Molokai Off grid system design help

vtmaps · September 2013

Re: Molokai Off grid system design help

molokaisteve wrote: »

Heard of anyone with experience with the low cost Costco GC2 batteries?

No personal experience, but for many folks they are cost effective.
How about this:

BB. wrote: »

Cheap batteries have their charm...

If they last 3-5 years vs 5-8 years for "mid range" batteries--How does the cost of ownership work out.

Also, if this is your first set of batteries--A set of "training" batteries may be a good start. Most of us have "murdered" our first sets of batteries... Over/under charging, forgetting to check electrolyte levels, "deficit charging", an "oops" were the inverter was left on or a guest used a hair drier+TV+lights all weekend long, etc....

Plus, if this is the first time off grid for the cabin, you really do not know how much power you will really need. Having a "cheap set" of batteries that only last a few years will give you a chance to wring out the system and see if you need a larger or smaller bank.

-Bill

--vtMaps

molokaisteve · November 2013

Re: Molokai Off grid system design help

Well, I'm back in Hawaii and all the parts (midnight charge controller, epanel and magnum inverter and panels, etc) are on there way here. I plan to start the installation in a couple of weeks. I am planning on purchasing 16 - GC2 Costco batteries and have two parallel strings of 8 ea wired in series to make up my 48 VDC battery bank. This is going into a fairly big (48' x 40') airplane hangar. I've searched google for pictures of battery banks and find some have built enclosed battery boxes while others just have them out in the open. As I remember, both Magnum and Midnight solar recommend not having their systems mounted above the battery bank (for corrosion reasons with the fumes??). What is best - build a single shelf and have all of the batteries lined up eight across and two deep at a convenient height in a enclosure or just open - or is it better to have two shelves with space enough tocheck the water level on the lower shelf of batteries and on each shelf eight batteries lined up in a row - again in an enclosure or open?

I remember being told it is better to build a wall with the batteries on one side and the electronics on the other but I don't have the room for that.

As always, thank you all for your wonderful advice.

BB. · November 2013

Re: Molokai Off grid system design help

Battery maintenance is going to be crucial for a long and happy battery life. Whatever works best for you. At least once a month you are going to be opening all 48 battery caps, checking water levels, specific gravity, cables, cleaning any acid mist/spills, etc... If you have too close of shelf space, that is going to be a real pain in the back. Get a small LED headlamp too--Makes looking down in the cells a lot easier.

And always think of safety... You don't need an insulated box (keep batteries warm/cold based on seasons), but you don't want kids wondering around contacting battery terminals or things falling on the battery bank (chips, tools, etc.)... So covering the battery tops/limiting access at a minimum. If you get a lot of acid mist/sulfur smell--A room/box to allow you to contain fumes and piping them outside would be helpful (you can power the fan only when the batteries are charging and/or battery voltage >~13.8 volts or so--When they are gassing--To save power/noise/wear and tear).

-Bill

vtmaps · November 2013

Re: Molokai Off grid system design help

molokaisteve wrote: »

I've searched google for pictures of battery banks and find some have built enclosed battery boxes while others just have them out in the open.

Safety first. Batteries in a box. The battery cables must be in conduit between the battery box and the ePanel... remember, the battery cables are unfused. All the DC breakers that come off the battery bus are in the ePanel.

Since you're a do-it-yourself type, I expect that you will be poking around in the ePanel from time to time. Therefore, I suggest that you put a large circuit breaker or switch in the battery cable between the battery box and the ePanel. There is a LOT of unfused battery bus in the ePanel... I'm afraid to even look in my ePanel without first de-energizing the battery bus.

molokaisteve wrote: »

As I remember, both Magnum and Midnight solar recommend not having their systems mounted above the battery bank (for corrosion reasons with the fumes??).

I think the rationale for not putting the batteries under the ePanel is that code requires clear access to the electrical panel.
EDIT: http://www.homepower.com/articles/solar-electricity/design-installation/workspace-clearances-and-accessibility?v=print
As far as fumes, the two issues are corrosion and explosion. Sulfuric acid mist causes the corrosion and hydrogen causes the explosion. Be sure that the opening of the conduit into the battery box is BELOW the tops of the batteries... hydrogen will not enter the conduit then. As for the sulfuric acid mist, I recommend 'Water Miser' caps. They come in three heights, the taller they are, the more effective they are. I bought mine from the manufacturer because I couldn't find a dealer (including NAWS) that carried the tall size.

molokaisteve wrote: »

What is best - build a single shelf and have all of the batteries lined up eight across and two deep at a convenient height in a enclosure or just open - or is it better to have two shelves with space enough tocheck the water level on the lower shelf of batteries and on each shelf eight batteries lined up in a row - again in an enclosure or open?

As for battery configuration, I recommend a single shelf. That also usually helps to keep the two strings at the same temperature.

--vtMaps

molokaisteve · November 2013

Re: Molokai Off grid system design help

Bill and vtMaps,

Thank you both - so helpful. I attached a pdf doc showing what I'm planning. I'll build a room and in it will locate a single shelf with two rows of eight batteries situated on it. How much space between the batteries do I have to allow for - heat and so on? What would the minimum space be? I will put the conduit below the battery fill height and go through the wall and into the ePanel. I already purchased a battery switch that I'll mount in the room to be able to power off the DC going into the ePanel (yes, talk about arc welding current - holy crap!) The water miser caps are nice - but over $200 for 48 - ouch! Probably do it...Attachment not found.

There will be 3' of space in front of the battery shelf and I'll research a fan and how to have it come on when they are charging or when the temp goes up... Since it will be in an enclosed room - don't plan to put a lid over the batteries - this OK? Maybe I should have a lockable door...

Planning on putting a light - just a 110VAC LED light in it so I can see when checking the levels and will use my Costco LED headlight.

Oh, I've purchased timers (10-20-30 and 60 min) for each light - no switches at all. That way "no one" can accidentally leave the lights on all night or for days that I'm not there.

On the outside wall of the battery room, I'll mount the ePanel, inverter, charge controller. Oh, I will wait to purchase my batteries from Costco until I have everything wired and ready to go...

Thank you both again, Steve

vtmaps · November 2013

Re: Molokai Off grid system design help

molokaisteve wrote: »

I'll build a room and in it will locate a single shelf with two rows of eight batteries situated on it.

If you arrange your strings like in this diagram, you MAY be able to have shorter battery cables. The diagram shows four batteries in each string, but you can modify it to have 8 batteries per string.
Attachment not found.
--vtMaps

mike95490 · November 2013

Re: Molokai Off grid system design help

a shelf for batteries, needs to be very strong. Why not place them on the floor ?

vtmaps · November 2013

Re: Molokai Off grid system design help

mike95490 wrote: »

a shelf for batteries, needs to be very strong. Why not place them on the floor ?

I think he is following the advice I gave earlier in this thread:

vtmaps wrote: »

Make the battery cables to the epanel as short as possible. If you put the battery box on a stand 20-30 inches off the floor, the batteries will be easier to service and closer to the epanel. Some folks build a four ft wall perpendicular to the exterior wall and put their electronics on one side of the wall and their battery box on the other side.

--vtMaps

molokaisteve · November 2013

Re: Molokai Off grid system design help

vtmaps wrote: »

If you arrange your strings like in this diagram, you MAY be able to have shorter battery cables. The diagram shows four batteries in each string, but you can modify it to have 8 batteries per string.
Attachment not found.
--vtMaps

vtMaps, Oh, that is clever! I will modify for my two strings of eight each. Thank you! How close can I set the batteries to each other. I noticed Mike in his post (thank you Mike for the pictures) that they were touching each other. Can I allow a 1/4" of space or do I need to allow 2" of space between the batteries??

vtmaps · November 2013

Re: Molokai Off grid system design help

molokaisteve wrote: »

How close can I set the batteries to each other. I noticed Mike in his post (thank you Mike for the pictures) that they were touching each other. Can I allow a 1/4" of space or do I need to allow 2" of space between the batteries??

Spaces of 1/2 inch or less do not allow much convection. When the space between the panes of a thermopane window is more than about 1/2 inch, the window become less effective because convection occurs between the panes. The lesson I take from that is that an inch between batteries should be adequate. Disclaimer: I don't have much personal experience trying to keep batteries cool.

--vtMaps

molokaisteve · November 2013

Re: Molokai Off grid system design help

Thank you vtMaps!

Bill, can you weigh in on this one as well? I'm in Hawaii so the OAT ranges from 66 to about 94 degrees. The hangar is not insulated and the batteries will be about 20-30 inches off the floor but when charging, I'm not sure what temperature they will reach.

How much space is adequate to have between the batteries. I like vtMaps logic on convection so it sounds like 1" should work. Your thoughts on this?

BB. · November 2013

Re: Molokai Off grid system design help

What vtMaps said is a good start...

Batteries (especially the larger they get) do not have very efficient heat transfer characteristics... And if you look at commercial systems like fork lifts, they have to pack larger (AH) cells close together to keep the foot print small/energy density high. Which all negatively affects heat transfer/dissipation.

I go back to rules of thumbs to start the design... Basically, if you limit maximum charging current to ~13%, you should not see too much heating.

Also, if you do have heavy charging current, below ~80% state of charge (say bulking up with a genset), the battery charging is much more efficient (less waste heat). When you charge >90%, and especially during equalization, the batteries generate much more waste heat (equalization should be be around 5% to 2.5% maximum rate of charge and monitor bank temperature).

Batteries like to be keep "cool"--for every 10C rise (18F) increase in battery temperature, life is cut by 1/2... So, if 77F is standard conditions, 95F, you batteries may age 2x faster.

These are Nickle Iron batteries... I like the stepped access of double rows--You are going to be spending years look at eletrolyte levels and measuring specific gravity--You want that to be as easy as you can:

Iron Bran wrote: »

Here are some actual Nickel Iron battery project photos from Iron Edison. This is a 24 Volt 400 Amp hour battery with an Apollo Pre-Wired Panel. The PWP includes the solar charge controller, inverter, and DC disconnect.

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-Bill

BB. · November 2013

Re: Molokai Off grid system design help

You can also do "racking"--But I worry that difficult access to the cells is going to dissuade rigorous monitoring of the batteries:

Iron Bran wrote: »

Here is a very recent project. Check out this 1000 Amp hour 48 Volt battery installed by Iron Edison in Colorado. This one battery can hold up to 48 kWh of stored energy. The battery is complimented by 15 kW of solar and dual SMA Sunny Island inverters. All told, there are 7 inverters in this AC coupled system.

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If you use Google and search for "Battery Bank site:wind-sun.com" and click on the "Images" search, you will get a bunch of pictures of what various folks have done on the forum...

If heat becomes a big concern, you may want to install a fan that circulates air when the batteries are charging--And/or draw air in overnight to force battery cooling (draw air in low, vent high (heat rises)).

Unfortunately, I am not the best person to answer this... My system is grid tied in a moderate climate (no batteries). Engineering wise, we usually design for "worst case" conditions--Which makes for better reliability/life, but does add to costs.

-Bill

molokaisteve · November 2013

Re: Molokai Off grid system design help

vtMaps and Bill,

Thank you both again. Here is the latest design of the battery room in the hangar. It is much easier to redo it on CAD and get it designed correctly before I start to build and all that is possible because of your help.
Attachment not found.

This method of wiring will shorten the length for sure (thank you vtMaps!). The shelf will be about 30" off the floor and I will make it Heck for Stout - those darn batteries weigh so much. I'll have a conduit going through the wall and into the bottom of the epanel with a disconnect switch in the battery room.

Thanks again,
Steve

BB. · November 2013

Re: Molokai Off grid system design help

Any issues with coolant mist/shavings/etc. from the lathe and mill (any grinders)?

Depending on the final hardware chosen--Some are air tight, others draw room air through the electronics). An option would be to put the batteries on the outside (secure box in shade with venting). And put the electronics in the room (probably more sensitive to ambient conditions).

-Bill

vtmaps · November 2013

Re: Molokai Off grid system design help

molokaisteve wrote: »

This method of wiring will shorten the length for sure (thank you vtMaps!).

What you've drawn is problematic, and is NOT what I suggested. When batteries are in parallel it is important that the current be equal in each string. Batteries are so low in resistance that the resistance of the wires, although low, is significant in steering the current unequally into the battery strings.

In your new diagram, the string of batteries on the left has a longer current path than the string on the right.

In my diagram I had a common point in the pos and the neg cables where equal-length cables connected to the ends of the battery strings. It is not necessary to do that.. there are other ways. A common way to connect two strings is the "diagonal" method:
Attachment not found.

--vtMaps

molokaisteve · November 2013

Re: Molokai Off grid system design help

Dang Nabit. I didn't understand that at all. My apologies. Thank you for catching it!!!
Attachment not found.
I redrew it and it is attached. If the wires for the serial battery set on the left are the same length as the battery set on the right - then I'm OK? Does it matter that the end batteries on both serial sets have a longer wire than the others in that series? I'm assuming that since they are wired in series, it is acceptable?
If you look at the attachment and I've screwed it up again, please continue to advise. Its funny how ignorant one can be... That is probably a proverb!

molokaisteve · November 2013

Re: Molokai Off grid system design help

Bill, thank you. I don't think it will be much of a problem. The use is so infrequent and I don't use coolant since I only build one of a kind items. The chips may fly around some not much of a chance for them to cause problems with the inverter or charge controller - all outside protected from chips.
Steve

vtmaps · November 2013

Re: Molokai Off grid system design help

molokaisteve wrote: »

I redrew it and it is attached.

Still not correct. I redrew the "inner four" batteries of your diagram... the key is that wire "A" is the same length as wire "B".
Attachment not found.

--vtMaps

molokaisteve · November 2013

Re: Molokai Off grid system design help

vtMaps,

Got it now!! A big thank you! I will make sure that wire A and wire B are the same length.

Steve

molokaisteve · October 2014

Re: Molokai Off grid system design help

Attachment not found.Attachment not found.All,

First I would like to say thank you to all who've helped me on this system. Hopefully, you can see two pictures. One of the outside wall of the battery room with the charge controller, inverter and my cb panels. Second picture shows the inside of the battery room. The battery room has a ceiling fan (12VDC brushless fan) that the charge controller turns on (I think in equalize mode). I have more than enough power to run anything we want. I have all the lights and outlets in the hangar on timers so I can't forget and leave them on over night or worse for many days. We have run two vacuums for hours cleaning the hangar, we've run a small pancake compressor on and off for a day, we've run power tools, and even have a small refrig on but it is on a timer so it only runs during the daylight hours when the sunlight is available - only have water and beer in it so if it warms up - no problem. We can run a small microwave - everything couldn't be nicer - so again, BIG THANK YOU to all who've helped especially vTmaps and Bill.

The only problem I have is in the amount of water I'm using. I have to fill the batteries once per month. Pretty sure that the equalization mode is coming on too frequent but as you know, I'm a newbie and don't know anything. How can I change my charge controller to keep this from happening if this is it or is this normal? I only fill just over the plates - the battery caps you suggested are so easy!

Thank you, thank you and thank you!
Steve

BB. · October 2014

Re: Molokai Off grid system design help

Very nice looking!

Regarding watering the batteries--You never want to have the plates exposed to air (pretty close to instant battery death, or at least "cell cancer" for the exposed sections).

Fill to "cover the plates" before charging--Fill the balance (too mark, or a bit below) when the batteries are fully charged (warm, bubbles under plates from equalization, etc.). That way, the batteries should not "flood" the tops (hot batteries+gas bubbles push liquid levels up).

Do you have Midnite's Whizban Jr. (remote current shunt) in your battery Negative bus connection?

-Bill

vtmaps · October 2014

Re: Molokai Off grid system design help

molokaisteve wrote: »

The only problem I have is in the amount of water I'm using.

Very nice clean installation. I'm glad to hear things are working out... you deserve good results for all the research you did on the system.

I suggest you turn off automatic equalization on your classic.

About the water... maybe you are doing too much equalization, but maybe you just have too high or too long an absorb. What are your charging parameters? What temp are your batteries running? The warmer they are, the more water they use. Speaking of temperature, you do have a battery temp sensor for the midnite, don't you?

How low do you draw down the batteries every day? If you are doing repeated very shallow overnight discharges, you can program your classic to skip a day (or more) of charging. This may prolong battery life.

--vtMaps

molokaisteve · October 2014

Re: Molokai Off grid system design help

BB. wrote: »

Very nice looking!

Regarding watering the batteries--You never want to have the plates exposed to air (pretty close to instant battery death, or at least "cell cancer" for the exposed sections).

Fill to "cover the plates" before charging--Fill the balance (too mark, or a bit below) when the batteries are fully charged (warm, bubbles under plates from equalization, etc.). That way, the batteries should not "flood" the tops (hot batteries+gas bubbles push liquid levels up).

Do you have Midnite's Whizban Jr. (remote current shunt) in your battery Negative bus connection?

-Bill

Bill - thank you.

I am a little dense. I don't think I completely understand how much to fill the batteries.

1. I get it that I shouldn't let the plates be exposed to air.
2. I should fill them when they are warm, fully charged to a "mark"? There is about a 1/2" distance from the plates to the top of the battery plastic housing and then there is another 1" or so to the lid on the fancy caps. I've always filled them when they are fully charged and only to about a 1/8" or so over the plates.

Good, bad or horrible?

And don't remember on the remote current shunt - I'll go and look. I built it last winter and was away all summer - had a friend fill the batteries once a month - he used 3 gallons of distilled water over the 5 months during the summer - very little to no battery drain on the system - almost idle but I didn't change anything on the controller from when I set it up. Now that we are back, I'm trying to see what I did wrong or should change.

Now that I'm thinking about it, I'll have to go through this thread. I think you or vtMaps told me to put it in a different mode during the summer - dang nabit - bad memory.

molokaisteve · October 2014

Re: Molokai Off grid system design help

vtmaps wrote: »

Very nice clean installation. I'm glad to hear things are working out... you deserve good results for all the research you did on the system.

I suggest you turn off automatic equalization on your classic.

About the water... maybe you are doing too much equalization, but maybe you just have too high or too long an absorb. What are your charging parameters? What temp are your batteries running? The warmer they are, the more water they use. Speaking of temperature, you do have a battery temp sensor for the midnite, don't you?

How low do you draw down the batteries every day? If you are doing repeated very shallow overnight discharges, you can program your classic to skip a day (or more) of charging. This may prolong battery life.

--vtMaps

vtMaps,

Thank you. I will turn off the automatic equalization on the classic. How do I know when (what parameters like voltage, days since or ?) to put it in equalization manually?

Charging parameters - I will go fetch my notes and reply back this evening. This system only gets used once a week or so, sometimes more frequent, when we go to the hangar and fly over to another island. Most of the time it is idle. Idle but very capable. Even when we've used it for hours and hours, the system is still well over 90% charged - most of the time it seems that the panels are feeding in and we are using that power and therefore the batteries are not being drained much since most of the time we use it during daylight hours. Now this is a laymen's point of view...

How do I know if I hurt the batteries over the summer?

I had more knowledge last winter but not being around it all summer, my knowledge has quickly evaporated - the joys of being "senior"

And thank you again for the time you spent with me - I really appreciate it!

Steve

vtmaps · October 2014

Re: Molokai Off grid system design help

molokaisteve wrote: »

I've always filled them when they are fully charged and only to about a 1/8" or so over the plates.

That doesn't sound right... if your electrolyte is only 1/8 inch over the plates, you're 1/8 inch from disaster. Remove the caps, look in the cell and you will see a slot on the side. Your electrolyte should at least reach the slot.

molokaisteve wrote: »

How do I know when (what parameters like voltage, days since or ?) to put it in equalization manually?

I think the question is not what parameters to use for equalization, but whether to do it at all. A corrective equalization is in order when the SG of your cells varies. Some battery manufacturers recommend routine equalization.

Why do a routine EQ? Charging a battery to 100.00% SOC is tough on the battery... the high charging voltages cause corrosion. You cannot tell (with a hydrometer) the difference between 99.9% and 100% SOC. If you repeatedly charge to 99.9% SOC, the 99.9% becomes your new 100%. After awhile you're at 99.9% of 99.9% of 99.9% etc. That's called slow deficit charging and it can take a couple of years to slowly kill the battery by sulfation. That is why some battery manufacturers recommend routine EQ every week or so... it breaks the 99.9% cycle of decline. The idea is to go easy on the battery most days, but then hammer it with an EQ once a week.

molokaisteve wrote: »

Charging parameters - I will go fetch my notes and reply back this evening. This system only gets used once a week or so, sometimes more frequent, when we go to the hangar and fly over to another island. Most of the time it is idle.

All the more reason to program your Classic to skip charging days. If you skip charging days, it will just go to float while you're away for a week. Do not leave a battery on float for months... you should do at least a bulk/absorb cycle once a week, if not an EQ.

--vtMaps

BB. · October 2014

Re: Molokai Off grid system design help

I am not an off grid battery guy--But you probably want around 1/2 to 3/4 of the space between the top of the plates and the bottom of the fill tube filled with water/electrolyte.

If the tube has a slot in it--Generally the water should touch the bottom of the split tube (like vtMaps says). But this final fill should be when the battery is near fully charged and warm.

I have filled cold batteries to the base of the split tube on car batteries--Only to have them overfill when charged/hot/gassing.

-Bill

mike95490 · October 2014

Re: Molokai Off grid system design help

BB. wrote: »

...If the tube has a slot in it--Generally the water should touch the bottom of the split tube (like vtMaps says). But this final fill should be when the battery is near fully charged and warm.....

I only fill just over the plates

Here's a nice photo/sketch at the bottom of the page, of the split tube, and add distilled water to top off the cells when they are warm.
http://www.trojanbattery.com/BatteryMaintenance/WateringDiagram.aspx

And be glad you don't have NiFe batteries, I go through about 15 gallons a month with those thirsty babies !

molokaisteve · October 2014

Re: Molokai Off grid system design help

Oh my. It never ceases to amaze me just how little I know. OK, the picture that Mike posted showing the split tube is very clear and I will fill all of them up to that level - thank you both for educating me.

Skip charging days - copy that and will look through the Classic manual on how to.

Steve

vtmaps · October 2014

Re: Molokai Off grid system design help

molokaisteve wrote: »

Skip charging days - copy that and will look through the Classic manual on how to.

The classic has had a few very worthwhile firmware updates in the past year... and some new manuals to download also. I don't recall when 'skip bulk' charging was added..... you may need to upgrade.

--vtMaps

Molokai Off grid system design help

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