How long can you run AC from batteries?

[VanFan]

Originally Posted by Winston

We use the Nations/Balmar pair to charge 500ah of lithium in a ProMaster setting. The disadvantage of the Nations 'kit' in the ProMaster is that it's very low . . . and subject to damage if one takes their off-roading too far. (And, of course, the notorious radiator hose 'cutting').

We also have the Nations kit in a Promaster, and the last time we took it out we experienced what you're probably referring to as radiator hose "cutting." We've added a skid plate to protect the alternator, but it flexed a bit when we hit a low spot at a dip in the road doing about 30 mph, and the plate pressed the radiator hose against the metal fitting where it connects to the lower radiator pipe, cutting through the rubber and resulting in a leak. However, upon carefully reviewing the installation instructions I realized the lower radiator pipe could be raised to get the hose connection slightly higher than the bottom of the alternator. Hopefully that will keep it from happening again. I'll try to upload a pair of photos showing the incorrect installation, and the way it ought to be. Never uploaded a file here before, so wish me luck...

[tex4judy]

James at Fit RV also reported road related damage to his secondary alternator on their ProMaster. My memory of his pictures left me with the impression that the ProMaster was a little different from the bare bones "stock" model that we purchased from a Mercedes dealer. When installed on our rig, the bottom of the Nations (secondary) alternator was a little higher than the black plastic skirt at the front of the rig. We mounted a small bracket and then bolted a piece of high density polyethylene sheeting below the alternator - from the front skirt and then covering the 4-0 cables past the cross member. I think I've attached some photos to this post

[Eraygunz]

I have four Trojan batteries in my RT.
And a small window type unit.
I can only get a couple of hours of run time max.
The math says it should run longer? But , thats what I get.
Eddie

[Dogman]

wow, I can say I have read this most informative POST. But have as yet read the answer to the main question. Now as for my two cents it has been stated the Galleria Li3 battery will last for up to 8-hours before recharging. So the question is, "what all" can you keep running while you sleep. Refrigerator, C-PAP, AC and WHAT MORE? or is this limited as well? Now another question is are there larger battery packs over the standard pack?

[booster]

Originally Posted by Dogman

wow, I can say I have read this most informative POST. But have as yet read the answer to the main question. Now as for my two cents it has been stated the Galleria Li3 battery will last for up to 8-hours before recharging. So the question is, "what all" can you keep running while you sleep. Refrigerator, C-PAP, AC and WHAT MORE? or is this limited as well? Now another question is are there larger battery packs over the standard pack?

On a large system like the Li3 you should be able to run most everything else all night if the AC isn't running, but if the AC is used, it could get dicey overnight. The AC will certainly always be the major determiner of run time on the batteries, as the other stuff is tiny by comparison.



Of course, all of these run times assume totally full batteries when you start the times. If you have run you AC all day and not full recharged, you aren't going to have anything left for the night.

[BBQ]

Originally Posted by Dogman

wow, I can say I have read this most informative POST. But have as yet read the answer to the main question. Now as for my two cents it has been stated the Galleria Li3 battery will last for up to 8-hours before recharging. So the question is, "what all" can you keep running while you sleep. Refrigerator, C-PAP, AC and WHAT MORE? or is this limited as well? Now another question is are there larger battery packs over the standard pack?

The Refrigerator, C-PAP, computer, cellphone, fan, use very little power.
(comparatively speaking, of course)

[Phoebe3]

Would this be a good equation?

Total number of combined battery AHs

MINUS 20% (battery reserve)

MINUS 15% (inverter power "cost")

DIVIDED by 120 (just 'cause that's how it works out)

EQUALS number of hours of AC

Example:

Starting with 400 AH of battery

MINUS the 20% you want to leave in reserve = 320 AHs

MINUS 15% inverter "cost" = 272 AHs

DIVIDED by 120 = 2.27 hours of AC use


Does that seem to be verifiable from those of you with real world experience?

[cruising7388]

Originally Posted by Phoebe3

Would this be a good equation?

Total number of combined battery AHs

MINUS 20% (battery reserve)

MINUS 15% (inverter power "cost")

DIVIDED by 120 (just 'cause that's how it works out)

EQUALS number of hours of AC

Example:

Starting with 400 AH of battery

MINUS the 20% you want to leave in reserve = 320 AHs

MINUS 15% inverter "cost" = 272 AHs

DIVIDED by 120 = 2.27 hours of AC use


Does that seem to be verifiable from those of you with real world experience?

A couple of things.

1. Most inverters operate at their peak efficiency at close to their maximum rating which is typically the case if running an AC so I would assign an efficiency loss of nearer 10% than 15% which would improve the computed run time.

2. AGM battery discharge capacity time can be skewed by the Peukert effect which says that as the discharge rate is increased the practical ah available decreases. For example, a 100 amp hour battery will pretty much provide one amp for 100 hours, but it won't provide 100 amps for one hour. It will be substantially less. Under the load conditions cited this will decrease the computed run time.

[Phoebe3]

Originally Posted by cruising7388

A couple of things.

1. Most inverters operate at their peak efficiency at close to their maximum rating which is typically the case if running an AC so I would assign an efficiency loss of nearer 10% than 15% which would improve the computed run time.

2. AGM battery discharge capacity time can be skewed by the Peukert effect which says that as the discharge rate is increased the practical ah available decreases. For example, a 100 amp hour battery will pretty much provide one amp for 100 hours, but it won't provide 100 amps for one hour. It will be substantially less. Under the load conditions cited this will decrease the computed run time.

I was kind of basing that final divisor on a comment in an earlier thread from, I think, MarkoPolo or Avanti or ? that s/he had 400 AH of AGM and could get about 2 hours of AC from it. But I didn't think it was perfectly scale-able. that is, I didn't think you could get 1 hour from 200 AHs or 4 hours from 800 AHs, but maybe you can - would certainly be an easier equation...

[cruising7388]

Originally Posted by Phoebe3

I was kind of basing that final divisor on a comment in an earlier thread from, I think, MarkoPolo or Avanti or ? that s/he had 400 AH of AGM and could get about 2 hours of AC from it. But I didn't think it was perfectly scale-able. that is, I didn't think you could get 1 hour from 200 AHs or 4 hours from 800 AHs, but maybe you can - would certainly be an easier equation...

Correct. Although the theoretical ah capacity is fixed, the actual ah capable of being delivered is dependent on the rate of discharge. But beyond that I have no idea how to quantify it for the table and whether even that figure might vary with different battery manufacturers.

The other factor that has to be thrown into the equation is the battery state of charge at the outset. As Booster et al has pointed out, assuming a 100% charged state at the beginning of the exercise is optimistic.

But in any event, your table does indicate that for typical conditions requiring the operation of the roof AC, it's unlikely that it can support an AC for eight hours with 400, 600 or even 800 ah unless the compressor duty cycle is fairly low.

[Bud]

The subject here is about a/c with batteries.

The question has been answered if someone wants to read this thread.

Bud

[cruising7388]

Originally Posted by Bud

The subject here is about a/c with batteries.

The question has been answered if someone wants to read this thread.

Bud

And your point is?

[Bud]

Originally Posted by cruising7388

And your point is?

Maybe just a reminder about the what this Thread is about:

"How long can you run AC from batteries?"

Bud

[BBQ]

.

People talk.
People talk about anything and everything.
People repeat themselves.
People go off-topic.
A forum is like a party.
Have fun.
If you got bored, take a break, go get a drink.
When you come back, the conversation will be different.
Or, you can always join another crowd.

[cruising7388]

Originally Posted by Bud

Maybe just a reminder about the what this Thread is about:

"How long can you run AC from batteries?"

Bud

The posts seem mostly on topic to me. Where do you think it's gone adrift?

Anyway, FWIW, some of the most illuminating posts I've read in general in the forum are on threads that veered from their original track.

[Bud]

BBQ, cruising, agree with what you have written above.

I thought back and realized this morning that I must have been in An Altered State of Mind. I'm sticking with that until I come up with a better excuse.

I have not gone back and scanned the thread to try recall what prompted the post. I may later. Thanking you both for the feedback.

Bud

[BBQ]

Originally Posted by Bud

BBQ, cruising, agree with what you have written above.

I thought back and realized this morning that I must have been in An Altered State of Mind. I'm sticking with that until I come up with a better excuse.

I have not gone back and scanned the thread to try recall what prompted the post. I may later. Thanking you both for the feedback.

Bud

No problem . . . All is good. Enjoy. Have fun.

[Phoebe3]

This question seems to come up all the time, which is why I asked here on the forum. After reading all the responses, I think the short, back-of-the-envelope answer is that you can run a typical rooftop AC for approximately 20-40 minutes per fully charged 100 AH battery. The primary variables being insulation and ambient temperature since the compressor will run a lot more if you are trying to keep the interior temp of a poorly-insulated van 40* below ambient than if you are trying to keep a well-insulated van 10* below ambient.

[booster]

Originally Posted by Phoebe3

This question seems to come up all the time, which is why I asked here on the forum. After reading all the responses, I think the short, back-of-the-envelope answer is that you can run a typical rooftop AC for approximately 20-40 minutes per fully charged 100 AH battery. The primary variables being insulation and ambient temperature since the compressor will run a lot more if you are trying to keep the interior temp of a poorly-insulated van 40* below ambient than if you are trying to keep a well-insulated van 10* below ambient.

Your time per 100ah is likely pretty close for most instances, but the caveat is that to get the AC to run at all, you would need at least two 100ah batteries, and in that case you would also likely get some amount less than your estimate due to low voltage cutout of the inverter with fewer batteries to feed it. Personally, I think the minimum if you plan on running AC off the batteries, even for fairly short times, would be about 400ah of AGM battery bank.

[avanti]

Originally Posted by booster

Your time per 100ah is likely pretty close for most instances, but the caveat is that to get the AC to run at all, you would need at least two 100ah batteries, and in that case you would also likely get some amount less than your estimate due to low voltage cutout of the inverter with fewer batteries to feed it. Personally, I think the minimum if you plan on running AC off the batteries, even for fairly short times, would be about 400ah of AGM battery bank.

Well, for awhile we only had 220AH of AGM, and we were able to run for almost an hour. This was with a pretty sophisticated (Outback) inverter, though. 440 is indeed mo betta, though.