A122S Wired for Solar by Zamp..Next Step

[Jeck]

Good news...wired for solar! Too bad the roofs are not solar panels.

Will I need more than my 12V battery to sometimes run thermostat/heater-fan, rare light use, built in radio, gas fridge, charge phones, and 1 all-night CPAP machine?

How many watts of panels will I need for 1 12V battery? Or for 2 12V batteries?

[Rich.M]

The answer to your question comes down to how much power your are expecting to use. You will need to realistically estimate how many hours / minutes of use for each of those items. Work out the amp hours for each and add them up. You can then make a determination on battery requirements. You will need to double your amphrs number to determine how many amp hours for batteries. Solar panels generally give you 20-25 amphours per day per 100 watt panel. If you require Cpap then plan to replace your entire daily use with some overage or bring a generator. The heater on gas uses a lot of power for the blower fan, your cpap may use a lot too. I wouldn't be suprised if you come up with 3 or 4 100 amp hour batteries and 300 to 400 watts of solar . If you want your system to work then plan starting with consumption then batteries then solar.

[Bluepill]

FYI, a second group 24 battery fits right next to the original one if you just cut one of the handles off.



It has been reported that the ZAMP wiring is very small gauge and not suitable for more than about 75 - 100 watts of panel output.

[jonshonda]

There is tons of info on how to calculate/estimate amp hour usage and how to determine battery size requirements.

You will need to add an invertor for the cpap as I am guessing they don't run off 12 volts?

My initial guess is you might need to 6v golf cart batteries which provide more capacity. Depending on where you live and camp, you might not be able to depend on solar to provide enough energy to re-supply the batteries.

[Jeck]

Originally Posted by Rich.M

The answer to your question comes down to how much power your are expecting to use. You will need to realistically estimate how many hours / minutes of use for each of those items. Work out the amp hours for each and add them up. You can then make a determination on battery requirements. You will need to double your amphrs number to determine how many amp hours for batteries. Solar panels generally give you 20-25 amphours per day per 100 watt panel. If you require Cpap then plan to replace your entire daily use with some overage or bring a generator. The heater on gas uses a lot of power for the blower fan, your cpap may use a lot too. I wouldn't be suprised if you come up with 3 or 4 100 amp hour batteries and 300 to 400 watts of solar . If you want your system to work then plan starting with consumption then batteries then solar.

Thanks for the clarity Rich...I have read the docs on my devices, but I am still learning which spec means rate of consumption...which sometimes seems to be a range. Thanks again.

[AB_SP295BHS]

A bit of a different angle here, I find that there's several factors associated with this and I'm working my way through them now.

1. A bunch of stuff in your RV consumes much more power than it seems as though they should. I suggest getting a voltmeter(handheld or otherwise) and watching your voltage like a hawk to get to know how intensively you're using the battery you have. Use charts like these to know where you're at and how much you're drawing your batteries down:
https://www.bing.com/images/search?q...hart&FORM=IGRE

2. Ratings on appliances don't mean a hell of a lot, what you're working with is how much they actually use over a sustained period. Estimating times and applying actual utilized amperages is a good start, much better than working from a rated perspective. Find one of these, plug it into your fuse bank and see how much power your system actually consumes in different states:
https://www.bing.com/images/search?v...ter&ajaxhist=0

Then share it here:
http://www.forestriverforums.com/for...ad-132974.html

For your CPAP, a unit like a kill a watt or this one will measure your utilized watts (I'm presuming it needs AC power):
https://www.amazon.com/UPM-Marketing.../dp/B000RKVK52

The other decent advice I've had is to always work in watts, its not that tough to figure through, but when you're starting it is easier to determine the total wattage something will use. You then work back from 50% (assuming lead acid) as a maximum drawdown on your battery you want to see, so, a 12V battery may be from 65AH to 110AH or so, so that means 12.4V * AH yields from 800 to 1350W are there in total so you have from 400W to 675W per battery to work with depending on its size. Once you know how much you're using, keep a safe 'freeboard' of storage so as not to destroy or age your batteries from big drawdowns. So, if you're working with larger capacity batteries of 1350W and you need 1000W per day then 1000/675 = 1.48 which means two batteries. 1000W drawn from a 2,700W storage is a 37% drawdown. If you're in that territory your batteries will last a long time if cared for when not being used.

3. From talking with commercial solar guys, the mean solar yield is 3 to 4 hours in summer, that's a general number and you'll be able to find local estimates, but in concept you're going to get an average of 300 to 400W of power from a 100W panel on the average day. If you do better, great, but don't plan on it.

4. Can your system utilize the power? Your solar charger needs to utilize all the peak power to have the best chance of charging your batteries, if you're generating 100W/12.4V = 8A. My Surveyor trailer has a 15A charger in it, so, with two panels at peak power you're doing as good as being plugged in...for a few hours a day. Its worth noting that you cannot overload a solar controller, at the extreme you can put 2000W of panels on a 900W controller and it is fine...it's a bit counterintuitive but what I'm reading says, that, to some degree you want to exceed to controller's capacity to improve its efficiency and allow it to charge fully over a longer period of time.

5. Charging efficiency is not 100%, I'm not exactly sure yet what I think I'm getting but, some resources say lead acid charging is <80% efficient, some say its nearly 100%...I dunno. The point is the energy is not all converted to storage. Then your solar charger isn't 100% efficient, if PWM the efficiency is probably in the 80's, if MPPT it's probably in the 90's. So, if I take 100W * 4 hrs for 400W from solar, multiply by 80% going through a PWM controller for 320W, then knock off (worst case) 20% for inefficient charging of a lead acid battery, then you're at 250W generated if you get 4 hrs full sun equivalent.

6. Shade...shade is self explanatory, yet impossible to plan effectively for.

[Rich.M]

Originally Posted by AB_SP295BHS

A bit of a different angle here, I find that there's several factors associated with this and I'm working my way through them now.

1. A bunch of stuff in your RV consumes much more power than it seems as though they should. I suggest getting a voltmeter(handheld or otherwise) and watching your voltage like a hawk to get to know how intensively you're using the battery you have. Use charts like these to know where you're at and how much you're drawing your batteries down:
https://www.bing.com/images/search?q...hart&FORM=IGRE

2. Ratings on appliances don't mean a hell of a lot, what you're working with is how much they actually use over a sustained period. Estimating times and applying actual utilized amperages is a good start, much better than working from a rated perspective. Find one of these, plug it into your fuse bank and see how much power your system actually consumes in different states:
https://www.bing.com/images/search?v...ter&ajaxhist=0

Then share it here:
http://www.forestriverforums.com/for...ad-132974.html

For your CPAP, a unit like a kill a watt or this one will measure your utilized watts (I'm presuming it needs AC power):
https://www.amazon.com/UPM-Marketing.../dp/B000RKVK52

The other decent advice I've had is to always work in watts, its not that tough to figure through, but when you're starting it is easier to determine the total wattage something will use. You then work back from 50% (assuming lead acid) as a maximum drawdown on your battery you want to see, so, a 12V battery may be from 65AH to 110AH or so, so that means 12.4V * AH yields from 800 to 1350W are there in total so you have from 400W to 675W per battery to work with depending on its size. Once you know how much you're using, keep a safe 'freeboard' of storage so as not to destroy or age your batteries from big drawdowns. So, if you're working with larger capacity batteries of 1350W and you need 1000W per day then 1000/675 = 1.48 which means two batteries. 1000W drawn from a 2,700W storage is a 37% drawdown. If you're in that territory your batteries will last a long time if cared for when not being used.

3. From talking with commercial solar guys, the mean solar yield is 3 to 4 hours in summer, that's a general number and you'll be able to find local estimates, but in concept you're going to get an average of 300 to 400W of power from a 100W panel on the average day. If you do better, great, but don't plan on it.

4. Can your system utilize the power? Your solar charger needs to utilize all the peak power to have the best chance of charging your batteries, if you're generating 100W/12.4V = 8A. My Surveyor trailer has a 15A charger in it, so, with two panels at peak power you're doing as good as being plugged in...for a few hours a day. Its worth noting that you cannot overload a solar controller, at the extreme you can put 2000W of panels on a 900W controller and it is fine...it's a bit counterintuitive but what I'm reading says, that, to some degree you want to exceed to controller's capacity to improve its efficiency and allow it to charge fully over a longer period of time.

5. Charging efficiency is not 100%, I'm not exactly sure yet what I think I'm getting but, some resources say lead acid charging is <80% efficient, some say its nearly 100%...I dunno. The point is the energy is not all converted to storage. Then your solar charger isn't 100% efficient, if PWM the efficiency is probably in the 80's, if MPPT it's probably in the 90's. So, if I take 100W * 4 hrs for 400W from solar, multiply by 80% going through a PWM controller for 320W, then knock off (worst case) 20% for inefficient charging of a lead acid battery, then you're at 250W generated if you get 4 hrs full sun equivalent.

6. Shade...shade is self explanatory, yet impossible to plan effectively for.

Your interchanging watthours for watts, that may be confusing for some to follow.

[ScottBrownstein]

There is a much easier way to figure out what you will get from a solar installation. Go to PVWatts Calculator, follow the forms and fill in your location and put in the panel wattage, generally open and flat rather than angled...and it will tell you my month what you can expect. This takes most of the variables into account like weather, sun angle and temperature.

[Bluepill]

Some interesting data supplied by another owner:

I just received a random email bump from the forum, and as it turns out I have some valuable info to share. I just spent the morning with a Fluke Multi Meter attached to my Surveyor sport, have taken these load readings.

For my base line I had to pull both 40 Amp fuses on the DC side of my converter to get Zero Load. The Converter has a 0.011 amp load with no other loads. I disconnected all other loads, and found there values by reconnecting them One-at-a-time...............

Nat Gas detector (hot all the time)......... 0.07 amps dc
Radio (hot all the time) off at idle........... 0.03 amps
Radio on FM at half volume................... 0.42 amps
Water heater calling on propane..............0.7 amps
Frig calling on Propane..........................0.81 amps
Fantastic fan on low..............................0.93 amps
'' '' med.............................1.22 amps
'' '' Hi................................1.54 amps
Water pump on, but satisfied..................0.025 amps
Water pump calling...............................3.0 amps
Furnace fan only...................................2.8 amps
Furnace calling ....................................3.3 amps
One incandescent bulb in my outside lite...1.56 amps (that's one bulb!)
dbl head overhead inside lite...................3.20 amps
I have LED lamps in my interior fixtures now, and
each lamp draws only ...........................0.20 amps

I am installing a switch on my Nat Gas detector for times when I am boon docking, and need max battery life. May pull the fuses on the converter too. Not much of a load, but constant.

[DRiveWell]

Bluepill, Thanks for your post. Covers almost all of what I use when boondocking. 224 amp-hour batt, 275 watt panel.

[AB_SP295BHS]

Originally Posted by ScottBrownstein

There is a much easier way to figure out what you will get from a solar installation. Go to PVWatts Calculator, follow the forms and fill in your location and put in the panel wattage, generally open and flat rather than angled...and it will tell you my month what you can expect. This takes most of the variables into account like weather, sun angle and temperature.

Thanks, that's useful. Had looked for something like that and had to figure it out on my own! Just make sure you put your array size in kw, not watts...sat here mystified looking at the results for a while till I redid the calcs. Looks to validate my rough rules but much better...

[AB_SP295BHS]

There's a solar simulator called SAM on that site, it includes selectable equipment lists, uses your local data and provides economic outcomes. If you've looked at this stuff much you'll be able to get some value from it quickly by using a lot of the defaults.

https://sam.nrel.gov/download

[Windjammingnc]

One thing to consider is even with a Deep Cycle Battery, you shouldn't discharge deeper than 50%, so a 200 AH battery will give you 100AH of usable discharge (you can go down to 25-30% occasionally but not regularly without damage to the battery).

I measured a friend's CPAP with the Kill-A-Watt and it was right around 105 VA Peak. So, if you estimate 8 hours of sleep, you are likely drawing about 100VA/12.5v = 8Amps or 64 Amp-Hours.

Our TT's electronics draw about 1.5A (no lights, etc) so another 12AH for that so you are talking 76 AH minimum not including any other 12V devices running for those 8 hours and not including 12V stuff during the period between loss of solar and sleep.

YOu likely need to recover at least 100AH during the day which is about 1200WH assuming 100% efficiency which is not really valid with charge eff. and other factors.

We have 200W of solar with a MPPT controller and during the day, we can net 10-11A of charge (less 1.5A for electronics) with full sun. Even with 8 hours of good sun, we wouldn't be able to recharge 100AH of discharge with what we have. But we typically only draw down about 60AH max. in the evening/overnight.

We carry a Honda 2000 as well and replaced the stock Converter with a PD 9200 with Charge Wizard to supplement the solar so we can add charge before/after sun.