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Old 11-02-2008, 09:25 PM   #1
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Consumer Electronics Labels 101

OK, I'll admit - I never worried about how much "juice" my clock, TV, computer, etc draws every hour. I've always lived in a house and just plug it all into the outlets, and pay the electric bill.

But in an RV, possibly boondocking for a long weekend, I know that EVERY amp matters.

My most recent project includes partially "converting" my minivan into a weekend camper, just to be sure this whole RV thing is for me (and before I drop a ton of money on a SMB). My fiancee and I both pretty much "live" on the computer, so a laptop coming with us on our trips will be a given (for email, posting, watching movies, etc). As will a few lights, a fan, and who knows what else....

So, I'm figuring I could hopefully invest in a "smaller" AGM battery, since I do NOT want to drain the van's starter battery at all. This battery will be inside the van. I need to figure out the total drain on the house battery, and figure out what size of battery I need to install. Right? SO, in trying to figure out all this stuff, I'm looking at the labels on all the electronics I'll be bringing along and installing.

But, I'm not understanding the "basics" I don't think.

For example (yes, these are only examples!), the label on a color HDTV indicates stuff like "16VDC" and "2.5A" and "40w"... so that means that at 16 volts DC (not 12v??), it draws 2.5 amps and uses 40watts? For how long? Are these numbers per hour?

Then I have an electric clock, from about 1980. All it says is "120VAC" and "7w." Again, is this hourly?

Then there's a little 7" portable DVD player. All that says is "DC 9V" and "13.5W" That comes w/ rechargeable batteries, and also an AC plug (w/ a big transformer on it). That means it's actually converting 120VAC into the 9V source, right? How do I convert the 9v over to battery (12v)??

And never mind that I'm not even sure what sort of lights I'll be using, so I have no idea how many watts they draw.

I know that "watts=amps x volts," but how does this all relate to sizing one's battery need (figuring out how big of a battery is needed), and battery drain? Aren't batteries measured in amp-hours (Ah)??

IIRC, you add up all the things drawing power in the RV, then make sure your battery has that capacity, right? Can you always figure that out based on the label? Or is some of this assumed or "golden rule" I haven't found yet? Or am I missing something?

I'm so lost.

Thanks for any help! I want to figure this out now before buying the wrong battery, and only having an hour's worth of battery power before it dies.

(and then, there's the whole "How do I recharge this battery?" question)....
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Old 11-02-2008, 11:26 PM   #2
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Dave, here's a simple-minded answer from somebody who is still learning. First off, you need to figure out the wattage requirements of anything and everything you'll be using AT 12 VOLTS. So if it's a 12-volt T.V. or a fan or a light unit, then just read the wattage from the label or the spec sheet. If it's, say, a 110-volt T.V. that draws, say, 40 watts, but you'll have to run it from an inverter connected to your battery, you've got to figure in that the inverter will draw more than 40 watts in order to convert 12 to 110 and run the T.V. For your computer, wattage can vary due to screen brightness, how much the hard drive is used, whether you run the DVD drive, etc. Probably your manufacturer will have some specs on wattage range when powering the computer with a 12-volt "car cord." Or you can figure the wattage required to recharge your computer with a 12-volt car cord.

So, after much fiddling, you've got general wattage figures. Remember you're dealing with 12 volts. And you're right that volts times amps equals watts. So take the highest wattage need you'll normally have all at once, like fan and T.V. running at once, and divide by 12 to get how many amps of current you'll be pulling out of the battery when running that load. E.g., if you need 72 watts to run your fan and computer together, your 12-volt battery will have to put out 6 amps of current, at 12 volts, to handle the load.

Okay. So then you decide how much $$ to spend for how big a battery. Say you get a 60 ampere hour (AH) battery. The AH rating means that, theoretically, that battery, fully charged, can crank out one amp of current at 12 volts for 60 hours before being fully discharged. And again, in theory, it could put out 60 amps at 12 volts for one hour. In practice, the battery's voltage drops somewhat as it discharges (so more amps are needed to maintain the same wattage). Also such batteries are able to do better when discharging slowly (like putting out your 6 amps for several hours) than they do with rapid discharge (trying to run 10 T.V.s and 10 fans for one hour).

Finally, most batteries are NOT meant to be discharged all the way. AGM batteries have many advantages, but in general I'm told they do not like to be discharged below 50 per cent and do not like to be overcharged. Some folks tell me that gel batteries are better for deep discharge and can "live" for more cycles. I don't know the truth of this.

How to charge them? My son-in-law has a popup camper that uses one 12-volt deep cycle marine wet cell battery. He uses a regular, plug-in charger at home and can go about three days using the battery for the lights in his rig and to run the propane furnace. Our SMB uses more complicated electronics to charge the seperate ("house") battery while we're driving. If we're camping without shore power, and the battery gets low, we fire up the generator installed as original equipment. We know folks who tent or van camp and take one of the little Honda gas generators with them (small and pretty quiet) to run their electronics and charge batteries. If you camp in state or national parks you'll encounter quiet hours each night when you can't run the generator, however, and who on earth wants to go camping and then listen to motor noise anyway?

I've "talked" your ears off. Others will have better informed, and likely different, answers. Welcome to the wonderful world of trying to figure out all this stuff. Hope you love camping out of your van - we love our SMB!
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Old 11-03-2008, 08:10 AM   #3
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Wow! Thanks Psomaki for the informative post! This is a lot of "stuff" to digest and figure out. BUT, I will do my best to come up w/ some numbers from your instructions.

Thanks again.
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Old 11-03-2008, 10:16 AM   #4
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Also you can read this Power Inverter Size

Consider renting a small RV as well, it won't be an SMB but you'll get a better idea of having a sink, small fridge etc. If you're concerned it's a small investment to make to be comfortable with your SMB purchase.
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Old 11-03-2008, 11:19 AM   #5
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We purchased the 2,000 watt Honda generator for our 3 week trip last May. It was to recharge the battery or to use the toaster oven if we were out in the boondocks too long. It worked great and was pretty quiet although we only used it a half dozen times. Since we seldom stay in campgrounds or around other people, the irritating noise of a generator is only a factor for us and we don't have to worry about getting the neighbors upset. For three day outings here in the Sierras we don't even bring it.
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Old 11-03-2008, 11:24 AM   #6
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Jage, thanks for the link to the excellent thread on your own "search. How has it all turned out for you? What electrical stuff do you normally use?

Dave, great idea from Jage to rent before you buy. Even in our kinda boondocks area there's one RV rental place - given current reality, they're hurting and can be talked into pretty good rates during the off season. Jage's input has reminded me that maybe our "altered life style" when camping may be of interest. Our used rig was set up 15 years ago by a guy who did not want on-board propane, so it's all electric and carries a big (2.8 kw, I think) genset, an Onan unit mounted under the van. So we can run a microwave or toaster oven or two-burner electric cooktop, and we do that sometimes. In the boonies that means running the noisy generator for, say, a half hour to cook breakfast or dinner and heat the water for dishes, while also topping up the house batteries. But we find we don't do this too often. We bought a good, two-burner propane stove and a small propane bottle - that little guy cooks, heats water, can toast (see Jage's thread), and even heats things up when used inside (with a window cracked, of course). Try all this out and you'll find what works for you.
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Old 11-03-2008, 11:58 PM   #7
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Here are a couple of older links but they have good info.


http://www.ccis.com/home/mnemeth/12volt/12volt.htm
http://www.ccis.com/home/mnemeth/12volt/12volta.htm
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Old 11-04-2008, 08:04 AM   #8
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Quote:
Originally Posted by jage
Also you can read this Power Inverter Size

Consider renting a small RV as well, it won't be an SMB but you'll get a better idea of having a sink, small fridge etc. If you're concerned it's a small investment to make to be comfortable with your SMB purchase.
Good thread, thanks.... It's not that I'm concerned about having a sink, fridge, batteries, etc to take care of, I just want to make sure I actually LIKE camping and RVing before spending the money on a SMB. That's why I want to convert my minivan to a little weekend camper. Also, this project will help me understand some of the RV systems better (hopefully).

Quote:
Originally Posted by oclv
We purchased the 2,000 watt Honda generator for our 3 week trip last May....
Thanks for your input. I'd rather not need to get a generator if I don't need to. Feeding it, the noise, lugging it around (space)... I'd prefer to eventually go to solar instead. Actually, I plan on getting 2 solar panels on my SMB.

Quote:
Originally Posted by Psomaki
... Our used rig was set up 15 years ago by a guy who did not want on-board propane, so it's all electric and carries a big (2.8 kw, I think) genset, an Onan unit mounted under the van.... We bought a good, two-burner propane stove and a small propane bottle - that little guy cooks, heats water, can toast, and even heats things up when used inside (with a window cracked, of course). Try all this out and you'll find what works for you.
Thanks for your post. I didn't mean to beat a dead horse w/ my thread. I'm sorry for that.... Again, I'd rather not get a generator. The little propane stove sounds like a versatile must-have. How long does the small propane bottle last for cooking?

Quote:
Originally Posted by daveb
Here are a couple of older links but they have good info.
Oh, of course! The 12v side of life articles! Why didn't I think of that! Thanks.
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Old 11-04-2008, 04:46 PM   #9
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Whoa, Dave (pun intended), I used that emoticon to show I was beating a dead horse, not that you were. I realized I was sounding off on stuff that both others and I myself have covered elsewhere in the Forum and was running on again about our gas stove. Now, about that stove! We got it at REI in Seattle. It's the Century Deluxe Stainless model, available online at http://www.rei.com/product/737001 for $80. It comes with a hose to connect to one of the little Coleman disposable propane bottles. We bought an adapter for that hose at our local outdoor store and got a 5-lb. propane cylinder at our local Home Depot. The 5-pounder is the smallest "real" propane tank. It's a foot tall but has the same outlet valve as the big guys we all use on our home grills. The tank and hoses store neatly under our dinette seat and the little stove lives in the bottom of a cabinet when not in use. It's got good wind shields, heats water or cooks really well, and has yet to use up $3.00 worth of propane after being used several days total. We carry one of the green Coleman bottles as a backup. This rig would not take up much space in your van. When (not "if," you'll note) you get your SMB, even if you opt for propane, this stove is great for setting up outside away from the SMB. There! Now that horse is really deceased!
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Old 11-05-2008, 10:28 AM   #10
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Quote:
Originally Posted by Psomaki
Whoa, Dave (pun intended), I used that emoticon to show I was beating a dead horse, not that you were.

Now, about that stove! ... Century Deluxe $80.... It comes with a hose to connect to one of the little Coleman disposable propane bottles. We bought an adapter for that hose at our local outdoor store and got a 5-lb. propane cylinder at our local Home Depot. The 5-pounder is the smallest "real" propane tank.... heats water or cooks really well, and has yet to use up $3.00 worth of propane after being used several days total. We carry one of the green Coleman bottles as a backup. When (not "if," you'll note) you get your SMB, even if you opt for propane, this stove is great for setting up outside away from the SMB.
Oh, OK. I thought the horse gif was for me...

That sounds like an awesome setup you use there! I will definitely look into these little camp stove things, and the smaller propane tanks. Thanks for your input. It sounds like it would work for me, too! I also like the stove/grill combo from the same manufacturer.... Please let me know the details on that adapter. Is it something like this?

Question: can you (or should you) use these types of stoves inside your RV (w/ ventilation), or must they only be used outside?
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