New use of UPS' as charge controller

[bstedh]

Does anybody know the efficiency of APC UPS' off hand. I will do a web search in a little bit anyway.

Here is my idea to use the stuff I have on hand for an off grid supply.

I have 2X 1000W load capable APC UPS'. I was thinking of using them in series with a solar panel on the first and driving it as an inverter and then plugging the second one into that one with the battery string only on this second one.

Solar Panel 48V ==> UPS 1 (no batteries) ==> UPS 2 (48V battery string) ==> Load

Draw backs that I see up front would mainly be the efficiency of the UPS' and the voltage sensitivity of the 48V input of the first UPS to be able to handle a direct connection to the solar array. Would the panels configured for 48V optimal output ever go above 54V ~ 55V?

The plus would be a power system out of items currently on hand other than solar panels. (still looking into those) Also the first UPS would be supplying the power during the day and the second during the night possibly doubling their life span??????

I assume the pannels would need to generate upwards of ~20 amps from experience. 1000W at 110 = ~9Amps, My sump pump pulls around 9 amps and it's battery backup pulls over 60A to run it through a 12V inverter.

Otherwise anybody know how the UPS would react if I where to hook up the solar array and a standard controller to it's battery bank?

With 1600AH of matched batteries that 20A draw would give me a usable 320AH to stay within the 20% rule and 16HR of power at full load.
(EDIT: wrong calculation, it would be 1600AH at 12V so I would only have 400AH at 48V =[.... only 80AH and 4HR of power. Not much with 16 batteries....) No wonder batteries are the killer to solar.

Ed

[bstedh]

what would be easier on the batteries?

1. high amp draw through a 12V inverter with all 16 batteries in parallel.

2. lower amp draw through a 48V inverter with 4X4 battery stings.

I have a 12V 2000W UPS that I could use instead if it would be easier on the batteries.

[Sunking]

This is easy. The lower the current, the more efficient the system is, and less stress on the batteries. Always use the highest voltage possible.

Battery rules:

1. Never ever parallel batteries unless absolutely necessary.
2. When necessary to parallel, refer to rule 1.

OK on a serious note the only time it is necessary to parallel batteries:

1. Is when the system is mission critical so you can take 1 string off-line for maintenance. Limit to 2 parallel strings.

2. When the required Amp Hour capacity cannot be had with a single string. Today the maximum AH capacity of a battery is 4000 Amp Hours, so it would be a very rare case that you would ever use a 4000 AH battery string. At 48 volts we are talking 12,500 pounds total weight.

[bstedh]

This is easy. The lower the current, the more efficient the system is, and less stress on the batteries. Always use the highest voltage possible.

That is kinda what I was thinking. Plus the higher voltage will travel through the wire safer along with more efficient.

[bstedh]

I guess the more I think about it the more I realize that either way each battery will be doing the same work so at the battery it shouldn't make a difference in what draw each one will see. The bigger question is - Do AGM batteries work better in series or parallel life cycle wise? That's a question I have never considered before.

[Sunking]

I guess the more I think about it the more I realize that either way each battery will be doing the same work so at the battery it shouldn't make a difference in what draw each one will see. The bigger question is - Do AGM batteries work better in series or parallel life cycle wise? That's a question I have never considered before.

Does not matter what type of battery you use. If you parallel them you significantly reduce cycle life. That is why I say never ever parallel batteries unless absolutely necessary.

[bstedh]

I guess I hurt myself there because I have 16 100AH batteries to work with. On the good side I paid very little for fairly new batteries.

The other good thing is that my sump pump backup rarely ever has to cycle... only during power outages. I have 3 70AH batteries in parallel on that so that it will run all day if needed. Had one basement flood already, never want to have that happen again...

[Sunking]

Are they 12 volt batteries?

I assume they are since you mentioned 12 and 48 volt configuration.

[bstedh]

Are they 12 volt batteries?

I assume they are since you mentioned 12 and 48 volt configuration.

Yea, 12V telcom batteries.

I know they are good quality as the same ones have lasted over 8 years so far on a continuous float charge with the occasional power outage running them all the way down to 46~45V in a 48V string with a 9~12A load.

[bstedh]

What is is about parallel setup that reduces life cycle vs. series?

[Sundetective]

This is easy. The lower the current, the more efficient the system is, and less stress on the batteries. Always use the highest voltage possible.

Battery rules:

1. Never ever parallel batteries unless absolutely necessary.
2. When necessary to parallel, refer to rule 1.

OK on a serious note the only time it is necessary to parallel batteries:

1. Is when the system is mission critical so you can take 1 string off-line for maintenance. Limit to 2 parallel strings.

2. When the required Amp Hour capacity cannot be had with a single string. Today the maximum AH capacity of a battery is 4000 Amp Hours, so it would be a very rare case that you would ever use a 4000 AH battery string. At 48 volts we are talking 12,500 pounds total weight.

There is a fellow using 12 Volt Batteries in parallel (as far as the eye can see) .
A 24 Volt set-up using: twenty-four (24) Roll's 4000 Series T12-250's at a cost of $9600.

He says for his welding set-up this is the way it needs to be.

"That bank of T12-250's can deliver 700 amps to my inverters and maintain voltage above nominal so the inverters don't kick out due to overload while I'm welding, plus simultaneously running other normal loads.

It takes a lot of parallel connections to deliver that kind of amps and maintain the voltage at or above 24.0 at full inverter surge load. With a series string every single battery in that string would have to deliver 700 amps and the voltage sags. With the parallel strings at 700 amps draw on the bank each battery only delivers 58 amps."

His last battery set-up lasted near 7 years. I don't know how similar the last bank was.

Bill Blake

[Sunking]

There is a fellow using 12 Volt Batteries in parallel (as far as the eye can see) .
A 24 Volt set-up using: twenty-four (24) Roll's 4000 Series T12-250's at a cost of $9600.

He says for his welding set-up this is the way it needs to be.

"That bank of T12-250's can deliver 700 amps to my inverters and maintain voltage above nominal so the inverters don't kick out due to overload while I'm welding, plus simultaneously running other normal loads.

It takes a lot of parallel connections to deliver that kind of amps and maintain the voltage at or above 24.0 at full inverter surge load. With a series string every single battery in that string would have to deliver 700 amps and the voltage sags. With the parallel strings at 700 amps draw on the bank each battery only delivers 58 amps."

His last battery set-up lasted near 7 years. I don't know how similar the last bank was.

Bill Blake

Bill I am not saying you cannot use batteries in parallel, I am saying you SHOULD NOT use them in parallel if it is not necessary. Unless you need AH capacity in excess of 4000 AH it is not necessary. I do not doubt he used them for 7 years, but I bet anything after 1 or 2 years the capacity was no where near rated capacity.

I certainly understand the current draw problem of 700 amps would have turned any single string in that set up to mush. You seem to know a bit about batteries and the problem is internal resistance. Now what strikes me odd is the battery type and size was completely miss-matched for the application. Even the voltage selection was wrong with a 16,000 watt inverter. Everything about it is miss-matched.

He would have been much better served using an AGM battery at a voltage of up around 200 to 300 volts with a 200 to 300 AH capacity. 30 to 50 amps is no problem on a 200 to 300 AH AGM battery with virtually no voltage drop issue. Not too mention a whole lot less copper.

[SunEagle]

Bill I am not saying you cannot use batteries in parallel, I am saying you SHOULD NOT use them in parallel if it is not necessary. Unless you need AH capacity in excess of 4000 AH it is not necessary. I do not doubt he used them for 7 years, but I bet anything after 1 or 2 years the capacity was no where near rated capacity.

I certainly understand the current draw problem of 700 amps would have turned any single string in that set up to mush. You seem to know a bit about batteries and the problem is internal resistance. Now what strikes me odd is the battery type and size was completely miss-matched for the application. Even the voltage selection was wrong with a 16,000 watt inverter. Everything about it is miss-matched.

He would have been much better served using an AGM battery at a voltage of up around 200 to 300 volts with a 200 to 300 AH capacity. 30 to 50 amps is no problem on a 200 to 300 AH AGM battery with virtually no voltage drop issue. Not too mention a whole lot less copper.

I still very new at this so I need to ask for a little more detail about what you said.

How do you get your system up to 300 volts using a 300AH battery? I presume you would series a number of them but what voltage do they come in and at what cost?

[Sunking]

How do you get your system up to 300 volts using a 300AH battery? I presume you would series a number of them but what voltage do they come in and at what cost?

Battery cost are pretty much fixed depending on the quality. A good quality FLA battery will cost you roughly $200/Kwh.

As for the voltage of the cells used is dependent the AH rating and how it relates to the weight of the battery. For example 12 volt batteries (6 cells in series) range in capacity of say 5 AH up to about 200 AH. At 12 volts @ 200 AH weighs in at 130 pounds. FLA Energy Density runs roughly at 40 wh/Kg. That 12 volt 200 AH battery has a capacity of 2400 watt hours which is a Energy Density of 41 wh/Kg.

So what if you need a AH capacity of 1000 AH. Well if you did that with 12 volt batteries they would weigh 650 to 700 pounds each. However you can buy 4 volt 1000 AH cells and they weigh roughly 200 pounds each which is manageable. The largest cells are 2 volts @ 4000 AH and weigh in at 700 pounds each. So if you wanted 12 volts would be 3200 pounds. But cells that large are usually used in 48 volt and up systems for large capacity. I have made several Telecom 48 volt battery plants @ 12,000 AH. But for something like a UPS the battery voltage is usually up as high as th eAC voltage involved. For example most industrial UPS systems generate 480/277 VAC and we use 560 volt batteries on them.

[SunEagle]

Battery cost are pretty much fixed depending on the quality. A good quality FLA battery will cost you roughly $200/Kwh.

As for the voltage of the cells used is dependent the AH rating and how it relates to the weight of the battery. For example 12 volt batteries (6 cells in series) range in capacity of say 5 AH up to about 200 AH. At 12 volts @ 200 AH weighs in at 130 pounds. FLA Energy Density runs roughly at 40 wh/Kg. That 12 volt 200 AH battery has a capacity of 2400 watt hours which is a Energy Density of 41 wh/Kg.

So what if you need a AH capacity of 1000 AH. Well if you did that with 12 volt batteries they would weigh 650 to 700 pounds each. However you can buy 4 volt 1000 AH cells and they weigh roughly 200 pounds each which is manageable. The largest cells are 2 volts @ 4000 AH and weigh in at 700 pounds each. So if you wanted 12 volts would be 3200 pounds. But cells that large are usually used in 48 volt and up systems for large capacity. I have made several Telecom 48 volt battery plants @ 12,000 AH. But for something like a UPS the battery voltage is usually up as high as th eAC voltage involved. For example most industrial UPS systems generate 480/277 VAC and we use 560 volt batteries on them.

Sunking

Thank you for getting back to me. I have some experience with Computer Room UPS systems. Normal power was from a 480/277 volt transformer. The batteries were 48 volt. Both were wired to a Liebert UPS system which inverted the DC and transformed it down to 208/120 vac for a couple of CPU boxes that fed the computer equipment. I would not have thought about using 560 volt batteries but I guess that would work instead of using a transformer to boost it to the desired level.

I never really thought about the battery charge controller before since it just came with the UPS system. Now that I am working on a small personnel system I want to better understand what are the right components that make it up. That is why I joined this discussion group to learn from those that have more experience with building the systems from scratch. I also want to learn about batteries and the different options to build my system correctly. I appreciate your guidance with this.

Vince