batteries

[Trevor_swfyc]

lights out

I'm not blond or female but I am confused this battery appears to be lasting longer and longer.
I think the server is about to go down so as i'm possibly the last posting on this topic Ill turn the lights out.
Bye
Trevor

 

[Chris_Stannard]

Sorry if I over complicated things. You are right, if you went into a shop and bought a brand new fully charged battery it would give you 150Ah. Please don't load it at 150 amps however as everything will get hot. The problem is that your battery would then never work again making it an expensive way to get 150 Ah. It would cost a few pence from the mains.
The lead acid battery fitted in most boats is designed to give you about half the amp hours in normal use at reasonable loads of its stated capacity. You will know when it is getting low because, like when we get run down we lack energy, so will the battery and the lights will go dim. Some of your electronics, in a boat, will stop working when the battery gets to low and you can set them to give an alarm when this happens. The alarm is set as a voltage.
One of your comments was correct, if you want to be able to serve a 5 amp load for 30 hours you do need two 150Ah batteries.
If you are really stuck find someone working on his boat and ask for help. Most of us will help each other willingly.

Chris Stannard

 

[LadyInBed]

Re: batteries - Links for further reading

http://www.attfield.dircon.co.uk/page13.html
http://www.solent.net/~hamwic/notes/battery charge.htm
http://www.uuhome.de/william.darden/
http://www.islandnet.com/robb/marine.html

 

[theduke]

if you stay connected to a shore power line,you will be able to keep your light going long after everyone else has gone out. (lights on no-one at home) it also is an excellent way of navigating back to the same place .

 

[jfkal]

In will last for about 20 hrs. Can't get any simpler.

 

[Guest]

Why ? Is the question to complicated for you robp?

Ok please explain the laws of diminishing returns Im sure someone would like to know.

Why dont you start your own thread on the subject? or dont you know how to.?

Beth

 

[Gordonmc]

Of course the maths in this thread is theoretical. 150 ah and a 5 amp light... simple division. While the reduction in capacity of batteries has been mentioned what has not is the resistance in the circuit which can increase the draw.
It is these variables which affect the outcome.

 

[steffen]

Fellow posters,
With great interest i have read this crash course on "How to confuse a blond". Fantastic. If you cant dazzle them with brilliance, baffle them with bulls**t. Not that all the posting are that i hasten to say; most touch the subject without answering the question.
NigelB gets the price for the most usefull answer.
Bedouin wins the "Have a go at the lady" award for asking for her background on the pretext of giving battery info.

But seriously; having read a lot about batteries because i need to buy two new ones, i collected a lot of info which is unfortunately in Dutch. Being originally trained a electrical engineer i do understand some of it but they did manage to confuse me. There are f.i. about 5 or 6 different ways to describe battery capacity (CCA, cold cranking amps, HCA, hot c.a., MCA, marine c.a., etc). Then there are differences between SEA and DIN definitions. And dont forget the Peukert coefficient.

Beth,
My advise: read on the the sites NigelB mentioned. They give a lot of info that is impossible to explain in a short message.

 

[Trevor_swfyc]

Answer (1) A battery of 150 amp hour is capable of holding this amount of electrical energy so to fully charge the battery at 5 amps would take 30 hrs.
In practice the voltage changes during the charge cycle reaching approx 14.2 volts, the charger will be designed to stop charging when this max is reached to avoid over charging and damaging the battery.

Answer (2) This question is a bit like if I have a car that does 30 mpg and I put in 5 gallon how far will I get before the engine stops. The theoretical answer is easy 150 miles. No petrol company would give you a breakdown refund because you failed to complete your 150 miles trip would they. You purchased 5 gallons of petrol and that is what you got. The same applies to the battery if theory its easy 150/5 = 30 hrs. others have all covered the in practice bit, did anybody mention temperature?.
Beth don't buy a 300 amp hr battery, you will never lift it or is that sexist?
Hope the cats OK
all the best
Trevor

 

[oldharry]

Like Steffen, I thought I knew about batteries - but after this lot I'm not sure who is most confused - Beth, me, or some of the posters.

Its dead simple really: 150ah is what the lable says. You dont discharge beyond 75ah because that will damage the battery and you would have to change the label to a lower figure each time you flattened it. But its a cold night so the capacity of the battery drops even further, so you only get around 60 ah.

Beths theoretical 5 amps now starts to dissappear after just 12 hours, and she certainly would not get the diesel going next morning.

Further complicate things by buying different types of battery: Engine cranking batteries will lose voltage on slow drain much more quickly, because they are designed just to give a huge blast of power to turn the engine for 20 seconds or so, not to run the cabin lights all night because you've got a good book on.

So you buy a leisure battery, which has exactly the same figures as the engine battery, and the cabin lights are working much better for quite a bit longer - but oh dear, the engine still wont start, because the leisure battery was not designed to do that, and doesnt turn it quickly enough to catch.

Both batteries will give (when fully charged, and in new condition) 1 amp for 150 hours, provided its a warm day (around 20C). But the engine battery will give a current usually in the order of 300- 600 amps for around 30 seconds (many more amps for larger diesels). Try it with a leisure battery and if it turns the engine at all, it will be overheating and destroying itself after 30 seconds.

You might get 1 amp for 150 hours, but if you take 10 amps out, neither battery will give 15 hours - what you will get varies with the type of battery, but you will be lucky to get much more than 10 hours - and probably considerably less before the battery begins to deteriorate irreversibly inside. So at that amperage you are probably only reliably going to get around 7 hours before things start to go wrong.

This is why when you leave the car headlights on for any length of time parked, it wont start next morning.

Trouble is Beth, amps or ah tucked up in a battery are not like grams or Litres on the supermarket shelf. The capacities given simply reflect the maximum possible power available in ideal conditions from a new battery. A bit like new car statistics: - 0-60 in 7.2 seconds, at 35 mpg is obviously going to be a faster vehicle than one doing 0-60 in 17 seconds at 60mpg.

But I gurantee you will never ever get away from the lights that fast, and when you come to fill up, it will be running nearer 28 to the gallon.

 

[robp]

My jest was in fun,as I was beginning to think your post was. Obviously that went over your head! A lot of guys tried to explain as best they could but to no avail.

150AH = 5A for 30H. Starting point. Batteries can't stand that punishment though.

6,000 revs on your car all day. Possible. Engine can't take that punishment though.

Law of diminishing returns:
Every time one returns from the drinks locker, it's contents is diminished.

Postings:
Plenty started in past - when I have time for anything but a quick comment.

Hey Ho

 

[ccscott49]

Heh! Beth, it was you who asked an unanswerable question, the guys have tried to explain this, including me. Starting to get naughty is not a nice way of saying thank you guys! but I'm still a little confused. The essence of the replies is that it is not a simple subject!