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PostPosted: Sep 30th, '06, 11:07 
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I too am challenged in this area AA.

Some things I do know are:

1. watts = amps x volts. Therefore the 12v 35 watt dc air pump that I have seen would run at a little under 3amps. I would ideally like something lower than this. I do not really need 50 litres per minute of air in an emergency situation.

2. I am told that just because the battery is 75 amp hours does not mean that I can expect that air pump to go for 25 hours (ie 75/3).

3. I am also told that it is a misconception that it is okay to drain deep cycle batteries of all their power. I am told that this will result in a significantly reduced life (say 100 cycles rather than 300) and on top of that possibly only very expensive chargers will be able to recharge them once they get to that stage. I was told that I should only use half the capacity at a time (of course for the backup power purpose, I will use it all if I need it all, but often I wont).


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PostPosted: Sep 30th, '06, 12:49 
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VB, on number 3, i thinks is just "more ok" than a normal car battery :)

you should NEVER run lead acid batteries COMPLETELY down. what happens is that one of the 6 "cells' discharges first. then the other 5 cells effectivly "reverseccharge" that cell .

From memory, i believe the voltage for a 12V LA battery to be considered "FLAT" is 10.4V. It is quite easy to make an "battery saver" device using some zener diodes and a relay to force cut off the battery when it reaches 10.4 V

On number two, that is dead right, the amp hour rate is generally given at the 20 hour rate, in your case it would probably give you the 75 hours ( I'm fairly sure on this, but i could be wrong) but for say a 3 amp hour battery, you definatly would not get 1 hour.

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PostPosted: Sep 30th, '06, 14:50 
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Bought the 75 amp hour deep cycle battery. It is Bosch brand (cost $132). Bought a charger - spent more than I wanted or needed to, but got the one I did because it will cover off on possible future needs. It charges 6v, 12v and 24v batteries. Am charging the battery now - not that it will be too much use without the failover switch - unless I am home when the power goes off of course. Was also eying off a 800watt generator ($120). Would only be suitable for the aqua pumps though and I would prefer to save up for something that can also run our chest freezer in the event of a blackout.


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PostPosted: Sep 30th, '06, 16:47 
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VB, i think you'll find that it will run the chest freezer as well. Pull it out and look at the placard.........can't see it being more than 200W and 800W allows plenty ofroom for start current.

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PostPosted: Sep 30th, '06, 21:39 
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Dunno Steve - I think there is something more to it than just a watt comparrison. Nobody I have spoken to at any shop has agreed that a fridge or frezzer should/could be run from one of these. I think it has something to do with the power spiking and stuff and possibly stuffing up the motor???


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PostPosted: Sep 30th, '06, 23:14 
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Hi,can a UPS trip a starter motor solenoid on a small generator in the event of a blackout and save the day?[font=Arial] [/font] [font=Arial] [/font]


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PostPosted: Oct 1st, '06, 00:25 
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o.k. most small gensets are recoil "pull start" thingies,but there are a lot of small 12 volt starter motors & automatic gearbox flywheels at your local wreckers. Automatic flywheels weigh almost nothing. ....So ,, ,, Genset ,,,home made welded frame,,( buy a hobby arc welder from K Mart ,Bunnings,etc. it's easy', really ), 2nd hand starter motor, matched auto. flywheel attached to genset,,somehow,, activated by UPS. hmmm,,comments


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PostPosted: Oct 1st, '06, 02:39 
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KIS please.

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PostPosted: Oct 1st, '06, 09:53 
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Vb, i read on more than one forum that people were using the GMC 800W gennies to run fridges. like i said even if the start up currnt is 4x the normal current at 200W then you're coverd.

The only thing i have heard is that they don't have good line regulation when a heavy load is switched off, but that going to affect delicate electronic equipment, not motors.

Look at the placard, if it had a LRA (locked rotor amps) then this will be your start up amps. sometimes it is listed as max currnet and operating current.
800W generator supplies 3.3amps @ 240v

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PostPosted: Oct 1st, '06, 11:23 
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Lets put this into perspective - this is a backup system for when power is lost, so it is probably only going to be used most of the time for a max of 4 hours and possibly only 3-4 per year (plus testing/maintenance runs).

Initially for AP, all that is required is an air pump which starts automatically on power fail, this then gives time to start a generator and move loads onto it if required - as for a freezer, if it is not being opened continuously then the items inside are not going to de-frost in a short period so it would not need to be on generator power continuously.

My thoughts on the subject, also if you are going to have a generator as a back-up make sure you have petrol handy to run it :wink:

For a commercial venture the goal posts are moved

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PostPosted: Oct 1st, '06, 11:51 
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You will have to have a whopping sized UPS to start a frig, run it maybe, but not to start it.
Mojo


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PostPosted: Oct 1st, '06, 12:22 
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LKB - power has been known to go out at my place for 24 hours - did so once last year. I hate having to take all the stuff out of the freezer and stow it at somebody elses place - hence my references to running a freezer.

Muzz - eccles was suggesting a UPS may be able to be used to trip a starter motor hooked into a generator, not to run the applicance itself.


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PostPosted: Oct 1st, '06, 13:17 
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VB,
When I lived in Port Moresby almost every home had a backup gen set that started automatically if the power went down which was almost every day. Such gen sets are commercially available and one would need to ring around to source such a thing, but they need to be wired into your mains power switch board. Not an inexpensive exercise.
They work a bit like the power fail switch I am sending to you, but on a bigger scale. They need a few more components in the loop, eg, a relay big enough to handle the load of switching the starter motor of the gen set, and then they have to be able to switch the gen set off when the mains power comes back on, so it is not a simple thing, especially if it is a diesel gen set, there are other relays that then must come into play.

It is a whole lot easier just to buy a gen set that has enough capacity to run your friges and basic lighting, and your Aquaponics pumps.
This gen set will be started manually when the power goes down. But to do it properly will entail some expense, the gen set needs to be wired into your switch board or alternatively you need to run out leads to the frig/s etc from the genset when the power goes out. (a bit hard to run leads to your house lights unless the gen set is wired into your switch board)

Personally I would not buy a gen set that was less than 5 KVA if you expect to run friges etc during a power outage.
Gen sets are like most equipment, whatever you think you need, buy the next bigger one, in general one always underestimates the need.

Muzza


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PostPosted: Oct 1st, '06, 14:54 
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veggie boy wrote:
LKB - power has been known to go out at my place for 24 hours - did so once last year. I hate having to take all the stuff out of the freezer and stow it at somebody elses place - hence my references to running a freezer.


Understand that - what I was getting at is the freezer doesn't need to be connected 24/7on a power fail, if power out for an extended period just switch on every 6-8 hours to keep all frozen then switch off the freezer, cuts down on the load to the generator.

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PostPosted: Oct 1st, '06, 16:28 
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Quote:
You will have to have a whopping sized UPS to start a frig, run it maybe, but not to start it.
Mojo


MUz, was talking about a gen, not a UPS

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