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Author Topic: Battery voltage and Wh limits?  (Read 1645 times)

johnshenry

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Battery voltage and Wh limits?
« on: June 15, 2016, 01:31:32 PM »
Ok, I hooked up a need battery voltage/current and energy meter in my trailer last night.  Had lots of fun turning things on and off to see the effect.  It also allows me to set high and low voltage limits and alarms.   We plan on doing a lot of boondocking and I am curious as to how well the battery power will hold up.  The meter shows a cumulative Wh value and allows me to reset it.  Long term, I'd like to add a solar panel controller to allow me to make up what I have used if the sun cooperates.

I have replaced all of the lights in my 21 ft TT with LEDs.  And I think that that water pump and furnace blower are the only other 12 volt consumers (for now, will add an inverter to get some 120 volt outlets later).  So my questions are:

What is the typical Wh's that I can get out of my battery?  I am sure it depends on the battery type and load-over-time profile.   Are there battery capacity specs on the battery label that should indicate what to expect?

What about voltage?  Of course lights will get dim, and fans/pumps run slow, but is there a voltage "limit" that most use, perhaps from over-depleting the battery?  I set my monitor to alarm at 9.5 volts, just seemed like a good number to me. 

TIA,

JH

Abendage

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Re: Battery voltage and Wh limits?
« Reply #1 on: June 15, 2016, 02:57:12 PM »
Your batteries should have an amp hour rating on them. Once you know that divide it in half and that is the number of amp hours you can safely use. Multiply by 12 to get watt hours. You don't want to drain your batteries past 50%. Doing so damages them. The voltage of a battery at rest at 50% is 12.06ish volts. Ideally you don't want to go below that. This is difficult to determine though because a battery in use will show a lower voltage than its resting voltage. If you have a way to track your amp hours used, and it sounds like you do, that is the best way to go. 9.5 volts and your battery is toast. Dead is in the 11.5v range.
2006 GMC 1500 4x4 Crew Cab 5.3L
2006 Fleetwood Pioneer 180CK, GC2's, 200 Watts Solar

byrogie

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Re: Battery voltage and Wh limits?
« Reply #2 on: June 15, 2016, 03:17:57 PM »
Yes, use amp/hr as your guide, it is the most common. Your monitor should be able to be set as such.
Look at the 20 hour amp rate to compare batteries, again it is the most common measurement.
And as Abendage says, you do not want to go less than 50% per the chart.
Byron and Sherryl
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2006 HR Savoy 33ft 5er
2008 Ford F250 Super Duty

John From Detroit

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Re: Battery voltage and Wh limits?
« Reply #3 on: June 15, 2016, 06:00:09 PM »
Ok batteries are rated in amp hours.. To convert to watt hours multiply by 12 for 12 volt stuff and 10 for 120 volt stuff (Stuff the inverter runs) why the difference?  Well, that compensates for losses in the inverter..It is not exact. but under 1,000 watts it's close enough.

Now the batteries:
For this I will give the capacity in the C/20 standard, this means how many amp hours if you discharge smoothly over a 20 hour period.  So for example on a Group 24 you woudl discharge at 74/20 amnpos or 3.7 amps.
THE FASTER YOU DISCHARGE.. The Faster still the battery runs down and the slower the longer still it lasts.
I still can't remember that dang discover's name.. Begains with P is all I can do.

Group 24  about 73-75 each
Group 27 around 95
Group 29 around 105
Group 31 130

NOTE: THese are usually MARINE/deep cycle batteries..  YOu should not use much more than 1/3 of their capacity

GC-2..(Six volt Golf Car DEEP CYCLE batteries) used in pairs to make 12 volt 220 amp hours give or take 15 depending on the brand and sub model.. Also applies to the 4D and 8D sizes  (Only they are 12 volt) if you can get 'em in Deep cycle.

DEEP CYCLE you can use half the power safely,, More than that and they get old much faster.

What's the difference between running down and getting old?  Run down.. Recharge.. Get old.> Replace.

So in order to find out how much battery you have,  Add 'em up and go for it.

Batteries in SERIES like the pair of GC2  Add voltage

Batteries in PARALLEL.. add amp ahours

Multiple pairs of GC-2.. Treat each pair EXACTLY as you would a single 4D 12 volt...  For that is what it is... Electrically.

Many battery questions regarding six volt pairs are swiftly answered if you think of the pair as a single battery.. Examples

Can I replace just one (Can you replace half of a 4D, same answer)
Must they be the same (Age, Make, Size, et-al) Again, can you imagine a single case 4D that is half and half?

See how it answers questions.
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Kevin Means

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Re: Battery voltage and Wh limits?
« Reply #4 on: June 16, 2016, 02:20:27 AM »
Since you said you plan to do some boondocking, you should seriously consider installing a battery monitor, like the Trimetric RV-2030. It takes all the guesswork out of knowing your battery-bank's condition. Boondocking without one is like driving without a gas gauge.

Kev
2011 Winnebago Tour 42QD
Towing a Jeep Rubicon Unlimited LJ or an Acura MDX
RVI Brake 2, Minder TM-66 TPMS, 970 watts of solar
(Can't wait to spend more time RVing)
Lakeside, California

johnshenry

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Re: Battery voltage and Wh limits?
« Reply #5 on: June 16, 2016, 08:46:31 AM »
Thanks for all the tips/info. After posting I read some web pages on RV batteries.  I will set my alarm at 12 volts, and use this little $12 device for now.  Longer term when I go solar, I'll spend the  bucks on some good electronics.

I should also have a better idea of what my energy usage is.


JH

Gary RV_Wizard

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Re: Battery voltage and Wh limits?
« Reply #6 on: June 16, 2016, 09:34:58 AM »
I think that awareness of battery consumption is more important than the accuracy of the measurement tool. Even voltage will tell you what you need to know if you pay attention and make some correlation between your power usage habits and battery capacity. If you don't, accuracy isn't much of a factor.

Where something like the Trimetric shines is the ability to tell you how much charge you put back in. Unlike discharging, voltage while charging doesn't signify much, so you estimate (based on experience) how much charge time you need based on the voltage start point. With the Trimetric, you can get an accurate picture of both the time needed and charging progress. As Kevin says, it takes the guesswork out of it. But if you aren't charging on the fly with a generator and won't recharge batteries till you get home or move to a electric hook-up site anyway, [IMO] there isn't much extra value vs just monitoring voltage.
Gary
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Gary Brinck
Summers: Black Mountain, NC
Home: Ocala National Forest, FL

johnshenry

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Re: Battery voltage and Wh limits?
« Reply #7 on: June 16, 2016, 09:42:01 AM »
We are doing a week+ trip in July with at least 2 night Boondocks and charging by truck in between.  Since will will be carefully managing water too, water pump on time should be very limited and not likely to use the furnace.  So really only LED lighting.    Should be do-able.

But I am retiring at the end of the year though and want to do more solo, longer duration boondocks next year. 

robertusa123

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Re: Battery voltage and Wh limits?
« Reply #8 on: June 23, 2016, 07:02:54 AM »
Don't forget the fridge need 12 volts for the controls.   My camper only get a 12 to 24 hr run on one battery mostly depending of if we are running a fan on the inverter or heat.   I'm planing on up gradeing to 3 battery so I can get a hole weekend out of them.
1996  26ft. 3 kids 2 dog and the wife too

johnshenry

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Re: Battery voltage and Wh limits?
« Reply #9 on: June 23, 2016, 08:49:02 AM »
Yes, I noticed, and was surprised that the fridge was pulling about 1.5 amps, but it also varied a bit.  Will be interesting to see if we can get 2 days out of it....

Gary RV_Wizard

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Re: Battery voltage and Wh limits?
« Reply #10 on: June 23, 2016, 02:18:43 PM »
Your fridge may have a 12v heater labeled as something like "humidity control" or "frost" or some such. It heats the area around the door seal to evaporate condensation on the cold metal. It's mostly a cosmetic effect, though it may reduce rust in the very long term. Turn that off if it has a switch (some do not) and save maybe 1.0 amps/hour in warm weather.
Gary
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Gary Brinck
Summers: Black Mountain, NC
Home: Ocala National Forest, FL

johnshenry

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Re: Battery voltage and Wh limits?
« Reply #11 on: June 23, 2016, 02:52:25 PM »
Interesting, I'll have a look for that.  I did get the manual for the fridge with the trailer.   Thanks...

JH

Len and Jo

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Re: Battery voltage and Wh limits?
« Reply #12 on: June 29, 2016, 12:29:58 PM »
Rough numbers can be helpful.  We boondock a large percentage of the time.  Our house batteries are new will degrade over time but this should be good for a 2-3 years.  Of course your battery set up and refrig are probably different from ours but I think this is the type info you would like to know for boondocking.

Len & Jo
The Green Tardis
We 'B' RVing   Berkley, Michigan
Van Development:   https://youtu.be/5Xqk_G6k95M
12 Years of Travels:  https://youtu.be/UMIf17CzdZo

johnshenry

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Re: Battery voltage and Wh limits?
« Reply #13 on: June 29, 2016, 01:18:56 PM »
Thanks for that info.  Does your fridge run off propane too?  Are those energy consumption rates vs. temp in addition to the propane your fridge uses?

JH

Len and Jo

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Re: Battery voltage and Wh limits?
« Reply #14 on: June 29, 2016, 04:20:09 PM »
My refrig is electric only, we do not carry propane.  My RV is a class 'B' and the refrig is 3.7cf.
Len & Jo
The Green Tardis
We 'B' RVing   Berkley, Michigan
Van Development:   https://youtu.be/5Xqk_G6k95M
12 Years of Travels:  https://youtu.be/UMIf17CzdZo

Wankel7

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Re: Battery voltage and Wh limits?
« Reply #15 on: July 03, 2016, 01:03:12 AM »
This has been a good tool to see what is being drawn from the battery.....cheap and easy to install.


https://www.amazon.com/bayite-6-5-100V-Display-Multimeter-Voltmeter/dp/B013PKYILS
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2005 Tundra V8

johnshenry

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Re: Battery voltage and Wh limits?
« Reply #16 on: July 03, 2016, 09:56:19 AM »
This has been a good tool to see what is being drawn from the battery.....cheap and easy to install.


https://www.amazon.com/bayite-6-5-100V-Display-Multimeter-Voltmeter/dp/B013PKYILS

Yep, I have that one.  I think I paid only $12 or so for it.  Will be useful to watch what we use out of the battery....

Len and Jo

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Re: Battery voltage and Wh limits?
« Reply #17 on: July 03, 2016, 02:21:36 PM »
This has been a good tool to see what is being drawn from the battery.....cheap and easy to install.


https://www.amazon.com/bayite-6-5-100V-Display-Multimeter-Voltmeter/dp/B013PKYILS

I wired two of them into the Green TARDIS.  One to monitor power drain on the house batteries and one to monitor power going into the house batteries.

« Last Edit: July 03, 2016, 02:25:35 PM by Len and Jo »
Len & Jo
The Green Tardis
We 'B' RVing   Berkley, Michigan
Van Development:   https://youtu.be/5Xqk_G6k95M
12 Years of Travels:  https://youtu.be/UMIf17CzdZo

 

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