But they are not dry charged. The ones I am showing are built, flooded with electrolyte, charged, then drained and dried. When you are ready to use them, you add the liquid electrolyte and start with a nearly full charged battery. I know they make smaller sizes also. These will last indefinitely on the shelf and be ready in just a few minutes. You can do a lot with 18 AH.
Smaller would be better. Once "resealed", can they be operated in any orientation? Or, do they have to be "This Side Up"? I.e., would I have problems tossing them in a pack where they could easily end up on their side (or even upside down)?
Agreed. I'm just saying that they would be impractical to *carry*.
If sheltering in place, you'd be hard-pressed to do better than genset. (until you ran out of fuel -- at which time, a solar panel and battery would win big!).
If driving out, you've got the car battery/alternator/engine.
The real pisser is walking out. Then, you want to limit the total weight that you carry to something small. "Bare Essentials".
NiMH is probably the most resistant to abuse. They'll take extended periods of being left dead or overcharged. Cheap to replace and dispose.
LiFePo4 - These are supposed to be tough mechanically, have 10 year lifespans, and tolerant enough of over/under charging that an on-board protector circuit works very well. Crazy expensive.
NiCd - Electrically and mechanically extremely tough. Usually fails in
2-3 years from corrosion. Used cells are toxic waste.SLA - Degrades rapidly when not kept charged. Momentarily tolerant of over/under charging. Rivets between cells corrode rapidly after mechanical shock. Worst power/weight ratio. Used cells are toxic waste.
LiPo - No tolerance to over and under charging but can be partially protected with onboard circuits. Life span of 1 to 3 years. Available in mechanically strong or soft packages. Prone to exploding when damaged.
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I've got a bunch of Tenergy cells, AAA AA and D. I just had to use the AAA (in a head lamp) and I don't recall charging them recently. So they must have been sitting for 6 months or more. They had some charge in them 1.2v pre cell, not bad. The AA's and D's were charged over in August. My usual routine for the east coast storms. I've had them for a few years and the D's are in the truck all year. They take a beating and not expensive, but not the best either. But these are a few years old so a new batch may have different chemistry.
I like the D's, 10000mAh. But they are a little finiky, unequal capacities from different self discharge rates.
Cheers
Maybe I'm misreading your requirements/constraints. But for my 2c worth I'd put the 7Ah SLA IN the BoB and connect a lead to it from an "intelligent" SLA charger (not one of those horrible floaters they fit on alarm systems). Quick-break connection, always ready to go, and the SLA can feed all the little dependents from a multi-voltage switcher. And there are simple/cheap/light chargers you could add to recharge the SLA from an auto source if the need arose.
[The only cells I have experience with that will recharge and perform "properly" after an extended period discharged were .... NiFe. Too heavy to contemplate, low power/weight, but bullet-proof.](snip)
?? IMOE cell reversal happens during the DISCHARGE cycle in series-connected cells, due to mismatched cells. If cells are all still "right-polarity" when charging is commenced, I have a problem seeing how the CHARGE cycle can result in reverse-polarity.
If Don's requirement is for a grab-and-run bag, hanging around to add sulphuric acid to a dry-charged battery isn't a good fit.
Mostly true. Discharge does do most of the intitial damage. Trying to charge it after a cell reversal finishes the job by overheating the damaged cell. For NiCd the reversed cell ends up shorted. I'm not so sure about NiMH cells. Subsequent slow charging keeps the reversed cell from overheating and with luck, will equalize the voltage across the series string.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
Dry charge is not too horrible. In the bad old days of automobiles, batteries were delivered to the auto shop with the electrolyte in a bottle. When they sold a battery, the dry charged battery was filled with electrolyte in a few minutes. However it was necessary to slow charge the battery after filling: As I vaguely recall, about an hour charging was typical.
However, that was in the days of mesh grid batteries, where the mesh was rather strong and could tolerate some banging around in shipping. Today's batteries are lead oxide sponge with rather thin separators. Without the electrolyte to distribute the load, dropping the dry charged battery will crack the plates. It was also difficult to maintain an air tight seal on the battery case. So, today's automobile batteries are shipped full of electrolyte which shortens their shelf life because of a tendency towards sulfation when stored discharged. You can still buy dry charged batteries but mostly they're smaller batteries, such as motorcycle batteries.
Note that I'm not endorsing using automobile batteries for emergency stationary service. Auto batteries are made for quick high current discharges, such as starting and perform rather badly when used as a stationary battery. I've killed a few automobile batteries during the "Learn by Destroying" process. Auto batteries also cannot be "deep discharged". Stationary batteries using more lead and with a sump area near the bottom to catch the sulfates are necessary for stationary service if the battery is filled with electrolyte. Dry charged batteries can be stored in any manner, without consideration for self-discharge, temperature extremes, etc. However, they do need to be sealed and filled with an inert gas.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
Leaving it "floating" in the garage still leaves me to wonder how well it will "stand up" to that environment. And, putting it in a *bag* (with other things that have varying degrees of combustibility) doesn't lessen that worry!
E.g., the batteries for the rainwater harvesting system sit on the floor of the garage close to the doorway -- any venting of gases tends to be a non issue as the door is opened regularly; they're at the coolest "elevation"; not enclosed in anything (which makes it convenient when I want to tap off them for some quick test load); etc.
Ideally, leave it "on the counter", ready to go -- so you see if anything wonky is happening to it, get a chance to check it periodically, etc.
Of course, that would go over like a lead balloon, here! So, I'd have to, instead, make a little "charging station" hanging on the wall by the entrance to the garage; some place easily accessible, a constant reminder of its presence, not subjected to the environmental extremes in the garage -- yet not likely to be regarded "with disdain". And,
*hope* seeing it every day acts as sufficient reminder to GRAB IT when bugging out!
I didn't suggest "floating" quite deliberately. Almost invariably, "float chargers" are about as intelligent as the chargers in cheap UPS units - aka brain-dead. You put the SLA in the bag, the charger is optional where you place it. In the bag if you want to take it, outside if you don't.
[Years ago, a local emergency services unit had a number of portapack/backpack radios on the bench ready for grab'n'go ops. These had a cable tail out via an in-line connector to a charger fixed on the bench. Even if the operators forgot, the in-line connectors provided a quick-break without any drama.]Venting will not be an issue with a sensible charger connected to your SLA.
See above re grabbing vs not grabbing. The "charging station" doesn't have to be a charging station either - one I use for SLA's is in a small jiffy box. Another system I have uses another charger in conjunction with an AC controller (*) in another small jiffy box, the combination ensures that the target battery does NOT sit on charge of_any_kind indefinitely. Rather, it monitors battery voltage and initiates a proper (*) charge cycle whenever the terminal voltage drops below a pre-defined threshold.
(*) This is little more than a 555 as a window detector, two trim-pots for on/off thresholds, and a relay to power up the SLA charger (or the "boss" charger for auto batteries). SImple but effective, removes the indefinite float from the equation. Equally applicable to alarm batteries or any other situation where a battery may have a continuous or intermittent load applied.
(**) For SLA charging, I recommend the Unitrode/TI UC3906 charge controller - there is an app-note incorporating some good care and feeding guidelines.
(snip)
No in itself, and for its intended purpose, but if grab'n'run is part of Don's scenario, the last thing I'd be wanting to do with the hammers of hell closing in is be fiddling trying to pour sulphuric acid into six cell vents.
I use a syringe but that's not the real problem. For grab and go purposes, the weight of a lead-acid battery is enough to make anyone look for alternatives. The other real problem is that he doesn't want to do any battery charging or maintenance which in my never humble opinion is a lousy idea.
As an alternative, I suggest a LiIon battery pack, possibly as used in a quadcopter[1]. The new requirement would be good energy density for the battery pack. Looking at the chart, LiIon has about 5 times the energy density by weight of a lead acid battery, and about twice the energy density by volume. That means he can run about 5 times as long for the same battery weight.
The problem is that LiIon doesn't like to be stored fully charged or fully discharged. 60% of capacity is considered to be a good value for extending the shelf life. So, his battery controller/charger will need to have a way to switch between standby and full charge levels. That's fairly common in todays coulomb counting charge controllers as used in laptops.
The charger should be built into or attached to the battery pack and become part of the grab and drag bag. It should also have a wide input range, so that it can tolerate being charged from everything from 12V automotive to 230VAC with maybe an MPPT controller for running off solar. Between disasters, it just sits in the bag, float charging to about 60% of capacity off 117VAC power.
However, there's yet another problem.
3 cells = 11.1v 4 cells = 14.8v Neither is idea. At 11.1v, most radios will complain about the low voltage. At 14.8v most radios will run, but if you connect it while charging at: 4 * 4.1v = 16.4v the radios will likely blow or burn up. So, you'll need either a DC to DC converter, or an LDO regulator to bring it up or down to 13.6V nominal. [1] 4S batteries (4 cell): Balance charger:-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
Sitting flooded lead acids on concrete was always cautioned against. The relative coldness at times causes condensation, and the electrolyte eventually overflows. I've not observed that happen though.
NT
or a couple of diodes
NT
With a switch to short them out as the cells discharge.
Regardless of where the electrons are and when they are prodded to move, you still need the battery "tethered" to a bit of kit while "in storage". And, at some point(s) in time, electrons *will* be flowing "into" the battery.
Chances are, the battery will want to be located near the bottom of the bag -- for the simple fact that it is heavy/dense and would crush other items placed beneath it (also runs the risk of imbalancing the bag).
So, even if the charger remains outside the bag (silly as that suggests you wouldn't be taking the charger *with* you -- e.g., when driving out!), there is the potential for heat to be trapped in the bag (battery fault, charger fault, etc.). Given that there are likely fuel sources also in the bag (propane cylinders, matches, magnesium block, vaseline, cotton balls, etc.), I'm not sure I'd want to put this in an out of the way place and ignore it for a year or more at a time.
"... fixed on the bench" not "hidden under a pile of clothing, etc."
I think I can use this idea with a deliberate "charging station" so the battery remains visible/accessible even when not a candidate for "emergency service". Yet, hopefully, also prominent so that it isn't casually forgotten when bugging out!
I suspect it would be wise to actually create a separate "carrying case" (shoulder strap, etc.) for the battery so you could carry
*just* the battery, at times (e.g., when "scouting ahead", you would want a power source for a walkie-talkie -- but, not necessarily all the rest of the kit in the BoB). [Of course, this makes it clear that you actually need *two* such battery packs as whomever is "left behind" will need a power source for *their* walkie talkie! Perhaps find smaller batteries with half the capacity -- gang them when you need more capacity; split them when you need multiple *sources*?]Significant difference in the sizes of the batteries! E.g., I probably have 100AHr (200??) sitting on the garage floor. They're convenient when I need to jump-start a car! :>
Making a (deliberate and prominent) charging station means the battery pack(s) won't be hidden away someplace. E.g., currently, the BoB's are stashed in the store room. Only things that see infrequent use hide in there (pinball machine, long term business records, shop vac, etc.). There's currently no power available in there -- though I could hack something together.
If the battery(ies) were set somewhere else (in the garage) to sit on a charger, then grabbing the BoB's might lead to failing to grab the batteries (in a rush/panic).
OTOH, if I make a nice ("pretty") wall mounted unit that I can site by the entrance to the garage -- someplace that we walk by
*daily* -- then the batteries will tend to get noticed regularly (e.g., if one starts corroding, bulging, etc.) so we can catch any problems before they become problems ("Oh, crap! Just when we NEED THEM, I discover the batteries are toast!"). And, they will hopefully remain in our minds so we don't neglect to grab them *in* an emergency.E.g., I can *rarely* tell you where my shoes are... *But*, I can tell you where every *flashlight* is at any given time (because they have fixed storage locations that I "see" with some regularity). Ditto every SCSI/Video/Printer/Serial/USB cable, power cord, PCI card, hammer, screwdriver, tape rule, etc. that I own! :> ("Priororities!")
QST magazine had a recent article on the topic: It uses a relay instead of a switch. I have a personal aversion to relays and other things that move in electronics, and suggest that a semiconductor equivalent would be more reliable.
One problem with the diode scheme is that the necessary voltage drop constitutes a substantial power loss which must be recovered by using a larger capacity battery. A higher efficiency DC to DC converter would be a better solution as long as the load current is fairly modest. Since the current drain in transmit for a typical 25 watt transceiver is about 12A, and the battery terminal voltage is depressed anyway at high currents, a suitably large DC to DC converter would just get in the way.
A DC to DC converter using 4S LiIon battery pack might be slightly awkward because the output voltage straddles the input voltage range and therefore requires a boot-buck regulator. Using a 3S LiIon pack at 10.1v nominal might be better since it can be done with only a boost regulator. Something like this for $10 at 5Amps:
I once tried to calculate what it would take to provide the necessary voltage drop with an inrush current limiter NTC thermistor. I got interrupted and never returned to the problem. My guess(tm) is that there will be overheating problems at medium current levels, where the thermistor dissipation is highest.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
BOB -> bug-out bag.
-- Best regards, Spehro Pefhany Amazon link for AoE 3rd Edition: http://tinyurl.com/ntrpwu8 Microchip link for 2015 Masters in Phoenix: http://tinyurl.com/l7g2k48
It needn't be that "hurried/frantic". The biggest issue is making sure you *have* what you need *if* you have to leave "in a hurry"... it's not like "taking a vacation" where you can sit down and PLAN what you are going to take ("Oh, I'll need THESE slacks in case we go out for a fancy dinner; and these others for casual activities...").
I tend to be pretty good at remembering "little things". E.g., came home from work one day to find a message that FinL had had a heart attack. We were out the door within minutes -- for a stay of indeterminate length -- yet managed to bring virtually everything we would need with us as well as ensuring the house was "safe to leave".
Of course, we could always have come *back* had we forgotten something. And, resort to credit cards to *buy* anything that wasn't worth that return trip. Neither of those scenarios are available in an "emergency".
I think the killer aspect is just the *weight* -- but, admit that I haven't looked to see how small these can be. For shelter in place or drive out, it would be a great way to have a *big* power reserve. OTOH, keeping some large SLA's (or even flooded batteries) on the garage floor works just as well -- and, if those are currently "in use", you *know* they work.
And, the potential "orientation" problem (I've never tipped a sealed, FLOODED lead acid batter on it's side to see how it fares... and how well the "seals" hold! What if *I* effectively have responsibility for "sealing" the battery?)
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