iRV2 Forums

iRV2 Forums (https://www.irv2.com/forums/)
-   Class A Motorhome Discussions (https://www.irv2.com/forums/f258/)
-   -   Replacing new Li-Ion batteries in Class A Motorhome (https://www.irv2.com/forums/f258/replacing-new-li-ion-batteries-in-class-a-motorhome-540270.html)

RichardE 06-12-2021 10:51 AM

Matt,

Sorry for the late reply, traveling and spotty interweb to blame.


Anyway, I totally agree with 757 that your recharge voltage is way too high and that will keep your batteries at 100% SOC, the charger will stay on almost all the time, and that is not good for the LiPo. This was the main issue with the Newell owner that I worked with.

Also good recommendations on LBCO and recharge voltage settings from 757.

I do prefer, but this is not the gospel, that the end charge be set up to stop on return amps. Your ME-ARC is capable of this but you may need to add the BMK (battery monitor kit) to access the capability. As you know the amps that flow into the battery bank when charging decrease as the bank approaches full charge. By setting the charge to end when a certain amperage is reached instead of a fixed time you are “listening” to the batteries to know when to end the cycle. Conventional wisdom is to end the charge at 5% of the bank size. So if you have 4 100aHr batts, then set the charge to end when the charger decreases to 20 amps.

I also prefer to float the bank instead of cycling it repeatedly. BB recommends 13.6 as the float. I keep mine at 13.4, but I do not have BB batteries. Again, this is not the LiPo gospel.
You may or may not achieve 100%SOC using float. If you don’t, and you know you are going to boonie for a couple of days, then initiate a full charge manually using the ME-ARC.

I am going to recommend a simple test that will give you a “practical baseline” for your new bank. Sometime in the future you will want to know if you have lost capacity. The test is simple. Turn on the inverter, reset the amp hour out counter, turn off the 120v breaker that feeds the inverter. Run off batteries that way until the LBCO turns the inverter off. You will now know just how much juice the bank will provide before you must recharge. This may or may not match the nameplate, but it doesn’t matter. You are collecting data on what your system provides using the charge and low cutoff parameters.

I tend to be rather conservative in setting up the charge/discharge parameters. After 6 years my 1000aHr bank still has over a 1000aHr usable. That is only a data point of one, but it works for me. If you really want to fine tune your bank, there is an interesting little experiment you can run if you care to. The overall idea is to “listen” to the batteries, and they will tell you what they like. The experiment is to collect data from each individual battery while charging to 100% SOC, and to collect voltages again from each battery whiled discharging to about 5% SOC. Why do this? I have read virtual fist fights posted by LiPo “experts” arguing over 0.01 volts. Oh horse hockey. Unless you are using a NIST traceable volt meter, who has instrumentation to measure absolute voltage. And who cares? After all, your charger is going to charge according to the voltage it measures. That includes all the unique variability in YOUR system.

So back to the experiment. If you will take the time to plot the voltage of the individual cells and the charger voltage as the bank approaches 100% SOC against time, you will see the sharp upward rise start. Compare the battery voltages, take the highest one, and note the charger voltage. You now know, looking at your charger voltage exactly where you are on the sharply rising curve. You can decide how far up that curve you want to go. Now do the same graph for discharging the bank. You can see where the voltage starts to drop. You can use that part of the curve to know where to set the LBCO on your inverter.

Using the curves generated by YOUR batteries, you have confidence in where to set the charge and discharge parameters instead of looking at 100’s of LiPo curves on the interweb and trying in 0.1 volts what is safe. Depending on how risky you want to be you can decide how far up and down the steep curves you want to operate. I stay pretty close to the flat part of the curve to maximize the battery life, but I never come close to using my 1000aHR, so the size of one’s bank and the needed use may dictate you operate further up and down the curves.

I hope this helps, and sorry if it was TMI.

mohospinner 06-13-2021 11:11 PM

Hi Richard,

Wow! Thank you for the plethora of information. This is great and I am looking forward to conduct a (certified) "RichardE" test :rofl: . However, we did put the batteries to our own tests this weekend and they really performed outstanding. We had coffee makers going, a tea kettle, a friend with a trailer that needed power, portable tool battery chargers, and basically everything you could throw at them and they did not disappoint! I will send you a note when I complete the "RichardE" test. Thanks again.

mohospinner 06-13-2021 11:18 PM

Just a random question here...Regarding the DC-DC charger: All my Victron equipment is shipping en route and I'm still thinking about the existing alternator charging system for the house batteries. I'm <ASSUMING:facepalm:> that I need to disconnect a wire from the alternator that currently charges the house batteries? Or does it not matter since the DC-DC charging will take over the charging? I have not found any viable information regarding this question. Thanks guys. You all are very helpful and I appreciate your input.

twinboat 06-14-2021 12:07 AM

Quote:

Originally Posted by mohospinner (Post 5790607)
Just a random question here...Regarding the DC-DC charger: All my Victron equipment is shipping en route and I'm still thinking about the existing alternator charging system for the house batteries. I'm &lt;ASSUMING:facepalm:&gt; that I need to disconnect a wire from the alternator that currently charges the house batteries? Or does it not matter since the DC-DC charging will take over the charging? I have not found any viable information regarding this question. Thanks guys. You all are very helpful and I appreciate your input.

There is no wire on the alternator that charges the house battery.
The alternator only connects to the chassis battery, and charges that.

There is what's called a charging or bridging solenoid or relay that connects the chassis battery to the house battery when conditions are right.
That needs to be disabled.

mohospinner 06-14-2021 09:56 AM

Thanks TwinBoat,

So by disabling this relay it will also disable the battery boost switch on the dash or is that something entirely different?

twinboat 06-14-2021 10:59 AM

Quote:

Originally Posted by mohospinner (Post 5791095)
Thanks TwinBoat,

So by disabling this relay it will also disable the battery boost switch on the dash or is that something entirely different?

Yes it will disable the boost switch, unless its a seperate wire to the solenoid. Then you can leave that on, only disabling the solenoid controler, if a seperate item.

WeaverBeaver 10-07-2021 08:51 PM

Hello,thank you all for very good information. I'm just about to complete a 1200AH Lifpo4 conversion this week with almost the same components mentioned.....Is it possible to keep the battery boost function with this dc-dc charging set-up? Would removing the ignition wire circuit and leaving the switch wire only activate the connection while holding down boost button?


All times are GMT -6. The time now is 01:07 PM.

Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2021, vBulletin Solutions, Inc.