Jump to content

Batteries and being off grid


rowland al

Featured Posts

Having been through the pain of trying to understand my battery requirements as an off grid CC'er I thought I'd share my currwnt thoughts.

 

Battery life is adversely affected when there is no means to trickle charge them up to near 100% capacity after each cycle. Solar panels do help (mainly in the summer) but I doubt the batteries will ever get close to 100% if the batteries are used on a daily basis. Those who have access to a shore line each night are in a much better position to keep their batteries healthy for a long time as they can be trickle charged for long periods at low cost. Diesel and petrol is very expensive way to trickle charge and you can't easily do it overnight.

 

Find out what your daily power requirements are in amps. Someone here suggested I buy a clamp meter to measure the demand from the battery. It was very helpful in helping me check my estimated useage and voltage drops. 

 

Try to find ways of reducing your battery demand. The whole exercise has resulted in us changing to LED lights and getting a 12v TV which runs on only 1.5 amps. We also have a gas fridge which reduces our electricity consumption by a lot but obviously costs more in gas!  Our consumption is now around 15-20 amps per evening. 

 

Once the power requirements are understood, choose the best battery to suit your needs. My current thoughts on this are that domestic batteries are more expensive than starter batteries and take longer to trickle charge them up to near 100% so are more likely to degrade quicker.

 

We are experimenting with a single 12v , 75 ah silver/calcium starter battery. Cost just under £100. So far it has met all our needs. It never drops below 12.3v (70% capacity) after an evenings use and charges back up to 13.0v (measured after 2 hours settling time) with 2-3 hours engine running per day. It also seems to handle heavier loads like pumps with less voltage drop. 

 

I understand that starter batteries like to work between 70-100% capacity unlike deep cycle domestic batteries which are happier down to 50%. So I guess it's important to make sure they don't drop below this

 

As I say, it's all a bit of an experiment at the moment and it's early days. Even if this single 12v battery cops out after 2 years. It cheaper to buy another one than 4 new domestics (which is where I started from!). 

 

 

Link to comment
Share on other sites

3 minutes ago, Tony Brooks said:

Just one point that has been raised so many times before.

"Our consumption is now around 15-20 amps per evening." No its not, Current (Amps) is an instantaneous measurement, NOT a measurement over time. I think you mean Amp Hours.

I don't really agree Tony. To say I use say 20 amps over 6 hours (evenings use) is a rate!

I could say my consumption is 3.33ah if that's better? However it isn't. It might be 5ah in one hour and 1ah in another.

BTW, thanks again for your help in getting me here  :) 

Link to comment
Share on other sites

18 minutes ago, rowland al said:

To say I use say 20 amps over 6 hours (evenings use) is a rate!

20a for six hours is a quantity, not a rate!  Anyway, you should listen to TB as he knows his onions.  You will have to understand Ampere-hours or Watt-hours if you want to understand batteries.  :D

Link to comment
Share on other sites

26 minutes ago, rowland al said:

I don't really agree Tony. To say I use say 20 amps over 6 hours (evenings use) is a rate!

So you’re saying that you use 120Ah in an evening then? 20A for 6 hours?

If not, then hopefully you will see why the correct choice of units is important. 

46 minutes ago, rowland al said:

My current thoughts on this are that domestic batteries are more expensive than starter batteries and take longer to trickle charge them up to near 100% so are more likely to degrade quicker.

The first assertion is correct. Both of the next two are incorrect. 

47 minutes ago, rowland al said:

I understand that starter batteries like to work between 70-100% capacity unlike deep cycle domestic batteries which are happier down to 50%. So I guess it's important to make sure they don't drop below this

This is also incorrect. All batteries will have a longer life (more cycles) at 30% DoD than they will at 50% DoD. Your point only emphasises the fragility of a starter battery when incorrectly used as a leisure battery. 

Link to comment
Share on other sites

50 minutes ago, rowland al said:

Even if this single 12v battery cops out after 2 years. It cheaper to buy another one than 4 new domestics (which is where I started from!).

Well yes, buying one battery will always be cheaper than buying four, by approximately 75%. 

You select the size of battery bank according to your usage and charging regime. 

52 minutes ago, rowland al said:

Solar panels do help (mainly in the summer) but I doubt the batteries will ever get close to 100% if the batteries are used on a daily basis.

It entirely depends on your cruising times. If you’re cruising for 6 hours in the summer then the Batteries will be pretty close to 100% when you moor up, and then the Solar will top them off. Many boaters regularly charge to 100% daily in the summer if they have solar. 

Link to comment
Share on other sites

22 minutes ago, mross said:

20a for six hours is a quantity, not a rate!  Anyway, you should listen to TB as he knows his onions.  You will have to understand Ampere-hours or Watt-hours if you want to understand batteries.  :D

No, you are right, it is a quantity. 3.33ah is a rate.

20 minutes ago, Stephen Jeavons said:

So what you mean is that the current never exceeds 20A throughout any one evening?

Yes.

Edited by rowland al
Link to comment
Share on other sites

17 minutes ago, WotEver said:

So you’re saying that you use 120Ah in an evening then? 20A for 6 hours?

If not, then hopefully you will see why the correct choice of units is important. 

The first assertion is correct. Both of the next two are incorrect. 

This is also incorrect. All batteries will have a longer life (more cycles) at 30% DoD than they will at 50% DoD. Your point only emphasises the fragility of a starter battery when incorrectly used as a leisure battery. 

No, I didn't say I am using 20a for 6 hours. I said 20a over the evening. Yes, you do have to choose words carefully. 

Link to comment
Share on other sites

30 minutes ago, rowland al said:

I don't really agree Tony. To say I use say 20 amps over 6 hours (evenings use) is a rate!

I could say my consumption is 3.33ah if that's better? However it isn't. It might be 5ah in one hour and 1ah in another.

BTW, thanks again for your help in getting me here  :) 

20 amps over 6 hours = 6 x 20 = 120 Ah

120Ah out of a 75Ah battery = dead flat and impossible so something is wrong.

OK, now lets try 3.33 Amps over 6 hours = 6 x 3.33 = 19.98Ah Say 20 Ah as a fraction of 75 Ah = around 0.4 and that is more in line with your 12.3 volts at the end of your evening.

Anyway it would never be 20 amps over 6 hours UNLESS you had a six amp load running. The current floe (amps) would vary over time as appliances were turned on and off.

In my view when dealing with consumption and battery capacity it is best to take the evenings (in your case) where the consumption is highest but ignore those that are way over the top and are only a rare occurrences. In those cases you simply have to charge for longer. On lower consumption days you can charge for less time.

 

Link to comment
Share on other sites

21 minutes ago, WotEver said:

So you’re saying that you use 120Ah in an evening then? 20A for 6 hours?

If not, then hopefully you will see why the correct choice of units is important. 

The first assertion is correct. Both of the next two are incorrect. 

This is also incorrect. All batteries will have a longer life (more cycles) at 30% DoD than they will at 50% DoD. Your point only emphasises the fragility of a starter battery when incorrectly used as a leisure battery. 

Can you show me any evidence to support your assertions? 

Link to comment
Share on other sites

1 minute ago, Stephen Jeavons said:

And anything that happens over a period of time is a RATE not a QUANTITY! If time is in the unit it's a rate

Are you sure?

I would say 20 amps for 6 hours is a rate while 20 Ah is a quantity. Its a measurement of battery capacity, are you saying capacity is a rate?

It is also a measurement of "electricity used" by the end of a period so again its a quantity.

Anyway arguing that point serves no useful purpose, what is useful would be to get the OP to understand and use the correct units.

3 minutes ago, rowland al said:

Can you show me any evidence to support your assertions? 

look on any data sheet from a reputable battery supplier. It will quote a cyclic at a certain percentage of discharge.

My Exides say 300 cycles @40%

If the cyclic life did not vary with depth of discharge the manufacturer would not specify the depth of discharge in their data.

Link to comment
Share on other sites

4 minutes ago, Tony Brooks said:

Are you sure?

I would say 20 amps for 6 hours is a rate while 20 Ah is a quantity. Its a measurement of battery capacity, are you saying capacity is a rate?

It is also a measurement of "electricity used" by the end of a period so again its a quantity.

Anyway arguing that point serves no useful purpose, what is useful would be to get the OP to understand and use the correct units.

look on any data sheet from a reputable battery supplier. It will quote a cyclic at a certain percentage of discharge.

My Exides say 300 cycles @40%

If the cyclic life did not vary with depth of discharge the manufacturer would not specify the depth of discharge in their data.

I meant more this statement -

"fragility of a starter battery when incorrectly used as a leisure battery."

Link to comment
Share on other sites

1 hour ago, rowland al said:

Having been through the pain of trying to understand my battery requirements as an off grid CC'er I thought I'd share my currwnt thoughts.

 

Battery life is adversely affected when there is no means to trickle charge them up to near 100% capacity after each cycle. Solar panels do help (mainly in the summer) but I doubt the batteries will ever get close to 100% if the batteries are used on a daily basis. Those who have access to a shore line each night are in a much better position to keep their batteries healthy for a long time as they can be trickle charged for long periods at low cost. Diesel and petrol is very expensive way to trickle charge and you can't easily do it overnight.

 

Find out what your daily power requirements are in amps. Someone here suggested I buy a clamp meter to measure the demand from the battery. It was very helpful in helping me check my estimated useage and voltage drops. 

 

Try to find ways of reducing your battery demand. The whole exercise has resulted in us changing to LED lights and getting a 12v TV which runs on only 1.5 amps. We also have a gas fridge which reduces our electricity consumption by a lot but obviously costs more in gas!  Our consumption is now around 15-20 amps per evening. 

 

Once the power requirements are understood, choose the best battery to suit your needs. My current thoughts on this are that domestic batteries are more expensive than starter batteries and take longer to trickle charge them up to near 100% so are more likely to degrade quicker.

 

We are experimenting with a single 12v , 75 ah silver/calcium starter battery. Cost just under £100. So far it has met all our needs. It never drops below 12.3v (70% capacity) after an evenings use and charges back up to 13.0v (measured after 2 hours settling time) with 2-3 hours engine running per day. It also seems to handle heavier loads like pumps with less voltage drop. 

 

I understand that starter batteries like to work between 70-100% capacity unlike deep cycle domestic batteries which are happier down to 50%. So I guess it's important to make sure they don't drop below this

 

As I say, it's all a bit of an experiment at the moment and it's early days. Even if this single 12v battery cops out after 2 years. It cheaper to buy another one than 4 new domestics (which is where I started from!). 

 

 

That sounds expensive for a starter battery!

Link to comment
Share on other sites

14 minutes ago, Robbo said:

No it's like saying.   "I travelled 20mph over 6 hours."

Isn't that a rate of a rate? ;)

6 minutes ago, Naughty Cal said:

That sounds expensive for a starter battery!

Yes, I could have bought one for about £55 but I didn't want to add 'crap battery' to the list of my variables.

Link to comment
Share on other sites

32 minutes ago, rowland al said:

I meant more this statement -

"fragility of a starter battery when incorrectly used as a leisure battery."

How much evidence do you need?  There is a large selection of leisure batteries, designed for leisure use, there are a large number of starter batteries, designed for starting engines. Starter batteries are good at supplying high current for short periods. Leisure batteries are good at supplying low to medium current for long periods  

A link at random (there are thousands):

https://www.yuasa.co.uk/info/technical/understanding-leisure-batteries/

46 minutes ago, Stephen Jeavons said:

And anything that happens over a period of time is a RATE not a QUANTITY! If time is in the unit it's a rate

No it isn’t. As previously stated, saying “I used 20 Amps over 6 hours” is the same as saying “I travelled at 30 miles per hour per hour”. Unless OP meant he uses 120Ah per night, which I doubt. 

Link to comment
Share on other sites

49 minutes ago, rowland al said:

No, I didn't say I am using 20a for 6 hours. I said 20a over the evening. Yes, you do have to choose words carefully. 

So you are using 20A ‘over the evening’. How long is the evening? If 6 hours then you are using (20 x 6) 120Ah. 

Or are you saying you use 20Ah over the evening? Over a 6 hour period that would average out at 3.33A. 

Link to comment
Share on other sites

2 minutes ago, WotEver said:

So you are using 20A ‘over the evening’. How long is the evening? If 6 hours then you are using (20 x 6) 120Ah. 

Or are you saying you use 20Ah over the evening? Over a 6 hour period that would average out at 3.33A. 

Give up Tony - I have.

There are none so ....................................................  etc.

 

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.