Invertor w/ Parallel Batteries Wiring

tommeyers

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I am going to extend the service time of my inverter by adding more batteries.

I have two 12v batteries in series as a set attached to the inverter. I intend to add a 2 more battery set that will be in series with each other and in aggregate in parallel with the other existing set.

The risk I introduce is if the battery sets are not "balanced" I will discharge good batteries through bad batteries; because eventually some become bad and the result is that I waste the life of my sets.

The solution is pretty simple: use a diode (and fuse) in each of the 2 battery sets. And ... that sounds simple. So I went to Bellon and 8a asking for the components and they could not help me. (Although the taught me how to say Diode in Spanish).

I am not surprised that batteries in this country are frequently connected in parallel without diodes. But, there must be someplace I can go to get the components (blocking diodes etc).

Your assistance please.
 

windeguy

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Jul 10, 2004
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A few points. How old are the original batteries? If more than a few months old it is a bad idea to add other batteries in parallel.

I have never seen any installation of batteries that use diodes in the DR, nor is it recommended in the user's manuals for the inverter chargers from Xantrex . Please explain to me the reason a diode (or diodes) would help "balance" the batteries when in parallel and explain where you are putting the diodes.
 

Space Ghost

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Mar 21, 2014
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It's Much More Complicated than a Diode or Two.

The risk I introduce is if the battery sets are not "balanced" I will discharge good batteries through bad batteries; because eventually some become bad and the result is that I waste the life of my sets. The solution is pretty simple: use a diode (and fuse) in each of the 2 battery sets.

The diodes in the wiring diagram you attached will indeed keep one bank of batteries from discharging to pull up another bank.

But that's not the primary issue.

The problem is that the inverter senses all banks as one when deciding whether or not the batteries need charging. If one bank requires more time to charge because its older the inverter will sense the voltage as not being sufficiently high, and continue to produce a slight overvoltage to complete the charge. In the meantime the newer bank which is already charged is being cooked while the older bank is topped off.

The blocking diodes can do nothing to prevent this.

The only solution would be to have multiple sensing and charging inputs from the inverter/charger to treat each bank individually. I have not seen such an inverter. Since the battery inputs to a Trace or other inverter is used for both discharge and charge it's not possible to separate the two functions, nor to distinguish which battery or which bank needs juice and which one does not.

The only way to do what you're suggesting that I can think of would be to home build a system that splits the banks and provides a charge for each, grid or solar based, then using the diodes to isolate the chargers, tie them together and use one large inverter (not inverter/charger) to supply the output A/C.

I have had to do something similar this month. A fancy new UPS for my office does not like the modified sine wave from my Trace inverter. I have 24V from the battery bank running through my office at a solar charger panel. I bought a 300W pure sine wave inverter for $70 to feed the UPS. The sine wave inverter is connected to two relays. When power fails, relay one immediately connects it to the 24VDC from the main battery bank, charged by the Trace. 5 seconds later on delay a second relay fires switching an A/C outlet from EdeNunca to the output of the sine wave inverter after it has had time to stabilize. The UPS is plugged into this outlet.

So when power fails it just sees a brief 5 second outage and goes back to happily charging from a pure sine wave A/C power source.
 

windeguy

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Jul 10, 2004
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With the inverter/chargers we use here you do not have a separate place to connect the "load" and "charger" connections as in that circuit. My suggestion is to forget about diodes and hook up the batteries as thousands of systems are used in the DR using as many parallel strings as you need (but the fewer the better due to the imbalance problems that do occur).

Be sure to take the positive and negative connections off the diagonally opposite corners of the battery bank (as is pointed out in diagram 6 of the Xantrex example diagrams) since that does tend to reduce the imbalances.
 

tommeyers

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Jan 2, 2012
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space ghost thanks. I understand better. It is good solution for supplying dc but does not address charging. Back to the drawing board for me!
I have seen manual bank switches. that wouldn't work for me i'm too lazy.
 

Space Ghost

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Mar 21, 2014
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No Problem

space ghost thanks. I understand better. It is good solution for supplying dc but does not address charging. Back to the drawing board for me! I have seen manual bank switches. that wouldn't work for me i'm too lazy.

I have been dealing with inverter power issues for the last month. Just yesterday we had to buy four new batteries because one battery in a 24v bank is dead. That means I have three good batteries I'll have to put on a maintainer while searching for a used one of the same age, and I probably won't be able to add that bank in with the new batteries, AND if I want to increase capacity I have to suck it up and buy more now while the new ones are new.

It's a HUGE waste and a HUGE PIA and so all of this has me thinking.

I am going to play and home build an a la carte system. Part 1) Either a 6V charger for each battery, or a 24V charger for each bank. Part 2) power relays to switch the batteries from individual chargers when street power is available to a combined 24v series-parallel wiring connected to an inverter when power fails, and 3) a 3600w pure sine wave inverter (not inverter/charger).

Each battery or each bank would be charged individually so that as long as the battery is good, it wouldn't matter if there are differences in charging times. Each battery would stop charging when it is charged, not continue to charge until all batteries in the bank are charged. In this way you could mix old and new batteries without fear of harming the new batteries. And with the added benefit of getting pure sine wave power instead of the modified sine wave most units here produce.

The replacement costs of having just one battery in a bank go bad a year or two after buying new ones would about pay for the whole thing.

I have some work to do getting specs on what is and isn't adequate as a charger, a quick search shows hundreds of interesting products like this:

G4 | Genius Battery Chargers

Anyone care to poke holes in the idea before I waste money on a science project?
 

tommeyers

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Jan 2, 2012
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Space Ghost: I like the way you think!! Google this: charge batteries in parallel and use in series. I found that yesterday. More diodes but simple too; (charger diodes were reversed relative to inverter diodes). Then if you separate the charge and from the discharge (inverter) and add a charger you will have the solution. Then add a bank monitor so you can spot bum banks and individual batteries.

(There are reasons why you and I are interested in doing something that 1000's of others don't do.)

Space Ghost: You have inspired me to think more about this. Thanks.
 

Space Ghost

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Mar 21, 2014
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Panel Meters

Then add a bank monitor so you can spot bum banks and individual batteries.

I already have digital panel meters for this. They cost $5 each. In the office one for each A/C phase, powered independently so it reads "0" when EdeNada goes out. A blue one for voltage incoming from the the solar panels, and a green one tied directly to the inverter banks showing the combined DC voltage in to the inverter.

I have just built a new panel for the casita with the inverter where I have eight green DC panel meters, tied across each battery terminal, a red one with total voltage, and a couple reading each A/C phase so while at the inverter I can see at a glance everything I need to know without picking up a meter. Had a tech out and his jaw dropped seeing it asking where I bought it. LOL.

BTW I drew up and costed out a system. Comes to about RD$25K without batteries. 4DPDT power relays with a 110VAC coil ($350ea). Each battery to common, NC to a 6V/12V charger ($1200), and NO wired in series (neg to pos) from relay to relay just like the batteries would normally be connected.

With power the batteries are being independently charged each by their own charger. Power fails, the relays disconnect the chargers and connect all batteries in series to a pure sine wave inverter ($12000-$16000) to supply A/C.

Repeat with as many banks as you want and never worry about different charging rates between batteries at one-time cost of maybe $1500/extra per battery.

Glad we solved that.

The problem living here is that technology marches forward while we get stuck just doing the same things over and over. The inverter technology is the same inverter technology in use when I came here 15 years ago. There are so many new products out there it seems you can build something off the shelf that works better if you just take the time to open your eyes and look around a little. You'd think there must be someone that builds all this into one box, but who cares, if you can do it with pieces?
 
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How about making a switch on a timer so the charger only detects/charges one side at a time? Or you could do it manually.
 

tommeyers

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I am seeing two paths: mechanical switch or a combination of a battery combiner and a battery isolator components and more. I am going to try the mechanical switch first (cheapest and easiest). I will switch between the two strings of batteries. Balancing problem solved; inverter time doubled.
 

Space Ghost

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I mostly want it to be hands off once installed. That rules out a plain switch. I also want the batteries charged intelligently which kills the idea of a timer that may leave one bank or the other under-charged. One advantage of an individual charger per battery (whether individual units or a intelligent bank charger) is that in that $30/per range many of them have new controller chips that allow some degree of battery repair and recovery, bringing back scaled electrodes and batteries that had been discharged down to as low as 1-2 volts (6vs12vdc). If so that would not only mean not tossing good batteries with the old, but a built in ability to fix automatically ones that might have been sold as scrap otherwise to whatever degree possible.
 

Olly

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Mar 12, 2007
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Tommewers,
This is always an interesting topic -which is basically how to extend the run time of your invertor versa the life of the batteries - in years . In your case you seem to have two twelve volt batteries in series to run a 24 volt invertor. You want to add another "bank" of batteries ( ie two Twelve volt ) to extend the time you have on the invertor. The Twelve volt batteries have a capacity of about 100 Amp hours so in parrallel you would have about 200 Amp hours.
From experience here if you have batteries that are around one year old it is possible to add them in parrallel without any problems. If they are older than that then you put the new batteries on in parrallel but with extended leads from the old. The old charge first and the small voltage drop from the charging leads to the new batteries "helps" stop the new batteries having an overcharging problems. On the system we have here the voltage drop on full charge was 160 Millivolts. This doesn,t sound much but it helps keep the new batteries from overcharging.

On the Discharge side unless you have a really bad battery it is not a problem as the old batteries will only go down to the "Bus Voltage" and stop discharging.

We have twelve batteries and FIVE years ago took on an experiment to see what happens when you mix batteries - new and old. The basic approach was to put all similar batteries in the same string. ( or bank) We now have one bank of two year old batteries, one bank on 8 month old batteries and one bank of survivors - one battery from the original lot 5 years old, one battery about 3 years old, one recivered battery the had "battery Viagra" as it was sulphated" and one from another osurce that was three years old.
These all measure good on a Battery Load tester. Currently we are getting over 16 hours on our batteries for a Villa that uses on average 18 kWh per day.
If you are looking for the " optimum" then go elsewhere. The Dr is not like that! If you are looking for workable system then add the batteries in parrallel using slightly longer connecting leads and you will not have any problems.
We have added solar helpers to the battery bank and start at 37 volts on the panels ( only 50 Watt ) and have a diode connected to stop discharge during the night. The Diode is a 50 amp 250 volt on availalbe at De KLancer. We have no heat sink on it but it works fine. The Solar helper saves about 30 kWh per month so 300 RD$so pays for itself as the panels were free from a lightning hit site.

The web sites you mention are interesting in that adding batteries in parrallel according to Trace "Can often lead to problems" .

The "Diode" solution is really for seperate Chargers and often used on Boats where the current source is an engine alternater.
You might want to look at your load and see what you really nead. The Twelve volt Battery solution is only good for small installations.

Hope this helps and we am sure we will get a lot of stick for saying this but we have the results of five years looking at this problem in situ in the DR and beleive it or not we have an ELECTRICAL ENGINEER on the Team!

Olly and the Team
 

Space Ghost

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Mar 21, 2014
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Great info from a direct trial. Funny how people who sell new batteries never suggest trying that ... :cheeky:
 

Olly

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Mar 12, 2007
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Tommeyers,
There is another aspect to this too. The new batteries you buy are only half charged in general and when you add them to an existing setup you need to have all the batteries at the same state of charge.
Suggest if you buy two new 12 volts Deep Cycle batteries then you charge them seperately on a batteriy charger to fully charged before adding them to the existing batteries in parrallel . Wait until the invertor has fully charged the existing batteries before adding the new ones as a new parrale string (or Bank).
Also be very careful when you connect them and make sure you do not short circuit any of the batteries when you are working on them.

Olly and the Team