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Author Topic: System question - thoughts please...  (Read 5806 times)
teledemon
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« on: May 05, 2009, 03:23:55 PM »

Here's the problem...we live on a remote site with 240v currently supplied via diesel generators 24/7.  Understandably the powers that be wish to cut our supply overnight for 7 hours as a cost saving measure...fine, but that will leave us with no way to power the C/H circulation pump, fridge, UV water filter etc.  My cunning plan is to use the mains power through the day to charge a battery bank of around 200Ah to supply the power overnight via an inverter. Is there a suitable charger/inverter which will do the job...I reckon around 500w max...and can the switchover be done automatically? The combi inverters and I've seen are hideously expensive...any more cost effective solutions out there?
Thanks
Dennis
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dhaslam
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« Reply #1 on: May 05, 2009, 03:37:42 PM »

You could use  a UPS with an external battery.     This will work automatically when the generator goes off.  I have three UPS  wired into the house wiring  to cover lighting, pumps and electronic shower controls.   They don't last long  without external batteries and they beep until the power button is pressed.  You will need to disconnect the beeper and make a connection for the external battery.
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DHW 250 litre cylinder  60 X 47mm tubes
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evan
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« Reply #2 on: May 05, 2009, 03:51:09 PM »

Here's the problem...we live on a remote site with 240v currently supplied via diesel generators 24/7.  Understandably the powers that be wish to cut our supply overnight for 7 hours as a cost saving measure...fine, but that will leave us with no way to power the C/H circulation pump, fridge, UV water filter etc.  My cunning plan is to use the mains power through the day to charge a battery bank of around 200Ah to supply the power overnight via an inverter. Is there a suitable charger/inverter which will do the job...I reckon around 500w max...and can the switchover be done automatically? The combi inverters and I've seen are hideously expensive...any more cost effective solutions out there?
Thanks
Dennis

If you look around you might find an older Trace inverter - they had models with switch-over with an integrated charger, but were heavy and only 500W.  Would suit you though.

Another alternative if the loads are restricted to the few you mention would be a computer UPS.  Again, choose an older second hand one, you should be able to get it for almost free, and add your own battery.  
They aren't ideal at charging batteries so adding a small PV panel or wind turbine and proper charge regulator might help.


Failing that, buy a separate battery charger and inverter, and add a DPCO relay that is held "on" by the mains - the normally open contacts go to the mains, the normally closed contacts go to the inverter, and the common contacts go to your appliances.  Use a second relay to keep the inverter switched off when it's not needed, to save a few watts.


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teledemon
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« Reply #3 on: May 05, 2009, 03:56:25 PM »

Thanks...I assume you mean a computer type UPS...never thought of that Roll Eyes
Are these things easy to wire into the mains? Is there any issue with backfeed, say if someone is working on the supply at the generator side?  Shocked
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evan
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« Reply #4 on: May 05, 2009, 03:57:46 PM »

Thanks...I assume you mean a computer type UPS...never thought of that Roll Eyes
Are these things easy to wire into the mains? Is there any issue with backfeed, say if someone is working on the supply at the generator side?  Shocked


You just plug them in...

Bear in mind, unless you like tinkering, the UPS solution might not be ideal for this. 

Firstly, you may find your UPS doesn't last very long.  They are only meant to run for a few minutes at a time, once in a blue moon, and the cooling isn't usually up to continuous use - you'd need to add a fan at least. 

Secondly you might find your batteries don't last very long - the UPS is designed to recharge a small sealed battery pretty slowly.  If it can put back 100AH in a day I'd be surprised, unless it's a really big one.  So the batteries might get chronically undercharged (see comment above about adding some renewables to compensate).  If you use a flooded external battery you'd definitely want a more serious charger for it, as the voltage just won't be high enough to charge it properly.

By the time it's quit a couple of times during the night and let your fridge get warm, you'll wish you'd spent the money on a proper inverter with charger and changeover Cheesy
« Last Edit: May 05, 2009, 04:24:42 PM by evan » Logged
dhaslam
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« Reply #5 on: May 05, 2009, 04:18:34 PM »

If you were connected to the mains you would need to be careful that the neutral wire on a UPS linked device  is not connected to the neutral  on an other circuit.   This just means bringing back a single three core cable from the pump or pumps to the UPS.   A fault in the pump will trip the trip switch as normal so there is no need to fuse the circuit after the UPS.
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DHW 250 litre cylinder  60 X 47mm tubes
Heating  180,000 litre straw insulated seasonal store, 90X58mm tubes + 7 sqm flat collectors, 1 kW VAWT, 3 kW heatpump plus Walltherm gasifying stove
teledemon
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« Reply #6 on: May 05, 2009, 04:27:32 PM »

Cheers for all that info.
Do you mean that each appliance should be fed individually? I had the idea of powering the whole mains circuit...well C/H circuit, lights probably...Meanwhile, I'm off to Fleabay..! Or if anyone's got some kit going free  Wink
Taking it all a step further, it would be ideal to be able to extend the battery capacity and add a small turbine at a later date (we have 8+m/s average) so that we can offset our usage during the day somehow. I guess batteries/inverter would be the way to go but the most expensive option.
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evan
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« Reply #7 on: May 05, 2009, 04:40:10 PM »

Cheers for all that info.
Do you mean that each appliance should be fed individually? I had the idea of powering the whole mains circuit...well C/H circuit, lights probably...

You can do that (I have done it), but I don't necessarily recommend it.  I think it might be better and safer to run a separate "low current" circuit for the few appliances that need it.

Reasons:
This avoids messing with the fuse box.  Unless you know what you're doing, you probably shouldn't.

It avoids accidentally leaving a few appliances on that you didn't mean to and using the battery up.

You'd need to run everything through the changeover relay on the UPS/inverter.  Unless you're buying a large, proper inverter, that relay isn't going to be very large, and would easily be overloaded accidentally when running on mains. 



Absolutely don't be tempted to just switch the main breaker off and plug the inverter output into a socket.

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sleepybubble
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« Reply #8 on: May 05, 2009, 05:33:53 PM »

I reckon around 500w max...

Coming to this discusion a bit late, first thought is to be really sure about your consumption needs through the night then start from there.

I use a second hand APS1000 UPS which has been modified to run from 2 deep cycle lead acid batteries(not from choice I just happened to have them!), with a total of about 180ah.
We only use it as back up for the heating pump and interlock, the heat source is a rayburn. The longest run it managed on batteries alone was about 16 hours. I have been toying with dropping the lighting circuit onto it as well but candles are fun for the kids when we have power cuts. Its a simply soloution for the occasional power cut but I don't think it would work out to great in the long run, I've been advised that the charger on the UPS is not up to the welly of getting the batteries back up to charge quickly enough by doing the same as you but opposite, ie, shutting off grid during day and running on batteries and then coming back on grid to coincide with E7 for charging.
I haven't experimented with it yet as it means taking the beeper off the UPS and its up in the attic, but I will do one day, I'm just ordering a 500w turbine as a toy though so I will be having to rethink a lot of what I do ;-)
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;-)
teledemon
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« Reply #9 on: May 05, 2009, 05:49:54 PM »

Good advice - I'd rather get it done properly and within regs; though I'm not averse to a bit of DIY I don't intend to get away with a bodge in this instance. Fire is a major risk and doesn't bear thinking about. I'll check the wiring and see if one circuit will do the job. All I need to do is supply the kit and source some suitably qualified person to hook it up...

Re the latest post, I'll only need about 6-7 hours worth of circulation pump.  Not a constant load as it will only kick in intermittently when the pipe thermostat on the back boiler says so. And maybe the fridge? Hmmm, now were getting down to it...my rough calculations took me to 200Ah if I went for a 50% discharge. I've been monitoring overnight consumption with my Efergy meter and it seems to agree, as long as I don't use the breadmaker Sad

Is the system permanently connected?
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sleepybubble
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« Reply #10 on: May 05, 2009, 07:17:09 PM »


Re the latest post, I'll only need about 6-7 hours worth of circulation pump.  Not a constant load as it will only kick in intermittently when the pipe thermostat on the back boiler says so. And maybe the fridge? Hmmm, now were getting down to it...my rough calculations took me to 200Ah if I went for a 50% discharge. I've been monitoring overnight consumption with my Efergy meter and it seems to agree, as long as I don't use the breadmaker Sad

Is the system permanently connected?

Yes our system is permanently connected, there is proberbly an overhead in powering the UPS all the time, but I can live with that.
If it was Just the heating pump and it was set at speed 1 then maybe you could extend the life out a bit, as for electric breadmaker forget it!
Do you need to power the fridge through the night? I did some messing around with temp sensors a while ago to optimise our fridge and freezer and found that if the door wasn't opened on the fridge overnight it only lost a few degree's same for the freezer. I only ask as the start up consumption on fridge/freezer pumps can be quite high. When I have run the house on our tiny 750w generator during really long power cuts I have to carefully add the fridge freezer in or else the genny overload trip operates.( I really out to buy a bigger Jenny!  whistlie)

If you could get by with just heating pump/lights/telly then you would be scraping by at 200ah, especially as the lights/telly would be off when you got to bed.
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teledemon
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« Reply #11 on: May 05, 2009, 08:10:21 PM »

Yes, I'd often wondered about speed settings on pumps. I could probably set it to the slowest and get by on that. Our freezer is pretty efficient, and we should really keep the fridge door closed (though with 4 kids the odd late night fridge raid is unavoidable); i've not done the sensor thingy but you're right...probably only a few degrees lost. We're not running a commercial establishment here so no H&S legalities to worry about. Start up in the morning wont be an issue as...we've got our genny power back  Grin BTW we have 3 diesel generators capable of providing about 112kW...no wonder they want to save money! Shocked
I'm wandering back to the UPS idea again, thinking I really should cut our usage to a minimum. if we ever build our own house it'll probably be off grid, so best we get used to it!
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billi
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« Reply #12 on: May 05, 2009, 09:02:40 PM »

Hi

How much diesel do you burn ?  or how much kwh a day you need ...... ? 

Sure you can start small and invest in a small inverter/charger Battery idea , but if you decide later on to  try to more reduce your Diesel generator running hours , you might have problems to combine/extend  and waste money

We had a Diesel inverter battery set-up  for a year ( then Photovoltaic ,windturbine ) was added , but 4 hours was the max the Diesel generator had to run per day ! Sure he did use quite a loot of diesel in this four hours , but how does this compare to 17 hours a day constantly on and running  on small loads ?

Perhaps think of an extendable  setup  in relation to inverter and battery


Billi

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1.6 kw and 2.4 kw   PV array  , Outback MX 60 and FM80 charge controller  ,24 volt 1600 AH Battery ,6 Kw Victron inverter charger, 1.1 kw high head hydro turbine as a back up generator , 5 kw woodburner, 36 solar tubes with 360 l water tank, 1.6 kw  windturbine
teledemon
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« Reply #13 on: May 06, 2009, 09:16:03 AM »

The generators supply several households; i'm not sure how much we use individually but suffice to say these burn a heck of a lot unnecessarily through the night to meet very little demand. We use 9-12 kwh a day depending on the amount of washing; we live (family of 6) in a very poorly insulated house and I'm a Stay At Home Dad so around most of the day. Price charged to us is about 20p per unit; this is heavily subsidised...if we were to pay full whack then we'd be looking at 70-80p  Shocked

Our community is in the process of commissioning a renewables study (most likely a wind/diesel hybrid) but realistically that's 3-5 years away  Sad might as well wait for tidal...

Re. the inverter; is bigger necessarily better...would say a 2kw beastie be under efficient if we're only using say 300w peak?

Batteries seem to be one of the extendable elements, but pricey...any recommendations re. system voltage etc?

Thanks so far to everyone for their input  Cool

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billi
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« Reply #14 on: May 07, 2009, 03:30:31 PM »

Quote
any recommendations re. system voltage etc?

i am on 24 Volt but would  go for 48 volt next live

I have two  3 kw  inverters ( i think my model can work with 5 of the same units in parallel )  so i can switch one of

Thats what i meant   about extending if needed   chose a model that can be doubled if needed later

Batteries i think donot like to be extended ( but we had recent discussions here that said different )
Some people here (me included) did source second hand forklift batteries   ( i reckon best value for money if you find a good one )


But sure if your community  is investing in renewables any how  then perhaps spending too much cash  makes little sense

Billi

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1.6 kw and 2.4 kw   PV array  , Outback MX 60 and FM80 charge controller  ,24 volt 1600 AH Battery ,6 Kw Victron inverter charger, 1.1 kw high head hydro turbine as a back up generator , 5 kw woodburner, 36 solar tubes with 360 l water tank, 1.6 kw  windturbine
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