National Luna Dual Battery Monitor & Controller

It came to my attention that myself & a couple of other users have had issues in the cold weather with these units.
The meters are reading a constant overcharge state on both batteries from cold start either until the engine has been run for a while or until electrical components are in use...all alternators concerned are outputting the correct charge...here's the response from Luna support...

Greetings Mr Fossett

(Looks like you're having one serious winter over there)
We are typically seeing more of this "error" especially with modern vehicles. In most of the reported cases, the alternator output voltage is over the over-charge warning voltage of the monitor (set at 14.65V). Most manufacturers of lead-acid batteries specify a maximum charge voltage of 14.6V.
We are also seeing an increase of battery failures due to excessive overcharge.

This happens quite often in cold conditions as many alternators compensate for the low temperature and increase their output voltage.
Normally this only happens for 10 to 15 minutes or until the engine temperature has increased sufficiently.
Turning on heaters, lights or other accessories help to bring the voltage down to within range by loading the alternator.

It is normal for the monitor to react in this way simply because it is warning of the potentially dangerous charging voltage. Unfortunatelly you will not be able to eliminate this warning.

We are working on an intelligent means of dealing with this type of warning while still keeping the health of the battery of high priority.

Kind regards
Steven Lambert
Product Development Manager
National Luna

foss said:

all alternators concerned are outputting the correct charge...

In most of the reported cases, the alternator output voltage is over the over-charge warning voltage of the monitor (set at 14.65V). Most manufacturers of lead-acid batteries specify a maximum charge voltage of 14.6V.

Click to expand...

Are yu saying that the Alternator is or is not overcharging, because those two statements appear to be contradictory.

Well , Luna are saying their monitors are set too low as not to compensate for an alternator giving a slightly higher than normal charge in adverse weather...set at .2 volts more they wouldnt flash & buzz at us like Daleks on speed!
Since the sub zero temps have gone, they seem fine

ah!
so - all it needs is a temperature compensation circuit built in then?

well....YEH!
you gonna knock one up for me?!

tiz easy enuf to do - only needs a thermistor (of the correct value. I am sure that Luna could do it easily enuf.
I am sure that if someone designed the circuit, I could make it for you.

interesting. I have not had any problems with mine.

It does say (somewhere) that those readings on the gauge are only accurate at around 20-25 degrees C. might help explain some issues.

G