Trick up your sleeve...New mebers please attend

[Lloyd]

Ok so here's the deal, I see this site growing in new membership, but I don't see but a few decide to participate once they join. We also have many old guard that don't participate anymore...or at least seldom.

I know I'm in the same boat..just lack the time sometimes.

I want to change how we, old and, new members interact with this site. So I got this wild idea, that we all post up a trick from up our sleeves, both old and  new members.

It can be anything related to this site.

Here I go.

How do yo take a 24 hr resting, specific gravity reading from a flooded lead acid battery bank, that you cant take off line?

It's a very simple procedure. It requires a turkey baster style battery syringe, and a real float style Hydrometer.

Modification of the hydrometer makes it easy, remove the bulb from the top, and the suction tube from the bottom. Now replace the suction tube on the bottom with a rubber stopper.

Now take the syringe, draw out enough electrolyte from your pilot cell, and fill the modified hydrometer, wait 24 hrs to take the reading, then remove the electrolyte back to the cell from which it came.

Lloyd

If ya want to know what a pilot cell is, then ya have to post up a trick of your own.

[Jens]

Ummmm  .....  I don't get that.
How is the electrolyte supposed to be different in 24 hrs if it has been withdrawn from it's environment ??
Another way of putting it .... if you take a sample of electrolyte (sulfuric acid), how is it magically going to change over a 24 hr period without any influence on it ??
Colour me confused ........

[Tom Reed]

Make that 2 of us. I could understand if it was left to react in the battery for 24 hours.

[mike90045]

SG is a very accurate snapshot of lead acid SOC.   You have to adjust for temperature, but anytime you read SG, it is always representative of the current SOC

[Thob]

Make that 3 or 4 - I don't think the specific gravity is going to change, except for temperature and/evaporation while it's setting in a glass tube with a rubber stopper.

And the trick up my sleeve - Google "lead acid battery pilot cell" - I get a bunch of hits that indicate that a pilot cell is just one of the cells in a string.  One post indicated that it should be chosen when the batteries are installed from the lowest specific gravity or lowest cell voltage (after the initial charge).  The pilot cell is one the one you then test periodically (weekly/monthly/whatever), instead of testing every cell in the string.  The test may include cell voltage, specific gravity, temperature, or all of the above.

After some time (like a year), you pick a different pilot cell.  Using the same cell over and over is good for consistent, meaningful readings, but you always loose a little electrolyte each time you test so over time you could loose enough from the pilot cell to throw it off from the rest of the cells.

[mobile_bob]

bravo Lloyd for testing to see if anyone is awake here 

in my opinion, and i have long argued that specific gravity is the only true method of determining a flooded cells state of charge, however the battery must rest for a period of time for the plates to fully diffuse and the specific gravity to stabilize.

the amount of time for resting depends on a number of factors, how big is the cell, what sort of load has it been servicing, and to some extent temperature.

if the cell is relatively large, the load relatively small and protracted over time, and the temperature near ambient, then the rest time probably is minimal.

on the other hand if the cell is smaller, and the load relatively large and over a short time, and the cell temperature is significantly higher than ambient, then the rest time ought to be significantly longer.

typically an accepted length of time is 24hours, however for most folks 12 is probably adequate.

the problem comes in when you sock a hard and relatively heavy load on a small battery over a short amount of time, usually the cell temperature will rise and it will not be evenly distributed.

while resting two things happen, the temperature becomes more uniform through the cell, and the plates have time to diffuse the acid and the specific gravity will shift a bit, sometimes significantly more than a bit.

on the other side of the spectrum, a large battery with a low current draw load over a longer time, will have a temperature that is pretty uniform throughout the cell, and the plates will not diffuse much of the acid, so the specific gravity won't change much if tested immediately from that if it was allowed to sit for 24 hours.

probably the most important thing is to arrive at a resting time one can live with, realizing it is going to be a compromise, and log that in the battery log book (we all religiously do that right) and then continue to use this same resting period in subsequent testing periodically...

of course that only will hold true if you have a relatively stable load on the batteries over time, if on the other hand you have irregular usage, irregular charging, then you probably ought to stick with a 24hour rest period if at all possible.

generally best to try to do what is the accepted standard, rather than reinvent the wheel, until such time one gets very familiar with his batteries, their charging, and their usage.

my .02 cents

bob g

[Tom Reed]

How would one arrange a rest time for an off-grid situation. I don't want to shut off the power for 1/2 a day to test the SG.

Also an opinion of another battery guru, the owner of Home Power magazine Richard Perez, is that your more likely to contaminate the cells using a hydrometer. I'm not saying I agree with this, but he and his crew have a lot more off-grid experience than I do. Comments?

[mobile_bob]

contamination is a concern i have too.

i get around this by rinsing the hydrometer with clean distilled water before and after testing a pilot cell, and carefully store the thing to keep it from getting dirt or anything else in or on it.

as for providing rest time, i plan on a dual system,
the main system that i can rest, and a secondary system that can provide for
lighting loads while the other rests.

my thinking is maybe i can go to the secondary battery late saturday afternoon, and use it to provide for minimal loads through the evening, through sunday morning, and maybe till late sunday afternoon.  with an effort to get to the 24 hour resting period.

i think i can do this once a month?  certainly once every 3 months?

i don't know that specific gravity needs to be checked every month?  probably could get by every other or every third month once one gets a little history with his battery bank and his charging ability vs his load/use?

maybe you start out every month, till you see that things look very stable, water usage tells us we can go another month?  then move to a every other month check?
if that looks good., maybe then move to every 3rd month?

i think that is what i would do,  if empirical evidence tells me that the batteries can go for 3 months before they need water, and the system is operating at a point where the specific gravity test tells me that my charging is sufficient for the usage, then i think i am doing about as good as i can expect to do?

what do you think?

bob g

[Tom Reed]

My battery bank cost $8k. Don't think I'll buy another one until it fails.  The only other option I see is to run the listeroid for 12 hours and see what I get. And that brings me to another problem. I've got 2 hydrometers, 1 is temp compensated with an arrow and fill line, the other is a float with a thermometer so the temp can be corrected for. The float one always measures lower than the other. So which one is correct???

[Thob]

...
So which one is correct???

Never go to sea with two chronometers.  Either take one, or three.

[mike90045]

....The float one always measures lower than the other. So which one is correct??? 

Old proverb : Man with one watch always knows what time it is. Man with 2 watches is never sure !

You can also get a "Refractrometer" to measure SG with, just needs a drop of fluid to test with.  Less fragile than a hydrometer with it's rattley glass bits.

[Thob]

OK - in the spirit of the original post - here's a little trick up my sleeve.

What do you do when you need a third hand, and you're too proud/embarrassed/alone to ask?

I wrap a rubber band around a pair of pliers.  The pliers will then stay shut and clamp onto whatever needs to be held.  I use it for soldering wires that won't stay still, for example.  You can put on more or fewer rubber bands to change the tension.  Works with needle nose and regular pliers.  You can also set a weight on the handles to help hold it down.