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Help calculating battery count/capacity to run 1,400 BTU AC

Thread starter #1
Hello all, first post here. If all goes as planned I'll be getting a 27 or so ft sailboat shorty, and I'm going to try to cool the v berth with this small ac. The plan is to run it at night on battery power, so I can at least sleep at night and get out of the heat when I must during the Fl hottest months during the day to cool down as it runs on pretty much solar only. I'll be living on the boat. I do realize it's minimal, but all I need is just enough to get by for now and the v berth is very small. They also make a 2,500btu but I'll get figures on the small one first and go from there, as it may be worth moving up the the larger unit.

The unit, and specs are here:.....

https://cozywinters.com/shop/dog-ho...ze145deAtuQKRIIp3l7nshWV0bubUZ5xoCb6gQAvD_BwE

....and I'll also post the specs below.

I assume this thing will run continuous on say, 400W of solar panel in full sun but it would be nice to know as close as possible how many watts of solar it truly would take after all loss is figured in.

And of course I need to know what size (in normal deep cycle speak) and how many deep cycle batteries it will take to run the AC, say, 8rs constant.

In summary

1) How many watts to run it on panels only, draining nothing from the batteries, in full sun?

2 ) Mainly, how many/what capacity batteries to run AC 8hrs on nothing but battery? Then if you would comment, the best battery set up for my needs (cost matters) and maybe even the best place to buy the deep cycle batteries.

I have a Centech 2000w/4000peak inverter that should at least run that fine. Thanks so much for your help, as I have always been terrible at math, even dropped out of electronics because of that, and though I've tried, I just decided to settle with the fact, I need help for figures like this and appreciate any I can get here.


Details Specifications for the Dog House Air Conditioner Unit:

Cooling btu: 1,400
Cooling Capacity**: Ideal for up to 40 cu. ft. dog houses
Volts: 120 volts
Amps: 3
Watts Input: 350 watts
Thermostat: Adjusts from 32 to 90 degrees F
Controls: Covered On/off Switch
Unit Dimensions (unboxed): 9" x 8" x 13"
Weight (net): 27 Lbs.
Refrigerant: R-134A
Noise - Inside: less than 10 decibels
Noise - Outside: 65 decibels
Color: Off White
Cord Length: about 4 Feet
1 Year Limited Warranty
 
Thread starter #3
Depending on the efficiency of your inverter, you will use 30-45 A-hr of battery for each hour the A/C runs.
Thanks, very helpful/something I can understand. Do they measure the deep cycles in Amp hrs? Seems all I could find was CCAmps but maybe I just haven't looked enough, and how many AH's is say a mefium capacity and your normal higher capacity deep cycles?
 
#4
From https://marinebatteryguy.com/deep-cycle-battery/ :
"
Deep cycle batteries and amp hours
Most deep cycle batteries are rated in Amp hours (Ah) — a unit that measures the amount of energy the battery can supply over a long period. For example, a battery rated at 1Ah is capable of supplying a one amp current over a period of one hour.

Small deep cycle marine batteries usually have ratings of 25-50Ah, while larger batteries are usually rated at 100Ah.

While amp hours might seem like a measure of time, the actual amount of time a deep cycle battery can act as a power source depends on the current required by your trolling motor, or other electrical devices.

The greater the current, the faster the battery’s capacity will be depleted. This makes it vital to understand the amount of energy required by your trolling motor or electrical equipment before you select a deep cycle battery."

The first site I looked at listed *some* of the batteries with an A-hr rating: https://www.walmart.com/browse/auto-tires/marine-batteries/91083_1074765_1104292_9720644 .

Looks like they are available as large as 200 A-hr. A 200 A-hr battery would probably run your A/C for about 4 - 6 hrs, again depending on the efficiency of your inverter.

A CCA spec is pretty much useless for your application. And don't forget, as someone else mentioned, that you will need to recharge the battery between uses.
 
Thread starter #5
From https://marinebatteryguy.com/deep-cycle-battery/ :
"
Deep cycle batteries and amp hours
Most deep cycle batteries are rated in Amp hours (Ah) — a unit that measures the amount of energy the battery can supply over a long period. For example, a battery rated at 1Ah is capable of supplying a one amp current over a period of one hour.

Small deep cycle marine batteries usually have ratings of 25-50Ah, while larger batteries are usually rated at 100Ah.

While amp hours might seem like a measure of time, the actual amount of time a deep cycle battery can act as a power source depends on the current required by your trolling motor, or other electrical devices.

The greater the current, the faster the battery’s capacity will be depleted. This makes it vital to understand the amount of energy required by your trolling motor or electrical equipment before you select a deep cycle battery."

The first site I looked at listed *some* of the batteries with an A-hr rating: https://www.walmart.com/browse/auto-tires/marine-batteries/91083_1074765_1104292_9720644 .

Looks like they are available as large as 200 A-hr. A 200 A-hr battery would probably run your A/C for about 4 - 6 hrs, again depending on the efficiency of your inverter.

A CCA spec is pretty much useless for your application. And don't forget, as someone else mentioned, that you will need to recharge the battery between uses.
Thanks so much, that get's me at least into an area where I can get some basic estimates on price...looking into the links now.
 
Thread starter #6
Looks like Walmart might be the way to go, and as one might think, that weight moves right up with the capacity so 100AH would be the max I'd want to go @ 100lbs. The beauty of it is, I can go with a couple, try it and always add on.

Just as example and I can take it from there, can you please tell me how long it would take a single 100w solar panel to charge a 100AH battery at optimal conditions? What are we discharging to? 50%? so whatever is best on that for the calculation.
 

JonSea

Well-Known Member
#7
One consideration: when using an invertor, you must consider VA (volt-amps) instead of Watts. VA adds the inefficieny of power factor, which can be crap for a small AC motor.

For example, I think our furnance blower motor is 1/2 HP, which corresponds to 373 watts. [Memory aid: watts per HP = (year Columbus Discovered America)/2 = 1492/2 = 746] But that 373 watts draws near the full load of 1100 VA from our invertor! That's nearly 50 amps from our 24 volt battery bank.
 
Thread starter #8
One consideration: when using an invertor, you must consider VA (volt-amps) instead of Watts. VA adds the inefficieny of power factor, which can be crap for a small AC motor.

For example, I think our furnance blower motor is 1/2 HP, which corresponds to 373 watts. [Memory aid: watts per HP = (year Columbus Discovered America)/2 = 1492/2 = 746] But that 373 watts draws near the full load of 1100 VA from our invertor! That's nearly 50 amps from our 24 volt battery bank.
That's a bunch, and something real world there to compare...thank you.. I need at least a couple hundred AH, even if I go with no AC at all, so I think I'm just going to get two for the moment, and play around with them and 3 or 400w worth of solar to get some real world specs on this. Then I can just multiply....done deal. Can't beat hands on.

Not sure what you paid for your batteries, but the link seems like a pretty good deal, right to my door from Amazon. The ratings seem pretty good as well. and it actually makes sense that would be one of the best, shipped prices, so unless someone knows of a better deal, that's what I'm going with.

https://www.amazon.com/Universal-Po...ep+cycle+marine+battery+100ah#customerReviews

I doubt all the work to find them for less would be worth the trouble, so I'll probably go with a couple of those for now and if I get a line on anything cheaper fine, I haven't already invested in many.
 
Last edited:

JonSea

Well-Known Member
#9
We ended up with four 6 volt golf cart batteries with we got at Sam's Club as I recall. I don't remember what the ratings on. We use the inverter system in our house to provide a little run time on the furnace and for the small current drain of the tankless gas water heater during power failures. It may be dark and cold, but we can take hot showers! ;)
 
Thread starter #10
We ended up with four 6 volt golf cart batteries with we got at Sam's Club as I recall. I don't remember what the ratings on. We use the inverter system in our house to provide a little run time on the furnace and for the small current drain of the tankless gas water heater during power failures. It may be dark and cold, but we can take hot showers! ;)
And that's worth a heck of a lot. :)

I have heard of those from Sam's, and that golf cart batteries are a good option for solar for some reason....
 
Thread starter #12
OK they do have some specs there, just need to figure out what they mean. Anyone else want to take a crack at these specs, and tell me what the basic AH's are for it?

Specifications
  • 20 amp hour rate: 230
  • 5 amp hour rate:174
  • 6 amp hour rate: 178
  • Battery electrolyte composition: acid
  • Battery end type: top post
  • Battery purpose: deep cycle
  • BCI group size: GC2
  • Freight class: 65
  • Minutes at 25 amps: 448
  • Minutes at 75 amps: 120
  • Terminal type: DIN
  • Volts: six
 

ChrisP58

Well-Known Member
#13
Unless otherwise specified, you generally assume the ampacity is specified at a 20 hour discharge rate. That means that you are using all of the charge in 20 hours.

If you spread it out over more than 20 hours, you'll get more than the specified amp hours. Less than 20 hours, you'll get less than the specified amp hours.

But the curve is not linear, so you need to look at the datasheet of the actual battery to know what that batteries performance at different load currents will be.
 
Thread starter #14
Unless otherwise specified, you generally assume the ampacity is specified at a 20 hour discharge rate. That means that you are using all of the charge in 20 hours.

If you spread it out over more than 20 hours, you'll get more than the specified amp hours. Less than 20 hours, you'll get less than the specified amp hours.

But the curve is not linear, so you need to look at the datasheet of the actual battery to know what that batteries performance at different load currents will be.
OK, very helpful, Thank you for the explanation.
 

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