Why No Inverters for Deep Cycle Batteries?

dwh

Re: Why No Inverters for Deep Cycle Batteries?

zone4guy wrote: »

kiped from the net so the people giving the advice can sound intelligent or educated.

Nah, mostly "kiped" from the net because those people were asking the questions and looked up the answers.

Their motivation was not - as you incorrectly and belligerently assume - to sound intelligent or educated. Their motivation was to learn.

Just because someone sounds intelligent and/or educated doesn't mean they are are faking it - they might actually BE intelligent and/or educated.

Run your batteries down to the point that they will no longer run your device or system then immediately recharge them. Leaving them discharged for more than a couple days will kill them. Let me repeat; I have not ever damaged a battery from running it down to 6V or even a little lower and then immediately recharging it. What have I run? Water pumps, Light Bulbs, Computers, DVD Players, and a ton of other things. I recharge them at 500ma to 1A on a solar charge controller even in the dead of Wyoming winter.

Here's where you just shot yourself in the foot. First you say, "immediately recharging it" and then you say 500ma.

I don't know what capacity batteries you're talking about, so let's just use 100 amp*hour as an example.

Okay, so it has 0ah in it, and you apply .5ah to recharge it.

That's going to take what? A COUPLE OF HUNDRED HOURS? to recharge.

I don't know in which universe that qualifies as "immediately", but it's sure not this universe.


Also...

I have a water pump in my camper. I've run my aux battery totally dead a number of times. I can state with absolute certainly, that the water pump in my camper WILL NOT PUMP WATER when the battery is at 10v.

I don't know what water pumps you were using (or I should say, "claim to be using"), but they must be something special. Mine is just a regular old Shurflo and it WILL NOT do what you claim.

That FACT makes me think that you must have made it up.

Also...

I have a netbook with a 12v adapter that I use in my camper, and that adapter WILL NOT power the netbook (which only draws 9w in power saving mode) at less than 10v.

EDIT: And now that I think about it...I also have a 12v DVD player and it too WILL NOT WORK when the battery is at 10v.


So I don't know where you're getting these special water pumps and computers and DVD players, but I would sure LIKE to know.

Maybe they sell them in that alternate universe.

This is important, because it allows me to go deeper into my batteries and still recharge them quickly

Quickly? In a pig's eye. See above.

john p

Re: Why No Inverters for Deep Cycle Batteries?

WARNING
Any person young ,old, newcomer ,or experienced is a foolish person if they take any of zone 4guys advice
WRECKED BATTERIES IS ALL YOU ARE GOING TO GET..
SUCH POSTINGS AS HIS DO A LOT OF HARM TO INNOCENT PEOPLE THAT MAY THINK HE KNOWS WHAT HE IS TALKING ABOUT.

icarus

Re: Why No Inverters for Deep Cycle Batteries?

I think that Zone4guy has come and gone like a cool breeze. I think we should let sleeping dogs lie until he resurfaces if he does.

He hasn't been back to visit since he posted his 1 post.
Tony

Cariboocoot

Re: Why No Inverters for Deep Cycle Batteries?

I think that particular poster has gone from among us, once he realized that the laws of physics apply here. I rather suspected his next post would be along the lines of "send me $10 and I'll tell you how." :roll:

At any rate he hasn't returned to try and back up his outlandish claims.

dwh

Re: Why No Inverters for Deep Cycle Batteries?

I just wanted to get my $0.02 into the archives so that when someone stumbles on this thread a year from now they'll see it.

mike95490

Re: Why No Inverters for Deep Cycle Batteries?

zone4guy wrote: »

We mock what we do not understand!

Had you asked I would have been all too happy to explain what I have done to get the results that I did, but as all of you are more than happy to shoot off your mouths instead of opening your minds and learning you can all (expletive deleted). Your loss.

Well, just maybe, you should have started off with, what you did, than asking about something that "as far as current tech understands it, don't pull a battery below 10.5V" That would have helped a lot.

Cariboocoot

Re: Why No Inverters for Deep Cycle Batteries?

Mike & others;

"zone4guy" has been banned. His last post displayed foul language, bad attitude, and a complete lack of scientific understanding. After john_p's tests prove what we already know, we don't need anyone promoting nonsense. There's enough of that garbage out there on the 'Net; it's not going to be on display here.

We deal in reality.

waynefromnscanada

Re: Why No Inverters for Deep Cycle Batteries?

Well done and well said Cariboocoot!
Thank you.

Ralph Day

Re: Why No Inverters for Deep Cycle Batteries?

2nd Wayne's comments.

I can't believe how rude some people get commenting on blogs and such. Personally I think it's because people feel anonymous and hide behind ''handles'' not using their real names (many, not all). Glad to see the moderation of this forum is active, makes it pleasant to visit.

Now with 2 of the moderators being Canadian it'll get even more polite :p

Ralph

Jim in Jersey

Re: Why No Inverters for Deep Cycle Batteries?

Very good answer. One clarification of which I am sure is just a typo based on the clarity, knowledge, and content of your answer, power is V^2/R or I^2 * R (Amps squared times R).

P.S I just signed up and am learning a great deal! Great posts and responses!

BB. wrote: »

What deep cycle batteries are you talking about? (link?).

From my point of view, there are several reason you will not find inverters that will cutoff at 5volts.

First, battery damage. Storage battery cells are not usually matched before connecting in strings (RC model folks will test discharge battery cells and match those in series strings with equal capacity). Standard storage batteries can have cell to cell capacity differences of up to 20% (roughly) between two series cells.

What will happen is when you collapse the voltage in the "weak" or low capacity cells, the other series cells can actually "reverse charge" the weak cell(s)--For most battery chemistry's--that will destroy those cells.

Second, is AC inverters are typically constant power devices... Remembering Power=Volts*Amps -- we see that an inverter that operates at ~15 volts (battery bank under charge) vs one operating at ~5 volts will draw 3x as much current to support the loads.

Generally, when batteries are below ~10.5 volts (for lead acid storage cells), there is little chemical energy to support any substantial currents.

Another reason -- Power is also equal Amps^2 / R [per Jim's catch--Should be I² * R. -Bill B] -- To design an inverter that can operate over a 3:1 voltage range (at constant power) will require 3x^2 or 9x as much copper, magnetics, capacitors, switching transistors, heat sinking, etc. to prevent overheating when operating at ~5 volts.

Most batteries are, more or less, constant voltage sources (solar cell/spanels are actually, more or less, constant current sources)--So for standard chemistry lead acid batteries, I would wonder how much useful energy for a 12 volt battery is available at ~5 volts.

My guesses--anyways...

-Bill

PS: I should clarify--the "matched series cells" for RC planes/cars/etc. is to prevent cell damage from reverse charging without having to add the electronics/costs to protect cells against "reverse charging".

I don't believe it is to gain more usable energy from the battery pack.

-BB

BB.

Re: Why No Inverters for Deep Cycle Batteries?

Jim in Jersey wrote: »

Very good answer. One clarification of which I am sure is just a typo based on the clarity, knowledge, and content of your answer, power is V^2/R or I^2 * R (Amps squared times R).

P.S I just signed up and am learning a great deal! Great posts and responses!

Welcome to the forum Jim!

And with the new forum upgrade from a few months ago (thanks to Windsun and NAWS), we can now use exponents directly:

• Power = V²/R = I²R = V*I (times Power Factor if AC)

-Bill

PS: Thank you Jim--I fixed the orginal post. -Bill

vtmaps

Re: Why No Inverters for Deep Cycle Batteries?

Jack Kessler wrote: »

Every inverter I have been able to find shuts off at 10 or 10.5 volts.

I'm coming in late to this thread, but with 41 responses I am surprised that only Bill (in post #2) alluded to the correct reason.

The reason has little or nothing to do with the fact that the battery is dead or nearly so at those voltages. The reason is to protect the inverter from the high currents that result from low voltage inputs. An inverter could be engineered to work at those low voltages, but it would raise the cost of the inverter and allow fools to discharge their batteries even further into the dead zone.

Now, that said, it would be nice if some inverters would go lower. The reason would be to allow for different battery chemistries and to allow those with LA batteries to remove a defective cell in a series string of 2 volt cells.

--vtMaps

Cariboocoot

Re: Why No Inverters for Deep Cycle Batteries?

vtmaps wrote: »

I'm coming in late to this thread, but with 41 responses I am surprised that only Bill (in post #2) alluded to the correct reason.

The reason has little or nothing to do with the fact that the battery is dead or nearly so at those voltages. The reason is to protect the inverter from the high currents that result from low voltage inputs. An inverter could be engineered to work at those low voltages, but it would raise the cost of the inverter and allow fools to discharge their batteries even further into the dead zone.

Now, that said, it would be nice if some inverters would go lower. The reason would be to allow for different battery chemistries and to allow those with LA batteries to remove a defective cell in a series string of 2 volt cells.

--vtMaps

Nope. Not it. Sorry. It's to protect the batteries.
Battery Voltage can drop low without any significant current draw. Fuses/breakers protect against over-current.
Really good inverters have programmable low Voltage disconnects. If it's to protect them against too high a current draw, why should it be changeable?
Many charge controllers have LOAD terminals with LVD disconnection. The function is to turn off the loads before the battery becomes too depleted to recharge. Same thing with inverters.

We're not talking about GT inverters that have minimum input Voltages to prevent them drawing high current (because a GTI will put out power based on whatever input is available).

Read john p's post on battery depletion.

BB.

Re: Why No Inverters for Deep Cycle Batteries?

Change battery bank voltage.

• 1/6 = 17% voltage drop (12 volt bank)
• 1/24 = 4% voltage drop (48 volt bank)

That is why it is much more difficult to"notice" a single cell failure in a 48 volt battery bank.

-Bill

tungsten

Re: Why No Inverters for Deep Cycle Batteries?

I think it's pretty definitive that you shouldn't discharge a lead acid battery under 10v but there are uses for inverters that could dip below 10v. Specifically I've been playing with a super capacitor bank and could use an inverter that doesn't have a low cut off. I understand that as the voltage drops the current increases but a thermal cutoff can protect the inverter without cutting out at 10 volts. Unfortunately most 12 volt inverters are 10-15 volts and the widest inputs I've been able to find are 14-28 volts (without spending thousands of dollars). So I'm resurrecting this dead thread to continue the discussion are there inverters that don't break the bank and can go below 10v or have a wide voltage input?

Cariboocoot

Re: Why No Inverters for Deep Cycle Batteries?

Lack of demand.
Companies only build what is commercially viable. Since that means 12 Volt inverters running off 12 Volt batteries whose performance characteristics are known there's no reason for them to build inverters that would operate outside of "safe" battery Voltages.

BB.

Re: Why No Inverters for Deep Cycle Batteries?

You can find 12 volt inverters that go upwards of 16-17 volts maximum input (still 10-10.5 volt minimum--And some 24/48 volt equivalent inverters).

Remember that, you stated, inverters are constant power devices... If you 1/2 the voltage, the current has to double to maintain the constant power.

But resistive losses (waste heat) will go up by a factor of 4:

• Power = I² * R

And electronics (such as FETs and Capacitors) have very little thermal mass and not great thermal conductivity. So, it is unlikely you will see a high enough temperature rise to use as a safety cutoff if the input voltage drops quickly (such as during starting a pump or compressor--~5x running current for starting/locked rotor current).

Do you have a specific requirement? (Voltage/Inverter Power, Application?).

Apparently, Exeltech offers semi-custom/built to order inverters through their distributors:

We can also order all of the MX series. The XP series are also available in 32, 48, 66, and 108 volt DC input on special order - typically 2-3 weeks. Prices somewhat higher. We can special order any Exeltech product.

My guess is--If you accept a lower rated output (i.e., derate a 2 kW inverter to 1.4 kW) for a wider input voltage range--Then they can build a product for you with some "stuffing" changes to change alarm limits/support a wider input voltage range.

You might contact our host, NAWS (Northern Arizona Wind & Sun) for details (most of us here are just volunteers and are not connected with NAWS).

-Bill

PS: I should add that running a 12 volt battery much under ~11.5 volts (nominal loads/temperatures) will usually shorten the life/reduce the capacity of a lead acid battery bank significantly.

My belief is that the 10.5 volt cutoff is simple there to protect the inverter from over current/overheating and probably "browning out" the AC load.

tungsten

Re: Why No Inverters for Deep Cycle Batteries?

Cariboocoot wrote: »

Lack of demand.
Companies only build what is commercially viable. Since that means 12 Volt inverters running off 12 Volt batteries whose performance characteristics are known there's no reason for them to build inverters that would operate outside of "safe" battery Voltages.

Unfortunately that's definitely the case, it's just redundant that my charge controller and inverter both have low voltage cutoffs. I guess I'll be opening up my inverter and seeing if I can remove the protection circuit, with any luck it might be a simple op amp voltage sensing circuit.

BB. wrote: »

And electronics (such as FETs and Capacitors) have very little thermal mass and not great thermal conductivity. So, it is unlikely you will see a high enough temperature rise to use as a safety cutoff if the input voltage drops quickly (such as during starting a pump or compressor--~5x running current for starting/locked rotor current).

You definitely might be right but I think it's worth looking into. I have a feeling that a quality inverter would be able to go a few volts lower depending on the out wattage

BB. wrote: »

Do you have a specific requirement? (Voltage/Inverter Power, Application?).

I've just been experimenting with alternate energy storage, no specific applications

BB. wrote: »

Apparently, Exeltech offers semi-custom/built to order inverters through their distributors:
You might contact our house, NAWS (Northern Arizona Wind & Sun) for details (most of us here are just volunteers and are not connected with NAWS).

I'll look into it thanks!

Vic

Re: Why No Inverters for Deep Cycle Batteries?

Just to be clear, a 12 V Lead Acid battery is essentially DEAD at about 11 V. There is very little remaining POWER left to be delivered by the battery. With any significant current demanded from the battery, the battery voltage will fall like a rock.

All IMHO, Vic

Cariboocoot

Re: Why No Inverters for Deep Cycle Batteries?

Vic wrote: »

Just to be clear, a 12 V Lead Acid battery is essentially DEAD at about 11 V. There is very little remaining POWER left to be delivered by the battery. With any significant current demanded from the battery, the battery voltage will fall like a rock.

All IMHO, Vic

That's exactly what john p's testing showed. As we all know (or should know) battey power is not a simple linear function. Once you get below that Low Voltage threshold the drop is much more rapid than above it. This is the inverse of the charging curve where it takes longer to put that last 20% in than the first 80%.

BB.

Re: Why No Inverters for Deep Cycle Batteries?

"Tungsten" was looking into using Super Capacitors (and other ideas?), not a lead acid battery bank... A whole different kettle of fish (super caps have many drawbacks in terms of energy storage, life, costs, etc.).

-Bill

waynefromnscanada

Re: Why No Inverters for Deep Cycle Batteries?

tungsten wrote: »

So I'm resurrecting this dead thread to continue the discussion are there inverters that don't break the bank and can go below 10v or have a wide voltage input? (for use with super capacitors)

In a word. no! .........

Vic

Re: Why No Inverters for Deep Cycle Batteries?

BB. wrote: »

"Tungsten" was looking into using Super Capacitors (and other ideas?), not a lead acid battery bank... A whole different kettle of fish (super caps have many drawbacks in terms of energy storage, life, costs, etc.).

-Bill

OH, Thanks Bill, so much for a drive-by post on my part. Saw the reference to Super Cap, but felt that it was on a battery bank. Sure hope Super Caps make a dramatic leap in energy storage capability (IMHO).

I am still continually amazed with the abilities of the 150 year-old FLA technology.
Good Luck Tungsten!, Vic