Simplest fix's.
The simplest fix would be to have the engine restart when the battery drops
to 12.2v, run for a while then go back into standby.
Alternate would maybe be a PIC that monitors voltage, if sees 12.2v for x
period time (overcome spikes etc) start the engine for y period of time,
providing that the controller is switched on etc.

Does anyone know of a stand alone voltage/current data logger kit that could
log the battery for a few weeks (UK).

John.

"Lane Lewis" wrote in message
...

"John" wrote in message
...
Hi Guys.
I have the following problem, could you please help provide a little
insight
into the calculation.

A piece of refrigeration equipment has a 50hp engine with a 12v control
system, an alternator for battery recharge and of course a 12v (100Ah)
battery for starting.
The control system has a remote temperature and standby/ready control.
To
use the remote standby function the main controller must be on.
The problem is this.
When in standby mode the current draw from the battery is about 500mA,
if
the system is left in this state for a few days then the battery does
not
have enough capacity left for the starter to crank the engine.

Question.
What is the lowest voltage/capacity that the battery can be allowed to
drop
to but still be able to start the engine (12.2v seems to be the industry
standard voltage).
Finally how does the result equate to time e.g. do we have 20 hours at
500mA
or 50 hours at 500 mA before the battery capacity is to low to crank.

Battery standard lead-acid deep cycle type 100Ah.

With a good battery during crank the voltage drops to 9.5v and rises to
10.5v.

Same battery, initial engine crank current (cold) is 135A dropping to
36A.

The engine is a direct injection diesel so starts in around 2 seconds.
Thanks.
John.

something mechanical that does not need power to initiate the control
system might work. You could probably go a couple of weeks with this type
of
system.

Lane