Off grid generator question

[strongmanmike (Michael)]

Just trying to clear something up in my head.

As many of you already know, I am currently constructing a new observatory. I will have a solar power system that will comprise 2 X 6V 550amphr heavy duty AGM batteries (wired in series to give 550amphr @ 12V), being charged by 4 X 170W 12V solar panels via a 60amp MPPT regulator. All power for the observatory will be supplied through a 2000W 12V-240V pure sine wave inverter connected to the batteries.

This battery storage will be adequate to power the new observatory and equipment even on the very longest 14hr+ nights in winter (approx. 350amphr) but I envisage some nights, especially these long winter ones, where there are two (or more) clear nights in a row but it turns cloudy during the day in between and the batteries aren't getting enough power from just the panels for sufficient charge ready for the next night, I'd like to have a small pure sine wave inverter generator just to help charge the batteries, when required.

How do I use the generator in this scenario? Do I simply run the generator and have a simple regulated battery charger plugged into the 240V socket on the generator and connect this to the batteries and charge as desired? Will it matter if the panels, via the regulator, are still connected and charging too?

Just need to get my head around how to do this..?

Thanks for any feedback

Mike

[Startrek (Martin)]

Without going into to much technical stuff, I would have 2 systems independent systems for redundancy maybe using an ATS , so that your solar will charge bank A and your Genset / charger will charge bank B and use a bus tie or automatic transfer switch to tie bank A and Bank B together when the voltage drops below a usable threshold
Or if you have the dollars have two totally independent battery systems ( one via solar and one via genset ) that can handle say 15 hrs of full load operation each and use a transfer switch when bank A voltage drops below useable threshold and bank B comes on line
I think a 1+1 redundancy system is the way to go if want really good reliability but it’s extremely costly !!!
I’ve been too long out of the game ( Commercial Industrial Electrical Engineering and Contracting )
Maybe some younger electrical guys can jump in

[xelasnave]

Hi Mike
Make sure you get the correct charger for AGM batteries.
My observatory batteries are lead acid iand I charge them at no more than 10% of battery capacity which is 500 amps therefore 50 amps however I prefer less. The house batteries are AGM and I recall they required a different charger and a lower charging rate...I can't look now to say if the charger is wired direct to the batteries or goes thru a regulator but I expect direct..but maybe not..I must check rather than guess.
However running the charger when the Sun is out happens often and so we don't regard doing so a problem..the main thing is to get the correct charger and not to exceed a certain charging rate..when we replaced the lead acid batteries with AGM we got another "special" charger and I took the old charger for the observatory.
I haven't done so but you don't need a large genny..I have a key start Honda 3 kva but I expect I could have got away with a 750 watt little Kipor ...guessing I would say you may find for your batteries the charge rate will probably be around 25 amps so a little Kipor would do I expect..
I can ask my "assistant" who is an electrical engineer and very knowlagable in all things solar..he recently gave lecture in town on solar and I think worked on the development of Solar Panels...he recomended and installed the charger for tbe AGM Batteries in the house now that I think about it.
I expect the charger in the house would be what you would need..anyways more tomorrow.
Alex

[strongmanmike (Michael)]

Originally Posted by Startrek

Without going into to much technical stuff, I would have 2 systems independent systems for redundancy maybe using an ATS , so that your solar will charge bank A and your Genset / charger will charge bank B and use a bus tie or automatic transfer switch to tie bank A and Bank B together when the voltage drops below a usable threshold
Or if you have the dollars have two totally independent battery systems ( one via solar and one via genset ) that can handle say 15 hrs of full load operation each and use a transfer switch when bank A voltage drops below useable threshold and bank B comes on line
I think a 1+1 redundancy system is the way to go if want really good reliability but it’s extremely costly !!!
I’ve been too long out of the game ( Commercial Industrial Electrical Engineering and Contracting )
Maybe some younger electrical guys can jump in

Cheers Martin but yes that sounds costly

Currently (pardon the pun) and if my calculations are correct (ish) after a full 14hrs or 350amphrs of operation and if my batteries drop to 200amphr it will take about 18hrs of full sunshine (3 winter days) to fully recharge them...?

I could have just forked out double the money and got a 2 X bigger solar system but the coin just isn't there (Eagle eyed wife ...seriously ) ...so I thought a cheap 3000watt genie might help and get under the Eagles radar..?

Mike

[strongmanmike (Michael)]

Originally Posted by strongmanmike

Cheers Martin but yes that sounds costly

Currently (pardon the pun) and if my calculations are correct (ish) after a full 14hrs or 350amphrs of operation and if my batteries drop to 200amphr it will take about 18hrs of full sunshine (3 winter days) to fully recharge them...?

I could have just forked out double the money and got a 2 X bigger solar system but the coin just isn't there (Eagle eyed wife ...seriously ) ...so I thought a cheap 3000watt genie might help and get under the Eagles radar..?

Mike

The max charging current limit of the batteries I am planning on getting, is 120amps.

I just want to know if it is ok to have the panels, via the regulator, pumping up to 36 amps (4 X 9 amps per panel) into the batteries, while I also have a charger (run from the generator) connected to and charging the same batteries..?

Mike

[xelasnave]

Being so cold I would not hesitate to run the genny after a session irrespective of Sun coming up or not. Batteries dont like the cold.

You need to first calculate the power you are using each hour...make a list, mount, camera..which has a Peltier which could be hungry, lap top, heated gloves...multiply by the length of the session...10 hours at 10 amp for example so 100 amp for the night ..then ask how does that fit your discharge guide..I looked but can't find their discharge but even if they say you can discharge 50 % does not mean you have to ..less is better.
Also your regulator should track the ins and outs if not get something that does.
Alex

[strongmanmike (Michael)]

Originally Posted by xelasnave

Being so cold I would not hesitate to run the genny after a session irrespective of Sun coming up or not. Batteries dont like the cold.

You need to first calculate the power you are using each hour...make a list, mount, camera..which has a Peltier which could be hungry, lap top, heated gloves...multiply by the length of the session...10 hours at 10 amp for example so 100 amp for the night ..then ask how does that fit your discharge guide..I looked but can't find their discharge but even if they say you can discharge 50 % does not mean you have to ..less is better.
Also your regulator should track the ins and outs if not get something that does.
Alex

As I said, a full 14hr long winter night will use up about 4.2Kwhrs or 350amphrs of the 550 available.

Mike

[xelasnave]

Pretty sure the regulator takes care of it by checking the batteries somehow... but say on an overcast day and my daughter is running her hungry gaming computer and graphics stuff she runs the genny and the Sun pops out she leaves the genny on...a byways I will ask the electrical engineer.
Alex

Originally Posted by strongmanmike

As I said, a full 14hr long winter night will use up about 4.2Kwhrs or 350amphrs of the 550 available.

Mike

I thought you said that. Seems too much discharge to me.
Leave it with me.
Alex

[strongmanmike (Michael)]

Originally Posted by xelasnave

Pretty sure the regulator takes care of it by checking the batteries somehow...

The charger that I would have connected to the generator in this scenario, would also read the battery state of charge I believe and adjust its charging accordingly, so I am wondering if the charger and regulator might be in conflict in some way, when connected to the same battery bank..?

Mike

[xelasnave]

550 is not "available" but only a percentage of the capacity...

I have 500 amps but lead acid has " available" 25 % I think it is and I try to use no more than 20 % ... AGM has more available but I don't know what it is and I just searched but could not nail it ..I never let the AGMs here go past 35%...1100 amp capacity so turn on the genny when 300 amps has been used as a rule.
The less discharge the longer they last and petrol is cheaper than replacing a battery bank.
I suspect you may need another set or need to run the genny half way thru the night..anyways I will get the experts opinion for you.
Alex

[strongmanmike (Michael)]

Originally Posted by xelasnave

I thought you said that. Seems too much discharge to me.
Leave it with me.
Alex

I will be powering a motorised fully automatic 3M Scopedome, two computers, a cooled CCD, digital focuser and AP1600GTO mount along with a few other accessories

Mike

[xelasnave]

Originally Posted by strongmanmike

The charger that I would have connected to the generator in this scenario, would also read the battery state of charge I believe and adjust its charging accordingly, so I am wondering if the charger and regulator might be in conflict in some way, when connected to the same battery bank..?

Mike

I will get the opinion of the expert,,what charger etc...your are in good hands with this man.
Alex

[strongmanmike (Michael)]

Originally Posted by xelasnave

550 is not "available" but only a percentage of the capacity...

I have 500 amps but lead acid has " available" 25 % I think it is and I try to use no more than 20 % ... AGM has more available but I don't know what it is and I just searched but could not nail it ..I never let the AGMs here go past 35%...1100 amp capacity so turn on the genny when 300 amps has been used as a rule.
The less discharge the longer they last and petrol is cheaper than replacing a battery bank.
I suspect you may need another set or need to run the genny half way thru the night..anyways I will get the experts opinion for you.
Alex

The specs claim about 1100 cycles, when discharging to 50% DOD and they are touted to handle deeper discharges than normal AGM's, hence why I was attracted to them. So as an observatory and not cycled every day, 1100 cycles should equate to several years use out of the batteries?

Mike

[xelasnave]

Originally Posted by strongmanmike

I will be powering a motorised fully automatic 3M Scopedome, two computers, a cooled CCD, digital focuser and AP1600GTO mount along with a few other accessories

Mike

A fancy electric jacket I suspect.

When they say battery bank you need to think of it like a commercial bank ...always keep track of your deposits and withdraws.

My observatory batteries now run my new fridge so I am back to square one...and really folk say solar is cheap but a full time genny and buying petrol is not so silly for an observatory...anyways you need an actual run to record your usage... like with my daughter's computers we thought 1500 watts but it has been half that...the thing that you have as a major unknown is how the batteries will perform in the cold...I suspect it will be something that may require a bigger bank...anyways leave it with me I have to recharge.
Alex

[strongmanmike (Michael)]

Originally Posted by xelasnave

A fancy electric jacket I suspect.

When they say battery bank you need to think of it like a commercial bank ...always keep track of your deposits and withdraws.

My observatory batteries now run my new fridge so I am back to square one...and really folk say solar is cheap but a full time genny and buying petrol is not so silly for an observatory...anyways you need an actual run to record your usage... like with my daughter's computers we thought 1500 watts but it has been half that...the thing that you have as a major unknown is how the batteries will perform in the cold...I suspect it will be something that may require a bigger bank...anyways leave it with me I have to recharge.
Alex

The 4.2kwhrs estimate is based on a very similar fully automatic, fully autonomous remote imaging setup using the same dome, and very similar mount and imaging rig (although more complex than what I am planning), that images every single moment of clear skies, so lots and lots of gadgets and backup fail safe systems etc running! I am pretty sure my planned, somewhat less automated/autonomous approach, will not use as much power but I was using it as a worst case scenario.

Mike

[xelasnave]

Originally Posted by strongmanmike

The specs claim about 1100 cycles, when discharging to 50% DOD and they are touted to handle deeper discharges than normal AGM's, hence why I was attracted to them. So as an observatory and not cycled every day, 1100 cycles should equate to several years use out of the batteries?

Mike

You would like to think so anyways we will have the advantage of an experienced expert speculating on expectations...as a practical approach during a session you check say half way thru and if you need to you put a couple of litres of petrol in the genny start it so the inverter does not shut down sensing too much power has been taken out of the battery.
You could put in an exercise bike with a genny and a chap like you should produce 90 watts I think a human at full tilt is limited to 100 watts ...

I will get answers tomorrow
Alex

[strongmanmike (Michael)]

Originally Posted by xelasnave

I will get answers tomorrow
Alex

Ok cool, thanks, be interested in their take on all this

Oh and at my peak strength and power, back in the day, deadlifting and squatting 300+kg for reps, I used to match and even smash the top rowers on the Concept II rowing ergo's at the ANU (in short sprints only of course)

Mike

[raymo]

A 170w 12v panel will only produce anywhere near 9 amps if the sky is cloudless and the panel pointed directly toward the sun. If the panels don't
track the sun you'll probably average 5-6 amps over the course of a day.
The cost of a cheap 3kva generator would fund some more solar panels.
raymo

[strongmanmike (Michael)]

Originally Posted by raymo

A 170w 12v panel will only produce anywhere near 9 amps if the sky is cloudless and the panel pointed directly toward the sun. If the panels don't
track the sun you'll probably average 5-6 amps over the course of a day.
raymo

Indeed, however that wasn't reeeally what I was asking but thanks for the input Raymo...I wish I had a bigger budget

Yes I was also thinking the Generator or more panels conundrum too...I could probably get two or three more solar panels for the cost of a cheap generator...

Mike

[raymo]

Even a cheap 3kva would cost more than four more panels, unless you are
committed to purchasing the Rolls Royce of panels. I put budget 160s on my van 12 yrs ago, and they still function just fine. Four of them would cost less than $1000, far less than a 3kva Genset, with enough left over for a larger
amperage regulator.
raymo