Quote:
Originally Posted by Jd1
You would start a sail cruise with a battery that's down at 20%???
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We actually do that with pretty good regularity. 20% SOC means two days + of energy left in our bank if I take it to 0%. I have never had to go there but have been down to 5% SOC and have had zero qualms about doing so. On those occasions it was usually because we were in a peaceful quiet cove and wanted a couple days more of quiet. On one occasion I flipped the solar back on at 30% SOC and we got 2.5 more days in that anchorage without the
motor...
With lead I would never do that but with LFP I could care less about the occasional dip to 5% SOC.. This summer we spent nearly an entire week at less than 60% SOC due to minimizing
motor run times.
At 20% SOC on a 700Ah bank you still have 140 amp hours. If you set an "occasional" oops floor of 5% then you still have 105Ah's to use,
if needed. 80% is not by any means an absolute with LFP. I know some guys in the LFP world who think I am crazy to not use all 100%...
This last 15% on your bank is the equivalent to an entire cruising
usable capacity, in lead acid, (cycling 50% SOC to 85% SOC) to a 300 Ah lead bank. Only occasionally dipping to 5% for LFP is like Mike Tyson picking up a feather.. No skin off its back.
On our way back from trips we usually wait for the
wind to come up then have a nice afternoon sail home and often don't get to run the motor. Our SOC is what ever it is when we get back.
I have also been leaving solar off so I can cycle to 80% DOD as frequently as possible, for testing purposes. As such we very often leave the boat on the
mooring at approx 15-40% SOC and go home. During the week I will sometimes try and sneak another cycle (for my cycle testing) but that again usually puts me back at 20% SOC before we
head off again.
If I run the motor for just one hour, we have
engine driven
refrigeration for quick chill downs, as well as DC refridge, that 1 hour gives us three full days of energy independence. Because the batteries charge so fast and can be cycled so deeply it is a very differnt mind set.
I am confident you will eventually see and come to understand exactly what I am talking about. I know this sounds counter intuitive but I no longer worry about charging. Talk to me in two years and we can compare notes again...
I know that is very, very, very hard for folks to wrap their heads around but LFP is NOT lead acid. Breaking that long time engrained mind set is very difficult. It was difficult for me too....
I had a good friend row over this summer and ask what our solar array was putting out? He wanted to compare notes. He was shocked when I said I had no idea because it was turned off. I flipped it on for him but he could not, for the life of him, understand how or why I had solar off.
With LFP there is no need to worry about
:
Getting back to 100% SOC
Worrying about dipping below 50% DOD
Worrying about dipping below 80% DOD
Worry about charging, it happens so fast
I have come to think of it not as charging but as simply placing energy in the bank. The term
charging to me paints
images of a long arduous process of an hour+ in bulk then 4-10 hours in absorption etc. etc... In LFP it is pretty much bulk almost all the time. heck I don't ever need to run to absorption and hold it there if I don't want to. The only real reason I do is to manually synch the Ah counter.
I can simply run the alt for what ever amount of Ah's I desire for the next day or two, or three, but no more than I care to... What point you get to in SOC does not matter, like it does with lead acid, so long as you don't go below 0% SOC, which is actually very hard to do....
Yes capitalize on
opportunities to charge, when you can, but don't stress over it. You'll soon find that you don't need to..
Sure you take
charging opportunities, when you have them, and we have, and do, recharge at 40% DOD or 30% but I don't think I have ever felt a pressing need to do so at 50% SOC when we are out enjoying cruising.
Quote:
Originally Posted by Jd1
The actual parameters will have to be worked out yet but the 50% figure happens to be the default with the SOC meter plus I do not want to get into a situation where I am forced to charge before I can settle down at an anchorage. At 50% charge I have enough power and don't need to worry.
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You are still in a lead state of mind. Lead
parameters don't apply well to LFP. I know this is very, very hard to grasp but you will come to see this and will likely look back and laugh....... As I have said many times before the biggest hurdles in LFP are about lead mindsets. Everyone, including myself, I feel underestimates this going into it.
Quote:
Originally Posted by Jd1
Going below that probably only makes sense if you know what your itinerary is for the next few days and you'd be controlling that manually which I don't want to get into.
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We don't roll with much of an itinerary, not how we cruise, and so far charging LFP has not been a concern. Not thinking about batteries all the time is a actually a big relief..
It takes so little time to put multiple days worth of energy back into the bank that charging and focusing on battery management has literally become a non-issue for us.
My wife is even to the point of asking if I want her to flip on the
alternator.
I occasionally glance at the Ah counter, and as we get close to 30% I may decide to flip the solar switch, if I don't want to hear the motor chilling the holding plate.
With lead we almost exclusively used the
engine driven
refrigeration. Because we needed to charge so much engine driven refrigeration was a good fit. With LFP it is now used very rarely.. Today we are almost all 12V DC refrigeration. Sure when running the motor I may boost the plate with the engine but we no longer find we
need to run the engine for charging anywhere even close to what we had to with lead.
Our time at
anchor is considerably quieter and considerably longer between engine charging
events. I don't panic when I see we are close to 20% SOC but it admittedly took a while to get to that point.
Quote:
Originally Posted by Jd1
Of course if you are into motoring that's a different kettle of seaweed!
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We are not into motoring, though with sailboats and cruising Maine and the Maritimes, in the summer, it can be a necessary evil. Lack of motor running is the main reason we like LFP so much. My wife is a huge fan of the LFP bank...! Just getting the lead bank back to 85% SOC took so much longer and bought us a lot fewer days of peace & quiet on the hook.