Generators

[pinstriper]

I caused the circuit breakers to blow, while hooked up to 30 amp shore power, when I used an electric frypan while running the AC. Fortunately, all I had to do was go to the fuse box and reset the circuit breakers. And turn off the AC until dinner was done.

[p]Yeah, too much - so much you can't do while running the A/C.[/p][p]
[/p][p]Though, most campsite poles I can recall also had a 15amp circuit available. So an extension cord to run the electric frypan or George Foreman or whatever directly off the pole while the TT runs off the 30 amp driving the air conditioning. I sure as hell wouldn't used the thing indoors, unless you have a good supply of simple green and paper towels and a stepladder to reach every inch of adzel.[/p][p]
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[leslie]

I caused the circuit breakers to blow, while hooked up to 30 amp shore power, when I used an electric frypan while running the AC. Fortunately, all I had to do was go to the fuse box and reset the circuit breakers. And turn off the AC until dinner was done.

[p]Yeah, too much - so much you can't do while running the A/C.[/p][p]
[/p][p]Though, most campsite poles I can recall also had a 15amp circuit available. So an extension cord to run the electric frypan or George Foreman or whatever directly off the pole while the TT runs off the 30 amp driving the air conditioning. I sure as hell wouldn't used the thing indoors, unless you have a good supply of simple green and paper towels and a stepladder to reach every inch of adzel.[/p][p]
[/p]

I cook outside. I plugged into the outlet on the exterior of my camper.

[pinstriper]

Ah, very sensible. So using the other circuit would work out fine if the pole has one.

[admin]

I personally like options. I have a generac 2000w unit with a peak of about 2200w. I also looked at that Hyundai model since it had such attractive numbers for its price point. I know my personal electrical needs are minimal for the most part, but I like the idea of being able to power my small AC unit and/or a small 120v fridge. So here is my current thinking/plan

Option 1: Minimal power needs.
-No AC or fridge will be used, thus only power needs would be for small lights and electronics.
-In this case the single onboard 12v battery with the 20w solar panel will allow for nearly indefinite supply.
-Downside is the need for other supplies such as ice for a cooler.

Option 2: Intermittent power needs.
-A small fridge will be used much like a cooler and thus will need to be cycled to maintain a relatively desirable temperature. This is still at a concept level idea since I dont have any real data to know how long a small fridge can maintain its temp between power cycles.
-The AC unit most likely would not be used in this situation. I say most likely because I have been in situations where its been mild enough to not require AC, but then humid enough that I wish I had the ability to draw some of that moisture out of the camper.
-In this situation the generator will be used on an as needed basis, but if my math is right I could run a relatively small inverter 400/800peak to power cycle the fridge. The 20w solar may not be able to keep up with this demand for very long, but for short trips it might be an option.

Option 3: Full power needs.
-High power demand times such as no electrical hook ups in the worst summer heat.
-Power will still only be needed on an intermittent basis, however the assumption is that it would be needed for much longer periods of time.
-I dont expect this scenario often but since we already own the generator at least we know its an option.

Option 4: Full power hook ups.
-No restrictions

[charliem]

[font size="3"]Sean,

Re your thoughts on cycling a small fridge: I think you will be very disappointed in the insulation qualities of the small fridges. The competing requirements of low cost, small exterior size, and large interior size result in poor thermal performance. There are some excellent coolers, Yeti comes to mind, that are optimized for long term storage. I'm thinking, if I ever had a similar situation, the space of the extra fridge might be better used by a good cooler filled with dry ice  . Or a BIG solar panel.
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[mitch]

Doesn't need to be a BIG solar panel. A very size and price manageable 100 watt panel will provide you enough power in 4 hours to use lights, water heater, 5cf fridge, and water pump all you need in a normal day.  

[charliem]

[font size="3"]Mitch,[/font]

[font size="3"]Interesting. For my own education how many amp-hrs per day are you figuring from the 100W panel? Does this assume clear sun, due south at solar noon, not tracked? I read differing numbers for the integrated output of a panel aimed south at proper elevation over a noon +/- X hours. Then, what are you assuming for the fridge? Probably on gas, so what DC current for electronics plus gas valve and what duty cycle over a 24 hour day? Seems like just the gas valve is in the order of 1A. I'd guess the duty cycle at better than 70% on a warm day.
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[mitch]

[font size="3"]Hi Charlie,

A 100 watt panel will give you 5.68 amps/hr in good sun.  Good in this case is regular old sunny day with the panel pointed at the sun the way a regular person would do it, ie calibrated eyeball. For draw I actually created a spreadsheet that takes into account all of the items in the trailer (including CO  monitor, Lights, Furnace, Fridge, Water pump and Water heater), a rough number of hours use per day and the either the manufactures rated amperage or a calculated one.  The fridge is by far the biggest draw because it runs 24 hrs and I calculate that to be 12 amp/hrs per day. My total estimated draw for all items comes out to a tad over 19 amp/hrs per day.

I can say for sure that this actually bears out in real life.  I use a 70 watt panel and I've measured it 8 ways to Sunday and gone 12 days of boondocking several different times under differing weather conditions with no problem whatsoever. At the end of 12 days, assuming some sun, my battery is fully charged.


I'm happy to send you the spreadsheet if you'd like.   You can plug in all sorts of numbers and see what the result is.  


Mitch

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[admin]

Charlie,

I agree that the small refrigerators are most likely going to be poorly insulated, I just dont know how poorly yet. I've used the 5 and 7 day coolers that claim extended performance even in 90 degree temps yet it has always been a disappointment. Ultimately I will probably end up with something like Mitch as I build my solar system. However the main reason I have yet to invest more in solar is the simple fact that most of the places I enjoy camping tend to be under cover. I also run into trouble with the requirement for keeping the solar mobile. With no solid roof to mount to, I have to be able to close it up easily and I haven't decided if its cost effective (or even worth the hassle) yet. The other caveat for me is the fact that I moved to the pop up for the minor luxuries such as having air conditioning, even if it is intermittent.

I guess what it all boils down to for me is the general purpose of the trip. I like the flexibility to do everything from simple tent camping on wheels, on up to basic luxuries with full electric and water, and sometimes that requires personally providing a couple thousand watts

[mitch]

Hey Sean,

I use a 25' flexible cord to run from the panel to the battery so I can put the camper in the shade but the panel in the sun. I fabbed a quick and easy stand to point the panel towards the sun at whatever angle seemed best at the moment and I do usually move the panel once over the course of the day.  Here's a [a href="http://livinlite.proboards.com/thread/748/solar-generator"]link[/a] to another thread where I laid out what I'd buy if I were doing this today. There are links for each component in the system.

[charliem]

[font size="3"]Mitch,

I'm with you on the loads though I would have expected the fridge a bit higher. The rest of the load calcs are straightforward and understood. The piece I can't get to is the 5.68 amps/hr. Amps/hr is not a valid unit since current (Amps) is an instantaneous value. Current times time (Amps X Hours) = Amp-Hours. Amp-Hours times voltage = Watt-Hours = Energy. Working in Watt-Hours gets rid of all the voltage and amperage conversion confusion. So, how do you get to 5.68? Is this a peak current when factored for efficiency; an average Amp-Hour product when integrated of some sun exposure period; the output of a PWM controller? Are you considering MPPT? Need some help and/or references here. BTW, no link in your most recent post  .


Sean,

Understand your desires. The fixed panel on the CL would be a problem because I also like trees/shade. And I'd be paranoid with Mitch's portable panel because it might get too portable (legs)  .  I don't do well without A/C when it's hot and don't like generators so I have to plan carefully. BTW, maybe you could wave your administrator wand and move some of these posts to a new solar thread. Just hate it when someone hijacks a thread  .
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[admin]

Yeah I have been toying with a few different options with my solar setup. I've actually been toying with the idea of making a quick disconnect for the batteries where I can move them to wherever the panel needs to be, rather than limit myself to x number of feet for the wire. Though I still get into a problem where if I'm going to move towards solar I really need a way of having a couple thousand watts/AC available to run my large appliances. Otherwise I can get by with nearly zero electrical needs, so its kind of an all or nothing venture if I commit to solar.

[david]

[p]I have cruised on sailboats for about 20 years while managing to live on DC only and have used solar panels for almost 15 years to power my DC needs. I am going to skip the physics, ie watts=amps*volts, but here are some rules of thumbs, facts and opinions. It is long and probably confusing so I apologize. It is full of data.

1. A 100 watt solar panel when mounted horizontally will generate about 33 amp hours of power on a sunny day in moderate latitudes when operated with an MPPT controller.  A PWM controller will drop it to 25 amp hours fixed horizontally. If you tilt it perpendicular to the sun manually several times a day then you might get 50 amp hours with a MPPT controller.

2. Most refrigerators again in moderate climates (80 deg daytime highs) will operate on a 50% duty cycle. I will measure the draw on my 6 cu foot fridge on my 16TBS when I get a chance but I am guessing 1/2 amp or less. So the amp hour draw for a typical fridge would be 24*.50*.5 or 6 amp hours. That does not account for frame heaters on the bigger units.

3. For best life, you should not routinely draw down your batteries more than 50%. A typical dealer delivered group 27 trailer battery has 80 amp hours of capacity. A couple of golf cart batteries has 220 amp hours.[/p][p]
[/p][p]4. If you only use lights in the evening (and we rarely use more than an hour's worth) a low power stereo system for ambiance, recharging your cell and iPad, a few amphours for the water pump and heater and 6 amphours for the fridge, then you can live on 10-12 amp hours each day. That is 3-4 days on our Group 27 batteries to stay above 50%. We never camp longer than that without hooking up the TV and moving. The TV will replace 40 amp hours at about 10 amps an hour average rate while driving- more at first and tapering off as the battery gets almost fully charged.

5. But some people want more- microwave or even the furnace at night. Charlie corrected my misimpression of microwaves in a previous post- I thought that they were rated as input power and that the CLs had a 600 watt unit so that a 1,000 watt inverter would run one fine. But even using Charlie's numbers a couple of golf cart batteries could easily run a microwave for 5-10 minutes each day with a 2,000 watt inverter. It would draw about 25 amp hours to do so, but due to the high 150 amp draw it would take down the batteries quite a bit and would probably take 50 or more amp hours to replace it. That is more you can expect from a 100 watt solar panel on a sunny day.[/p][p]
[/p][p]The furnace blower  probably takes at least 5 amps and at a 25% duty cycle (lows in the 40s) you might draw another 10-15 amp hours overnight.

6. But solar panels are really cheap. I just bought a Renogy 100 watt unit for my boat and it cost $150. You could put together a system consisting of two 100 watt panels for $300, a 12 amp rated Morningstar PWM controller for $70 ($150 for MPPT), a couple of golf cart batteries for $200, a 2,000 watt inverter for $200 (Chinese/Chinese) or $380 (American/Chinese) and $50 for wire and fittings. That system will power everything discussed above almost indefinitely.[/p][p]
[/p][p]You could cut that about in half for a single 100 watt panel and use your existing Group 27 battery. That would power everything above except the microwave and recharge it on a 2 out of 3 sunny day basis.

8. So for not much more than the Hyundai generator mentioned above, you could have a completely quiet, self sufficient, solar powered RV that would cover your needs almost indefinitely. But you could not run your A/C of course. And that assumes that you are not shaded. We like to camp in shade.[/p][p]
[/p][p]9. Moving the panels to a sunny spot doesn't really work for me. A 100 watt panel weighs about 30 lbs, is about 40"x20" and needs to be securely mounted to the rooftop. I had a 30 watt panel that I could store in the basement, take it out and set it up 20' away from the camper in a sunny spot. But in the places we like to camp that spot quickly moved and I never got more than a few hours worth of sun.[/p][p]
[/p][p]Finally let me talk about PWM and MPPT controllers. So called 12V panels have an open circuit voltage of 21 volts and a maximum power point voltage of 17 V. A 100 watt panel is rated at its MPPT of 17 volts approximately and its current at that point is 5.9 amps which gives 100 watts output. Solar panels are pretty much constant current sources, ie it doesn't vary much from 12 to 20 volts. So if you connect it directly to a half charged battery of about 12 volts, you will see only 12*5.9= 71 watts, increasing to 80 or so as it gets recharged and the charging voltage rises.[/p][p]
[/p][p]PWM (pulse width modulation) controllers simply take the solar panel's output and when the battery gets pretty well charged and no more current is needed they pulse the output to average 13.5 volts. Otherwise the battery would continue to charge and start to gas (disassociate water to hydrogen and oxygen) which is very bad for batteries.[/p][p]
[/p][p]MPPT controllers work differently. While charging, the controller adjusts its input impedance to keep the solar panel loaded at its optimum power point of 17 volts. It then electrically converts that 17 volts to whatever voltage  the battery needs to charge efficiently- starting at 12 or so for a 50% charged battery and rising to 14+ as it gets fully charge and finally cutting back to about 13.5 when fully charged. But except for internal losses you are still getting 100 watts output so the amps go up to 8 or so at 12 volts. So the MPPT controller is about 17/13= 31% more efficient less its internal losses of about 5% for an overall improvement of maybe 25%.[/p][p]
[/p][p]But in the two 100 watt system discussed above, the price difference between a PWM and MPPT controller is more than the cost of another panel. If you have the room, just add another panel, up to a point.

David[/p]

[mitch]

[font size="3"]Charlie,

The 5.68 number is instantaneous amps you are absolutely correct.  My terminology is bad, so it's 5.68 amp-hrs generated.  (It's actually 5.29 amps according to the panel manufacturer)  The fridge is the 5 cf model so there is no frame heater maybe that's why it's a bit lower then you'd expect?  Finally, the missing link is actually the work "link".  My current 70 watt panel is rated at 3.98 amps, I've actually measured it during a sunny day and lo and behold it's right on the money.


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[daplumbr]

Great info. Classic mix of stuff when it comes to electricity; start with generators and end with solar   

Anyway, I'm intrigued by the very low usage of the fridge! At our cabin we have an older Dometic 6 cu ft that is propane or AC. When on AC it draws 185 watts during the on cycle. I guess the DC powered fridges have a motor driven compressor that's super-efficient if it draws less than an amp. That gives me hope for our future solar power. Of course the daily power usage of a fridge depends on how often it's opened too!