Just Started

[Rvnquest]

My first attempt at building a battery back up for my cpap machine (and other small electronics). Had a 20% discount, and bought two deep cycle batteries. Inverter is on the way. Next step, the solar component. Figure until I can afford all the parts, a short term outage, I can use a regular auto battery charger?

[Tiker]

I think since they are mostly just lead acid battery's. Do use a conventional charger (not one that also discharges) as some do if you use them to keep connected in the winter, this will reduce the life span of you deep cycle batteries.

[Caneman]

Originally Posted by Rvnquest

My first attempt at building a battery back up for my cpap machine (and other small electronics). Had a 20% discount, and bought two deep cycle batteries. Inverter is on the way. Next step, the solar component. Figure until I can afford all the parts, a short term outage, I can use a regular auto battery charger?

what you need is a battery maintainer... it will top off the charge and then "trickle charge" it so that batteries don't discharge and get ruined while keeping them in backup... you will want to use the batteries once per month to ensure they work properly...

[Rvnquest]

Think what my parents have is just a normal charger. I will be buying the solar component soon.

[Rvnquest]

Considering this: http://www.cabelas.com/product/Sunfo...h-All+Products as it all is pre-wired. Other option would be one of the trickle type, 5-12 w.

[Caneman]

if all you are doing is keeping a few 12v or 6v batteries chareged, or charging them, you may want to look at the HF kit... i think it comes with everything: panels, charge controller, not sure if it comes with fuses/wiring/lugs etc.

[Rvnquest]

Originally Posted by Caneman

if all you are doing is keeping a few 12v or 6v batteries chareged, or charging them, you may want to look at the HF kit... i think it comes with everything: panels, charge controller, not sure if it comes with fuses/wiring/lugs etc.

HF? Harbor Freight?

[Caneman]

yes, sorry... Harbor Freight

http://www.harborfreight.com/solar-p...att-68751.html

[Rvnquest]

Has anybody used CEA Solar panels? A USA made panel, portable.

[Rvnquest]

Originally Posted by Caneman

yes, sorry... Harbor Freight

http://www.harborfreight.com/solar-p...att-68751.html

Will add that one to the list as well. Thanks!

[Rvnquest]

OK, talked to a company with portable solar panels (I don't own my house) and I like the kits, plus they are made in the USA. Company indicated to do what I want, to power one cpap, charge a cell phone, and run a coffee pot (OK, this is a luxury, and could skip it), I would need 135 watt panel with my two batteries. He indicated if I don't have one, would need a 1500 watt inverter.

A question about inverters: I have ordered one, just for the cpap machine, until I can get the whole solar portion of the system set up. BUT . . . the cpap machine needs pure sine wave inverters. Pure sine wave 1500 inverters are very expensive, and vary in price from about $200-$500. Modified sine wave inverters are less expensive. Can you put two inverters on the batteries? One, which I already have, for the cpap only. The other for the other appliances? Or should I lay out the bigger dollars for the better inverter?

[Caneman]

you can put two inverters off of one battery or battery bank, so long as their combined loads (running at the same time) do not over-discharge the batteries... rule of thumb i learned is 50% of the batteries rating for momentary loads, 20% of the batteries rating for short durations, and 10% for continuous use...

example, your battery bank is rated for 200 amp-hours at 12 volts, that is a total of 2400w available: startup load @ 50% = 1200w, short duration load @ 20% = 480w, continuous loads @ 10% = 240w

about 90% of the time the modified sine wave will work with most appliances just fine, but since your cpap is a life-dependent machine, and if it was me, i would spend the extra money for the PSW inverter...

what is the cpap continuous load and startup load? if you need a 1500w inverter then it seems like a pretty big load...

[Rvnquest]

It was for the coffee maker that he stated I needed a 1500 watt inverter. The cpap is 40 watts. Wouldn't be running them at the same time.

[Caneman]

^^^ if all you need is 40w for the cpap you can get a 300w PSW inverter for it for around $125... the coffee maker only needs a MSW inverter and you can get a 1500w for around $200...

a 1500w PSW inverter would run you about $500-$800...

resistive loads like a coffee maker or electric heater are not good for solar power systems, imo, they draw too many watts too quickly from your batteries and that is not good for the battery bank... its OK if it is is just once in a while, but not so on a regular basis...

if your cpap draws 40w, and you run it say 8 hours per day, that is a total daily load of 40*8 = 320w...

you only want to draw your battery down about 50% daily as a maximum (actually the lower the better, like 20%), so your battery bank should be at least 320w/0.5 = 640w (two 6 volt golf cart batteries in series would work well and give you 200 amp-hours at 12v)...

you can harvest the sun about 5 hours per day on average, problem is during the winter and if it is cloudy/overcast you will only be able to harvest about 20% or so of your solar array max (if it is cloudy the suns rays still hit the panel, but at much less intensity).... so what i am getting at is that your panel array size should be 320/(0.2) = 1600w, but because of losses from the panels all the way to your to your cpap you will only have about 60% of the energy harvested... your array size should be 1600w/0.6 = 2667w... and you can harvest the sun 5 hours per day, 2667/5 = 533w... using 135w panels that would be 533w/135 = 3.95, which means 4 panels! -this is the worst case scenario

i know this seems like overkill, but if you design your system for the 100% harvested sun energy available you will be disappointed! I have a 1KW system at home for backup, and it uses about 1000w daily for the house just to keep the system running and for fun... the system can harvest 720w to the battery bank at its best moment in the middle of summer, in the winter on a cloudy day it tops out at 120w! not trying to rain on your parade just hoping you are not disappointed in your system after you spend the time and $$$ getting it put together

solar always demands more than you think, and delivers less than you expect