Battery Bank

[Tarheel]

Has anyone found a serviceable locatation for multiple batteries? I would love to have an inverter along with additional batteries to store the energy. I have a 94 34 with dual 27 series batteries. Being a limited the propane tanks are horizontal in lieu of vertical this pretty much eliminates the tongue area.

[Silvertwinkie]

Instead of engineering all that have you considered just getting a small generator to top off the batteries if you boondock a bunch?

Eric

[RoadKingMoe]

I also have a 34' Limited, and have decided there just isn't sufficient space (and not a lot of weight capacity either) for more batteries. And more batteries is certainly what I'd want for an inverter of any size.

The Airstream really isn't laid out well for a whole house inverter either. While my tanks are vertical and I could replace the converter under the couch with a big inverter/charger, there wouldn't be sufficient cooling at full output. There's a guy here who put one in a couch arm but I sure don't like the looks of it.

I'd have to run about 40' of heavy gauge wire from the trailer cord in the bedroom overhead down under the trailer and forward to the inverter/charger's transfer switch, then run another 40' back to another AC breaker box. One could get by with one long run with a separate transfer switch at the breaker box. I wouldn't want the breakers for the AC or electric water heater element powered off the inverter.

If you calculate the Peukert capacity and factor for your two batteries, you can then see what a typical coffeemaker run from an inverter actually takes out them. A Melitta coffeemaker filled with water boiled on the stove is a lot less energy intensive. A microwave is pretty hard on them too. A small inverter for the TV (which I'd prefer to be 12V), satellite receiver, DVD player, etc isn't bad though.

The little Honda EU2000 is the route for us. We have two for air-conditioning.

See if the 130AH Trojan Group 31 deep-cycles will fit in the battery compartments. I think they will, but haven't had a change to measure.

[Tarheel]

I opted for the Honda EB 3000 genset because I couldn't seem to find the right place to store extra batteries. I was just curious if someone out there had found a magic hidden space that I had failed to consider. I worked on Nuke Subs for 35 years and there is always one more marginally adequate space to stuff one more thing. Airstreams remind me a lot of those black boats.
A maul and a shoehorn will get a 29 series in the trays but only an act of God will get them out. I have 27's in there now.
We go to rallys and are taking the Southwestern in April, don't do a lot of boondocking but even at international there were times that a little extra 120 would have been nice, not necessary but nice.

[RoadKingMoe]

The 115AH Trojan 24TMH is 12-3/4 X 6-3/4 X 9-3/4

The 130AH Trojan 31XHS is 13 X 6-3/4 X 9-1/2

I think 1/4" longer but 1/4" shorter batteries should fit.

[nellie the elephant]

Tarheel,
This is a relevent topic for me, and right up my alley of recent A/S projects. I am personally not one for the sound of generators, or the smell. My efforts latley have been in the area of trying to figure out how to get more battery space as well...for my 22 foot safari, and how to keep them topped off all the time using PV solar panels. I have recently managed to aquire three smaller sized PV panels that I intend to wire in paralel and mount permanently on my roof. I found the perfect charge controller online (sun systems), which will keep my batteries from getting overcharged.

Now, the dilema of space. I concluded that there where two options in my case: 1) one spot under the sleeper sofa, behind a cubby (I had to take the sleeper apart to realize this spot was there) or 2) on the floor of my stand-up closet.

The closet just so happened to be very close to the rear, where the batteries are stored, so I thought that the cable run would be easier. I ended up using a 12' jumper cable (just cut off the ends) to connect the two batteries in paralel. It was a doozy trying to fish the cables from the back of the closet, under the tub, to get to where the other battery is kept. I bought two brand new 115 AH batteries from Costco (nice price btw).

I then built a little wooden enclosure around the battery on the closet floor (it's like a little step to put shoes or a tool box on). I am however a bit concerned about venting the battery....

This is where I need help from the forum: will the fumes or vapor coming from the battery inside of my closet, be released into the room, and toxify me while I am sleeping? Is it so minute that I will never notice?

Also Tarheel, I bought a mini inverter at Costco for 40 bucks, that will plug into my cig lighter, in case I want to run the tv, or whatever.

I will keep you posted on how the solar panels work once I get them all wired up.

[RoadKingMoe]

Had you bought sealed absorbed glass mat (AGM) batteries, you wouldn't have to worry about hydrogen building up in the closet. The box MIGHT keep the corrosive mist off the clothes in there though.

[thenewkid64]

You need to vent the space some how. The boom factor is more of an issue that the fumes in your sleep.

The bigger issue is the localized weight. I have heard stories of towing over rough roads that caused batteries mounted like you have to pulverize the floor, or at the worse over stress an outrigger and the floor and fall through. I would consider adding some additional structure to the floor/frame there if you plan on doing nay rough towing. JMHO

[RoadKingMoe]

That's another issue with Airstreams... roof area for panels. You'd be surprised how little there is up there on a 34 for solar panels after two Fantastic Vents, two skylights and the air-conditioner. We only have one 56" stretch and one 52" stretch of roof available for panels.

A horizontally mounted 110-120W panel such as the Shell SM-110 (52") or Kyocera KC-120 (56"), puts out about 20AH/day in Spring and Fall, and 30AH in Summer with a MPPT controller. About enough to run a Fantastic Vent on medium for 8 hours Spring and Fall, 12 hours in Summer.

Two panels wouldn't look too bad on the roof, but they wouldn't even keep up with our daily use if one vent fan was on. Four would fit, but they'd so wide they'd be pretty obvious and detract from the Airstream appearance. Three of them might take care of one day's use plus one fan. The fourth would be there to make up for one rainy day over three following sunny days.

Using 40% of two 130AH batteries (90% charge down to 50%charge) would give us two days use at 50AH. One night's use, plus one might of backup for a rainy day.

Since rainy days often come in twos, threes or more, we'd need a generator any way.

So instead of buying a $2500 solar system to go with it, we just skipped the solar system, and bought a second generator for $859 so we could have air-conditioning too.

[Tarheel]

I guess in reality the extra batteries, solar panels and generator are just niceties rather than necessities. I have a 30 amp service dedicated to the trailer at home and I stay in campgrounds when we travel. The only time that I have camped without full power has been at the Sugar Creek Rally and the International in Vermont. I have lost power at home and moved into the trailer and used generator power several times. Just knowing that the power is there if you need it be it a bank of batteries or an aircooled engine is a lot of reassurance. My working world was one of redundancy but I don't live in a submarine and a day with limited electrical power in my Airstream would not be a life threatening situation. So I guess I'll just take along the little genset which doesn't weight anymore than two batteries and keep it in the back of the pick-up just in case.

[Tinsel Loaf]

RoadkingMoe
The inverter in the arm of the couch works perfect. It runs everything without worrying about turning off something even on the hottest days when plugged into shore power or running on the generator. The unit has never overheated or shutdown because of excessive load or heat. There is more than ample air flow around the inverter in this location.
One must be aware about loads while the unit is in the inverter mode otherwise you will drain your battery or batteries in short order. Also if you demand to much power the battery voltage will drop ( my low limit is set at 10.8 volts) and the inverter will go to sleep. Adjust your load and you can restart or it will restart itself in a few seconds. As for wiring you do not need to run any wires out side of the AS. I measured the wire run both ways, cut, labeled and pulled the wires through flexible conduit outside and next to the trailer in the driveway leaving some bare wire for pulling through the AS floor conduit. Examine your unit carefully you will find that you can pull the conduit from the ac junction box in the storage compartment through the unit to just below the microwave and through the Airstream 2" conduit under the floor and up under the couch. I attached any DC wires like the rear camera, alarm and extra wires to the outside of my conduit using electrical tape. When you get to the Airstream conduit there are two pieces, one for AC and one for DC wire. My conduit stops a couple of inches into the Airstreams 2" AC conduit and pull the rest of the AC wire through the AC Airstream conduit and the DC wires goes through the DC conduit. Don't pull your conduit through the AS conduit, just the wires. The wires that from the Airstream conduit under the couch pull it through some extra conduit and push the conduit a couple inches into the Airstream conduit, run it to a breaker switch which you mount by the inverter that is now your main. You can now wire the inverter according to the inverter instructions. All the AC wires are in conduit from the from the back to the front and you never even touch the Airstream OEM breaker system, all the AS wiring is done in the storage compartment where the AC inters the Airstream in the storage compartment, junction box. It is helpful to run a fish from under the microwave to the rear storage to get the wire to that point. Then run your fish through the AS conduit starting at the couch end which is next to the wall and pull your wire through. Absolutely no AC wires are exposed, everything is in conduit.
Maurice, you have judged a book by it's cover, and would appear that you have not looked really closely at your Airstream as I have mine. This system works and works well.

[RoadKingMoe]

Tinsel Loaf, I haven't misjudged anything. All I said was, "I sure don't like the looks of it." I've seen your picture of it, and you did the best you could locating it in the couch arm, but to put it politely, I think it detracts from the appearance of your trailer interior.

There was no need to go into the explanation of the conduit. I agree that's what I'd use also. I personally would not wire it so that the AC or electric element in the water heater could operate off it. Your trailer, your call.

[RoadKingMoe]

Let me add something here, Tinsel Loaf. You say, "It [the inverter] runs everything without worrying about turning off something even on the hottest days when plugged into shore power or running on the generator."

From this statement, and from your previous posts, it's clear you don't understand how your inverter/charger works. When you are plugged into shore power or running on the generator, your inverter isn't running anything. The transfer switch in it disconnects the trailer from the inverter output and connects it directly to the shore power or generator.

Your inverter does not condition or augment the shore or generator power as you've claimed previously. When that power is out of spec, the inverter switches out of charging mode, disconnects the shore or generator power from the trailer, connects the trailer to the inverter output and begins providing the ENTIRE AC power from the batteries. When the shore or generator power comes back into spec, your ProSine switches the trailer off the inverter output, onto the shore or campground power.

That ENTIRE AC load is murder on two batteries if the air-conditioner and/or electric element in the water heater is on. If the campground power dropped out with these on while you were gone, the big 3KW inverter could cook the batteries before they dropped below the shut-off voltage. Those battery temperature sensors are only used when the ProSine is charging, not when it is inverting.

Marshall Swartz and I've explained this in more detail in this thread.

[RoadKingMoe]

Let's look at what a larger inverter can do to a pair of batteries. We'll pick the Trojan 27TMH which has 115AH at the 20 hour rate (115/20=5.75A discharge rate) and a Reserve Capacity of 200 minutes (3.3 hours) at a 25A discharge rate. At best, two of these give us 115AH before dropping below 50% charge.

The formula to calculate the Peukert Exponent n is n = (logT2 - logT1) / (logI1 - logI2) where T is time and I is current. That's n = (log20 - log3.3) / (log25 - log5.75) = 1.23 for our Trojan 27TMH batteries.

The formula to calculate the Peukert Capacity Cp is Cp = I^n X t so at our batteries' amp-hour rating, 5.75A^1.23 X 20hrs = 172 for our Trojan 27TMH batteries.

The formula for how long the battery charge will last at a particular discharge current is t = Cp/I^n

We can verify this for our batteries by 172/5.75A^1.23 = 20 hours and 172/25A^1.23 = 3.3 hours

Let's make a pot of coffee. Our 120VAC Mr. Coffee is rated at 1025W, so we'll say the inverter is pulling 100A out of the batteries while it's on. That's 50A from each battery. At that discharge rate, our 100% battery charge life is 172/50A^1.23 = 1.4 hours, so our 50% usable capacity is .7 hours. Multiply that 100% life times the 50A discharge rate and each of our batteries' capacity at this discharge rate is 70AH, rather than 115AH at 5.75A discharge.

If we only run the coffeemaker for 15 minutes (0.25 hour) we would think we had used 100A X .25 = 25AH out of our total capacity. But to have something to subtract from our 5.75A 115AH battery capacity, we have to multiply that 25AH by 115/70 and find we've used the equivalent of 41AH at a 5.75A discharge. We've used 41/115 = 36% of our usable battery capacity for one pot of coffee! We can verify this by dividing .25 hours by .7 hour usable capacity at this rate and find 36% of the capacity used this way.

Can you see now why I recommend boiling water on the gas stove for a Melitta coffeemaker? In that 15 minutes at that rate, our batteries will be warming up, but there's quite a bit of mass to heat up, so we probably won't damage them from overheating.

Let's look at using a microwave oven off an inverter. A 1000W cooking power oven draws about 1500W when the magnetron is on, and on high power, that would be about 2/3 of the time (67%). When on, it causes the inverter to draw about 150A, or 75A from each battery. At that discharge rate, our 100% battery charge life is 172/75A^1.23 = .85 hours, so our usable 50% is .425 hours. Multiply that 100% life by 75A and our batteries' capacity at this discharge rate is about 64AH, rather than 115AH at 5.75A discharge.

If we heat a coupla mugs of water on HIGH for instant coffee for four minutes, the magnetron will be on about 2.68 minutes (0.045 hours) each time. If we do that three times to approximately equal that 12-cup coffeemaker (6 mugs), we've run the magnetron 0.134 hours. Not counting the power the microwave uses for the light and turntable when the magnetron is off, we'd think we've used .134hrs X 150A = 20.1AH, but multiplying that times 115/64 gives the equivalent of 36AH, maybe 38AH including the light and turntable, at a 5.75A discharge rate. So you can see the microwave is a bit more efficient, but it still uses about 38/115 = 33% of our usable battery capacity just to make the equivalent of a pot of coffee.

Now let's look at what a 3000W inverter can do to our batteries. At full output, it will be pulling 300A from our batteries or 150A out of each. This is the rough equivalent of cranking two small cars that won't start, continuously. At that discharge rate, our 100% battery charge life is 172/150A^1.23 = 0.36 hours (under 22 minutes). Multiply that times the 150A discharge rate and each of our batteries' capacity at this discharge rate is 54AH, less than half 115AH at 5.75A discharge. However, our batteries are now heating up three times faster than with the coffeemaker, and there's a chance we can warp the plates, permanently damaging the batteries. THAT's why I would not want any situation where the air-conditioner and/or water heater element could be powered from the inverter. Yes, with the AC cycling, we may get 30 minutes or more to full discharge, but that's insignificant if we aren't at the trailer. It becomes more significant if we've left pets in the trailer in hot weather.

So I'd leave the larger inverters to the RVs with larger battery banks where the high current is spread amongst more batteries of higher capacity.

[thenewkid64]

Maurice,

You calculations do make sense, but. You have not taken into account any incoming amperage form any type of solar array. I will admit that the array will not keep up with the demands that you outlined, but they will make a difference. I know on your 34 footer you have precious little roof room. On units without the skylights there are room for panels. On smaller units there is room. I had 4 panels on my 31 foot 77 that did not have as flat a roof as you do.

We installed 4-50 watt 3 AMP panels. I had 2 group 27 series batteries and a 1500 watt inverter. On a sunny day I could make bread in the bread machine (4 hour run time) and still have a full battery bank at the end of the day. Edie was able to run her Hair dryer for as long as was necessary, and we did not have a microwave. But others with the same setup did and they used them. I would not go with a bigger inverter because I could not achieve any additional run times without more batteries. It was a trade off.

I did not have to cart gasoline in the back of my truck, or load and unload even a light 64 LB genset. I could not run my AC. But I was able to do 85% of what I wanted without shore power, or making the guy next to mad because I am running a genset.

I understand the I want to use 100% of the coach's features attitude. Using the AC, Microwave, a hair dryer, etc. That is why I have a MH now. I have my genset at the flip of a switch. In th past I had 85% of it at the flick of a switch too.

Cost wise I think on a 3-5 year plan you are close to break even once you factor gas, and maintenance. Not to mention the possible theft. I also like the idea that whenever the sun shines I am getting power for free.


Bottom line. Some like gensets, some like Inverters, and some like solar + Inverters.

[nellie the elephant]

RoadKingMoe,
Since you seem to be superior at "new math", maybe you can help me to calculate my needs for a solar array. My original intention was to just have a solar battery maintanance program while my A/S was in storage, and not hooked up to shore power. I found some Siemans panels that are aluminum laminate...and completely shatter proof. The size on them is perfect (16" x 16"), and I figured I could put two in front of my Air Conditioner shroud, and one behind. Since they put out 10 watts each, I would have 30 watts peak. Keep in mind that I will not be using hair dryers, or any other heating elements with an inverter...infact I only have a tiny inverter for the 13" tv if the kids just have to watch it on a rainy day. I am only really concerned about having the juice for my interior lights, and the water pump, and possibly the heater (however in a pinch, I have a portable propane "flameless" heater that doesn't use batteries).

I have two 115 AH sealed batteries from Costco. My question is, will the 4-5 hours a day that those three panels are charging my batteries, make up for the basic 12v demand that I plan to put on them?

I don't want to waist my energy installing the panels if they will be worthless. I guess at the very least, they will be keeping the batteries healthy while in storage.

Any help is appriceatted.

[RoadKingMoe]

When looking at solar industry ratings, keep in mind that to acheive that rating, the panel has to be in the conditions they are rated (i.e. sun 90 degrees to the panel on a clear day, and a panel temperature no higher than 77F degrees). To get the rated output with a horizontally mounted panel, that's solar noon, on July 22nd, on a boat 1 degree (60 nautical miles) south of Key West Florida, with an ambient temperature in the 50's Farenheit. When it's that cool at that latitude at that time of year, we might say hell has frozen over.

The further north from that position you go, the further from July 22nd, and the further from solar noon, and the cloudier the day, the lower the panel output current. The further from temperatures in the 50's, the lower the panel output voltage. Watts=amps X voltage, so power goes down as either goes down.

I can't find the panel you're talking about to see the specs. While it isn't the same type panel you're talking about, here's a 10W monocrystaline Shell/Siemens ST10. I like Shell/Siemens because their flyers give you an idea of best real-world output in a section titled Typical Data at Nominal Cell Operating Temperatures. It says the ST10 10W panel is really about a 6.8W panel.

Here you can see that at 68 degrees F ambient, with a slight breeze, the ST10 output voltage is down to 13.7V (due to the panel temperature), .1V lower than the typical output of a Magnetek or Univolt. At higher ambient temperatures, it will be even lower, and by the time voltage drop across the cables is taken out, it will be even little lower than that.

I believe you'd be lucky to get a 13.2V "float" charge at the batteries from the ST10. Dividing the 6.8W by 13.7, you get about 1/2A real-world peak current, or only enough daily power to run a 1.4A 12V light bulb for 2 hours.

Two of these would be good for keeping the batteries up during storage, except perhaps in the winter, and even a third might be marginal then. And at this low of a power input into the batteries, you don't really need a controller.

For a small vintage Airstream, you already have a lot of battery capacity. If you run one two-bulb incandescent lamp (1.4A per bulb) for 5 hours in the evening (really four hours but an hour of bathroom light too), that's about 15AH, the water pump doesn't use much, maybe 1-2AH. Add an hour of bathroom vent fan and you're still under 19AH/day, with no radio, TV, or other electrical use like modern RVs have with all their circuit boards and modern radios.

If you left on a Saturday and came back on the following Sunday, that's 8 nights, taking your batteries from fully charged down to maybe 30% charge, with no solar or generator. No radio, no TV. Yeah, that depth of discharge is hard on the batteries. Even with 2 rainy days, the 3 ST-10 panels producing maybe 6-7AH/day total over 5 of the 7 camping days, would keep discharge to no lower than about the 50-60% level. So yes, on a much older Airstream, those 3 panels could make a significant difference, if nothing else, in your battery life.

I can't help you with the TV power calculation because I don't know what size or wattage it is. Do you use an amplified or unamplified antenna with it?

And if you can get me a link to a specs page for the panels you're looking at, I could give you a little more accurate picture.

[RoadKingMoe]

One thing I should add about solar is that you can't park in the shade to use it. If parking in the sun means having to run a Fantastic Vent on medium (2.5A) for 10 hours, that's more than doubling the daily electical usage I calculated above. It takes the best daily output of an 100W panel (17-25AH/day depending on time of year) just to offset that fan use.

So you may find times you'd rather park in the shade and skip the gain of the 3 little panels.

[Theo]

I have four batteries, two in the standard boxes, and two in separate boxes in the front compartment, under the couch. The two extra are sealed batteries, so no fumes to worry about. I have not found out much about my solar panels.. I will try to get a close look, when I get the trailer, and a ladder in the same place..

I will be carrying a Coleman 3500 gen set as well, so I may be sufficiently powered..

Theo -- really enjoying his Long, Long Trailer..

[RoadKingMoe]

Let me give you an example of TV use. Our 9" Philips color TV is rated at 50W, which at 120V should be about 420 milliamps (mA). It might draw that much with a scene of a snow covered field on a sunny day, with brightness and contrast turned all the way up, as well as the 1812 Overture playing with the volume turned all the way up! LOL! On average while watching most shows, it runs around 210mA, or about 25W. A small inverter powering it would be drawing about 2.5A on average from the batteries. So 4 hours use would be 10AH, 8 hours would be 20AH and so on.

Our satellite receiver is rated at 120VAC, 1A, but doesn't pull anywhere near that. Feeding our two dual-LNB antenna, it draws about 170mA normally, and goes up to 210-220mA when searching for a satellite. So it's normally running about 20W and an inverter powering it should be drawing 2A from the batteries.