Power supply system for 3 purposes

[Camp20144]

I’m new to this and trying to design a system with three purposes in mind.
1) just run my cpap (home power outages) and 1-3 night camping/fishing trips
2) longer camping/fishing more power requirements, longer power outages
3) camping with the addition of a 2200 Watt inverter with 30Amp camper plug

Purpose (1) is as simple as a battery (or 2 batteries) and a 12 volt cigarette socket (I have 12 volt dc power cord for cpap)
Purpose (2) is one or two batteries and maybe 200 watts of solar
Purpose (3) is two batteries, 2200 watt inverter and up to 400 watts of solar (camping in camper possibly using more 12 volt and some 110 volt)

As I move up through (1) to (3) the increased power requires larger sizing of power handling components (wiring, fuses, etc). In consideration of (2) and (3), can I size wire and fuses to meet Purpose (3) and if my power needs fall within Purpose (2) just connect one or two batteries and maybe 200 watts of solar? I’m wondering if I can size/take the system to meet my anticipated needs when I know I don’t need the “full meal deal” (400 watts solar and inverter)?

If the system components are sized to handle the 2200 watt inverter, 400 watts of solar and more 12 volt loads, do I need to have all 400 watts of solar and the inverter connected if it will not be used? I think the answer is “No”, but I want to verify that is correct.

Thank you in advance,
Mark

 

[MisterSandals]

if I can size/take the system to meet my anticipated needs

Have you done an energy audit to be able to quantify your needs in terms of watt hours per day?
From here, everything else can be worked out, including amount of solar panels.
What are your anticipated AC loads (amps and watt/amp hours)?

 

[Camp20144]

@MisterSandals Thank you for your reply
I’ve not done an energy audit.
For the first two purposes I’m looking at cpap and possibly minimal LED lighting in the evenings. If I have the camper, I may have minimal use of the microwave (800 or 900 watt). I would guess 10-15 minutes a day at most. Limited evening LED lighting. Most cooking, coffee, hot water via propane stove. Microwaving is optional as I would have other hot/non-hot food options available. If I were to use the camper fridge, it would be on propane. I don’t know what the power draw is on propane but the fridge circuitry uses a 3amp fuse. This is an old school fridge (ammonia absorption?) (circa 1998). I usually use an ice chest on these boon-docking type trips.

 

[Camp20144]

@MisterSandals
A rough energy audit Calculation errors? Corrections? Comments?
Must have
Cpap - The 110 volt power supply supplies 12v-6.67amps = 80 Watts
7 hours of sleep = 7x80 = 560 Whrs

Optional
Camper
LED lights, large LED light = 12.8v-0.06amps = 7.68 Watts
2 hours of LED lights 7.68x2 = 15.36 Whrs
Fridge
Propane uses 12 volts - 3 amp fuse = 36 Watts
24 hours x 36 = 864 Whrs

Microwave
900 Watt for 15 minutes a day = 225 Watts but need inverter overhead.
Inverter running microwave 900 Watts
Inverter efficiency .85
900/.85=1058.82 Watts
Microwave for 15 minutes = 264.7 Whrs

If I calculated everything correctly and I had the camper and I used everything as listed above I would use 1704 Watt hours. With two 100Ah LiFePO4 batteries, I have 1900 W hours available if I pull them down to 20%. The cpap is calculated from the power supply output. I can reduce the power required by not using the heated hose and using the humidifier passively. The 2 hour LED light use was a “luxury” level and can be reduced or not used. I have other optional light sources. I’m able to use an icebox instead of the fridge. My fridge power use was based upon the fuse (3 amp) and using power 24 hours a day - worst case power use? Inverter off unless used for 110 volt supply.

Thank you,
Mark

 

[MisterSandals]

I would use 1704 Watt hours. With two 100Ah LiFePO4 batteries, I have 1900 W hours available if I pull them down to 20%.

Great work!
2x 12.8V nominal x 100Ah = 2560Wk
Probably more than enough for your CPAP.

To recharge, not knowing your location will guess 3hrs solar winter, 5 hrs summer.

Recharging 2560Wh (empty!):
2560Wh / 3h = 853W solar operating at 100% efficiency.

Summer 5hrs
2560Wh / 5h = 512W of solar

 

[Camp20144]

@MisterSandals Thank you!
Most of my travels would be eastern Washington state from the Oregon border north to the Columbia river as it runs the east/west path at about 47.9 degrees north latitude.
Looking at your recharge numbers, are you saying I would need 9 100 Watt panels in the winter and 6 100 W panels in the summer, to fully recoup 2 fully depleted 100Ah batteries?

 

[MisterSandals]

Looking at your recharge numbers, are you saying I would need 9 100 Watt panels in the winter and 6 100 W panels in the summer, to fully recoup 2 fully depleted 100Ah batteries?

Yes but you should get bigger and cheaper panels than 100W if you can Tetris them.

Get your location specific solar hours here... it may take more panels if flat on roof:

Solar Irradiance Calculator

www.solarelectricityhandbook.com

 

[Camp20144]

@MisterSandals Thank you. Great calculator. Very helpful information relating back to system sizing/usage.
I was looking back through the posts based on your “larger than 100 Watt panels”. I see where larger panels make sense in certain instances. I did find I was not clear/left out some important information. In the smaller two camping situations, I may be “out of the back of my pickup” or boondocking/“dry camping” island camping from my boat. In these instances the panels would have to be ground mounted and may necessarily limit panel size and how many.
Looks to me that my different camping situations will self limit system size/ability. I may be at cpap only more than I thought. But, that’s okay.
For a SCC I was considering the Victron Smart 100/30. But if I need at least 600 Watts of solar, do I need to get the Smart 100/50, or other? Will the Smart 100/50, or larger, operate with only 200 Watts of solar connected? Or, would it be better to have two 100/30’s?

 

[MisterSandals]

But if I need at least 600 Watts of solar, do I need to get the Smart 100/50, or other?

600W / 14V charging = 42A
The 100/50 would be a great choice (i have 100/30, absolutely love the bluetooth).

Note that you would be limited to 100V array so having Voc working out for panels in series is important.

 

[Rednecktek]

So just a couple thoughts here...

Are you sold on Victron? There are many cheaper options out there that will turn solar DC into battery DC. If you've got unlimited budget you can't go wrong, but if you're on a budget there are better options.

While larger than 100w panels are great for energy density, if you're having to manhandle the panels around that 50lb per panel really gets exhausting quick. On the other hand having to pull and set up 8 or 10 panels can be a lot of your time each day. Consider how much physical effort you're wanting to put into moving panels..

It sounds like a 1500w inverter might be enough which would save you some standby energy, but either way if you can wire in a breaker to the inverter that you can use as a disconnect you can shut off the inverter when it's not in use and save some of that battery power.

If it's possible to have a mounted array AND a deployable, figure on a separate controller for each array. It makes wiring easier and lets you have different size arrays on the same battery bank.

As a rule of thumb for sizing controllers, figure 10a of controller for every 100w of panel. If you need 800w of panel you're going to have to come up with 80a worth of charge controller @ 12v which probably means multiple 40a controllers as those tend to be the sweet spot.

But those are just my thoughts.

 

[Camp20144]

The 12 volt cig socket that I ordered arrived today.
I checked the 12 volt output of my 110 volt cpap power supply. It puts out 12.2 volts. I don’t see that the cpap 12 volt power supply cord could “correct” LiFePO4 battery voltage to 12 volt output for the cpap. I was concerned with shorting the LiFePO4 battery so I didn’t test the cpap power cord. I looked at some of the lithium (lithium-ion) cpap travel batteries for output voltage. Some didn’t list output voltage, a couple stated “12 volts nominal”. It appears that I may need to add a dc-dc converter that will allow me to set/control the output voltage from the LiFePO4 at 12.2 volts consistent with my cpap power supply.

 

[Camp20144]

@MisterSandals Thank you. From reading, exceeding SCC input voltage is fatal for the SCC. Exceeding the input amps results in clipping. What I didn’t understand is when the SCC manufacturer listed max solar Watts when it looked like you could alter series/parallel and stay under the the volts/amps?
@Rednecktek Thank you for your thoughts. I already have Victron’s BMV-712 battery monitor, so I was going to try to stay within their system. I’m thinking about HQST panels to save money. Will Prowse tested them and liked them for value. I appreciate your other food for thought also.
Again, thank you,
Mark

 

[MisterSandals]

It appears that I may need to add a dc-dc converter that will allow me to set/control the output voltage from the LiFePO4 at 12.2 volts consistent with my cpap power supply.

"12V" equipment is designed to accept a pretty wide voltage range. I think its something like 11V to 15V so you can use your LiFePO4 battery without worry. Consider a standard car battery is 12.8V nominal and while the vehicle is running, it gets hit with over 14V from the alternator. Its a pretty wide spec.

 

[MisterSandals]

you could alter series/parallel and stay under the the volts/amps?

The volts, particularly the Voc (open circuit voltage) is the critical number. This is rated at 25C (77F) so when it gets colder, the voltage rises by the panels temp coefficient per degree you expect your panels to experience (record lows are a good temp to use).

Before buying panels andSCC, run them by the gang here to see if they match up well.

 

[Camp20144]

The volts, particularly the Voc (open circuit voltage) is the critical number. This is rated at 25C (77F) so when it gets colder, the voltage rises by the panels temp coefficient per degree you expect your panels to experience (record lows are a good temp to use).

Before buying panels andSCC, run them by the gang here to see if they match up well.

Will do. Thank you very much for your assistance!

 

[Camp20144]

"12V" equipment is designed to accept a pretty wide voltage range. I think its something like 11V to 15V so you can use your LiFePO4 battery without worry. Consider a standard car battery is 12.8V nominal and while the vehicle is running, it gets hit with over 14V from the alternator. Its a pretty wide spec.

Good to know.

 

[Camp20144]

Found a thread on a cpap forum where the person inquired about a cpap model prior to mine but by the same manufacturer, Philips Respironics. Based upon what @MisterSandals said and this answer my cpap should be the same tolerance. This person was concerned as their lithium-Ion battery full charge was said to be 16+ volts. Here is the answer

Subject: RE: DC voltage tolerance? reply MJ
Hello,
The device will not operate above 15.5 VDC and below 10.8VDC.
Regards,
Product Support

 

[Rednecktek]

This person was concerned as their lithium-Ion battery full charge was said to be 16+ volts.

Yikes! He should be concerned then. 16v is 4v per cell, and his BMS should have cut off at 3.6v per cell, or 14.4v total. That's a problem with his battery and will probably be releasing the magic orange smoke shortly.

 

[MisterSandals]

Yikes! He should be concerned then. 16v is 4v per cell, and his BMS should have cut off at 3.6v per cell, or 14.4v total. That's a problem with his battery and will probably be releasing the magic orange smoke shortly.

It sounds like they are NOT talking about LiFePO4 but perhaps lithium cobalt (charges to 4.2Vpc) or lithium nickel (NMC, charges to 4.2Vpc).
So 16V+ is not unusual for some lithium ion batteries.

 

[Camp20144]

Looked into panels a little more. It appears to me that these options would fall under a Victron 100/30 SCC. I like the options that allow me to use pre-made 100 foot 8 gauge pv wires giving me more freedom in case of shade. I used Solarwiresizecalculator.com for the pv wire length calcs. The highest voltage loss was 5% to stay at 8 gauge. The only one that went to 6 gauge wire was 2s2p Rich Solar 200 Watt panel configuration. For a mobile ground set array, the 200 Watt panels are a little on the large size (especially for boat access beach camping, no dock) for handling (wind sail 60”x26”) but their weight isn’t bad (26lbs).

HQST 9BB 100 Watt solar panel
Voc = 24.3V
Isc = 5.21A
2s2p = 48.6V 10.42A - 400W solar
3s2p = 72.9V 10.42A - 600W solar

Rich Solar Mega 200 Watt solar panels
Voc = 24.3V
Isc = 10.2A
2s2p = 48.6V 20.2A - 800W solar
3s = 72.9V 10.2A - 600W solar
3s2p = 72.9V 20.4A - 1200W solar

I return to the solar rating that Victron states in the Victron 100/30 SCC documents - “nominal solar input 440W”. I don’t understand why they state this. I have one array below that is 1200 Watts, but it is only 72.9V 20.4A, well below the rated 30A and voltage 100V. The coldest I envision this camping system use is 0 degrees F. In reality any trips below 40 degrees F would probably be “long weekends” - well within 200 Ah of cpap only use - recharge LiFePO4 upon return home.