prolonging the life of a battery? (cheapskate edition)

[Inevitability]

Hi myBB,

Alot of the talk on the forum is around "serious" batteries : Deep cycle, Gel, AGM, Crystal etc.

I just want to power some LED strip lights, so my power requirement is very low (15W x 4 hours), which is why I'm going the cheapskate route and getting 7.2Ah SLA batteries at around R100 a pop ...no pun intended. (like this one). But I want to get the longest possible lifespan out of these things (... going cheapskate, remember? I don't want to spend alot)

Which brings me to the crux of this post...
How do I get the best lifespan out of cheap 7.2Ah SLA batteries?

In the discussions on the "serious" batteries (deep cycle, gel, agm, crystal etc) they talk about:
- making sure the DoD isn't below the spec which will kill the battery quick
- not over-charging
- 3-stage chargers

Regarding DoD, I would assume the same holds true for a cheap battery, so I thought I'd only discharge it by 25% (i.e. to use 1.8Ah per battery) ... Thing is: How does one know when the battery is at 100%/90%/80%/75% etc??
Same goes for overcharging ... How do I know when it's 100% charged, or 95% etc?

Then regarding "3-stage" chargers, or to generalise it a bit more: charging a battery "the right way"...
Any tips/tricks?
What should I expect to pay for a charger that will charge "the right way"?
(I've seen chargers in the region of R3k, which makes no sense for me to buy to charge R100 batteries ...only because my aim is to be cheapskate and squeeze out the best value possible from this cheap stuff)

I would guess there is a huge market for cheap solutions (that offer good value for money) to fight being in the dark during loadshedding

This is where I am positioning this thread, since I myself am in that audience.

 

[Aardvark]

Hi
I have been looking for 12v dc led strips myself
What have you found.
Thanks
Johnathan

 

[BigEars]

You can start by looking at reputable manufacturers spec sheets. See attachment:

 

[upup]

slow charge them, 800 milli amp's ,slow drain them. look at poles for corrosion. Keep battery in a temperature controlled place. Refill cells after 2 years with about 20 ml battery water each, as per youtube videos.

 

[supersunbird]

What the intended use of your idea? Emergency lighting for loadshedding? Use every day lighting?

Maybe look at these products:

http://www.bushpower.co.za/products.asp?pid=546 at R251.99 (no battery or LED light), if you don't have the batteries already, maybe add the lead crystal batteries as linked at bottom of product page at R296.40.

http://www.bushpower.co.za/products.asp?pid=525 at R540.00 (with AGM battery and LED light)

 

[Inevitability]

First off... I found this link to be very interesting and useful information : 3-stages of smart charging

Onto replies:

I have been looking for 12v dc led strips myself
What have you found.

I did some quick research and found that the standard 5050-type LED strips are old technology and should be avoided if alternatives are available. So I checked on eBay and ordered the 2835-type LEDs from China (there are many many many Chinese sellers on eBay) ... I just ordered one 5-metre strip to check if it's any good. Its not just the LED-type to consider, cos different manufactures produce vastly different qualities of product. Which is why I'm just buying one to test.

You can start by looking at reputable manufacturers spec sheets. See attachment:

The datasheet has alot of useful info, but I can't see the part where it tells you the loss in Volts per decrease in % of capacity as you draw from the battery. And I still don't know how to practically implement it ... So if the 75% mark is at 12.2V, how would I implement a 12.2V cutoff to make sure I don't over-draw the battery?

slow charge them, 800 milli amp's ,slow drain them. look at poles for corrosion. Keep battery in a temperature controlled place. Refill cells after 2 years with about 20 ml battery water each, as per youtube videos.

Thanks! But ... Errr.... can you refill cheap 7.2Ah alarm batteries?

What the intended use of your idea? Emergency lighting for loadshedding? Use every day lighting?

Yes. And eventually, yes.
For now I just want loadshedding lights. But whatever I put into place now must not be wasted later... So, one day, I would love to hook up a solar panel to charge these same cheapo batteries and run the LEDs off them every night so that my lighting is completely off Eskom.

Technology is rapidly improving (see here) and prices are falling so the only logical course of action (...for me) is a to try and squeeze out the best lifespan from a cheap solution cos the better quality options just wont ever pay themselves off.

 

[BigEars]

Another member here gave a snapshot of a spreadsheet he created to work out depth of discharge etc. I took the info, created the sheet...and then added more stuff. See attachment:


Edit: Thanks TehStranger

 

[supersunbird]

Another member here gave a snapshot of a spreadsheet he created to work out depth of discharge etc. I took the info, created the sheet...and then added more stuff. See attachment:


Edit: Thanks TehStranger

Geez, I hope you're not right.

Because if I want to run a 200W load at 220v for 14 hours I will need nearly 1000ah of batteries, if I use that spreadsheet, and I'd still be left with a DoD of 100%.

 

[chromedome]

I bought the Techmate Optimate 3 at Midas for R690 a few weeks ago, it's a smart 800MA charger. I use it for 3x 7.2ah batteries and an old car battery, so far no problems.

 

[Inevitability]

I bought the Techmate Optimate 3 at Midas for R690 a few weeks ago, it's a smart 800MA charger. I use it for 3x 7.2ah batteries and an old car battery, so far no problems.

Do you charge the batteries individually, or connect them all in parallel and charge them together?
I want a system that requires minimal manual input, so I was [-]dreaming[/-] thinking I'd have the batteries connected in parallel and permanently hooked up to a charger ... whenever Eskom is available, it will charge the batteries. I see that your OptiMate is the infamous )) 3-stage charger, so it will maintain the "float charge" if it's connected to the batteries all the time

By the way ... I was Googling this weekend and check this out for an auto cut-off circuit to prevent over-discharging:

[video=youtube;1BKEMDYAGBA]https://www.youtube.com/watch?v=1BKEMDYAGBA[/video]

 

[BigEars]

Geez, I hope you're not right.

Because if I want to run a 200W load at 220v for 14 hours I will need nearly 1000ah of batteries, if I use that spreadsheet, and I'd still be left with a DoD of 100%.

I get 14.4Hrs to 30% DOD with 1000Ah of batteries...

 

[TehStranger]

Another member here gave a snapshot of a spreadsheet he created to work out depth of discharge etc. I took the info, created the sheet...and then added more stuff. See attachment:


Edit: Thanks TehStranger

No problem, nice sheet Theo.

Geez, I hope you're not right.

Because if I want to run a 200W load at 220v for 14 hours I will need nearly 1000ah of batteries, if I use that spreadsheet, and I'd still be left with a DoD of 100%.

The voltage rating is actually linked to the UPS (i.e. 12v, 24v, 48v model), not the voltage that your appliances run at.

i.e. If you have a 24V UPS with two 12v 100Ah batteries in series, put in 24v and 100Ah into the spread sheet, along with your W load requirements.

 

[Inevitability]

I used 7.2Ah as the capacity, and 15W as the load, and I get :
20% DoD = 0.92
30% DoD = 1.38
... but what does this mean? What am I looking at? Amps / Volts?

What I'm trying to get to is to know how to determine what's the 75% point (or any other % for that matter) of the battery / battery bank, and then to have a way to auto-switch off the supply from the batteries once the capacity drops to that point.
From my understanding the batteries will lose voltage as the capacity drops... I am looking for the graph that says:
13V = 100%
12V = ?? %
11V = ??%
10V = 0%
And then a mechanism to make sure i don't draw beyond the 75% without manually having to read a meter i.e. an automated cut-off.
Hopefully the circuit I found above can do that job.

 

[cfvh600]

I used 7.2Ah as the capacity, and 15W as the load, and I get :
20% DoD = 0.92
30% DoD = 1.38
... but what does this mean? What am I looking at? Amps / Volts?

Running time? In hours.

 

[Inevitability]

Running time? In hours.

Now why didn't I think of that?!!
That makes a hell of a lot of sense!

 

[chromedome]

Do you charge the batteries individually, or connect them all in parallel and charge them together?
I want a system that requires minimal manual input, so I was [-]dreaming[/-] thinking I'd have the batteries connected in parallel and permanently hooked up to a charger ... whenever Eskom is available, it will charge the batteries. I see that your OptiMate is the infamous )) 3-stage charger, so it will maintain the "float charge" if it's connected to the batteries all the time

By the way ... I was Googling this weekend and check this out for an auto cut-off circuit to prevent over-discharging:

[video=youtube;1BKEMDYAGBA]https://www.youtube.com/watch?v=1BKEMDYAGBA[/video]

View attachment 214764

Individually.

 

[Inevitability]

Individually.

Anyone got any idea if the batteries can be charged in parallel?
If yes, do they need to be at an equal charge level for this to happen?
And if I set them up in parallel to supply my lights, will they discharge at an equal rate?

 

[savage]

Anyone got any idea if the batteries can be charged in parallel?
If yes, do they need to be at an equal charge level for this to happen?
And if I set them up in parallel to supply my lights, will they discharge at an equal rate?

Yes, yes, and yes...

 

[Inevitability]

Yes, yes, and yes...

 

[elbow]

How do I get the best lifespan out of cheap 7.2Ah SLA batteries?

Call me a "me too".

I have a 7.2Ah gel lead acid battery. I've hooked it up to power my ADSL modem, RB750 router and a wifi access point. All conveniently expect 12v and regulate internally so should be tolerant.

Looks like they are drawing about an amp between them (my multimeter only reads up to 500mA so I'm estimating by how energetically the needle passed full-scale ;-) ). I would have guessed about 15W so that seems about right.

12v x 7Ah = about 80 AH. I'm not inverting so no power factor to be considered. So that's 80 WH ?

So I'd estimate the setup should keep me online for at least 4 hours before the battery would start getting near to flat?

I might add a 5.5W LED light too, I'd still expect 3 hours then.

Only expecting to require the 2 to 2.5 hours of load shedding. Though with stage 3 it might not recharge enough for a second round in the same day.

I connected a charger in parallel on the battery and nothing unpleasant happened - voltage didn't exceed 14v, my gear is still working, my battery isn't bulging.....

But I will upgrade to a Optimate tomorrow which obviously is properly designed to "float charge".

Anyway - very inexpensive and a fun little experiment.

Steve