Expanding existing system question?
northerner
Solar Expert Posts: 492 ✭✭✭✭✭✭
I'm looking at expanding an existing system which consists of 2 banks of 4, 6v L16 batteries (ie 8 total) giving me 24 volts, a 24 volt Outback inverter, and a Midnite Classic 150 charge controller.
I would like to double the number of batteries, add another inverter in series with the existing, and another charge controller. I could keep the second addition totally separate, except for the linked inverter to give me 2 legs of 120 volt (using an auto transformer).
Another option I was contemplating, was to place the two new battery banks in series to make 48 volts, but run each inverter off the separate banks. The advantage of this would be charging the larger battery bank at 48 volts which is more efficient. Disadvantages I can think of are unbalanced loading on each bank can lead to a slight imbalance with the charging. Also, the negative of only one bank (and corresponding inverter) can be connected to ground. So I'm thinking it's not a good way to go. Thoughts?
The batteries I have are almost a year old, but paralleling them would result in 4 separate strings in parallel. Not good. I'm thinking in hindsight that I should have went with a 48 volt system, but it's too late for that now.
I would like to double the number of batteries, add another inverter in series with the existing, and another charge controller. I could keep the second addition totally separate, except for the linked inverter to give me 2 legs of 120 volt (using an auto transformer).
Another option I was contemplating, was to place the two new battery banks in series to make 48 volts, but run each inverter off the separate banks. The advantage of this would be charging the larger battery bank at 48 volts which is more efficient. Disadvantages I can think of are unbalanced loading on each bank can lead to a slight imbalance with the charging. Also, the negative of only one bank (and corresponding inverter) can be connected to ground. So I'm thinking it's not a good way to go. Thoughts?
The batteries I have are almost a year old, but paralleling them would result in 4 separate strings in parallel. Not good. I'm thinking in hindsight that I should have went with a 48 volt system, but it's too late for that now.
Comments
-
Re: Expanding existing system question?northerner wrote: »I'm looking at expanding an existing system which consists of 2 banks of 4, 6v L16 batteries (ie 8 total) giving me 24 volts, a 24 volt Outback inverter, and a Midnite Classic 150 charge controller.
I would like to double the number of batteries, add another inverter in series with the existing, and another charge controller. I could keep the second addition totally separate, except for the linked inverter to give me 2 legs of 120 volt (using an auto transformer).
Another option I was contemplating, was to place the two new battery banks in series to make 48 volts, but run each inverter off the separate banks. The advantage of this would be charging the larger battery bank at 48 volts which is more efficient. Disadvantages I can think of are unbalanced loading on each bank can lead to a slight imbalance with the charging. Also, the negative of only one bank (and corresponding inverter) can be connected to ground. So I'm thinking it's not a good way to go. Thoughts?
I will try to answer a few of your questions:
The whole idea of connecting a pair of 24 volt inverters to a 48 volt battery bank is not worth exploring unless you will have only 240 volt loads. Even then it will not be a good idea for the grounding and other reasons you mention.
To produce 240 volts the two inverters will have to be from the same manufacturer and be designed to be linked together with one inverter synchronizing its output to the other. Using a transformer to get 240 volts instead is often less expensive and more stable.
You are right in being concerned about having 4 strings in parallel. Although some members say that it has worked fine for them with careful design and monitoring, others think it is too unlikely to work to justify the effort.
But for that kind of current and power capacity, it might be better for you to replace all of your batteries with larger 2-volt RE batteries so that you can have only one string of 12 batteries in series.SMA SB 3000, old BP panels. -
Re: Expanding existing system question?
Welcome to the forum.
The 48 Volt bank powering two 24 Volt inverters is not good for just the reasons you think.
If you need 240 VAC you can get it with the autotransformer without a second inverter. Unless you need more actual power you don't need a second inverter.
When it comes to adding Outbacks together, they have quite a large assortment of wiring diagrams available showing the many possible combinations, including series stacking for 240 (with or without transformer for balancing the legs) or parallel stacking for more Wattage on 120 (which can also then use the transformer to supply 240 if needed).
One problem you'll have any way is adding new batteries to old. This is generally not a good idea unless the batteries you have are fairly new and in top condition. Otherwise the old batteries will 'pull the new ones down' right away. How severe the results of this will be depends on just how much difference in actual condition there is.
You already know that if you increase the battery capacity you have to increase the charging capacity as well. -
Re: Expanding existing system question?
I have no problem with adding another inverter. I would like to hookup directly with an existing house panel, and 2 inverters will give me 60 amp service, a full 240 volts, and back up if one inverter fails.
The question is with the battery bank expansion. I'm starting to think it may be best to keep the banks totally separate and charge them separately, with separate controllers and panels. -
Re: Expanding existing system question?northerner wrote: »I have no problem with adding another inverter. I would like to hookup directly with an existing house panel, and 2 inverters will give me 60 amp service, a full 240 volts, and back up if one inverter fails.
The question is with the battery bank expansion. I'm starting to think it may be best to keep the banks totally separate and charge them separately, with separate controllers and panels.
Just off the top of my head, it seems more wasteful of energy and flexibility to have two separate arrays and two separate battery banks, since you do not know how well the load will be balanced between phases in your current panel. You may find it is the time to just let go of your old batteries or keep them as a backup energy source, kept floated but not used, rather than lock yourself in for a longer time to a poor battery configuration.
PS: Have you done a load test or better a capacity test to see just what shape your current batteries are in? Many people find that they abuse and murder their first set of batteries. From your current choice of equipment that is less likely in your case, but I have to ask the question. :-)SMA SB 3000, old BP panels. -
Re: Expanding existing system question?Just off the top of my head, it seems more wasteful of energy and flexibility to have two separate arrays and two separate battery banks, since you do not know how well the load will be balanced between phases in your current panel. You may find it is the time to just let go of your old batteries or keep them as a backup energy source, kept floated but not used, rather than lock yourself in for a longer time to a poor battery configuration.
PS: Have you done a load test or better a capacity test to see just what shape your current batteries are in? Many people find that they abuse and murder their first set of batteries. From your current choice of equipment that is less likely in your case, but I have to ask the question. :-)
My batteries are near new (less than a year old) so to throw them away is just not feasible. They are Trojans and have an expected life of close to 10 years if looked after properly. The batteries are still in good condition to my knowledge.
If the banks are kept separate, the charging will still be kept up, just like a standalone system. The only complication to work out is the charging from a generator if only one generator is used. Some form of switching would be needed to charge the appropriate bank. -
Re: Expanding existing system question?
Less than a year old on the batteries is good; there shouldn't be any trouble with adding to them. -
Re: Expanding existing system question?
Would you be getting a second set of panels to go with the second charger? Or would you split the current panel array in half?northerner wrote: »
If the banks are kept separate, the charging will still be kept up, just like a standalone system.
What I am concerned about there is whether you have enough panel for 1/2 of it to charge one battery bank which has taken most of the loads.
You also did not mention what the size of your current array is. If it was originally oversized for your batteries, you may be just fine as long as you can get a C/10 charge rate for each bank from it.SMA SB 3000, old BP panels. -
Re: Expanding existing system question?Cariboocoot wrote: »Less than a year old on the batteries is good; there shouldn't be any trouble with adding to them.
Only down side is having 4 strings in parallel. Deciding whether to go that route or just keep them separate. -
Re: Expanding existing system question?Would you be getting a second set of panels to go with the second charger? Or would you split the current panel array in half?
What I am concerned about there is whether you have enough panel for 1/2 of it to charge one battery bank which has taken most of the loads.
You also did not mention what the size of your current array is. If it was originally oversized for your batteries, you may be just fine as long as you can get a C/10 charge rate for each bank from it.
I didn't mention that I will also be expanding the solar array, so no problems there. -
Re: Expanding existing system question?
From the energy viewpoint, it is certainly more economical to have one bank.
From reliability standpoint, two banks will not help much. You already have two strings, so if a battery fails you can disconnect the second string and live with one string for a while.
If I were you, I would sell the inverter and would buy a new 48V 240V inverter. This would let you keep a single bank and would give you a support for 240V. Also, 48V system is likely to be more efficient. -
Re: Expanding existing system question?From the energy viewpoint, it is certainly more economical to have one bank.
From reliability standpoint, two banks will not help much. You already have two strings, so if a battery fails you can disconnect the second string and live with one string for a while.
If I were you, I would sell the inverter and would buy a new 48V 240V inverter. This would let you keep a single bank and would give you a support for 240V. Also, 48V system is likely to be more efficient.
Very good plan.
A Magnum 4448 is about $350 more than an Outback 3524. No transformer, easier array/battery set up, slightly more efficient. Some difficulty with handling the higher Voltage (fuses/breakers/disconnects) but not insurmountable.
If you don't need the 7kW potential it would work fine. -
Re: Expanding existing system question?
From a reliability stand point, I was thinking it would be better to have 2 inverters, rather than just one. It would be potentially devastating to have an inverter go down in the middle of winter, when a furnace must keep running. Temperatures here can go below -40C.
I am not too fond of the Magnum Inverters. Their surge capacity is not as good as the Xantrex and Outback inverters, and they appear to be more susceptible to problems with static (ie nearby lightning strikes) after all the reports I have read from other users. I'm not sure if this is the case, but I do live in an area that is frequented with electrical storms in summer.
From an efficiency standpoint, all is not lost. In winter, spring and fall, the heat that is lost due to inefficiency, will help to heat the home. In summer, there will be a surplus of power anyway. -
Re: Expanding existing system question?
That's actually not a bad idea to sell the inverter and switch to 48 volts. I would likely stay with the Outback, however. -
Re: Expanding existing system question?northerner wrote: »That's actually not a bad idea to sell the inverter and switch to 48 volts. I would likely stay with the Outback, however.
The Outback radian has some nice features (like generator support) that you won't get by stacking two fx inverters. Of course, you won't get inverter redundancy with the radian. Just wondering about redundancy here: if lightning took out one inverter, wouldn't it also take out the other?
Another way for you to expand is to run two completely separate systems. Keep your existing system and build another 24 or 48 volt system. Use a step-up transformer on one system for the 240 volts. Depending on your loads, you may need to divide your circuit breaker panel into two distribution panels.
--vtMaps4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i -
Re: Expanding existing system question?
It's funny how perceptions are made about different products. I go down to a Inverter Service Center often scavenging for parts and picking up repairs, from what I get from their Bench guys is that Magnum Inverters are the ones they have the least problems with and they sell and service all brands including OutBack, Xanterx and Magnum. I don't know if lightening strikes have a way to discriminate between brands, I wouldn't think they would.
. -
Re: Expanding existing system question?The Outback radian has some nice features (like generator support) that you won't get by stacking two fx inverters. Of course, you won't get inverter redundancy with the radian. Just wondering about redundancy here: if lightning took out one inverter, wouldn't it also take out the other?
Another way for you to expand is to run two completely separate systems. Keep your existing system and build another 24 or 48 volt system. Use a step-up transformer on one system for the 240 volts. Depending on your loads, you may need to divide your circuit breaker panel into two distribution panels.
--vtMaps
Your absolutely right. Lightning could take out both inverters. At least that would happen in the summer when it's not as critical to lose power.
I am putting a good effort into surge arresting, so I'm hoping (fingers crossed) that I never have a run in with lightning. I likely won't have a problem other than with a direct or near direct strike, which is very difficult to protect from.
Heat can also affect the lifespan of a product, causing problems with reliability. Running 2 inverters (and sharing the loads) and running them well below their capacity will keep them running cooler. So with 2 units, you have redundancy and share the work load, which should lead to a long, reliable life. -
Re: Expanding existing system question?Blackcherry04 wrote: »It's funny how perceptions are made about different products. I go down to a Inverter Service Center often savaging for parts and picking up repairs, from what I get from their Bench guys is that Magnum Inverters are the ones they have the least problems with and they sell and service all brands including OutBack, Xanterx and Magnum. I don't know if lightening strikes have a way to discriminate between brands, I wouldn't think they would.
Reading online, I see many issues with Magnum's going down. I guess it really depends on how and where they are run. I talked to one fellow who installs systems and deals with problems in the field, and he has yet to see a major failure with an Outback inverter. Plus as mentioned, the Magnum doesn't have the surge capacity of some of the other units. -
Re: Expanding existing system question?
Whatever works for you, makes us all happy.:cool:northerner wrote: »Reading online, I see many issues with Magnum's going down. I guess it really depends on how and where they are run. I talked to one fellow who installs systems and deals with problems in the field, and he has yet to see a major failure with an Outback inverter. Plus as mentioned, the Magnum doesn't have the surge capacity of some of the other units. -
Re: Expanding existing system question?Blackcherry04 wrote: »It's funny how perceptions are made about different products. I go down to a Inverter Service Center often savaging for parts and picking up repairs, from what I get from their Bench guys is that Magnum Inverters are the ones they have the least problems with and they sell and service all brands including OutBack, Xanterx and Magnum.
The number of units having problems not only depends on the brand, but also on the number of installations. I guess, there are much less Magnums out there than Outbacks or Xantrexes. So, this statistics may not be entirely correct.
I actually wanted to buy Magnum first and I probably would if they had a 6kW model. -
Re: Expanding existing system question?northerner wrote: »From a reliability stand point, I was thinking it would be better to have 2 inverters, rather than just one. It would be potentially devastating to have an inverter go down in the middle of winter, when a furnace must keep running. Temperatures here can go below -40C.
If you use them split-phase then only one inverter will run the furnace (assuming it is 120V). If this inverter fails, the other one will not help. You will have to rewire to make the furnace work.
You probably have a generator. If your inverter fails, you can run the furnace from the generator while you're replacing your inverter.
I'm worrying about furnace operations too. See this thread. However, the probability that the furnace fails is much greater in my mind that the probability that inverter fails.northerner wrote: »Heat can also affect the lifespan of a product, causing problems with reliability. Running 2 inverters (and sharing the loads) and running them well below their capacity will keep them running cooler. So with 2 units, you have redundancy and share the work load, which should lead to a long, reliable life.
Usually your peak loads are much higher than your usual loads. An inverter sized to handle peak loads will not heat up during regular opearations. -
Re: Expanding existing system question?
With a stacked pair of Outbacks, if it is the Master that fails the Slave will shut down also so there is no redundancy to provide power. The Radian can lose one or two of its internal sections and keep going, but it's the only one that can.
Lightning is such a random thing that you can not rely on any statistics gathered as a result of such failures. They mean nothing.
Magnums, btw, can also be stacked. -
Re: Expanding existing system question?Cariboocoot wrote: »With a stacked pair of Outbacks, if it is the Master that fails the Slave will shut down also so there is no redundancy to provide power. The Radian can lose one or two of its internal sections and keep going, but it's the only one that can.
Lightning is such a random thing that you can not rely on any statistics gathered as a result of such failures. They mean nothing.
Magnums, btw, can also be stacked.
You easily could keep a furnace inverter going with a transfer switch. That's a good point about the master failing however. One would have to be there to manually disconnect the failed master inverter, and make the slave inverter run independent, temporarily. But at least you wouldn't have to wait weeks while the failed inverter is out for repair.
As for the gathered statistics, they don't necessarily mean anything, right. However, when I am reading about multiple failures out in the field, in areas that are active with electrical storms, then there is reason for concern. You do have to look at what is really happening. Perhaps, there are others that are not protecting and/or grounding their systems properly. -
Re: Expanding existing system question?northerner wrote: »As for the gathered statistics, they don't necessarily mean anything, right. However, when I am reading about multiple failures out in the field, in areas that are active with electrical storms, then there is reason for concern. You do have to look at what is really happening. Perhaps, there are others that are not protecting and/or grounding their systems properly.
Protection is definitely part of the issue, but even with it lightning tends to be highly random in its effects. I would distrust any stats that say "Brand 'A' is subject to more failings due to lighting" because of this. It could simply be that more people install that brand without arrestors or its more popular in heavily struck areas.
As far as in normal use goes, there's little quality difference apparent amongst the top name brands. -
Re: Expanding existing system question?Cariboocoot wrote: »The Radian can lose one or two of its internal sections and keep going, but it's the only one that can.
If the Radian lost one or two of it's internal sections, it would still have to be sent out for repair. This would mean waiting for weeks without your inverter, or using it with only part of it's capacity. If you have 2 inverters and one fails, you can send the failed unit out, and still have a working system. You would want to design your system to have all the essentials on one inverter leg. If that inverter fails, you could swap inverters by switching wires or through using a transfer switch. -
Re: Expanding existing system question?northerner wrote: »If the Radian lost one or two of it's internal sections, it would still have to be sent out for repair. This would mean waiting for weeks without your inverter, or using it with only part of it's capacity. If you have 2 inverters and one fails, you can send the failed unit out, and still have a working system. You would want to design your system to have all the essentials on one inverter leg. If that inverter fails, you could swap inverters by switching wires or through using a transfer switch.
They understand this. Most likely, you can arrange for replacement inverter to be sent to you first. For example, Xantrex did that when I needed inverter replacement. -
Re: Expanding existing system question?They understand this. Most likely, you can arrange for replacement inverter to be sent to you first. For example, Xantrex did that when I needed inverter replacement.
Ok, but not necessary if you have a 2nd inverter. -
Re: Expanding existing system question?
How critical is the load? How much redundancy do you really need? How much can you afford?
Most of the time when an inverter fails it is due to "outside influence" (lightning, shorts, overloads, incorrect input Voltage, even bugs crawling inside) and with two installed side-by-side what happens to one will likely affect the other as well.
And remember that a brand new inverter sitting in a box on your shelf waiting to be installed can also drop dead. Meanwhile the warranty is still ticking down.
By the same token, many of us have some quite old inverters kicking around that still work. You can't predict everything. -
Re: Expanding existing system question?Cariboocoot wrote: »How critical is the load? How much redundancy do you really need? How much can you afford?
Most of the time when an inverter fails it is due to "outside influence" (lightning, shorts, overloads, incorrect input Voltage, even bugs crawling inside) and with two installed side-by-side what happens to one will likely affect the other as well.
And remember that a brand new inverter sitting in a box on your shelf waiting to be installed can also drop dead. Meanwhile the warranty is still ticking down.
By the same token, many of us have some quite old inverters kicking around that still work. You can't predict everything.
I'm not so concerned about up front cost as I am about long term cost effectiveness and overall reliability. The nemesis of all electronic equipment is heat and power surges. If you can keep both of these to a minimum, then you should have a good reliable system that will give you years of trouble free service. With 2 inverters load sharing, you will minimize overloading and overheating problems. -
Re: Expanding existing system question?Cariboocoot wrote: »... even bugs crawling inside ...
My Xantrex definitely has bugs. I hope they're not crawling. LOL. -
Re: Expanding existing system question?
Look at it another way:
The purpose of the expansion is;
1). to get 240 VAC?
2). to get additional power capacity?
3). to provide back-up power in the even of an inverter failure?
4). all of the above?
If #1, it's easier and cheaper to just get an autotransformer for the 240 Volt load(s).
If #2, you pretty much have to add the second inverter or else switch out to a bigger unit.
If #3, you could buy a 'reserve' inverter that would handle the essential power needs while the main was down. It would not necessarily have all the abilities but would cost less.
If #4, you're back at doubling up on the Outback.
Categories
- All Categories
- 222 Forum & Website
- 130 Solar Forum News and Announcements
- 1.3K Solar News, Reviews, & Product Announcements
- 191 Solar Information links & sources, event announcements
- 887 Solar Product Reviews & Opinions
- 254 Solar Skeptics, Hype, & Scams Corner
- 22.3K Solar Electric Power, Wind Power & Balance of System
- 3.5K General Solar Power Topics
- 6.7K Solar Beginners Corner
- 1K PV Installers Forum - NEC, Wiring, Installation
- 2K Advanced Solar Electric Technical Forum
- 5.5K Off Grid Solar & Battery Systems
- 424 Caravan, Recreational Vehicle, and Marine Power Systems
- 1.1K Grid Tie and Grid Interactive Systems
- 651 Solar Water Pumping
- 815 Wind Power Generation
- 621 Energy Use & Conservation
- 608 Discussion Forums/Café
- 302 In the Weeds--Member's Choice
- 74 Construction
- 124 New Battery Technologies
- 108 Old Battery Tech Discussions
- 3.8K Solar News - Automatic Feed
- 3.8K Solar Energy News RSS Feed