Good Morning. I am hoping someone can provide a simple answer or 4 for me. I just read a post on the TC forum about flexible, light weight 100 watt solar panels and love the look of this, I have a Northstar 850SC pop up that this would go on. I have plenty of room over the bed end for these with out shadows from roof top stuff. I currently have 1 Interstate SRM-27 listed as 160 RC. (I will be adding a 2nd) I would prefer 31s but am not sure about the space available yet.#1- Does the 160 RC on the battery mean 160 amps?#2-50% discharge or 80amps (If #1 is yes) or 12.2 volts is the lowest I want to take this battery on a regular basis, correct? Therefore 2 would give me 160 amps? #3- The listed optimum amps for this 100W panel is 5.7 amps with a max fuse of 10amps. Does this mean that 2 of these on the 20 amp controller is appropriate as the minimum? 30 safer? Could I run 3 on a 30?#4- What is the rule of thumb for minimums watts per battery? I know sunlight hours and shade, etc affect all of this. I see some with 270 or more watts but no mention of how many batteries this supports.My goal with all this is to get my wife out more with me. We both use CPAP (12v ). She is not as comfy with out some of the comforts of home as I am. We live in NH and the State Parks in NH and VT as well as the White Mt. and Green Mt. National Forest sites are almost entirely off grid.I have learned a lot from this forum and want to thank every one for their posts.

kjenckes wrote:Good Morning. I am hoping someone can provide a simple answer or 4 for me. I just read a post on the TC forum about flexible, light weight 100 watt solar panels and love the look of this, I have a Northstar 850SC pop up that this would go on. I have plenty of room over the bed end for these with out shadows from roof top stuff. I currently have 1 Interstate SRM-27 listed as 160 RC. (I will be adding a 2nd) I would prefer 31s but am not sure about the space available yet.#1- Does the 160 RC on the battery mean 160 amps?#2-50% discharge or 80amps (If #1 is yes) or 12.2 volts is the lowest I want to take this battery on a regular basis, correct? Therefore 2 would give me 160 amps? #3- The listed optimum amps for this 100W panel is 5.7 amps with a max fuse of 10amps. Does this mean that 2 of these on the 20 amp controller is appropriate as the minimum? 30 safer? Could I run 3 on a 30?#4- What is the rule of thumb for minimums watts per battery? I know sunlight hours and shade, etc affect all of this. I see some with 270 or more watts but no mention of how many batteries this supports.My goal with all this is to get my wife out more with me. We both use CPAP (12v ). She is not as comfy with out some of the comforts of home as I am. We live in NH and the State Parks in NH and VT as well as the White Mt. and Green Mt. National Forest sites are almost entirely off grid.I have learned a lot from this forum and want to thank every one for their posts.1. Maybe 105 amp hours (not "amps" BTW)2. Correct, except two 52s3.a. Use the panel's Isc for your "expected amps" in full sun. The usual 100w panel has Isc about 6.3a3.b. Size the controller to have a 20% margin over the total Isc. So two 100w in parallel gets you expected amps of 12.6 and 20% of that is 2.5 so plan for a controller at least 15a, so a 20amp is plenty.4. There is no valid rule of thumb since there is no common scenario for each Rver. The weatherman runs the show anyway, so you get what you get on any given day. Just get as much solar as you can fit or can afford and be ready to run the generator if the weatherman is in a bad mood. But in general, for the likely usage of a truck camper, 200w is bags of solar most of the time unless you are in the woods where solar is fairly useless no matter how many watts you have.5. An inverter will let you run 120v stuff off grid. DW will love having some 120. (as long as she knows not to run the batteries down too much)6. Find the "Screwy 31" thread. Read it and weep. Don't get 31s

Lots needs to be considered to properly set up solar for your rig. You can base it on how much power you use. How much battery you have. What kind of conditions you are in. Honestly though, it's a combination of all of them.A properly balanced system starts with you knowing how much power you use daily. You need enough battery to support that use for X amount of days. I say X because it is affected by room and budget. Once you know how much battery to have, get enough solar to get them back up quickly after a few days of clouds. A prudent thing to have is a back up means of charging for when MR sun doesn't play nice for too long.Now that you know how much solar to get, balanced with amount of room on the roof and budget, you can start thinking about which panel/s fit your needs and conditions the best. The most efficient panel in bright sun sucks in lower light. The panel that can provide in lower light is huge in foot print for the watts it produces. The choice is a balance of room, budget and production. In the end you may have to compromise.One thing I have learned about batteries from the forum is that some of the cooler ones are just a PITA to keep charged up. I have the same grp 27 as you and it is easy to keep up. I would have to replace my charge controllers and converter to switch to fancy AGM batteries. Again, making sure al of the components work well together is part of the balance.You asked about the watt vs AH ratio. We have 720w of panel for 345 ah of battery. That gets the batteries up fast when we have limited sun and keeps them in float all day unless we run a big load like the microwave. Even then the recovery is very quick and the batts are always fully charged by night fall. Loads that are smaller than the output of the panels are not seen by the battery at all. The TV/sat runs all day and never has a effect. next year I'll run a 5000 BTU AC unit and if it doesn't run straight off the panel, what comes out of the battery will be very little.My panels are huge and not 12v, so I'll let others advise you on the proper set up.

Don't get all that excited with 100WATT SOLAR PANELS... A 100WATT Panel will only produce around 4-5AMPS DC CURRENT for the time they are in HIGH SUN. The rule of thumb is around 5-6 hours each day is the normal time you can expect full output of the panels. Out west in wide open country gives you more high sun of course...Your SRM-27 with a Reserve Capacity of 160 minutes will only produce 12VDC Power@25 AMPS for around 160 minutes (2.7Hrs). Having two in parallel will raise this to around 5.3 HRS... If you do this your batteries will be drained to their 0% charge state or 10.5VDC. You really don't want to ever do this to your batteries and most of us respect the 50% charge state and I really get excited when my batteries drop below 12.0VDC. Most of us think continuing to drop below the 50% charge state will do harm to your batteries. My thinking is to beef the battery banks and battery associated battery cables etc to run the thing you want to run when camping off the power grid so that you can operate things until 8AM the next morning when you are allowed to run a generator to re-charge your batteries...To me adding solar panels only enhances this operation and perhaps you won't have to run your generator as long each day to keep up with battery drains.All of us knows that in order to re-charge a 50% depleted battery it will take around 14.4VDC at a 20AMP DC Source for each battery in the battery bank. This will drop back to 13.6VDC after a two hour run and give you a safe 90% charge state on the batteries in around three hours total time. With a 90% charge state you can do the run off the batteries again for the next day/night battery run.If by adding solar panels you can expect around 5AMP of charge current going into your battery bank and if you have enough panels you might get this up to around 15AMPS for 6 hours on your TC roof size. In 5-6 hours this will put back around 30AHs into your batteries. If you day/night run off the batteries is less than 30AHs then the solar panels will be great for you to have. You will never get behind the battery drain curve having them.Of course this is not always guaranteed as some days will be cloudy and this could last several days where you won't get any charge at all that you can use. You would need to have the generator running your on-board converter/charger to replenish your battery charge for these days... I have been playing this day/night run on my batteries for a few years and we get by pretty good with our routine with around 255AH Battery Bank capacity. This of course have to be re-charged each day starting at 8AM each morning with our 2KW Generator running our trailer and allowing the on-board converter/charger to bring them back up to their 90% charge state so we can do it all over again the next day/night run off the batteries.My OFF-ROAD POPUP Trailer roof is much the same size as your TC ROOF and I am planning on adding two 120WATT Panels in the front and then a 240large panel on the rear side. This 480 Watts of solar should give me a good 14.4VDC @ 20AMPS for around 5-6 hours a day (160AHs) and really help me out keeping my battery bank drain so that using the generator will be minimal. Since my three batteries normally draw about 53AMPS DC current when first hit with 14.4VDC charge voltage I will have to use the generator for that first 0NE hour charge period. After the battery start tapering off the solar panels can deal with the charge source amps pretty good then. Then I can hopefully switch to the solar panels for the rest of the day to top off my battery bank to the 90% charge before the high sun goes away... This is going to be my basic routine at any rate when camping off the power grid. This is my take on adding solar panels for our camping off the power grid routine. All of this takes planning... Others have different ideas on what to expect but I am pretty confident based on my few years of running entirely off the batteries this is what will happen for us when we finally get solar panels installed. We watch our BATTERY MONITOR PANEL like a hawk knowing when it hits 12.0VDC we have to shut it all down... This is planned to happen at 8AM the next morning when I can deal with it... For your situation you may get by just fine having the solar panels and not get into your battery reserve capacity. What happens if it doesn't work like you have planned. Got to have a good PLAN B hehe... Not fun when lights go out at 10PM at night especially for needing the CPAP at night... For us a generator is must have item and as you know we folks that live on the East side of the US have all of the generator run time restrictions to deal with. So bigger battery banks and solar is good way to go...Just adding another GP27 battery will only give you an additional 96AH of capacity. So you question is can you live on 192AHs of battery capacity especially when you can only use 96AHs of that total so that your batteries will not go below 50% charge state. Add up your DC power drain and how long you expect to use it and see how you want to be battery wise. i.e your CPAP draining 12VDC@3AMPS needing to run for 8 hours will consume 24AHs of capacity... Just considering that only leaves you 72Ahs for other 12VDC drains. Not much to play with. Watching TV for 6 hours will eat up at least 24AHs... Hopefully you have changed over to LED lights already. Just passing along for food for thought on your end...Roy Ken

Battery length 10-3/4" Group 24 85 amp hours12" long group 27 100 amp hours13" lone group 29-30-31 110 amp hours

RC 160 does not indicate amphours and most group 27 batteries hover around 100 amphours give or take and that is for a 100% fully charged, non-sulphated battery in prime condition.Adding a second battery would indeed add amphours, but the second battery will be dragged down by the older battery. You would add the amphours if using 12 volt jars giving you around 200 amphours with roughly 100 amphours to burn before reaching 50% discharge. Of course these are estimates and real world performance is usually lower than expected. Pairing batteries of the same age, specs, and manufacturer would yield better results.As long as amps don't exceed a controllers capabilities you could group as many as the controller is rated to handle. A 100 watt panel will require a 10amp controller, but you could group four 100watt panels on a 30amp controller. The max amps delivered by the 100watt panel will only occur for a few hours a day if conditions are ideal. That is not an easy question to answer as there are too many variables involved. The main concern is what exactly do you expect from your solar array. Are you needing to get through a few days of camping and just need to get battery bank to roughly 80-90% SOC, or are you planning month long excursions where you want to reach full SOC on a regular basis. A 100 watt panel for each battery would be a good start without knowing your actual daily amphour consumption, with decent sunshine you would more than likely get into the 80-90% SOC daily which is fine for a week or so of camping. Actual results will vary of course, metering the amount of amphours you consume and amps delivered by your solar array will yield pertinent information for fine tuning your system to achieve the expected results you desire.Solar has worked well for us, but camping in the White Mountains of NM or AZ in our neck of the woods usually means that solar will be limited due to the tree cover, for those situations we use our generator and Iota converter to quickly restore consumed amphours. Additionally, having the genny along we can run high amperage items like the microwave/convection oven, AC unit, portable space heaters, and heated hair appliances used by my DW and 3 DDs when camping off the power grid. We prefer boondocking and being 100% self-contained makes everybody happy knowing we can power our entire rig as if we were connected to shore power.

Solar and battery help | Good Sam Community

kjenckes
Explorer
Oct 25, 2014
Thank you everyone for all of your time and help. With 238 views to this point I imagine it has helped many others as well.
time2roll
Nomad
Oct 25, 2014
RC is reserve capacity in minutes. 160 RC = 25 amps for 160 minutes before you reach 10.5 volts. It is a hybrid rating as it does measure a deep cycle but at a fairly heavy load. More capacity available with a slower discharge.
Almot
Explorer III
Oct 25, 2014
kjenckes wrote:

My goal with all this is to get my wife out more with me. We both use CPAP (12v ). She is not as comfy with out some of the comforts of home as I am. We live in NH and the State Parks in NH and VT as well as the White Mt. and Green Mt. National Forest sites are almost entirely off grid.

She won't be too happy on solar. Not with 2*100W for sure. "Some" comforts of home can draw more than 70% of your daily solar harvest, and nearly all of those comforts you can either live without or find low-energy substitutes. But when lady wants something, there is no use in reasoning. My friend living fulltime in 5-er with 400W solar has to run a generator every time when DW sits down with her favorite pastime - quilted blankets, it needs big 120V iron.

#3: With nominal 12V panels, i.e. up to 160W each, the controller amps rating = total panel amps + 20%. So with 4*5.7A you need roughly 30A controller. With larger panels like 200W each, controller rating is calculated differently.

I don't know why you've set your mind on flexible 100W - bigger wattage rigid panels are cheaper per watt. Also, more durable. Like Roy said, try getting as much solar up on the roof as you can. It should be possible to put more than 400W on a TC.

#4: The rule of N watts per M amp-hours of battery (roughly 1W per 1 AH) is a minimum wattage, to make sure that battery will get fully charged on a good day. There is no such thing as too much solar, the more - the better. On a dark day a 500W solar will collect as little as a 100W solar on a good day.

And, as soon as you batteries will start showing signs of aging (shouldn't take long) - replace them with proper deep-cycle ones. This is NOT an option.
scrubjaysnest
Explorer
Nov 04, 2014
kjenckes wrote:
Good Morning. I am hoping someone can provide a simple answer or 4 for me. I just read a post on the TC forum about flexible, light weight 100 watt solar panels and love the look of this, I have a Northstar 850SC pop up that this would go on. I have plenty of room over the bed end for these with out shadows from roof top stuff. I currently have 1 Interstate SRM-27 listed as 160 RC. (I will be adding a 2nd) I would prefer 31s but am not sure about the space available yet.

#1- Does the 160 RC on the battery mean 160 amps?

No RC is reserve cranking amps; 160 RC implies 95 to 105 aH

#2-50% discharge or 80amps (If #1 is yes) or 12.2 volts is the lowest I want to take this battery on a regular basis, correct? Therefore 2 would give me 160 amps?

12.2 volts is a good choice; two size 27 deep cycles will be 190 aH to 210aH

#3- The listed optimum amps for this 100W panel is 5.7 amps with a max fuse of 10amps. Does this mean that 2 of these on the 20 amp controller is appropriate as the minimum? 30 safer? Could I run 3 on a 30?

Depends on the controller size; fuse sizing is determined by NEC

#4- What is the rule of thumb for minimums watts per battery? I know sunlight hours and shade, etc affect all of this. I see some with 270 or more watts but no mention of how many batteries this supports.

The rule of thumb is 80 to 100 watts per 100 aH of battery

The output of a solar panel will vary quite a bit over time of year and full sun vs cloudy or shade. Max output usually occurs between 10 AM and 3 PM in full sun but this is another general rule. We have two 80 watt panels feeding a TS-45 controller which charges a pair of Exide Stowaway 105 aH batteries. All main lighting is LED, no microwave, TV, or other high usage (wattage) devices. We are very conservative with power usage and get 7 to 10 days before the batteries reach 12.2 volts(60% soc). Connecting the solar panels at that point takes 4 to 6 hours to recover the 40% used.
I suggest an internet search for the 12 volt side of life and a visit to batteryfaq.org.
Wiring between the panels should be as short as possible and no smaller the 10 awg. Batteries should be the same age and wiring from the controller to the batteries no smaller then 8 awg.
If you decide on 3 panels you may find the cost of a mppt controller to be worth while(300 watts is right at the dividing line).

For cpap you want the most efficient your budget can afford if going with 12 volt.
RJsfishin
Explorer
Nov 05, 2014
Quote:
No RC is reserve cranking amps;
---------------------------------
Readers, beware !!
Almot
Explorer III
Nov 05, 2014
scrubjaysnest wrote:
We have two 80 watt panels feeding a TS-45 controller which charges a pair of Exide Stowaway 105 aH batteries. All main lighting is LED, no microwave, TV, or other high usage (wattage) devices. We are very conservative with power usage and get 7 to 10 days before the batteries reach 12.2 volts(60% soc). Connecting the solar panels at that point takes 4 to 6 hours to recover the 40% used.

You're lucky somebody like BFL13 haven't read this, or you would've been labeled as a caveman :)... Every time I'm telling that one CAN live on 30-35 AH a day and have hot meals, warm trailer and some laptop or TV time, a lot of people get skeptical. Living without a microwave is considered impossible, for some reason.

8 days down to 60% on a pair of 105AH batts means 84 Ah total or 11 AH a day. I would say, this is too low even by my standards. Propane fridge draws at least 8 AH a day. AGM battery self-discharge is negligible, alright, but remaining 3 AH (or less) leaves you with a couple of LED lights and not much more. No fan in a hot weather, no heater (other than non-vented propane).

It would be difficult harvesting 84 AH in one day with 160W solar. With flat permanently mounted panels - very difficult. With portable panels - still difficult, but maybe, yes. Tilting and changing the azimuth angle every hour, and on the longest day of summer and if it's really sunny and not too hot. The bottom line - I wouldn't count on getting that much. Unless you are somewhere close to equator.
BFL13
Explorer II
Nov 05, 2014
His real crime is taking a week to get down to 50% all the while his batteries are undercharged and sulfating like mad. Too long between recharges.

Another crimes is using a TS45 when a $15 RJ Special controller would do. :)

As for 84AH with 160w, I was getting 56AH flat, 70AH tilted, and 90 AH tracking with my 130w in May at 49.3N
Almot
Explorer III
Nov 06, 2014
Must be one of those occasions when I (almost) agree with BFL.

Yes, TS45 is overkill unless there are plans to expand to at least 500W. Some 10A-15A Morningstar or Steka would do - or Xantrex PWM 35, they all cost about the same. I would not buy $15 gizmo when solar is the only source of power and therefore needs to be reliable.

I'm not sure about sulfating in AGM. What he is doing is a one week-long cycle 100 to 60, and only then charging it to 100 again. Kinda self-discharge, only faster. You can let AGM sit and self-discharge all year, it will drop to about 60% over that period without major consequences.
Though I would rather keep them charging every day, getting 11 AH a day shouldn't be difficult unless the weather pattern is 7 days of rain and then all sunny. In fact, with daily charging they would need less than 11 because some juice would've got directly to devices in daytime, so the battery would discharge by less than 11 AH a day.

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