you probably know this, but I'll throw it in just in case - your wet-cell lead acid battery is only twelve volts, but it can throw a whole heck of a lot of current at you if short circuited.

 

Hi ziyad,

Your comment about candles for 2010 cup, reminded me about a joke I heard in SA.

1st Guy: what did they use for lighting in SA before they used candles..?

2nd Guy: electricity....

I'll do some sums, now that I know your requirement, get back to you.

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

 

hi ziyad,
With the 12v 25AHr battery, recharging at 2.5A is not going to be the problem.
eg: assume a fully discharged battery [down to 10.8V] 25Ahr/2.5A = 10hrs at 100% efficiency, it actually about 60%, so its recharge time would be around 18hours.

If your invertor is driving a 150W invertor at full load, assuming 100% eff, then its drawing 12.5A from the battery, actual eff% is more like 80% for an invertor so you are talking about 16Amps.!

So, 25AH/16 = 1.5 hours of operation from fully charged to discharged.

For at least 4 hours operation you need 16A * 4 hr = 64AHr.

Recharging at 2.5A, 64/2.5 = 25hrs at 100%, at 60%, gives abour 40 hours recharge time.

These are rough figures, but they should give you an insight into the problem..

Can you confirm the 'actual' current drawn by the water filter system and also more info on the invertor.?

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

 

At faster rate of charging, the positve electrodes do loose their material by shedding in case of lead acid batteries. In gel type and SLA batteries, i had experience of the interconnecting leg from the post to the plate inside, fusing off and thus creating a break of certain cells. these were manufactured in India under American collaboration.

Also temp raise becomes an important issue that limits the increase of of charging rate. There after it will result in reducing the life of the battery. Of course where time is prime and battery life is not that important like cases of battery operated motor bikes, it is a compromise, I feel.

__________________
Regards,
Sarma.

 

If you can get your hands on another battery, identical to the first, in parallel will give you 2x the run time (more than 2x actually due to slower discharge rate), but at a cost of 2x the charging time. Unless you can scrounge up another charger. Or use 'em sequentially instead of simultaneously.

You might know the answer to a question I've been wondering about lately...if you used a water level sensor (the kind with bare leads) in a 20 gallon tank, would fish in the tank suffer any ill effects? I'm talking fish in excess of a pound or so, in fresh water.

Thanks!

 

I notice he's been unbanned.

Why the change of heart Nigel?

__________________
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Screen name: Aloone_Jonez
And http://www.silicontronics.com, same screen name as here.

 

It was never a permanent ban, only 7 days.

__________________
PIC programmer software, and PIC Tutorials at:
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I don't suppose it makes any difference. He will probably never return.

__________________
I also post at the following sites:
http://www.stop-microsoft.org http://www.heated-debates.com
Screen name: Aloone_Jonez
And http://www.silicontronics.com, same screen name as here.

 

Yip.
that oubt to be fun huh!

 

Until he reads that post in his e-mail.

Hey you......... every time I see this up again it reminds me of "Pink Floyd"

__________________
Truthiness Monkeys : Obedience, Ignorance, Fear.

 

LOL!!!!
Simple , but hillarious!

 

The inverter i am using on all my aquariums is the same. its a Powersonic 150W.
On my main tank, the two motors are 81W and 38W centrifugal pumps. (a sealed coil on a casing that spins a magnet with the the alternating frequency)

Since i dont like calculations, i just measured it all up and found that the inverter draws 200mA with no load, and with the above load of the 2 motors draws 5.3Amps on average.
my other aquaria are much smaller in terms of power consumption,
one draws 1.3Amps, and the other 2 only 600mA each, so they will work off 12Ah SLA's instead.
its just the big tank that needs a bit of attention.
I have 2 of those 25Ah batteries, which i will configure separately, for the charging that is, and i will make the circuit such that when in opperation, they will switch to parallel.
This way i would hope 2 get about at least 7 hours or so out of them.
I was thinking of increasing the charge to maybe 4 Amps or so, since i found a dual 15V 5A switching power supply that i had bought before and never used.
So wat ya think?

 

Yip, i have considered that thanks, see above.
As for the level sensors, i doubt the fish will suffer in any way with the current, but, any current will cause oxidation (i think thats what it's called) on one or both electrodes, and then you will have problems. if its a marine tank, multiply those problems by 100!

I have installed water level sensors in my 600litre tank, so i can have the internal filter shut off before the pump runs dry (while doing maintenance)
However, i did not use electrodes, nor did i use commercially available float switches. It took me a while to figure out a solution, and then........
WALA or shall i say KABOEM!...................
it struck me:
i used a reed switch on the outside of the tank, and used a cylindrical magnet in a plastic tube (from a fax paper roll), and then used carbon fibre rods and tubes to attach to the end of the magnet, and then used poly styrene to fill up all the space in the tube around the magnet. Then i sealed the ends with epoxy leaving a cm. or 2 sticking out each side.
Then i siliconed one sliding track (plastic) on each side and slotted the "floating'' magnet into it so it can run freely up and down depending on the level.
It was all alot easier than it sounds, but it works like a charm, and costed me only a couple a bucks. (waaaaaaaaaaaaay cheaper than commercial units).
I have never seen this type of a system anywhere before, so i guess i'm a genius!

Patent pending.....so dont get any ideas!!!!!
.......just kidding

 

oh ya i forgot to mention... about the inverter,
it has an automatic cut off at around 10.7V, so it will shut down before the battery gets killed.
...It also says MADE IN CHINA,
so we'll just have to see about that!
tomorro is power cutting time, so will keep you fellaz posted on any new findings.

 

Wet-cell batteries perform better at lower discharge rates, and amp hour rating periods vary by manufacturer, rating period being the number of hours they use to fully discharge a battery for purposes of rating, commonly 20 hours, sometimes 10 hours, sometimes a different period altogether. Usually expressed as "C/20", "C/10", etc. So if yours are rated at 20 hours, your battery will provide 1.25 amps for 20 hours (25ah). But it won't do so well at higher discharge rates; at 5.3 amps, it would be good for somewhere between 3.1 and 4.1 hours (16 to 22 amp hours). If rated at a 10-hour rate, expect to see 3.8 to 4.4 hours at 5.3 amps. With the two combined, you should be able to make it past 7 hours.

If you weren't so averse to math, I'd give you the formula. What the heck.
T = C/(I/(C/R))^n * (R/C) where
T is time to completely discharge
C is stated capacity (25ah)
I is discharge current
R is rating period (20-hour or 10-hour rating, etc.)
n is a constant for battery type, typically 1.1 to 1.3 for flooded batteries and increasing with age.

The reed switch idea looks like a winner - thanks!