Looking to set up new battery bank.

bc buck · December 2016

I destroyed my Trojan 260AH bank not keeping them charged and equalized. Iv ran them through equalization charge 6 times this past month and only get about 100 ah before completely dead. Now I have 435w of panels installed I am thinking of investing in new battery's.

I read a article on a renewable energy web sight stating batteries wired parallel will loose 50% of there life. Said internal resistance will vary causing weaker battery to be undercharged. I have spent hours trying to find that article again with no luck. Installing batteries parallel seems to be common practice.

This is my weekend retreat. Summer months 100% solar charge is good. Winter I use generator 5 hours at night and end up needing about 130 ah per day.

Currently I have two scs225 parellel set up using 12v at 260 ah.
If battery life is extended, I could buy two trojan t145 260 ah 6 volt and wire in series.
Was also thinking I could buy two new scs225 and wire in series at 24v with 130ah. My panels are Kyocera KD145, 3 12v in series using a MPPT charger.

Do you guys see advantages of any of these configurations Thanks.

Estragon · December 2016

It would help to know more about your loads. Are you running an inverter? Any motor loads like pumps or fridge? I would avoid parallel battery setup, but a two battery setup with good wiring isn't so bad.

softdown · December 2016

What you read about parallel batteries may have some truth. I'm not sure and have not read that. I think most of the people here have at least one parallel battery or battery string.

A rule I have heard is 4/0 for parallel and 2/0 for series. Battery banks seem a bit mysterious at times.

bc buck · December 2016

Estragon said:

It would help to know more about your loads. Are you running an inverter? Any motor loads like pumps or fridge? I would avoid parallel battery setup, but a two battery setup with good wiring isn't so bad.

Loads are all light. Winter 9a furnace load. Year round 15a lights fan tv. Use Prosine inverter/charger.

Estragon · December 2016

Wiring 12v battery in series for 24v will likely be a problem unless you want to buy a new inverter.

When you say 9a load for furnace is that 9a @ 120vac? How did you arrive at your estimate of 130ah (@12v?) usage?

mcgivor · December 2016

In order to make a rough calculation a run time needs to be established, or better yet is to use a Kill a Watt device to be more accurate, although the loads may seem light, my guess is your battery is undersized as is your array.

bc buck · December 2016

Estragon said:

Wiring 12v battery in series for 24v will likely be a problem unless you want to buy a new inverter.

When you say 9a load for furnace is that 9a @ 120vac? How did you arrive at your estimate of 130ah (@12v?) usage?

No the furnace runs off 12v dc at 9a. My instrumentation tells me what everything draws. Then figure how many minutes used in 24 hours. Im pretty sure my inverter/charger can run 12 or 24v but will need to check.

mcgivor · December 2016

If you convert to 24V you will not have 12V to run your furnace unless you get a DC DC converter, don't be tempted to tap off from one 12V battery !!! It WILL result in the death of one, if not both batteries

mike95490 · December 2016

bc buck said:

... I read a article on a renewable energy web sight stating batteries wired parallel will loose 50% of there life. Said internal resistance will vary causing weaker battery to be undercharged. I have spent hours trying to find that article again with no luck. Installing batteries parallel seems to be common practice....

Just because it's common, does not mean it's correct. read this about parallel batteries, simple work-arounds
http://www.smartgauge.co.uk/batt_con.html

Estragon · December 2016

bc buck said:

Estragon said:

Wiring 12v battery in series for 24v will likely be a problem unless you want to buy a new inverter.

When you say 9a load for furnace is that 9a @ 120vac? How did you arrive at your estimate of 130ah (@12v?) usage?

No the furnace runs off 12v dc at 9a. My instrumentation tells me what everything draws. Then figure how many minutes used in 24 hours. Im pretty sure my inverter/charger can run 12 or 24v but will need to check.

As you have no large amp draw loads, and presumably no plans to add same, you should probably stick to 12v. Even if your furnace could run at 24v, I doubt your inverter will, and it's much easier to find 12v marine/auto accessories and appliances than 24v you may want in future. Going to 24v would make sense if you planned on expanding substantially in the near future.

Like Mcgivor, I think you might want to expand battery capacity. Assuming your 130ah estimate is accurate, you'll be using about 50% of capacity daily. Presumably thing might be higher at times depending on use, weather, etc., so that means you may end up drawing the bank down to well under 50% state of charge (SOC). The sweet spot in terms of battery life versus replacement cost we use for deep cycle batteries is around 50-75% SOC. Higher than 75% SOC means higher costs for batteries and also for charging sources with little benefit in most applications. Lower than 50% SOC means much shorter battery life, especially if the bank is allowed to sit at that SOC for long.

I used a small bank for several years while renovating, and it worked well because I was running the generator regularly for power tools anyway, so I charged the small bank pretty much daily. If that's the case for you, it may work for you too. Just be sure to charge the bank to at least 80% SOC before you leave, and avoid going to below 50% SOC.

To cut down on generator use and reduce the risk of taking bank down to far, another option would be to go with 2 strings of 2x 6v golf cart batteries. This type of battery is pretty widely available fairly cheap (~$100US/$135CAD). This would give you around 440ah @12v Panel charging would be on the low side, but should work for a weekend cabin as bank should get to fully charged during the week with no loads. 3x145w should give you around 25-30a @12v or about 6%. If the forecast is for lots of cloud after you leave, you should run the generator for an hour or two before you leave, so the panels can still get the batteries to full. Wiring 2 banks in parallel isn't so bad as long as you use beefy cables and make the parallel connection with the same (short) length of cable to a common point between banks. On my 12v bank I think I used 12" 4/0 cables bolted together and to a 5' 4/0 cable to inverter/charger/load busses.

Estragon · December 2016

mcgivor said:

If you convert to 24V you will not have 12V to run your furnace unless you get a DC DC converter, don't be tempted to tap off from one 12V battery !!! It WILL result in the death of one, if not both batteries

I'm not certain, but I think the Espar marine furnace on my boat will run at either 12v or 24v. I know the fridge does. Absolutely agree tapping 12v off a 24v bank is a really bad idea.

bc buck · December 2016

mike95490 said:

bc buck said:

... I read a article on a renewable energy web sight stating batteries wired parallel will loose 50% of there life. Said internal resistance will vary causing weaker battery to be undercharged. I have spent hours trying to find that article again with no luck. Installing batteries parallel seems to be common practice....

Just because it's common, does not mean it's correct. read this about parallel batteries, simple work-arounds
http://www.smartgauge.co.uk/batt_con.html

That smartguage link has some great info. Thanks

bc buck · December 2016

Estragon said:

To cut down on generator use and reduce the risk of taking bank down to far, another option would be to go with 2 strings of 2x 6v golf cart batteries. This type of battery is pretty widely available fairly cheap (~$100US/$135CAD). This would give you around 440ah @12v Panel charging would be on the low side, but should work for a weekend cabin as bank should get to fully charged during the week with no loads. 3x145w should give you around 25-30a @12v or about 6%. If the forecast is for lots of cloud after you leave, you should run the generator for an hour or two before you leave, so the panels can still get the batteries to full. Wiring 2 banks in parallel isn't so bad as long as you use beefy cables and make the parallel connection with the same (short) length of cable to a common point between banks. On my 12v bank I think I used 12" 4/0 cables bolted together and to a 5' 4/0 cable to inverter/charger/load busses.

Good post, I called Sams club and they do offer cart battery's. When I get info on specs I make a post.

softdown · December 2016

mike95490 said:

bc buck said:

... I read a article on a renewable energy web sight stating batteries wired parallel will loose 50% of there life. Said internal resistance will vary causing weaker battery to be undercharged. I have spent hours trying to find that article again with no luck. Installing batteries parallel seems to be common practice....

Just because it's common, does not mean it's correct. read this about parallel batteries, simple work-arounds
http://www.smartgauge.co.uk/batt_con.html

I like Method 3 the best by far. Interesting that this is so rarely discussed here. Good terminal posts? Hmmm.

Searched the net for 4/0 terminal posts and found nothing. Nothing even remotely close. Our host has plenty of terminal posts for much smaller cables from companies like Outback and MidNite.

Once again, you probably have to do it yourself to do it right. Smash a 3/4" copper pipe in a large vise then drill appropriate holes. Voila!

EDIT: Found this 4 cable terminal block with our host:

4 Port Dual Entry Insulated Power Distribution Block #6 AWG to 250 kcmil

$32.47

SKU: USAD2504

A 5th port may be needed for the cable to the inverter. What then?

The overwhelming majority of larger power distribution blocks seem to be geared for 12 volt car audio systems......and tap out at ~2awg. People run some pretty serious car stereos. For when everyone around you must feel your crappy music?

softdown · December 2016

Alright....just spent awhile studying distribution blocks for "solar cables" (4/0 is what comes to mind). Was surprised at the scarcity of offerings and the prices.

A professional distribution block unquestionably looks hefty and professional. Yet this is my suspicion/theory: Connect your cables with a bolt (insulate everything of course) and use the savings for good fuses.

Was forced to conclude that large distribution blocks are usually not employed.

Estragon · December 2016

I just used bolts and it seems to work fine. Just two strings in parallel though. I'd avoid doing more than two, but if I did I'd likely make a buss.

softdown · December 2016

Estragon said:

I just used bolts and it seems to work fine. Just two strings in parallel though. I'd avoid doing more than two, but if I did I'd likely make a buss.

The buss would seem like the right thing to do. Is there a way to beat the connectivity of a flattened copper pipe?....which (copper pipe) performs far better than even 4/0 cable.

I also max out at two strings. That is easy to do in the 48 volt, and even in the 24 volt, world.

I would also bet that most off grid applications may be 12 volt. One could argue that every 12 volt battery is a "string" in 12 volt applications. Or that each battery should be treated as a string.

Sure....it would be nice if everybody could afford solar batteries that weigh well over a 100 pounds/each. They either can't, or won't, for several reasons. So....they use a group of batteries. We see this almost every day here it seems. These are also people who took their solar efforts seriously enough to open an account here and post. Possibly the upper crust of the do it yourselfers....a somewhat scary thought in some ways.

Using a bolt as a buss is an absolutely gigantic improvement over the extremely common Method 1 found here: http://www.smartgauge.co.uk/batt_con.html

Shoot, I know an electrician that uses 12awg to connect his 12 volt batteries.

westbranch · December 2016

Look for car stereo distribution blocks (ebay) for an example of screw down blocks, lots for 12 volts..

softdown · December 2016

westbranch said:

Look for car stereo distribution blocks (ebay) for an example of screw down blocks, lots for 12 volts..

Oh yea.....and they max out at 0/0, mostly at 2awg. I use 4/0.

westbranch · December 2016

I guess you will have to build your own with some SS bolts and a piece of copper plate or?

Looking to set up new battery bank.

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