Multiple "House" batteries, mixed state-of-charge?

Herbie

Rendezvous Conspirator
So here's an odd question, with explanation to follow:
If I have two AGM house batteries of arbitrary capacity, but likely at different states-of-charge, voltage wise, would I need two (parallel) isolating/charging systems? Moreover, shouldn't they be isolated whenever not being charged?

Explanation:
I'm in the phase of my van build where I need to start worrying about the house-power system. "Version 1" of the plan was to just install either 1 or 2 Group 22NF AGMs into a convenient cubby that's in the rear quarter panel of the van, using the usual National Luna or similar battery isolator/charging system.

However I've been trying to think about life in Bear Country - specifically that with the wife and daughter along, there will be times when we'll end up in State or National park campgrounds where bears are well accustomed to humans and their goodies. (A different use case versus "wilderness" camping.) In these scenarios, it seems moving the fridge and a battery to the bear box would be a prudent step.

Fortunately, the location I've chosen for my batteries will be readily accessible, and I have a ready store of all the high-amperage connectors I would need to make the battery easily removable. "Version 2" was just that, a removable house battery with quick disconnects and the appropriate sockets so that I could put battery and fridge into a bear box.

However, while the fridge is my MAIN house-power consumer, I would really prefer to wire the reading lamps, other house lights, and any future accessories like on-board water pump, etc. to house power as well, lest I negate the whole value of a house a battery. My thinking there is that these demands are relatively light (compared to the fridge), so maybe I could have a smaller-capacity "auxiliary" battery to run things after the fridge was stored for the night or whatever.

When I started drafting up this "version 3", though, I started to worry about what happens in the morning when I reconnect the big battery - If everything is tied together, the main and aux house batteries would try to equalize, right? (assuming the alternator wasn't charging). If I started driving first thing in the morning, then at least everybody would be getting charged, but it still seems like I would need two charge controllers to keep everything happy and safe. Suddenly the cost of 2x NL smart relays, etc. starts looking very daunting.

Am I missing anything?

A thought that's just occurred to me (Version 3.1?) is that rather than run a permanent main/aux setup, I could just use one of those portable jump-packs as a SUBSTITUTE battery to run the lights, etc. whenever the main house battery was in the bear box. (I'm thinking a cig-lighter adapter to the fuse-panel input.) When the main battery was installed, the same cig-lighter connection to the house voltage would become an input to charge the jump-pack. The advantage here is lower cost, plus I could leave the jump-pack at home if I new I wasn't going anywhere with bear boxes. I assume these jump-packs have some (rudimentary) level of isolation? Or is this just the same problem?
 

wrcsixeight

Adventurer
Batteries in parallel with find the same voltage, so the higher fill feed the lower.

While it is better if the batteries in parallel are the same age make and size, it is not absolutely necessary. Perhaps with flooded batteries of 2 different makes, one would use a lot more water, but with AGM, no biggie.

You do not need 2 NL systems. If you are leaving the next morning, just hook the bear battery back up to your house battery and drive on.

If you are not driving the next day, keep the fridge running on the 'Bear' battery. If the Bear battery needs charging, do you have solar, or just an alternator. Idling the engine is a waste of fuel, just to charge a battery, and disgustingly slow.

Most Jumper packs usually have only a 18 amp hour max battery inside, so it might not last the night, or it will be heavily abused when draining it below 50%. For the price of a jumper pack, you could get an AGM battery with double or triple the capacity of a jumper pack. Just make a nice handle for it and add a ciggy plug, or anderson connectors.

Are Bear boxes air tight? If there is no ventilation the fridge will heat up the box, and run more and use more battery overnight.
 

Herbie

Rendezvous Conspirator
Most Jumper packs usually have only a 18 amp hour max battery inside, so it might not last the night, or it will be heavily abused when draining it below 50%. For the price of a jumper pack, you could get an AGM battery with double or triple the capacity of a jumper pack. Just make a nice handle for it and add a ciggy plug, or anderson connectors.

Are Bear boxes air tight? If there is no ventilation the fridge will heat up the box, and run more and use more battery overnight.

In my experience with bear boxes (2-3 NPs and 2-3 SPs), the boxes are tightly constructed but not strictly airtight, although probably close enough that a thermal loop "runaway" is a realistic concern during the day time. On the plus side, most places where we've camped in bear country its pretty cool at night, and the big steel boxes are always covered in condensation late in the evening, so I think if I limit use to overnight, it should be OK.

Thanks for confirming some of my understanding and helping me worry a bit less.

I agree that a jumper pack wouldn't service the fridge for any length of time. My thinking was to move the big AGM to the box and only use the jumper as a substitute battery to run the LED reading lamps or water pump for brief periods in the evenings and mornings when the fridge would be in the box.

Doing some more research on the jumper packs I've found that they may not actually include much, if any, isolation circuitry, so you're probably right that my money would be better spent on a proper AGM (even a small one) and a handle or carrier box.

Given that design criteria, I could probably even fit everything into the same cubby I intend to use for the "big" AGM. This idea sort of appeals too because then for non-bear areas, I could enjoy the added capacity of both AGMs as a house array, and only pull out the once pack when I needed to move the fridge... :wings:

Now the hardest part is to design the battery rack for the cubby such that its easy to remove one battery, preferably without tools. OK, back to the drawing board... :coffeedrink:
 

ldivinag

Adventurer
check out TREMORS setup:

http://www.expeditionportal.com/forum/showpost.php?p=477396&postcount=40

view the whole thread to see diagrams and stuff.

i am looking at a setup similar to this.

your version 3 is this. buy 2 new AGM batts. buy the big anderson connectors. then a 200 amp relay.

my only mod to this and this is what NL does, is put in a 10 minute delay to activate the relay. that way, or NL's logic is that the 10 minutes should be adequate to charge the main batt. then after 10 minutes, it kicks in and starts charging the secondary one...

here's what i was looking for as the delay circuit:

http://www.electrokits.com/electronics/relays-remotes-switches-timers/33.htm
 
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Bogo

Adventurer
Remember if you evict the refrigerator, you must evict all food, toiletries, cooking gear, etc. to get the benefit. Also you can't even cook inside your rig as cooking odors will linger. In Yellowstone it wouldn't be a problem to keep your food in the van, but in Yosemite, I'd be a bit more worried.

If you are that worried, then give them a jolt. Get a bear electric fence. They have been in use for years in Alaska and by the Forrest Service and are very effective. They are used to not only protect food stashes, but also hunting carcases, camp sites, smoke houses, etc.. I've used them in the past when doing distributed camping in grizzly country. Of course using one in a regular campground may have side issues...

Note: the kits on the market are just using regular electric fence equipment. Nothing is special about the fences used except that they tend to run the wires a little closer to the ground and a few more wires than used for cattle. This is because of how a bear normally keeps it's head when wandering around hunting for food.
 

Bogo

Adventurer
Now the hardest part is to design the battery rack for the cubby such that its easy to remove one battery, preferably without tools. OK, back to the drawing board... :coffeedrink:

Use a hasp or two. You would obviously need one with a longer bar than the one in the photo, but that could be fabricated easily. A lynch pin could be used for holding the hasp closed.

First photo is a hasp. Second photo is of 4 types of lynch pins. The round one in the top right is the most common one I see around.
 

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Herbie

Rendezvous Conspirator
Remember if you evict the refrigerator, you must evict all food, toiletries, cooking gear, etc. to get the benefit. Also you can't even cook inside your rig as cooking odors will linger. In Yellowstone it wouldn't be a problem to keep your food in the van, but in Yosemite, I'd be a bit more worried.

Already standard procedure for us. The van isn't setup for indoor cooking and all the "smellables" are packed in their own plastic bin to make loading the bear box in the evening easy. Up until this point we've had coolers, so we just chuck everything into the box after dinner, but we recently added the fidge, hence the questions.

If you are that worried, then give them a jolt. Get a bear electric fence. They have been in use for years in Alaska and by the Forrest Service and are very effective. They are used to not only protect food stashes, but also hunting carcases, camp sites, smoke houses, etc.. I've used them in the past when doing distributed camping in grizzly country. Of course using one in a regular campground may have side issues...

Yeah, I think I'd only go that far for brown bears. Our California black bears are sufficiently intimidated by yelling and clapping. This exercise is mostly about minimizing their temptation to start sniffing around and/or banging on the van.
 

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