Go Back   IceInSpace > Equipment > ATM and DIY Projects
Register FAQ Calendar Today's Posts Search

Reply
 
Thread Tools Rate Thread
  #1  
Old 16-06-2014, 10:58 PM
strongmanmike's Avatar
strongmanmike (Michael)
Highest Observatory in Oz

strongmanmike is offline
 
Join Date: May 2006
Location: Canberra
Posts: 17,689
Generator and a battery question

Question:

I have a new petrol generator that I plan to run my new observatory with but the fuel tank will not last a whole night, so in order to avoid having to shut everything down while I refuel...can anyone set me straight on the following - can the 12v charge leads from the petrol generators 12V output socket be connected to say a 100amphr deep cycle battery for example, which is connected to a 12V-240V inverter which then powers my lappie, scope and cameras etc and can the Generator be used to top up the battery during imaging?

Mike
Reply With Quote
  #2  
Old 16-06-2014, 11:55 PM
glend (Glen)
Registered User

glend is offline
 
Join Date: Jun 2013
Location: Lake Macquarie
Posts: 7,121
Most generators do not produce much 12V amperage, and its actually more efficient to use the generator to power an AC battery charger. My generator only outputs 4.5 amps at12V but can easily run my Cetex AC battery charger which will output 7.5 amps (12v). Work out how many total watts of load you need to run all of your equipment, then get a pure signwave inverter that can handle that load continuiously, then build the battery bank to supply the necessary 12V amps.

Why not use a solar panel to charge your battery? I have a 250W panel feeding a bank of three 100amp batteries, through a smart controller, and a 2000w pure signwavr inverter off the bank - this supplies all the power my shed needs, and recharges my scope battery box as well. I only ever use the generator at a dark site if my portable panel can't keep things topped up for an evenings use.

You need to be careful about isolation of the generator AC output if your powering your building, and it should never be refueled while running. If you build a battery bank of sufficent capacity your inverter coukd run all your gear without interuption, regardless of whether the generator was charging or shutdown for fueling. I'd just keep the generator for backup and use solar to chrage the bank of batteries . Wire the batteries in parallel to maximise amps and keep the voltagevat 12V

Last edited by glend; 17-06-2014 at 12:07 AM.
Reply With Quote
  #3  
Old 17-06-2014, 12:09 AM
strongmanmike's Avatar
strongmanmike (Michael)
Highest Observatory in Oz

strongmanmike is offline
 
Join Date: May 2006
Location: Canberra
Posts: 17,689
Cheers Glen

Yep have the solar panel in mind for down the track.

Thing is I needed to buy the generator to have power available to build the observatory as there is no mains power available. I also will have a good size completely separate and livable warm control room building (4.8m X 2.4m site shed) so my idea was that I could run both the scope gear (inside the Sirius Observatory) and the Shed (lights, heater, kettle etc) from the generator but in the case of the power going to scope gear I was imagining I could have a battery in line so that when I power off the generator to refuel, the power to the scope and cameras - delivered via an inverter connected to the battery, would be uninterrupted...does this sound feasible?

Mike
Reply With Quote
  #4  
Old 17-06-2014, 12:27 AM
strongmanmike's Avatar
strongmanmike (Michael)
Highest Observatory in Oz

strongmanmike is offline
 
Join Date: May 2006
Location: Canberra
Posts: 17,689
Quote:
Originally Posted by glend View Post
You need to be careful about isolation of the generator AC output if your powering your building,
What exactly does this mean?
Reply With Quote
  #5  
Old 17-06-2014, 01:01 AM
Star Catcher (Ted Dobosz)
Registered User

Star Catcher is offline
 
Join Date: Feb 2006
Location: Bankstown
Posts: 984
Hey Mike

Going way back to my techy days many decades ago, so here goes.

Unless the generator's 12V output was designed for charging a battery, it is unlikely to charge your 100ah battery effectively because it is designed to simply run 12V appliances i.e. it unregulated. This means the output voltage range may vary by up to 3 volts and the DC voltage may be dirty with AC ripples. These conditions may damage your battery or fail to charge it properly.

The charging voltages for batteries vary somewhat with battery types, however typically 14.4V is required for bulk charging deep cycle batteries. Once charged, it requires about 13.2V-13.4V for long term float maintenance. So a dumb 12V outlet won't cut it.

If it generator has a 12V outlet that is designed with a battery charging function, then it would provide charging, however it must also have the smarts to regulate how much charge pours into the battery i.e. it must modify the charge rate to prevent overcharging the battery.

If we assume there is a well controlled battery charging function at the generator end, then it will control both the current and voltage delivered to the battery. Ideally for a 100ah battery the charge current delivered should be about 10amps per hour (10Ah). It may be larger than this, however this figure is quoted as an optimal rate for 100Ah batteries. Hence we can assume the generator would pump about 10Ah into the battery.

On the inverter side, you have to add up the Ah (ampere hours) being taken out of it. So go around and check current drawn on all AC adapters for laptop, camera, scope. keep in mind these are maximum or worst case draw from these devices. Your mount may momentarily draw 5amps or more, but when going sidereal, it may only be tens of milliamps. The laptop will be more constant, however simple image acquisition will draw no where near maximum current, unless you are doing image crunching. The camera will be fairly constant draw and rises towards maximum in hot weather. At a guess, I would assume 0.25Ah for mount, 2Ah for lappy, 2Ah camera, heating 1.5Ah, 0.5Ah lighting etc.

So ball park around 6Ah max is required from the inverter. Keep in mind inverter efficiency is around 87%, the inverter will pull almost 7Ah from the battery to deliver 6Ah. So in very rough terms, 10Ah come in from the generator and about 7Ah go out, you have 3Ah worth of charging occurring whilst generator is running.

I would be very careful ensuring isolation between equipment end and generator chassis to avoid ground loops/feedback.

I have probably stuffed something in my assumptions and calculations and no doubt others will kick in to sort it out. Hope this helps.

Ted
Reply With Quote
  #6  
Old 17-06-2014, 08:53 AM
glend (Glen)
Registered User

glend is offline
 
Join Date: Jun 2013
Location: Lake Macquarie
Posts: 7,121
Quote:
Originally Posted by strongmanmike View Post
What exactly does this mean?
As Starcatcher said:

"I would be very careful ensuring isolation between equipment end and generator chassis to avoid ground loops/feedback. "

Most generators have a booklet that comes with them that 'suggests' grounding the frame of the generator, this is to protect you in the event of it becoming live. The appliance or equipment that is attached to the generator should also be protected in the same fashion. Never connect generator or solar system inverter AC to a building that also has grid AC (unless on a completely separate system) UNLESS YOU HAVE AN APPROVED PHASE MATCHING SYSTEM INSTALLED BY PROFESSIONALS.

I use a Earth Leakage Protection power board off my shed inverter, and the inverter chassis is earthed.

If in doubt of your expertise, don't rely on advice here but get a professional to either design it for you or install. There are plenty of solar and off grid companies that will provide design advice.
Reply With Quote
  #7  
Old 17-06-2014, 10:40 AM
strongmanmike's Avatar
strongmanmike (Michael)
Highest Observatory in Oz

strongmanmike is offline
 
Join Date: May 2006
Location: Canberra
Posts: 17,689
Cheers guys, some excellent feedback from you both, much appreciated

Just so I don't get confused this is what I envisage...so how would you guys go about setting it up?

I will have two structures - the Sirius Observatory with all the imaging gear inside and nearby (4m) will be a separate fully wired (power points and lights) and fuse boxed industrial site shed (not connected to mains) as a control/warm room, I will also have a 3.5kva generator/inverter that can provide up to 2500W (2200W continuous) of pure sine wave 240V AC power.

I would like to setup the generator system to be able to power both the shed and the Observatory but have a mechanism in place to allow me to refuel the generator safely without interrupting the imaging.

Can I do this and if so how might I approach it?

Thanks heaps for the input

Mike

Last edited by strongmanmike; 17-06-2014 at 10:50 AM.
Reply With Quote
  #8  
Old 17-06-2014, 11:10 AM
coldlegs's Avatar
coldlegs (Stephen)
Chopped its rear end off!

coldlegs is offline
 
Join Date: Jul 2009
Location: adelaide, sth aust
Posts: 331
Mike
I would be tempted to put a couple of car batteries
on a hand truck, charge them up during the day
and wheel them over to the obs and plug them in to
do a complete nights imaging. That way you won't
blow up the obs with charging gasses and don't have
to worry about interrupting the imaging by re-fueling
or ground loops. You could still have a generator/mains
connection to the obs as that is always useful.

Cheers
Stephen
Reply With Quote
  #9  
Old 17-06-2014, 12:04 PM
mikerr (Michael)
Registered User

mikerr is offline
 
Join Date: Mar 2011
Location: NSW Australia
Posts: 324
Mike, have you thought about increasing the fuel tank capacity? Either built on to the generator or beside it.
I'm thinking of the freestanding boat fuel tanks with the big black bulb primer in the fuel line.
Should not be difficult to have connected properly/safely as though it was an outboard engine.

Michael
Reply With Quote
  #10  
Old 17-06-2014, 04:48 PM
tlgerdes's Avatar
tlgerdes (Trevor)
Love the moonless nights!

tlgerdes is offline
 
Join Date: Mar 2009
Location: Sydney
Posts: 2,285
Hi Mike,

A computer UPS might be the trick. The generator powers through it to your equipment at 240v. It will usually give you 10-20 mins runtime to refuel, depending on the size of the UPS and the load attached. 2000va units are between $600-1000 at the low end.
Reply With Quote
  #11  
Old 17-06-2014, 05:34 PM
Star Catcher (Ted Dobosz)
Registered User

Star Catcher is offline
 
Join Date: Feb 2006
Location: Bankstown
Posts: 984
Hi Mike

Just to clarify things, your generator has both a 240V and 12v outlet? You were thinking of having a 240V feed to non critical equipment that can be shut down during a refuel. Another feed goes to critical equipment that must continue to run during a refuel. You were thinking of using the 12 volt feed on the generator to charge a 100Ah battery, that would feed an inverter, that feeds 240V to your imaging gear during a refuel.

If my description of your requirement is right, then Trevor's solution of using a UPS is the neatest and most efficient 'one box' solution. The size of the UPS can be worked out by multiplying your voltage by amp draw e.g. 240V X 6A = 1440Va. It means that you could safely rely on the 2000Va unit for 20 minutes without damaging the battery in the unit. Of course all this assumes you have not already spent up big on an inverter and 100Ah battery.

Ted
Reply With Quote
  #12  
Old 18-06-2014, 07:20 PM
strongmanmike's Avatar
strongmanmike (Michael)
Highest Observatory in Oz

strongmanmike is offline
 
Join Date: May 2006
Location: Canberra
Posts: 17,689
Thanks guys, all helpful, thought provoking replies and Yes, you had it correct Ted.

Besides...went to start my brand new Chinese 3.5kva generator inverter and what do you know, it won't start ...on the phone to a call centre/support..waiting, waiting... I need this to power the tools to build the damn observatory, JESUS!

Mike
Reply With Quote
  #13  
Old 18-06-2014, 11:02 PM
gregbradley's Avatar
gregbradley
Registered User

gregbradley is offline
 
Join Date: Feb 2006
Location: Sydney
Posts: 18,185
I use a Yamaha 3.8KVA generator and the full tank lasts about 20 hours+.

I used to use a Honda 2000iu and it lasted about 8 hours. So you topped it up just before dark.

I also have a Chinese yellow 3.5 KVA (I think that's it output Genquip or similar name). It worked for a while but was not very dependable. The pull cord snapped many times due to a very sharp edged metal cord guide.

The Yamaha or Honda will cost more but they will be fuss free and last a long time as long as you change the oil regularly.

Greg.
Reply With Quote
  #14  
Old 19-06-2014, 11:14 AM
julianh72 (Julian)
Registered User

julianh72 is offline
 
Join Date: Jan 2014
Location: Kelvin Grove
Posts: 1,301
Wouldn't the best idea simply be to have the generator power a suitably sized 240 V UPS (Uninterruptible Power Supply), and power your computer and all the other gear from the UPS?

For a couple of hundred dollars, you could get a UPS with 1000 / 1500 VA rating, which could power all of your gear for a couple of hours, while you refuel the generator. They UPS would also have the advantage of "smoothing" the power output, isolating your sensitive equipment from any voltage fluctuations that you might otherwise see as the load on the generator fluctuates.
Reply With Quote
  #15  
Old 19-06-2014, 04:02 PM
strongmanmike's Avatar
strongmanmike (Michael)
Highest Observatory in Oz

strongmanmike is offline
 
Join Date: May 2006
Location: Canberra
Posts: 17,689
Yep, now looking at that Julian, cheers

A couple'a big batteries and a solar panel will come eventually too.

Mike
Reply With Quote
Reply

Bookmarks


Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +10. The time is now 10:23 PM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
Advertisement
Astrophotography Prize
Advertisement
Bintel
Advertisement