John - as you may not have "standard" batteries fitted it would be best to look for the data sticker on the batteries this will give the capacity.
I expect Christopher or Clive have a cunning formula that shows how capacity reduces with age - a bit like my brain cells.
John Byrne a ?crit :
The car batteries can put several hundred amps, but I think you would be
interested in looking at the capacity of the battery as well. The
capacity (reserve of energy) of a battery is given in amps times hours.
For example, a battery of 65 A.h capacity will be able to push 65 amps
during one hour, or 130 amps during 1/2 an hour, or 32.5 amps during 2
hours... and so on. But your typical starter batteries have an actual
useable capacity of about half of what they are supposed to. The "deep
cycle", "marine", "leisure", or "solar panel" batteries are designed
differently (don't ask me how), they have a lower peak amperage
capability, but a more useable capacity.
If you're using your batteries a lot when the truck isn't running,
you're taking a risk to not being able to start your truck again. Hence
the numerous auxiliary setups and or voltage separators I know nothing
When driving, the factory electrical system more than likely has enough
spare amps to power the DVD and fridge, but if you're using a lot of
auxiliary lights, a stupid powerful sound system and an electric heater
at the same time, you will have to do your math about it.
I have two 70 AH batteries in mine, and starting is absolutely instant.
The worst time for a battery is starting in cold weather: you've
previously had heaters, lights etc on so it hasn't charged as quickly as
in summer; the engine oil is cold so the engine is harder to turn over;
and battery capacity drops with temperature.
However we get the "cold weather" dual battery setup which, in the
temperate European climate, is total overkill - and you would have to
murder your batteries before it wouldn't start. However if you are
planning a trip to Siberia think again ...
In my experience car batteries here die of old age, and anything over 7
years is probably borrowed time. The easiest and cheapest way to test
the state of your batteries is with a hygrometer, which is a sort of
squeezy pipette with a floating thingy in it.
You suck in acid from a cell, and the floating thingy will rise to some
level dictated by the "specific gravity" of the acid. You correct for
temperature and get an instant indication of battery health. Messrs
Quickfit, Halfords, etc will do it for you for free if you pop in (in
the hope that they can sell you a new battery).
If you plan to replace a battery it is best to do both at the same time.
There are two reasons for this:
- The older one may tend to discharge the new one (they are normally
connected in parallel)
- When starting they are connected in series, and a duff cell in the old
one may stop current getting to the starter.
However you should be guided by what a hygrometer says: if all the cells
in one battery are fine there is no real reason to throw it away.
If you are thinking in terms of battery drain for all these electrical
goodies you are planning to run then:
- If the engine is running don't worry about it. The alternator will
cope with 50+ amps.
- If you are planning on running them with the engine off then you will
need to do some simple maths:
Add up the total current consumption in amps (I think you said 16 Amps).
Multiply this by the number of hours you plan to use them, and this will
give you the Amp Hours you will consume. For example 16 amps for 5
hours =3D 80 Amp hours.
To be safe you should not discharge your batteries below their half-way
point, so if you currently have 2 x 70 AH batteries you have a total
capacity of 140 AH (when new & fully charged) so half of that is 70 AH,
giving you about 4 and a half hours capacity at 16 Amps.
HOWEVER: Batteries age, and to be conservative you have to assume that
by seven years old they are down to about 1/4 of their "new" capacity
and that they will have very little margin left to start the engine, and
you could kill them very easily.
This is why people with camper vans and the like usually fit an
auxiliary battery: they know they can run it flat without prejudicing
their ability to start the engine, and also "leisure" batteries will
stand up to the "run flat, recharge fully" (otherwise known as "deep
cycling") treatment in a way that ordinary car batteries will not.
I hope that answers the question.
Oh, and by the way thanks for the Christmas card!
| John - as you may not have "standard" batteries fitted it
| would be best to look for the data sticker on the batteries
| this will give the capacity.
| I expect Christopher or Clive have a cunning formula that
| shows how capacity reduces with age - a bit like my brain cells.
| Regards Gareth.
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Appreciate this topic was talked to death earlier but this ppoint
wasn't cvovered as far as I know ;-)
I know you're not supposed to mix and match old, new and different
types of batteries but what about this.......
Have 3 batteries all bog standard acid type.
2 for starting + 1 for fridge etc.
Now I need a deep cycle for the fridge because despite the fact that
the fridge has an automatic low voltage cut off - will be draining it
on an ongoing basis.
Question is if I go for a deep cycle auxiliary battery - will I need
to change out the 2 main batteries for deep cycle as well. The only
thing these are used for is starting and so in theory should never be
Will having one deep cycle and 2 acid batteries mess up my electrical karma?
Any knowledgeable insight appreciated
HDJ80 - T minus 27 days to lift off
You need not to worry. The split charger isolates the deep cycle
battery from the rest of the circuit.
For my own setup, (which is like yours, only some OEM circuits have
been switched to the deep cycle battery) I have bought, but not yet
fitted, a little gizmo called Priority Start, one for each battery.
I am hoping that in case of a malfunction or oversight, Priority Start
will prevent the two starter batteries from being discharged below
11.7V. Will report later how it performs.
Roman (London, UK)
'92 HDJ80 (auto)
On Mon, Mar 3, 2008 at 2:42 PM, Niall __ <[Email address removed]> wrote: