Help with inverter battery sizing

russellw1 said:
The efficiency of lead acid batteries is bad, usually about 70% when new and they go down to less than 50% after about 500 cycles or 2 yrs. That means you need a lot more solar panels and about double the capacity (Whr) for calculated usage for a new system. Lithium (lifepo4) batteries start at about 95% efficiency and can last 5000 to 6000 cycles so they might be worth the extra cost.

The Americans have sold A123 systems to the Chinese so prices might fall soon.
Click to expand...

While LA or SLA batteries are known to be less efficient than the new designs, we have done very well for quite a few decades with LA batteries. The figures are not as bad as you claim. The only persons who get that sort of poor efficiency out of their LA batteries are those that fail to maintain their batteries properly. All the years I have owned a car, I have never got less than 8 years out of a LA battery.
Yes I am all for buying the best you can afford when replacing batteries.
 
If you use Japanese Panasonic type batteries you might get better results than other LA types but at a cost which might be as much as LiFePO4 (A123 26650 cell) packs.
 
Last edited:
russellw1 said:
If you use Japanese Panasonic type batteries you might get better results than other LA types but at a cost which might be as much as LiFePO4 (A123 26650 cell) packs.
Click to expand...
Cost?
 
russellw1 said:
If you use Japanese Panasonic type batteries you might get better results than other LA types but at a cost which might be as much as LiFePO4 (A123 26650 cell) packs.
Click to expand...

A few issues, although these are the batteries we use:

Panasonic stopped making VRLAs for a while, and I don't know what they're actually making at the moment.

CBI is no longer the local agency, so you've got to deal with Panasonic SA. I'd rather have an ice-pick through my balls.

On a positive note, VRLAs don't need complicated chargers (unless you're Geoff), so you can just stick them into your existing system.

Also, they definitely weren't expensive - Our last purchase was at about R1000 each, inc VAT, for a 42Ah. You won't get lithiums at that price. Edit: and I don't want to hear any bull**** about depth of discharge - if this is for a UPS, depth of discharge is 100%, finished and klaar.
 
Drunkard #1 said:
A few issues, although these are the batteries we use:

Panasonic stopped making VRLAs for a while, and I don't know what they're actually making at the moment.

CBI is no longer the local agency, so you've got to deal with Panasonic SA. I'd rather have an ice-pick through my balls.

On a positive note, VRLAs don't need complicated chargers (unless you're Geoff), so you can just stick them into your existing system.

Also, they definitely weren't expensive - Our last purchase was at about R1000 each, inc VAT, for a 42Ah. You won't get lithiums at that price. Edit: and I don't want to hear any bull**** about depth of discharge - if this is for a UPS, depth of discharge is 100%, finished and klaar.
Click to expand...

Sigh. I could not resist to see what you have to say, in the naïve hope that maybe you have something useful to share. But what do you do? You start by making vague insinuations. I actually have not got round to post anything about charging of batteries yet so where you get this comment from only you know.

Actually the "experts" disagree with you, (Exide is one such group of experts), DoD is important for ANY system. You may not know what your UPS is doing and how it has been designed to discharge the batteries it uses.

Here is an extract out of a manual written by Exide that show what happens when you discharge batteries too deeply and the effect that has on how long it takes the battery to return to its fully charged state. Also the next curve show what effect DoD has on the total number charge cycles and hence the lifetime of a VRLA battery.

Dod.jpg

The DoD versus life cycle picture:

dod2.jpg
 
Last edited:
Geoff.D said:
Sigh. I could not resist to see what you have to say, in the naïve hope that maybe you have something useful to share. But what do you do? You start by making vague insinuations. I actually have not got round to post anything about charging of batteries yet so where you get this comment from only you know.

Actually the "experts" disagree with you, (Exide is one such group of experts), DoD is important for ANY system. You may not know what your UPS is doing and how it has been designed to discharge the batteries it uses.

Here is an extract out of a manual written by Exide that show what happens when you discharge batteries too deeply and the effect that has on how long it takes the battery to return to its fully charged state. Also the next curve show what effect DoD has on the total number charge cycles and hence the lifetime of a VRLA battery.

<worthless graph>

The DoD versus life cycle picture to follow.
Click to expand...

No surprises - Geoff posts a page of technical gibberish; not a worked example in sight. Oh, and before you post your second graph (not that the first was any use without a title or x axis), convert the "number of cycles" to "years" based on actual average discharges and number of power failures per year. Otherwise it's nothing but the usual worthless technical FUD we've come to expect from you.

Oh, and in case you don't realise it, it's your acceptance of parallel strings that necessitates a complicated charging system in your installations (although I doubt you've actually done any).
 
Drunkard #1 said:
No surprises - Geoff posts a page of technical gibberish; not a worked example in sight. Oh, and before you post your second graph (not that the first was any use without a title or x axis), convert the "number of cycles" to "years" based on actual average discharges and number of power failures per year. Otherwise it's nothing but the usual worthless technical FUD we've come to expect from you.

Oh, and in case you don't realise it, it's your acceptance of parallel strings that necessitates a complicated charging system in your installations (although I doubt you've actually done any).
Click to expand...

I never said parallel "strings" is a good idea. I commented on the fact that a number of suppliers of inverter systems in SA, show in their specifications that this is possible without any reference to the risks and issues with such designs.
 
Considering my original question was actually for a UPS and we've only had one power outage in the last year, and I only need the batteries to last for the next 5 years, I could easily just run them to 100% dead?

I don't care how long they take to charge, and neither do I care if only 90% is available after running them flat. 90% is still more than 50%
 
Geoff.D said:
I never said parallel "strings" is a good idea. I commented on the fact that a number of suppliers of inverter systems in SA, show in their specifications that this is possible without any reference to the risks and issues with such designs.
Click to expand...

That's not what I remember you saying, but I'm too lazy to check.

mister said:
Considering my original question was actually for a UPS and we've only had one power outage in the last year, and I only need the batteries to last for the next 5 years, I could easily just run them to 100% dead?

I don't care how long they take to charge, and neither do I care if only 90% is available after running them flat. 90% is still more than 50%
Click to expand...

This is why you need to be upfront with your questions. Say the word inverter and the solar nutjobs crawl out of their caves. If you mean UPS, say UPS.

To answer your question, good batteries will last more than 10 years with a design depth of discharge of 100%, since the number of cycles is so low, and 90% of power failures don't discharge fully anyway.
 
mister said:
Considering my original question was actually for a UPS and we've only had one power outage in the last year, and I only need the batteries to last for the next 5 years, I could easily just run them to 100% dead?

I don't care how long they take to charge, and neither do I care if only 90% is available after running them flat. 90% is still more than 50%
Click to expand...

Well at least you now have all the info at your disposal to make an informed decision.

Assuming your expectation is that you will only have one power failure a year, and that the power failure will last for ? hours and that the time taken for the batteries to recharge is not important, and that you are not expecting the batteries to last more than 5 years anyway, you can discharge the batteries completely if you so wish. Or, more accurately, that batteries will discharge until the inverter can no longer operate and will cut out.

So in terms of your original question you are now happy. As to anyone else reading this thread, I trust that they will be able to now evaluate or set the brief for their UPS requirements more accurately. Regardless, it is still important for you when you get around to purchasing the inverter, to make sure it has the capacity to charge the batteries correctly after a typical discharge.
 
Drunkard #1 said:
That's not what I remember you saying, but I'm too lazy to check.



This is why you need to be upfront with your questions. Say the word inverter and the solar nutjobs crawl out of their caves. If you mean UPS, say UPS.

To answer your question, good batteries will last more than 10 years with a design depth of discharge of 100%, since the number of cycles is so low, and 90% of power failures don't discharge fully anyway.
Click to expand...

Maybe you should read comments more thoroughly before starting with your insults? There is no reason at all to insult anyone else for offering their insights regardless of which area they come from. In fact the solar guys and those of us that have designed and implement power systems used for outdoors conditions away from normal stable grid power are always interested in efficiency, reliability and making sure our systems are maintained properly. If we don't, we do not get the expected lifetime out of our batteries and other equipment.
 
Last edited:
Sorry guys I thought it was obvious by my original question that this was related to powering equipment during outages and had nothing to do with solar. It was only after looking at Geoff's DOD charts that it occurred to me that it really does not matter in my situation, and that I can forget about worrying about discharging to 50%
 
Last edited:
You must log in or register to reply here.
Back
Top
Sign up to the MyBroadband newsletter
X