RV News RVBusiness 2021 Top 10 RVs of the Year, plus 56 additional debuts and must-see units → ×
 

Go Back   Thor Forums > Thor Tech Forums > Motorhome Tech Topics
Click Here to Login
Reply
 
Thread Tools Display Modes
 
Old 12-06-2016, 01:15 AM   #1
Senior Member
 
Brand: Still Looking
State: Alabama
Posts: 333
THOR #3789
House batteries

Would 4 Trojan T125 240 amp batteries keep enough of a charge over night not to have the Generator start up? Not sure how to do the math on this one. Right now with the main fridge on and what ever small LED radio dash lights on I am using about 28 amps. With the TV, satellite, fridge and a few lights I am at 36 amps. With nothing on over night but the fridge the Generator starts up about every 3 hours for a hour. I need to try and get closer to 8 hours with no Gen. Would these batteries be close?
__________________

__________________
mustang94 is offline   Reply With Quote
Old 12-06-2016, 02:00 AM   #2
Senior Member
 
Oneilkeys's Avatar
 
Brand: Still Looking
Model: Travato
State: Florida
Posts: 2,435
THOR #1765
https://www.batterystuff.com/kb/tool...to-a-load.html

This web site has a simple calculator for sizing batteries to a specific amp load over time. While you may have a 240 amp hour capacity, remember that you only get to use 120 amp hours before you drain your battery down to 50% - as low as you want to routinely draw down to, if you do not want to kill your batteries. For a 36 amp draw for 8 hours down to 50%, the calculator says you need 750 amp hours of batteries. For a 28 amp draw over the same 8 hours it would be about 3/4 of that.

28-36 amp draw is a lot. My small Axis draws less than 20 Amps with the A/C and everything else except the microwave.
Attached Thumbnails
Click image for larger version

Name:	IMG_4051.jpg
Views:	165
Size:	157.6 KB
ID:	3476  
__________________

__________________
Oneilkeys is offline   Reply With Quote
Old 12-06-2016, 02:29 AM   #3
Senior Member
 
Brand: Still Looking
State: Alabama
Posts: 333
THOR #3789
Quote:
Originally Posted by Oneilkeys View Post
https://www.batterystuff.com/kb/tool...to-a-load.html

This web site has a simple calculator for sizing batteries to a specific amp load over time. While you may have a 240 amp hour capacity, remember that you only get to use 120 amp hours before you drain your battery down to 50% - as low as you want to routinely draw down to, if you do not want to kill your batteries. For a 36 amp draw for 8 hours down to 50%, the calculator says you need 750 amp hours of batteries. For a 28 amp draw over the same 8 hours it would be about 3/4 of that.

28-36 amp draw is a lot. My small Axis draws less than 20 Amps with the A/C and everything else except the microwave.
So correct me if I am wrong. At a 36 amp draw for 8 hours I would need 750 amp per hour. So for me to get even close to this I would need 6 of these T125 batteries @ 240 amp. Not a bad calculator...
__________________
mustang94 is offline   Reply With Quote
Old 12-06-2016, 02:44 AM   #4
gmc
Senior Member
 
gmc's Avatar
 
Brand: Thor Motor Coach
Model: Hurricane 32A
State: Florida
Posts: 1,871
THOR #2829
A couple of clarifications/corrections I think...

Quote:
Originally Posted by Oneilkeys View Post
While you may have a 240 amp hour capacity, remember that you only get to use 120 amp hours before you drain your battery down to 50% - as low as you want to routinely draw down to, if you do not want to kill your batteries.
Don is using FOUR T-125 batteries... These are 6V flooded golf cart batteries rated at 240amps EACH - so assuming a serial/parallel connection - he will have 480amps of 12v available... The 50% comment is right on (though golf cart batteries are meant for deep discharge and can likely take a little more - 50% is still a safe number for long life of an approximate $600 investment) - so 240amps available...

Quote:
Originally Posted by Oneilkeys View Post
For a 36 amp draw for 8 hours down to 50%, the calculator says you need 750 amp hours of batteries. For a 28 amp draw over the same 8 hours it would be about 3/4 of that.

Using the calculator - IF you had a solid 28amp draw all night - as Oneilkeys said - you need almost 600amps (584).. (the 75% number he referred to) *BUT* I wouldn't expect the fridge to run continuously unless someone is staring inside it with the door open all night - so the question is how much does it run??
(or what is the current battery capacity - and we can probably extrapolate from there how much longer you will get...)

IF it ran half the time (still excessive in my mind) - your average load would be 14 amps - and need 292amps to make 8 hours... driving under the 50% line (would have enough for 6 hours staying over 50% - double your current performance of 3 hours.)

If it ran 25% of the time (probably more reasonable) - your average load is under 10 amps and you should make 8 hours using less than 50% of the capacity. (10 amps would need 208amps 12v to make 8 hours)

Probably not much you can do to reduce the draw of the the fridge - but if your lights aren't all LED - that can help reduce draw significantly when using lights (your 36amp number)

Quote:
Originally Posted by Oneilkeys View Post
28-36 amp draw is a lot. My small Axis draws less than 20 Amps with the A/C and everything else except the microwave.
28-36amps may be a lot if it were 110v.. but at 12v, the amps will be much higher to get the same watts (watts = volts * amps).
A 20 amp draw at 110 volts generates 2200 watts... To produce the same wattage at 12v is just over 200 amps.
Don's 28 amp draw at 12v would be under 3 amps at 110v.
__________________
Greg
Not yet retired...
Florida (Michigan transplant)
2014 Hurricane 32A
2000 Infinity (previous)
gmc is offline   Reply With Quote
Old 12-06-2016, 02:53 AM   #5
gmc
Senior Member
 
gmc's Avatar
 
Brand: Thor Motor Coach
Model: Hurricane 32A
State: Florida
Posts: 1,871
THOR #2829
An additional note from the calculator website:
"If you know how much power your application takes to run, and the time you would like to run it, we'll recommend a 12 volt battery with a safe amount of AH (Amp Hours) that will give you the runtime you need."

They state a 'safe amount' of amp hours - so they are assuming some cushion - I don't know how much of the 50% they use... Have to do more math to see.
That cushion on top of the fridge only running part of the night - I am thinking your four T125's will do it...

To confirm - what is your current batteries that make 3 hours? For a sanity check...
__________________
Greg
Not yet retired...
Florida (Michigan transplant)
2014 Hurricane 32A
2000 Infinity (previous)
gmc is offline   Reply With Quote
Old 12-06-2016, 03:12 AM   #6
Senior Member
 
Oneilkeys's Avatar
 
Brand: Still Looking
Model: Travato
State: Florida
Posts: 2,435
THOR #1765
The original question indicated that you wanted enough amp hours so that the generator did not automatically run at night. Another question is when does the automatic turn on operate? When the batteries are 50% drained or 40%? That will also determine how many amp hours you actually have to work with before the generator automatically starts.

In addition, unless you move the RV every day or plug in to shore power, you need to think about how you are going to recharge these 2-300 amp hours you are draining. Unless you run your generator for many hours, you will probably not be able to charge the batteries above 90% for the next night. Then you would only have 40% (or less) or your amp hour capacity to work with - if you draw down to 50%.
__________________
Oneilkeys is offline   Reply With Quote
Old 12-06-2016, 04:15 AM   #7
Senior Member
 
Brand: Still Looking
State: Texas
Posts: 4,857
THOR #2121
Quote:
Originally Posted by gmc View Post
....cut....

Using the calculator - IF you had a solid 28amp draw all night - as Oneilkeys said - you need almost 600amps (584).. (the 75% number he referred to) *BUT* I wouldn't expect the fridge to run continuously unless someone is staring inside it with the door open all night - so the question is how much does it run??
(or what is the current battery capacity - and we can probably extrapolate from there how much longer you will get...)

....cut.....
Excellent point. If you look at typical residential refrigerator energy consumption, most newer ones use around 2 kWh or less of energy per day on average. Divided by 24 hours that's less than 100 watts on average, and we should expect that nighttime power consumption to be lower than daily average.

If using 28 Amps (over 300 watts) to primarily run the fridge (a few LEDs are insignificant), it means one of a few things:

1) Refrigerator is an energy hog (not efficient)
2) Refrigerator isn't running most of the time at night
3) Inverter isn't very efficient at that low power rate
4) A combination of above

My sister's 5er has a large residential fridge with 4 golf cart-size batteries (don't recall brand) and it runs overnight without generator. And to me that makes sense because these Trojan batteries store 1.6 kWh of energy each (that may be at 100-hour rate so actual is a little lower). Four batteries is therefore 6.4 kWh. At 50% that's still 3.2 kWh usable energy, which is more than most modern refrigerators should use in an entire day.

Personally, I would want to break down the 28 Amps in more detail because it seems high to me also if it is suppose to be mostly the fridge.
Attached Thumbnails
Click image for larger version

Name:	image.jpeg
Views:	136
Size:	89.8 KB
ID:	3477  
__________________
Chance is offline   Reply With Quote
Old 12-06-2016, 11:22 AM   #8
Senior Member
 
Brand: Still Looking
State: Alabama
Posts: 333
THOR #3789
WOW.... so much info here. This weekend I am going to see what all I can unplug, turn off or even disconnect and check amp draw with each item and post it.
Not sure how close my 140 amp batteries are to 50% when generator starts because it is set to come on once batteries drop to 12 volts and then run for one hour.
A year now with these stock batteries from Thor and the quite time keeps getting shorter.
__________________
mustang94 is offline   Reply With Quote
Old 12-06-2016, 01:41 PM   #9
Senior Member
 
Miramar Owner's Avatar
 
Brand: Thor Motor Coach
Model: Miramar 34.4
State: Iowa
Posts: 668
THOR #4488
I assume you know you can change the settings for the automatic start on the generator. After adjusting mine I can go 7 hours on 2-6 volt batteries. I plan to add 2 more batteries but will wait until I need to replace the 2 I have so I can have 4 of the same age. In the mean time I don't use the generator auto start for overnight. I use the generator in the evening for a few hours to top off the batteries and shut it off at 10:00. At 7:00am the fridge is still below 40 degrees.

I do use the auto start but only in the daytime if I plan to be gone.

Hope this helps.
__________________
Miramar Owner is offline   Reply With Quote
Old 12-06-2016, 02:39 PM   #10
Senior Member
 
Oneilkeys's Avatar
 
Brand: Still Looking
Model: Travato
State: Florida
Posts: 2,435
THOR #1765
One thing to remember. If you routinely discharge your batteries below 40% (about 11.9v) you will significantly reduce the life if your deep cycle batteries. They are designed to be discharged down to 20% ( about 11.6v) but battery manufactures tell you not to go below 40%. If you want to prolong the life if your batteries, don't routinely discharge them below 50% (about 12.06v).
Attached Thumbnails
Click image for larger version

Name:	IMG_4053.jpg
Views:	123
Size:	197.4 KB
ID:	3478  
__________________
Oneilkeys is offline   Reply With Quote
Old 12-06-2016, 03:00 PM   #11
Senior Member
 
Brand: Still Looking
State: Alabama
Posts: 245
THOR #4160
Okay, I just installed 4x 6v Trojan T125s. http://www.thorforums.com/forums/f27...nger-5753.html
I would never discharge below 50% as it will eventually ruin them and they will no longer hold a charge for very long. Ensure to keep them topped off by ordering the Hydrolink watering system. It is expensive but any other like the Flow-Rite will void your Trojan warranty.

As for the amp hours, I have the Whirlpool residential refrigerator (side by side) that utilizes 7.2 amps per hours. For my calculations, I added an additional 2.8 amps, which covers lighting, and parasitic device draw and it makes the math easy.

10 amp hour x 16 hours a day = 160 amp hours per day.
Before I go to bed, I turn my inverter off and the refrigerator stays cold.
I can go about two days without any issues. It takes me about 4 hours of running my generator to charge my batteries back up to do it all over again. When I dry camp again, I will report back on exact amp draw per day. I hope this helps.
__________________
Techn0 is offline   Reply With Quote
Old 12-06-2016, 03:06 PM   #12
Senior Member
 
Brand: Thor Motor Coach
Model: 2013 31L
State: Florida
Posts: 1,989
THOR #908
Trojan's can go down a lot deeper than that.
Per the trojan battery user guide:
- Do not discharge your battery more than 80%. This safety factor will eliminate the chance of overdischarging and damaging your battery.
that means you should be ok going down to 100-80=20%.....
20% state of charge is 5.83 V on a 6 volt battery or 11.66V on a 12 volt battery, according to their user's guide

http://www.trojanbattery.com/pdf/Tro...UsersGuide.pdf
__________________
blw2 is offline   Reply With Quote
Old 12-06-2016, 06:10 PM   #13
Member
 
doubravsky's Avatar
 
Brand: Thor Motor Coach
Model: Four Winds 31W
State: California
Posts: 99
THOR #1414
+1 on turning the fridge off (inverter) when you go to bed. It will stay plenty cold enough... I've done it in the desert in summer and the ice cubes stay solid all night. That will cut way back on your amp draw for the night.
__________________
doubravsky is offline   Reply With Quote
Old 12-06-2016, 06:58 PM   #14
Axis/Vegas Enthusiast
 
JamieGeek's Avatar
 
Brand: Thor Motor Coach
Model: Axis 24.1
State: Michigan
Posts: 9,193
THOR #1150
Question for those of you who turn off the fridge at night: Have you ever paid attention to how long the fridge runs in the morning when you turn it back on? (Which would be an indication of how much it warmed up overnight) Or put a thermometer inside the fridge to see what the morning temp was?
__________________
2014 Thor Axis 24.1
2018 Chevy Bolt
blog - https://spareelectrons.wordpress.com/
JamieGeek is online now   Reply With Quote
Old 12-06-2016, 07:13 PM   #15
Senior Member
 
Brand: Still Looking
State: Alabama
Posts: 245
THOR #4160
Quote:
Originally Posted by JamieGeek View Post
Question for those of you who turn off the fridge at night: Have you ever paid attention to how long the fridge runs in the morning when you turn it back on? (Which would be an indication of how much it warmed up overnight) Or put a thermometer inside the fridge to see what the morning temp was?
Very valid point. I will do that test next time too. I will plug my voltage meter into my fridge to read it directly and see how it draws over time. Thanks, great idea.
__________________
Techn0 is offline   Reply With Quote
Old 12-06-2016, 07:21 PM   #16
Senior Member
 
Oneilkeys's Avatar
 
Brand: Still Looking
Model: Travato
State: Florida
Posts: 2,435
THOR #1765
Quote:
Originally Posted by blw2 View Post
Trojan's can go down a lot deeper than that.
Per the trojan battery user guide:
- Do not discharge your battery more than 80%. This safety factor will eliminate the chance of overdischarging and damaging your battery.
that means you should be ok going down to 100-80=20%.....
20% state of charge is 5.83 V on a 6 volt battery or 11.66V on a 12 volt battery, according to their user's guide

http://www.trojanbattery.com/pdf/Tro...UsersGuide.pdf

That's really interesting and significant. I read thru the User Guide and they say nothing about not routinely discharging below 40 or 50%. Everything I have read (see below for an example) says that a deep cycle battery will last up to twice as long if you do not routinely discharge it below 50%. If Trojan stands behind its ability to routinely discharge its battery down to 20%, that gives you 30% more amp hours that you can use before you have to turn on your generator. I think I would get Trojan to confirm that before I did it, but it would be a good reason to buy Trojan batteries.
Attached Thumbnails
Click image for larger version

Name:	IMG_4057.jpg
Views:	114
Size:	257.5 KB
ID:	3479  
__________________
Oneilkeys is offline   Reply With Quote
Old 12-06-2016, 07:34 PM   #17
Senior Member
 
Brand: Still Looking
State: Texas
Posts: 4,857
THOR #2121
Not to change subject too much, but this issue seems to be a short-term problem until manufacturers offer more DC refrigerators. If not for inverter inefficiency which can drop off significantly at low power, it seems that leaving the fridge running overnight would be just as efficient overall. Of course if you plan to run a generator in morning anyway, or are waiting for solar to kick-in in the morning, that's a different situation.

At Palm Beach RV Show a few weeks ago I saw a Norcold DC558 12/24 Volt DC small fridge that was rated at 42 Watts (3.2/1.6 Amps). It's too small for large motorhomes or trailers but seemed great for van-size campers/RVs.

A few companies have also announced DC residential-type RV-specific refrigerators that can run directly from batteries. And some are made to fit in same RV cabinet space while increasing fridge capacity.
__________________
Chance is offline   Reply With Quote
Old 12-06-2016, 07:36 PM   #18
Member
 
doubravsky's Avatar
 
Brand: Thor Motor Coach
Model: Four Winds 31W
State: California
Posts: 99
THOR #1414
I've never measured how long it runs in the morning, but I did put a thermometer in the fridge a few years ago for the night, and I don't remember the exact number, but I remember thinking it was less than 5 degrees different.
__________________
doubravsky is offline   Reply With Quote
Old 12-06-2016, 07:52 PM   #19
Senior Member
 
Brand: Still Looking
State: Texas
Posts: 4,857
THOR #2121
Quote:
Originally Posted by Oneilkeys View Post
That's really interesting and significant. I read thru the User Guide and they say nothing about not routinely discharging below 40 or 50%. Everything I have read (see below for an example) says that a deep cycle battery will last up to twice as long if you do not routinely discharge it below 50%. If Trojan stands behind its ability to routinely discharge its battery down to 20%, that gives you 30% more amp hours that you can use before you have to turn on your generator. I think I would get Trojan to confirm that before I did it, but it would be a good reason to buy Trojan batteries.
In my opinion battery cycle life is not a black-and-white issue. You are always going to get more cycles if you don't discharge them as much -- that's a given. Manufacturers haver charts which estimate how many cycles we can expect based on repeated discharges to different levels.

If prolonging battery life (in cycles) was only measure, then we should install a lot more batteries and discharge each less amount. But initial cost would be much higher, which begs the question whether it's better to have less battery capacity and replace them more often?

There has to be an optimum balance depending on total cost, functionality, convenience, etc. The 50% number (or even range of 40 to 60%) seems to be a good all around number many feel comfortable with and recommend. I can't believe that there is just one "right" answer for everyone considering how many variables there are.
__________________
Chance is offline   Reply With Quote
Old 12-06-2016, 09:01 PM   #20
Senior Member
 
Oneilkeys's Avatar
 
Brand: Still Looking
Model: Travato
State: Florida
Posts: 2,435
THOR #1765
Quote:
Originally Posted by blw2 View Post
Trojan's can go down a lot deeper than that.
Per the trojan battery user guide:
- Do not discharge your battery more than 80%. This safety factor will eliminate the chance of overdischarging and damaging your battery.
that means you should be ok going down to 100-80=20%.....
20% state of charge is 5.83 V on a 6 volt battery or 11.66V on a 12 volt battery, according to their user's guide

http://www.trojanbattery.com/pdf/Tro...UsersGuide.pdf
Quote:
Originally Posted by Chance View Post
In my opinion battery cycle life is not a black-and-white issue. You are always going to get more cycles if you don't discharge them as much -- that's a given. Manufacturers haver charts which estimate how many cycles we can expect based on repeated discharges to different levels.

If prolonging battery life (in cycles) was only measure, then we should install a lot more batteries and discharge each less amount. But initial cost would be much higher, which begs the question whether it's better to have less battery capacity and replace them more often?

There has to be an optimum balance depending on total cost, functionality, convenience, etc. The 50% number (or even range of 40 to 60%) seems to be a good all around number many feel comfortable with and recommend. I can't believe that there is just one "right" answer for everyone considering how many variables there are.
That is all true. However, if Trojan certifies that you can discharge their batteries routinely down to 20% without harming or shortening the life of their batteries, it would make a difference to me. I try very hard to not take my batteries below 12.1v because I do not want to shorten their lives. When I am boondocking, if I can routinely take them down to 11.6V knowing that I am not shortening their life span, it would you make my life easier and it would be a good reason for me to buy Trojans.
__________________

__________________
Oneilkeys is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


» Featured Campgrounds

Reviews provided by

Disclaimer:

This website is not affiliated with or endorsed by Thor Industries or any of its affiliates. This is an independent, unofficial site.




All times are GMT. The time now is 10:38 PM.


Powered by vBulletin® Version 3.8.8
Copyright ©2000 - 2021, vBulletin Solutions, Inc.
Content Relevant URLs by vBSEO 3.6.0 PL2
×