I want to add a mini fridge to the trailer since going for more than a week makes it hard to have enough food in the 5 ft propane fridge. two trips ago we over loaded it, then knocked the sensor off of its holder and ended up tossing quite a bit of meat.
I have space on the two unused bunks with 24 inches up top, 32 1/2 inches in the lower. I can adjust the supports for the top bunk to allow for more on either but still use it as a guide.
I am also mindful of the fact that it has to run off of batteries and solar, so amp draw is big thing. Oddly a small cube fridge can use more than one that is three times its size and nearly as much as one 10 times it's size.
Now if we were going snowbirding tomorrow or start full timing I would have a Edgestar 321ss 3.2 mini fridge for the lower bunk in a heart beat. It is by far the lowest draw I have seen for a mini fridge this side of a 12v compressor model yet. It draws .64 amp at 120v, that's 6.4 amp plus losses at 12v. That's incredible when you consider a 1 ft cube generally draws 1.3a at 120v.
The downside of the 3.2 is that it is big and until we start going on extended travels, we just don't need that much space yet.
That leaves the upper bunk. Aside from 1 foot cubes, I have only found one mini that fits in the space. it has a tiny freezer and pulls 1.0 amp at 120v.
The other option would be cube sized freezer or edgestar has a cube fridge that can do either fridge or freezer. That would do because frozen food holds much longer than refrigerated food. Sadly the fridge/freezer combo uses more power and cost more than the 3.2 mini. It would probably be cheaper to get a mini freezer as we would rarely use it as a fridge anyways.
The two edgestar units would be new purchases and done in the spring. That gives me plenty of time to continue the research and possible find something acceptable on craigslist or get lucky and find a 12v unit.
A 12v unit would be wonderful for the low current draw but for the expense and size, they don't hold much. The mini fridges use more power but that's the one thing I have to spare.
Our trailer
Sunday, September 20, 2015
MPPT vs PWM
Let me begin by saying I am not a highly versed person in technical terms, I tend to speak in laymen terms. Let me also say that neither MPPT or PWM is better, they are just two different ways of doing things with advantages and disadvantages to both.
Lets star with a basic discription of each.
PWM is Pulse width modulation. We call most simple controllers this even though even MPPT controllers use PWM for their charging. The difference is how the power is connected to the battery and controlled. With a PWM controller the battery is directly connected to the panel and its voltage and acceptance rate are what controls the output of the system. The downside is that when the batteries voltage is low, say 12v, that anything the panel produces above the battery voltage is lost until that voltage comes up to what the panel puts out. Your 100w panel will not be worth 100w's until the battery is near fully charged.
MPPT or Maximum power point tracking is the program that controls the output of a MPPT controller. Here the panel is not connected directly to the battery. It comes in to a buck converter that takes the DC current from the panel, turns it in to AC and then back to DC again. The buck converter allows for the full use of the panel no matter what the battery voltage is. It doesn't happen in just bulk mode, the bulk converter is in use in all modes.
So what is the MPPT part then you ask. Since the battery no longer controls the system, something has to decide how the power is applied in bulk mode. The program can somehow tweak the array to get the most out of it as well as decide how to best bring the batteries voltage up. So not only does the buck converter allow the use of higher voltage panels or even panels in series, it gets you the most power when you need it the most early on when the battery is down.
Aside from the additional cost, MPPT controllers have a disadvantage in high heat. Actually the panels will lose voltage in heat and the controller uses that voltage to create current. The lower the voltage, the lower the amps. The loss isn't big, maybe a amp or so and usually only mid day when your battery is likely to be in float anyways.
So why go one or the other. For me it was equipment related as my panels are 24v grid tied panels and had no choice. They have higher voltage and lower amperage and while I could get a PWM controller that would clip the excess volts, it would give me the amps of a panel half it's size. Quite the waste of roof space.
Part of the decision can be budget. Until recently MPPT controllers cost considerably more the PWM controllers. The common thought was it wasn't worth the cost of buying a MPPT controller for less than 400w of panel. You coujld get a MPPT controller a single 12v panel or run two in series but the advantage you would see at peak wouldn't be enough to justify the expense. Three things this doesn't take into account are early production when the advantage is higher, the fact that less expensive MPPT controllers are available or the fact that 24v grid tied panels can be had for less than a 12v panel half it's size.
An example is I am looking for 140-150w panels to make a hinged portable. They each cost more than a 250w 24v panel does.
On the other hand say you have one or two 100w panels and want more power. You would be better off adding a third panel to the PWM set up than running what you have on MPPT. MPPT would get you more out of what you have if you were out of room for more panels.
So don't start the design of your system by choosing one form of charging controller first. Consider it a option as you look at how much room you have for panels, what panels are available to you, what the budget is and even what type of batteries you have. Find the balance that is best for you out of the different options before you start buying.
Last thing is to check on what your batteries require before you pick a controller. Know what voltages, modes and features you want before you buy. A cheap controller of either type may not properly charge your batteries and replacing them is certainly not cheap.
Lets star with a basic discription of each.
PWM is Pulse width modulation. We call most simple controllers this even though even MPPT controllers use PWM for their charging. The difference is how the power is connected to the battery and controlled. With a PWM controller the battery is directly connected to the panel and its voltage and acceptance rate are what controls the output of the system. The downside is that when the batteries voltage is low, say 12v, that anything the panel produces above the battery voltage is lost until that voltage comes up to what the panel puts out. Your 100w panel will not be worth 100w's until the battery is near fully charged.
MPPT or Maximum power point tracking is the program that controls the output of a MPPT controller. Here the panel is not connected directly to the battery. It comes in to a buck converter that takes the DC current from the panel, turns it in to AC and then back to DC again. The buck converter allows for the full use of the panel no matter what the battery voltage is. It doesn't happen in just bulk mode, the bulk converter is in use in all modes.
So what is the MPPT part then you ask. Since the battery no longer controls the system, something has to decide how the power is applied in bulk mode. The program can somehow tweak the array to get the most out of it as well as decide how to best bring the batteries voltage up. So not only does the buck converter allow the use of higher voltage panels or even panels in series, it gets you the most power when you need it the most early on when the battery is down.
Aside from the additional cost, MPPT controllers have a disadvantage in high heat. Actually the panels will lose voltage in heat and the controller uses that voltage to create current. The lower the voltage, the lower the amps. The loss isn't big, maybe a amp or so and usually only mid day when your battery is likely to be in float anyways.
So why go one or the other. For me it was equipment related as my panels are 24v grid tied panels and had no choice. They have higher voltage and lower amperage and while I could get a PWM controller that would clip the excess volts, it would give me the amps of a panel half it's size. Quite the waste of roof space.
Part of the decision can be budget. Until recently MPPT controllers cost considerably more the PWM controllers. The common thought was it wasn't worth the cost of buying a MPPT controller for less than 400w of panel. You coujld get a MPPT controller a single 12v panel or run two in series but the advantage you would see at peak wouldn't be enough to justify the expense. Three things this doesn't take into account are early production when the advantage is higher, the fact that less expensive MPPT controllers are available or the fact that 24v grid tied panels can be had for less than a 12v panel half it's size.
An example is I am looking for 140-150w panels to make a hinged portable. They each cost more than a 250w 24v panel does.
On the other hand say you have one or two 100w panels and want more power. You would be better off adding a third panel to the PWM set up than running what you have on MPPT. MPPT would get you more out of what you have if you were out of room for more panels.
So don't start the design of your system by choosing one form of charging controller first. Consider it a option as you look at how much room you have for panels, what panels are available to you, what the budget is and even what type of batteries you have. Find the balance that is best for you out of the different options before you start buying.
Last thing is to check on what your batteries require before you pick a controller. Know what voltages, modes and features you want before you buy. A cheap controller of either type may not properly charge your batteries and replacing them is certainly not cheap.
Saturday, September 12, 2015
Why we have the Garden Treasures propane fire pit.
From the time I was a kid camping with the folks, a camp fire has been part of the daily routine. Gathering the wood, cutting it to size, preparing the pit and building the fire is part of what keeps me busy while camping. There are times when a fire ban is in effect, times that the wind is too high to safely have a fire and times that we just don't feel like being out there long enough to make it worth while to have a fire. For these times we have the Garden treasures propane fire pit.
Garden Treasures propane fire pit
We decided that this one was the best balance of size, flame height and convenience. At $99 it is on the low end for cost. It is big enough to look realistic and has enough flame to feel that way too. The lava rocks start glowing red like coals after a while and the lid makes storage a breeze. Drop it down in to a stone fire pit and from a few feet you can't tell it from a real fire.
These picture were taken with the pit on medium setting. We found that on high propane pits produce hissing that all but goes away on low. We also found out that on low the heat stays at the sitting level, on high it goes right over us.
It does take some getting use too. With a real fire we tend to stay out of the down wind side due to the smoke. With a propane pit we sit down wind because that's where the heat is.
With a real pit you are stuck with where it is. With the propane pit we would move it around depending if we wanted to watch the sun set, be closer to the trailer so the dogs could see us or be in a area where the wind was blocked. Don't like the spot you have it in, in a few moments you can be in a different one.
Now there isn't any smoke with a propane pit, that's nice but it means there is no camp fire smell either. I keep the sweatshirt that I wear out by the fire real or not in a bag between times. It always has that campfire smell even when using the propane pit.
The easiest thing about getting use to a propane pit is the ease of set up and take down. Pull it out of storage, hook up the hose and you are done. No chopping cutting, hauling of wood. At the end of the night it is as simple to put it out with a twist of the knob. No waiting for it to burn down, dousing the flames or worrying that a stray ember will get you on the news as the starter of the latest wild fire. As I said the rocks do get red hot after a while a it's nice to sit there a few minutes after we shut it down as if we were watching a real fire burn down to coals. Like coals the rocks still put out a considerable amount of heat, enough to use the pie irons on.
The biggest reason we have one was the fire bans we had for a few years in a row. At 9000-10,000 ft of altitude the temperatures drop quickly as the sun does even in the summer. Without a fire you are just sitting outside in the cold and dark. There is no TV reception and you can only rent so many movies for two weeks, so it gets boring inside where it's warm and toasty too. We have used our IR grill like a propane fire pit, it looks funny but puts out a lot of heat fast. More than enough to enjoy the sunset on a cool evening.
That's when I decided to get a proper propane pit. The two most popular were the campfire in a can at somewhere around $300 and the Lil red campfire around the same price as the Garden treasures at Lowes. The Campfire in a can is king of the heap for it's ability to be turned up to bon fire size. It does burn a lot of gas doing it too. The Lil red campfire is little. Seeing one in person makes you think it has a large ashtray for a burner plate. Both have lids like upside down pots that cover everything top to bottom. There is also now big red campfire in the $150 range as well as others.
This last trip we used it not because of the weather or bans but because the firepit was trashed out and full to the brim with half burnt coals. Picking up the trash was one thing but digging out and rebuilding the stone pit was more than I wanted to do for the few nights we were there. Some trips it's a real fire one night and the propane the next, the trip before we never took it out at all. Ya just never know.
Garden Treasures propane fire pit
We decided that this one was the best balance of size, flame height and convenience. At $99 it is on the low end for cost. It is big enough to look realistic and has enough flame to feel that way too. The lava rocks start glowing red like coals after a while and the lid makes storage a breeze. Drop it down in to a stone fire pit and from a few feet you can't tell it from a real fire.
It does take some getting use too. With a real fire we tend to stay out of the down wind side due to the smoke. With a propane pit we sit down wind because that's where the heat is.
With a real pit you are stuck with where it is. With the propane pit we would move it around depending if we wanted to watch the sun set, be closer to the trailer so the dogs could see us or be in a area where the wind was blocked. Don't like the spot you have it in, in a few moments you can be in a different one.
Now there isn't any smoke with a propane pit, that's nice but it means there is no camp fire smell either. I keep the sweatshirt that I wear out by the fire real or not in a bag between times. It always has that campfire smell even when using the propane pit.
The easiest thing about getting use to a propane pit is the ease of set up and take down. Pull it out of storage, hook up the hose and you are done. No chopping cutting, hauling of wood. At the end of the night it is as simple to put it out with a twist of the knob. No waiting for it to burn down, dousing the flames or worrying that a stray ember will get you on the news as the starter of the latest wild fire. As I said the rocks do get red hot after a while a it's nice to sit there a few minutes after we shut it down as if we were watching a real fire burn down to coals. Like coals the rocks still put out a considerable amount of heat, enough to use the pie irons on.
The biggest reason we have one was the fire bans we had for a few years in a row. At 9000-10,000 ft of altitude the temperatures drop quickly as the sun does even in the summer. Without a fire you are just sitting outside in the cold and dark. There is no TV reception and you can only rent so many movies for two weeks, so it gets boring inside where it's warm and toasty too. We have used our IR grill like a propane fire pit, it looks funny but puts out a lot of heat fast. More than enough to enjoy the sunset on a cool evening.
This last trip we used it not because of the weather or bans but because the firepit was trashed out and full to the brim with half burnt coals. Picking up the trash was one thing but digging out and rebuilding the stone pit was more than I wanted to do for the few nights we were there. Some trips it's a real fire one night and the propane the next, the trip before we never took it out at all. Ya just never know.
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