C/10 Battery Charging Rate: Individual Battery or Battery Bank?

**Sunking** · 07-28-2012, 07:40 PM

OK I hope you have not bought any batteries as of yet because you are about to make a serious mistake. You DO NOT WANT to make 2 parallel strings unless you want to replace them every 2 to 3 years. You want one single string, so that means you have chosen the wrong battery. If you need 48 volts @ 2700 AH you need to buy cells that are 2700 AH like 24 of the Rolls 2YS31PS. It is a 2 volt 2430 AH cell.

Now for some more bad news your are going to be a poor person. The C/10 charge rate is for the total AH capacity. So if you have 2700 AH you need 270 amps of current. To do that will require 14,500 watt solar panels and 4-80 amp charge controllers with each charge controller connected to 3625 watts of solar panels. You are looking at a $60,000 to $100,000 system. Of that the batteries will cost you roughly $20,000 which you will need to replace in about 5 to 7 years. Those batteries weigh some 7000 pounds and will require a room of their own with ventilation. If you need to pull permits you are going to be required to have spill containment system and yearly inspections from you local FD and have to register them with the EPA so they can track them to the grave. If you ever have a spill, you will be held liable for all clean up cost to the EPA satisfaction.

**Anawa** · 07-28-2012, 08:04 PM

The Good News is.... I haven't bought the batteries

But, not good news about the controllers. Since the Genset is far more than I need, any thoughts on how I can maximize it with a hybrid set-up that is heavy on the aux AC input and reducing the battery storage? About 40% of the load during the summer is for mini-split AC units, but to dedicate it totally to this function doesn't make a lot of sense.

BTW, the Genset was a gift. I do have a bit of luck every-once-and-awhile.

Thanks
Anawa

**Sunking** · 07-28-2012, 08:46 PM

To use the Genset effectively you will need a charger that can provide a C/8 charge rate to the batteries. Don't worry Rolls batteries can handle C/8 as C/12 is the minimum and C/8 is the max with C/10 being the middle ground.

As I said it makes no difference if your battery capacity is 1, 2, 3, or whatever number of parallel strings there is. You charge based on the total AH capacity of the whole battery bank. What i would suggest is a bit of a different approach. You are now stuck in the Renewable Energy box mind of thinking. The 48 volt battery world is dominated by the Telephone Company world as every telephone office in the world uses very large 48 volt DC battery plants. There are hundreds if not thousands of salvaged or retired 48 volt rectifier plants out there. They are as small as 100 amps up to 10,000 amps and everything in between. The modular units with switch mode rectifiers use 100 amp 240/208 rectifiers. Get a 4-position shelf and 3 or 4 plug in 100 amp rectifiers, and wire each one back to the genset with 240 VAC. Each requires a 30 amp 240 VAC circuit. You can GOOGLE thenm using the term "48 Volt Rectifiers" look fo rnames like PECO, Realtec, Lorain, Marconi, and Emerson.

This is the kind of thing you are looking for.

**Anawa** · 07-28-2012, 09:42 PM

New Direction

Thanks SK... I'll do the research.

Anawa

**billvon** · 07-29-2012, 01:28 AM

Originally posted by Anawa

Is the charge controller sized to the Ah capacity of the individual battery capacity or the total storage in bank?

Total storage. A 2P configuration splits the current in two (in an ideal system) - thus a 2700AH battery wired in 2P sends half the current to each 1350AH string. Full current to both or half the current to half the array gives you the same rate.

In reality it's never quite half, which is an issue with frequently cycled battery systems. One string ends up cycling harder than the other.

**Anawa** · 07-29-2012, 04:14 PM

SK - I will definitely need your help to walk me though this "new direction". But first, what do you mean by "You are now stuck in the Renewable Energy box mind of thinking." Is this a good thing or... a not so good thing?

Now, to help me with this in very small steps: Is my initial understanding is that a rectifier assembly's primary function is: (a) convert AC to DC, (b) serve as a charging control, and (c) provide a means to distribute the DC? If I'm able to understand the fundamentals, hopefully I will not waste your time as you help I figure-out how I can best utilize your suggestion.

Anawa

**Anawa** · 07-29-2012, 06:10 PM

Off-grid: Array Sizing dependency on Battery Bank

Another question for the forum. Since I now realize that the sizing of the array becomes dependent on the size of the battery bank, at what point in the Off-Grid PV design process does this occur?

**Sunking** · 07-29-2012, 07:15 PM

Originally posted by Anawa

But first, what do you mean by "You are now stuck in the Renewable Energy box mind of thinking." Is this a good thing or... a not so good thing?

Neither good or bad. What I was pointing out is you got locked into thinking you had to use a charger made by a RE manufacture, when there are many more alternatives. So are much better and less expensive. For example I have not looked at the specs for the equipment you listed but I bet the inverter has a built in battery charger and generator input? If correct what amperage is the built in charger? Will it meet your needs of 270 amps? See where I am going with this?

I am willing to bet you could buy a standard battery inverter, salvaged Telco 48 volt rectifier for a whole lot less money. I am just trying to get you to look at all the options, not just the RE box mind solution. Give you an example most people who come here are stuck in a 12 volt box. All they know is 12 volt car batteries. The fools go out and buy 10 to 20 12-volt batteries to parallel them all up to get some unrealistic Amp Hour capacity at 12 volts. It is a disaster because what they really needed to do was use a 48 volt plant made from 2 or 4 volt cells of the correct AH capacity. Understand?

Originally posted by Anawa

Now, to help me with this in very small steps: Is my initial understanding is that a rectifier assembly's primary function is: (a) convert AC to DC, (b) serve as a charging control, and (c) provide a means to distribute the DC? If I'm able to understand the fundamentals, hopefully I will not waste your time as you help I figure-out how I can best utilize your suggestion.

Yes you understand correctly. But understand I am talking about a specialized rectifier used in battery plants. A rectifier by definition is just something as simple as a diode that converts AC to DC. Every AC powered battery charger has rectifiers of some kind.

A Telco rectifier is an AC battery charger with 2-stages of Float and Equalize. The current and voltage can be adjusted to satisfy any battery type in the lead acid family. You can also buy consumer grade AC battery chargers. The better units have 4 stages of Bulk, Absorb, Float, and Equalize. But I dare you to find one that can supply you with 270 amps.

So now you must be thinking well 4 stages are better than 2 right? Not really if you understand what each stage means. I will not go into that much right now but the Telco rectifiers can do exactly what the 4-stage chargers can do by just a simple voltage adjustment. Float voltage on a 48 volt flooded battery is 52.8 volts. But remember I said the Telco rectifiers voltage can be adjusted to meet any battery type. So all you do is adjust the voltage to the Absorb voltage of a 4-stage charger of 57.6 volts. When you do that the rectifier will then be a constant current charger of the Bulk stage until it reaches 57.6 volts, then becomes a constant voltage current taper of the Absorb stage. Which is perfect for using a generator because that is the fastest method to charge a battery. Once you see the voltage get to 57.6 volts, you wait until the current tapers to 27 amps and shut it down.

Questions?

**Sundetective** · 07-29-2012, 07:55 PM

Telco Rectifier - King of Efficiency?

King,

Do you have a Telco model that you can recommend?
I'm wondering how adjustable the voltage is.

Thanks, Bill Blake

**Anawa** · 07-29-2012, 08:07 PM

Questions? .... Yep I do, but not sure where to go from here.

You are correct regarding the Outback Radian Inverter/Charger: The charger output Max is 115Adc. 30 Amps @ 240Vac. I did not bring this up when I started this thread, but I viewed it to be a troublesome issue also.

Now, I think I know where you're coming from regarding the RE "box". The more I researched PV renewable over the last few years, the less enthusiastic I have become. The tax credits that created my initial enthusiasm don't work much anymore. Frankly, it has impacted me moving forward in constructing my home.

I am very interested in your suggestion to explore the rectifier solution for my particular situation. I don't mind plunging into the nuts and bolts (perhaps the reason my waning enthusiasm in PV RE), but before we begin, I don't think I would be comfortable being 100% dependent on a propane Genset. Aside from the constant drumming of the engine, I would be concerned about the cost (and as some believe, the eventual availability) of the propane fuel. Perhaps there is a way to reasonably mesh both the RE and rectifier equipment. Note: "reasonably" means cost effective. If this something worth pursuing I will gladly consider any guidance you are willing to offer.

BTW, I revisited my usage calc's and found that my estimated daily power consumption for the AC (ductless mini-splits) would be at least 60% of my load. Thus, my battery storage needs for the "rest of the house" would be greatly diminished. I'll do some more "deciphering" if need be.

Thanks
Anawa

**inetdog** · 07-29-2012, 09:32 PM

Originally posted by Anawa

BTW, I revisited my usage calc's and found that my estimated daily power consumption for the AC (ductless mini-splits) would be at least 60% of my load. Thus, my battery storage needs for the "rest of the house" would be greatly diminished. I'll do some more "deciphering" if need be.

Thanks
Anawa

An excellent outcome. As long as your panels can produce good power during the peak A/C time and still have enough extra to recharge the batteries for night use, you will not necessarily need enough battery capacity to run the A/C. But keep in mind that there may be times when you need to run the other 40% for several days of no sun.

**Sunking** · 07-29-2012, 10:46 PM

Originally posted by Anawa

Aside from the constant drumming of the engine, I would be concerned about the cost (and as some believe, the eventual availability) of the propane fuel. Perhaps there is a way to reasonably mesh both the RE and rectifier equipment. Note: "reasonably" means cost effective. If this something worth pursuing I will gladly consider any guidance you are willing to offer.

OK I will be totally honest with you with a question you need to ask yourself and answer yourself seriously:

Why do you want to pay 10 to 20 times more for electricity for the rest of your life?

By going off-grid battery that is the decision you are making. In addition you also choose to have a lifetime part time job maintaining and monitoring the system and counting every watt hour you you generate and consume. You do not have to answer, but you had better be honest with yourself. Two things are certain if you go through with this. You will not save a dime, nor do the environment any favors. Think about it.

**Sundetective** · 07-29-2012, 11:07 PM

Originally posted by Anawa

Questions? .... Yep I do, but not sure where to go from here.

You are correct regarding the Outback Radian Inverter/Charger: The charger output Max is 115Adc. 30 Amps @ 240Vac. I did not bring this up when I started this thread, but I viewed it to be a troublesome issue also.

Now, I think I know where you're coming from regarding the RE "box". The more I researched PV renewable over the last few years, the less enthusiastic I have become. The tax credits that created my initial enthusiasm don't work much anymore. Frankly, it has impacted me moving forward in constructing my home.

I am very interested in your suggestion to explore the rectifier solution for my particular situation. I don't mind plunging into the nuts and bolts (perhaps the reason my waning enthusiasm in PV RE), but before we begin, I don't think I would be comfortable being 100% dependent on a propane Genset. Aside from the constant drumming of the engine, I would be concerned about the cost (and as some believe, the eventual availability) of the propane fuel. Perhaps there is a way to reasonably mesh both the RE and rectifier equipment. Note: "reasonably" means cost effective. If this something worth pursuing I will gladly consider any guidance you are willing to offer.

BTW, I revisited my usage calc's and found that my estimated daily power consumption for the AC (ductless mini-splits) would be at least 60% of my load. Thus, my battery storage needs for the "rest of the house" would be greatly diminished. I'll do some more "deciphering" if need be.

Thanks
Anawa

Anawa,

If it's going to be a high dollar operation what are the Other Alternatives besides a generator running
all the time but using a high efficiency rectifier if possible and IF feasible.

Did a quick look for people using the 'Telco Rectifier' anytime in the past but there is only a little
that was said without some much deeper digging.

I see where some Rectifier people are talking about 96% Efficiency which stomps the 89% (and change)
from a battery charger that is a tinker toy compared to the Amps your talking about.

DC to DC Charging may come in handy under certain conditions but I have never seen better than
80% to 85% Efficiency for REGULATED, DC to DC Charging so far.

There may be a lot of room for new thinking since Solar prices came down so much in spite of all
the forums and all the posts. Time will tell.

A fairly small generator that wasn't too noisey used only during emergency or unusual conditions would
be ideal. This pre-election dip in fuel costs won't last forever.
Propane seems mighty expensive unless it's 1/2 $ what it was years ago.
Don't like the storage and stockpile game with Propane either. Fuel is a business with No Honor.

At a Crippled amount of BTU's per gallon compared to Diesel or Kerosene unless someone had money to
really burn I never did see Propane after doing them all for business and personal uses.
There are special situations in Survival, Construction, Etc. set-ups but running a generator for an
off grid house just doesn't seem that special.

While I'm at it I don't buy the C/10 line either. I don't go off about it like some do but I figure old Bill has
been charging plenty of batteries about as long as anybody around here and for Lead Acid,
if being lightly used,
C/60 (or so) has been just fine with a good C/8 Boost shot thrown to the badboys every week to every
month (or so) depending on usage.

I let the charger decide when to Equalize since it says that it's smart. Seems to know just fine.
Found that C/8 can wear some LA batteries out before their time - if done all the time.
I owned a couple of Fuel Delivery business's for years and worked my way through school as the pit man
at a huge Truck-stop close to 50 years ago so I just didn't fall off of the turnip wagon with
BTU's and Batteries.

Bill Blake

**Anawa** · 07-30-2012, 01:49 PM

Bill Blake - Please keep posting. I will respond to your post in a little while.

SK - The reason I am considering PV renewable energy has nothing to do with a need to save the environment, I'll leave that to the likes of Al Gore and his minions.

But rather, my house site is currently "way off" the grid. Although the local EMC generously offers to install the service to my site, it will cost me, at an absolute minimum, somewhere between $25k-$30k+. This cost arrangement applies only if I hire at my expense a third party installer, assume total responsibility for the installation, assume all future maintenance/failures on the line, and purchase the cable and equipment from them at "their cost". Otherwise, they will install the service at $95 LF for 5k+ feet, or somewhere in the neighborhood of $50k+. I may be missing something here, and I'm open to any comments and informative view points, but it seems that if I assume a lot of unknown risks with the installation and take-on future maintenance issues that will eventually occur, I'm still looking to a bear minimum front-end expenditure of $30k+ for electrical service. This reality lead me to explore PV Renewable Energy.

About Net Metering: subsequent to the power supply installation with a net metering agreement, there is a monthly fee of $5 plus an additional "fixed rate charge" yet to be determined, and any power purchased will cost me the prevailing rate of $.8kWh, with any sell-back at only $.0442 per kWh. Additionally, the net metering agreement is only good for one year, and subject to cancellation at any time. and sell-back is on a first-come-first-serve basis that will cease when the total Net Metering Membership reaches 0.2% of the Cooperative. It is obvious this EMC deals with the national energy "cooperative mandate" by making it very unappealing to customers investing in Net Metering accounts. I may be missing something, but I do not believe there are any benefits in the grid-tie Net Metering arrangement with this Utility. This Net Metering arrangement in no way helps off-set any front-end expenditures, indeed it only increases the front-end costs.

I've been advised, "well, just move and go where the power is". I find that an unacceptable response, not only is it condescending, but neither is it very creative. I own the home site land free and clear (341 acres), I have more than adequate space for gardening, a fishing lake, existing PV installations provide 11 gpm of clean well water, I have all the farm equipment I will ever need in my lifetime housed in two barns with PV lighting, thus I ain't interested in going no where.

So, here I am, without deep pockets (land poor), but knowing that I'm stuck with a $30k front-end cost. My thinking may flawed on this, but with the federal tax credit at 30% and the state of Georgia at 35%, a gross expenditure of $55k (my budget) on PV Renewable (or some hybrid) leaves me with a net cost of around $20k+. Preliminary PV configurations (see beginning of this thread) for the equipment and labor fall within this range, but I know I'm not done yet.

Yes, the cost of PV panels is lower than it has ever been (since I've begun researching) and it helps in reducing the overall RE costs, but what I have discovered to be most problematic with medium size Off-Grid installations (7kW +/-) pertain to the batteries. This thread is revealing to me that the problems with high-grade Off-Grid batteries is not limited to just their staggering cost (an initial quote on the 24 - Rolls-Surrette 4ks-25PS is about $26k), but the equipment necessary to ensure the health of the batteries for longevity, efficiency, and cost effectiveness bring to the table even more trying issues.

SK - Hopefully this diatribe lets you know this is something I'm not doing on a whim and I'm committed to work this through to the most cost effective solution achievable. You help, as well all other forum members, will be appreciated.

Thanks
Anawa

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C/10 Battery Charging Rate: Individual Battery or Battery Bank?

C/10 Battery Charging Rate: Individual Battery or Battery Bank?

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