Question on battery placement

Started by suburbancowboy, September 16, 2013, 10:17:53 PM

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suburbancowboy

This weekend I will be building the battery box for my solar setup.  I will be using 8 - 6 volt golf cart batteries.  It will be a 24 volt system.  I will be using an outback FM60 charge controller with temperature sensor.  My question is should I keep the batteries as close as possible to help conserve heat, especially in the winter, or should I space them out an inch or so to give them some ventilation?

MountainDon

I guess it depends on whether or not the pattern of use will make tightly spaced batteries get too warm in the center of the pack, or not.    ???   Our winter use is widely spaced and I did not think our use would be sufficient to make much chemical reaction heat as they are located outside. So ours have an approx. 1/2 to 3/4 inch space between them. It seems to work for us. I would like to be able to keep them warm, but the short daily maintenance charge would have little temperature effect, IMO. OTOH, the spacing helps keep them cooler in the warmer months and that can prolong their life.   FWIW, I also like the slight spacing as it does enable me to wash down the sides as well as the tops. 

That's the theory I am working under. No guarantee it will make any difference.

Just because something has been done and has not failed, doesn't mean it is good design.


Squirl

QuoteTo plan a successful battery box layout, draw out the batteries on paper, or make cardboard templates. Leave room around battery cases for ventilation, to hide rope handles, to maneuver a distilled water jug, and to get fingers and tools into the box for service. Leave 3 to 6 inches above the battery tops for cables and interconnects. Plan the placement and lengths of your interconnects so that all fill caps are readily accessible and battery cables do not lay over the cell tops

QuoteInsulating a battery box seldom makes much difference if the insulated box is located in a cold environment. Insulation slows the rate of heat loss from a warm space or object to a cooler space. Batteries are not a significant heat source; the normal charge/discharge process produces a negligible amount of usable heat.

http://www.homepower.com/articles/solar-electricity/design-installation/battery-box-design

Many more helpful tips in the article too.  With pictures.  [cool]

suburbancowboy

Squirl thanks for the link

Don I have to give you a big thank you.  I am designing my system similar to what you did at your cabin.  I have printout of a schematic that you did some where out there on the net.  I also refer to several pictures that you have put out on the net.  I have a couple of questions for you.

1. How do your three panels keep up with your 12 batteries?  I have 3 250 watt panels.
2. You have 15amp dc breakers in your combiner box.  Have you ever seen a need to go to 20 amp?
3. You have lots of extra breaker other than in the combiner box.  Do you still think that they are necessary?
4. What would you do different now after living with it for a while?

PorkChopsMmm

SC -- we live off grid with an all Outback setup with 8 6V golf cart batteries. I built an insulated plywood box around the batteries with a removable lid. In the summer I open the box up and take some insulation out and the batteries are cool. In the winter I put the insulation back in and close the box up. I have the batteries tight against each other for warmth. No issues with overheating in the summer and in the winter my batteries stay warmer longer (usually around 50 degrees F, but with negative temps for a week or two and little sun they get down to just above freezing).

I am thinking of going with a similar approach but with a big plastic rubbermaid bin. We had mice find the warm enclosure and sneak in through joints in the plywood. I think a sealed plastic container will keep them out.


MountainDon

Quote from: suburbancowboy on September 17, 2013, 11:11:16 AM
1. How do your three panels keep up with your 12 batteries?  I have 3 250 watt panels.
Our panels keep up with the way we use our 12 GC2 golf cart batteries.**

** We use the batteries lightly. We are blessed with mostly sunny skies most of the year. With normal weather we could be quite comfortable with 8 GC2's. We have 12 GC2 batteries because of winter and the attendant cold weather capacity loss of lead acid batteries. I wanted to minimize generator use.

Quote from: suburbancowboy on September 17, 2013, 11:11:16 AM
2. You have 15amp dc breakers in your combiner box.  Have you ever seen a need to go to 20 amp?
We have never had a breaker trip. Panels all in series = maximum amps worst case, 12.6
OTOH & FWIW we have had one of the GFCI's trip on occasion. Like when I was mixing concrete with the electric motor powered mixer.


Quote from: suburbancowboy on September 17, 2013, 11:11:16 AM
3. You have lots of extra breaker other than in the combiner box.  Do you still think that they are necessary?
Do you mean the ones just before and after the charge controller? One in the line from the PV array just before the CC (15 amp) and one on the line to the batteries from the CC (60 amp).  Some DC breakers are rated for use as a disconnect switch as well as the usual current interruption service. Those breakers were placed in part, because when activating and setting up the CC it is necessary to first connect to the batteries. Then the connection is made to the PV array after the initial programming is completed. Breakers like mine or DC disconnects make that easier than actually physically disconnecting a wire.

IF the PV array was much closer to the CC that incoming breaker could be dispensed with as the disconnect at the PV panels could be more readily accessed. As it is I like having a breaker/disconnect at the PV array as well.



Quote from: suburbancowboy on September 17, 2013, 11:11:16 AM
4. What would you do different now after living with it for a while?

OK. Over 4  1/2 years have passed since we bought the PV panels. PV prices are less than half what they were then. We paid just under $4 a watt and thought we had a great deal. Today I could drive across the river and pay less than a dollar a watt (warehouse pickup price).  I have not done any fine calculations on this but my feeling is that today I might like to...

- buy twice as many panels
- buy 12 L-16RE-2V Trojan 2 volt batteries, instead of the GC2's. Connect in series for 24 volts.
- buy an energy efficient electric refrigerator instead of the propane refrigerator. The money saved on the fridge would pay for the extra PV panels.
- buy a Honda EU3000 generator. It has electric start and could be auto started by the Outback equipment if the batteries charge dropped low enough. Convert the Honda to propane fuel.


As it is I  have swapped out the CFL's for the LED's.
Just because something has been done and has not failed, doesn't mean it is good design.

MountainDon

I meant to add this note since it was mentioned my schematic was being used...  There are a couple of changes made to the equipment setup.

#1 is the addition of a Class T fuse between the buss bar connection and the large breaker that serves the VFX3524M inverter. The breaker is a 250 amp. The Class T fuse is a 300 amp. Class T fuses are a fast blow type. It is there to act as a safety in case of a catastrophic dead short circuit. Class T have a very high AIR rating and ensure the fuse will blow rather than the batteries.

#2 is the addition of another Class T fuse after the 60 amp breaker from the charge controller (to the batteries). This is a 110 amp Class T. It is also to serve as a safety valve in case of a catastrophic dead short at that end.

Other than that the PV system is the same as it was when I flipped the switch and it worked.

Our electrical use has grown some with the addition of power to the gazebo and to the barn built last year. Not a lot but it has grown.
Just because something has been done and has not failed, doesn't mean it is good design.

Redoverfarm

Quote from: MountainDon on September 17, 2013, 01:32:16 PM
Our panels keep up with the way we use our 12 GC2 golf cart batteries.**


- buy twice as many panels
- buy 12 L-16RE-2V Trojan 2 volt batteries, instead of the GC2's. Connect in series for 24 volts.
- buy an energy efficient electric refrigerator instead of the propane refrigerator. The money saved on the fridge would pay for the extra PV panels.- buy a Honda EU3000 generator. It has electric start and could be auto started by the Outback equipment if the batteries charge dropped low enough. Convert the Honda to propane fuel.


As it is I  have swapped out the CFL's for the LED's.

Wonder what an electric refrigerator would do in the cold when you are not there.  Generally they do not operate properly in unheated spaces subjected to the cold like you would have in the mountain.

MountainDon

Excellent point John. Thing is that coming up soon we'll turn the propane fridge off for the winter anyhow. From then to spring we rely on the portable ARB fridge we cart in the truck. Then when we can't drive we use the nearest snow pile.

However there are some fridges made that can work in cold weather. Google for garage fridge. They are not so cheap though.
Just because something has been done and has not failed, doesn't mean it is good design.