24hr A/C runtime on batteries - how to do it?

[markopolo]

Some interesting info came up in the topic "What is your solar controller telling you?" topic yesterday.

Jim from Roadtrek wants to greatly extend the off grid air conditioner run-time in a new Roadtrek.

Originally Posted by gerrym51

....... Jim Hammill is now offering something called the 'warp core option package' on a CS. I thought he was kidding at first but now he seems serious. 24 hours of air conditioning..................

Here's the link: https://www.facebook.com/groups/road...7105083115144/

This is exciting stuff. And, a lot of fun for anyone on the development team at Roadtrek.

So, can they do it and if so how will they do it?

The runtime part is the easiest bit to accomplish from a tech point of view. You just need enough power stored in batteries. Sounds simple enough but immediately you have start thinking about where to put the batteries and the added weight etc. Cost has to be considered also.

The hard part (I think) is being able to recharge that battery bank fast enough to be useable again quickly.

A much larger battery bank than the E-Trek might actually prove to be a tremendous advantage. Think of wind turbine farms. There are times when they produce excess power. Our RV's can do that also (think alternator - not wind) when you are driving around. It would be ideal to be store any not-needed-now power that is being efficiently generated. A really high capacity battery bank would take advantage of that by storing that excess power. Traditional wet cell batteries would not be a good choice because they periodically need to fully charged and need to be stored near full charge. Lithium Iron Phosphate would seem to be a better choice.

Victron Energy highlights this advantage of Lithium Iron Phosphate over lead-acid batteries in their "Why lithium-iron phosphate?" brochure.

A LFP battery does not need to be fully charged. Service life even slightly improves in case of partial charge instead of a full charge. This is a major advantage of LFP compared to lead-acid.

I'm hoping there's enough interest for Roadtrek to proceed with this idea. E-trek 2.0

[gerrym51]

since this is a conjecture thread-i think it should be thought out from a different perspective.

If batteries-of any kind-are going to be used-you have the obstacle of weight. even lithium batteries are going to weigh something.

right now i only see the dual rear wheeled sprinter van with a gvwr of 11030 as a van-we are talking vans here- that can handle the weight-whatever it is.

as far as the future-the highest gvwr transit van i could build at Fords website was a gvwr of 10,300. I don't know if it would have enough capacity for this.

[markopolo]

That's a good way to start - how many batteries? What would they weigh? How much space would they need?

15 amps AC at 120v is 1800 watts. It's a whopping 150 amps DC at 12v (75 amps at 24v). 24 hours x 150 amps x duty cycle average

Too many unknowns
But we can guess

24 hours x 150 amps x 50% = 1800 amp hrs
Assume 80% max discharge: 1800/80% = 2250 ah capacity battery bank (at 12v).

Here's a 2000AH 12v battery http://en.winston-battery.com/index.php ... ory_id=176
It weighs approx 350 lbs - probably 1/3 of what equivalent lead acid batteries would weigh.
Size: 23" x 21" x 16" (Onan 2800 is 22" x 16.3" 12.8")

[Davydd]

That whole thread seemed weird. How do you get 1500 watts of solar on a Class B roof? Advanced RV was looking at 600 watts tops I think. As far as li-ion batteries go they could pack quite a few in considering they are already installing as many as 8 AGMs and li-ion are about a third in weight. Heck, that means 24. Anyway, it seems physically way too much so I have to suspect they are looking at something other than batteries. A different power system other than generator? Then, who in the world would want a Class B and sit in it 24/7 enclosed with air conditioning or even need to?

BTW, not that I need to, but having at least 4 li-ion batteries and maybe 300 watts of solar is going to save me probably 500-600 lbs in weight versus what I presently have in an Onan generator, propane system and tank, and two lead-acid batteries. All I want is full use of my appliances and AC outlets while dry camped along with a short stop over air conditioning run, and no need to have an electrical hookup campsite as long as I continue my touring driving habits.

[markopolo]

I don't know if they'll pursue the 1500 watts solar idea but they'll probably try to max it out balancing cost and ease of use for the end user. It gets a bit trickier to implement with li-ion batteries because the data indicates they store better with less than full charge. Solar controllers will want to / try to keep the batteries full.

[gerrym51]

Originally Posted by Davydd

That whole thread seemed weird. How do you get 1500 watts of solar on a Class B roof? Advanced RV was looking at 600 watts tops I think. As far as li-ion batteries go they could pack quite a few in considering they are already installing as many as 8 AGMs and li-ion are about a third in weight. Heck, that means 24. Anyway, it seems physically way too much so I have to suspect they are looking at something other than batteries. A different power system other than generator? Then, who in the world would want a Class B and sit in it 24/7 enclosed with air conditioning or even need to?

BTW, not that I need to, but having at least 4 li-ion batteries and maybe 300 watts of solar is going to save me probably 500-600 lbs in weight versus what I presently have in an Onan generator, propane system and tank, and two lead-acid batteries. All I want is full use of my appliances and AC outlets while dry camped along with a short stop over air conditioning run, and no need to have an electrical hookup campsite as long as I continue my touring driving habits.

Davydd-you are a very experienced b traveler. you know what to do and when to do it. you make your travel with the seasons and avoid high temp situations-in effect you have limitations-either physical plant wise or self decided.

Some of us want no limitations-that's the bling of the thing-even if we will rarely need to actually use. you say potato-we say yowza.

[gerrym51]

Originally Posted by markopolo

That's a good way to start - how many batteries? What would they weigh? How much space would they need?

15 amps AC at 120v is 1800 watts. It's a whopping 150 amps DC at 12v (75 amps at 24v). 24 hours x 150 amps x duty cycle average

Too many unknowns
But we can guess

24 hours x 150 amps x 50% = 1800 amp hrs
Assume 80% max discharge: 1800/80% = 2250 ah capacity battery bank (at 12v).

Here's a 2000AH 12v battery http://en.winston-battery.com/index.php ... ory_id=176
It weighs approx 350 lbs - probably 1/3 of what equivalent lead acid batteries would weigh.
Size: 23" x 21" x 16" (Onan 2800 is 22" x 16.3" 12.8")

Mama Mia-thats a really big battery.


Just an update-Jim Hammill said this morning at the roadtrekking website that he would NOT be adding anymore AGM's for this. since he specifically chose the word AGM i'm deducing lithium.

[markopolo]

Pricing sure has dropped on Lithium Iron Phosphate Batteries. $1 per ah
1000 Amp Hour Lithium Iron Phosphate $1000.
http://www.balqon.com/store-2/#!/~/p...91&id=11905253

Put three of those in your van ..............

[Davydd]

Originally Posted by markopolo

That's a good way to start - how many batteries? What would they weigh? How much space would they need?

15 amps AC at 120v is 1800 watts. It's a whopping 150 amps DC at 12v (75 amps at 24v). 24 hours x 150 amps x duty cycle average

Too many unknowns
But we can guess

24 hours x 150 amps x 50% = 1800 amp hrs
Assume 80% max discharge: 1800/80% = 2250 ah capacity battery bank (at 12v).

Here's a 2000AH 12v battery http://en.winston-battery.com/index.php ... ory_id=176
It weighs approx 350 lbs - probably 1/3 of what equivalent lead acid batteries would weigh.
Size: 23" x 21" x 16" (Onan 2800 is 22" x 16.3" 12.8")

I believe the height would prevent it from fitting under the floor of a Sprinter like the Onan generator. It is slightly deeper than a diesel Onan which is why no one is putting one in.

[Davydd]

Originally Posted by gerrym51

Davydd-you are a very experienced b traveler. you know what to do and when to do it. you make your travel with the seasons and avoid high temp situations-in effect you have limitations-either physical plant wise or self decided.

Some of us want no limitations-that's the bling of the thing-even if we will rarely need to actually use. you say potato-we say yowza.

Does it matter? I mean c'mon, who in there right mind would want 24/7 air conditioning in a Class B? If you are that anal to need to sit inside with a noisy air conditioner all the time then you are better suited to park at a KOA with an electrical hookup.

BTW, I noticed Hammil also said the whole system would be in a sealed box that the owner would not have access to to protect the proprietary idea I guess. Would you agree to such a deal?

[markopolo]

I don't know if anyone would actually need to run the A/C for 24hrs but the ability to do it eliminates any concerns a prospective E-Trek buyer might have about whether there is enough A/C run-time in that model. I hope they get to build one.

[gerrym51]

Originally Posted by Davydd

Does it matter? I mean c'mon, who in there right mind would want 24/7 air conditioning in a Class B? If you are that anal to need to sit inside with a noisy air conditioner all the time then you are better suited to park at a KOA with an electrical hookup.

BTW, I noticed Hammil also said the whole system would be in a sealed box that the owner would not have access to to protect the proprietary idea I guess. Would you agree to such a deal?

Davydd- i believe you are getting testy. this from a man who is spending a lot of money on a van to replace another van he just bought 3 years ago..the van you are selling is better than most out there already. Why not the E-trek concept for us the Alvar concept for you.

[markopolo]

Picking a new B van now would be difficult - so many choices. And, it seems like we're near the point where things like lithium batteries with mega amp hours will be the standard choice.

[gerrym51]

Markco-for your information-Jim Hammill has removed this post which also seemed to eliminate all responses to it.

[markopolo]

Maybe he found a buyer It probably gives us an idea of what they might do next.

This topic can continue. It would be fun to figure out what it would take to recharge a 2,000 or 3,000 ah battery bank.

[gerrym51]

Originally Posted by markopolo

Maybe he found a buyer It probably gives us an idea of what they might do next.

This topic can continue. It would be fun to figure out what it would take to recharge a 2,000 or 3,000 ah battery bank.

he posted another post. said he did not know what happened to the first one but that he has a buyer and will build it. good practice for us in the future

[Davydd]

He found a buyer to build it. A new thread was started. But like I said before, if you read the original thread, the system would be in a sealed box that only Roadtrek would service and it was implied even the owner would not know. It has got a lot of discussion going.

Why not the E-trek concept for Alvar? Simple. I've analyzed my needs and am balancing my systems to hopefully meet those needs that I think I have stated very clearly. Want to read them again? Sure I could add more and I can afford more. I could easily double my solar and double my planned batteries (all under floor) with the known stuff available and not sacrifice my interior design. But what would I achieve? I don't have a decade of history to remotely justify it.

[gerrym51]

Originally Posted by Davydd

He found a buyer to build it. A new thread was started. But like I said before, if you read the original thread, the system would be in a sealed box that only Roadtrek would service and it was implied even the owner would not know. It has got a lot of discussion going.

Why not the E-trek concept for Alvar? Simple. I've analyzed my needs and am balancing my systems to hopefully meet those needs that I think I have stated very clearly. Want to read them again? Sure I could add more and I can afford more. I could easily double my solar and double my planned batteries (all under floor) with the known stuff available and not sacrifice my interior design. But what would I achieve? I don't have a decade of history to remotely justify it.

Davydd-no one said you should make Alvar an e-trek. your the one criticizing OUR desire to have an E-trek type van. you got yours we want ours.

[booster]

Originally Posted by markopolo

I don't know if they'll pursue the 1500 watts solar idea but they'll probably try to max it out balancing cost and ease of use for the end user. It gets a bit trickier to implement with li-ion batteries because the data indicates they store better with less than full charge. Solar controllers will want to / try to keep the batteries full.

I think that having a huge solar array and lithium might tend to work out very well if set up right. I think the big weakness in solar right now is that it is very hard to get your batteries as full as the really should be for longest life, regularly, because the last 5% of charge takes a long time, and all you have is daylight time. The lithium likes to cycle in the middle of the state of charge range, and that is also where the solar does the best job of providing maximum output, so you get a win/win on that part.

Marko's concern about the solar filling the batteries to full all the time is a very valid point, and with a big solar system, it could very very easily happen, especially when the van is sitting between trips. Two things could be done to, I think, to totally eliminate the issue.

1. Use a solar controller that goes to float based on ending amps, and set the ending amps much higher than actual full charge ending amps. The charge amps taper as the battery fills, so you could pick any state of charge you wanted to have the charger stop charging. This feature is already in the better solar chargers.

2. Have the solar controller not even come on if the batteries are over 90% full. I don't know if this feature is available in current products, but would be easy to do on the units that have built in battery monitors.

As a sidelight to this. You would also need your shore charger and engine alternator charging to do the same thing, especially the alternator which can very easily overcharge any batteries.

[Davydd]

How can they get 1500 watts of solar on a Class B? Can anyone speculate? Here is what I believe is 500 watts of solar on an extended body Sprinter - Advanced RV's Mzungu.