This topic contains 26 replies, has 6 voices, and was last updated by 
Anonymous 1 year, 1 month ago.
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AnonymousI thought these may be of some use to others who are planning on boondocking. I isolated each circuit, and measured the draw with the ammeter on my multimeter. Many of the draws I measured were quite a bit lower than some of the numbers I read on the web, so it’s best to take actual measurements rather than depending on others information, even the manufacturer’s.
Of particular interest is the furnace duty cycles. I read many stories of the furnace being blamed for killing the batteries, but the math says it isn’t so. If you are still using the 921 bulbs, your lights are the most probable cause!
Water Pump 5.0 amp
Furnace 6.0 amp
921 bulb 1.3 amp
Stereo on 0.4 amp
Exhaust fan stove 1.4 amp
Exhaust fan bath 1.25 amp
Signal booster 0.1 amp
Monitor panel 0.25 amp
Water heater burn 0.6 amp
Water heater @ temp 0.02 amp
Parasitic draw 0.35 amp (radio, CO detector)
Refrigerator At rest auto 0.34 amp
At rest gas 0.34 amp
Auto cooling 0.58 amps
Gas cooling 0.71 amps
Furnace run time @ 10 C (50 F) 10.66 minutes/hour
Furnace run time @ 5 C (40 F) 17.28 minutes/hour
Furnace run time @-5 C (22 F) 32 minutes/hour
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Sue’s computer AC draw Charged = .16 A = 19.2 W Charging = .34 A = 40 W
My computer AC draw Charged = .10 A = 12 W Charging = .29 A = 34.8 WThanks, Roger
Thanks Roger for the numbers. I find our furnace really can suck down the batteries on a cold night. I think part of the reason is the batteries lose capacity the colder it gets. A battery at 32F has less capacity than at 72F.
RVHH Chief Cook and Bottle Washer - LoveYourRV.com
Anonymous“Thanks Roger for the numbers. I find our furnace really can suck down the batteries on a cold night. I think part of the reason is the batteries lose capacity the colder it gets. A battery at 32F has less capacity than at 72F.”
True, but then act of discharging or charging creates heat, plus yours are in a battery box, inside a compartment, so the temperature variation shouldn’t be that great.
Using my unit as an example, at 22F the furnace runs 32 minutes per hour or.533 hr. This equals about 3.2 amp/hr per hour. This is only slightly more than running one double light fixture with 921 bulbs for a hour, which equals 2.6 amp/hr per hour.
I suspect from my own experiments with the inverter that there are other, larger draws going on constantly. Computer transformers, chargers for cell phones, and other 120 vac loads, combined with the efficiency/conversion level of the inverter can have a significant impact. Our first try was 12 hours on 12 VDC only, we did everything the way we normally do, and consumed 30.8 A/Hr overnight. After the inverter install, we did the same thing, the only difference was we left the inverter on overnight with the computers plugged in, and used inverter power to make coffee in the morning with a 600 watt unit, and we turned it off once the coffee was made. We consumed 60.3 A/Hr, nearly double of our previous test! Just as well I had put the new batteries in!
I intend to test this further, the better I understand what and how my system is working, the better I’ll be able to manage our power consumption.I guess the problem we were facing on occasional cold nights in the desert when it is still winter, sun goes down at 5pm and temps get down to freezing pretty fast in the dry air if it is a cold snap.
The means we have a good 14 hours or so to have to run the furnace before the sun comes back. Even at 3-4 amp/hours it adds up when you are also having to run lights in the evening. I have about 110 usable AH from the two Trojans before they hit 50% discharge, in the cold that is likely down to 80-90 Ah. My front storage is open to the air because of the propane openings and open space to the front jacks, so basically the storage area is at outside air temps.
Adding to it is my wife likes it to be around 70 degrees in the rig, even overnight. Furnace ran a lot!
Then on top of that my generators after a day or so are not able to bring the Trojans back to a full charge using the lame converter in the rig in just a few hours of run time. So my batteries are likely only able to have about 50-60 AH for a night, starts to get pretty tight. By morning the batteries are run down.
This is where the Big Buddy heater and LED lighting really helps out, in those dark, cold waking hours before hitting the sack we run that. Saves a lot of juice.
I do keep a fully charged 12 volt battery in reserve. Comes in handy some mornings or if we want to spit early, I just switch over to it and we have some good power to pull up the jacks and pull in the slide.
RVHH Chief Cook and Bottle Washer - LoveYourRV.com
AnonymousI’m still pretty green at this, still experimenting and learning. I have changed all my lights to LED.
I’ve ordered my solar kit, chose the 250 watt model. We’re going to need it very soon, the property we bought has no services, and I don’t intend to install any unless we absolutely can’t get by without them. I do have an older 2400 watt generator with less than 10 hours run time on it, I’ll finally get some use out of it.
I’ve installed Interstate GC-2 batteries, 232 AH, had to get the boxes from Amazon, couldn’t find any locally.
I’m the one that is like Ann, I run cold and will turn the furnace on before Sue needs it.
I guess after a lifetime of having as much power as you want, new habits have to be learned in order to stay comfortable. Definitely a work in progress!I’ll be following your progress and findings with the solar install, taking notes.
RVHH Chief Cook and Bottle Washer - LoveYourRV.comBob and I are grateful for you sharing with us! This will help when we are in fulltime living!-Nancy :clap:
AnonymousSolar kit showed up yesterday, we’ll be heading out to the trailer tomorrow to start the install. I’ll probably get the charge controller and wiring roughed in, but don’t expect to get the panel on as it’s extremely windy, and our site is very open.
Also have to get our shed on skids for the move to our new spot.
Pictures to follow.Lots going on ! Have Fun!
AnonymousInstall Part 1
As I expected, wind was a factor. Had to weigh everything down on the roof or lose it. The construction of the trailer provided other challenges, the curved part on the front of the roof has nothing behind it, as well as the whole front of the trailer. For the curve, hollow wall fasteners were used to anchor the conduit, sealed with no-sag Dicor, extremely messy stuff. For the flat front part, there are three thickness of metal where the siding sections join, I was able to use screws there. Doesn’t look like much, but it took nearly six hours to do!It DOES look like much! There’s always something more going on than what you see…
Following your progress, Roger. Thanks for sharing!!
How did you arrive at the size solar kit you got? Did I miss that?
(I’m trying desperately to understand the math of all this.)
1996 Honorbuilt Eldorado C320 "Lurch" | Chewbacca is my co-pilot
AnonymousMy personal approach to sizing a system was to do a power audit first, and see how much was going where. Example, my water pump draws 5 amps, but if you only use it for 10 minutes a day, the amount of draw isn’t significant.
Two basic maths you need to understand.
1. Ohms law, Amps times volts = watts. This becomes more important if you plan on running an inverter as you could ruin your batteries by using to large a unit at capacity, the high rate of discharge can severely damage batteries. Example, your vacuum cleaner draws 500 watts at 120 volts, working Ohm’s law we find 500/120=6 amps @ 120 volts, to get this amount of power from your inverter you will be drawing approximately 60 amps from your battery. 12 volts x 60 amps = 500 watts. There’s a little more to it than that, inverter conversion efficiency,and so on, but this gives the basic idea.2. What is an amp hour? This means 1 amp draw for 1 hour. Most deep cycle batteries are rated in amp hours, the battery the dealer installed was rated 60 amp hours, and the batteries I have installed now are 232 amp hours. You could say I’ve installed a bigger electric fuel tank. Repeatedly draining the battery below 50% charge will greatly shorten the life of the battery, so even with a 232 amp hour battery, I only have 161 amp hours available for use.
However much you remove from the battery has to be put back, plus a little bit more, as a battery is a chemical device, and isn’t 100% efficient. Batteries take a large amp charge at the beginning of a charge cycle which rapidly tapers off as the battery starts to come back to full charge. Kind of like a car that you have to dribble fuel into or the nozzle kicks out, we’ve all had one like that!
Solar systems are rated in watts, the one I’m installing is a 250 watt unit. This means under absolutely perfect conditions, it will produce about 20 amps of charging power. The highest rate of charge I saw on my new batteries was 33 amps, which rapidly tapered off over time. This doesn’t sound like much, but as soon as the solar panel voltage is higher than the battery voltage, it starts to charge. Output will peak around noon, this is the time to use any heavy power demands while the charging capacity is there to put the power back. As most of the batteries charge cycle is at low amperage (less than 10 amps), this system should be adequate to my needs.
Needless to say, there are a lot more nuances than I’ve mentioned here.
AnonymousThe pictures didn’t come with the post.
http://rvhappyhour.com/members/rogerfell/media/1290/
See if this works.
AnonymousInstall Part 2
Monday morning, just gorgeous out, extremely quiet with most of the place empty.Got going by 6:30, installed charge controller and monitor, new battery boxes which just barely fit the tray, re-routed cables, shortened some of the factory wiring, new wire ends on factory grounds. The area under the hitch no longer has wiring and hose hanging low under it, that had been bugging me for a long time!
Just before noon, the skies opened up, thunder, lightning and rain. Waited for breaks in the rain to finish up what I could. Sorry, no outside pictures, next weekend.
By the time we left, the rain gauge registered 4/10″. Had to pull another camper out of his site onto the road, truck plastered in mud, really glad I got the locking differential, as it was, I was spinning on the incline to get out of the campground. It’s OK, we’re going to a better place!
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