Amps

[oldnjung]

If an appliance draws 3. Amps AC, will it draw 30 Amps from my battery bank DC?&nbsp; If so, wouldn't a 900 watt microwave (120 volts) draw about 75 Amps DC from the batteries? Wouldn't use the thing for an hour straight, but theoretically? Also, how large (watts) solar panel would be advised to recharge a battery bank of two 12 volt(68 amp hrs. each) batteries? I was thinking about 45 watts on a bright, sunny day in about (hopefully) 2-3 hours.<br>Thanks to one and All for the great info.!<br>

 

[Hammer]

I admit, others on here will have a clearer nderstanding, but the rule of thumb I'm using is basically this = if it draws 3 amps AC @120V then it'll draw 30 amps DC @ 12V (through an inverter).<div><br></div><div>As for Solar, I haven't the foggiest. &nbsp;Would love to know the answer though!</div><div><br></div><div>Hammer</div>

 

[blars]

AC amps have the complication of power factor, which means that multiplying Volts times Amps may give you something higher than the Watts actually used.&nbsp; Also, ratings of AC appliences tend to be absolute maximum rather than average.<br><br>Your 900 watt microwave will use 900 watts plus 10-20% inverter loss of DC.&nbsp; So it might require 90 amps of 12V DC.<br><br>Solar panels are optomisticly rated, and you need to add another 20% or so for loss in a good mppt controler, wiring, and even more for battery inefficiency.<br><br>A rough ballpark is you would need 400 watts of solar panels to recharge your batteries from 1/2 hour of microwave use in 2 hours.<br><br>You'll also need a larger battery bank.&nbsp; Amp-hours of batteries are rated at a 20-hour discharge rate, and you will get less at a faster rate.&nbsp; Your 136 AH battery bank is rated at a 6.8 A load.&nbsp; AGM batteries are better for heavy loads and fast charging.&nbsp; For your fast discharge fast charge senario, I would recomend 200 AH of AGM or 600 AH of lead-acid at a minimum.<br><br>

 

[oldnjung]

Thanks blars and hammer!&nbsp; Now I have to decide if it is worth the expense for solar. It might be better overall to recharge batteries (and I think they would be at least $600. or $700.; AGM 6volt&nbsp;OR 12volt!) with a Honda or Yamaha portable generator.&nbsp; Or, give up the idea of a micro-wave&nbsp;and using my existing Dell desk top. The two biggest draws next to an electric fridge.<br>jb&nbsp;<br>

 

[akrvbob]

Your 45 watt solar panels are making about 3 amps per hour so maybe 24 amps total in the winter and 30 in the summer. A 100 watt panel would recharge your two 68 ah batteries in the summer.&nbsp; A good mppt controller would easily give you another 25% more amps per day into the battery.<br><br>You would rarely use your microwave for more than 5 minues at a time. If your batteries are connected to the alternator, and you started your engine before you began the microwave, it wouldn't draw too much off your battery bank.&nbsp; Bob<br><br>

 

[sl1966]

Hi JB,<div><br></div><div>From everything I've read my understanding is that most people (who can afford it) usually go for a combo of solar panels and portable generator. They live primarily off solar power and use the generator for those rare instances when they need more juice. You know, firing up the blender to make margaritas or possibly watch a game via sat tv. I'm using the time on my current contract to save up and get both myself.</div><div><br></div><div>I'm not sure how big your rig is, but these panels might be what you're looking for ..&nbsp;<a href="http://www.amsolar.com/rv100.html" target="_blank">http://www.amsolar.com/rv100.html</a>. They came highly recommended over the Kyocera's from a full timer.&nbsp;&nbsp;</div>

 

[oldnjung]

Thanks sl1966. I hadn't seen the amsolar.com site, but that 100 watt panel looks like a pretty good deal. The technology for solar and batteries is really improving fast. I plan on being where it is sunny part of every day, except when I visit Oregon. I have a 1996 Ford Econoline 150 Conversion high top. It is 5'7" inside and I am 5'9". The top is concave (rounded). Bob said he would take a look and perhaps install my roof vent(s). Hope to see him over by Bishop, CA, but for sure up by Shaver Lake, so if you read this Bob, I will be happy to take advice re. the solar panels. Some people just build (or buy) stands and set them out on the ground.&nbsp; Thanks again for the suggestions one and all!<br>jb<br>

 

[akrvbob]

So you have a figerglass high-top? I've never worked with fiberglass and i would be afraid to learn on someone elses rig. The same thing with installing solar on a fiberglass roof, I just don't know how to work with it.Some people use quick connects and put the panels outside the rig. The problem is finding room for them when you are traveling. Here at the RTR we had several rigs without room on their roof for panels, si we set them up with flexible solar panels with a quick disconnect. When they aren't charging with them, they just roll them up and store them under the bed. That also has the advantage of letting you park the van in the shade and run the panel out to the sun. Bob <br>

 

[oldnjung]

Thanks Bob, for the info onthe solar panels (some fold up also) and for saying you don't have experience with fiberglass. But, I have seen pics of some of your woodworking work, and from all you know about other things I am sure you could do it. However, like I said earlier most of what I know comes from trial and&nbsp;error (a LOT of error), so I will&nbsp;probably try myself.&nbsp;Auto body guys will know how to "fix" what I mess up. Not only is the roof fiberglass, it is also a bit concave on top. The edges of the vent frames will stick up a bit.&nbsp;Maybe an eigth of an inch. The&nbsp;non-fan vent&nbsp;has some flexibility, so the screws, super glue, bondo or fiberglass patch might keep it down solidly. Maybe skinny bolts through the roof which I think is pretty thin. The liner is not more than 1/2 inch.&nbsp; The fan vent (Fantastic Vent) is pretty rigid. Both plastic.&nbsp;<br>I will check with an RV place or&nbsp;two to see what they would charge for install. &nbsp;<br>

 

[polecat77]

Did you know that a desktop reduces to 12 DC? You could figure out how to run a desktop off 12v cig lighter plug very easy.

 

[blars]

There is a super-strong double-sided tape that some places recomend for attaching solar panels to fiberglass RV roofs.&nbsp; Seems to have been used a couple of years with no problems reported.<br>

 

[1oleman]

OK, I'm dumb: how can I convert my PC to work on 12VDC?<br>

 

[oldnjung]

I just checked (Googled) double sided, fiberglass tape and there are several options. Not expensive, high temp capable and can even order from Amazon.com. Must be stores that sell it. Thanks! I am constantly amazed by the knowledge,&nbsp;experience and willingness to help on this site!<br>jb<br>

 

[Vern M]

You can see how I solved the solar microwave needs at the Solar Stealth site to the left. But, as I say, I rarely use the microwave for more than 90-seconds to a couple of minutes to cook what I want. I can scramble eggs or make an omlette in 90-seconds. Heating water for tea utilizes an immersable heater in the cup and takes just a few minutes too. And my Group 27 battery hasn't let me down yet.<br><br>As for putting solar panels on the ground or elsewhere that is non-permanently connected to the van, I'd worry a bunch about someone coming along and taking them. I've heard too many stories of such of late.<br>

 

[gadgetMe]

I&nbsp; become concerned about using tape in wet applications,<br>another option may be to use molly bolts<br><img src="data:image/jpg;base64,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"><br>I have used them on a rubber roof with a light plywood under-layment.&nbsp; purchased at Home depot or any hardware store<br><br>or use nutserts<br><img src="http://www.nutsandbolts.com/bmz_cache/c/cd93ebea70229b764e39d35f3e878e68.image.100x69.JPG"><br><a target="_blank" href="http://www.nutsandbolts.com/14-20-u...nutserts-inserts-qty-25-p-586.html#googlebase">Link to web site</a><br>After installation I use sealer to make sure there are no water leaks<br>Putz

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[blars]

The type of tape used is <a target="_blank" href="http://solutions.3m.com/wps/portal/3M/en_US/3M-Industrial/Adhesives/Product/Bonding-Tapes/VHB-Tape/">3M VHB tape</a>.&nbsp; It also sticks to a varity of other surfaces, and would probably be fine for metal roofs.&nbsp; Don't use it on a rubber RV roof, not because it won't stick, but because the rubber will tear.<br>

 

[blars]

Desktop PCs use a variety of voltages, not just 12v.&nbsp; Either use an inverter (relitivly cheap but inefficient to conver voltages twice) or replace the power supply.&nbsp; For a low-power desktop with one disk drive you might be able to use <a target="_blank" href="http://stores.homestead.com/KwanChiKin/-strse-176/12V-120W-DC-dsh-DC-Auto/Detail.bok">this</a>.&nbsp; (Cheaper than the other options I found.)<br>

 

[oldnjung]

There seems to be a wide variety of battery types, size, etc. that works for everyone. I don't have the roof for even 200 watts of solar, so I'm thinking of a Yamaha 1000 watt generator/invertor. Would two Odyssey PC1500's (68AHrs each, I think) be enough power to run micro 10 minutes a day, run/recharge laptop, run Mr. Coffee? Maybe a 12 volt electric fan in the summer? I plan on being stealthy half the time&nbsp;in a city/town so I wouldn't want to run the&nbsp;Yamaha all the time. Need battery power.<br>&nbsp;jb<br>

 

[akrvbob]

Jb and Hilda, I don't think that is going to be enough battery if you are in a city. It would be fine if you were in the country where you could just fire up the Yamaha for 10 minutes to run the micro or coffeemaker. But in the city where you can't run it, you will need more battery&nbsp; storage. The ideal solution is solar panels, 200 amp hours of batteries, charging off the alternator and a generator. And learning to use as little power as possilbe is pretty important as well. Bob<br><br>Also, the 1000 probably will NOT run a microwave or the coffeemaker. You will need a 2000.<br><br>

 

[oldnjung]

I was thinking of firing up the yamaha once a day to recharge the batteries and running appliances through an inverter connected to the batteries. Lots of places to park and do that. Roll up or fold up solar panels would be great out of town. I guess I need about 300 amp hours of battery storage (so I don't run them down more than 50% = 150 amps per day) . We probably would not use that much, but adding "leeway" to be safe.&nbsp; <A href="http://www.macandchris.com" target=_blank>www.macandchris.com</A> has a good worksheet. Would that be about 6 T105's or 3-100 Amp Trojans/Odyssey's? (If so, do I hear volunteers for lifting them?) One or two Group 27's?&nbsp; Would 200 Amp hrs storage (100 usable) if&nbsp;we were conservative, watched the battery monitor carefully and&nbsp;used the 2000 watt generator to recharge once a day be enough? Generator is flexible and smaller than batteries.&nbsp; It's all expensive, but cheaper than buying a house! I really appreciate How To Have Electricity in your Vehicle Home, Robert. Thanks again!<br>