Using old UPS as inverter

[Jimster]

Hi There, I'm new here, so don't shoot me down in flames just yet.

I'm thinking of building a Windturbine, but want to make sure I will be practical for my to use, as I would like to use it in my residential home.

I was thinking of using an old UPS I have rated at  3000VA / 2200W 15A as an inverter. Would this be a good idea, or is there better ways todo it.

I have been reading up on this for a while but there is one thing I cannot work out.

What I would like to achive is a wind turbine charging batterys, but when the batteries are low, or when pulling high current loads,  I would then pull power from the grid? is this possible without spending large amount of money on windyboys etc?

Thanks in advance,

Cheers

Jim

[ghurd]

Most UPS have quite low efficiency.

Probably better to get an inverter.

My plan is a grid fed battery charger, being controlled by my "ghurd controller" circuit with a few twists.

Battery gets low, grid charger turns on.

The rest of the time the power comes from the windmill.

G-

[scottsAI]

Jimster,

Many things can be made to work... sometimes not worth it.

A test of concept, the UPS can be a quick and dirty solution for testing, knowing better electronics can be had for a price. Might want to check that price before you get started to help deterring how far you will go with it.

As ghurd said UPS efficiency is low at light load (tested at 50%), not bad fully loaded. My APC SmartUPS 3000 draws 48 watts just hooked up, no loads.

48 w all day is 1.152kwhr each day, how much will your wind gen make a day?

More than 48 w from the battery when acting like an inverter with NO load. Beware!

An APC SmartUPS 1000 draws 24 watts all day.

Disconnected the battery on both, near same draw (with a fully charged battery).

Realized the transformers are warm... root cause for most of the current.

The UPS to charge would need to be connected to the Grid...

To supply loads from the battery then must disconnect from the grid. Now you cant charge.

Or add circuitry to do it for you automatically.

Battery (FYI)

UPS use Sealed Lead Acid battery (SLA), most larger batteries are flooded, charging voltages are different. The UPS will not fully charge a flooded battery, the wind can do it for you.

BTW, I use several different sizes of UPS for different load conditions... 100w, 300w, 1000w, 3000w. I use UPS to backup my home.

Have fun,

Scott.

[hamitduk]

One of the main problems is the UPS need to see AC to come online, if anyone is looking for things like this  www.allelectronics.com has 1500VA - 1200W with 24Vdc batt packs, they are Minuteman, the batt pack is charged independently.  They are True sine and only $149 US (used)

[Madscientist267]

Scott -

The latter is actually incorrect, in fact the opposite is actually true - I have several UPS units that I replaced the internal SLA with external FLA when the internals inevitably die.

SLA actually 'like' a higher voltage than FLA, and the result is tight maintenance is even more of an absolute MUST to run with FLA on a UPS than the designed SLA. The UPS chargers gas FLA batteries much more heavily than the originally intended SLA type.

A 12V APC UPS floats at about 13.8V when the battery is fully charged; This is fine for charge recovery (or equalization), but since the charger doesnt stop when the battery is full, it becomes a problem, and will destroy an FLA from overcharging.

Unfortunately for me, I had to learn the hard way to keep closer tabs on the water levels than normal. The concept is well ingrained in my mind - I boogered a rather expensive 8D on my original main UPS setup by not realizing that it was overcharging, and it gassed itself to death in just over a year's time. Total inverter time was minimal, only about 2500WH in short bursts; the longest recorded outage ever was calculated out to 86% SOC, nowhere near the 'danger' mark. I was upset to say the least.

For anyone interested, the ultimate solution for what I had was a 'catch' relay, as after the 8D failure, I decided to go for broke and redesign the entire system (I found out about the boiled 8D in the process of moving). Sadly, I could not simply re-wire the UPS units; the charge source is derived directly from the MOSFETs that operate the inverter... sigh.

Sooo....

I now operate two APC 24V 1400VA UPS units paralleled on a bank of four 'isolated' 8D deep-cycles wired in series-parallel. I use a cheap set of lawn/tractor batteries (U1-3) to take the abuse (they stand up a little better to overcharging somehow anyway, about 3 years) and for $50 a set, I won't complain. They hold the UPS system hot during a mains failure as the catch relay is kicking in to engage the main bank. For anyone who has not utilized such a relay, 500A continuous duty contacts aren't exactly 'quick' - not enough to use for this purpose without some kind of buffer at these power levels, lest ye defeat thy entire purpose!

Someone mentioned Farad caps to me at one point, rather than the disposable concept. I just looked at them with a gist that reminded them that testosterone was hard at work here! But after the fact (more importantly, the money, heh), I did a little math and as it worked out, they might be right. Maybe in place of the next set.

Anyway, during charge recovery, the 8D bank stays connected to the 'disposables' until the combined bank reaches 27V, then the catch relay kicks out and a small balancing trickle charger lets them fall to 12.75V on each side and holds them there. Once released, the catch relay is disabled until a mains failure once again occurs, preventing overcharge.

I've found that this configuration works almost flawlessly, and has saved me the trouble of having to constantly monitor my bank for water. I only need to check it now once a year (for peace of mind), but I also check after several hours of inverter operation, whichever comes first.

This configuration also saves me a little on wasted charge power, since each 12V side of the bank only draws 40mA or so holding at 12.75V. The UPS transformers show it too - everything runs much cooler after the catch relay disconnects post-cycle.

Of course, this doesnt really apply to RE, because for that, the batteries are used every day, and soaking up the charge whenever you can get it is sometimes the only name of the game. I threw all this in here for someone surfing through, that may find applicable info in it (as I did - looking for a current booster for a 20V 8W solar panel, to make charging single cell LiPo batteries more practical (and I think I got it now - Turns out the principle is very similar to the booster for a water pump - Thanks to all who had insight to be found)...

Steve

[ghurd]

"SLA actually 'like' a higher voltage than FLA"

Most everyone will disagree with that.

G-

[jonas302]

I have thought about doing this even manually plugging the charger in there must be a break even point with the size of re input- loosing power to the charger and then to the inverter I'm pretty sure it would cost more with my wimpy  harbor freight  panels than just using the grid ):  

[ghurd]

Your 'wimpy' solar charging system is suited to a 'wimpy' load.

It should work on any scale, as long as the RE charging and load are a semi-balanced system.

The grid charger is something like the off-grid big boys do when the wind and sun won't keep up.  They start a generator.  You and I plug in a grid charger.

Neither is efficient.  Both work!

My personal plan is for only 12V devices. Feeding them from the grid is low efficiency too, unless I want to get fancy.  It won't have inverter losses.

G-

[Madscientist267]

If you say so, but in my personal experience with both types, the proof is even in the settling voltages. Do the charge-and-sit routine on both types; assuming both are healthy, the SLA will read between .4 and .5 Volts higher than the FLA for a 12V configuration. If not, one of two things is wrong; either the SLA is damaged, or not fully charged.

The pictures below are taken on one of each type; both were taken to completion, and have been sitting for about a week, with no interaction with external electronics since.

FLA at full charge:

SLA at full charge:

Note: Please excuse the fact that the SLA's are not visible - there are 4 of them in the box, independently brought to the connector. The load connector determines which configuration the batteries are wired in, so that I can have 12, 24 or 48 Volts in a quick snap without a bunch of rewiring. The FLA is an 8D.

Steve

[ghurd]

I am quite familar with the settling characteristics of both types.

MorningStar SS-X manual (because it is easy to find) shows 14.1V for sealed and 14.4V for flooded.

Higher voltages will 'boil out' water that can not be replaced, resulting in an early death.

The settling results will not change.  I don't understand how it is relevent to the charging voltage either way.

G-

[Madscientist267]

SLA also top out at a given C/x rate at higher voltages. Left to trickle on their own, SLA and FLA of identical capacities, the SLA will level off at a higher voltage at identical charge rates. Also, when pushed into overcharge, the phenomenon I've always referred to as 'retro-dip' happens at about that same .5V difference between them (when overcharging causes the terminal voltage to start dropping rather than rising any further), although this phenomena is significantly more prevalent in SLA.

As for the relationship between charging and settled OTV, it shows the point of equilibrium in the natural balancing act that each type has a tendency toward; a natural indicator of what the cells establish as 100%. Going over this value is only for the purpose of making current flow, so that the battery gets a complete charge.

This has been the case with every experience I have had with both types. That being said, one thing that comes to mind that may not be obvious to either of us is charge 'style'...

Using a hard and heavy charge current (as might be expected in cyclic use such as RE), the rated finishing voltages may be different by different people as to what is considered 'full'.

My use for them is somewhat lax; they are primarily standby, and rarely see high charge rates (except after an extended grid-down condition, ie the bank for the servers). Even the solitary 8D in the picture above has never seen more than about 5A of charge current. IMHO, thats partly why they last so long for me; a slower charge is more thorough and doesn't stress the cells as much.

Holding 12.75 on a 12V FLA has never been a problem for me, SOC or water-wise; I have a battery that is 10+ years old, that still performs almost as well as the day I bought it, and never added a drop. There's nothing special about it either - It's a cheapy run-o-da-mill autocraft that I bought for a car, but never ended up using it for that purpose, so I just added it to my stash of 'quickie power sources'. It more or less stays on the trickler, and occasionally I burn off some juice with a 400W inverter when I'm doing real-world power measurements on a piece of equipment.

Trying this with SLA's however has always proven insufficient in available capacity terms. A 12.75V OTV on an SLA is little more than a valid bounceback reading from a hard 25% or so discharge.

Most SLA batteries even indicate on the sides that depending on standby or cyclic use, the charge voltage needs to be limited accordingly. Usually what I see is 15V for cyclic, 13.5 for standby. I've never seen nor heard anyone talk of pushing an FLA to 15V, with only a slight potential prospect of an equalization charge being the wildest exception I can think of. The magic numbers (that I was taught) for FLA have always been 13.8 and 12.9 respectively.

The problem with that 8D boiling was only somewhat of a surprise to me - I knew that it was being held high, but ignorantly held disbelief that it would have a major effect in the relatively short time it was in service. She was a work horse, designed to take a little abuse, right?. Turns out, I was wrong. Dead wrong. Now she's a 150 pound gravity assertion system for the 2 square feet of dead grass she's holding down on the side of my house. Damn expensive weed control, I tell you... :~(

My conjuring of 12.75 for FLA is a home-brew calculation based on a compromise of never needing to add water, but high enough to ensure maintenance of 100% SOC. So far, hasn't done me wrong, when I am able to follow it, that is.

I don't want to exactly dispute someone else's years of experience, but this is what I've seen over the years for myself. Losing that 8D flat out sucked, she was pricey (well over $400), and I wanted to make sure it never happened again. I'm curious if the charge rates/usage cases are what is ultimately responsible for our discrepancies in the numbers...

To me, 14.4 on FLA has always meant 'oh crap, pull the plug', and depending on the capacity and how long I think it's been in this state, it may include 'check the temp (and water levels if they haven't been checked recently)'.

Conversely, On an SLA, 14.1 isn't even done charging yet (for cyclic), although this indicates low 90% completion, and isn't exactly of concern even for standby, so long as it hasn't been over 13.5 for more than 24 hours, and it gets terminated at that point.

Let me ask you this - On a typical use case for the controller that is calling for these voltages, what would be considered a 'normal' C/x rate at near completion?

Pseudo-Update - I found something that kinda supports both POV - About 1/4 of the way down the page, it lists various scenarios and architectures, we both may be right... hahaha

http://www.answers.com/topic/lead-acid-battery-1

I guess it all really does depend on what neck of the woods you're from and what you're using them for...

Steve

PS - Sorry, I have a tendency to rant - Passionate subject (electronics that is) :/

[scottsAI]

Madscientist267,

Very interesting read. Nice solution to a problem.

As a Mad scientist I know you require impeccable reference documentation. Took some hunting

Battery maintenance from Trojan Battery company:

http://www.wholesalesolar.com/pdf.folder/Download%20folder/battery_maint.pdf

Table 2 on page 4. Acceptable?

and

Battery charging profile for flooded Lead Acid Battery:

http://www.batteryuniversity.com/partone-13.htm

Figure 1.

Over the years I have taken care of many batteries the biggest 1Mwhr, today down to a 10kwhr.

Your numbers for SLA (sealed lead acid) and FLA (flooded lead acid) are a bit off in some ways and fine for others.

All battery voltages are at 25c, voltages as you know are temperature dependent.

Fig 1, shows battery voltage starts charging above 2.15v (12.9v), then increases to 2.40 (14.4v) to complete the charge.

My APC 1kw SmartUPS charges to 27.89volts and stays there (24 hr so far). Fine for SLA, yet not so for FLA according to Table 2. (table 3 has error for 24v float on gel (SLA)).

The UPS charging voltages are OK for day to day FLA charging, yet long term not high enough to get the battery fully charged which it requires periodically. (depend who you talk to monthly to quarterly for an equalizing charge. I understand the lower voltage will charge FLA given time for the bulk of the charging (as a guess something in mid to high 80's percent SOC), yet NOT good enough long term. For a Back up battery I would finish charge before left on float long term. The voltage is not even close for an equalizing charge at 15.5 volts (31v 24v bat).

The higher float voltage will burn off water from FLA, checking the water MONTHLY is required (recommended in many battery manuals). If kept watered will not harm the battery. IF battery is warmed by the floating voltage then something is wrong. Automatic watering systems are available, helps reduce battery maintenance, not too costly any more.

Have fun,

Scott.

[Madscientist267]

Scott -

Megawatt/hour banks? <drooling> Bet they're huge. Where do I sign up?

I guess it becomes apparent that the use-case is the biggest difference. Most of the numbers for standby FLA are about half way between where 'my' limits are, with SLA being a little toward the low side in the tables compared to what I have found for myself over the years. The cyclic use is definitely outside of the range that I am used to using them in, particularly the FLA.

It does make sense, in some ways I suppose, that cyclic use of FLA could have a higher rating since the consumer can get to the cells to add water. Are the higher voltages for a more complete charge in cyclic use because the battery never really 'sees' the elongated absorption phase? Since water loss seems to be one of the bigger problems for FLA, and it has an easy fix (when it's done that is, heh), I wonder if that's what they are basing it all on. The SLA being lower for cyclic since water loss is permanent for these cells?

There is still some confusion, however. If I am understanding this correctly, according to various statements in the battery university page, a long term float of 12.75V on FLA after a full charge will eventually sulfate if not topped and/or equalized periodically? From the battery university page:

Doesn't the 12.75 (2.125V/cell) cover this, holding the overall charge at 100%, while almost completely eliminating gassing? At this voltage, my long term graphs plot them pulling less than 20mA [each] as they settle into niche at this voltage. So, keeping this in mind, as well as the fact that the batteries I am using are much larger (8D) than the example car battery in the following statement, what gives?

Know what I mean? Conflicting information here. It's apparently a delicate balance between full capacity/preventing sulfation, and slowing down the gassing. And if the UPS charge output isn't sufficient to charge FLA, why is the gassing so high? The caps on the cells could be heard popping on a regular basis when I had it set up this way; something I haven't heard since dropping to 12.75 (thought this was in the right direction). Now I second-guess myself - Too far?

Temperature shouldn't be an issue, it stays at 22c in here for the most part.

Any ideas?

Thanks,

Steve

[scottsAI]

Madscientist267,

All good questions, will attempt to answer what I can. Wow this turned out much longer than I expected.

Where do I sign up?

Go Navy! Ships (submarine) battery backup.

SLA last 3 to 5 years tops (observation from my UPS), where as FLA can double that and more if taken care of and it cost a lot less. I figure the reason SLA only last 3 to 5 years, they never get an equalizing charge thus are sulfating to death. When the UPS declares them bad, not much life in them.

My current SLA batteries have written on the side: charge to 14v or 14.5 if cycled frequently. Wonder if the higher charging voltage would allow them to last longer? Nothing charges my SLA to 14v let alone to 14.5. I use a regular FLA deep cycle charger to charge a SLA backup set, have to watch the voltage, stop it after 14.5v, couple times did not catch it before 15v, battery is older than some in UPS, still working OK. So maybe the higher voltage helps it last longer! Yet if done too often might dry it out.

This is my understanding of FLA. Charging efficiency is 91% up to 81% SOC, good. Then falls dropping to 0% when 100% SOC is reached. Saw several references claiming FLA are 70%, where SLA are 90% efficient. My conclusions based on this is SLA are only charged to 80+% and ultimately sulfate to death. FLA most often are murdered, not allowed to live their natural life!-) Due to poor maintenance. You are guilty!-) (so am I).

To charge a battery above 80+% the battery voltage must be raised, the higher voltage causes the water to split into H2 and O2, thus the decline of the charging efficiency. The higher the SOC the more gassing that occurs the lower the charging efficiency. The gassing is a good thing, mixes up the electrolyte keeping the battery fresh. To reach 100% SOC the battery voltage must be raised to 2.6v/cell. The time at 2.6v must be limited or battery will be damaged by water loss / heat.

Yet if equalizing charge is not done the battery will die a slow death. Yin/yang thing.

Sulfating is a long term effect. Have not found any creditable time line for it, were talking tens of hours looking. The best advice I have read is to charge cycle a battery 5-10 times, charging to mid 80's% SOC, after the 5-10 charge cycles do a full charge to 90's% (light gassing) or at least Monthly do a full charge if the battery has been deep cycled that month. (charge cycle is defined as 2 discharges to 50% = 1 cycle also a deep cycle. Or 4 discharges of 25% (medium cycle) etc.) Quarterly do equalizing charge or at 5th full charge do an equalizing charge if needed more frequently, yet do no more than 6 equalizing charges a year. Important to equalize charge twice a year for FLA even if not being used. Good idea to equalize charge if battery discharged below 20% SOC (or discharged 80% very deep cycle or also called deep cycle discharge limit on most batteries).

Sulfating - time is the killer, depth of discharge and amount of time discharged are the key to sulfating. Based on this concept, an 80% (20% SOC) discharged battery will be killed in weeks due to sulfating, Were as a 20% (80% SOC) discharged battery will take years as in SLA. Please remember these are generalizations, SLA is a slightly different chemistry, yet is a lead acid basically, they claim the lead alloy results in different effects.

Now to your direct questions: >my answers!

Know what I mean?

>Yes.

Conflicting information here. It's apparently a delicate balance between full capacity/preventing sulfation, and slowing down the gassing. And if the UPS charge output isn't sufficient to charge FLA, why is the gassing so high?

>14 v as shown on the charts should get the battery charged to 85-90+?%, not quite a full charge but for daily charge cycled it is more than fine. Quarterly just add an equalizing charge.

The caps on the cells could be heard popping on a regular basis when I had it set up this way; something I haven't heard since dropping to 12.75 (thought this was in the right direction). Now I second-guess myself - Too far?

>Maybe, maybe not. 14v float, FLA limited gassing will occur, like you have to listen for it. Vigorous bubbling is Bad long term. FLA as shown is best floated at 13.5v just at the limit of gassing.

I would live with the 14v, and water battery monthly or more as needed, if watering is needed more frequently get an auto watering system, down to $6/cell on a bigger battery.

In the Navy taking care of the battery got me out of some clean up details. Took very good care of it! Funny thing was nobody else wanted to do it!

Have fun,

Scott.

[Madscientist267]

Scott -

You've definitely got me thinking a bit - In a small fit of paranoia, I pulled out my big charger and laid it on the solitary 8D to give it a good solid charge, others to follow.

The tricky part will be topping the UPS bank. I never set it up for a heavy charger in the design since I didn't think anything but the UPS chargers would be required for bulk recovery, and I'm reluctant to individually equalize them, as imbalance (as you know) is a whole 'nother post. Time for a visit to the drawing board.

As for automatic watering, what would you recommend? I've been aware of their existence, but I have a tendency to not trust things like this, due to the potential for something to go wrong. Also, from what I understand, there are a few different ways that they operate. Estimating (based on time and charge levels) and sensing (detecting the water level in each cell, maybe others (a hybrid?). I know in my case, the bank is up underneath the back deck in kinda a tight space, manual watering will be difficult as well as tending toward inaccurate, since I can't easily see into the cells to determine the levels without disconnecting and pulling them out (not feasable).

Thanks again for all the insight, there are definitely some things I hadn't thought about over the years... the failures in the other parts (at least as far as lead acid goes) has been pure laziness. I've lost batteries here and there to both sulfating and  gassing, with both (like you said) falling under the category of murder due to negligence. Heh, maintenance free? Guess there is no such thing.

Steve

[scottsAI]

Madscientist267,

I'm reluctant to individually equalize them, as imbalance (as you know) is a whole 'nother post.

Equalizing charge brings all the batteries cells up to max potential, individually equalizing batteries in a bank should not be a problem if the bank is OFF line, equalizing charge couple times a year.

automatic watering

Not bought one myself, manually water ($144 vs $12). Many designs available, prices are all over the map. The Flow-Rite design looked interesting, could be had for $6/cell on sale, yet it has two vent holes in the cap, I wanted ONE vent/cell, to connect a vent tube to each cell and vent outside of the enclosure. Should eliminate battery top cleaning. Did not plan to connect all cells to one vent, flash over is the concern, rather one battery then the whole thing.

Watering systems suggest to water once a month, or as needed. Why not just leave it on?

HydroCaps another option, reduces watering, does not eliminate it. Little cheaper than the auto watering systems, I would pay the extra buck/cell and get auto water system. Deionized water is cheap from my RO system.

The best indicator of a battery problem can be found by measuring specific gravity, not so easy to do, Battery voltage is a good second. If the battery is not accessible, provide connection to measure each battery's voltage. When you do the monthly watering check each batteries voltage before the equalizing charge and after. If your worried about battery life, recored the numbers.

Using the above systems gets the next best thing to SLA for much less money and a much longer lasting battery system. Very near maintenance free!-)

Have fun,

Scott.