Battery capacity vs. weight

[slowmover]

Electrical use. Needed, and desired.

Needed: Furnace fan, and water pump.

Desired: Anything else. (Unnecessary).

As with tow vehicles, desires get ahead of need.

To recreate a house, buy a diesel bus with a 12.5Kw genset.

To go camping, exercise some restraint.

Gensets and solar add marginal value at high cost, complexity (non-durable), and with genuine safety risks.

Sure, we all love our comforts. Physical and psychological.

The convenience of a car is in avoiding public transportation. One doesn't need a four ton farm vehicle to accomplish this.

The "convenience" of a camping trailer is to hopefully avoid the public altogether. One also does not need that four ton farm vehicle.

Choose the camping locale to avoid modification of air temperature.

Choose to avoid "the sanitized public" of media, and telephone.

One doesn't need electricity to store or prepare food. Nor to clean or bathe.

Start from basics.

Step One is separating need and want.

THEN are modifications made reasonable.

If one just has to spend money on the trailer, then (again) reason portends that safety trumps convenience. Anti-lock disc brakes outweigh any solar electric or lithium battery installations.

Get stuff in order.

.

[GammaDog]

Originally Posted by larry9000

Gammadog- I asked for other ideas, and you came up with a logistically clever one! I like it. I assume you hook the extra battery up with a set of standard battery clamps. I also like having it ride just in back of the rear axle. I even have room in my rear storage compartment. Once at camp, pull it out and attach. Clever.

Is there any issue during traveling that the hitch battery is being charged by solar, while the interior one is dormant? Or any consequence that the usage between the two batteries won't be completely symmetrical?

I'm not a battery expert, but those on the Forums who are say that there can be issues with a battery bank containing a mismatched mix of batteries. They point out that mixing batteries of varied age, size, type, state-of-charge, etc. can all lead to shortened battery life. I believe them. However, I'm a pragmatist, philosopher and (dare I say?) traveling adventurer. When it was 23 degrees in Utah last year and we were traveling with our 18 year old dog (who didn't make 19... rest her furry soul) I was delighted to have enough battery capacity online to keep the heat at 65 degrees and not discharge the bank below 50% state-of-charge (the point at which those same experts say permanent damage is done to a flooded lead/acid battery like the Interstates I have). For the few times a year I need the capacity, I'm comfortable with this solution. If I have to replace the batteries in three years instead of four but I don't have to tell my wife "Honey, the dog froze overnight, but the trailer batteries still have years of good camping in them", I'm good with that. Especially since I keep my truck within tongue weight specs and didn't spend a year's worth of gas and campground budget to get the battery capacity I needed.

I would not mix types (e.g.: some flooded, with some AGM and I certainly wouldn't mix Lithium with anything else), and my three batteries are all Interstate Group 24 of the same age

As for clips versus other connectors, I would strongly prefer not to use clips. In my opinion, they simply do not make reliable contact and could even be jarred loose when unattended. An alternative to adding quick disconnects (I think I have pics of the Anderson Power connectors I use in my gallery on the Forums... private message me if you don't see it and I'll post a better view) is to see if your battery has a threaded steel post connector versus the type cars usually have with the lead lugs and big clamps. When I added my third battery, I didn't have time to add the Andersons..l they came later. What I did was to get two battery cables with eyes on each end. I'm thinking they were 24" zero gauge... something like that. I hooked them to the third battery and coiled them in the battery case so they wouldn't contact one another. When I needed the battery, I'd open the battery box on the trailer, unscrew the nut from a negative post on my batteries, hook the negative cable from the third battery and replace the nut. Repeat for the positive side. Voila! That was a very solid connection!

(From the "more than you asked for" department: I have a similar view on the fridge and leveling... sure, being even a bit out of level can shorten fridge life according to the "fridge experts". I believe them, too. However I'm not in a contest to see if my fridge can make it to the Smithsonian Museum. My goal is to see America up close... stay in places where people with airplane tickets, rental cars and hotel rooms can't go (look at Firehole Canyon, WY in the Ashley National Forest for a modest example)... and return home without having contracted ptomaine poisoning. We go places where the very best possible site might be a degree or two out of level. The fridge still works. If it dies one day, but we're still well fed and healthy I'll get a new one and keep the memories of where we ate from the old one. For us, a shortened life of the things that can be replaced is acceptable if it lets us get out and see America and do so safely.)

I hope that helps!

[larry9000]

Thanks Gammadog,

Got it. I looked at your photo as well. Since I will be planning ahead before our next trip, I'm likely to add 50A Anderson connectors and make adding the 2nd battery easy. As long as the cables between the batteries are heavy gauge, the solar charger (I have 50W factory install on the roof) should charge the two pretty evenly. The AGM I currently have was new this year, so if I get one another in the near future they should be of approximately the same age. I guess if I really worry about the two batteries having different experiences, I can swap the role of the two batteries occasionally (the "permanent" mounted battery becomes the second battery for a bit, etc.)

You have a nice setup with the Renogy panels. I'm leaning that way as well, adding 100-200W of portable solar. Since I don't have a truck bed to store them in, I'm also playing with the idea of getting flexible panels that will slide under the bed. Of course, I have the whole "building the frame" challenge if I do that.

I liked your idea of using magnets to attach the controller to the A frame. I need to think about how much weather protection I need. In theory, I won't be charging in the rain, but Colorado mountains often produce short afternoon rain showers.

Back to the topic at hand: I need to decide on the front battery box design. I could have two battery boxes, and plug in between them. Or one large battery box, with the permanent one mounted securely inside. I'm leaning to the idea of two boxes. The mobile battery would be carried by a strap and set inside while moving. Then returned to its own box while camping. Just one more task on the arrival and departure checklists.

[larry9000]

Thinking about this some more, I may go with the eyelet method of attaching the second battery. I can mount the cables to the permanent battery, and thread them into the empty battery box, with some sort of method to keep them apart. When I bring in the second battery from the trailer, I'd just use some heavy duty brass wing nuts to attach the two cables to the second battery. Very heavy duty cables with no connectors in the path, but easy to attach.

[uncle_bob]

Hi

The biggest practical risk on a lead acid battery with deep discharge is that a cell shorts when you charge it back up. That's essentially a "game over" situation for the battery. The likelihood of it happening is very much a "that depends" sort of thing. There is plenty of evidence in posts here on the forum that shorted cells are a very real thing.

If you are out at 23F with a normal battery bank (outside the trailer) (and no temperature probe on the charger) be very careful about battery management. The batteries will only have about 80% of the capacity you expect if you fully charge them. The gotcha is that 12V is no longer the 50% charge point. The "magic voltages" all move higher at cold temperatures. Your thresholds on the charger/converter are no longer high enough to fully recharge the battery at cold temperatures.

Tossing a warm "just out of the basement" in with a batch of 23F batteries produces "interesting" results. The batteries are not / can not be sitting at the same voltages. The cold batteries go dead while the warm one is loafing along. If you pair up batteries, let them get to the same temperature before you start doing stuff with them. That can take a while.

None of this says you *can't* do it. It's simply a caution about what to watch out for when you *do* do it. It's also a strong hint that a temperature probe on the charger is a real good idea if you do this kind of thing regularly. The probe usually is cheap. Running the wires is usually a pain.

Bob

[larry9000]

Originally Posted by uncle_bob

Hi

If you are out at 23F with a normal battery bank (outside the trailer) (and no temperature probe on the charger) be very careful about battery management. The batteries will only have about 80% of the capacity you expect if you fully charge them.

... If you pair up batteries, let them get to the same temperature before you start doing stuff with them. That can take a while.

Bob

All good points. I was imagining connecting the 2nd battery once we arrived at a campsite, not waiting until the first battery was low. So I wouldn't be pulling out a warmed battery per se, but there still could be a bit of temperature difference. Yes, a temperature probe seems like a good idea, 2nd battery or not. One advantage of the two battery strategy above is that it would be easier to find a battery with a bad cell, as you could measure the two voltages before combining them.

After considering this idea for a while it occurred to me that in place of carrying a 56 pound battery back and forth, I could be carrying a 50 pound propane generator instead. Hmmm...

[uncle_bob]

Originally Posted by larry9000

.....
After considering this idea for a while it occurred to me that in place of carrying a 56 pound battery back and forth, I could be carrying a 50 pound propane generator instead. Hmmm...

Hi

The battery makes a lot less noise .... until you drop it on your foot

Lead acid batteries are not champs in terms of power per pound. Lugging one around is not my idea of fun. The weight also counts when you have to strap it down for transport. Toss in self discharge when in storage as a negative. The 1 or 2 KW inverter generator at 30 to 40 pounds sounds better and better. There's way more "power" in a one pint container of gas than in that spare battery.

Bob

[switz]

We modified our pair of Honda 2,000 watt generators to the GenConnex propane conversion. One less fuel to carry inside the Mercedes when towing the 23D. We did retrofit a real automatic transfer switch and front 30 amp power inlet to the 23D. I made a six foot custom power cord and can plug the generator into the propane outlet on the front of the 23D that is also the grill outlet.

We also have five 100 watt solar panels the roof.