One big one or two small ones.

[Laysula]

I need to replace the domestic battery, is it best to get one 180 ah or two smaller ones of 110 ah each giving a higher capacity and costing less?

 

[prv]

Makes no real difference electrically, just depends on what fits best in your locker. A single battery would tend to occupy slightly less volume than the same capacity in two, but the shape of the pair might actually fit better.

All else being equal, it's more convenient to have lighter individual units. My 210Ah is a bit of a beast to lift; a pair of 105s would be easier to handle (but wouldn't fit in my locker, and in any case I don't intend to lift it out any time soon).

Pete

 

[oldbilbo]

If no difference electrically - as 'prv' says - there may well be a consideration of the cost/weight/space requirement for the extra battery cabling and connectors.... and fusing.....

 

[JumbleDuck]

Makes no real difference electrically, just depends on what fits best in your locker. A single battery would tend to occupy slightly less volume than the same capacity in two, but the shape of the pair might actually fit better.

It may be the same as engines. If having full power/capacity is important, buy one big one. If having some power/capacity is important, buy two smaller ones.

That aside, I went for 2 x 60Ah in my rather cramped battery space, rather than 1 x 120Ah, because the big one would have been a b*gg*r to handle.

 

[prv]

there may well be a consideration of the cost/weight/space requirement for the extra battery cabling and connectors.... and fusing.....

Connectors are about 40p each, extra cabling length is within the rounding error of the whole installation (ie, I didn't specifically add any length for interconnects when making my materials list). It would not be usual to add fuses within a bank.

Pete

 

[prv]

It may be the same as engines. If having full power/capacity is important, buy one big one. If having some power/capacity is important, buy two smaller ones.

I really don't think it makes much difference. Each lead/acid cell generates about two volts. A load of them are connected together in series (and possibly also parallel) to form the overall battery bank. How you arrange the plastic boxes around that collection of cells matters only from the point of view of physical handling and dimensions.

Pete

 

[JumbleDuck]

I really don't think it makes much difference. Each lead/acid cell generates about two volts. A load of them are connected together in series (and possibly also parallel) to form the overall battery bank. How you arrange the plastic boxes around that collection of cells matters only from the point of view of physical handling and dimensions.

Well, sort of. If each battery has 6 x 2V cells in series, and if the chances of a 2V cell going tits-up are fairly constant, then having two batteries doubles the chance of a failure but leaves you with half battery when failure occurs. Or, to put it another way, putting all your coulombs into one battery halves the chance of failure but ensures that any failure is total.

As I said, it's the same argument as for engines: fighters tended to have a single engine because half-power isn't much use in a dog fight while bombers tended to have two or more engines because losing all power over Frankfurt was a lot worse than going down to 3/4 power, even if the 3/4 power problem happened four times as often.

 

[Burnham Bob]

as for the argument about aeroplanes is that why the mosquito with two engines is called a fighter bomber? but seriously, if it's a new battery its not likely to fail for ages so having two batteries in case one fails is a bit too much belt and braces. as for weight, you'll only have to move it occasionally so just grimace and heave. and you won't have to check electrolyte in 12 cells - just 6.

 

[JumbleDuck]

as for the argument about aeroplanes is that why the mosquito with two engines is called a fighter bomber?

In that remarkable case it was designed as a bomber but turned out to be a fighter too, and yes, I think the number of engines is significant there.

I agree with you about batteries, by the way. The fewer the better, as long as you can move them when required.

 

[prv]

Surely the engine thing is just coincidence. Bombers had to be bigger to carry the bombs and to have the range. In the early 1940s, the only way to get enough power for such an airframe was multiple engines.

Pete

 

[JumbleDuck]

Surely the engine thing is just coincidence. Bombers had to be bigger to carry the bombs and to have the range. In the early 1940s, the only way to get enough power for such an airframe was multiple engines.

That was the only practical way, yes, because a single big engine, or even two biggish engines, would have been unacceptably vulnerable. Bombers needed redundancy, fighters didn't - or couldn't afford it.

 

[Laysula]

Well quite a short drift from batteries to fighter bombers,but thank you. Two smaller ones it is then.
Thanks
steve

 

[NickRobinson]

Ignoring the huge issue of the Mosquito leading to the invention of 'cascamite'....

Below just refers to house batts.. the start is separate

I have a shiny new 110 Ah and a tired but functioning 85 Ah (c. half capacity now). I could parallel them but (yes I would insert an ammeter and have a look-see) would there be a significant permanent drain from the new to the old/er ?

Cascamite? Apparently the animal glue prototypes came to bits if it rained....

N

 

[Buck Turgidson]

Glad you got back to batteries as most of the fighter bombers of WW2 had 1 engine not 2.
Light bombers suffered very high losses early on so fighter designs were adapted to carry Bombs.

 

[William_H]

To the OP yes on the basiss of weight to fit andf the ability to delete one battery if you get a failure I would go for 2. Do check the batteries individually for performance especially after a few years of service. ie that each alone will start engine and apparent capacity of each.
Regarding aircraft engines, during WW2 they did not have piston engines of sufficient power they seemed to be stuck with the limit of 1000 hp or so of the RR Merlin or the American P&W or Wright radial engines so the only option for a bigger plane was more engines. Like Howard Hughes creation with 8 engines.
Today with gas turbine there seems to be no limit to the power that cna be built. Less engines equals more efficiency and cheaper running costs. If it weren't for passenger and regulatory redundancy requirements they would go for one engine on the biggest planes. As it is of recent times we have seen many regular twin engine operations over vast oceans simply becuase engines are so reliable. Similarly a popular plane around here is the Pilatus PC12. This is a bigish 20 seater pressurised turbo prop which has just one engine on the nose. Very reliable and cheap to run.
Now if you were bombing in WW2 would 4 engines with 4 times the chance of a hit on an engine be better than 1 engine? Probably arguable except that those piston engines were not so reliable so multiple engines is good. But mostly bigger bomber means more gun placements and better defence against fighters so overall bigger is safer.
olewill

 

[JumbleDuck]

If it weren't for passenger and regulatory redundancy requirements they would go for one engine on the biggest planes. As it is of recent times we have seen many regular twin engine operations over vast oceans simply becuase engines are so reliable.

The regulations insist that a multiple-engined passenger plane must be able to climb away with one engine out, so there is always a lot of power in reserve when all are working. I was once (pre 9/11) in the jumpseat of a practically empty 757 which had to take off from Heathrow on full power because a technical problem with the limiters. It was pretty spectacular.

 

[Skylark]

I need to replace the domestic battery, is it best to get one 180 ah or two smaller ones of 110 ah each giving a higher capacity and costing less?

Steve, lifting and fitting two smaller ones will be less damaging to Lou's back and you'll also be saving beer tokens into the bargain. What decision needs to be made ?

When will you have completed the missionary work on the south coast and be ready to return to non congested waters?

 

[Vara]

I asked this question a few years ago and took the advise that three batterys would be easier to handle than one big one, having assisted a neighbour to change his 225ah battery I'm glad I did, hernia time.

Meant I had to spend a bit of money on terminal connections, but was worth it when i had one dead cell and could isolate offending battery before replacement.