Originally Posted by colemj
But your example was of a dead start battery?
Actually, the only lesson I can take away from your misfortune is to not trust batteries that you know are at their end of life.
The necessity of a dedicated start battery is not born out by your example.
Changing the subject, I am interested in how you are charging mixed chemistries. I understand the 13.8V for the LiFePO, but is that also the charging voltage on the AGM? Also, I though Li was not supposed to be float charged?
Edit: oops, I think you added a bit more to your post while I was writing mine.
My example was of SNAFU - FOOBAR - TARFU and that having a good battery that was just sitting around saved the day. Of course I should have had a good start battery, of course I should have had a good house bank. And of course if nothing goes wrong (human error or otherwise) you only need one bank.
My example was of a real world event where human error trumped and a spare battery (dedicated windlass) saved the day, or at least a long dinghy
Not to hijack the thread. The LiFePO4
is the main bank and fed with 13.8 in bulk mode and then 13.2 in absorbtion/float. 13.2 v is below the resting voltage of a LiFePO4 bank and thus current
is supplied (for the most part) by the LiFePO4 bank and not charging it. This is per MaineSail's recommendation.
The start and windlass batteries are both fed from a 10 amp trucharge battery charger
and echo charge for isolation between the 2 batteries. The charger is powered by the main inverter
and is manually activated. Not a well thought out configuration for automatic use.
An improvement would be to get a small sine wave inverter and only power it when the engine is running. Let the small charger and echo charge handle the charging profile for the AGM and LA batteries. I should add that this is built from what I had lying around.
The point about the Ah draw for the start and windlass batteries is that they would typically consume less than 5 Ah total and are quickly restored to full charge even with the 10 amp charger and the losses in the inverter, etc.
As MaineSail said (and place any errors, mis-statements on my shoulders) the trick is to get the AGM fully charged once in a while.
As a side note I'm playing around with using a HP Proliant 60 amp 12 V supply for charging the LiFePO4 bank. Other areas I'm looking at is to make a 16 v charge bus and use point of need charger converter at each battery bank. But that is for a different thread.