Max Lead Acid Discharge Current. at The Alternative Energy Store

Posted by James Cormican on July 29, 2008, 06:01:21 PM

Re: Max Lead Acid Discharge Current. (Reply #10)

putting in a 200a fuse and 175a breaker would to limit your inverter output to 2100-2400, depending on the duration of the surge. you could do this as an artificial barrier, but usually it is easier to know your loads than to replace fuses.

there is nothing wrong with starting small and using the generator. the only real problem is once batteries are used for 6 months to a year (depending on how they are cycled) they generally do not take well to new batteries added to the mix, and self discharging occurs. other than the battery issue it is often wise to start small.

i would recommend getting beefy balance of system equipment that can stay the same as the system grows; things like combiner boxes and load centers that can accept growth and limit re-running of wires and conduit.

james
Alt-E staff

AltE
"Making Renewable Do-able"
http://www.altEstore.com/

Tel: 877.878.4060 x107 or +1.978.562.5858 x107
Fax: 877.242.6718 or +1.978.562.5854

Posted by Ken Hall on July 30, 2008, 04:28:29 PM

Re: Max Lead Acid Discharge Current. (Reply #11)

Jerry

Your list is a good one. Following it, will prolong the battery life. In daily use, the batteries would have a 3-5 year life expectancy. You can get 4-8 if they do not get abused. Abuse them on a regular basis, and they will only last a year or two.

You asked again about limiting surge loads. Surge loads are very short duration, lasting from a few cycles, to several seconds. They are most commonly caused by motor startup. While they may draw large currents, the short duration of them will not normally harm the battery.

Although the inverter makers call anything above their rating to be surge capability, most of this is really peak loads of limited duration. So, are you asking about surges ? Or are you asking about peak loads of short duration ? (eg 1-5 minutes of microwave, 5-10 minutes of blowdryer) These are the ones that I worry about controlling.

The DC fuse is there to protect the inverter. While it would also provide some level of protection for a large battery bank, it doesn’t provide any significant protection for your small bank. Downsizing the DC fuse to 200amps would not be worthwhile. It would just limit the inverter, without adding significant protection for your battery. A sustained 200 amp load will do almost as much damage to your bank, as a 300 amp load.

IIRC, the Prosine uses a 300 amp class T fuse. It takes about 100 seconds at 600 amps to blow it, or about 1,000 seconds at 450 amps. That is why you can peak and/or surge the inverter above 3600 watts. And the inverter is supposed to load limit itself, before blowing the fuse.
A 300 amp breaker is supposed to kick out within a few cycles of exceeding the 300A. It would effectively limit the inverter to 3600 watts of surge/peak.

What is your current wiring situation in the cabin. What is the main breaker ? How many 15 amp circuits do you have/plan ? And how is the generator wired in, if it is ?

ken

Posted by Thomas Allen Schmidt on August 03, 2008, 08:09:35 AM

Re: Max Lead Acid Discharge Current. (Reply #12)

Well, after reading the other postings on this thread, I can more clearly understand your questions and, I would like to clarify, I was not suggesting that you, move to a higher nominal voltage, just that, generally speaking, sustained higher amperages might necessitate higher nominal voltage systems. Also, the calculations I performed are/were not intended for sizing any part of a PV battery charging/inverter system, it was just an effort to deduct where you got your "numbers" from. Enough of that.
If you're up for it, here is some, more or less technical articles you might find enlightening in regards to your system.
http://photovoltaics.sandia.gov/main.html
In particular,
http://photovoltaics.sandia.gov/docs/BattIntro.htm
and,
http://photovoltaics.sandia.gov/docs/John_Wiles_Code_Corner.htm
Personally speaking, when I size a battery bank for an off grid PV battery charging system, after calculating the number of amp hours of capacity anticipated per 24 hour day/night cycle (all things, such as inefficiencies, included), I multiply that by a factor of 5. Then I size the PV array to replace that amount used in a 24 hour day/night cycle in one sunny day. This has allowed me, in my region, to not have need of a generator. Of course this, genrally speaking, doesn't always fall within a prospective budget, so sometimes improvises are made.

Posted by Tim F on August 18, 2008, 03:55:19 PM

Re: Max Lead Acid Discharge Current. (Reply #13)

Quote from: Thomas Allen Schmidt on August 03, 2008, 08:09:35 AM

Well, after reading the other postings on this thread, I can more clearly understand your questions and, I would like to clarify, I was not suggesting that you, move to a higher nominal voltage, just that, generally speaking, sustained higher amperages might necessitate higher nominal voltage systems. Also, the calculations I performed are/were not intended for sizing any part of a PV battery charging/inverter system, it was just an effort to deduct where you got your "numbers" from. Enough of that.
If you're up for it, here is some, more or less technical articles you might find enlightening in regards to your system.
http://photovoltaics.sandia.gov/main.html
In particular,
http://photovoltaics.sandia.gov/docs/BattIntro.htm
and,
http://photovoltaics.sandia.gov/docs/John_Wiles_Code_Corner.htm
Personally speaking, when I size a battery bank for an off grid PV battery charging system, after calculating the number of amp hours of capacity anticipated per 24 hour day/night cycle (all things, such as inefficiencies, included), I multiply that by a factor of 5. Then I size the PV array to replace that amount used in a 24 hour day/night cycle in one sunny day. This has allowed me, in my region, to not have need of a generator. Of course this, genrally speaking, doesn't always fall within a prospective budget, so sometimes improvises are made.

T.A.S.,

Just read some of the papers and still reading others. Very, very helpful. And so far not too technical as I would think coming from Sandia Labs, etc.Thanks for posting the links.

Tim F.

Posted by Ken Holt on August 24, 2008, 02:52:28 PM

Re: Max Lead Acid Discharge Current. (Reply #14)

I have a similar small system that I have been slowly
trying to improve over the last 20 years.

Golf cart batteries have a moderately high internal
resistance when new, and the resistance goes up fairly
quickly with use and age. This means that the batteries
are somewhat self-protecting when used with a high-power
inverter - the battery voltage drops dramatically at
high currents, and the inverter shuts off.

For the AC power mentioned, 2 GC batteries are much
too small, and I would also go to 24 volts - something
I wish I had done on my system from the beginning (most
DC devices were only 12V back then, though).

Since there is no way to size a system for never having
a power loss, most off-gridders around here assume to
use their generators often, keeping the PV system only
moderately sized. For most of us, the cost and complexity
of a near-perfect system is not worth it.

Max Lead Acid Discharge Current.

Posted by James Cormican on July 29, 2008, 06:01:21 PM

Posted by Ken Hall on July 30, 2008, 04:28:29 PM

Posted by Thomas Allen Schmidt on August 03, 2008, 08:09:35 AM

Posted by Tim F on August 18, 2008, 03:55:19 PM

Posted by Ken Holt on August 24, 2008, 02:52:28 PM

cart

latest posts

top members