around Texel Island. So Lahure and 128 men simply rode up to it and demanded surrender. No shots were fired.
Melvin
Teardrop Master
 
Posts: 220
Images: 14
Joined: Sat Apr 08, 2006 3:04 pm
Location: Kamloops BC Canada
Top

Postby cracker39 » Fri May 26, 2006 2:48 pm

Most of the time, it won't be a problem, as I'll usually be camping where there is shore power and won't be draining the battery. When I won't have shore power, I'll probably just be using it for some overnight fishing on one coast of the other.
Dale

Sometimes I pretend to be normal. But, that gets boring...so I go back to being me.

Squidget Pop Top Build Pages http://www.thesquidget.com/ptbuild/ptbuild.html

Squidget and Pop Top Plans Info and Photos: http://www.TheSquidget.com
User avatar
cracker39
3000 Club
3000 Club
 
Posts: 3069
Images: 233
Joined: Thu Jun 30, 2005 2:18 pm
Location: Lake Alfred, Florida, USA
Top

Postby angib » Fri May 26, 2006 4:08 pm

Beware - all those battery charge .vs. voltage charts are specific to one type of battery, so for example the data from a flooded lead acid battery won't be the same as for a gel battery.

Andrew
User avatar
angib
5000 Club
5000 Club
 
Posts: 5783
Images: 231
Joined: Fri Apr 30, 2004 2:04 pm
Location: (Olde) England
Top

Postby Chris C » Fri May 26, 2006 4:32 pm

Dale,

Your chart is for a flooded battery.

I have flooded batteries. When I charge them with a 3-Stage charger, the charger will show as high as 14.6 volts when I check it during the end of the charging cycle. When I take the charger off and let them set unused for a couple of hours, and check them with a Volt/Ohm meter, they both drop down to 12.9 volts. The chart you've shown is essentially accurate for most of our situations. And the site from which you pulled it, indicates to not use the battery down below 40%.....................but from all I've read and had "beaten" into my head, 50% is kinder to the life of the battery.
Chris :D

The tension between what is good enough and what is beyond that creates the space for character to become our work.

Teardrop Trailer Build Pictures: http://tinyurl.com/px5cd
Chris C
.
 
Posts: 3302
Joined: Sun May 15, 2005 7:24 pm
Location: Norman, Oklahoma
Top

Postby cracker39 » Fri May 26, 2006 5:37 pm

Mine is a flooded type...that is, a standard deep cycle lead acid battery. It sits at 13.5 as long as the converter/charger has power to it. I turned off the main breaker a short while ago and will see in the morning what it reads. Then, I'll start using power off the battery alone to watch the voltage readings to see how long it takes for it to drop to 50%. I just received amp data on the Fantastic fan from their tech support. It uses 3.0 amps on high speed, but I probably will run it on medium, which uses 2.29 amps per hour. I'm not sure what the light bulbs use, but it seems that I've seen 1.2 amps per bulb somewhere.
Dale

Sometimes I pretend to be normal. But, that gets boring...so I go back to being me.

Squidget Pop Top Build Pages http://www.thesquidget.com/ptbuild/ptbuild.html

Squidget and Pop Top Plans Info and Photos: http://www.TheSquidget.com
User avatar
cracker39
3000 Club
3000 Club
 
Posts: 3069
Images: 233
Joined: Thu Jun 30, 2005 2:18 pm
Location: Lake Alfred, Florida, USA
Top

Postby cracker39 » Sat May 27, 2006 12:30 pm

Battery charge monitoring will take some getting used to. I can see now why it's important to let the battery stabilize, and can see that checking the voltage level while you are using it won't help much because it isn't accurate.

I turned off my shore power yesterday when the meter showed 13.5 volts. This morning, it read 12.7. I turned on the fan to medium and two interior light bulbs, and the meter dropped almost immediately to 12.4. An hour and 20 minutes later it read 12.1. After 4 1/2 hours, it read 12.0, which is supposedly down to 50% capacity. So, I turned off the fan and lights, and within 5 minutes, it was reading 12.4, or 80% capacity. Five minutes after that, it read 12.5, or 90% capacity.

I'll wait another hour and a half and log the voltage and resume power usage. I'll probably use power for 3 hour intervals and log the voltage before I turn it off and wait 3 hours and log it again and start the cycle over again tomorrow. This way, I'll get a rough idea of the amount of power I can use before needing to recharge. While at home or camping where there is shore power, this won't be necessary anyway as the converter/charger will be supplying all of the 12V power, not the battery.
Dale

Sometimes I pretend to be normal. But, that gets boring...so I go back to being me.

Squidget Pop Top Build Pages http://www.thesquidget.com/ptbuild/ptbuild.html

Squidget and Pop Top Plans Info and Photos: http://www.TheSquidget.com
User avatar
cracker39
3000 Club
3000 Club
 
Posts: 3069
Images: 233
Joined: Thu Jun 30, 2005 2:18 pm
Location: Lake Alfred, Florida, USA
Top

Postby cracker39 » Sun May 28, 2006 3:13 pm

Let's see if I really do understand this subject now. At 8:30 this morning, I turned on the fan and two light bulbs again. The meter read 12.5 when I turned them on. At 11:00, I turned them off again. Just before I turned them off, the meter read 11.8. At 12 noon, the meter was back up to 12.3 and remained there. So, no matter that the meter was reading 11.8 while the fan and lights were on, after turning them off for several hours, the reading of 12.3 is the accurate battery charge level?
???

At that time, I had a total of 7.25 hours of power drain with about 5.2 amps draw per hour (I found the amps for the light bulbs...1.44 amps each). I just turned them back on for another hour. I intend to repeat the cycle every few hours until it reaches a stabilized level lf 50% to see how long I can run these two items together. When camping, I probably won't use the lights or fan all that much, and the fan will probably be on low most of the time anyway.
Dale

Sometimes I pretend to be normal. But, that gets boring...so I go back to being me.

Squidget Pop Top Build Pages http://www.thesquidget.com/ptbuild/ptbuild.html

Squidget and Pop Top Plans Info and Photos: http://www.TheSquidget.com
User avatar
cracker39
3000 Club
3000 Club
 
Posts: 3069
Images: 233
Joined: Thu Jun 30, 2005 2:18 pm
Location: Lake Alfred, Florida, USA
Top

Postby WarPony » Wed May 31, 2006 10:23 pm

Dale, I have a deep cycle marine battery and I assume mine is a "flooded" type. Does "flooded" mean a lead acid battery? I always check the resting voltage before I leave and after I get home. The starting "resting" voltage is around 12.95V and around 12.6V when I get home. Am I also to assume, from the chart you provided, is that anything above 12.6V is 100% charged?

I'm not holding you to being an expert on this type of stuff at all but I am really interested in your experiments. :thinking:
ImageImage

Still a million dollars away from being a millionaire!!
User avatar
WarPony
Donating Member
 
Posts: 2089
Images: 289
Joined: Tue Sep 14, 2004 12:10 pm
Location: Kansas, Topeka
Top

Postby angib » Thu Jun 01, 2006 4:42 am

WarPony wrote:Am I also to assume, from the chart you provided, is that anything above 12.6V is 100% charged?

Depends on what accuracy of meter you are using - it's quite possible that a cheap meter would read 12.6 when connected to a 12.95V battery!

Andrew
User avatar
angib
5000 Club
5000 Club
 
Posts: 5783
Images: 231
Joined: Fri Apr 30, 2004 2:04 pm
Location: (Olde) England
Top

Postby cracker39 » Thu Jun 01, 2006 6:45 am

I found that my meter (a cheap one from Wal Mart) reads about 12.5 or 12.6 when the converter/charger is turned off and the battery is fully charged. I haven't checked the battery with my volt/ohm meter that I use around the house, but I will just to see how they compare. So, I suppose that chart is accurate for my battery.

I thought my trolling motor battery battery was really low as I used it fishing several months ago and forgot to charge it. I checked it before putting the charger on it and it was around 12.3, so it didn't get below the 50% level. I put a charger on it and got it back to full capacity. I haven't checked my starting battery yet, but it shouldn't be too low either. My outboard motor doesn't have a charging system.
Dale

Sometimes I pretend to be normal. But, that gets boring...so I go back to being me.

Squidget Pop Top Build Pages http://www.thesquidget.com/ptbuild/ptbuild.html

Squidget and Pop Top Plans Info and Photos: http://www.TheSquidget.com
User avatar
cracker39
3000 Club
3000 Club
 
Posts: 3069
Images: 233
Joined: Thu Jun 30, 2005 2:18 pm
Location: Lake Alfred, Florida, USA
Top

Postby GeorgeTelford » Fri Jun 02, 2006 5:37 am

Hi Dale

You are seeing some of the things that I was trying to explain before.

Especially the settled voltage bit, ie voltage readings in themselves do not give an accurate picture of State of charge UNLESS you have allowed the battery to settle. As you have seen even when you disconnect the charger the reading stays high for quite a while, which is why I disagreed with the person who claimed that a valid state of charge reading could be had by measuring voltage while the charger was still switched on.

It as already been pointed out that the chart is only valid for a certain type of battery, hence the reason I suggested that fully charging any battery and then finding its settled voltage is the starting point you need to have any chance of finding a decent reference. All you need to do is start your chart at 12.7 Volts (BTW did you use a decent charger 2 3 stage?) for your battery 12.2 Volts would be 50% if the 12.7 is the real top reading.

But as you are also finding if you measure while the battery is in use it gives an inaccurate lower reading, leave it a while and it recovers, the battery must be rested a while to get the settled voltage, this the mains resean that I dont believe vltage readings are that accurate while camping, while out in the field are you going to leave everything switched off long enough to get a decentsteady state reading?

PS Modern Meters even the cheap ones have an accuracy within 0.5% more than accurate enough to give you an idea of the state of charge
User avatar
GeorgeTelford
500 Club
 
Posts: 677
Joined: Mon Jul 11, 2005 2:10 pm
Top

Next

Return to Electrical Secrets

Who is online

Users browsing this forum: Bing [Bot] and 2 guests