Possible to go 12v only? - Page 4 - Fiberglass RV


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Old 11-05-2015, 01:08 PM   #43
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Originally Posted by Jon Vermilye View Post
You can find some (some made by the same manufacturers as the RV ACs) built for the boating industry. Not roof top, more expensive, but far more efficient.

For example, a 5000BTU unit that draws 4.4 amps: Webasto Marine AC FCF 5000 BTU Air Conditioner - Star Marine Depot
The unit you link to is 120 VAC. Is there a 12 VDC unit?
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Old 11-05-2015, 01:26 PM   #44
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The unit you link to is 120 VAC. Is there a 12 VDC unit?
While they exist (for example, here is one for only $3K listed at amazon:http://www.amazon.com/12-Volt-Marine.../dp/B0052N39LC), however it has no BTU rating so who knows how much cooling is available. The review notes it used 18 amps on low overnight; again, no useful information.

If you went with a standard boat AC, you would still need an inverter to run one, plus finding a place for it, ducting, etc. Not all that practical for a fiberglass trailer...
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Old 11-05-2015, 02:08 PM   #45
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It is all a matter of personal perspective of course, but I am with Dave B. on this one. I would not call $3600 and a requirement for a sunny day "practical".

I do wonder though, as much as I am impressed with my 12V compressor Truckfridge, where the heck are the very efficient 12V compressor A/C units?
I wonder the same, but I want a 12VDC, separable AC with a remote evaporator.

The problem with 12VDC AC would be the current require to run it. Power = Volts x Current. A 500 W load would draw 42 amps at 12 VDC. Twice that for 1000W.
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Old 11-05-2015, 04:00 PM   #46
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The power at 12 volts would be the same as at 120 volts (ignoring efficiency of inverters), but the current would be 10 times higher.
my 9000 BTU heat pump that draws a maximum of 8.7 amps cooling and 7.4 heating would draw 87 amps at 12 volts cooling and 74 amps heating.
Since this is an inverter compressor there would be little inrush surge starting and it rarely "starts". It runs hard enough to meet its setpoint an varies load to satisfy demand.
That being said I can easily operate the entire trailer with a Harbor Freight 2500.2000 watt inverter generator so the inverter for the heat pump doesn't seem to care if it is pure sine wave or not.
Since it is mostly idling and modulating the 84 amps would not be seen all of the time, but is still more than most 12 volt systems could handle.

As to camping with 12 volt only I would say why not?
A propane reefer might be desirable to reduce power demand, but I decided against it because I did not want all of the vent holes in the trailer shell. Every floor section below any penetration was rotten and my wife wants a critter free environment too.
Currently I have propane for the tankless water heater on the tongue and the portable grill with a 12 volt compressor reefer, and a heat pump.
This should work for us since we are looking for a mobile motel room more than anything. The solar may work or not, but we plan to use hookups mainly.
I have the generator for hurricane backups and we may use it camping or not.
There is no propane that passes within the shell.
Depending on how the final weight and balance works out I may mount the generator on the tongue next to the heat pump and power it from propane with a 3 way conversion. However there is a of stuff up there already.
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Old 11-05-2015, 04:40 PM   #47
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Originally Posted by redbarron55 View Post
The power at 12 volts would be the same as at 120 volts (ignoring efficiency of inverters), but the current would be 10 times higher.
my 9000 BTU heat pump that draws a maximum of 8.7 amps cooling and 7.4 heating would draw 87 amps at 12 volts cooling and 74 amps heating.
Since this is an inverter compressor there would be little inrush surge starting and it rarely "starts". It runs hard enough to meet its setpoint an varies load to satisfy demand.
That being said I can easily operate the entire trailer with a Harbor Freight 2500.2000 watt inverter generator so the inverter for the heat pump doesn't seem to care if it is pure sine wave or not.
Since it is mostly idling and modulating the 84 amps would not be seen all of the time, but is still more than most 12 volt systems could handle.

As to camping with 12 volt only I would say why not?
A propane reefer might be desirable to reduce power demand, but I decided against it because I did not want all of the vent holes in the trailer shell. Every floor section below any penetration was rotten and my wife wants a critter free environment too.
Currently I have propane for the tankless water heater on the tongue and the portable grill with a 12 volt compressor reefer, and a heat pump.
This should work for us since we are looking for a mobile motel room more than anything. The solar may work or not, but we plan to use hookups mainly.
I have the generator for hurricane backups and we may use it camping or not.
There is no propane that passes within the shell.
Depending on how the final weight and balance works out I may mount the generator on the tongue next to the heat pump and power it from propane with a 3 way conversion. However there is a of stuff up there already.
12 Volt wiring in most travel trailers designed to handle no more that 20 amps, some go down below that to 15 or 10 amps. Trying to run higher current is asking for fires.
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Old 11-05-2015, 07:21 PM   #48
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12 Volt wiring in most travel trailers designed to handle no more that 20 amps, some go down below that to 15 or 10 amps. Trying to run higher current is asking for fires.
I would hope that anyone installing a large inverter would wire between the inverter & batteries with the proper size wire and fuses so that fire is not a problem. I have a 1000 watt inverter that is wired with #0 wire; while it draws 65 amps when I make a pot of drip coffee, the wiring doesn't even get warm...
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Old 11-05-2015, 09:10 PM   #49
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Jon, One nice feature of coffee pots and toasters, though they draw a fair amount of current on 12 volts, they don't do it for long, making toast and coffee really takes minutes.
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Old 11-06-2015, 09:58 AM   #50
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True. Making a 4 cup pot of coffee cost me 6 amp hours. On a good day 200 watts of solar puts it back in around an hour.
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Old 11-09-2015, 10:09 AM   #51
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With my limited budget, I can't prove you wrong, but it is my understanding that a 5000 btu AC unit consumes ~500W of power to operate, and possibly double that to start. So, a 1000W inverter combined with about 1000W of solar should do it. I understand that 1m of solar cells produce ~150 W of power. The footprint of my Trillium 4500 is approximately 2m wide and 4m long, or ~8m. This should be able to produce ~1200W of power.

Of course the solar array would have to be in direct sun and as close to perpendicular to the sun as possible, but I see this as doable. This would have the added benefit of providing shade for most of the trailer. A linear actuator on the array, and a powered wheel on the tongue of the trailer to keep it pointed at the sun. That and the necessary controls to make it work. This is all fairly inexpensive, other then the solar cells them self.
At about $2/W, the cells would cost $2400.
Solar battery charger: $200
Batteries: ~$400?
Controls: I could do it cheep, I am a controls tech after all. But lets say another $600.

So for on the order of $3600, you could provide enough power to run AC on a sunny day.
For far less than the above, you could buy a 2200w generator, propane conversion kit, have it permanently mounted, and carry your own shore power for the times you need it. you could also probably provide about 10 years of propane fills ., just saying.......
for most (of us) the cost (if you have to worry about cost) doesn't reach a payback point if you have to go full solar to be able to run large draw appliances.
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Old 11-09-2015, 11:26 AM   #52
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Can't see how you can safely "Permanently" mount a 2200 watt generator on a 13' FGRV.
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Old 11-10-2015, 02:36 PM   #53
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I am thinking about it on my extended frame version of a 16' Scamp.
It depends on how the weight and balance works out as the build-out progresses.
At the present time it looks good to be mounted next to the heat pump, but there is still a lot to be worked out if it is possible or desirable,
The Generator I have is the Harbor Freight Predator 2500 watt inverter generator at about 64 lbs.
I bought one for work where we keep small inverter generators for backups for out control rooms etc. we had a number of Honda units and I bought one of these to see how it compared in the real world at 40% of the cost.
They are about the same noise level with the higher powered HF unit heavier.
Both put out rated power and the Honda uses a little less fuel.
I don't see the added cost of the Honda necessary for my use, but the lesser weight might be nice at 46 lbs. 18 lbs might make the difference, who knows.
However the HF unit has a rating of 600 watts less. the HF has 39 watts per lb and the Honda is 35 watts per lb.
Converting for LP gas means no additional gasoline storage needed. Kits are available to convert both units.
I actually bought the HF generator as a Hurricane backup unit ans several of the guys at work have also purchased them after comparing with the Hondas.
I got a discount coupon and paid about $440 for the unit including freight and tax.
The HF unit easily runs the AC and the microwave (at the same time!)
As to how you safely mount the generator... I guess I will work that out when necessary. Of course you can't safely mount the tankless water heater I have installed either!

I figure a mounting shelf on the far side of the heat pump unit similar to the water heater on the near side. Of course the "A" frame is linger and reinforced on my trailer so it is not a stock 16' Scamp.
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Old 11-11-2015, 05:26 AM   #54
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I see the outside toilet. Will you be building an outhouse around it?
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Old 11-11-2015, 07:03 AM   #55
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The outside loo is for sale if anyone needs one. I replaced it with one more confined.
Steve you have pretty sharp eyes!

Sent from my SCH-I605 using Fiberglass RV mobile app
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