Bank Wiring

[ChrisOlson]

I have 24 Rolls T12-250's, 24 volt system.  I have pairs wired series, then parallel two series pairs, and that group of four batteries has a #2 positive and negative going to the bus.

I got 12 more T12's at a really good price and am wrestling with how to add them in to my bank.  How would the battery experts do it?  I can either wire them the same, in groups of four - or I can add a pair to each of the six groups I have now.

The six #2's feeding the bus can already deliver way more amps than my inverters can draw.  So it seems like a waste of copper cable to connect three more groups of four with #2, because then I'd have nine #2 positives and nine #2 negatives going to the bus from the battery bank.
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Chris

[bob g]

just drop them off at my place, and get on with life



surely you can't be bothered with something this complex, right?



only joking

sure would like to have them though, as i am just about ready to put a bank to work

bob g

[ChrisOlson]

sure would like to have them though, as i am just about ready to put a bank to work

Well Bob, I think I'd like to get at least 10 years or so of use out of them before I drop them off at your place   

We put in the first 24 batteries in August - replaced our entire bank, which was 7 years old.  It's amazing how much power you can waste charging worn out batteries.  We can work the living snot out of the new bank and it takes two cloudy days with no wind to get it much below 25.0 volts.

At any rate, I've heard that it's not a good idea to have more than four batteries in a parallel hookup.  So I'm wondering if it will make a difference if I put two more on each group I already have, and parallel them with the rest of the batteries there instead of at the bus, being I already have enough copper from the bank to the bus to handle the amp load.
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Chris

[ghurd]

Keep each string the same.  Old with old.  New with new.

Do not mix new and old in the same series string.

[ChrisOlson]

Being the T12's are 12 volt, right now I have 12 pairs of batteries in series.  What I have done is parallel two of those series strings (let's call this a Group), then run #2 cables from that four battery Group to the bus.  So as it is right now there is six positive cables and six negative cables going from the bank to the bus (6 series/parallel Groups).

When I add the 12 new batteries I just got, I will form six more series strings using those batteries.  So the two month old ones and the newest ones will not be mixed in the same series string.

But what I was wondering was, is if it is best to connect the new ones in Groups (which will mean three more Groups) and run #2 cables from the Groups like I have done with the other ones.

OR -

Simply add the new series strings to the present Groups, which will then become six battery Groups.

The first way, there would be one parallel connection in each Group with nine groups paralleled at the bus.

The second way there would be two parallel connections in each Group (six batteries per Group), and there would still be six Groups paralleled at the bus.

I guess I can't see how it would make any difference where the parallel connections are made between the series strings.  But in the online battery bank designers I've looked at for 12 volt batteries and a 24 volt system, it shows each series string should have dedicated cables to the bus (or inverter).
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Chris

[Lloyd]

Being the T12's are 12 volt, right now I have 12 pairs of batteries in series.  What I have done is parallel two of those series strings (let's call this a Group), then run #2 cables from that four battery Group to the bus.  So as it is right now there is six positive cables and six negative cables going from the bank to the bus (6 series/parallel Groups).

When I add the 12 new batteries I just got, I will form six more series strings using those batteries.  So the two month old ones and the newest ones will not be mixed in the same series string.

But what I was wondering was, is if it is best to connect the new ones in Groups (which will mean three more Groups) and run #2 cables from the Groups like I have done with the other ones.

OR -

Simply add the new series strings to the present Groups, which will then become six battery Groups.

The first way, there would be one parallel connection in each Group with nine groups paralleled at the bus.

The second way there would be two parallel connections in each Group (six batteries per Group), and there would still be six Groups paralleled at the bus.

I guess I can't see how it would make any difference where the parallel connections are made between the series strings.  But in the online battery bank designers I've looked at for 12 volt batteries and a 24 volt system, it shows each series string should have dedicated cables to the bus (or inverter).
--
Chris

Hi Chris,,

I have a couple of Q's.

 1. What is your 48 hr load..ie amp draw from the bank?

 2. What is your charge rate capable for 24 hrs?

 3. On a safety note, those bats are capable of a short circuit discharge of 5 times the rated amp hr of the total of the bank...I don't think I would be installing #2 cables.   I always size for a maximum of less then 3% voltage drop of the greater, of the amp draw or charge source, and then up size the cable to an overhead of 5 times the amp hr of the bank, which ever is the greatest.

Without knowing the load, but just from what I've read so far, I might consider a dual bus, and use one bank for 48 hr loads, while the other bank is in the charge cycle, and then alternate, the banks. It can even be done on a time regulation.

Sometimes a bigger is not always better

lloyd

[ChrisOlson]

1. What is your 48 hr load..ie amp draw from the bank?
 2. What is your charge rate capable for 24 hrs?

The 48 hour load is about 30,000 watt-hours.  The maximum continuous charge rate they would see is 300 amps.

And yes, I know about the amp delivery capacity, however, each #2 cable going to the bus has a 150 amp ANL inline fuse.
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Chris

Edit:  Lloyd, I may not have answered your questions correctly.  So I'd better clarify.  The above number I gave you for 48 hr load is the typical amount of discharge that has to be recovered after a couple bad days of cloudy weather with no wind.

Looking back thru my power logs to determine the 24 hour charging rate, our average is 29,200 watt-hours per day over the whole year.  However, in summer both discharge rate and charging rate is lower because of longer days and less wind.  If I take the summer months out our average 24 hour charging rate is 31,060 watt-hours and our average 48 hour load is 66,000 watt-hours.  The generator tends to run more in the winter, and when it starts, the inverters charge the bank at 300 amps initially, then tapers the charge off as the batteries fill up.

So the actual full load for 48 hours would be 66,000 watt-hours if there was no power at all for two days and we strictly ran on batteries.  However, that has never happened because one of two things occurs - either we get some solar power even on a cloudy day, or the generator starts.

[Lloyd]

1. What is your 48 hr load..ie amp draw from the bank?
 2. What is your charge rate capable for 24 hrs?

The 48 hour load is about 30,000 watt-hours.  The maximum continuous charge rate they would see is 300 amps.

And yes, I know about the amp delivery capacity, however, each #2 cable going to the bus has a 150 amp ANL inline fuse.
--
Chris

Edit:  Lloyd, I may not have answered your questions correctly.  So I'd better clarify.  The above number I gave you for 48 hr load is the typical amount of discharge that has to be recovered after a couple bad days of cloudy weather with no wind.

Looking back thru my power logs to determine the 24 hour charging rate, our average is 29,200 watt-hours per day over the whole year.  However, in summer both discharge rate and charging rate is lower because of longer days and less wind.  If I take the summer months out our average 24 hour charging rate is 31,060 watt-hours and our average 48 hour load is 66,000 watt-hours.  The generator tends to run more in the winter, and when it starts, the inverters charge the bank at 300 amps initially, then tapers the charge off as the batteries fill up.

So the actual full load for 48 hours would be 66,000 watt-hours if there was no power at all for two days and we strictly ran on batteries.  However, that has never happened because one of two things occurs - either we get some solar power even on a cloudy day, or the generator starts.

Chris,

I am assuming that you mean 2/0 cable instead of #2...tell me I'm right!

You're well above the over current fault with  the ANL fuse, NEC requires a Class T fuse for that kind of OCP.

Man you use a lot of power, how many households are you powering?

Lloyd

[ChrisOlson]

I am assuming that you mean 2/0 cable instead of #2...tell me I'm right!

You're well above the over current fault with  the ANL fuse, NEC requires a Class T fuse for that kind of OCP.

Man you use a lot of power, how many households are you powering?

No, it's #2.  There's six positives and six negatives going from the bank to the bus, all #2 cables, and each positive cable has a 150 amp ANL fuse on it at the batteries.  So the total fused amps to the bus is 900.  The inverters can pull about 375 if they're at full load (dual Xantrex inverters, 120/240 split phase).

We power just our house.  We lived with junk for 7 years, all the while our daughter was in college.  When she graduated and we no longer had all the college bills to pay we made a lot of upgrades to our system in the past year so we can live like "normal" people for a change.  All our stuff is electric - 240 volt electric range, 240 volt clothes dryer, dual 240 volt 55 gallon water heaters, etc..  We just about burned our house down several years back due to a malfunctioning gas valve on a water heater.  Since then, my wife will not have a gas appliance in the house.

When we get a lot of power and we got 100 gallons of hot water my wife will wash several loads of clothes and dry them.  She tends to do more baking with the electric range when we got power.  I got a machine shop and most of my machining equipment is 240 volt, so I tend to use a lot of power too.  I got the inverters set to bring the generator online if the total load is over 32 amps (7.5 kW) to help out with the heavy load.

It all adds up when you have a totally electric home.  And we have added more solar panels and more powerful turbines (three of them), but it seems that the more power we add, the more places we find to use it up.  No matter how much power we make it seems the batteries can never quite keep up.  So I think the 12 extra ones I got will help out a lot.
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Chris

[Lloyd]

Chris,

How do monitor amps in and out of the banks.

I am assuming you have one dc bus and both inverters are tied to a single bus.

How are you controlling charge source into the banks from 3 wind gennys, and the solar panels?

When running the AC gen are the inverters also charging the bank?

Have you measured your voltage drop at each battery, the bus, and at the inverters when you have a major amp load running?

One thing about running multiple banks paralleled at the bus, as opposed to running parallel banks tied singly to the bus w/pos & neg coming from opposite ends, some of the bats will do lazy work while the stoutest will do most the work, then the charge regime tends to create cell imbalance among the 3 different banks. This is especially at issue when you have amp loads that approach or exceed the pukert rate of the bank.

I would be curious of what the individual bats read for voltage and V/drop during heavy discharge current events.

I really thinking that you might be better served by having 2 separate banks for the kind of loads, and the battery count you now have with the addition of the 12 new bats.

I'm still not comfortable with using #2, nor the ANL fuses, I have measured a huge voltage dorps across the ANL fuse, a class t fuse has almost no voltage drop. Also I'm thinking you may be getting a serious voltage drop across the #2 during heavy current discharge events.

As a singular bank, I'm thinking that the additional 12 bats, is going to be questionable.

Lloyd

[Lloyd]

One other thing to consider, would be using gas safely for cooking and cloths drying. And certainly that is possible especially if you use a solenoid valve at the tank, that only allows gas to flow when there is a consumer on line, then tie that together with a gas sniffer placed at the consumers, that will automatic shut off the gas in the event of a leak.

Lloyd

[ChrisOlson]

Hi Lloyd,

Boy, I'll try to answer all this the best I can.

I have two Morningstar MPPT controllers on the solar arrays that keep track of their power.  I have a Doc Wattson with an external shunt on each wind turbine.  I have a regular old utility kWh meter (an old one with gears and the big wheel in it) between the inverters and the main panel.  That old meter does not have the dials on it - it has numbers on it like a car speedometer and it only shows our usage in increments of 10 kWh.

On the voltage drop issue, the wires from the bank to the bus are only about 4-5 feet long.  At the full 375 amps that the inverters can draw, there's only a little over 60 amps flowing in each of the #2 wires, which is well within the safe limits for #2 cable at 4-5 feet.

The wires to the inverters are a little longer - about 10 feet.  Those come from the bus and are 4/0.  All the turbines and the solar arrays feed the bus.

Voltage control on the bank is done with two methods - I have Morningstar MPPT controllers on both solar arrays, which handle bulk, absorption and float charging.  And I have a Morningstar RD-1 Relay Driver that turns on water heating elements in the water heaters to control excess power from the turbines.  The primary water heater's bottom 2,500 watt element is on all the time and has a thermostat on it set at 125 degrees.  That provides us with 55 gallons of water at 125 degrees at all times.  The top 2,500 watt element in that heater is turned on by the RD-1 if the bank reaches 30.0 volts and the thermostat on that element is set at 170 degrees.  The top element (also 2,500 watts) in the water pre-heater comes on at 30.5 volts and its thermostat is set at 125 degrees.  The bottom element (2,500 watts) in the pre-heater comes on at 31.0 volts and its thermostat is set at 170 degrees.  If both water heaters are hot and no auxiliary heating load available (happens very rarely) I got a second RD-1 that shuts the solar arrays and turbines down in stages starting at 31.7 volts.  It shuts the solar arrays down first to prevent the open voltage on the arrays going over 150 volts into the MPPT controllers, then it shuts the turbines down.  When the voltage comes back down to safe levels, then it fires the turbines and solar arrays back up.

I have never measured the voltage at the batteries with the inverters fully loaded.  I just go by what the inverters say they see for voltage and I know I can load them at 7.5-8 kw and with a fully charged bank the voltage stays above 24.  The inverters show actual voltage and compensated voltage, and I always look at the actual voltage.

Yes, when the gen is running it uses the inverter's chargers to charge the bank.

Every two months for the last seven years I fully charge the batteries on a poor power day with the generator, then pull each battery out and test it and service it.  I leave the house on gen power so there's no load on the inverters or bank, then I put a piece of masking tape on the battery and hook up my Sun AVR to it.  I record the at-rest voltage, apply a 25 amp load for three minutes and record the loaded voltage, then let the battery recover for one minute and record the at-rest voltage on that piece of tape.  The numbers I like to see, respectively are 12.85, 12.35, and 12.65.  That tells me I have a healthy battery.  I just serviced our new bank for the first time about a week ago.  Every battery was just about dead on the nuts perfect.  None of the readings varies by more than about .03 volts between the different batteries.  That tells me after two months in service they're all pretty equal and there's nothing bad happening with my wiring system to get them out of balance.

I'd really like to keep all the batteries in one bank to simply it.  Having to manage two banks would be a pain.  If it's best to connect the new ones like I got the old ones connected, I'll just buy the extra wire to do it.  I was just wondering if that was necessary, or if could add them in pairs to the six groups I already have.  I got these 12 batteries for $310 each, including truck freight to my door.  For that price, and the additional 16,000 watt-hours they can store pulling them down to 50% SOC, I figured I couldn't go wrong.  And it will improve my heavy load times like when my wife runs the clothes dryer because each battery doesn't have to deliver as many amps.  The amp-hours a battery can deliver at light loads is a lot more than what it can do at heavy loads.  So with the additional 12 batteries I figured that at 1.5 kW nominal load each battery only has to deliver 3.5 amps to the inverters.  At that amp draw the 36 batteries will supply 1.5 kW nominal for about two days and still be above 50% SOC.  I NEVER draw my batteries below 50%.  If the loaded voltage drops below 24 for more than two hours, the inverters bring the gen online.

So my thoughts were that by adding the extra batteries that it won't work the bank as hard, won't as deeply discharge them, and they'll last longer.
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Chris