Re: Alternator charging a Lithium bank
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When I was lost in the weeds in all the design decisions and particularly with regard to integration, the best advice some one gave me is design your charging systems to manage themselves! Don't rely on communications between systems. That is good advice. I have a Venus GX system and I have had to reboot it every month or two because the basic coms I use to monitor my system needs to be reset.
When you set up your charging systems don't try to count amp/hrs. That's nice for monitoring, but control your charging to battery voltage, preferable measured at the battery or the shunt right at the battery. Use the conservative values that your battery maker provides for your charge profiles. Others may suggest that you can be more aggressive, but your battery capacity should allow you to easily support your daily needs between 40%-80% SOC.
For my batteries that is 26.72v float and I charge to a max of 27.5v when topping/balancing the battery (about once a month). I think that the lowest I've pulled the battery is to about 25.5v.
If you have not upgraded your Alternator controller yet, then I encourage you to look at the WakeSpeed 500 controller. I think that it still has features that are ahead of the others, and it has a layer of programmability above that. I did not need to do any programming. I used it right out of the box. But a couple of features I really like are:
1) the WS 500 measures temperature at the alternator negative terminal,
2) it measures voltage AND current from your BMV shunt,
3) a dip switch on the box de-rates the alternator to 75% output to protect the alternator (and drive belts).
4) When using the out of the box Lithuum charge profile you can add a switch that switches the controller between normal charge profile or "float". When it is set at the "float" setting it charges to and holds the battery at 26.72v (approximately 75% SOC), but it also monitors the current flow at the shunt to react quickly to large current draws (winches, windlasses, bow thruster). I love that feature and leave it on float as a default. I only switch it the "charge" mode when I need to charge the batteries and then I am paying attention and monitoring the BMS.
This is a different philosophy from set it and forget it, but the common theme of battery failure (lead acid, AGM, or Lithium) is that something happens when no one is watching and the result is a pile of trashed batteries at the next marina while you scramble to get a replacement shipment.
I hope that helps a bit.
Best regards Daniel Carlson on sv BeBe, SM #387