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Author Topic: Backup power supply  (Read 7793 times)
pontiff
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« on: November 15, 2011, 12:30:52 PM »

Hello,

I've made a backup power supply to supply leccy for lights, computer, wifi etc  out of a 1000w computer UPS and some leisure batteries. I've tested it pretty thoroughly and it will happily supply 650W for over an hour ( or a couple of hundred watts for a few hours.). I've added some extra cooling fans to keep it happy, and upgraded the wiring.
In inverter mode it powers my pc  and tv without killing them as it apparently produces a pure sine wave.

My question is, in a power cut, could i plug it into a bog standard 2kW genny ( as opposed to an expensive inverter type suitcase genny) to recharge the backup batteries? Would the UPS cope with this and still supply a suitable quality electricity to power sensitive equipment like computers?
Bear in mind this is just for occasional use in power cuts.

Cheers  Cheesy

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knighty
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« Reply #1 on: November 15, 2011, 12:44:35 PM »

some will be ok... some won't.... depends on which ups you have and how good the genny is...

chances are it wouldn't work... if the ups doesn't see a nice clean sign wave it probably won;t accept it... some will even see it as a power spike and short it out to protect the equipment connected to it !

(which is why you can't connect 1 ups to another)

it would probably be easier to just connect the generator to a battery charger and charge the 2 batteries ?

it might be worth charging them with a battery charger once in a while anyway.... the ups charger might not be man enough to charge up a couple of big leisure batteries (just because the ups gauge says fully charged doesn't mean it is)
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pontiff
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« Reply #2 on: November 15, 2011, 02:36:12 PM »

some will be ok... some won't.... depends on which ups you have and how good the genny is...
it would probably be easier to just connect the generator to a battery charger and charge the 2 batteries ?

it might be worth charging them with a battery charger once in a while anyway.... the ups charger might not be man enough to charge up a couple of big leisure batteries (just because the ups gauge says fully charged doesn't mean it is)

Cheers Knighty,
I've thought about using a charger attached to a generator then came up with more questions.....

1. Would the charger be ok being powered by a cheapo generator?
2. Would I be able to charge the batteries whilst they are under load ( supplying about 500watts to the house) or would the charger end up drawing too much from the generator and overload.
3. Could anyone suggest a 24V charger that could cope in this way?

Cheers,
Pontiff
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knighty
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« Reply #3 on: November 16, 2011, 01:29:46 AM »

the charger will be fine powered by the cheapo genny....

500watts at 24v is about 20 amps, so you need a charger capable of 20amps min.
(really want one which can do twice that so it has an easy life)

500watts at 240volts is only 2amps, so you'll only be drawing 2 amps from the generator, which is hardly anything

best bet will be to look for a cheap used 24volt charger on ebay....  a good new charger is expensive... but they're cheap 2nd hand :-)
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biff
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« Reply #4 on: November 16, 2011, 02:33:21 AM »

a good idea would be,,2 x 80watt x 12volt solar panels and a nice xantrex contoller, you could beef up your bank  and every so often do an equalising charge with the xantrex for about 10 minutes every fortnight. this is a mighty fuel saving move.
the charging side of the ups,s is pretty usless but the sine wave is exellent. dont forget that different brands of ups,s have different methods of starting up,some are cold start and some need a little donkey inverter, some inverters can start immediatly on connection to a battery but some like apc need to go through a whole ringmaroll.a lot of new apc upss are set to shut down after 20 minutes of operation and cannot be changed to continious operation,which is a pity for offgridders.upss really are a fantastic source of good lecky.
                                                                                                    biff
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clockmanFR
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« Reply #5 on: November 16, 2011, 09:58:52 AM »

Just bagged another 3.7kw UPS, APC (American made bullet proof designed to run continuously for ever) , the same as i have allready, for a wad 100.

The best test i can give you is to see if your ups will run a fridge or freezer.
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Justme
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« Reply #6 on: November 16, 2011, 11:58:44 AM »

What the UPS's charger amps?

I looked at using one before I got the Victron but they all had chargers that were to small as they are sized so that after an outage they have a day or two to recharge the bank.
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pontiff
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« Reply #7 on: November 16, 2011, 12:18:23 PM »

What the UPS's charger amps?

I looked at using one before I got the Victron but they all had chargers that were to small as they are sized so that after an outage they have a day or two to recharge the bank.

Yes its way underpowered which is why using a big powerful batt charger powered by the genny might be a solution.

Another question has now popped into my  tiny mind.... When the UPS is running on mains rather than battery backup, does it clean up the grid leccy at all or just leave it alone?

i've come across somebody who is using a cheap generator which is attached to one of these

 http://www.ebay.co.uk/itm/APC-LE1200I-Line-R-1200VA-Automatic-Voltage-Regulator-/160656562629?pt=UK_Computing_LaptopAccessories_PowerSupplies&hash=item2567e099c5

before going into the ups. The idea being that the ups batts are just to maintain power whilst the genny is refuelled/cools down?



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clockmanFR
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« Reply #8 on: November 16, 2011, 06:31:19 PM »

pontiff, I only know about the APC 5000 Ups in some detail. It took me some time to research and get the right inverter, this one runs on 48v batteries that are sitting there awaiting the call, so the 2 huge transformers, 14kg each, are running full time and give a 240vac supply at 3.7kw. It will handle from 174vac to 253vac and all spikes etc. According to APC recharge time from total drain is 2 to 5 hours to full for the internall 48ah battery system.

The power connection to the mains is wired in direct and is 20amp type.  In general the design is robust and is commonly used as a server Power supply.

Obviously i took the piddly little sealed lead acid's out, and modified the 2  100amp fuse connections, that have  bolt on 16mm/2 cables from my 48v 700ah battery bank. And the machine cold starts by just pushing the start button without the need of any mains.

This guy is helpfull and has some reconditioned jobs available, and will modify a UPS for you if required,  http://www.upsshop.plus.com/
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guydewdney
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« Reply #9 on: November 16, 2011, 08:55:48 PM »

I still have a gert big HP ups up for grabs for free. cant bear to throw it away. 96v though - I think.
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SimonHobson
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« Reply #10 on: November 22, 2011, 09:20:50 PM »

I still have a gert big HP ups up for grabs for free. cant bear to throw it away. 96v though - I think.
I've got a dead one at work - needs a new converter module (too much load for just two) and a 1/4 ton of batteries Roll Eyes 4kVA/2.8kW per module, and 120V batteries.

Back to some of the earlier questions ...

Does a UPS clean up the power ?
Depends on the type.
Most budget (and many not so budget) units are "offline" which means they just sit there watching the mains and the load runs off whatever the mains gives. If the mains fails (or goes out of spec), the unit fires up an inverter and runs the load from that. Often the battery charger uses the inverter running the other way round - an APC 3kVA rack-mount I pulled apart had a custom transformer designed to step up the low "loaded" battery voltage to mains, or to step down the mains to the much higher "charging" battery voltage. An offline unit will do little to the power quality while running on mains - it may have some surge protection and filtering, some units have some basic voltage regulation.

At the other extreme, an online (or double conversion) unit converts the mains to DC, and then inverts it to power the loads. These are true "no break" changeover as the load is always running from the inverter, and they always regulate supply quality. The downside is both cost and the continuous power losses from the conversions.

Can you run a USP from a genny
Yes, but ...
Ideally you need a significantly oversized genny to cope with the varying load. I recently did this for a customer after we (or rather the other guys dealing with it) had struggled to get all the data shifted to other servers in our server room. They had an all-day outage planned at their head office. As a last minute things, I grabbed my "no-name" 3kVA genny and an extension lead and dashed up there. Their load is about 50% of whatever an APC 3kVA does (according to it's software) and at first it wouldn't switch over - because it was an all or nothing situation, the genny would drop it's output every time the UPS tried to switch back to mains. After adjusting the sensitivity, we got the UPS to stay on mains, and it ran all day - made the genny chug while it was recharging the batteries Shocked

If setting up a system as described, then I'd be tempted to go down the separate charger and inverter route as suggested. Note that many gennies have DC outputs and can charge batteries directly.
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biff
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« Reply #11 on: November 22, 2011, 10:14:37 PM »

as posted before,
             i use a 120vdc symmetra rm,in fact we have kept the origional 120 chinese sine wave inverter(low frequency job,a bit like a concrete block with nice pale metal and a happy little chinaman smiling at me,,so long as i dont overload and knock out the inverter,then he has a glum look on his face,,quite cute and effective.
  this symmetra can take 3 phase but i have not conquerd that yet.it is ideal during a storm because it can take all the power the turbine throws at it and quite often our turbine is pumping out 3kw plus,so it works fine with the controller now,origionally it was fighting and overcharging and causing the controller to get hot and bothered,but i just removed its internal battery module(it is connected to an external 120vdc x 600ah forklift pack) and it settled down beautifully,during a heavy heave in a force 9 the symmetra breathes hard and the fans all begin to blow as well as the ones on the controller.
    the power modules in the symmetra are 2kv each(1.4kw) and can be inserted and removed under load safely in seconds,it tells you exactly what is happening. the symmetra is double conversion and origionally i though that it might be easier on juice than the chinese 2kw but it takes 200watt plus to run it,however that is nothing when the wind gets really going,thats when it comes into its own. so in balmy weather we use the chinese one and switch on the symmetra if we have a few days force 6 or more,one thing i did notice,,,it can hold the voltage up on the controller steady at 130vdc even when the wind is beginning to drop and longer than the 2kw with the same loads,i cannot explain that,
  it is an exellent piece of kit,very reliable,parts are easily come by and not to expensive,95.00 for an intelligence module.i would recommend then to anyone.,,,,,,,biff
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pontiff
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« Reply #12 on: November 22, 2011, 10:39:44 PM »

Thanks everyone,
Some great advice here. I shall digest it all then email my Christmas present list to Mrs Pontiff/Santa.

p.s We had a power cut last night. I rushed to the garage, faffed about setting up extension cables back to the house, powered up the UPS and cooling fans, hooked it up to the boiler, wifi and a couple of lamps in the lounge.......

....and the mains power came back on.  Roll Eyes
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SimonHobson
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« Reply #13 on: November 22, 2011, 11:09:35 PM »

If it's worth the effort of all that lot (which suggests you have a lot of power cuts), it's probably worth wiring in separate cabling and sockets that can either run off the UPS or the mains. Either let the UPS handle the changeover, or fit a changeover switch.
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biff
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« Reply #14 on: November 23, 2011, 01:40:33 AM »

seperate ring main is a brilliant idea,
               you can use different design and coloured double sockets.no call to go near the consumer unit at all.
    join the 2 ends of the ring into a good quality plug,install a double approx 500mm from the ups,plum the line from the ups into the double,when you want to complete the circuit just plug the circuit into the double next to the inverter.if you do it this way you can have alternative power sources using the same circuit.
a mini trip between the inverter and the circuit is an option but the inverter will trip anyway if it spots any thing wrong. a fuse between the batts and the inverter is a must.you can never tell,someone might accidentally block the cooling fans access and in a matter of minutes the thing could cook and short out,maybe cause a fire,        biff
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