Inverters

lockwood

My question is :
If I have two inverters one is a 3000Watt 24V DC impute and the other is 2000 Watt 12V DC impute and both with a 110v AC output.
Can I parallel the two Inverters on the output, 110V AC side so that way I have a line with more power.
Thanks.
Joe

ChrisOlson

Re: Inverters

Hi Joe,

No - you will need to power separate panels with them. The sine waves of both inverters have to be synchronized to run two inverters in parallel. This usually requires a "stacking cable" so the inverters can communicate with one another and provide that necessary synchronization. I doubt that two inverters that have different input voltages are stackable.
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Chris

lockwood

Re: Inverters

ChrisOlson wrote: »

Hi Joe,

No - you will need to power separate panels with them. The sine waves of both inverters have to be synchronized to run two inverters in parallel. This usually requires a "stacking cable" so the inverters can communicate with one another and provide that necessary synchronization. I doubt that two inverters that have different input voltages are stackable.
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Chris

Hi Chris
Thanks for the fast response.
OK, since I can not do that here is my next question:
I have a bank of 4 12v batteries, series parallel to give me 24v DC connected to a 3000 watt inverter, can I had another bank of batteries, series parallel 24v DC to the same inverter.
Thanks.
Joe

techntrek

Re: Inverters

Paralleling batteries usually requires that they are the same age and size from the start.

lockwood

Re: Inverters

techntrek wrote: »

Paralleling batteries usually requires that they are the same age and size from the start.

So what can I do if I need more power? another words if I need my bank of batteries to last me longer time? more solar panels and more batteries, right?

ChrisOlson

Re: Inverters

lockwood wrote: »

Hi Chris
I have a bank of 4 12v batteries, series parallel to give me 24v DC connected to a 3000 watt inverter, can I had another bank of batteries, series parallel 24v DC to the same inverter.

Yes, that you can certainly do that. I noticed the comment about battery age. Batteries in parallel can be any age or any size. You can parallel a 12 volt motorcycle battery with a 8D if you want, and nothing bad will happen.

However, batteries in series must be the same age and of the same level of overall health. If you series an old battery with a new one, the new one will more than likely have more capacity than the old one. So when you charge them in series the internal resistance of the old one is going to come up faster than the new one - with the end result that they will be out of balance and the new one will get deficit charged. On a 24V system the old one might hit 15.0 volts while the new one is only at 13.0 (still in bulk stage) and the system charging voltage is 28.0
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Chris

BB.

Re: Inverters

I always suggest that people start with their loads/power needs... Then design the battery bank to support those loads (Watts, Watt*Hours, battery voltage, etc.).

Once you know what battery bank you will be using and how many Watt*Hours per day (and how much sun for your location), then we can define the solar array, support hardware, backup genset AC charger, etc...

Or, you start with a battery bank, define the maximum AC inverter and Watt*Hours of load it will support. And the size of solar array needed to properly recharge the battery bank.

A "balanced" system will be the most cost effective and reliable solution. If you start with bits and pieces, it is difficult to get to a system that will support the loads you need.

For example, 3-5kW of inverters off of 4 golf cart batteries is not really practical of an off grid cabin use... 4x 220 AH at 12 volt batteries will supply about 9kWH of power... Put a 5kW inverter with full load on that, and you will probably bring the battery bank to dead in 1-2 hours.

Start with your load requirements first (and type of use: daily, seasonal, emergency backup, etc.)--Then we can help with the supporting equipment and get a system that (hopefully) will meet your needs.

-Bill

ggunn

Re: Inverters

lockwood wrote: »

My question is :
If I have two inverters one is a 3000Watt 24V DC impute and the other is 2000 Watt 12V DC impute and both with a 110v AC output.
Can I parallel the two Inverters on the output, 110V AC side so that way I have a line with more power.
Thanks.
Joe

Only if the inverters are grid tied or have another way of phase matching their output.

vtmaps

Re: Inverters

lockwood wrote:

I have a bank of 4 12v batteries, series parallel to give me 24v DC connected to a 3000 watt inverter, can I had another bank of batteries, series parallel 24v DC to the same inverter.

ChrisOlson wrote: »

Yes, that you can certainly do that. I noticed the comment about battery age. Batteries in parallel can be any age or any size. You can parallel a 12 volt motorcycle battery with a 8D if you want, and nothing bad will happen.

However, batteries in series must be the same age and of the same level of overall health.

I agree with you about batteries in series, but I disagree that it OK to parallel dissimilar batteries. I'm of the school that even similar batteries should not be wired in parallel. Too many problems with even current distribution, wiring complexity and fusing, and they are thermally unstable. When the batteries are dissimilar they will deteriorate at an accelerated pace and you may have one string discharging into another string. If you do parallel your batteries, be sure to fuse each parallel string.

--vtMaps

techntrek

Re: Inverters

ChrisOlson wrote: »

Yes, that you can certainly do that. I noticed the comment about battery age. Batteries in parallel can be any age or any size. You can parallel a 12 volt motorcycle battery with a 8D if you want, and nothing bad will happen.

However, batteries in series must be the same age and of the same level of overall health. If you series an old battery with a new one, the new one will more than likely have more capacity than the old one. So when you charge them in series the internal resistance of the old one is going to come up faster than the new one - with the end result that they will be out of balance and the new one will get deficit charged. On a 24V system the old one might hit 15.0 volts while the new one is only at 13.0 (still in bulk stage) and the system charging voltage is 28.0
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Chris

Everything you said about batts in series applies to parallel, too. One will charge before the other, one will drain before the other (possibly reversing polarity).

ChrisOlson

Re: Inverters

vtmaps wrote: »

I agree with you about batteries in series, but I disagree that it OK to parallel dissimilar batteries. I'm of the school that even similar batteries should not be wired in parallel.

I know some folks get worried about it. I just go by experience. I have a set of Group 24 marine deep cycle batteries from our boat, plus two 4D's from our RV. I've only been hooking the 4D's to our home bank in the winter for the last two years. But the Group 24's from the boat were 8 years old this last spring and they have been removed from the boat and hooked to our house battery bank every single year since they were new.

They get the snot worked out of them on the house bank, hooked in parallel with batteries that are 3-4x times their size. We have Surrette batteries that like high absorb voltages (31.0 volts) and those little 24's even take that just fine. They just keep coming back for more, year after year. They're 95 ah capacity, and when I load tested them this spring at the 20 hour load rate, before putting them back in the boat, they both tested at 4 amp load for the full 20 hours (~82 amp-hours) before they got down to 10.5 volts. That's as good as a new battery yet.

Most people are lucky if they get three years out of a set of those little Group 24's in their boat.

That's one example of extreme mismatch in parallel battery configurations without a single issue.
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Chris

ChrisOlson

Re: Inverters

techntrek wrote: »

Everything you said about batts in series applies to parallel, too. One will charge before the other, one will drain before the other (possibly reversing polarity).

No, they won't. Batteries in parallel always stay the same voltage between the different batteries in the string. The larger ones will handle more of the load, and require more the amps during charging. During charging the internal resistance of the different batteries in the string determine how much of the total charging amps they will draw.

Parallel battery configurations are used almost exclusively in heavy equipment and Class 8 trucks. A typical semi tractor has four Group 31's in parallel, and two Group 29 deep cycles for the sleeper with an isolation switch so the sleeper batteries don't kill the six starting batteries. When the truck is started there is massive mismatch in SOC between the sleeper batteries and starting batteries - the isolation switch closes and all six are charged in one big string - usually from a big 195 amp Leece-Neville brushless alternator.

Stationary gensets are the same way. A 1.0 MW Cummins standby or prime power set is 24 volt starting, but there's 16 Group 31 batteries in the starting bank. They are hooked in parallel strings with 8 batteries in each string, and the two strings are hooked in series.

Two examples of commonly used parallel battery configurations that have been proven for reliability over years and years of operation.
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Chris

BB.

Re: Inverters

Different capacities in series (from age, or size/capacity) is the big issue of reverse polarity during discharging (one cell goes "dead" and begins to "reverse" charge). Different types of batteries in series are probably a problem too (AGMs have lower self discharge and don't like over charging/equalizing current--and the flooded cell need equalization to get all cells back to full charge).

In parallel, I am not completely sure that it is "death to batteries" to have them in parallel.

As long as they are all the same chemistry (lead acid), the charging voltages (within reason) and discharging behaviors are going to be "close enough" that they can function fairly well (in my humble opinion).

I believe here you get "into trouble" is at the edges of the envelope...

If you have AGM/GEL batteries in parallel with flooded cell and try to hit them with 15-16 volts for equalization (vs the 14.2 to 14.4 typicall maximum charging voltage for AGMs)--You can over charge/over heat/damage catalysts/etc. in the sealed batteries.

If you have high surge currents (starting loads), and/or high charging current, the lower impedance batteries will probably carry more of the current than the others (AGM/GEL are very low impedance, flooded cell storage batteries have higher impedance/resistance). It is possible the lower resistance batteries will carry more of the cycling loads/charging and could "fail earlier" because of this (just a guess).

Conversely, if you have a short circuit in the smaller battery bank--As already stated, you should have a fuse to protect the smaller capacity string with a fuse/breaker to prevent a puddle of copper or lead from forming from the power of the larger bank feeding the smaller bank.

And the other issues of paralleling--Problems getting current to share, more connections/fuses/breakers/wiring costs, more cells to check water levels, problems diagnosing/catching shorted/open cells, sorted cells discharging balance of bank, temperature stability between strings, etc...

More or less, I use an engineering rule of thumb... If the battery string AH capacities are within in a factor of 2 or less of each other--They are pretty similar in terms of performance.

If the battery strings are 10x different (or more) in capacity--Then the smaller string really does not even "exist" in the overall performance of the entire bank--and probably is not even worth adding in parallel for its (very small in relation to rest of bank) storage capacity.

-Bill

ChrisOlson

Re: Inverters

You can tell those little tiny batteries are there too when they're in parallel.

We have our bank wired like you would see on a megawatt-class diesel genset where there's two long strings of parallel batteries, and then the two strings are in series for higher voltage. This has the effect of putting two huge batteries in series.

When we had the EcoGen it required 120 volt power fed back to it for it's battery maintainer (bad design for off-grid but that's another story). Well, I didn't like that. So I hooked up a Morningstar RD-1 to activate a relay when ever the bank voltage got above 12.7 (x2 for 24 volt) and de-activate the relay when the voltage got above 14.0. The relay connected the genset's starting battery with one of the big T12-250's in our bank. This was my method to maintain that starting battery without using the onboard battery maintainer on the genset.

Well, turns out this didn't work. I got a set of very sensitive analog volt meters on my bank to monitor bank balance. The meters keep tabs on the two halves of the bank, and if I ever get a battery in there that runs out of water, or has a problem, it will show up on the volt meters so I can do something about it before I get further damage to the bank. That little genset battery being hooked up to one of the big ones caused that side of the bank to run .1 volts low and the other side to run .1 volts high. I was walking thru the utility room and I glanced at the meters. If they're a needle's width difference there's 0.1 volt differential between the two sides of the bank - and they were a needle's width off.

I swapped the genset battery to the other side of the bank just to make sure that's what was doing it, and sure enough - now the other side of the bank ran low on voltage.

This is a 58 kW battery bank with just a little tiny AGM battery the size of a motorcycle battery on one side putting it out of balance.

I ended up scrapping that idea and put a small solar panel on the genset instead. My wife couldn't figure that out. She looked at the genset one day, frowned a little bit, and said matter-of-factly, "our generator has a solar panel on it......."
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Chris

PhilS

Re: Inverters

ChrisOlson wrote: »

II ended up scrapping that idea and put a small solar panel on the genset instead. My wife couldn't figure that out. She looked at the genset one day, frowned a little bit, and said matter-of-factly, "our generator has a solar panel on it......."
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Chris

I also ended up putting on one panel dedicated to charging the genset's starting battery. I couldn't figure out a better way either.

Phil

ggunn

Re: Inverters

martin1025 wrote: »

what will be the maximum capacity required for home back ups inverters...........

As my dad was fond of saying in response to questions like this: "How long is a piece of string?"