View Full Version here: : Off grid generator question
strongmanmike
20-02-2022, 09:50 PM
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 :thumbsup:
Mike
Startrek
20-02-2022, 10:17 PM
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
20-02-2022, 10:24 PM
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
20-02-2022, 10:29 PM
Cheers Martin but yes that sounds costly :question:
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 :scared2:...seriously :help:) ...so I thought a cheap 3000watt genie might help and get under the Eagles radar..?
Mike
strongmanmike
20-02-2022, 10:38 PM
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
20-02-2022, 10:41 PM
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
20-02-2022, 10:44 PM
As I said, a full 14hr long winter night will use up about 4.2Kwhrs or 350amphrs of the 550 available.
Mike
xelasnave
20-02-2022, 10:45 PM
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
I thought you said that. Seems too much discharge to me.
Leave it with me.
Alex
strongmanmike
20-02-2022, 10:55 PM
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
20-02-2022, 10:57 PM
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
20-02-2022, 10:59 PM
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
20-02-2022, 10:59 PM
I will get the opinion of the expert,,what charger etc...your are in good hands with this man.
Alex
strongmanmike
20-02-2022, 11:03 PM
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
20-02-2022, 11:09 PM
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
20-02-2022, 11:17 PM
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
20-02-2022, 11:19 PM
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
20-02-2022, 11:26 PM
Ok cool, thanks, be interested in their take on all this :thumbsup:
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) :D
Mike
raymo
20-02-2022, 11:37 PM
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
20-02-2022, 11:41 PM
Indeed, however that wasn't reeeally what I was asking but thanks for the input Raymo...I wish I had a bigger budget :sad: :thumbsup:
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
20-02-2022, 11:52 PM
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
strongmanmike
20-02-2022, 11:56 PM
My 170W panels were $200 ea and I can get a 3Kva Generator (https://www.4wdsupacentre.com.au/solar-power/generators/3kva-inverter-generator/adventure-kings-3-0kva-inverter-generator.html) for $500...:shrug:
You are quite right but I was wanting to know how one goes about actually connecting a generator into such a solar system to charge the batteries while the panels are charging them too..?
Mike
xelasnave
21-02-2022, 12:30 AM
Now I cant sleep worrying about this;)
If 350 amps is your consumption ...and your batteries at 50% discharge when fully charged can provide 275 amps you clearly have a short fall...on the face of it you need another battery purchase...then you will have 1100 amp hour capacity and a available supply of 550 amp hours giving you a 200 amp hour buffer ..if you need another battery bank you need to buy it now so you start with the intended bank and not adding later.
Being realistic what ever you do you need first a genny and a charger...if I were you I would buy genny, charger and another set of batteries or plan on imaging less hours...namely 11 hours...that is 275 amps worth and 275 amp is all you have to spend...
Have a look at Kings the 4wd folk for a cheap genny..$500 should get you a good one..( they are good to deal with I have found)
AND your charger will need to charge at ,and your batteries able to accept, 25 amps. given that is your usage..30 would be better...I really think the solution may be accepting less capturing time..say 10 hours...you can do that now any more the genny and charger are a must have....anyways more tomorrow..oh it is tomorrow:lol:
Alex
strongmanmike
21-02-2022, 12:40 AM
Just found these diagrams in the Regulators manual :D, seems a battery charger via a generator, can be connected to the batteries..? Still cant confirm if this can be run while the panels are also charging the batteries..? I imagine so..?
Also not sure what
7) (Generator/load) dry contact enable switch
and
13) (Utility/Generator) dry contact OFF interface
are, in relation to all this..? :question:
Any idea..?
Mike
strongmanmike
21-02-2022, 12:47 AM
Yes but that max discharge figure will be quite infrequent, so dropping below 50% DoD (Depth of Discharge) will be infrequent, more often than not the DoD will be much less and probably only around 30% in mid summer....so I was thinking those heavy duty AGM's could handle that for a few years..?
Also see my previous post, there were diagrams and info with my regulator (who would have thought :rolleyes: :lol:) referencing generator use...but I'm not clear on what it is telling me exactly..:question:
Mike
raymo
21-02-2022, 01:00 AM
Hi again Mike. You can charge a battery or a bank of batteries using several
charging methods simultaneously. Solar panels do not allow reverse current,
and battery chargers are protected against reverse current. For example, I
can have my car engine running [ so obviously the alternator is charging the battery]whilst the solar panel is still connected to the battery.
I had forgotten how much cheaper open frame tradesman's style generators
are than the enclosed quieter recreational style ones. I don't know how many amps you are looking at contributing via the generator. Recreational ones all have a 12v charging outlet of 8amps or a little more obviating the need for a separate charger. Any recreational generator will charge at 8 amps, doesn't have to be a heavy, large noisy 3kva unit. My 750w charges 8amps using a minimal amount of fuel.
I note the model in your link doesn't seem to have this feature.
raymo
strongmanmike
21-02-2022, 01:07 AM
I imagine I would be using a standard battery charger like this one (https://www.caravanrvcamping.com.au/victron-blue-smart-ip22-charger-12-30-230v-au-nz?gclid=EAIaIQobChMI56nQ67eO9gIV94 ZLBR2AEQNkEAQYBiABEgJv0_D_BwE), operating off the 240V outlet on the generator, I need to confirm that this won't conflict with the regulators "intelligent" charging of the same batteries, using power from the panels..?
Mike
raymo
21-02-2022, 01:18 AM
Solar panels are in effect diodes, and as such do not allow any reverse current from any source, be it the battery itself, or any kind of charging system such
as a charger or an alternator. Charging systems are themselves protected from reverse current,so you have no problems. The only current that can go through the regulator is what comes from the solar panels, so no conflict.
raymo
Joshua Bunn
21-02-2022, 01:35 AM
Hi Mike.
Short answer is you can have two charge controlers paraleled on a single battery bank. As you say, conect a Rectifier to the geny and conect it to the battery in parallel with the MPPT. Make sure the two current supplies don't supply more current than the batteries are designed to charge at.
https://cleversolarpower.com/multiple-charge-controllers/
strongmanmike
21-02-2022, 02:10 AM
Thanks guys together that's what I needed to know I think :thumbsup:.
So, if I get myself a pure sine inverter generator (eg. the one from Kings) and a good AC to DC charger, say ~30amp, plug it into one of the 240V outlets, then connect it to the battery, as per the regulator is ie. both positives on the same positive terminal on the battery bank and both negatives on the same negative terminal, then, I could switch on the generator at anytime and have it contribute to charging the batteries whether or not the solar panels are pumping current in ...that sound right?
I guess I was concerned that given different chargers/regulators use different sequences/algorithms to charge batteries, I thought having two different ones connected to the batteries might cause conflict in charging..? But seems not so. ?
I assume there would also be no issue with this setup if I was to turn on the generator with charger "during" an imagaing session, should I notice the batteries are getting low..?
Mike
raymo
21-02-2022, 02:24 AM
Yes, You can start extra charging whilst imaging. As long as the system voltage remains within the stipulated range acceptable to your mount's motors, say 11-15v for example, the motors will just keep motoring along.
raymo
xelasnave
21-02-2022, 09:18 AM
Good morning Mike.
I have spoken to my expert and as he is a member here hopefully will log on and offer direct input.
He has told me he has difficulty at times logging on so may read as a guest and give me his comments which I can post.
Alex
strongmanmike
21-02-2022, 09:27 AM
Everything will be running off the 12V DC to 240V AC 2000W inverter.
Mike
xelasnave
21-02-2022, 10:36 AM
I have spoken to Peter but he cant log in and will catch up with me later.
Here is the charger he recommended and installed for the house system which uses AGM batteries...
More later.
Alex
Paul Haese
21-02-2022, 11:49 AM
When we had our solar power station designed for Swan Reach we are advised of a couple of things which I think are pertinent here.
We were advised that the generator should be around 6kva in general to allow for good charging of batteries and this gives you a level of expansion into the future. Our system is pretty large at 79kwh of storage. We opted for a 11kva generator to allow welding and the like on site and for fast charging. The generator also has a autostart system installed so when the batteries get to down to a certain power level (we programme that) it will start up and commence charging the batteries.
Secondly we went with Vitron equipment and an inverter from them. The equipment decides how much power to provide for charging and this then prevents over charging. Generally up to 98% charge of the system it will work in bulk, then it will work in absorption and then finally in float at 99%. Paying for this piece of kit in the system was worth every cent. Our solar charger is a 150/100. The brains of the unit is the Gateway unit and that decides where power is coming from for charging and how much is needed. It can disregard the full solar panel system load.
I think it is worth discussing this with a Vitron Rep and get them to advise you what you actually need. You might actually be covered well now but you might also need more equipment to protect the system.
Hoges
21-02-2022, 12:03 PM
Hi Mike,
Our house runs on solar. We have two sets of four panels, both going into their own regulator which are both connected to the batteries along with a 50amp Victron charger than runs from a Yamaha 2400w inverter. The whole lot can be going at once if need be (though that would be a bit much charge for the batteries for any length of time). So we are essentially running the system your thinking of no problems. Each controller/charger looks at the battery volts and adjusts accordingly and I've never noticed any conflict. Batteries are 660ah 2v cells x 12 for a 24v system.
I would wire the panels in series - I find I get better results on cloudy days with the higher voltage/mppt controller setup than running the panels in parallel. (or two parallel sets in series).
Wow, you're drawing 25 amps / 300w continuously from your setup? That's a goodly amount of juice! One of those little 2kva Honda generators would do the trick and be easy to cart around and would power a little 20amp 12v charger no problems. They have a pretty good rep in the caravanning groups. I'd put some big fuses on the battery too. I'm also a big fan of the Victron brand of gear too - chargers/mppt's/inverters etc - very good gear.
xelasnave
21-02-2022, 02:17 PM
Here are some pointers from my assistant.
He would have posted under his handle but is having problems logging in.... So he has emailed me and I now pass it on.
Alex.
Sounds like you are pushing the batteries with a discharge of 350 amp hours every day. A lead acid battery generally is designed for a cycle of not more than 10%, of the 20 hour rating if daily. So a 550 amp hour battery shouldn't be discharged more than 55 amp hours, over the period the rating applies for, usually 100 hours, or 5.5 amps continuous. Taking the 20 hour, or 1 day rate, the battery capacity of a 550 amp cell is probably around 350 amp hours, so this means a daily discharge cycle of no more than 35 amp hours, so you are pushing them and they will fail prematurely. Neglecting to account for the daily discharge rating of the battery, and using the published, usually 100 hour rating, results in many failed battery's after a few years.
As for the charge current, a decent battery should accept charge at the 10 hour rate, at least until the voltage rises, then you must back off the charge as the battery, sealed types, must not be allowed to gas under any circumstances. Hence the recommendation for a regulated charger, or keep a close eye on the voltage and back off the charge when approaching the gassing voltage, which should be published in the manufacturers data.
Example, our main house battery's are rated at 2,700 amp hours, 48 volts, and that's a 24 hour rating. The 100 hour rating is well over 3,000 amp hours, and the main charger from the generator, is 500 amps, yes, 25 kw of battery charging, but they can absorb that easily and I have a voltage sensitive relay that disconnects the charger at about 56 volts, to prevent gassing. (Its actually a submarine battery and weights 4.5 tons). We also have over 20 kw of solar connected,
Also, if you are drawing around 30 amps from the battery's, to charge the battery's, you will obviously need more than 30 amps going in.
A little about efficiency is called for here.
Power (losses), is proportional to the amps squared. So, at 12 volts, we can say its efficiency is 1, at 24 volts, the current is 1/2 that of 12 v, so the efficiency is 4 X better, or 1/4 the losses at 12 v (amps squared, remember ?), and at 48 volts, the losses are 1/16 those of 12 volts. Ah ha, you now say, that's why we transmit power at high voltages, yup, you got it in one.
The currents you are seeing are quite heavy for 12 volts, and it may be useful to go to 24 volts, and use a Victron inverter/charger (which will automatically regulate the charge rate and switch over to run the gear off the generator if its operating), giving max power into the battery's. This is how most professional systems operate. To operate the scopes electrics, 24 to 12 volt converters are available from Jaycar, and the efficiency of such a system will be much better.
As for auxiliary charging whilst the solar is connected, as long as you don't exceed the gassing voltage for your sealed battery's, it will be OK. Although, too much current can cause the battery's to reach gassing voltage before they are fully charged, so its a bit of a two edged sword. Any decent solar regulator will sense the increased battery voltage and probably switch itself off. Also, be aware that the inverter will have over and under voltage sensing and may react to boost charging by switching itself off, hence the advantages in a combined inverter/charger.
In a previous life, I owned a company that designed and installed solar, hydro, wind and grid systems, and still am an accredited design and installer.
On another note, I operated a homemade 10 foot radio telescope dish at our other farm, and if I can find the traces, may publish them if enough are interested.
........
Me again.
There is a other email but I will do another post..in a minute or two.
Alex
Contents of second email....
Add this in as well please.
Temperature also affects the charge acceptance. The colder it is, the less battery capacity you have available. Also, the colder the battery's, the less efficient they are. Generally you need to put about 10 % more back in than taken out, for lead acid types, but this gets worse as the battery ages and also varies with discharge rates, high discharge means less efficiency and more losses and more energy needed to go back in, not unsubstantial with a battery our size.
Alex
Malewithatail
21-02-2022, 03:26 PM
Managed to log in finally, will stay logged in for a while, ask away.
xelasnave
21-02-2022, 03:42 PM
Thanks for your help and I am happy you got logged in.
Alex
strongmanmike
21-02-2022, 10:08 PM
Ok another question :)
If I have a 3000 watt, pure sine inverter generator with a 15amp 240V outlet, what size (amps) 240V to 12V battery charger can it safely run?
Mike
strongmanmike
21-02-2022, 10:09 PM
Ok another question :)
If I have a 3000 watt continuous, pure sine inverter generator with a 15amp 240V outlet, what size (amps) 240V to 12V battery charger can it safely run?
Mike
raymo
21-02-2022, 11:40 PM
Mathematically 3,000w @240v =12.5amps, so your 15amp outlet would be fine. A 240v to 12v charger would
give 250amps minus a few % for converting from 240v a/c to 12v D.C. and
voltage drop, which would depend on the length of the cable from charger to
battery, and the diameter of said cable.
So your 3,000w running comfortably would give around 200amps, which would be a brute of a charger, and I imagine far more than your battery
would be happy to accept.
raymo
xelasnave
21-02-2022, 11:59 PM
You should not charge more than 10 % of your batteries capacity ie 55amps.
Although personally I go for a little less.
The important thing is to get a charger that is for AGM batteries...
Alex
Have a look at these
https://www.rpc.com.au/shop/advanced_search_result.php?keyword= Chargers
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