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Old 07-11-2020, 07:21 AM
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miki63au
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Off grid powering the obsi

Hello everyone

Nearly finished my ROR obsi and thinking of how to power it.
Instead of digging a trench from the house for power cable I thinking
going off grid with batteries. Scored some free 12V 200Ah heavy batteries
and now looking at cheap(er) second hand solar panels and chargers, inverter. For old second hand solar panels any degradation over time?
Anyone did similar arrangements? How many batteries need to run a desktop comp and eq mount etc? Most of the chargers 30A ... any suggestions for brand? For winter how many panels need to get charged enough despite the clouds?

Thanks for any advice
Mik
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Old 07-11-2020, 09:20 AM
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mldee (Mike)
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Off Grid Obs

I live on the edge of a small village on the Darling Downs and when I moved here about 5 years ago, decided to remain off grid rather than pay $27K to have power run 200 metres from the nearby lines. All works well.

I have just finished my roll off obs and it also is off grid, totally separate to the house, although only about 40 metres apart.

I have a mix of 12 x 2V 1000Ah sealed lead acids feeding the main house inverter plus 16 x 3.2V 100Ah LiFePO4 prismatic cells with BMS, feeding the backup inverter used for pumps, etc,

Based on my 12 month experience with the Lithium Phosphates, I decided to go that route (2 x 13.4V 100Ah packs with BMS) with the Obs, and they work well. I use two 200W used solar panels with a Renogy Rover 30A MPPT charger. Highly recommended, only cost about $90 on Amazon Oz and will do Lead acids and Lithiums, and has remote monitoring capability, which I installed but rarely bother with.

You will be using your 12V 200Ah lead acids, and you should be able to find used 250W panels for about $50 each. All my 19 panels are at least 8-10 years old and don't seem to noticeably degrade.

I would suggest you consider 4 x 250W panels to ensure decent charging during cloudy days, and to put them in a 2s x 2p array so that the input voltage to the solar charger is nice and high (~60V) even on cloudy days. Yes, theory says you'll lose half the current capability, but experience shows that is more than compensated for by the higher (and therefore longer) charging time availability during low solar intensity times such as dawn, dusk and cloudy periods.

Based on my five years house lead acid battery experience, I would also recommend you set the initial charge absorption voltage to 14.4 for about 4 hours and the float to 13.8. I had mine set to the lower recommended voltages as shown on the cell casing, but the batteries didn't get fully charged. I suspect the reason is that daily solar charging voltage is so variable, plus there's none at night, whereas charging via the grid allows a stable 24/7 voltage. As an example, my monitoring system shows that the lowest voltage my lead acids produce is 24.4V at around 5am.

I would also suggest you consider running your obs directly from 12V and don't bother with the expense of an inverter. This is the reverse of what I would do with a house, but for an Obs is more power-efficient and also easy to do.

Lucky last comment, I would use either a laptop or NUC-style computer in the obs, with an ethernet cable back to the house if practicable. Reduces the need for routers and wifi hassles. I just changed mine from wifi (range extenders, etc) to one Cat 5 cable, it just works so much better.

I've got lots of pics etc if you want to see some examples. Good luck
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Old 07-11-2020, 09:54 AM
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Great help Mike! Tanks a lot




Quote:
Originally Posted by mldee View Post
I live on the edge of a small village on the Darling Downs and when I moved here about 5 years ago, decided to remain off grid rather than pay $27K to have power run 200 metres from the nearby lines. All works well.

I have just finished my roll off obs and it also is off grid, totally separate to the house, although only about 40 metres apart.

I have a mix of 12 x 2V 1000Ah sealed lead acids feeding the main house inverter plus 16 x 3.2V 100Ah LiFePO4 prismatic cells with BMS, feeding the backup inverter used for pumps, etc,

Based on my 12 month experience with the Lithium Phosphates, I decided to go that route (2 x 13.4V 100Ah packs with BMS) with the Obs, and they work well. I use two 200W used solar panels with a Renogy Rover 30A MPPT charger. Highly recommended, only cost about $90 on Amazon Oz and will do Lead acids and Lithiums, and has remote monitoring capability, which I installed but rarely bother with.

You will be using your 12V 200Ah lead acids, and you should be able to find used 250W panels for about $50 each. All my 19 panels are at least 8-10 years old and don't seem to noticeably degrade.

I would suggest you consider 4 x 250W panels to ensure decent charging during cloudy days, and to put them in a 2s x 2p array so that the input voltage to the solar charger is nice and high (~60V) even on cloudy days. Yes, theory says you'll lose half the current capability, but experience shows that is more than compensated for by the higher (and therefore longer) charging time availability during low solar intensity times such as dawn, dusk and cloudy periods.

Based on my five years house lead acid battery experience, I would also recommend you set the initial charge absorption voltage to 14.4 for about 4 hours and the float to 13.8. I had mine set to the lower recommended voltages as shown on the cell casing, but the batteries didn't get fully charged. I suspect the reason is that daily solar charging voltage is so variable, plus there's none at night, whereas charging via the grid allows a stable 24/7 voltage. As an example, my monitoring system shows that the lowest voltage my lead acids produce is 24.4V at around 5am.

I would also suggest you consider running your obs directly from 12V and don't bother with the expense of an inverter. This is the reverse of what I would do with a house, but for an Obs is more power-efficient and also easy to do.

Lucky last comment, I would use either a laptop or NUC-style computer in the obs, with an ethernet cable back to the house if practicable. Reduces the need for routers and wifi hassles. I just changed mine from wifi (range extenders, etc) to one Cat 5 cable, it just works so much better.

I've got lots of pics etc if you want to see some examples. Good luck
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  #4  
Old 07-11-2020, 10:55 AM
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xelasnave
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I have been off grid since 1996 and it is fun however my advice is buy a good 240 volt lead and save yourself time, money and frustration...It should not happen but does so often you will wonder if you are all there sometimes..is reversing polarity..I know there is a plus and minus sign and red and black wires ...but it happens and most times you blow up something.

I disagree with run stuff 12 volt... use an inverter and go 240 volt...sure I have 12 volt batteries but everything in the observatory is plugged into a 240 volt power boardjust like in the city...the mount, camera lap top and in the van..an electric fan, desk top, two miscroscopes and phone and tablet chargers...lights in the van are 12 volt but again if I did the lighting it would be 240 volt $10 lamps from Crazy Prices ... I got sick of $70 12 volt floro going just.

If you insist on going off grid make sure you include in the mix a small genny that will charge your batteries for the occasional times you find you run out of power halfway through an imaging session on a perfect night.

And before you do a thing consider the maintenance...topping water levels or at least checking, cleaning terminals, cleaning the solar panels...actually make a list and see how fun it really is...and price 12 volt wire and just how short runs should be kept.

I am off grid..my genny is broke so no charge if it clears tonight..I could run the car and get a charge..you find even the ride on lawn mower can get called upon when it's a clear night and your battery won't cut it....honestly even if you have to lay out your lead and wind it up every session you will be miles ahead.


I have found solar panels last forever in some cases but a lot don't.. batteries are not a one off purchase either...anyways if fun is what you want go for the off grid 12vlt and tell me what you think three years from now.

If I could connect to the grid for fifty grand I would do it in a heart beat...you end up using a lot of petrol...just do the sums.
Alex

Last edited by xelasnave; 07-11-2020 at 11:07 AM.
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Old 07-11-2020, 11:13 AM
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mldee (Mike)
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Off Grid obs vs House

Hi Alex,
Totally agree with your comments regarding off gridding for a house, avoid 12V like the plague and if you can afford a grid connection, go for it.
For a simple Obs, 240V is OK too, BUT, most everything in an obs wants to see 12V anyway:
Mount - 12V
Camera(s) 12V
Dew heaters 12V
Focussers 12V.
Couple of lights 12V or even dry battery.
NUC 12V

The days of battery water checking etc have long gone and I have never cleaned any of my panels. All still going strong.
My main concern in my obs was KISS wiring and keep the cost down. A conglomeration of power blocks is a PITA. If you already have acquired sufficient batteries, why not use them? You can even run your extension cord out to a battery charger to ensure they're ready for a night's imaging.
YMMV
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  #6  
Old 07-11-2020, 03:28 PM
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xelasnave
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Hi Mike

It would cost five hundred thousand for me to go grid at the moment.

I was going to replace the 12 volt at the main house, where I don't live, with 48 volt system but you run out of $30 k real fast...even with a huge battery bank you won't last past three or four days ..the main house has 1300 amp hours of battery which cost me $5 k ( replacement recently) and really is good for a day or two so just for batteries to see out a cloudy week I would say $15 To $20 k ...usually if cloudy they start the genny the second day...it is best not to run them down.

In my first and second observatories I went for everything 12 volt but with obs three and four (the current ones..1 was stolen 2 is still in Sydney) I have last two all 240 volt ( not the dew heater yet..but soon) ...part of the reason is I have two groups of batteries and it is much easier running a lead to an inverter at a particular bank than any alternative in a 12 volt swap...at the moment one battery system is out of action as it is being given a new home in the new observatory...And when I get time I will buy another five hundred amp hour battery bank...my main problem is I have gone thru four gennys in the last 12 months..I had 2 @2kws and 2@ 700 watts ( just for charging)..I had the big ones running all the time last summer for the air conditioning...expensive but it literally is a life saver as the van heats to 40 c...and as I near died cause of heat stroke once in Sydney I figure one has to pay the price...been looking for another genny all day and am starting to think I will have to fix the two that won't run..one has key start but has not on the latest model...damn it.

Anyways still plenty to do before I can have both obs working it seems...near finished the lining today so not far off now...

Alex
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Old 08-11-2020, 09:05 AM
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Tanks Alex and Mike!
I just upgraded the desktop comp with SSD drives ... not feasible to convert to 12V DC.

Probably end up with 3x 200Ah sealed battery and buy a 30A charger. Most of the second-hand bank of solar panels include a inverter.

Mik
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Old 20-11-2020, 03:12 AM
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I'm curious as to how you guys with roll offs protect your inverters and chargers from the elements when the roof is open? Do you have hoods or use enclosures?
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Old 20-11-2020, 09:09 AM
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mldee (Mike)
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About 3m length of my 6m x 3m obs has a fixed roof, and the area under this is for desk, eqpt storage, solar charger, LiFePo4 batteries, etc. This roof sits about 20cm higher than the 3m RO section, and overhangs it by about 30cm when closed. Flexible rubber flaps keep the wind and rain out there.

Only drawback is that the fixed roof section slightly blocks OTA visibility to the low West, but only below about 30deg elevation in that direction.

The white roof in the pic is fixed, the grey roof is polycarb RO section. One solar panel on white roof, one on North wall at rear. Additional blue pier on old wind turbine foundation slab at rear RH of obs.
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