Energy audit...

[jakub]

I was just trying to perform energy audit of my new boat...but being a bit lazy I just had a thought that maybe somebody actually has done it before and has some nice spreadsheet I can use?

Year ago or so I had seen some spreadsheets with Peukert's Law to download.

Are they still around?

 

Thanks,

Jakub

 

Edited later:

Ps. What will be the best estimation of power output (let's say in Ah) of the 70 A rated alternator charging two 110 Ah batteries over one hour reaching the voltage of 14.1 V and having initial output 50 A (those measured with accuracy).

I know it is not linear and I know it is not simple at all, but I hope that Chris is going to spot it...

Edited April 7, 2009 by jakub

[Tony Brooks]

I was just trying to perform energy audit of my new boat...but being a bit lazy I just had a thought that maybe somebody actually has done it before and has some nice spreadsheet I can use?

Year ago or so I had seen some spreadsheets with Peukert's Law to download.

Are they still around?

 

Thanks,

Jakub

 

Edited later:

Ps. What will be the best estimation of power output (let's say in Ah) of the 70 A rated alternator charging two 110 Ah batteries over one hour reaching the voltage of 14.1 V and having initial output 50 A (those measured with accuracy).

I know it is not linear and I know it is not simple at all, but I hope that Chris is going to spot it...

 

 

I can not help you with the parameters you define and I doubt Chris or Gibbo can because the charge will be dependant on the state of charge of the batteries when you starts measuring your hour. I could even see a situation where the alternator may not reach 14.1 volts after an hour.

 

From empirical observation over a range of boats & battery banks it seems to me as if the best you can do is to assume an average charge rate at about half the alternator's rated output over about three hours. Less than three hours and the average is higher and more/much than three hours and it is less - a lot less over 6 hours because the last two or more will be a well under 15 amps.

 

Another reason or my belief is that you are interested in how well charged the batteries become and that depends upon things like temperature and battery condition which is why simple "amp + time counter" battery condition indicators will always be less than accurate. The answer to the state of charge question will be different on hot & cold days for instance.

 

Not much help, but its the best I can do.

[chris w]

I was just trying to perform energy audit of my new boat...but being a bit lazy I just had a thought that maybe somebody actually has done it before and has some nice spreadsheet I can use?

Year ago or so I had seen some spreadsheets with Peukert's Law to download.

Are they still around?

 

Thanks,

Jakub

 

Edited later:

Ps. What will be the best estimation of power output (let's say in Ah) of the 70 A rated alternator charging two 110 Ah batteries over one hour reaching the voltage of 14.1 V and having initial output 50 A (those measured with accuracy).

I know it is not linear and I know it is not simple at all, but I hope that Chris is going to spot it...

I would tend to agree with Tony on his AH's out of the alternator. In the first hour you will be close to 50AH if the batteries are about 50% down. If say 20% down you will get around 30AH approx. Remember though that only about 70% of these figures actually ends up in the battery as useful charge due to battery physics. So with a 50% discharged battery, one hour will get you about 35AH actually into the battery from your alternator.

 

As we often say on here, battery charging takes 6-8 hours at least normally.

 

Chris

Edited April 7, 2009 by chris w

[Theo]

I can provide you with the spreadsheet but what answers it gives depend entirely upon what data you enter. It may give you some sort of and idea.

 

If you want it would you let me know whether you want it in OpenOffice format or Excel, please.

 

Nick