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Old 06-15-2022, 02:48 AM   #1
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A few electrical questions..

Hi all!

First time here and I have a few questions about our solar set-up. It seems as though everything works the way it should, but Iím hoping Iím missing something and I have a few questions.

We live in Phoenix, Arizona, which is synonymous with hell in itís summers. Weíre having a hard time keeping our bus cool at night. Our batteries seem to drain pretty quick running a window AC.

Hereís a few pictures of our bus, weíll do a build thread one of these days but in the mean-time if youíre interested you can show love on most social platforms: @thisisfr33dom

Click image for larger version

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Okay, here is our setup:

Solar: (2) S-Energy 305W Mono Solar Panels
Batteries2) Battle Born 100 Ah 12V LiFePO4 Deep Cycle Battery
Inverter: Reliable 1500W 12v Inverter 120VAC
Charge Controller: Fangpuson 50a Charge Controller - https://www.fangpusun.com/mppt100_15d-mppt150_70d0


My questions are:
1) My inverter shuts off all power at around 11V on these batteries, shouldnít these batteries be able to drain a lot lower?

2) Does my charge controller need to be set, or can it be set, to charge more efficiently for these batteries?

3) Will adding another battery increase the amount of time that we can run things off of the batteries?

If Iím not providing enough information, let me know and Iíll dig up whatís needed

thank you TONS in advance.

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Old 06-16-2022, 07:21 PM   #2
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1. No.
11V/ 4 = 2.75 Volts per cell. There is almost no energy left below this (or really even below ~3Vpc / 12V). The minimum voltage for LFP is 2.5Vpc / 10V, but nobody recommends going that low.

2. Not enough info given about your controller and settings. Is it PWN or MPPT, what is the charge profile / settings are being used?

3. Yes, it will increase the amount of time you can run things off the battery by whatever % you increase total battery capacity (eg: add 200ah to the 200ah you have already and you increase your capacity by 100% and should have twice the runtime so long as you can replenish what you use), but you need to make sure you are able to recharge what you use overnight, so the system needs to scale proportionally.

also consider efficiencies/inefficiencies such as insulation and idle draws of various components like the inverter as well as the efficienculy of the A/C itself
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Old 06-16-2022, 07:34 PM   #3
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Quote:
Originally Posted by dontoh View Post
Hi all!

First time here and I have a few questions about our solar set-up. It seems as though everything works the way it should, but Iím hoping Iím missing something and I have a few questions.

We live in Phoenix, Arizona, which is synonymous with hell in itís summers. Weíre having a hard time keeping our bus cool at night. Our batteries seem to drain pretty quick running a window AC.

Hereís a few pictures of our bus, weíll do a build thread one of these days but in the mean-time if youíre interested you can show love on most social platforms: @thisisfr33dom

Attachment 66178
Attachment 66179


Okay, here is our setup:

Solar: (2) S-Energy 305W Mono Solar Panels
Batteries2) Battle Born 100 Ah 12V LiFePO4 Deep Cycle Battery
Inverter: Reliable 1500W 12v Inverter 120VAC
Charge Controller: Fangpuson 50a Charge Controller - https://www.fangpusun.com/mppt100_15d-mppt150_70d0


My questions are:
1) My inverter shuts off all power at around 11V on these batteries, shouldnít these batteries be able to drain a lot lower?

2) Does my charge controller need to be set, or can it be set, to charge more efficiently for these batteries?

3) Will adding another battery increase the amount of time that we can run things off of the batteries?

If Iím not providing enough information, let me know and Iíll dig up whatís needed

thank you TONS in advance.
3) yes, though the devil is in the details.

If you provide information on the A/C system (mostly, how many amps does it draw and how long do you run it) you can calculate demand, and from there, determine whether your solar panels can provide those amps over the course of a charging day.

If you cannot produce at least that required amount of charge (measured in amp hours), no amount of extra storage will keep the AC running. So first figure out how many amp hours you need, then look at your solar panel production (in amp hours) to see if you need more solar charging capacity.

Your batteries will need to have that same capacity, plus more for the other loads you will place on the system.

If you increase your solar panel capacity it may require you increase the capacity of the solar charge controller (and wiring etc).

Alternatives are 1) shore power; 2) generator power; 3) better window shading....
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Old 06-16-2022, 09:53 PM   #4
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Quote:
Originally Posted by dontoh View Post
We live in Phoenix, Arizona, which is synonymous with hell in itís summers. Weíre having a hard time keeping our bus cool at night. Our batteries seem to drain pretty quick running a window AC.
...
Okay, here is our setup:

Solar: (2) S-Energy 305W Mono Solar Panels
Batteries2) Battle Born 100 Ah 12V LiFePO4 Deep Cycle Battery
Inverter: Reliable 1500W 12v Inverter 120VAC
Charge Controller: Fangpuson 50a Charge Controller - https://www.fangpusun.com/mppt100_15d-mppt150_70d0


My questions are:
1) My inverter shuts off all power at around 11V on these batteries, shouldnít these batteries be able to drain a lot lower?

2) Does my charge controller need to be set, or can it be set, to charge more efficiently for these batteries?

3) Will adding another battery increase the amount of time that we can run things off of the batteries?

If Iím not providing enough information, let me know and Iíll dig up whatís needed

thank you TONS in advance.
The LiFePO4 battery chemistry is generally capable of utilizing about 80% of its total charge capacity compared to the 50% or so of PbSO4 chemistries and forms. What you may not be seeing, or getting, depending on the settings inside the charge controller, are the max voltages on those cells which should be capable of hitting almost 14V at max charge. Make sure that your charge controller is set to a Lithium setting, first, because each battery chemistry has its own charge profile based on the chemical reactions that need to take place inside the cells of the battery, which requires a certain voltage and amperage input, as well as for a certain time period.(an example: https://mowgli-adventures.com/chargi...isure-battery/)

I can think of NO 12V battery that should ever be discharged that low safely without causing some kind of damage to the internals of the battery itself. The nominal charge of a healthy 12V battery should be around 12.8V, and a full one should be above 13.5V in basically all cases. And in some cases much higher than that.

Yes, adding more battery storage (in parallel) will increase both the amount of power you can draw, as well as the maximum current you can draw, assuming your wiring can handle the current flow (https://astrolabesailing.com/2017/05...ng-wire-fuses/). But the bigger your bank, the longer it takes to charge, as well--which probably isn't that much of an issue where you are, since I would assume that it's mostly sunny, and the days are long enough to give you plenty of power.

But you're kind of brave trying to run an A/C unit off solar... Even a small one (that looks to be about 650-750W?). The compressor kicking on will take a toll on the electronics, as well as the batteries, and warm up your already warm wires even further. But simple math can save the day;

Assuming that you're trying to run a 750W A/C unit off a 1500W inverter, with 200 AH of batteries, in a perfect world where there are no conversion or efficiency losses for any reason, and no other loads on your system, you would have a 6.25 Amp current draw on the 120V side which would translate into a 62.5-Amp draw on the 12V batteries, with a 3.2-Hour life on the batteries until they are completely discharged.

But we don't live in a perfect world, and there's usually about a 5-10% 'tax' on voltage transformations, as well as resistance to electrical flow on the lines themselves, and the LiFePO4 chemistry has only about an 80% Depth-of-Discharge before it goes kaput, and your controllers are probably set by default to shut off a little bit earlier than that, because to actually do that usually causes some damage and 'weakening' of the batteries, so the electronics are programmed to keep people from making expensive mistakes because of ignorance over things like this kind of engineering.

Assuming that you're an AZ native, and familiar with things like solar screen shielding (in the tint), high R-values of insulation (to keep the cool air inside), and other kinds of what-not, I would double up your battery bank to give you more battery capacity, and thus more time to run your A/C before things shut down. You could also check into beefing up your charge controller, instead of using that 50A chinesium piece that can't even handle the power your panels are putting out.

You're losing usable power because your charge controller is under-powered for your panels, it's only a matter of time until that burns out.

Your charge controller isn't capable of keeping up with the demands your A/C alone is putting on the system, assuming that you have nothing else plugged in or being used, which I doubt.

Your battery bank is inadequately sized to the power demands that you are placing it by at least a factor of 2, possibly more.

And considering the improper sizing of the above, I would also question if your wire sizes are appropriate to the demands being placed upon them, which could lead to a possible fire hazard.
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Old 06-16-2022, 10:13 PM   #5
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Not too many A/C units out there that will draw less than the maximum amount of energy your panels are capable of producing. Add in the self-consumption of the inverter & in the absolute best case (which assumes you have a very small window unit, among other things), you can only 'break even'. That's with the sun shining, at full intensity, running nothing else. In all other cases, you're running a deficit... especially at night when the sun isn't shining. All this to say, running your A/C in your vehicle as equipped, in this environment, is simply not sustainable. You'll always be pulling from your batteries more than you put back in if you want to stay anywhere close to cool. Which is why you're draining your batteries down to nothing.

Which brings me to this warning: Do not keep draining your batteries down that low. You'll be testing BB's warranty out real soon if you do. Each time you drain them down that far you're shortening their lifespan and decreasing their capacity by a non-insignificant amount. Those batteries aren't cheap... you really need to avoid allowing them to discharge so far. I know a couple volts doesn't sound like a lot, but it's A LOT, particularly with lithium, which maintains a very flat voltage curve right up to near the point they're completely discharged.

Without adding more panels, or supplementing with shore/gennie power as Rucker says, you're not going to have the juice to run the A/C the way you want. Adding batteries alone isn't going to matter... you're never going to have any surplus available to take advantage of the extra storage.
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Old 06-16-2022, 10:26 PM   #6
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Answer below in blue

Quote:
Originally Posted by dzl_ View Post
1. No.
11V/ 4 = 2.75 Volts per cell. There is almost no energy left below this (or really even below ~3Vpc / 12V). The minimum voltage for LFP is 2.5Vpc / 10V, but nobody recommends going that low.

2. Not enough info given about your controller and settings. Is it PWN or MPPT, what is the charge profile / settings are being used?
It is an MPPT controller, Iíd need to double check the settings however I believe it was set to lithium if thats an option.

3. Yes, it will increase the amount of time you can run things off the battery by whatever % you increase total battery capacity (eg: add 200ah to the 200ah you have already and you increase your capacity by 100% and should have twice the runtime so long as you can replenish what you use), but you need to make sure you are able to recharge what you use overnight, so the system needs to scale proportionally.

also consider efficiencies/inefficiencies such as insulation and idle draws of various components like the inverter as well as the efficienculy of the A/C itself
Thank you tons for your help
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Old 06-16-2022, 10:48 PM   #7
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Response in blue

Quote:
Originally Posted by Rucker View Post
3) yes, though the devil is in the details.

If you provide information on the A/C system (mostly, how many amps does it draw and how long do you run it) you can calculate demand, and from there, determine whether your solar panels can provide those amps over the course of a charging day.

Ideally I’d like to run it all day. At the minimum we can get away with 6-8 hours however.
Here are the A/C numbers:
Volts: 115
Hz: 60
BTU/h: 5000
Amps: 4.6A


If you cannot produce at least that required amount of charge (measured in amp hours), no amount of extra storage will keep the AC running. So first figure out how many amp hours you need, then look at your solar panel production (in amp hours) to see if you need more solar charging capacity.

Your batteries will need to have that same capacity, plus more for the other loads you will place on the system.

If you increase your solar panel capacity it may require you increase the capacity of the solar charge controller (and wiring etc).

Alternatives are 1) shore power; 2) generator power; 3) better window shading....
Thanks for your help
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Old 06-16-2022, 10:53 PM   #8
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Thank you for being so thorough

Response below in blue

Quote:
Originally Posted by Albatross View Post
The LiFePO4 battery chemistry is generally capable of utilizing about 80% of its total charge capacity compared to the 50% or so of PbSO4 chemistries and forms. What you may not be seeing, or getting, depending on the settings inside the charge controller, are the max voltages on those cells which should be capable of hitting almost 14V at max charge. Make sure that your charge controller is set to a Lithium setting, first, because each battery chemistry has its own charge profile based on the chemical reactions that need to take place inside the cells of the battery, which requires a certain voltage and amperage input, as well as for a certain time period.: (https://mowgli-adventures.com/chargi...isure-battery/)

I tried setting this to itís lithium setting, however it just defaults back to default which looks like its set up for Gel deep dischard, gel oxide a200, AGM deep discharge, OPzS, rolls marine flooded, rolls solar flooded. I canít imagine this is a good thing?


I can think of NO 12V battery that should ever be discharged that low safely without causing some kind of damage to the internals of the battery itself. The nominal charge of a healthy 12V battery should be around 12.8V, and a full one should be above 13.5V in basically all cases. And in some cases much higher than that.

Yes, adding more battery storage (in parallel) will increase both the amount of power you can draw, as well as the maximum current you can draw, assuming your wiring can handle the current flow (https://astrolabesailing.com/2017/05...ng-wire-fuses/). But the bigger your bank, the longer it takes to charge, as well--which probably isn't that much of an issue where you are, since I would assume that it's mostly sunny, and the days are long enough to give you plenty of power.

But you're kind of brave trying to run an A/C unit off solar... Even a small one (that looks to be about 650-750W?). The compressor kicking on will take a toll on the electronics, as well as the batteries, and warm up your already warm wires even further. But simple math can save the day;

Assuming that you're trying to run a 750W A/C unit off a 1500W inverter, with 200 AH of batteries, in a perfect world where there are no conversion or efficiency losses for any reason, and no other loads on your system, you would have a 6.25 Amp current draw on the 120V side which would translate into a 62.5-Amp draw on the 12V batteries, with a 3.2-Hour life on the batteries until they are completely discharged.

I misspoke, I have a 2000w inverter


But we don't live in a perfect world, and there's usually about a 5-10% 'tax' on voltage transformations, as well as resistance to electrical flow on the lines themselves, and the LiFePO4 chemistry has only about an 80% Depth-of-Discharge before it goes kaput, and your controllers are probably set by default to shut off a little bit earlier than that, because to actually do that usually causes some damage and 'weakening' of the batteries, so the electronics are programmed to keep people from making expensive mistakes because of ignorance over things like this kind of engineering.

Assuming that you're an AZ native, and familiar with things like solar screen shielding (in the tint), high R-values of insulation (to keep the cool air inside), and other kinds of what-not, I would double up your battery bank to give you more battery capacity, and thus more time to run your A/C before things shut down. You could also check into beefing up your charge controller, instead of using that 50A chinesium piece that can't even handle the power your panels are putting out.

You're losing usable power because your charge controller is under-powered for your panels, it's only a matter of time until that burns out.

Your charge controller isn't capable of keeping up with the demands your A/C alone is putting on the system, assuming that you have nothing else plugged in or being used, which I doubt.

It seems as though during the day it runs the AC without problem and keeps the battery around 13V. Itís just when the sun starts to not be direct it starts to struggle

Your battery bank is inadequately sized to the power demands that you are placing it by at least a factor of 2, possibly more.

And considering the improper sizing of the above, I would also question if your wire sizes are appropriate to the demands being placed upon them, which could lead to a possible fire hazard.
The wires were something that I made sure was accurate, in fact a little larger in some areas incase we decided to upgrade our electronics

Thank you tons !!
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Old 06-16-2022, 10:54 PM   #9
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This is great information - very important to know so that we protect the batteries.

Quote:
Originally Posted by TheHubbardBus View Post
Not too many A/C units out there that will draw less than the maximum amount of energy your panels are capable of producing. Add in the self-consumption of the inverter & in the absolute best case (which assumes you have a very small window unit, among other things), you can only 'break even'. That's with the sun shining, at full intensity, running nothing else. In all other cases, you're running a deficit... especially at night when the sun isn't shining. All this to say, running your A/C in your vehicle as equipped, in this environment, is simply not sustainable. You'll always be pulling from your batteries more than you put back in if you want to stay anywhere close to cool. Which is why you're draining your batteries down to nothing.

Which brings me to this warning: Do not keep draining your batteries down that low. You'll be testing BB's warranty out real soon if you do. Each time you drain them down that far you're shortening their lifespan and decreasing their capacity by a non-insignificant amount. Those batteries aren't cheap... you really need to avoid allowing them to discharge so far. I know a couple volts doesn't sound like a lot, but it's A LOT, particularly with lithium, which maintains a very flat voltage curve right up to near the point they're completely discharged.

Without adding more panels, or supplementing with shore/gennie power as Rucker says, you're not going to have the juice to run the A/C the way you want. Adding batteries alone isn't going to matter... you're never going to have any surplus available to take advantage of the extra storage.
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