Is it OK to parallel batteries when infrequently cycled?

[sdold]

Where I work, we've traditionally used large batteries having 2V cells in series, but some of the people here have become convinced (by battery salesmen) that several batteries in parallel are OK for our use since they are cycled only occasionally, maybe 5-10 times a year, and spend the rest of the time on float. An example would be ten 170AH 12V batteries in parallel for a 1700 AH 12V system.

I wondered if there is anything to what the salesmen are saying about infrequently-cycled service, or if we might end up with a lot of early replacements. These are Deka Unigy AGM model 12AVR17OET.

Steve

[SunEagle]

They look like a primary usage for UPS applications. Which can sit there dumb and happy for years but provide all the power you need when you need it.

The question is how many times will they give you all they can give. And I would guess it will be less than 5 cycles a year. But then again they may handle the load.

[Sunking]

Where I work, we've traditionally used large batteries having 2V cells in series, but some of the people here have become convinced (by battery salesmen) that several batteries in parallel are OK for our use since they are cycled only occasionally, maybe 5-10 times a year, and spend the rest of the time on float.

Steve the reps are correct. In telecom I have built more -48 vdc battery plants than I can count. Many of those plants have up to 20,000 to 60,000 AH. They are constructed using 2 volt 2000 to 4000 AH cells. So we are talking about 5 to 30 strings in parallel. Those monster plants have up to 170,000 pounds of batteries in a room.

Where you want to avoid parallel strings is with daily cycle applications. No problem using parallel Emergency Standby applications. We do a few things to combat resistances. We use a special custom designed overhead buss bar. At the load end is only 2 6-inch wide 20 feet long copper buss bars. Th enext drop has 2 more buss bars, laminated onto the first two bars and so on down the line. So by the time you get to the far end can have as many as 30 bars sandwiched up lamination. Several thousand pounds of copper suspended from the ceiling, or under a raised floor deck.

Here is the part you might like and is a great option for you because you are using single 2-volt cells. I even use the method in cell tower sites and switch office today. Use a ladder connection method. You can use as many parallel cells as you want in a daily cycle application. It is absolutely brilliant, stole it from the EV guys.

NOTICE. CAN ONLY BE DONE WITH 2-VOLT and/or SINGLE CELLS. DO NOT ATTEMPT WITH 4, 6, 8, or 12 volt Pb batteries.

[sdold]

Thanks Dereck, I feel better about the parallel systems now. We're not using the 2V cells anymore, so I guess we can't use the alternative method. I wish we could because they are connecting the same 12V batteries in parallel strings of 4 to make the 48V plants.

[Sunking]

Thanks Dereck, I feel better about the parallel systems now. We're not using the 2V cells anymore, so I guess we can't use the alternative method. I wish we could because they are connecting the same 12V batteries in parallel strings of 4 to make the 48V plants.

Is this typical Telecom application where the equipment runs off the Rectifiers? Batteries are online in the event power is lost to the rectifiers?

If true, no worries, standard MOP used by all of Telecom, Utilities, Military, Gov, Biz, and IT. Sounds like a small remote, relay, or telemetry?

[sdold]

Is this typical Telecom application where the equipment runs off the Rectifiers??

Yeah, the rectifiers float the batteries but also power the equipment. We have about 250 radio sites and most of the batteries are between 200 and 500AH in 12V and 48V. Some of them are 2000-4000 AH, but not many

[Sunking]

OK Steve relax, no worries with Parallel Batteries in your application. I am curious though about your operation. With that many radio sites operating at 48 volts suggest either Cellular or Private/Government/Law Enforcement Repeater Network. Cellular is usually 24 volts with 1500 to 3000 AH batteries. I just do not see many if any cell sites using 12 volt batteries and multiple strings. Pretty much see this kind of thing in cell sites. 24 volts @ 1800 AH. Makes me wonder what the designer was thinking or perhaps inexperienced.

A lot of younger designers get lost or on the wrong tracks. Example in school they teach parallel strings offer redundancy which is partially true, but fail to teach the downside of Parallel Strings.

Used in Mission Critical operations Parallel Strings does have advantages. It allows you to take a string off-line for maintenance. However DC Plants used in this fashion are not using Battery Power under normal operations. The Batteries are just FLOATING and the Rectifiers are supplying all the power to the equipment.

However things change when batteries are used in CYCLE SERVICE, and they do not teach that in school. That is when it becomes important to match and balance distribution resistance so all cells share equally. Problem is no two batteries, cables, or connectors have equal resistance and capacity.

Anyway what you are doing Steve is standard best practice MOP for your application. So relax.



balance resistance. That is snot easy to do

[sdold]

I am curious though about your operation.

Thanks for the info and taking the time to answer. These are all state public safety radio vaults. Most of them have a -48V system for the microwave, usually two or three paths using around 500-700 watts average for each.

A few of them have large 12V systems of 1000 or 2000 AH for all of the 12V radios in the vault. Other sites have each radio on its own AC power supply with a battery at the bottom of the rack for backup.

You mentioned once that we could use a 48V system with a buck converter for the 12V loads. I like that idea for a small stub MW site, but we keep them separate at major sites because the microwave is typically on a backbone that isn't just serving that site.

In both systems (12 and 48) the rectifiers are sized to run everything and charge the batteries too. If the utility power goes away, the generator starts (usually) and runs the site for a few hours, and the batteries stay charged. The only time the batteries are used is if the generator doesn't start, or runs out of propane. Running out of propane usually happens because a) No one noticed the "Gen Running" alarm, so no one called the power company, or b) Nobody remembered to get the tank filled over the summer, and now the snow is too deep to get a truck up there with propane.

los pinetos 48V.jpg sweetwater major hub site.jpg

[SunEagle]

Thanks for the info and taking the time to answer. These are all state public safety radio vaults. Most of them have a -48V system for the microwave, usually two or three paths using around 500-700 watts average for each.

A few of them have large 12V systems of 1000 or 2000 AH for all of the 12V radios in the vault. Other sites have each radio on its own AC power supply with a battery at the bottom of the rack for backup.

You mentioned once that we could use a 48V system with a buck converter for the 12V loads. I like that idea for a small stub MW site, but we keep them separate at major sites because the microwave is typically on a backbone that isn't just serving that site.

In both systems (12 and 48) the rectifiers are sized to run everything and charge the batteries too. If the utility power goes away, the generator starts (usually) and runs the site for a few hours, and the batteries stay charged. The only time the batteries are used is if the generator doesn't start, or runs out of propane. Running out of propane usually happens because a) No one noticed the "Gen Running" alarm, so no one called the power company, or b) Nobody remembered to get the tank filled over the summer, and now the snow is too deep to get a truck up there with propane.

[ATTACH=CONFIG]n326866[/ATTACH] [ATTACH=CONFIG]n326867[/ATTACH]

Sounds like you need a few more bells and whistles to keep the humans awake so they take care of the power systems .

[Sunking]

Steve I am completely familiar with what you are doing. Done a lot of radio work for Public Safety like you are doing, to cellular and military. All use the exact same MOP as you are. It is the bases of all Critical System design. So you are actually working with LMR network using MWR to transport backhaul. Years ago when I was young wondered why LMR used 12 Volts for base and repeaters. until I actually had to work with them. The base stations and repeaters are the exact same radios used in vehicles in a rack. When you move to Telecom the radios are +24 or -48. Same with MWR can be either +24 or -48.

You can buy -48 to +12 converters but there is a serious hurdle to overcome. If over looked is smoke. Anything strike you as odd when I say -48 and +12? I know you know this, but you might not have thought of the consequences of mixing a positive ground system with a negative grounded system. Does that get your attention real darn fast? It should because if you understand what I am saying if you connect the two systems without Isolation, you have SMOKE.

So whatever Converter you use MUST HAVE ISOLATION in the form of Galvanic Isolating via an Isolation Transformer. There can be NO DC interconnection. In other words no continuity between between systems. That is not hard to do, you jut have to know what kind of Converter to look for. Having said that may not be in the best and optimum configuration. That is why you see so many Radio Sites like yours that uses LMR or 12 volts have two DC plants. One for 12 volts and 24/48 for everything else.

But what you are doing Rectifier>Battery>Load is standard MOP for all Critical Mission systems. Some things that vary is sizing of batteries as an example, and how do you handle extended outages. Most do use generators for say outage lasting longer than an hour. That means you can use smaller batteries. But what if the site dies have a genny, but the nearest technician or mechanic is 4 hours away if the genny does not start. What if the site is real remote with no generator, just a genny Spout for a portable genny when it arrives up to 24 hours later. You get the point, just letting you know you are in my area of expertise.

[sdold]

Sounds like you need a few more bells and whistles to keep the humans awake so they take care of the power systems .

If I told you what the alarm sound is,you wouldn't believe me. I'll tell you anyway. It's a line printed on a dot matrix printer. In 2016!

[SunEagle]

If I told you what the alarm sound is,you wouldn't believe me. I'll tell you anyway. It's a line printed on a dot matrix printer. In 2016!

Wow. Reminds me of an old science fiction movie from 1971 where a piece of paper got between a bell and a striker. The alarm went off but it never "rang the bell" so no one ever noticed the message on the printer. It was in the movie "Andromeda Strain" and the message called for a nuclear bomb to be dropped but it wasn't.

They do make some cheap and simple I/O devices to light up lights and ring bells that also talk to dot matrix printers. Seems like a prudent backup way to send an alarm to me.

[inetdog]

If I told you what the alarm sound is,you wouldn't believe me. I'll tell you anyway. It's a line printed on a dot matrix printer. In 2016!

Is it interlocked so that the "alarm" is silenced when you run out of paper?