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Old 08-02-2018, 05:07 PM   #21
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Keep in mind:

'THE or the ONLY reason an absorption refer exists is that there is not enough reliable electrical power.' Want to use batteries, a compressor refer. How much battery power is required varies by application.

Bud

Yep, adding more battery power so you can run an absorption frig would be pretty silly, IMO. A compressor frig would use maybe 1/4 of the power of the absorption on batteries and it would actually stay cold all the time.
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Old 08-02-2018, 05:58 PM   #22
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That's something that's unclear to me. My situation: I have one house battery that gives me 100AH. What would I need to be able to comfortably run a compressor fridge that's say 3-4cf (the size of my small Dometic)? What would that system look like?

1. Would a need a higher output alternator?
2. An inverter?
3. Solar (I have 100W Renogy suitcase)?
4. What size (AH) battery storage? Lithium necessary? Preferred?

Assumption: I'm never in one place longer than 3 days w/o hookup without driving.

I'm guessing that some of you have gone through this process and asked the same questions or figured this out on your own. Any comments would be GREATLY appreciated.........
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Old 08-02-2018, 06:17 PM   #23
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That's something that's unclear to me. My situation: I have one house battery that gives me 100AH. What would I need to be able to comfortably run a compressor fridge that's say 3-4cf (the size of my small Dometic)? What would that system look like?

1. Would a need a higher output alternator?
2. An inverter?
3. Solar (I have 100W Renogy suitcase)?
4. What size (AH) battery storage? Lithium necessary? Preferred?

Assumption: I'm never in one place longer than 3 days w/o hookup without driving.

I'm guessing that some of you have gone through this process and asked the same questions or figured this out on your own. Any comments would be GREATLY appreciated.........

It does vary a lot with conditions, but in general this is what we have seen.


Our 3.1CF frig uses between 17 and 40 amp hours per day, so if you needed 3 days you would use 120ah above what you do now in the worst cases.


100 watts of solar will give you about 30ah maximum under very good sun conditions, so it would nearly keep up in many conditions. But you might also only get 5ah a day if it is rainy or very shady, so tough.


Driving in most class b setups will charge the batteries at somewhere between 50-80 amps, although some older ones may be less. That high rate would only apply until the batteries get to about 70% and then they start to taper how much they will take and it will take a long time to finish charge to full.


If there is not much other battery use, having the semi-norm of 220ah of batteries and 100-200 watts of solar would likely cover almost all of the conditions as you describe them, although multiple bad weather days, batteries that don't get fully charged before starting a no electricity stay, etc could put you outside the range. The fallback position would be if you get really bad conditions and wind up low on power, an hour drive would get you a days worth of charge back.


You would certainly need a battery monitor to keep track of where you are on battery charge, but that is a good idea anyway.
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Old 08-02-2018, 06:29 PM   #24
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Thanks for the extremely helpful answer, booster. So does your system not make use of an inverter? Where my fridge currently sits it has 12v leads necessary to run the 12v heating element (mine is so old it doesn't have a board running an auto light, etc.). Unfortunately, PleasureWay insists there's no build manual available for consumer consumption (hard to believe on a RV like mine that's 20yrs old). Also are you running AGMs or Lithium? I assume the former since I've read that one of the advantages to Lithium was it's ability to charge faster. And, last, did you upgrade your alternator?

Again, thanks for the very helpful info. It IS much appreciated.

Glenn
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Old 08-02-2018, 07:31 PM   #25
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Originally Posted by booster View Post
It does vary a lot with conditions, but in general this is what we have seen.


Our 3.1CF frig uses between 17 and 40 amp hours per day, so if you needed 3 days you would use 120ah above what you do now in the worst cases.


100 watts of solar will give you about 30ah maximum under very good sun conditions, so it would nearly keep up in many conditions. But you might also only get 5ah a day if it is rainy or very shady, so tough.


Driving in most class b setups will charge the batteries at somewhere between 50-80 amps, although some older ones may be less. That high rate would only apply until the batteries get to about 70% and then they start to taper how much they will take and it will take a long time to finish charge to full.


If there is not much other battery use, having the semi-norm of 220ah of batteries and 100-200 watts of solar would likely cover almost all of the conditions as you describe them, although multiple bad weather days, batteries that don't get fully charged before starting a no electricity stay, etc could put you outside the range. The fallback position would be if you get really bad conditions and wind up low on power, an hour drive would get you a days worth of charge back.


You would certainly need a battery monitor to keep track of where you are on battery charge, but that is a good idea anyway.
My setup is the 160 watt panel and two AGM 6 volt batteries...in series..

I'm also running a 3.1 Dometic propane refrigerator...

Can any of you tell me if you think I have enough power to run the fridge and for how long?
Seems to be a lot of different answers here.. maybe I didn't provide you with enough details earlier on what size refrigerator I had.. sorry.
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Old 08-02-2018, 07:38 PM   #26
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Originally Posted by Roadtrek Adventuous RS1 View Post
My setup is the 160 watt panel and two AGM 6 volt batteries...in series..

I'm also running a 3.1 Dometic propane refrigerator...

Can any of you tell me if you think I have enough power to run the fridge and for how long?
Seems to be a lot of different answers here.. maybe I didn't provide you with enough details earlier on what size refrigerator I had.. sorry.
Did you miss booster's post? Your answers are there.

Bud
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Old 08-02-2018, 07:43 PM   #27
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Originally Posted by Roadtrek Adventuous RS1 View Post
My setup is the 160 watt panel and two AGM 6 volt batteries...in series..

I'm also running a 3.1 Dometic propane refrigerator...

Can any of you tell me if you think I have enough power to run the fridge and for how long?
Seems to be a lot of different answers here.. maybe I didn't provide you with enough details earlier on what size refrigerator I had.. sorry.

15 amps is what I have heard in the past for the absorption frigs on DC, so 15ah per hour of use. Two 6v batteries are usually in the 200ah range of capacity, or 160an usable. 10 hours of use would kill them totally dead assuming they were 100% full to start, which is very iffy with Roadtrek charging systems.


The solar would give a maximum, under good conditions of about 45ah per day, and only during the day would be putting out something like 8 amps during peak hours with great sun.


Realistically, you would be likely limited to 3-5 hours per day and then only for a day or two unless you ran the van engine a lot.



Also remember that absorption frigs don't cool well on DC, so it might not be any better than the propane at altitude.
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Old 08-02-2018, 07:52 PM   #28
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Thanks for the extremely helpful answer, booster. So does your system not make use of an inverter? Where my fridge currently sits it has 12v leads necessary to run the 12v heating element (mine is so old it doesn't have a board running an auto light, etc.). Unfortunately, PleasureWay insists there's no build manual available for consumer consumption (hard to believe on a RV like mine that's 20yrs old). Also are you running AGMs or Lithium? I assume the former since I've read that one of the advantages to Lithium was it's ability to charge faster. And, last, did you upgrade your alternator?

Again, thanks for the very helpful info. It IS much appreciated.

Glenn

We do have a big inverter, big alternator(s), 300 watts of solar, and a 440ah AGM battery bank, but for other reasons than just running the frig. We want longer off grid/no sun capability and with microwave and some other higher draw things being used.


For the frig you just need batteries and charging sources. In testing before we built the big system, we used 260ah of wet cells with 200 watts of solar, standard Chevy alternator with 80 amps to the coach, and a 40 amp shore charger. For 1-3 day stays, we were almost always just fine as long as we didn't run high load things like the surround sound system on the TV, that used 10+ amps. If we would have gotten low, an hour drive would give back a days use. We did get 3 days of rain and heavy shade once, and at 3 days were in need of a charge, but still a ways from dead.
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Old 08-02-2018, 10:02 PM   #29
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Booster: Perfect. Thanks for all of your information. It dawned on me that I read a thread on electrical where you and a few others were designing some type of split system where low AH lithium was used to top up AGM. How did that turn out? I got to the end of the first thread where you were going off to test it. Did a new thread start up after that?

thanks again.glenn
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Old 08-02-2018, 10:26 PM   #30
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Booster: Perfect. Thanks for all of your information. It dawned on me that I read a thread on electrical where you and a few others were designing some type of split system where low AH lithium was used to top up AGM. How did that turn out? I got to the end of the first thread where you were going off to test it. Did a new thread start up after that?

thanks again.glenn

Harry has a thread going on the hybrid system he put together, and by all accounts is working well. A couple of others are considering trying to do similar. He does have a thread going on his system.
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