100ah Battery Voltage Question

[therealmo]

Hey,
So i have recently acquired a 12Volt 100ah Lead acid battery...Thanks work
The Battery was brand new, I mixed and filled the electrolyte myself.

My drama seems to be the charge level it's holding.

I have a dual battery setup under the bonnet with my starter and a 50ah. So off the 50ah, i have run some 8mm cable back to the tub, into a inverter, than CTEK into my 100 ah battery. (Thanks to the shared knowledge off this site)

The CTEK is great and charges the battery fine, however once fully charged, i remove the CTEK and throw the multimeter on and watch the voltage trickle down to about 11.6 Volts with nothing attached.

Is this what i should be reading??
My waeco cuts out at 10.9 Volts, so i am not getting as much as i thought i would out of it.

Is this setup the best way to do it??
What could be the dramas??

Thanks,
10 Days on Moreton this xmas will be funny without power

 

[Old.Tony]

11.6V is too low. Fully charged, it should stabilise at about 12.6V. All lead-acid batteries will do this, regardless of their Ah rating.

Check the electrolyte gravity, then try getting your CTek charger to "Recondition" (press the mode switch until 'Recon' is lit) the battery a couple of times.

 

[dunkmuddie]

Does it do the same thing when charged from 240v if so its a battery problem.
i agree with old tony but about the voltage it should be up about 12.6.
Dont know about the set up going from 12volt to 240 then back to 12 seam inefficient to me why not run straight to the 100ah battery .

 

[Matt76]

Maybe the alternator can't keep up? Might be a silly suggestion. Try charging it from 240v with the ctek and see what it does

 

[Old.Tony]

Dont know about the set up going from 12volt to 240 then back to 12 seam inefficient to me why not run straight to the 100ah battery .

In my tub, I have a 12V supply from the car that feeds into an inverter, which drives a battery charger, that charges the battery.

The alternator can only ever charge your battery to about 70-75% of its rated capacity. A 240V-supply charger will get it to 100%. Also, while the inverter is active, I have it driving the fridge as well, so the battery is completely unloaded and will charge better and faster.

There's a method to my madness!

 

[therealmo]

How do i check the electrolyte gravity??

Have tried the CTEK on recondition, same outcome.

Apart from electrolyte, what else could be the problem? It was brand new

 

[KraftyPg]

Are all cells reading similar voltages if one is down it could be a dead or dying cell.

 

[Old.Tony]

Electrolyte is tested with a hydrometer. Here's a page with a picture that explains how it works.

If 2 recondition cycles hasn't helped the battery, it must be related to either the specific gravity of the electrolyte, or there's not enough electrolyte in the battery (top it up with distilled water).

 

[therealmo]

Cheers guys

 

[maddogrc]

similarly related question...

what is the lowest voltage i should let my battery get down to?

the engel doesnt have an auto cutoff yet so i'm currently just doing a test run on my dual setup to see how quickly it drops down.

i'm guessing 12v would be the lowest i should let it go?

possibly a bit lower???

cheers!

 

[Old.Tony]

Depends on the battery type.

Gels and AGMs can (according to the manufacturers) be run down to 20% of their charge - when there's no load on the battery, this is about 12.06V (25%) (that's at 20C, increase the voltage by 0.022V for every degree C).

With a load, you could find that voltage falling to mid 11's and the battery will be fine. The fridge SHOULD disconnect at about 11.2V (from memory) although I think some models didn't stop until the loaded voltage reached 10.75V, although I think that's a bit low.

Starter batteries have thinner plates, they can deliver a lot more current in a rush but they don't like sustained draws or deep discharges - the plates inside crumble, buckle and generally cause the battery to shit itself if it's repeatedly drained. An "ordinary" deep cycle battery will have thicker plates, so they're less likely to have this problem, but they're more expensive. The Gels and AGMs are even more expensive, but again they suffer a lot less too.

Just a note about the manufacturer's spec: yes, they made the battery and should know it very well, but remember they're a company and they have a vested interest in your battery lasting no longer than the warranty period.

For my piece of mind, here are my limits:

Max charge voltage (Gel): 14.4V
Max float voltage: 13.5V
Lowest voltage under load: 11.5V
Lowest voltage no load: 12.2V

That's basically 50% of charge, below which sulphation starts in earnest and destroys batteries really fast. Gels and AGMs would survive that depth of discharge many more times than an ordinary car battery, but since they're cheaper, just go for it. The battery will pack it in after about 2 years anyway (usually).

 

[maddogrc]

yeah sorry, its just my 8 month old century 660cca cranking battery (replaced starter with a 710cca heavy duty century).

its just your basic wet type battery as you know.

its only to run my fridge over night (i dont do camps of just sitting around for a few days) and the few lights for a few hours. so i'm guessing it should be fine?

according to the century website it says they're designed for cranking, but also are designed to keep todays ancillary items such as fridges, gps, lights, etc running for plenty of time.

the reason i didnt go with a deep cycle is because i did some research and found that the landcruisers output charge voltage from the alternator is too low and causes deep cycles to sulphate pretty quick and thus kill the battery, where as newer cars dont have this issue...

so yeah, lowest safe voltage for the wet cell 2nd batt under load would be 11.5v you reckon?

 

[Old.Tony]

Yep, should be fine at 11.5V under load.

Battery sulphation starts at any charge level below 100%. It increases more as the battery discharges. If your alternator can keep your starter battery charged, it can charge a deep cycle as well - they are identical batteries (except the Gel cell type) so they can be charged the same way. Gel cells can't be charged with a typical alternator that might put out 14.7V, they have to be restricted to 14.4V.

In other words, you could have put a deep cycle in there, although the engine bay is a warm place and deep cycles don't like the heat so much. On the top of your battery will be a "RC" with a number - that's the important bit. 710CCA just means it can dump 710A, but it couldn't do that for long. The RC number is the "Reserve Capacity" and is usually a measure of how many amps it can deliver over (I think) 20 hours until it reaches 10.75V (it's the magical "battery can't start the car below this level" number).

 

[maddogrc]

well the 710cca batt has 170RC and the 660cca batt has 140RC

hmm about that sulphation bit, i'll try dig up where i read about it...

 

[terryc]

1."Mixed the electrolytic myself" Are you sure the specific gravity is right (test as as discussed).

2. Run it through a few cycles. I usually order mine then pick them up a week later in wet state and the guy does some "conditioning" of it. Load? 100W 240V flood light off an inverter is mine.

3. Use the c-tek to do the initial recharges off the mains 240V so it isn't restarting its charge cycle each time you start up the vehicle. Give it 48 hours recharge time. Which model.

4. 11.5% Volts is apparently 50% discharged and that is a good maximum discharge for deep cycle lead acid batteries.

however, the lower you discharge it, the more cycles/life you get from it, e.g.
300 cycles @ 80% DOD
600 cycles @ 50% DOD
1000 cycles @ 20% DOD

Maddogrc; this might help you out (not a rec, just first found)
GSL Electronics | Low Voltage Disconnects And Cutouts

 

[maddogrc]

i've seen a few on ebay, i'll just try find one with a 11.5 to 11.8v cut off to be on the safe side of things.

not keen on killing the battery too quick haha

 

[maddogrc]

is this the Ctek charger you guys are talking about??

CTEK XS15000 - Battery Charger 15 Amp

 

[Old.Tony]

That's the brand of charger, but this charger is the one that I have.

The difference is that the XS-7000 has a "Supply" mode that the others don't have. If you want to take your battery away and need 12V still, this puppy will do the job.

Lead Acid (deep cycle) batteries shouldn't be charged faster than about 10% of their capacity anyway - so a 100Ah battery should be charged at 10A per hour. For my money, that 7A charger is perfect!

Don't forget that you aren't charging the whole 100A either. Typically you'll use 30-40A overnight and that will take a 7A charger about 6 hours to recharge. If you're using a solar panel, you can almost get that sort of charge time in winter and summer's not a problem at all.

Don't choose a charger that charges too fast. You'll boil the electrolyte away rapidly, and the charger won't be able to tell until it's all over. If it's a VRLA, Gel or AGM battery, you'll basically destroy it by charging it too fast. With a wet cell (refilllable), you will get away with it as long as you carry distilled water with you - but I do recommend more reasonable rates to improve the longevity of the battery.

 

[maddogrc]

if i buy a deep cycle batt, say a 75Ah for my dual battery system, is it ok to run my fridge off it pretty much every single day?

the car gets driven every day, so the batt would drain over night a bit, and then i'd drive for an hour or so each day (just because of work and that) which would charge it back up again.

is this constant partial draining and recharging ok/good for a deep cycle battery? or will it wreck it?

i know how you said that constant deep discharges will kill the cranking batt i've got setup as my aux batt, however, leaving the fridge on over night isnt really a deep discharge... plus it'd get recharged each day from driving as i stated. would that still kill it?

 

[Old.Tony]

If you're driving for 1 hour, you're draining the battery for 23. If the fridge is cycling for 50% of the time, you're drawing 4A for 11.5 hours = 46Ah. If you charge a deep cycle battery fast you will destroy it - they should be charged at no more than C/10 which in your battery's case is 7.5Ah, so it will take 6 hours to charge not the 1 that is available.

Your cranking battery can handle being charged faster, but can't handle the amount of discharge.

Moderate discharging/recharging cycles won't kill a deep cycle battery, but you're not getting enough charge time each day to top the battery back up.