# Inverter

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## Comments

32,314adminRC,

You are probably correct... Plugging in 55% as efficiency:

- 4,000 watts * 1/0.55 inverter eff * 1/10.5 volts cutout = 693 amps peak

Obviously, as you start researching the details--things look even worse.-Bill

17,615✭✭Which is why you don't try to run a 4kW inverter from 12 VDC. :roll:

32,314adminJust to be clear, it is a 2kW inverter with 4kW surge (which is why we use rules of thumb so we don't hurt our heads ).

-Bill

125✭✭✭✭✭BB. question about the 24volt inverter. If I went 24 I would be using 12volt batteries in series. If I bought the 24vdc inverter with the built in battery charger would that work on this type of battery bank? Seeing that they are not 24volt batteries.

Also if i wanted to run 12volt lights/or just get 12 volts out of it how would I do that?Because anything connected to the plus and neg leg would come out as 24.Or I would be able to only connect in between the 1st two batteries and that should be 12volt.

tks all

John

1,973✭✭✭No problem there. Lead acid cells are actually 2V; whether a battery is 6V, 12V, 24V, etc. is just a matter of packaging. Most very large battery banks use separate 2V cells connected in series to get whatever voltage they want.

You don't want to do that. You want all your batteries to be at the same SOC (state of charge) at all times, or as close to it as you can get them. Drawing current from a single battery in a series string is a bad idea.

32,314adminJohn,

No, it is a very bad idea to pull 12 volts from a 24/48 volt battery bank.

It unbalances the bank, so when the series connected batteries are recharged, the other batteries will be overcharged and the 12 volt battery will be under charged.

There are devices that can balance charge between the batteries (like on 24 volt bus RV's that need to also power 12 volt loads). Or there are various forms of 24 to 12 volt down converters and 12 volt battery chargers.

Yes, a 24 volt inverter/charger (or 24 volt charger) will recharge 2/4/6/12 volt cells/batteries connected in series.

You need to make sure you wire the parallel connections properly (not simple "ladder style"). If you do not wire parallel battery strings properly, you will get unbalanced charging/discharging.

And, personally, I prefer one series string of batteries rather than a bunch of battery strings connected in parallel (for proper AH bank capacity). You have too many cells to check for electrolyte levels, spend lots of money and time on the interconnects, and you should have a fuse/breaker on every parallel connection point (more money and complexity). Also, if you have a bad cell or open connection--it is much more difficult to "see" a failure--And a cell/wiring fault may damage the rest of the batteries in the string, or even the entire bank if not caught quickly.

If you must connect in parallel, I would suggest limiting to two or three parallel strings maximum. There are people who have done more in parallel and have been very happy--But it is not something I would recommend.

For DC Power Systems, I highly recommend a DC Current Clamp Meter (this one is functional and not very expensive). Much easier, safer, and able to meter up to 400 amp circuits.

There are many more battery options these days for Home Power people... There are larger 6 volt and even 4 or 2 volt cells with pretty high AH ratings.

These 2 to 4 volt cells can have high AH ratings but still be small enough for one or two people to move around the home/cabin without needing a fork lift.

And allows you to have large battery bank AH capacity without a bunch of parallel connected batteries.

-Bill

125✭✭✭✭✭I would like to know who on this board has a 24 volt system,or 48 volt.

Im now thinking of going to the 24 volt, seeing my charge controller will do both.The only thing that I don't like about 24 volt is that if you want to use anything 12 volt you will be wasting power to convert it again.

John

I just emailed the company to see if the automatic battery charger in the 24 volt inverter would charge the 12 volt batteries wired in series. I going to say it will.

9,511✭✭✭✭✭I'm Mike, and I'm 48 Volt. Only way to go, unless it's just lights for the privy.

|| Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||

|| VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

solar: http://tinyurl.com/LMR-Solar

gen: http://tinyurl.com/LMR-Lister ,

125✭✭✭✭✭Mike. would you know if a 12volt input inverter with built in battery charger would charge 4 batteries [deep cycle] x 115 amp hours wired in series. I don't want to buy the wrong one.

John

9,511✭✭✭✭✭MAYBE. It depends on the quality of the inverter charger, if the charger has enough output power to recharge 4 batteries in a reasonable time.

I use a VEC1093 12V Charger, which can go to 40A, but that would take a long time to bring a large bank up to full.

|| Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||

|| VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

solar: http://tinyurl.com/LMR-Solar

gen: http://tinyurl.com/LMR-Lister ,

17,615✭✭A 12 Volt inverter-charger runs on 12 Volts and charges 12 Volts. It will not charge 24 or 48, nor will it run from such a battery bank. The other issue is the charge current, and that will vary with the particular inverter-charger.

I use a 24 Volt system off-grid and it's fine. Many of the cabins here have 12 Volt systems that are fine. There is no need to buy more system than you can use.

And that is the bottom line: you must base your system design, including nominal Voltage, on your power requirements. Running a 6kW 48 Volt inverter to supply <300 Watts of power is a foolish waste of money.

As usual it comes down to the two basic questions: how many total Watts do you need at any given time? And; how many Watt hours do you need in a day?

I suppose you could add: are loads DC, AC, or mixture of each? What Voltages? What types of loads (inductive, resistive, mixture)?

125✭✭✭✭✭.

Mike the spec. for the 2000watt inv. that im thinking has a built in charger with 35 / 70 amp. So they must mean for a 12 vdc sys. it would charge 35 amps. and a 24 vdc sys. it must be 70 amps.

Most of the time its just going to be topping it off, i think.

32,314adminYou need to look at those specs. closely... Chargers in a specific profile usually are limited by watts--So a 1,000 Watt form factor will be listed as different voltage models as:

- 1,000 watts / 14.5 volts = 70 amps
- 1,000 watts / 29 volts = 35 amps
- 1,000 watts / 58 volts = 17.5 amps

The above numbers are just made up for the example.For Solar Charge Controllers, they are typically rated at a maximum current at any output current. For example a "typical" 60 amp MPPT solar charge controller would charge:

- 60 amps * 14.5 volts = 870 watts
- 60 amps * 29 volts = 1,740 watts
- 60 amps * 58 volts = 3,480 watts

For charge controllers, the limiting factor is amperage for magnetics and I^2*R heating issues.-Bill

125✭✭✭✭✭Im sorry i have to ask again.But im stumped on the 12 or 24. Im telling myself to buy the 2000watt 24 volt inverter with charger, but then im thinking, well what if i ever want to sell it for one.Ok next, I have 2 12volt batteries now. All the difference that I can see between the both is the size of wire and the amount of batteries.I most likely stay with the 12v batteries. For the 12v sys. all I would need is more batteries to get my AH. Yes heaver wire!or bus bars, to go 24v sys, I would need TWICE as many batteries to get the same AH,so that would cost more.I know,Smaller wire. But all in all the rest is the same,.[isn't it. ha ha }

But i think the factor is the Twice as many batteries.

So lets hear the come back's,.

Now if someone has alot of money and wants to Donate one to me, that would be nice.LOL

Tks

John

17,615✭✭Actually John you're looking at

Watthours.100 Amp hours @ 12 Volts is 1200 Watt hours.

50 Amp hours @ 24 Volts is also 1200 Watt hours.

It's a matter of two things: how many Watt hours you need to store (it's better to go up in system Voltage to store more power) and how much total power you need at any one time (more Watts at once means either more current or more Voltage).

32,314adminRemembering that power = voltage * current ... 12 or 24 volt banks of equal energy (power * time) will cost about the same. You pay for weight of lead and battery electrolyte.

In general, I like one serious series string of batteries, although with care, two or three are ok.

Problems with parked parallel batteries can include:

More cells to check

Difficulty getting even current sharing

You should have a fuse or breaker per parallel string

Open cell can stop one string from working

Shorted cells can kill a string or discharge the bank

Not to say that there are many users with four or more parallel strings who are very happy.

One recommendation I like to make is buy a dc current clamp meter so you can check current sharing between strings during heavy charging and discharging once a month or so. You want to catch problems early.

-Bill

125✭✭✭✭✭cari. where you showed this"100 Amp hours @ 12 Volts is 1200 Watt hours.

50 Amp hours @ 24 Volts is also 1200 Watt hours.""

This is what I mean,you need 2 batteries for the 24v to get the same as the 1200 watt hours in the 12.

Right.

So back to my point.you would need twice as many batteries to get the same as 12. I know that you cant take and put will say 4 -12 batt. and hook them in parl. and then take 2 more at the end of the string of the 4 and then connect them in series, and end up 500 ah. That is saying each batt. is 100ah.

Im laughing over here now.

tks

John

lets say i want to run 2 computers[100watt per hr.,,AC] for 8HR.

1 Fax, 100 watt per hr AC. for 1 hr

1 LCD TV 200 watt per hr AC. for 6 hr

.........................

Im not going into if the power goes of because of a storm. LOL

Most likely SHUT DOWN and have sex. ha ha ha

32,314admin- 2 computers * 100 Watts * 8 Hours = 1,600 WH per day
- 1 fax * 100 Watts * 1 Hour = 100 WH per day
- 1 LCD TV * 200 Watts * 6 Hours = 1,200 WH per day
- =====================================
- Total = 2,900 WH per day

A battery bank with 1-3 days of no sun and 50% maximum discharge is the typical range... Say 2 days and 50% max discharge:- 2,900 WH * 1/0.85 Inverter Eff * 2 days * 1/0.50 max discharge = 13,647 WH per day

For a 12/24/48 volt battery bank (all banks will be roughly the same costs):- 13,647 WH battery * 1/12 volts = 1,137 AH @ 12 volts
- 13,647 WH battery * 1/24 volts = 569 AH @ 24 volts
- 13,647 WH battery * 1/48 volts = 284 AH @ 48 volts

Solar panel wise, I will do the calculations two ways... One based on Hartford Connecticut and second based on size of battery bank.Using PV Watts with a fixed array at 42 degrees from horizontal for Hartford Connecticut: The lowest hours of sun per day (average) is 10-October at 3.92 hours of full noon time sun per day. Using 52% end to end system efficiency:

- 2,900 WH per day * 1/0.52 system eff * 1/3.92 hours of sun = 1,423 Watts of solar panel for ~9 months of year

And based on battery rate of charge (5% to 13% rough rule of thumb), I will pick 10% as a good sized solar array:- 13,647 WH battery * 1/0.77 solar+charger deratings * 0.10 rate of charge = 1,772 Watt Array (10% rate of charge)...

So a recommended array would be around 1,423 to 1,772 watts of solar panel based on my guesses...Note a solar charge controller output is rated in amps... A good sized one is 60 amps at 12/24/48 volts. So, ~10% rate of charge would be:

- 1,137 AH @ 12 volts * 10% = 114 amps @ 12 volts
- 569 AH @ 24 volts * 10% = 57 amps @ 24 volts
- 284 AH @ 48 volts * 10% = 28 amps @ 48 volts

So, with a 60 amp charge controller, you would need 2 controllers at 12 volts; and 1 at 24 volts. And at 48 volts, you could install a 2x larger array and still use only 1 charge controller.Anyway--some basic numbers.

Your thoughts?

-Bill

17,615✭✭John; they'd be two

differentbatteries @ 1200 Watt hours on each system.Look at what happens with two of the same batteries:

2400 Watt hours on 12 Volts: two 100 Amp hour 12 Volt batteries in

parallel.2400 Watt hours on 24 Volts: two 100 Amp hour 12 Volt batteries in

series.Parallel battery connections = more difficulty in maintaining even current flow through all batteries. The more in parallel, the worse it gets. The larger the battery bank becomes the greater the likelihood for trouble. When you need to go really big you use 2 Volt cells which have very large capacity (around 1000 Amp hours) which reduces the number of connections and cells to check. Example:

1000 Amp hours @ 12 Volts using 100 Amp hour 12 Volt batteries would be ten in parallel. That's sixty cells to check and nine sets of interconnecting wires.

1000 Amp hours @ 12 Volts using 1000 Amp hour 2 Volt batteries would be six in series. That's six cells to check and five interconnecting wires.

Now if you really needed 12000 Watt hours of power you would use a 48 Volt system and a 250 Amp hour battery bank. That could be eight 6 Volt batteries in series: 24 cells to check, seven interconnecting wires.

That is an extreme case.

The other issue is the peak current. It's not just about wire size, although that is an issue, but also about the battery bank's ability to supply that current. The greater the current draw the fewer Amp hours the battery is actually capable of. In some cases the load can be heavy enough all at once to cause the Voltage at the inverter to drop to where it shuts down. Higher current = less efficiency as well, as more power goes to heat and not work.

Again an extreme case.

The point is, once you know how many Watt hours you need to store and how many Watts you'll need to deliver at any one time you have a better idea of whether you should go up in system Voltage or not. It can be a tough choice when the power requirements are on the threshold, so to speak.

125✭✭✭✭✭.

.Hi BB. All of what you said is about what I was thinking of,i mean amount of solar panels/watts.

I see now that the charge controller would handle more panels/watts,one good thing.

I guess the more I hear everyone saying go 24v ,I think that is which way I will go.It's hard to change a Mind Set.lol

tks

John

sure do like this board and all the people one it. Very Very Helpfull.

32,314adminHi John,

A couple of side points... First, picking an inverter with all of the bells and whistels that make sense for your installation (search mode, remote on/off, etc.) can be quite difficult. If you stick with a 12 volt battery bank, the MorningStar 300 watt TSW 12 VDC inverter is, hands down, the best deal for that power class.

When you go higher voltage, then you usually get stuck looking at larger inverters, which cost more, and have more "tare" loads (need 10, 20, 40 or more watts just to turn on). Which means more batteries and more solar panels--So you end up designing the system just to support more of the system.

Which gets us back to your loads and conservation... Each of your computers using ~100 watts per (remember to include monitors, printers, networks, etc. too)--That is close to what a refrigerator uses, on average (computer 100w*8h=800WH; energy star fridge might be as low as 1,000WH per day).

If possible, I would highly suggest looking at laptops. They will run, as low as, 20-30 Watts and fall back into sleep mode (mine are less than 1 watt) when nobody is there. Also, a laptop comes with its own, very efficient, UPS (batteries).

Getting a Kill-a-Watt or equivalent meter and measuring your loads is a great way to plan your system needs and just very handy for conservation in a grid connected home.

-Bill

292✭✭I will add to what coot said. If you have two 12v batteries, either way you wire them you will get the same power from them. In series you get 24v. In parallel you get 12v. That is the difference. You don't need two more batteries, just alter the way they are wired.

In parallel 12v you are adding the amp hours of the batteries together and multiplying by 12. twice the ah, half the voltage.

In series you are using the ah of the single battery, but you are multiplying times 24. Half the ah, twice the voltage.

100x12

50x24

Same same.

1,973✭✭✭Well, OK, if you want to look at it that way, but the two batteries you need only have to be half as big. Two 12V 50 Ah batteries in series gives you the same power as a single 12V 100Ah battery.