Finding The Right Batteries

[Gary D]

1 hour ago, Dave Hounddriver said:

Thinking out load:

My NORECO electric bill tells me I use approximately 500 kwh per month. That does not sound like a lot but the highest bill I have had was for 600 kwh per month which cost me somewhere in the mid 5,000 peso range.

600 kwh divided by 720 hours in a month is only about 820 watts per hour, on average .  That does not seem very much considering I use a 1 HP split aircon unit approximately 20 hours a day.  Its almost always on so what's wrong with these numbers?  Seems they should be higher.

Your aircon is not running continuously, it cuts on and off so it may be taking  820w when running but only run 30% of the time it's on.

[AlwaysRt]

12 hours ago, Dave Hounddriver said:

Thinking out load:

My NORECO electric bill tells me I use approximately 500 kwh per month. That does not sound like a lot but the highest bill I have had was for 600 kwh per month which cost me somewhere in the mid 5,000 peso range.

600 kwh divided by 720 hours in a month is only about 820 watts per hour, on average .  That does not seem very much considering I use a 1 HP split aircon unit approximately 20 hours a day.  Its almost always on so what's wrong with these numbers?  Seems they should be higher.

Thinking out loud with you:

Your increase of 100 kwh was probably close to if not 100% aircon so can be ignored for battery calculations. 500 kwh divided by 30 days is 16667 watts/day. If your aircon is 'running' 7 hours a day (7 * 820 is 5740) it brings your daily usage to 16667 - 5740 = 10927 watts/day.

My usage last month was 280 kwh without aircon, divided by 30 days is 9333 watts/day. 

Averaging and rounding off to 10,000 watts/day divided by 15 hours of 'up time' is 667 watts/hour. Yesterday I researched and used high estimates for the equipment I want to run during brownouts and came up with 600 watts/hour so it looks like we are in the ballpark. 600 watts/hour divided by 12 volts is 50 Ah. So, since buying sealed deep cycle storage batteries instead of a car battery allows drainage to 20% vs 50%, we need:

for 1 hour - 50Ah divided by 80% requires a 62.5Ah Battery

for 2 hours - 100Ah divided by 80% requires a 125Ah Battery

for 4 hours - 200Ah divided by 80% requires a 250Ah Battery

A 100Ah Battery should last for (100*.8) divided by 50Ah is 1.6 hours

A 200Ah Battery should last for (200*.8) divided by 50Ah is 3.2 hours

Any comments or critiques of this math?

[Dave Hounddriver]

25 minutes ago, AlwaysRt said:

600 watts/hour divided by 12 volts is 50 Ah

Having read that the Amp hour rating on a battery is only valid if it is discharged over a period of 20 hours, then I suspect you would need a larger capacity battery than you are suggesting for maximum battery life and best performance.  So 50 amp hours X 20 = 1,000 Amp hours of battery rating to get best performance.

That said, I know that you can get by with fewer batteries than that but what is the downside to using fewer batteries?  Do they wear out that much faster?  Do they just run out of charge faster?  (That would not be a problem if you only need them for a couple hours a day.)

I'm thinking, like you, that one 200Ah battery would be enough to get me through a brown out.  But I'm not gonna try it first.  Lets have a few beers on Thursday and get you brave enough to go buy a 200Ah battery and a charger and see if it works 

Edited July 12, 2017 by Dave Hounddriver

[Huggybearman]

1 hour ago, Dave Hounddriver said:

Having read that the Amp hour rating on a battery is only valid if it is discharged over a period of 20 hours, then I suspect you would need a larger capacity battery than you are suggesting for maximum battery life and best performance.  So 50 amp hours X 20 = 1,000 Amp hours of battery rating to get best performance.

That said, I know that you can get by with fewer batteries than that but what is the downside to using fewer batteries?  Do they wear out that much faster?  Do they just run out of charge faster?  (That would not be a problem if you only need them for a couple hours a day.)

I'm thinking, like you, that one 200Ah battery would be enough to get me through a brown out.  But I'm not gonna try it first.  Lets have a few beers on Thursday and get you brave enough to go buy a 200Ah battery and a charger and see if it works 

My set up uses 200ah of batteries (2 x 100ah wired in parallel) and is fine for our particular needs. The vast majority of the brownouts last less than 2 hours and our batteries rarely use more than 20% of their capacity. For that we run an internet modem, 2 x 11w lamps, 2 fans, an LED TV if its an evening brownout and an internet TV box. The longest I have run these is about 4 hours, but that is very rare.

We have been running that setup now for over two years and the batteries appear to have lost little, if any, of their capacity.

Ken

[not so old china hand]

I have come rather late to this thread and I remember similar threads in the past: however the following comments may be of use. They are based on my experience of using batteries and an inverter-charger as the main day-to-day source of electricity on a live-aboard junk.

1) The capacity of a battery in AH does indeed decrease with increasing current draw. Battery manufacturers publish performance curves showing the capacity for different current draw.

2) Deep cycle batteries are the way to go. Not only do they allow more of the nominal capacity to be used but they are designed to support a significant constant current draw (tens of amps for hours). Car batteries are optimised to provide a short burst of energy to crank the engine (hundreds of amps for a couple of seconds). Drawing a significant current from a car battery for any length of time will kill the battery fairly rapidly.

In terms of bang-for-the-buck the cheapest deep cycle batteries are probably 6-volt golf cart batteries. It's also easier to lug around two 6-volt batteries than the equivalent 12-battery.

3) Doubling the battery capacity will more than double the life of the battery/batteries. Deep cycling reduces the life of the battery. Battery manufacturers publish curves showing battery life against depth of cycling.  The higher capacity also results in more efficient charging (see the next point). So in the long term doubling the battery capacity will save money. (This may not be so significant if the batteries are used infrequently.)

4) An "ordinary charger" is probably not the way to go. At least not if that means one purchased for a few dollars from an automotive accessories shop. These are designed for car batteries, either to keep a battery topped-up or to get a battery re-charged to the point where it can start the car. They do not match the charging profile of a deep-cycle battery. At best it will never fully charge the battery and, at worst, it may significantly reduce the life of the battery. A "smart charger" will cost more but will enable you to get the optimum performance out of your battery. They also allow for the differing charging profiles of flooded, gel or AGM batteries.

 

As always JMHO.

Edited July 22, 2017 by not so old china hand

[Dave Hounddriver]

6 hours ago, not so old china hand said:

A "smart charger" will cost more but will enable you to get the optimum performance out of your battery.

It is so very difficult for some of us oldtimers to be "smart chargers".  By that I mean I go to the hardware store and some pyt (pretty young thing) sells me a charger and insists its the right one for the job.  Indeed its the only one they have that will do the job.  She explains how it will take 24 hours to charge my particular battery from empty and the charger has this pretty little meter that shows how much charge the battery has and indicates to the charger when to stop charging.

I said: "Great!  Charge it!"  Now I hope I was one of those "smart chargers".  It looks like this:

 Its a Panther 6 amp charger  You can click on the link that switches from 6v to 12 as needed.

Tell me its going to work for a 170 Ah deep cycle battery  or at least not hurt the battery.  If its going to work but work "imperfectly" I can live with that as I bought it to test a "system" I want to use involving that battery and a 1000 watt inverter and keeping some power on in the house during brownouts.

If the basic plan works for me I will upgrade to more batteries, solar charging etc etc as budget allows.

[robert k]

12 minutes ago, Dave Hounddriver said:

 

Tell me its going to work for a 170 Ah deep cycle battery  or at least not hurt the battery.  If its going to work but work "imperfectly" I can live with that as I bought it to test a "system" I want to use involving that battery and a 1000 watt inverter and keeping some power on in the house during brownouts.

If the basic plan works for me I will upgrade to more batteries, solar charging etc etc as budget allows.

Dave, 6 amp is a modest charge, I can't see it damaging a battery unless it keeps trying to charge after the battery is fully charged. Most likely yours will shut off or step down the charge to a maintenance trickle after the battery is fully charged. Verify by reading the instructions...if they aren't in Chinese or by watching.

[AlwaysRt]

1 hour ago, Dave Hounddriver said:

Tell me its going to work for a 170 Ah deep cycle battery  or at least not hurt the battery.  If its going to work but work "imperfectly" I can live with that as I bought it to test a "system" I want to use involving that battery and a 1000 watt inverter and keeping some power on in the house during brownouts.

Here is the link to the PSW 1012E (pure sine wave, 1000w inverter, 230v) with LCD inverter/charger I am looking at. It is a bit more than 4 times what you paid but includes a 1000w pure sine wave inverter with 3000w surge capacity and a 35 amp smart charger.

https://www.enfsolar.com/Product/pdf/Inverter/569f2e0362e74.pdf

picture of actual unit

[Dave Hounddriver]

14 minutes ago, AlwaysRt said:

35 amp smart charger.

It looks great and its something to look forward to in the future but I have to ask, how will those deep cvcle batteries handle a fast charge like that?  I assumed (yeah I know, never assume) that if they are designed to discharge slowly and over a long time that they are also expecting to be charged slowly and over a long time.  False assumption or not?

[AlwaysRt]

8 minutes ago, Dave Hounddriver said:

It looks great and its something to look forward to in the future but I have to ask, how will those deep cvcle batteries handle a fast charge like that?  I assumed (yeah I know, never assume) that if they are designed to discharge slowly and over a long time that they are also expecting to be charged slowly and over a long time.  False assumption or not?

False, especially false with the North Star Blue+ battery line which were designed specifically for deep discharge/high cycles (2050 cycles of 50% discharge), and fast charging (charging limit - none). Here is the link for the battery specs. https://www.northstarbattery.com/product/nsb-170ft-blue