lipo newbie

[bluecolumbia]

hi there i am seeking some advice on my lipo upgrade.

i've converted my house bank to lipo... 2x 12v 190ah w/150amp bms each in parallel. i installed a balmar xt 170, with 618 controller, which seems to be working well with the batteries (now that i have enabled field limiting on the alternator).

i'm keeping lead acid for my start battery, and charging it with a dc/dc charger from the house bank. (and keeping a jump box on board as the engine start backup.)

my questions are about charging the lipo while at shore. my boat generally consumes about 10amps of 12v while in the slip.

at present i just have the small (20amp) charger that came with the lipo batteries, i'm trying to figure out what my shore power strategy should be.

with the simple charger i have now, i'm seeing that if i reduce ship consumption to 1amp, the charger eventually reaches the 2nd stage (constant current) and remains there. if ship consumption is at 10amps (as it normally is) the charger remains in 1st stage (constant voltage) and never reaches the second stage. is this expected? i assume this would wear the batteries prematurely (if they are always charging at constant voltage)?

i'm looking at getting a 12v power supply to power the ship load while in the slip, bypassing the batteries when shore power is available. this seems like it would prolong battery life, but i haven't seen much info about doing so...

if i do this, how do i move the load between the power supply and the batteries? i haven't been able to locate a 12v auto transfer switch, can i use a 1-2-both switch, and briefly parallel the lipo battery and power supply while the load is transferred?

is there a device that does all of this (battery charging/ship power supply/switching)?

i would appreciate any suggestions or advice thank you...

...bluecolumbia

[hjohnson]

Originally Posted by bluecolumbia

i would appreciate any suggestions or advice thank you...

...bluecolumbia

Don’t make things more complicated than you need to. Get yourself a better shore power charger and be done with it. Victron makes some nice smart chargers that are on the order of 50A. Then you don’t need to worry about transferring circuits or anything like that.

[wholybee]

Lipo refers to Lithium Polymer. I believe you mean Lithium Iron Phosphate, ( LFP or LiFePO4 ). It's a detail, but an important one.

What are you using for a battery meter? You need a good quality battery meter to know the battery state, relying on a charger to determine state of charge is a dangerous thing. Victron makes a great one. If your battery has bluetooth those are often good enough, but not as good as a Victron.

You have the charge stages reversed. First is Constant Current. Then, as the battery reaches fully charged, it changes to Constant Voltage. I *strongly* suggest not using the simple charger the battery came with while plugged in at that dock. The purpose of that simple charger is to charge the batteries, and then it is expected that you will disconnect the charger as soon as the battery is charged. Leaving an LFP battery on an active charger 24/7 is the fastest way to shorten an LFP batteries life. Get a good programmable smart charger like a Victron. It sounds like a 30 Amp charger would be sufficient to both power the loads on the boat, and also (slowly) charge the battery. What a smart charger will do, is charge the battery to 100% (usually 14.6V), and then after being charged, drop voltage to 13.5V. This allows the charger to continue to power boat loads, but because it is a lower voltage than what the LFP was charged to, it is no longer charging the battery.

Even that will reduce LFP life, because the LFP is left at nearly 100%. This would be ok if you use the boat frequently (ideally multiple times per week), but if the boat will be in the slip for a long time, the best practice is to leave the LFP battery at 50%-60% and only charge it to 100% when you are getting ready to leave. A good smart charger will do this as well. Many Victron chargers have a "storage mode" for this purpose.

Done this way, you don't need a 12V power supply, and I recommend against that.

[T1 Terry]

LFP and LYP cells like to work, they are the opposite of lead acid batteries that like to stay fully charged. Do your drop in batteries have any way of monitoring the cell voltages? To get a decent cycle life, never charge any cell above 3.6v and never discharge below 2.8v. Look after the cell voltages and the terminal voltages will look after themselves, but you can't do that the other way around. You can't divide the terminal voltage by 4 to determine the cell voltages, LFP/LYP cells just don't work that way, nor can you expect a built in balancer to keep all the cells at the same voltage, you can't even expect a top of the line external balancer to be able to achieve that while charging ...... unless the charging current is less than the balancer current .... and that would take a very long time to recharge a battery. Even the very good units only move a max of 5 amps, your batteries would take 76 hrs to recharge and you couldn't be drawing any load from them while they were recharging ..... simply not a practical solution.
By monitoring the cell voltages and stopping charging when a cell reaches 3.6v and giving the balancer time to move the capacity from the high voltage cell to the lower voltage cells, then recommencing the charging and repeating the process, the battery will remain within the safe upper voltage range and not suffer any damage. The lower storage voltage of 13.5v or less with the charging being controlled by a high cell voltage, only charging for say 12 hrs on and 12 hrs off and leaving the constant load on the battery, it will get to work during the off charge part of the cycle and recharge/balance during the charging cycle.

This idea will work fine for while the boat is on shore power, solar and or alternator charging is for a shorter period but still require the charging to be stopped if a cell goes over 3.6v and not resumed until the high cell voltage has dropped and remains below the 3.6v for more than 1 min or what ever time it takes for the balancer and/or loads to pull the high cell back down.

T1 Terry