How long can you run AC from batteries?

[markopolo]

Originally Posted by Knit

Here is what the depth of discharge (DOD) vs number of cycles looks like for my Amstron AP-GC2’s looks like. Limiting DOD to 50% increases the number of cycles substantially according to the manufacturer.

Attachment 6355

That chart appears to illustrate Booster's point extremely well.

Look at the energy that you get out of the battery. It's almost the same at 100% DOD as 50% DOD. (10% penalty maybe?) You could choose to spend the extra money up front for doubling the amount of batteries and carry the extra weight around for years or just replace fewer batteries more frequently as needed.

2 x GC2 210Ah 6V batteries (210Ah @ 12V)
500 cycles at 100% DOD = 12v X 210Ah (100% DOD) X 500 = 1,260 kWh total output until replacement
675 cycles at 80% DOD = 12v X 168Ah (80% DOD) X 675 = 1,360 kWh total output until replacement
1100 cycles at 50% DOD = 12v X 105Ah (50% DOD) X 1100 = 1,386 kWh total output until replacement

[booster]

Yep, just as Marko explained. IMO, this is one the premier "battery legends" around, and can always seem to find lots and lots of followers who insist that you should never go under 50%SOC. If anyone is interested in the science and facts behind the disagreement with the 50% rule, there are several very good discussions here on the forum. IMO, it is particularly of concern for most of the class b folks who want/need increased battery capacity as with a b you can run out of load capacity if you are using it all for batteries (unless you run out of money for batteries first).


As I mentioned earlier, most of the evidence I have been able to find is that you are much more likely to shorten your battery life by having less than stellar charging control, than by going under 50%SOC and it is very difficult to achieve good charging control from all you charging sources, all the time. Without a good battery monitor, that has all the parameters set correctly for your system, you aren't able to tell if you are getting good charging, or not. Even if you regularly get the "fully charged" indication on your properly setup monitor, all that means is that you got the batteries to totally full in that charge cycle, and although that is a very good and necessary thing, it is also necessary to makes sure the high voltage charging stops at that point to prevent overcharging the batteries, and the monitor won't tell you that.


It has been stated well by some that undercharging is a slow early death for batteries, and overcharging is a quick early death for batteries.

[booster]

I think Monica998 should divulge the fact that she is representing a battery manufacturer, so may not be completely objective.


It is nice to have the manufacturers give their input on many of these topics, as they can have data and insight that is unavailable to the rest of us, but they should not try to hide who they really are so the information can be properly evaluated.

[InterBlog]

300 watt solar
300 AH lithium
2000 watt Xantrex inverter
11,000 BTU roof a/c (one of the older, smaller ones)

= about 2.5 hours of air conditioning. Duration almost all depends on the lithium SOC. Solar can't touch that kind of draw in terms of supply.

*However*

the fly in that ointment is that we ended up damaging a 200 A Bosch alternator that was only 17 months old. Theory says that with a Sterling battery to battery charger configured correctly, that kind of deep draw on the lithiums should be safely recoverable on a continual basis using the "under-hood generator" (= upgraded alternator). We now believe that there are things happening in the system that are not well understood (reasoning omitted for brevity; may revisit later).

ARV produced a video showing their modified alternator (I'm off grid, low cell signal, so I can't search it out). I'll go out on a limb and venture a guess that, unless they really needed to make that investment, they would not have done it. Their customers were losing alternators, is my suspicion. So they had a different alternator designed and implemented. We may eventually go with two alternators in our Sprinter.

Moral of that story: a/c is not necessarily as simple as a calculation would show. En route from Houston to Nova Scotia a few weeks ago, I had to divert to Philadelphia to have millionmilesprinter.com put in a new alternator for me (he's a great guy BTW).

[avanti]

Originally Posted by InterBlog

the fly in that ointment is that we ended up damaging a 200 A Bosch alternator that was only 17 months old. Theory says that with a Sterling battery to battery charger configured correctly, that kind of deep draw on the lithiums should be safely recoverable on a continual basis using the "under-hood generator" (= upgraded alternator). We now believe that there are things happening in the system that are not well understood (reasoning omitted for brevity; may revisit later).

I look forward to hearing more of your story. As we have heard numerous times, connecting significant external loads to modern vehicle charging systems can be very dicey--upgraded alternator or not. Don't know if your issue is related to that or not.

One terminology nit:
I think that the term "underhood generator" is probably best reserved for a second alternator. I think it kind of confuses matters to apply it to an upgraded chassis alternator.

[booster]

Originally Posted by InterBlog

300 watt solar
300 AH lithium
2000 watt Xantrex inverter
11,000 BTU roof a/c (one of the older, smaller ones)

= about 2.5 hours of air conditioning. Duration almost all depends on the lithium SOC. Solar can't touch that kind of draw in terms of supply.

*However*

the fly in that ointment is that we ended up damaging a 200 A Bosch alternator that was only 17 months old. Theory says that with a Sterling battery to battery charger configured correctly, that kind of deep draw on the lithiums should be safely recoverable on a continual basis using the "under-hood generator" (= upgraded alternator). We now believe that there are things happening in the system that are not well understood (reasoning omitted for brevity; may revisit later).

ARV produced a video showing their modified alternator (I'm off grid, low cell signal, so I can't search it out). I'll go out on a limb and venture a guess that, unless they really needed to make that investment, they would not have done it. Their customers were losing alternators, is my suspicion. So they had a different alternator designed and implemented. We may eventually go with two alternators in our Sprinter.

Moral of that story: a/c is not necessarily as simple as a calculation would show. En route from Houston to Nova Scotia a few weeks ago, I had to divert to Philadelphia to have millionmilesprinter.com put in a new alternator for me (he's a great guy BTW).

Sad to say, I am not at all surprised you lost the alternator, as vehicle alternators, unless special ones like the monster ARV now uses, are not rated, or capable, of the percent of output that engine generator setups with big batteries use.


Many OEM generators will overheat at 40% of rated output if it is continuous (it takes maybe 20 minutes to get that hot from what I have seen). They then will cycle up and down on the internal or external regulator if they are equipped with thermal output reduction. The thermal cycling will eventually kill the regulator or the alternator. Marine rated alternators claim 100% full output duty cycle but have all kinds of disclaimers about adequate cooling air, which is tough in an engine compartment.


The Sterling may have actually made the whole thing worse, depending on what size it was, as most of them will hyper excite the field to get more power out of the alternator, worsening heat issues.



In "normal" engine generator setups that are commonly used, there will be an isolated to the coach only 280 amp Nations/DC Power alternator with a Balmar "smart" regulator. The regulator will do the same turn down when hot as mentioned above, and they can have same type of failures. This appears to be what ARV addressed with alternator change. Avanti posted some great data on his system that indicated that the 280 amp alternator, heat cycling, netted about 165 amps average.


On our system we addressed the heat issue by using two big alternators in parallel, 530 amps rated, and a Ample Power regulator (no longer available) that allowed us to turn down the output of the regulators in two stages, which I can switch control from the dash. One step is at about 180 amps, and it will run continuously there without overheating, even at idle. The second is at 280 amps and can be run for about 20 minutes for a quick boost to get a days power back. The actual output is usually a bit higher than the above as that is to the coach and the alternators are also running the engine and accessories. We could go higher than 180 amps if driving, but the batteries (AGM) start to get too warm over long periods.


Since the ample power is not available anymore, which is too bad because it also allowed forcing the unit to hold absorption for those of us with lead acid batteries, you can get reasonable turn down by using the Balmar regulator on a standalone alternator, or even on both or the stock alternator, if your vehicle computer allows it. The Balmar also has two turndowns that can be switch controlled or hardwired if wanted all the time. One of the turndowns is a fixed 50% reduction in field voltage (may or may not be right at 50% output) and the other is a settable reduction of 5 to 40% reduction (on/only not switch adjustable). For reference, the Balmar turns down the output to 50% field if it senses the alternator getting too hot. It is likely you could just set a 280amp alternator at 60% field and not have it heat cycle, which should increase the life a lot.

[BBQ]

.

I wish the vendors (or anyone with a vested interest) would add a disclosure in their tagline.

[Monica998]

Originally Posted by booster
I think Monica998 should divulge the fact that she is representing a battery manufacturer, so may not be completely objective.
It is nice to have the manufacturers give their input on many of these topics, as they can have data and insight that is unavailable to the rest of us, but they should not try to hide who they really are so the information can be properly evaluated.

booster, actually I take the positive attitudes for the questions always. Because we just provide the LiFePO4 batteries for the RVs, therefore it has no effects for the answer.

And because of the rules about the forums, we cannot show it directly, hope you can understand. Any questions, please feel free to tell me or contact me, thanks!

[booster]

Originally Posted by Monica998

booster, actually I take the positive attitudes for the questions always. Because we just provide the LiFePO4 batteries for the RVs, therefore it has no effects for the answer.

And because of the rules about the forums, we cannot show it directly, hope you can understand. Any questions, please feel free to tell me or contact me, thanks!

While I understand what you are saying, just going around the "rules" and hoping not to get caught is not the right way to address it, IMO.



We have had employees of RV related companies on this forum in the past, and I think since the forum changed management. I think that most of the members are not concerned about that kind of relationship as long as it is declared up front and the forum is used just like the rest of us use it, and not as a sales opportunity. Folks that work in an industry often have more and better information than the rest of us have access to, so it can be mutually beneficial, as we get a chance to learn about the industry and the industry gets to learn about the market in a non sales atmosphere.


I think perhaps if you had contacted the forum owners, they may have been OK with you being here as long as you divulged your manufacturer affiliation and didn't try to sell product or link the business.


What put me over the edge is when you used the forum to contact me, and maybe others, to try to sell your products. IMO, that is not using the forum in good faith, and coupled with the fact you intentionally skirted the rules, would not indicate that you were here to just be a member of an RV forum like the rest of us.


For the rest of the forum members here is the email I received:

Dear booster,


I'm Monica998 from here: http://www.classbforum.com/forums/f23/how-long-can-you-run-ac-from-batteries-8125-2.html, do you remember me?


We both discussed the question: How long can you run AC from batteries?

And your replies seem much better than I do.


I searched the forum and find your contacts, hope not to bother you.


Actually we're a LiFePO4 batteries manufacturer based in Suzhou, China. We produced the LiFePO4 batteries for the RV, because it has better performance and long-life utility, and also the other batteries. For more, please access to https://www.creabest.com/collections/all.


So do you have some interests in it? If you have any questions, please feel free to let me know.


Looking forward to your reply!



Best regards,


Monica

[Winston]

Originally Posted by booster

In "normal" engine generator setups that are commonly used, there will be an isolated to the coach only 280 amp Nations/DC Power alternator with a Balmar "smart" regulator.

The Balmar also has two turndowns that can be switch controlled or hardwired if wanted all the time.

We're impressed with the breadth of your large alternator/external regulator experience. Our observations generally parallel yours.

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'). The advantage of the Nations 'kit' in the ProMaster is that it's very low . . . and therefore gets reasonably good cooling while in motion.

We've chosen - - for the time being - - to limit charging currents below 150 amperes. The Balmar programming is quirky . . . so we're not using those programmable 'turn-downs'; instead, we have forced the Balmar into constant Bulk mode, then selected our target voltage to achieve the level of charging we desire. Currently we're set to 13.8 volts. This works reasonably well for lithium due to the comparatively flat Voltage vs. State of Charge curve . . . yes, the current slumps over time . . . but that's just a matter of selecting the voltage to 'give us a little more' than we want, initially, balanced, later, by "a little less than we want".

Seems that a better solution might be to obtain an alternator with external diodes/heat sinking - - it's our understanding that this approach controls heat issue much better.

[73shark]

Originally Posted by Phoebe3

I need some help with my math and, also, with real world experience.

If I have a 13,500 BTU AC, does that translate to 3,956 Watts?

Does 3,950 Watts at 120V translate to 33 Amps?

Therefor, does a 13,500 BTU AC require 33 AH?

If so, then in theory, I could run an AC for a couple of hours on a 100 A battery.

But, practically speaking, that load is only while the compressor is running and the compressor doesn't run all the time, correct? So, how long could you run an AC from a 100 A battery?

FWIW, my 2011 AI A/C would draw 17-19 amps from the Onan depending on the outside temperature. IIRC, it would run about eight hours on a full tank of propane.

[cruising7388]

Originally Posted by booster

The regulator will do the same turn down when hot as mentioned above, and they can have same type of failures. This appears to be what ARV addressed with alternator change. Avanti posted some great data on his system that indicated that the 280 amp alternator, heat cycling, netted about 165 amps average.

I don't think that ARV's introduction of the Delco 330 alternator was a response to Nations alternator failures. I think it was a response to the fact that the Nations unit running hot could not simultaneously support both an air conditioning load and still provide sufficient charging capacity to prevent the battery shut down by the BMS. But I don't think this notorious "death spiral" damaged the battery(s) or the alternator/regulator.

The Xantrex package on the Galleria has presumably addressed this problem with an interesting innovation that's less expensive than the bulky and very expensive Delco alternator. When the Nations alternator is in the bulk charge state, it triggers a network that parallels that Nations unit with the OEM alternator to provide a substantial increase in total charging capacity. How this parallel condition is accomplished with dissimilar alternators and regulators is puzzling and defies conventional wisdom, but if it works, it's a cost effective solution for beefing up charging capacity.

[avanti]

Originally Posted by cruising7388

The Xantrex package on the Galleria has presumably addressed this problem with an interesting innovation that's less expensive than the bulky and very expensive Delco alternator. When the Nations alternator is in the bulk charge state, it triggers a network that parallels that Nations unit with the OEM alternator to provide a substantial increase in total charging capacity. How this parallel condition is accomplished with dissimilar alternators and regulators is puzzling and defies conventional wisdom, but if it works, it's a cost effective solution for beefing up charging capacity.

MAYBE that could be made to work on some platforms. But on vehicles with modern charging systems, such as the Sprinter I4, it sounds like madness to me.

[cruising7388]

Originally Posted by avanti

MAYBE that could be made to work on some platforms. But on vehicles with modern charging systems, such as the Sprinter I4, it sounds like madness to me.

Xantrex is not a peach tree operation and if they have successfully implemented it, they certainly deserve that credit. But I share your reservation about how you can get the Nations alternator to parallel productively with an OEM alternator receiving CANBUS instructions from the computer that might defeat the process. But perhaps it's not as difficult as it seems. At the point the alternators parallel, perhaps the CANBUS sees what's actually a discharged coach battery as a discharged engine battery and increases charging from the OEM alternator. So the CANBUS protocol isn't being tampered with, but just being fooled into thinking that it's the engine battery that needs charging. And as described to me, this parallel operation only takes place when the Nations Balmar regulator is in the bulk charge mode. This of course begs the question of what either engine or coach batteries see when one charging source is operating in bulk charging mode while the other charging source is operating in an absorption charging mode.

[booster]

Originally Posted by avanti

MAYBE that could be made to work on some platforms. But on vehicles with modern charging systems, such as the Sprinter I4, it sounds like madness to me.

Yep, and if the Balmar takes the Nations alternator into overheat output reduction, the van alternator will pick up way more load than it can put out for long periods, and you could be looking at problems like interblog had with the stock alternator.

[Gary Mn]

Originally Posted by Phoebe3

I need some help with my math and, also, with real world experience.

If I have a 13,500 BTU AC, does that translate to 3,956 Watts?

Does 3,950 Watts at 120V translate to 33 Amps?

Therefor, does a 13,500 BTU AC require 33 AH?

If so, then in theory, I could run an AC for a couple of hours on a 100 A battery.

But, practically speaking, that load is only while the compressor is running and the compressor doesn't run all the time, correct? So, how long could you run an AC from a 100 A battery?

You have gotten a lot of good information from many experienced users. I may have missed it but wanted to comment about two things in your post.

First BTUs are a unit of energy and Watts are a unit of power so are not directly converted one to the other. As has been suggested you would be better off knowing the current draw of the AC and proceed from there determining the A Hr demand of your AC unit.
Secondly the battery you quoted at 100 A. I assume you mean that it is 100 A HRs which would be the number you would want to compare to your demand from the AC
Gary
2008 RS

[tex4judy]

I have installed the Nations alternator, Balmar regulator, Xantrex inverter and 400 AH Lithionics batteries with the internal BMS. The Nations alternator and the coach alternator are isolated from each other (except that we use ignition voltage in the BMS - Balmar - alternator exciter.)

We drive a lot in NM summer temps. And we have parked for 2 hours several times leaving the 1100 BTU air conditioner running. No problem - including several times the compressor shut off and then restarted. Our AC has a locked rotor amp rating of 45 (if I'm remembering that right, but I think so.)

This system has worked flawlessly for the last 15 months. We have no generator and no propane. I have no reservation in recommending this arrangement. And agree with the thought of running the AC until the rig is cool and then using the vent fan for the night. A lot quieter than a generator.

[cruising7388]

Originally Posted by booster

Yep, and if the Balmar takes the Nations alternator into overheat output reduction, the van alternator will pick up way more load than it can put out for long periods, and you could be looking at problems like interblog had with the stock alternator.

Sure, your scenario is possible but it's equally possible that they have accounted for this. Perhaps they use Nations alternator temp sensing as the logic for inhibiting the parallel operation or maybe they implement some controllable duty cycle for parallel operation the width of which is responsive to the Nations operating temperature. Who knows? I sure don't. Your and Avanti's points are well taken but the fact is that Xantrex is apparently making it work. That system is only one year old so it's admittedly early in the game but so far, I haven't read any complaints regarding any of the alternators failing on Gallerias. You have to agree that if there is some practical non-damaging way of getting occasional coach battery charging assistance from the 200+ amp OEM alternator that normally just loafs, that it's a useful feature.

[avanti]

I simply don't see how such a system could possibly be designed to work reliably across the range of OEMs and models. For example, the Sprinter OM-651 engine has sensors mounted directly to the starter battery terminal, which feeds multiple parameters to the ECU, which does unknown things with the information, likely including mild "dynamic braking". Which side of this sensor (which almost certainly includes a shunt) should the external system be connected to? Which you choose will have profound effects on what the Sprinter "sees" about the performance of the aftermarket system. No doubt other manufacturers have similar obscure designs, and they are all proprietary. As I said, it sounds like a nightmare.

The other question is what, exactly, constitutes a "substantial" increase in charging capacity. Remember that the Mercedes Upfitters guidelines require any takeoff from the OEM electrical system to be limited to 40A. No upfitter who participates in the Master Upfitters program (i.e., almost all of them) could install such a system if it exceeds this draw.

It may well be that this system is intended for more conventional setups (or for boats, which have fewer of these kinds of issues). But these will become fewer as time goes by.

[cruising7388]

Originally Posted by avanti

I simply don't see how such a system could possibly be designed to work reliably across the range of OEMs and models. For example, the Sprinter OM-651 engine has sensors mounted directly to the starter battery terminal, which feeds multiple parameters to the ECU, which does unknown things with the information, likely including mild "dynamic braking". Which side of this sensor (which almost certainly includes a shunt) should the external system be connected to? Which you choose will have profound effects on what the Sprinter "sees" about the performance of the aftermarket system. No doubt other manufacturers have similar obscure designs, and they are all proprietary. As I said, it sounds like a nightmare.

The other question is what, exactly, constitutes a "substantial" increase in charging capacity. Remember that the Mercedes Upfitters guidelines require any takeoff from the OEM electrical system to be limited to 40A. No upfitter who participates in the Master Upfitters program (i.e., almost all of them) could install such a system if it exceeds this draw.

It may well be that this system is intended for more conventional setups (or for boats, which have fewer of these kinds of issues). But these will become fewer as time goes by.

You guys remind me of the biologist that proved beyond a shadow of scientific doubt that bumble bees can't fly.

I don't remember the details but I vaguely recall that 40 amps of assist from the OEM alternator was mentioned. BTW, I don't know for a fact that this parallel feature is still included in current production. I think that Coachmen has already made rolling changes on the Galleria since the initial Li3 production but I have no idea whether this particular feature was involved. I'll try and get an update.