Lithium battery question

D

dlochner

.
Jan 11, 2014
12,688
Sabre 362 113 Fair Haven, NY
If it is difficult to wire the sense wire directly to the battery, measure the difference between the location of the voltage at the sense wire and the the actual battery voltage measured across the terminals. Use the difference to adjust the settings in the regulator and charger. For example, if the voltage at the sense wire is 13.15v and the voltage at the battery is 13.20v, then add .5v to any setting that is based on battery temp.

Depending on where the sense wire is located and how it is connected to the battery the voltage difference may actually be trivial. My sense wire is on the DC+ bus and the difference between the battery voltage and the sense voltage is couple of hundredths of a volt, close enough.

Current thinking about charging seems to be leaning towards lower voltages and longer charge times. With maximum charge voltages around 13.8v or 13.9v. Rod has written about this in his LFP and Electrical Systems FB groups. Maybe on his website too. The advantage seems to be longer cell life. With a 10 year 10,000 cycle life, I'll probably be dead before the batteries die.

Bob S said:
I'm still concerned for an over current or under current disconnect with three different charging sources and the new batteries. We have to start somewhere.
Click to expand
I wouldn't worry too much about this so long as you are using regulated power sources to charge the battery and they are programmed correctly. This can be a problem if an old style battery charger is used and if the charger is fused incorrectly or not at all. With your 600 ah bank, you would need 120amps of charging to just get to .2C. 525w of solar is only 43.75a @12v, a 100a alternator, and a 50a charger (?) is only about 200a if everything is pumping out all the power it could. In reality, the alternator and charger will never or only rarely be running at the same time and the solar will seldom if ever make its rated output.
 
  • Like
Likes: Bob S
Bob S

Bob S

.
Sep 27, 2007
1,794
Beneteau 393 New Bedford, MA
Actually I have a 150a alternator. I’m semi retired. I have Monday and Friday off which gives me a four day cruising weekend. If need be I can plug in for the three days it sits in her slip. I guess there is a learning curve we all go through. Curious if you ever tried the Overkill Solar app with your Kilovaults?
 
C

colemj

.
Jul 13, 2004
448
Dolphin Catamaran Dolphin 460 Mystic, CT
dlochner said:
Depending on where the sense wire is located and how it is connected to the battery the voltage difference may actually be trivial. My sense wire is on the DC+ bus and the difference between the battery voltage and the sense voltage is couple of hundredths of a volt, close enough.
Click to expand
Absolutely. Ours is connected there also, since the only connections to the actual battery are the pos and neg wires to the buses. I only meant the sense wires needed to go back to where the battery is. They are often connected to the alternator pos terminal, or somewhere shortly thereafter, which is not representative of what the battery is seeing.

Mark
 
C

colemj

.
Jul 13, 2004
448
Dolphin Catamaran Dolphin 460 Mystic, CT
Bob S said:
I'm still concerned for an over current or under current disconnect with three different charging sources and the new batteries. We have to start somewhere.
Click to expand
There is no way your alternator and solar together at full output is going to produce a 200A over-current event, so you don't need to worry about that. Over-voltage is different thing, but if you set your charge sources appropriately, you won't need to worry about that either.

If you never experienced an electrical shutdown with your lead batteries, you definitely aren't going to experience one with the LFP, so you don't need to worry about that. A 200A load is a lot, and if you have the ability to draw that, just pay attention to what you turn on.

Mark
 
You must log in or register to reply here.

Top Bottom