12V Backup Power - using Solar Cell Batteries + PC UPS

aquanoob

Hi all,

Found some 'new' ie. never installed, 2V - 660AH @ 8HR Rated cells which I managed to get 'permission' to test out. Got quite a few (and the rest for sale - placed into another thread which included the pictures), so won't be worried too much for now.

Going to use an 'expired' UPS from our computer room, still working, but the 12V 7AHr battery in there is useless. Going to replace that 12V 7Ahr SLA with 6 x 2V - 660AH cells in series to achieve the 12V.

I figure that's going to give roughly (assuming age/loss of charge 10%) 600AH x 12V = 7200W.

The UPS should then be able to send that out via the 240V plug and allow me to tie it into the pumps and aerators. Pump should be around 60W and aerator less than 10W so that should give me 100hrs or 4 days continuous duty should there be any loss of power.

That sound about right???

PS. the only downside is these cells are bl**dy heavy, total weight of the above is at least 350kgs. Those cells were meant for solar power storage - maybe store in the garage/shed??

PSS. I might consider installing solar but with the WA rebate gone, it's hardly worth it, and I'm not sure if those grid tie inverters have a secondary outlet to tie to backup batteries either. Then how to tie those batteries to mains house power? Sorry, I failed my electrical units so it's really limited sparky knowledge I have :oops:

.

SuperVeg

Beat in mind the ups may not handle charging the batteries. Our it could just take a really long time to charge, but that probably ok in a backup scenario.
Solar panels are so cheap now IMHO. but then cheap is relative :grin:

Sent from my Chinese phone using Tapatalk

gorotsuki69

aquanoob wrote:

PSS. I might consider installing solar but with the WA rebate gone, it's hardly worth it, and I'm not sure if those grid tie inverters have a secondary outlet to tie to backup batteries either. Then how to tie those batteries to mains house power? Sorry, I failed my electrical units so it's really limited sparky knowledge I have :oops:

.

AFAIK solar PV systems must go out if there is a mains blackout. i.e it is illegal to hook up batteries to it. This is so that anyone working on the lines will not get zapped. I asked about it when I had mine installed and that was what I was told

ps. you don't happen to have a spare "expired" UPS by any chance?

aquanoob

gorotsuki69 wrote:

AFAIK solar PV systems must go out if there is a mains blackout. i.e it is illegal to hook up batteries to it. This is so that anyone working on the lines will not get zapped. I asked about it when I had mine installed and that was what I was told

ps. you don't happen to have a spare "expired" UPS by any chance?

So the only way this would work is to tie the UPS to a normal plug output from the mains, and basically leave the solar alone, which kinda was the idea to start with. This option pretty much limits the power supply only to the output appliances that are plugged to the UPS.

Oh well, never hurts to try to reach further than one can...

Thanks for the info.

aquanoob

SuperVeg wrote:

Beat in mind the ups may not handle charging the batteries. Our it could just take a really long time to charge, but that probably ok in a backup scenario.
Solar panels are so cheap now IMHO. but then cheap is relative :grin:

Yep, that'd be my guess too. I don't mind that it'll take a long time, I'll have to dig up some books to find out how long, but hey, it's all about patience .... just like cycling the water :laughing3:

PS. gorotsuki ... I had to order the office a 'new UPS' to get that 'expired one' to myself. Lucky they didn't think it was worth replacing the 7AH SLA inside that unit.

aquanoob · 2012-02-22 10.07.39.jpg [ 209.27 KiB | Viewed 3195 times ]

Well, opened up the UPS and took out the 2x 12V-9AHr SLAs. Voltage readings on them are 9-10V. Going to check what's working and what's not.

1) Going to check on the UPS and find out what the charging voltages/current are and then try to find someone who can advise on whether the input charge current (spec says 1.2A) is even able to charge up the solar batts.

2) Test the 2x SLAs (got a spare 12V charger) and see if they are still workable, and possibly if the UPS itself is faulty - in which case, I'm stuffed and have to look for another...

Looks like the 12V pairs are connected in parallel, so I guess I could just tie one off and use only one charging circuit only. Not sure if it'll work though.

Time to dig up books and hit g**gle for the answers!

SuperVeg

there might be just a resistor or something that limits the charge current.
You would need to do a bit of reverse engineering to figure it out.. know any electronics technicians/engineers ?

aquanoob

Well, I've been advised that it's not a good idea to go 12V charger charging up a 2V cell. And as I'm not keen on lugging around 350kgs of equipment, I'll go hit someone up for a small variable charger down to 3V and charge one cell first

Can't be bothered reverse engineering at this point. I know the UPS will do what I want, which is to supply AC current to the pump/aerator and continue in event of outage. I just need to test the UPS out to ensure it's still working right.

Someone's charging up the 12V 9AH cell for me now, will find out if it's dead or still workable, in which case, I need to fiddle more with the UPS.

Fun times playing with equipment, eh! :cheers:

SuperVeg

oh i didnt realise you were charging only one cell !
If you overcharge those batteries by putting too much voltage on them they will outgass hydrogen.. bad :naughty:

You can safely charge them with just an adjustable benchtop power supply.
Just set it to 2.2 -2.3v and keep an eye on the current/voltage. When the current drops right off @ 2.3v it will be mostly charged.
You will probably find it hard to exceed the maximum charging current, which is around 150A for that capacity :shock:

Privatteer

aquanoob wrote:

PSS. I might consider installing solar but with the WA rebate gone, it's hardly worth it, and I'm not sure if those grid tie inverters have a secondary outlet to tie to backup batteries either. Then how to tie those batteries to mains house power? Sorry, I failed my electrical units so it's really limited sparky knowledge I have :oops:

.

You can add battery backup to solar systems. But it has to detect the AC failure and cut the mains supply so you can't feed the grid before it provides any power.
SMA have a system, others do as well but cost is a problem.

aquanoob

Privatteer wrote:

aquanoob wrote:

PSS. I might consider installing solar but with the WA rebate gone, it's hardly worth it, and I'm not sure if those grid tie inverters have a secondary outlet to tie to backup batteries either. Then how to tie those batteries to mains house power? Sorry, I failed my electrical units so it's really limited sparky knowledge I have :oops:

.

You can add battery backup to solar systems. But it has to detect the AC failure and cut the mains supply so you can't feed the grid before it provides any power.
SMA have a system, others do as well but cost is a problem.

Privatteer,

Thanks for your reply. So it follows my original statement earlier, as I'm not too keen to muck about with live power and water in any proximity... using the K.I.S.S

principle.

"So the only way this would work is to tie the UPS to a normal plug output from the mains, and basically leave the solar alone, which kinda was the idea to start with. This option pretty much limits the power supply only to the output appliances that are plugged to the UPS."

Still workable.

aquanoob · 2012-02-24 15.47.58.jpg [ 202.27 KiB | Viewed 3110 times ]

Just hooked up the multi meter to the 12V bank to check the cells are still ok. :dontknow:

Yippeee!!! Reading shows 11.9V - 11.98V on the digital multi.

So am happier now that I know, though I did have some doubts at first, but I guess with a 20yr rated lifespan, and the fact it's been sitting never been used, still holding the charge is good.

Almost brand new then :mrgreen:

Now I'll need to check if I can charge these beauts with a baby UPS :laughing3:

Privatteer

That is a lot better that I would have predicted.

Do you have a car charger? They should have a higher current output than that small UPS. Just keep an eye on it and take the charger off when it gets to about 13.8v.
Then it would be worth trying the UPS.

SuperVeg

Just be VERY VERY careful around those exposed conductors.
A short with those sort of batteries would be absolutely catastrophic.
Have you heard of a plasma ball ? (not sure you can get them from 12v)
These batteries can produce a HUGE amount of current and a short circuit could cause an explosion and fire etc.
Much more dangerous IMHO than protected (RCD + over current) mains power.
Don't treat these things like car batteries

Also be careful with jewelry, catching a ring or watch (or necklace) across those terminals would cause instantaneous heating (think white hot). People have had their fingers amputated after shorting rings etc across high current sources.

I'm sure you are already aware of the dangers...

aquanoob

sheesh, ok, thanks for the warning :headbang:

SuperVeg.

Well, I don't wear jewelry, and I know about 'shorting', but I DIDN'T know about the plasma ball. (not that I'm not curious about it)

Just glad I'm past that point of getting useful info on the batt cells, and will now go and find out about whether the UPS will be able to do the job. (max charge current is 1.5A from that Computer UPS 12V charger -but I take Privatteers point that the typical car charger with 4-5A input current would probably be a lot more 'efficient'.)

Well, I'll see what I can drag up. I got a car battery charger at home, need to check the specs on that (it's really old). It'll be good to see if the UPS charger would work though, as that's what I'm hoping to use for the backup power supply to the 240V pump/aerators.

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