Looking For Smallest Battery For Depth Sounder

[A96Honda]

I know this might be a slightly offtopic. But I recently bought a nice little alumi boat. Came with some cheap depth sounder/finder. Dont feel like spending the cash for a nice quality fish finder yet, so I'm going to make due with what I have. Came with a small Rayovac 12v "Lantern Battery". Even though the current battery is relatively small, I'm wondering if there's something even smaller I can work with.

The specs for the depth finder is;

Power Requirement : 11-14Vdc, 200mA max
Current Drain : 40mA, Nominal


I need to build a new housing for both the battery and gauge. I want it to be as small as possible so I can mount it whereever I want and move it whereever I need it.

 

[Blinding]

There are a lot of batteries that COULD work but might not be practical. There is a small 12V battery used in garage door openers that would work but it would drain it very quickly. Basically the smaller the battery the shorter the run time.

Almost any combination of cells that will total 12 volts would work. I.E. four CR123 or eight AA. You would just need to find a battery holder.

Why do you need it smaller? Or, how small do you want it to be? How many hours do you need it to run? Do you want it to be rechargeable to reduce operating costs?

I would get a small lead acid 12V battery. Something like they sell for motorcycles along with a 1 to 2 amp charger.

 

[VidPro]

i would use a SLA or gell cell IF it was sporatic use, they come in many sizes from 3-13lbs all with relative capacity, CHEEP, but suckey weight, and difficult to keep going great over time. problem is it would have to be maintained constantally, and treated well. might be good for having more storage than needed normally, beings it doesnt like to be deep discharged or left discharged. so Cheep, heavy, get it bigger than your needs, then maintain it.

if i was planning on using it a LOT, i would get a holder for some AA LSD cells, 10 or 11 depending on how long the cord will be to it. then either slow charge in series, or seperate out of holder to charge faster. ni-mhy packs always blow away Lead acid junk for maintance and runtime and dependability, even if the price will be a bit higher at first. lighter , easier , more costly, more pieces assembled, much longer life.
If i needed more runtime i would go C or D LSD cells, which would replace even a larger Lead Acid. Potentially in the right holder casement, you could even use the batts in other places when not in use. then you could toss in alkies in an emergency or one time use. (i specifically said LSD, anything else isnt going to be as maintance free and work in serires as well)

If i was sick of carrying it around, AND i knew how to deal with li-ion properly, i would go with , 18650s in li-ion, or if i didnt need a lot of runtime 18650s in Li-Fe-Po. lighter weight, less pieces in the pack, not as long of a Years Life as the ni-mh, proper assembly charging or purchacing required. best for say using at least 25times a year, when lightweight small size is important. same idea Square it up or have it fit in a case better, with li-poly, same high knowlege needed to apply properly.

potentially you could use 4x123s and even lithium AA x8-9 , which would be really freaking light , but a waste of money if your going out more than 5-6 times a year. lightest, most avilable power for size, zero maintance, big problem of going out with unknown capacity, so you either have spares, or keep paying for newer cells to insure runtime.

we really do need to know your maximum runtime between charge locations, and should know your uses per year.

 

[A96Honda]

I'm usually out on the water for ~3 hrs or so.

How many times I go out, will depend on a lot of things. At the moment, I'm guessing twice a month.

 

[VidPro]

probably a rack of AA rechargables ni-mhy lsd, then even if you forget one charge you will still be good.

also never misjudge the power requirements , remember they do that with cell phones 5days standby my butt depending on how your using some devices they may use more power than presented, like if there is a backlight, or a "feature" that takes more power.
so it might be good to do a quick check on your Actual runtime or the actual Ma usage before getting in to deep , with the depth finder.
they expect that these things are going to be connected to a virtually unlimited source of power (trolling motor battery, or engine battery), and specs are what specs are , something in a LAB.

 

[qwertyydude]

Why not get an 8AA battery holder and just use alkalines? Readily available and with such low current requirements you could easily power it. AA alkalines have about 3000 mah if drained very slowly and have a very long shelf life.

 

[TorchBoy]

Why not get an 8AA battery holder and just use alkalines? ... AA alkalines have about 3000 mah if drained very slowly and have a very long shelf life.

Because they won't have enough voltage for a reasonable runtime. Alkalines only start at 1.5 V but drop quickly from there even with light loads, so they won't have 3,000 mAh while maintaining the voltage required. The power requirement says 11+ V, so that would be 1.375 V/cell with 8 cells. You might get down to that in less than half an hour. I suppose if the device isn't too fussy it might possibly last for a 3 hour trip.

 

[A96Honda]

Because they won't have enough voltage for a reasonable runtime. Alkalines only start at 1.5 V but drop quickly from there even with light loads, so they won't have 3,000 mAh while maintaining the voltage required. The power requirement says 11+ V, so that would be 1.375 V/cell with 8 cells. You might get down to that in less than half an hour. I suppose if the device isn't too fussy it might possibly last for a 3 hour trip.

What about 4 CR123's? Does the math come close?

 

[VidPro]

What about 4 CR123's? Does the math come close?

yes, should work,as long as the rate mentioned was the actual rate. you might not get ALL the capacity out of them before the device quit working right but it should be fine for primary $$$ :-(

 

[marschw]

Or, to be weird, you could use 4 D-size LiSOCl2 cells like these in series and not need to change them for the next 5 years or so (capacity is around 15Ah at 40mA discharge rate according to the datasheet, 15Ah/40mA=375 hours, you said about 3 hours per trip, twice a month, so 72 hours a year, so about 5.2 years). Maybe put a resistor or power diode in if you're concerned about the nominal voltage being a bit high. But at least, being normal D-sized cells, you could use an off-the-shelf battery holder.

But that would be kind of overkill, unless you're *really* lazy about changing cells and really want to keep it light.

 

[A96Honda]

yes, should work,as long as the rate mentioned was the actual rate. you might not get ALL the capacity out of them before the device quit working right but it should be fine for primary $$$ :-(

So according to the numbers, how long is 4 CR123's suppose to last?

 

[VidPro]

So according to the numbers, how long is 4 CR123's suppose to last?

according to the speced numbers more than 10 hours, my guess would be probably be less than 10 hours though. a little less for the batteries not having the full claimed capacity http://www.candlepowerforums.com/vb/showthread.php?t=67078 (discharge rates there are all higher than your device)
and completly dependant on the battery quality.
and a little less for device specs often use more power than the stuff they list, plus a little more because i suspect that the device will still operate down to 10.5v.
you should get at least one full trip out of one set.

 

[qwertyydude]

At 40 mA with a peak of 200 mA alkalines will output their rated 3000 mAh. AA alkalines are rated at 100 mA drain rates so voltage should be reliably stable, of course you can add an extra cell and start at 13.5 volts and it should end at about 10.8 after being expended.

 

[marschw]

Not to mention that, presumably, its original 12v lantern cell was 8x Alkaline F cells (or maybe Carbon-Zinc, even worse).

 

[TorchBoy]

At 40 mA with a peak of 200 mA alkalines will output their rated 3000 mAh. AA alkalines are rated at 100 mA drain rates so voltage should be reliably stable, of course you can add an extra cell and start at 13.5 volts and it should end at about 10.8 after being expended.

What are you basing that capacity claim on? Not the datasheets, surely.

No AA alkaline that I know of has 3 Ah capacity with a 100 mA draw. If you know of one, please let do tell. To get a capacity approaching that Energizer uses a mere 25 mA draw. At 100 mA the E91 actually rates at less than 2.5 Ah. Duracell seems to do better - at a steady 40 mA (assuming no 200 mA peaks at all) Duracell's datasheet indicates you might get 2.8 Ah, but that's draining it down to just 0.8 V. How many extra cells are you planning to add? Start off with 8 cells and finish with 14 to get the required voltage? Not going to happen. (OK, so you're now thinking of 9 cells only.)

How do you consider an alkaline battery voltage varying from 1.6 V to 0.8 V over its life to be stable? Do you mean it doesn't jump around unexpectedly while being used?

Your suggestion of finishing at 1.2 V per cell will leave at least half the capacity unused, so you're basically suggesting a battery with an effective capacity of about 1.3 Ah tops. That may not be an unreasonable solution but it seems a little wasteful.