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 > Absorption Fridge Running on Solar/Battery/Inverter System

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valhalla360

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Posted: 07/15/22 06:20am Link  |  Quote  |  Print  |  Notify Moderator

12thgenusa wrote:

valhalla360 wrote:

12thgenusa wrote:

A little correction to your understanding. There is no solar power going to waste. You have excess capacity, so the potential to produce power is going unused. Power is not produced until there is a load to use it. So, I suppose in one sense you either have a wasted opportunity, or an overbuilt system for your needs. Since you already have the system, finding ways to use the capacity is good, however you have to weigh the costs of having that system vs the cost of a couple of tanks of propane.


Semantics.

If you are pumping gas and spill 5gal on the ground because you overfilled, if you only consider what was in the tank when you pull away, there is no waste but we all know 5 gal was wasted.

Same thing. X KWH of capturable power hit the panels and it would be wasted if not used because the system can't hold it.


Not semantics. In your example actual gas is spilled and wasted on the ground. In a solar example, the energy is not even produced, so it can't be wasted in the same way. You don't think in terms of wasted energy when your truck is parked and the engine is not running.


I'm pretty sure the sun did produce the power and deliver it to the solar panels...then it went wasted.

If it bothers you that the RV is parked, think in terms of solar vs generator and you get a similar result.


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StirCrazy

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Posted: 07/15/22 07:20am Link  |  Quote  |  Print  |  Notify Moderator

3 tons wrote:

I have a similar set-up (at 400a/h LFP and 660w) and get the temptation but in the vagaries of the real world harvest, not too sure it’ll always pencil out -

In theory something like this: a gallon of propane has about 91,400 BTU’s, while 325w (ac power) at say a more conservative 75% duty cycle (considering local and inverter losses…) would equal 5850w over 24hrs equals 15.6 hrs refer operation per gallon of propane or 78 hrs per 5 gal tank…Just saying…

3 tons


Im not sure what your trying to say, but my fridge in my camper is a old one where the burner stays on all the time and I can easily let it go 3 months running 24/7 on a single 5 gal tank. once I start it up in the spring it stays going all summer until I winterize it in the fall, so three years now it has done this. I do this with my 5th wheel also and same thing, I fill my bottles in the spring and they don't get filled untill winter when I am doing inclimate camping. the 5th wheel does have a DSI large fridge, but it has 7lb bottles.


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pianotuna

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Posted: 07/15/22 09:24am Link  |  Quote  |  Print  |  Notify Moderator

78 hours for five gallons of propane is far wide of my use. It is astronomically high. When I was full time and mostly boon docking 20 gallons of propane would last three to four months.

I did wish I had more solar at that time.

Now that I'm back to part time, I can't justify the cost of an upgrade. I may go back to a larger battery bank or double the usable capacity of the existing bank.

It is really too bad that the only LI battery that tolerates extreme cold is so very expensive. But fortunately there is another chemistry that meets my desires (not my needs) so it is very much an optional upgrade.


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My ride is a 28 foot Class C, 256 watts solar, 556 amp-hours of Telcom jars, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.

3 tons

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Posted: 07/15/22 09:50am Link  |  Quote  |  Print  |  Notify Moderator

StirCrazy wrote:

3 tons wrote:

I have a similar set-up (at 400a/h LFP and 660w) and get the temptation but in the vagaries of the real world harvest, not too sure it’ll always pencil out -

In theory something like this: a gallon of propane has about 91,400 BTU’s, while 325w (ac power) at say a more conservative 75% duty cycle (considering local and inverter losses…) would equal 5850w over 24hrs equals 15.6 hrs refer operation per gallon of propane or 78 hrs per 5 gal tank…Just saying…

3 tons


Im not sure what your trying to say, but my fridge in my camper is a old one where the burner stays on all the time and I can easily let it go 3 months running 24/7 on a single 5 gal tank. once I start it up in the spring it stays going all summer until I winterize it in the fall, so three years now it has done this. I do this with my 5th wheel also and same thing, I fill my bottles in the spring and they don't get filled untill winter when I am doing inclimate camping. the 5th wheel does have a DSI large fridge, but it has 7lb bottles.


Well, in retrospect it does seem oddly high but was only a rapid back of the napkin calc..

However, I believe converting BTU’s into watts is the proper way to draw conclusions…

3 tons

mbloof

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Posted: 07/15/22 10:05am Link  |  Quote  |  Print  |  Notify Moderator

IDK, everyone has different use patterns for their RV.

In the winter months the challenge is having enough AH to power the furnace. After that then it is enough propane to power the furnace, HW, stove and fridge.

IMHO: the fridge is the LEAST propane use item in a camper.

Personally, I no longer use the HW heater. While the furnace gets used more if the weather drives us inside (in the winter) otherwise it is only used at night and 1st thing in the AM to get the 'chill' off.

So my propane use in the summer is mostly stove (cooking/coffee) and fridge. I'll generally need to fill 1 5gal propane tank 1 maybe 2x a year.

My fridge is a 2014 - I can hear the gas valve open and gas flow while it is running - which is not all that often.


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3 tons

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Posted: 07/15/22 10:40am Link  |  Quote  |  Print  |  Notify Moderator

Ok, upon a recalc (me dummy!!…) I found my error, now revised…

At 325w per hr, and a 75% duty cycle for 24 hrs = 244w (admittedly conservative numbers), watts convert to 19,968 btu/day.

Propane at 91,451 btu/gal / 19,968 = 4.58 days of refer operation per gallon…

5gal of propane x 4.58 days p/gal = 22.9 days of refer operation…

Sounds much more realistic (sorry for my bad)…

3 tons

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Posted: 07/15/22 11:28am Link  |  Quote  |  Print  |  Notify Moderator

If you had not recently updated your fridge, I would say an upgrade would make sense with the power you are capturing and the efficiency you could gain. With your fridge update, you have a reliable unit that really does not need to be replaced but could be supplemented with a DC heater element. I do know I only capture about the half as much in the winter with the short days and overcast skies than the long summer days, so I am not sure how much reserve you will have if you camp year round verses seasonally or if you cannot chase the good weather and camp through the bad.

I have used AGM batteries that don't hold as much charge and typically just barely get to full charge in the summer when camping. In the winter, I still may supplement charge if am boon docking more than a couple days. What is nice is that every time we head out (about twice a month), the batteries are fully charged even though the camper is not plugged in.

Another thought is to add a hot rod to your water heater so you can heat water via AC instead of LPG. Maybe being able to switch the fridge and hot water heater between electric and LPG based on season and available sun would be a good option?


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WarrenS65

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Posted: 07/15/22 09:11pm Link  |  Quote  |  Print  |  Notify Moderator

How about getting one of the medium sized lithium battery packs to recharge your electronics? You can charge it off the camper and recharge your stuff without drawing on the camper batteries.


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Camper_Jeff_&_Kelli

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Posted: 07/16/22 12:33am Link  |  Quote  |  Print  |  Notify Moderator

StirCrazy wrote:

3 tons wrote:

I have a similar set-up (at 400a/h LFP and 660w) and get the temptation but in the vagaries of the real world harvest, not too sure it’ll always pencil out -

In theory something like this: a gallon of propane has about 91,400 BTU’s, while 325w (ac power) at say a more conservative 75% duty cycle (considering local and inverter losses…) would equal 5850w over 24hrs equals 15.6 hrs refer operation per gallon of propane or 78 hrs per 5 gal tank…Just saying…

3 tons


Im not sure what your trying to say, but my fridge in my camper is a old one where the burner stays on all the time and I can easily let it go 3 months running 24/7 on a single 5 gal tank. once I start it up in the spring it stays going all summer until I winterize it in the fall, so three years now it has done this. I do this with my 5th wheel also and same thing, I fill my bottles in the spring and they don't get filled untill winter when I am doing inclimate camping. the 5th wheel does have a DSI large fridge, but it has 7lb bottles.


I would dearly love to know what brand of propane you use because I do go through the stuff when on the road. Water heater, cooktop and oven, furnace in the winter. My fridge is 8 CU FT so I may use more just for that if you have a smaller fridge. I do plan to change my regulator and hoses soon as I suspect a small leak though I don't smell anything.


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Camper_Jeff_&_Kelli

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Posted: 07/16/22 12:42am Link  |  Quote  |  Print  |  Notify Moderator

3 tons wrote:

StirCrazy wrote:

3 tons wrote:

I have a similar set-up (at 400a/h LFP and 660w) and get the temptation but in the vagaries of the real world harvest, not too sure it’ll always pencil out -

In theory something like this: a gallon of propane has about 91,400 BTU’s, while 325w (ac power) at say a more conservative 75% duty cycle (considering local and inverter losses…) would equal 5850w over 24hrs equals 15.6 hrs refer operation per gallon of propane or 78 hrs per 5 gal tank…Just saying…

3 tons


Im not sure what your trying to say, but my fridge in my camper is a old one where the burner stays on all the time and I can easily let it go 3 months running 24/7 on a single 5 gal tank. once I start it up in the spring it stays going all summer until I winterize it in the fall, so three years now it has done this. I do this with my 5th wheel also and same thing, I fill my bottles in the spring and they don't get filled untill winter when I am doing inclimate camping. the 5th wheel does have a DSI large fridge, but it has 7lb bottles.


Well, in retrospect it does seem oddly high but was only a rapid back of the napkin calc..

However, I believe converting BTU’s into watts is the proper way to draw conclusions…

3 tons


Your calculations are probably pretty close. I have not done a solid 24 hour test yet. My feeling is it may be a losing battle trying to maintain the charge in the batteries with the fridge going 24 hours on electric. I think the fridge would deplete down to 10% charge overnight on the second or third day. I will do that test in a couple weeks when I'm on the road in the camper to moniter the conditions. If it was 4 AM and the batteries were down to 20 or 25%, I would end the test there knowing the batteries will not supply enough power till the sun came up high enough to begin supplying sufficient regenerative current. Even if I decide to do this during the daytime, it's still a winner.

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