Batteries calculation ?

[Wiz]

Hear, hear Buzz !,

Benz, you are not quite getting it. It is probably a failure of my explanation, but I can't do much more. My old shrivelled wizard's brain is failing.

But just a couple of points:

The de-rating figure is to compensate for features of the battery and not of the system. However, the compensation for the battery is adjusted by features of the system. Your previous post explains the circumstances when you would use a de-rating figure of 1 or 1.75. These circumstances are not in the BS recommendation.

Have you ever considered doing what BS recommends instead of what you think is right? It might save you grief in the future.

With respect to your comment in yesterday's post  ....but to the positive side, D = 2 is just more safer de-rating factor, but it does not mean it's wrong or against BS; I agree a de-rating figure of 2 could be considered 'safer' than a de-rating figure of 1, because you just end up with a higher capacity standby battery. However BS doesn't recommend a catch-all de-rating figure of 2. So by using that figure in that way, it is clearly going against the recommendations of BS. You will end up with a bigger battery than you might otherwise need to meet BS recomendations.

More importantly, sometime in the future, when you commission a system designed by me and you use the catch-all de-rating figure of 2 in your calaculations, and subsequently write on your certificate that the batteries do not have sufficient capacity to run the system, thereby giving everyone the impression that I don't know what I'm doing, I will sue the a**e off you!
In court, I will show the BS recommendation of calculation to the judge and leave it to you to argue with him why you think you know better than BS and have used another figure. Will the BFPSA back you up? I suggest that they will say that you misunderstood their advice.

Brain now totally failed and shutting down for urgent repairs- A drink at the Banter Bar might help.

[GregC]

Of course that is all very well for Life systems, whats the calculations for a P system witha back up generator, UPS and windfarm ?

[Benzerari]

One of the major issues behind the need to get batteries calculation in every service visit is, the temperature impact on the batteries life cycle, according to 'Arrhenius’ equation (Findings), For every 10 °C increase in temperature the reaction rate doubles. Therefore, an hour at 35 °C is roughly equivalent in battery life to two hours at 25 °C. In one side we can say the heat is the enemy of the battery and according to ‘Arrhenius’ even small increases in temperature will have a major influence on battery life cycle affecting both the desired and undesired chemical reactions.

The following figure explains this:


http://i472.photobucket.com/albums/rr87/BenzFerari/BattTemp.jpg

Benz - without trying to appear rude you have a tendancy to overcomplicate and go into too much detail on what are simple enough topics.
If the BS says use this calculation then I use it and if it is wrong for some reason then that's not my fault - I calculated to the formula given by BS5839!
Some of us are but mere fire alarm engineers!!

This reply doesn't coincide with the quote buzz!

Otherwise where is the complication and in relation to what post, we are discussing issues to learn better, and none is forcing none to uses what so ever  

[Benzerari]

The de-rating figure is to compensate for features of the battery and not of the system. However, the compensation for the battery is adjusted by features of the system. Your previous post explains the circumstances when you would use a de-rating figure of 1 or 1.75. These circumstances are not in the BS recommendation.

Wiz; No one said that circumstances are in the BS, however I quoted what you have stated in your previous posts, which are the following

Using a de-rating factor in your calculations provides a calaculation as taking into account of the fact that the battery's stated capacity in AH is a nominal figure because most batteries can't actaully meet their capacity rating on HIGH LOADS and are likely to exceed it on LOW LOADS. I.e a 24AH would probably be able to provide 1A for 30 hours but only 8 hours at 2.4A. The battery capacity is normally rated as if 1/20th is being taken out of it i.e if 1.2A was taken from a 24AH battery it would last 20 hours (i.e what you would expect from a 24AH battery!)

That's from where that circumstancies I stated come from

[Benzerari]

Have you ever considered doing what BS recommends instead of what you think is right? It might save you grief in the future.

Wiz;

This forum is to discuss many issues in fire industry even issues coming from BS, or any other institutions, and the purpose is to understand better what is what, it is simple just to apply what is recommended by BS or BFPSA or any other recommender, but this will not prevent us to try to understand why things are done that way, it doesn't mean necessarely we know better than BS. since trying to understand is not against the standard in any way. also if some one prefered not to get involved to 'Why' and 'How' and just applies what is recommended, it still his own choice. and nothing wrong with that

[Wiz]

Of course that is all very well for Life systems, whats the calculations for a P system witha back up generator, UPS and windfarm ?

Don't you start as well!

[Allen Higginson]

One of the major issues behind the need to get batteries calculation in every service visit is, the temperature impact on the batteries life cycle, according to 'Arrhenius’ equation (Findings), For every 10 °C increase in temperature the reaction rate doubles. Therefore, an hour at 35 °C is roughly equivalent in battery life to two hours at 25 °C. In one side we can say the heat is the enemy of the battery and according to ‘Arrhenius’ even small increases in temperature will have a major influence on battery life cycle affecting both the desired and undesired chemical reactions.

The following figure explains this:


http://i472.photobucket.com/albums/rr87/BenzFerari/BattTemp.jpg

Benz - without trying to appear rude you have a tendancy to overcomplicate and go into too much detail on what are simple enough topics.
If the BS says use this calculation then I use it and if it is wrong for some reason then that's not my fault - I calculated to the formula given by BS5839!
Some of us are but mere fire alarm engineers!!

This reply doesn't coincide with the quote buzz!

Otherwise where is the complication and in relation to what post, we are discussing issues to learn better, and none is forcing none to uses what so ever  

Sorry Benz but there would have been too many quotes to insert to back up my statement.

[Wiz]

Have you ever considered doing what BS recommends instead of what you think is right? It might save you grief in the future.

Wiz;

This forum is to discuss many issues in fire industry even issues coming from BS, or any other institutions, and the purpose is to understand better what is what, it is simple just to apply what is recommended by BS or BFPSA or any other recommender, but this will not prevent us to try to understand why things are done that way, it doesn't mean necessarely we know better than BS. since trying to understand is not against the standard in any way. also if some one prefered not to get involved to 'Why' and 'How' and just applies what is recommended, it still his own choice. and nothing wrong with that

The hope of resolving a lack of understanding is the reason why most of us post on Firnet.

Whilst I fully agree that it is great to discuss various things on a Forum such as this, we are mostly talking about life safety systems that are covered by design and installation recommendations which, if ignored, can involve serious legal issues.

There may be 10 ways to do something but only one of these may be included in the recommendations. In such cases, that one way is probably the right way.

For those that just 'dip' in and out of Firenet on an irregular basis seeking advice, we must make it totally clear which way is recommended by the standards and that anything else is just ideas, opinions and guessing. Most people don't want unrecommended options, they only want to know the 'right' way. The least we can do is to ensure they can recognise which is which.

I hope that this has been achieved.

[Benzerari]

Thereby giving everyone the impression that I don't know what I'm doing, I will sue the a**e off you!

Wiz;

You really surprised me here, I have just realise that, I don't mean to be silly, we are just discussing things in a technical way, we may learn some thing new from each other, and that's the point.

If you technically convice me I will tel you thank you, as usually I do, if I convince you, you probably may have to say thank you ( if you want, but you are not obliged )...etc, and that's it.  It's done.

Apart from the need to applying the recommendation of BS which every body knows that, this will not prevent us from discussing and sharing views..etc

have a nice day

[Graeme]

As Buz mentioned.

i have paid for,sat  all FIA/BFPSA training schemes and i will continue to use their method i was taught and if it's wrong then i'm not to blame.

[Benzerari]

Further readings in BFPSA books, Unit 5, Maintenance course, page 33, issue August 2006.

I found the following:

---------------------------------Start of BFPSA wording---------------------------------------------------------
Most batteries are designed to be fully discharged over a 20h period.

Design load = C / 20h.  

De-rating Factor is:

The alarm load is usually much higher than the stand by load and this high current has to be allowed for in the battery calculation as the de-rating factor.

When the alarm load exceeds the design load then the battery could be considered of highly stressed and de-rating factor should be assumed to be D=2,

Example1:

The design load for a 2Ah battery would be 2Ah/20h = 0.1A

Example2:

The design load for 10Ah battery would be 10Ah/20h = 0.5A

For some systems the alarm load is quite low, perhaps nearly equal to the stand by load. In this case the battery is not stressed and factor D=1. This can make a small reduction to the calculation battery capacity.
-----------------------------------------------------End of BFPSA words-------------------------------------------

This is quite different to what wiz mentioned about BS version:

My question is:

1  -  If the batteries are stressed means: (Alarm load > design load) and (D=2) what equation revealed that?

2  -  If the batteries are not stressed means: (Alarm load = stand by load) and D=1 what equation revealed that?

I haven’t got a clue what’s going on in here

[Benzerari]

although annex D of BS5839-1 2202 assumes a D factor of 1.75 the FIA/BFPSA recommends using a D factor of 2,which,whilst making very little difference to the final figure,will greatly simplifybattery calculation because a D of 2 multiplied by a T2(alarm time) of 0.5
will equal 1 and can therefore be ignored

furthermore by leaving the multiplication by 1.25(the ageing factor) until last will simplify the actual workings even more....

The quote above is word by word taken from BFPSA maintenance course, unit 5, page 33, issue: August 2006

All OK except: 2202 it should be 2002, and just to tel you Grame the brackets are there, they are a bit thin, hence no need to claim your money back

[Allen Higginson]

I think you have to take into account what the BFPSA is in relation to the British Standards Institute and how relative each is in regards to recommendations or regulations.
My contracts state that a system is either designed,installed,commissioned or maintained to relevant BSI standards and to the recommendations within said standards.

[Graeme]

although annex D of BS5839-1 2202 assumes a D factor of 1.75 the FIA/BFPSA recommends using a D factor of 2,which,whilst making very little difference to the final figure,will greatly simplifybattery calculation because a D of 2 multiplied by a T2(alarm time) of 0.5
will equal 1 and can therefore be ignored

furthermore by leaving the multiplication by 1.25(the ageing factor) until last will simplify the actual workings even more....

The quote above is word by word taken from BFPSA maintenance course, unit 5, page 33, issue: August 2006

All OK except: 2202 it should be 2002, and just to tel you Grame the brackets are there, they are a bit thin, hence no need to claim your money back

thanks for pointing out that typo benz and just to let you know that i slept well last night for the first time in ages,as i was not worrying about de-rarting factors...

[Wiz]

Further readings in BFPSA books, Unit 5, Maintenance course, page 33, issue August 2006.

I found the following:

---------------------------------Start of BFPSA wording---------------------------------------------------------
Most batteries are designed to be fully discharged over a 20h period.

Design load = C / 20h.  

De-rating Factor is:

The alarm load is usually much higher than the stand by load and this high current has to be allowed for in the battery calculation as the de-rating factor.

When the alarm load exceeds the design load then the battery could be considered of highly stressed and de-rating factor should be assumed to be D=2,

Example1:

The design load for a 2Ah battery would be 2Ah/20h = 0.1A

Example2:

The design load for 10Ah battery would be 10Ah/20h = 0.5A

For some systems the alarm load is quite low, perhaps nearly equal to the stand by load. In this case the battery is not stressed and factor D=1. This can make a small reduction to the calculation battery capacity.
-----------------------------------------------------End of BFPSA words-------------------------------------------

This is quite different to what wiz mentioned about BS version:

My question is:

1  -  If the batteries are stressed means: (Alarm load > design load) and (D=2) what equation revealed that?

2  -  If the batteries are not stressed means: (Alarm load = stand by load) and D=1 what equation revealed that?

I haven’t got a clue what’s going on in here

Benz, I demand that you read my previous posts again and reconsider your latest comment:

This is quite different to what wiz mentioned about BS version:

You will find that much of what I have previously been explaining to you, you have now suddenly uncovered in your BFPSA book. Therefore it certainly is not quite different.

I would also point out that what I have been trying to get over to you is partly what BS recommends and partly my knowledge of the behaviour of batteries (which is not mentioned,as such, in BS). Both these elements are included in your latest BFPSA quote. Therefore I have previously mentioned every factor you now highlight in the BFPSA advice. You will also note that I have correctly highlighted the BFPSA advice that varies from the BS recommendations. I have even explained why they might use some different calculation figures, but explained that I do not agree that they should give this advice.

You do me a great dishonour by rubbishing my advice.

You seem to have an in-built system of misunderstanding, ignoring, disbelieving anything that I am telling you despite the fact that it is you that has asked for the advice in the first place. I appreciate that I may be poor at putting my points accross, although I have trained dozens of fire alarm engineers over the past 25 years with great success. Therefore I must assume that you either do not read my posts properly or are unable to understand them.

I'm sure you'll understand why I may well, in the future, choose not to join in on any of your posts.

Finally, I would, however make one final comment about the latest BFPSA advice you have quoted as follows:

When the alarm load exceeds the design load then the battery could be considered of highly stressed and de-rating factor should be assumed to be D=2,

Please note that the nearest equivalent advice in the BS recommendation quotes a figure of D=1.75 and finally, and most importantly, and as I explained at the very beginning, the BS recommendation is that any specific de-rating factor be obtained from that actual batterys' manufacturer, and in the absence of such, the figures of 1 or 1.75 should be used. BS never mentions the de-rating figure of 2.

In respect of your last two questions, the answers to both is that it is based on the behaviour of batteries to different discharge rates found through experience and testing by the manufacturer. There is probably a precise formula to calculate the behaviour and it will almost certainly include elements of chemical reaction. I do not know this formula. I suggest that you ask a battery manufacturer about it.