batteries

[Guest]

could somebody please explain in terms that a blond can understand

1) a battery is 150ah what does this mean?

2) if i have 150 ah battery and i am using 5 amps how long before my lights go out?

Beth

 

[JeremyF]

Do you want the theoretical answer, or the much more complicated practical issues that arise in this area?

The theory is simple. A 25w 12v device would consume 2 amps. A 150 amp/hour battery would theoretically drive this for 75 hours.
Does this mean it would last 75 hours, and be chargeable afterwards - no.

Jeremy Flynn

www.yacht-goldeneye.co.uk
New pics 11.02.02

 

[JerryHawkins]

The AH rating of a battery gives an indication of the amount of energy the battery can store. Most batteries are quoted at the C/20 rate which means that 150ah battery will give 7.5amps for 20 hours (150/20). The same battery will theoretically give 1 amp for 150 hours or 150amps for one hour. In practice with a higher current drain than C/20, the battery will not last for the theoretical time it should - there are all sorts of complex formulae than can be applied to estimate the actual time it would last.

Your 5 amp drain is less than C/20, so you should get 30 hours or so (150/5). This assumes, of course, that you start with the battery fully charged, which it won't be unless you using a smart 3 or 4 stage battery charger or have an external alternator regulator fitted to your engine(s).

Hope this helps,

Jerry

 

[Guest]

Now Jeremy I am confused and this is exactly why I asked this question.

You give me two answers I understand the maths one but not the other one

Remeber I am blond please try to explain "would it last -no"

Beth

 

[Viking]

Re: Gentleman -please!

Gentleman - Please remember she a blond!
That reminds me - About the blond who was so feed-up with being thought of as being dump, decided to die her hair. Out in the country one day she meets a shepherd with his flock and asks "If I can guess how many sheep you have, can I pick one?" "Yes" said the shepherd. The number 352 come into her head, which happens to be the correct number. The shepherd being a gentleman offers her the pick of his flock. She looks the flock over and likes the look of a lively, cute one at the back of the flock, which she selects. The shepherd then offers his own challenge. "If I can guess the real colour of your hair, can I have my sheep dog back?"

<P ID="edit"><FONT SIZE=-1>Edited by Viking on Wed Feb 27 13:22:05 2002 (server time).</FONT></P>

 

[bedouin]

For every complex question there is a simple answer - and it's wrong!

In the simplest possible terms. 'Ah' is short for amp hours - so a fully charged 150 Ah battery will drive a 5A load for 150/5 = 30 hours before the lights go out.

Unfortunately life is never that simple - so if you need more details you are going to have to give a bit more background

 

[Stemar]

There are two main types of battery

1. Engine starting type. This is designed to give a high current belt for a short while, then be recharged. If it's discharge more than about half way, it suffers. If this happens regularly, it won't last long. Capacities tend to be given as a cold starting current, rather than in amp hours

2. Deep cycle battery These are desgned to give a lower current over a longer period. They will survive being disharged more than a starting type, but will still suffer if discharged too far. Capacities would normally be given in amp/hours. This is probably the type you are asking about

Any battery, if it is discharged to where the lights go out will suffer. Your 150amp/hour battery can give close to 30 hours (150/5) the first time you do it, but each time you try it, it'll last a shorter time until it will only last a couple of hours.

The moral is: don't try to make it last longer than about 15 hours before recharging, then your battery should last for years.

 

[Guest]

What more background do you want ?I just told Bill Mcfartland I dont wear pants

Its simple I have a fully charged battery 150ah I use 5ah on my indicator but it dosent last 30 hrs I know I am blond but can you explain please.

I know a lot has been asked and said about batteries in other threads but it gets to technical for me and I would like to understand.

Beth

 

[bedouin]

A few things.

1. Although the battery might have been 150Ah when you bought it, they do wear out for a number of reasons, and so it is probably nowhere near that capacity now.

2. The figure of 150Ah assumes that battery was fully charged to begin with. Most battery chargers / alternators aren't capable of charging a battery fully (many only get to about 75% of charge).

3. By the time you have used the 150Ah from the battery the voltage will be very low - so may not be enough to power the light.

4. Your load may draw more than 5 amps.

 

[Guest]

So what you are saying is to use 150ah@5ah= 30 hours I need a 300 ah battery?

Beth

 

[Guest]

To try to keep thing simple(blond dont forget) lets say its 5ah so it may last 30 hrs first time but only 22½hrs after that

Beth

 

[Chris_Stannard]

Agreed. Simply Beth you should not discharge your battery below 30% of its capacity, and with an ordinary alternator and regulator you rarely will be able to charge it much above 80%. So your 150 Ah battery will give you about 75 Ah usable (50% of the capacity) or 15 hours for your lights.
If you connect to shore power, and charge your battery by that means, you will get up to about 95% capacity which will give you about an extra 4 hours for your lights.
When you engine is charging the battery the rate of charge goes down as the battery fills so it does take some time before your battery will be recharged. When steaming overnight I would reckon on a four hour engine run to recharge the battery to a reasonable level. A smart alternator regualtor will improve the situation, by increasing the rate of charge, and getting you up to about 90% capacity.
If you are thinking of overnight sailing then you should do a power budget, including things like the fridge, instruments, radar if fitted etc. It may be that if you boat has had lots of things added you need to consider a second domestic battery. If you are thinking of having a smart alternator regulator fitted, cost about £150 plus three to four hours to fit, get the electrician to do this for you.

You will also note, from remarks above, that the engine start battery, which is required to provide a high current for a short time, should not necessarily be the same type as the domestic battery which provides a steady current over a long period. In any case do not use your engine start battery for the services if the domestic battery runs down. Use it to start the engine to run the electrics.

Final thought, if all the lights are internal, what about fitting halogewhich gives more light for less power

Good Sailing

Chris Stannard

 

[Guest]

Ok please understand what is simple to you may be difficult for others

If i go into a shop with something that uses 150 ah with an indicator and ask for a 150ah battery fully charged and I clip this thing on should it last for 1 hour?

Beth

 

[bedouin]

Something like that; it depends a lot on the specific battery.

As has been mentioned by someone else, if you want the battery to last then you shouldn't plan on using more than half the capacity between charges.

 

[JeremyF]

Thats a good summary Beth, as you would then not be discharging the batteries beyond 50%. They should survive this treatment and give a decent service life if they are service/domestic batteries (and not car/start batteries which are designed to give a blast of energy over a short period of time)

The question I have is what are you using that takes 5 amps for 30 hours before recharges?

Jeremy Flynn

www.yacht-goldeneye.co.uk
New pics 11.02.02

 

[Guest]

Well Jeremy its like this I dont if understand something I would like to try and have it explained in a way that i can understand. Now if its a case where I will have to do a 5yr electronics course ok i have to let it go. the 5ah is to simplify it , its just a number.However if I go into a supermarket(I think they sell anything now) and buy a battery then it should say on the product what it can do and it should do it. I think there are a lot of people that dont understand these things and are sold things that are not whats good for their requirments. So I just want to understand .Understand?

Beth

 

[JeremyF]

Message understood! understood?

Final topic in this area is duty cycle. Take the thirsty fridge. It may take 60w while running, but they assume decent insultation, and therefore quote a 33% duty cycle, i.e. runs 1 minute out of 3. Therefore its average consumption is 20w, or 1.75 amps

Jeremy Flynn

www.yacht-goldeneye.co.uk
New pics 11.02.02

 

[ccscott49]

Beth,
all this is theoretical, if you run a lead acid battery down more than 60%, it will suffer damage. You can discharge it to 60% of its capacity, if its 150 ah, thats 90 ah, so you could run your 5 amps for 45 hours, without damaging your battery, it would then recharge. Every time you re-charge a leaqd acid battery, a little bit of lead sulphate falls off and lies in the bottom of the battery, this degrades the battery. After a while the sulpahte gets so thick in the bottom of the battery and so thin on the plates, the battery will not hold a full charge and the sulphate starts to short out the bottom of the plates, further degrading the battery. Now if you wnat to keep your battery healthy, do not discharge it past 60% and try and keep it topped up as much as possible. Your lights will go out after about 100 hours, but they will never come back on again! if you discharge it like that a few times. I hope you understand, being a blonde has no bearing on the debate, most people don't understand battery theory, even the people who build them, its not an exact science! If you want further clarification, you can contact me, I'll try and help.

 

[Guest]

Jeremy - someone is pulling your jump leads

 

[robp]

Beth, what makes me think you're making blonds out of everyone else? Shall we start on the law of diminishing returns?