Amps oh my

Clean1

Observer
Alright so I've been lurking on this forum for awhile now getting ideas for my own build out and I was hoping some of you knowledgable, kind folks could help me out. I have a new long wheel base, medium roof transit van that I am going to outfit for travel with my wife and dog to central and south america at the beginning of next year. My questions are in regard to the electrical requirements and loads. I am trying to find an Air conditioner that I can run off the battery bank (600ah) for a couple hours. There will be places I will go where one cannot simply take ones dog or wife, and they will need to be in comfort while I/we are away. I have looked a several roof top units, for example:

Coleman Mach 3 P.S
13,500 BTU
Full load cooling is approximately 12amps
Lock rotor amps approx. 58 (I do not know how to figure this in)

Now if I am gone for 4 hours and the a/c has been running the entire time 12amps x 4 hours=48amps. Correct? I have come to understand that there will be a loss
of energy from converting the d/c battery power to a/c for the air conditioner. I am not sure what that is and it probably varies but lets say its an additional 4 amps. Thats 52 amps plus whatever else is running like a fridge 3amps per hour (4)=12 amps so now we are at 64 amps for the 4 hour period. Now the solar gains
lets say 2 panels (Renogy 100W Poly panel) provides 5.5 amps per panel =11 amps per hour x 4hours= 44amps.
A/C load 52 amps
additional loads 12 amps
Total Amps load for 4 hours= 64 amps
Solar panels provide 44 amps (hopefully)
Total amps used for 4 hours 20 amps

With a 600ah AGM battery bank that can be dropped to 50% this does not seem like a huge load on the batteries. Charging would be handled by generator and or
inverter to battery charger provided by the van later that evening. I feel obviously I am missing something because it would seem to work ok. Could someone
please politely plumb me up and steer me in the correct direction? Thank you!
 

Bbasso

Expedition Leader
From my little experience and little time with my single renogy 100 watt panel the most I've ever seen it put out so far is 5 amps and that's when the sun is directly over head...
And from all the reading I've done on this forum alone, depleting your batteries that much would take at least 24 hours to properly recharge them off of a generator or grid tie in.
I would strongly consider having a generator to run the AC for the few hours your puppy needs to sit in the van with AC on. I've been researching and reading about solar powered on for a long time finally pulled the trigger myself but it has limitations. More panels would allow you to charge your battery faster, more panels won't let the battery drop so much but in the end a rooftop air conditioner or any a/c will draw too much unless you have a ridiculous amount size battery storage.
I know south America and Central America are very humid places but have you considered a swamp cooler to keep it more comfortable?
 

IdaSHO

IDACAMPER
Maybe Im missing something.... but my quick google search about the Coleman Mach 3 P.S shows that it is a 110V unit. NOT 12v

The Coleman Mach 3 P.S is listed as roughly 13000 watts.

13000 watts / 110 V = 11.8 AMPS

13000 watts / 12 V = 108 AMPS


:Wow1:
 

Clean1

Observer
Hey Bbasso,
Thanks for the prompt reply, I am not exactly sure why the batteries would take 24 hours to properly recharge and if they did would that be such a bad thing? I apologize if my
questions are way off but I am just trying to understand how and why of these systems. I am not sure why the batteries have to be fully charged all the time. I understand that
the batteries like to be in a fully charged condition but if they were discharged 10% for a couple days does it really matter? Ultimately are the batteries ever 100% charged? There will always be some kind of drain like the refrigerator or computer etc. I guess it ultimately could have an effect on the long term life of the batteries but I do not think it would cut the life cycle in half or anything. I haven't looked into the swamp cooler yet but definitely would if you had any suggestions. Thanks again for the help.
 

zelatore

Explorer
Doesn't that unit run on AC, not DC? At least the spec sheet I found on-line shows it being 110VAC, which is what I would expect based on aircon units I deal with in the marine world.
.
While it is possible to run an aircon from 12v, it's really not feasible. Right now I have a client who had another shop set up an inverter to power his aircon in a 34' boat - and just as I predicted it's been nothing but trouble.
.
I'll second the above opinion - you want a gen to run aircon.

(beat to the punch!)
 

Clean1

Observer
Maybe Im missing something.... but my quick google search about the Coleman Mach 3 P.S shows that it is a 110V unit. NOT 12v

The Coleman Mach 3 P.S is listed as roughly 13000 watts.

13000 watts / 110 V = 11.8 AMPS

13000 watts / 12 V = 108 AMPS


:Wow1:
This is what I came up with for the 13,500 BTU, If I'm missing something please help me out.
Thanks!

unning Watts (cooling) Desert Condition (100 F. DB 72 F. WB Indoor, 120F. DB Outdoor) 1440
 

Clean1

Observer
Doesn't that unit run on AC, not DC? At least the spec sheet I found on-line shows it being 110VAC, which is what I would expect based on aircon units I deal with in the marine world.
.
While it is possible to run an aircon from 12v, it's really not feasible. Right now I have a client who had another shop set up an inverter to power his aircon in a 34' boat - and just as I predicted it's been nothing but trouble.
.
I'll second the above opinion - you want a gen to run aircon.

(beat to the punch!)

Is it not possible to convert AC to DC? And I am not looking to run the air conditioner all day just a couple hours when I am away from the van.
Thanks for your input.
 

Darwin

Explorer
Seems much simpler to just run a smaller AC off a 2000 watt genny. How much does 600 ah agm batteries weigh? Will it leave much room for you take your personal belongings with you? You need to charge the batteries back to above full is how I understand it if you want to maximize battery life, and 6 agms are expensive, the only way to do that would be to run the generator or car engine for at least 24 hours, just to replenish 4 hours of airconditioner run time? Doesn't make much sense to me but others here know way more than me about batteries and electrical. RVnet is also a good source, some real battery and electric gurus there.
 

DiploStrat

Expedition Leader
Some Numbers

IdaSHO and I don't always agree, but his numbers are correct; you are grossly underestimating the draw of your air conditioner, by a factor of about 10. You are looking at the numbers for 110v operation. 12v operation will be at least 10x + about 15% inverter loss.

My Tiger has a 6,000 BTU Sharp air conditioner, a 2800w inverter, and 600Ah of batteries.

With the compressor running it draws about 60A at the inverter, with losses, call it 70A from the batteries. Starting surge is generally guesstimated at 5x the run, so call it 300A for two seconds.

How long does the compressor run? Depends on the outside temperature and the temperature inside the camper. When it is 90-100F outside, you can count on the compressor running all the time, so 300Ah usable divided by 70 = just over four hours of air conditioner run.

My solar panels will produce between 20 and 30A per hour, depending on the temperature. With MPPRT you get less current when the panels are really hot, so call it 25A maximum.

The means that the air conditioner is:

-- Great for keeping the camper, and the cat, cool for a two hour lunch break.

-- Fine for keeping the camper cool on long drives in really hot weather. (Assuming that you have the same heavy duty wiring between your starter batteries and your camper batteries that I do.)

-- Reasonable for cooling the camper down between 6PM and 9PM, especially if you ran it for the last part of the drive.

-- REALLY dubious for cooling the camper all night.

It really comes down to the duty cycle of your compressor.

Starting a 13k BTU Coleman is probably impossible without an inverter of at least 6kW and some form of soft start capacitor. Beyond that, I doubt that your Transit can carry 600Ah of AGM battery; Lithium, perhaps. And finally, where are you planning to go in LatAm that you can't take your wife or dog? THAT fascinates me.
 
Last edited:

LeishaShannon

Adventurer
Can you mount something like this on the rear bumper? https://www.mhiaa.com.au/index.php/products/wall-splits?view=products&layout=default&id=96

Its the second most energy efficient AC available and draws just 350W running flat out. We have 300Ah @ 24v of Lithium / 1600W of solar and can run ours 24/7 provided its reasonably sunny.

All RV air conditioners are terribly inefficient and next to impossible to use for any length of time from solar alone. The systems made for houses use much better technology and are 2-3 times as efficient, the problem is working out how to mount them to a vehicle...
 

zelatore

Explorer
Diplostrat summed up the numbers pretty well. Yes, it's technically possible to run an aircon from a large inverter and battery bank. No, it's not really feasible in practice. I would think it would be much preferable to have a small gen to power the aircon (the Honda and Yamaha portables are extremely quiet and light) and charge batteries when the truck is parked. You could then reduce your house bank to a more manageable size, use a smaller inverter just to run the odd item you want regularly w/o the gen on, and even downsize the solar since you'd have the gen to provide charging if needed.
 

Bbasso

Expedition Leader
By no means am I an expert or even knowledgeable but common sense would tell me the 24 hours of running a generator cost alone will be more than 3 or 4 hours you would need to just run a generator to keep the air conditioning on.
As for Batteries being fully charged all the time.... that's almost what you want in my opinion, the solar panels keep the battery is topped off and then when you have a large drain such as a coffee maker or toaster that temporarily pulls down the batteries the solar system can restore that power quickly and efficiently.

I honestly would love to have 3 - 600 amp hour batteries for storage, my 100 watt panel what have a hard restoring or should I say replacing the batteries back to 100% but then again my needs are minimum. The reason why I would like to have such a large battery bank is so I can go to 3 possibly 4 days in a cloudy or rainy environment and still be able to charge one of the many gadgets or turn the lights on.

And yes everybody is correct a Coleman or any other rooftop air conditioner for rv does run on 110. of course you can use an inverter to swap it over from DC but as mentioned before you're taking a loss on power there so back to the point of running air conditioning I would just get a Honda 2000 or similar generator for the time needed. That's what I plan on doing down the road.
 

AMBOT

Adventurer
The mitsu Mini-Split AC units I've seen are only available in 240V. I will be able to give you some feedback on cooling with a 9000 btu Friedrich mini split in 2 weeks. I have 185 usable AH on my battery bank, 480W of solar, dual alternators, and 2 Yamaha 2000 generators.

While I expect to use the generator the majority of the time I will test out battery draw and see how much usable time I get. I have not seen other units that feature a 115V inverter compressor so I'm hoping that it offers less startup draw and more run time. I'm hoping the generator will run in ECO.
 

228B

Observer
.
The only way one can have a working 12V air conditioning system is with a BIG, HEAVY battery bank... and an internal-combustion generator to recharge it. The photovoltaic componentry requirements alone would smother your two-axle rig, and serve as a ridiculous sign of ostentation in the third world that no tourist with any degree of prudence would willingly display.
 

Haf-E

Expedition Leader
.
The only way one can have a working 12V air conditioning system is with a BIG, HEAVY battery bank... and an internal-combustion generator to recharge it. The photovoltaic componentry requirements alone would smother your two-axle rig, and serve as a ridiculous sign of ostentation in the third world that no tourist with any degree of prudence would willingly display.

I don't think its impossible or that it would require a PV array that is ostentatious - just need to keep the size of the PV array a small as the roof top (then its harder to notice), insulate the van well, use a small but super efficient AC unit, limit the amount of glass windows and use curtains to block off the front area which has the most glass for heat gain. A heavy, full height curtain right behind the driver/passenger seats is useful to reduce the amount of area required to be cool and also helps block people from viewing into the back area when parked.

The other question I have is if its not safe to take the wife and dog is it safe to leave them with the van alone then?
 

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