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Old 10-19-2022, 01:34 PM   #1
MrGallegos
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Default Operating fridge on propane and battery usage

I am planning on letting a friend borrow my TM while he works on building a cabin. However, there is no electricity on the property, and I do not have any solar or generator, so the only power will be from the TM 100 amp battery. The only thing he really needs, besides a roof over his head, is the refrigerator, so it will have to run on propane. Interior light use will be very minimal, and no water will be used from the TM, he will have water jugs and toilet will be an outhouse.

My question is approximately how long the fridge could run on propane? How much battery will be used, if any, to keep the fridge running? I am trying to get an estimated time that can be realistically be used before the battery gets too low to recharge.

I do [not] want to tell him 5 days only for the battery to die in 3, and I want to make sure the battery has enough power to work the brakes when I tow it back home.
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Old 10-19-2022, 02:11 PM   #2
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If there are no experienced-based responses, I will try to take a reading of actual power consumption soon. Remember that there are certain parasitic (always on) loads in a TM or any other RV.

In the meantime, I would suggest:
No use of lights. Bring a propane lantern or battery-powered lights.
Get a small self-regulating solar panel. I have a 5-watt panel on my boat battery (no drain) that keeps it up nicely. You can get a 10-watt panel for less that $20, no controller necessary.
Pull the fuses on other 12-volt circuits.

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Old 10-19-2022, 05:20 PM   #3
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Originally Posted by MrGallegos View Post
I am planning on letting a friend borrow my TM while he works on building a cabin. However, there is no electricity on the property, and I do not have any solar or generator, so the only power will be from the TM 100 amp battery. The only thing he really needs, besides a roof over his head, is the refrigerator, so it will have to run on propane. Interior light use will be very minimal, and no water will be used from the TM, he will have water jugs and toilet will be an outhouse.

My question is approximately how long the fridge could run on propane? How much battery will be used, if any, to keep the fridge running? I am trying to get an estimated time that can be realistically be used before the battery gets too low to recharge.

I do want to tell him 5 days only for the battery to die in 3, and I want to make sure the battery has enough power to work the brakes when I tow it back home.
If your 100AH (amp hour) battery is less than 1-year-old, filled to the fill line with distilled water and charged all the way up. You MAY get 50-60(useable)AH out of that battery before you damage it. The rest is math. an 1156 light bulb draws 1.7A per hour. You can run 1, 1156 bulb for approx 35 hours (60AH / 1.7A) with the above, new battery. Anything else is just finding out the amp draw of the item, multiply that by the number of hours used and subtract that from the 50-60AH. Take the water pump for instance. It draws 8A (that's 8A per hour of usage). If the water pump is run 10 seconds at a time and runs 5 times a day, that's 50 seconds. There are 3600 seconds in an hour so you are talking 2.25amps per day.

When I say fully charged, I mean charged to a full 13.8V with a battery charger. Your tow vehicle will never fill the battery on the TM through the TM wiring. It's a lot of math that I won't go into..... just trust me..... it won't happen. You will get about a 75% charge, meaning that your 100AH battery only has about 75AH of charge and you can only use it down to 40-50AH which means you only have about 30AH of usable battery life.

If the only source for charging that battery is with the tow vehicle. Be sure to bring a set of jumper cables and charge the TM battery directly from the tow vehicle battery, with the engine running, for at least an hour every-other day. Not worth skimping on.

Even at that, I would HIGHLY recommend that you have a spare (brand new) battery as a back-up. If you can get your hands on a used solar panel (minimum 100W), 20' of MC4 solar wire and a cheap ($15) solar controller, you'd be set with sparing use.

Check Craigslist for used solar panels. Anything above 100W will work, 250-350 would be great, in case of cloudy days. Just se it on the ground at a 45% angle and pointed south. Problem solved.

As for the fridge on propane, it'll run for years if you have enough propane. If you are talking about the 2-tanks on the tongue, cool weather, you should be good for 2-4 weeks. That incudes using the stove top, once a day.
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Old 10-19-2022, 05:34 PM   #4
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Thank you Wavery and Bill for all your help.
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Old 10-19-2022, 05:40 PM   #5
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Thank you Wavery and Bill for all your help.
I added quite a lot more into that post. You may want to look at it again.
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Old 10-19-2022, 06:23 PM   #6
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If the fridge in your 2003 is a Norcold 300.3 or a Dometic 3383 then it uses ZERO electricity to run on propane. None, nada, zip. If you’ve swapped to something else I can’t comment.
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Old 10-20-2022, 07:30 AM   #7
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If the fridge in your 2003 is a Norcold 300.3 or a Dometic 3383 then it uses ZERO electricity to run on propane. None, nada, zip. If you’ve swapped to something else I can’t comment.
Thanks for the information!!!
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Old 10-21-2022, 12:50 PM   #8
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I am planning on letting a friend borrow my TM while he works on building a cabin. However, there is no electricity on the property, and I do not have any solar or generator, so the only power will be from the TM 100 amp battery... I am trying to get an estimated time that can be realistically be used before the battery gets too low to recharge... I do [not] want to tell him 5 days only for the battery to die in 3
Mr. Gallegos -

Short answer? I made the measurement, and when all appliances are turned off, my TM pulls about 0.2 amps from the battery. This means that if you have a 100 A-h battery, it will take 250 hours to discharge it halfway (50 A-h). In other words, your battery is good for a little more than 10 days. In the scenario you described, you are good to go, with plenty of margin.

More? You described a 5-days-on, 2-days-off work schedule, with (presumably) a battery recharge during the 2-days off. But suppose the work schedule gets tight, and he can't leave the work site. Now you need to replace the charge as you use it, so he never runs out of power. Both Wavery and I mentioned solar panels. How big a panel would you need? The answer goes this way. A current of 0.2 amps at 14 volts is 2.8 watts. The TM will draw those 2.8 watts for 24 hours a day, so in 24 hours it will use 2.8 watts x 24 hours = 67 watt-hours. A solar panel will produce useful power for only about 6 hours per day. Replacing 67 watt-hours in 6 hours means that during those 6 hours, the panel must produce about 11 watts. You can buy a brand-new 15-watt solar panel - more than you need - for less than $25 from Amazon, including any needed charge controller. Just set it on the ground, aim it south, tilt it at about 45 degrees, and you are good to go forever.

Of course, if you want to give your friend a more cushy experience, a couple hundred watts of solar power will go a long way toward that.

By the way, all this talk of amps and amp-hours and watt-hours can be confusing. There is no such thing as amps per hour, so it can be even more confusing to try to follow a discussion based on that term.

Bill
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Old 10-25-2022, 01:39 PM   #9
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Thanks again Bill and Wavery, all this information is helpful.
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