Another Lithium Ion batteries question

The batteries the previous poster is using are of a different Li ion technology than LFP.

Just had another look at LFP on the Cruiser Sailing Forum. The thread on use of LFP is up to 270 pages and 4300 posts. If you want information, this is the place to go and I am starting there tonight. It may take a while
Reed and Elaine

I've bought regulated 18650 Li ion batteries for numerous flashlights and other goodies to power. Most of mine are regulated with wafer circuits in the base, such that they stop charging at 4.1 or 4.2V and cutoff at 2.9 to 3.0V. Just sharing with you what my observations have been on these 2500mah TrustFires from Deal Extreme in China.

pianotuna wrote:
Hi Phil,

The battery management system often won't allow the LI cells to get more than 80% discharged. That is why it "appears" the battery is suddenly empty.

An easy work around would be two battery banks. Use one til it is empty--switch to the other and charge the first one up.

X2 Reed and PT

Hi Phil,

The battery management system often won't allow the LI cells to get more than 80% discharged. That is why it "appears" the battery is suddenly empty.

An easy work around would be two battery banks. Use one til it is empty--switch to the other and charge the first one up.

pnichols wrote:
With my lithium powered small home gadgets I get very little warning as to when the batteries are getting low - everything just almost suddenly stops. .

If you want a lot of information on LFP battery usage, go to the Cruising Forum. There are over 100 pages of posts on LFP usage.

The simplest way of handling the voltage is from a post I just found on this forum

"...Regulated voltage control and monitoring is essential, keep any cell below 3.6v and above 2.8v so set the charging voltages and load disconnect with these in mind. I highly recommend monitoring individual cell voltages, a $28 Junsi cell logger from a hobby store is idea for this job, set the alarm voltage to the figures suggested above and you will have a warning if something goes wrong..."

Reed and Elaine

We think you really should use monitors if you go to LFP. I know a few folks whose opinion I value on various fora who disagree but automating as much as possible makes life simpler. We have the following:

TriStar Monitor: power rate in watts (or night), voltage of battery bank, watts "harvested" that day, state of battery charge (absorb, float)

Manzanita Micro monitor: voltage of battery bank, voltage of each individual cell (16), watt-hours from full charge

Magnum inverter monitor - can check all kinds of things of which I am ignorant and should read up some day.

Of importance is voltage of the cells. 3.4 V is float and which many (who do not like using BMS) set their system. 3.6 is maximum the cells should reach and our BMS controls system to stop at 3.6 V and go to float. Many believe that severe damage occurs above 3.6 V (cells will go to 3.9 V). 3.1 V is where one worries about very fast drop of charge.

Reed and Elaine

Actually I'm not quite sure I like the flat discharge curve of lithium batteries in all applications ... unless some metering is involved as to how much energy is left in the batteries.

With my lithium powered small home gadgets I get very little warning as to when the batteries are getting low - everything just almost suddenly stops. With the standard dry cells powering items things get gradually dimmer/weaker near the end of battery life, which serves as a "time to change or time to charge" advance warning. I wouldn't want those kind of sudden power stops on a battery bank in my RV.

pnichols wrote:
Thanks much for the link to StarkPower lithium deep cycle batteries! I hadn't run across them in my research.

I'd sure like to tuck a couple of these under the step in our Itasca:

https://store.starkpower.com/12V-125AhStarkPower-UltraEnergy-Lithium-Ion-Battery-LiFePO-Energy-Storage-Battery_p_65.html

Yeah Pnichols, lookin' good. 200 AH vs 250 AH would be enough for me since it can be drained to 20% over and over. Another thing that I would want to get is a TriMetric battery monitor to track the current to/from the battery. With that flat discharge curve the basic monitor will always read full until just about discharged.

reed cundiff wrote:
Is this 740 A-hrs at 6 V or is it 12 V equivalent.

740 amp-hours at 12V (6V in series/parallel).

Hi Reed,

400 amp-hours @ 12 volts.