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Old 10-31-2023, 08:18 PM   #1
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Unclear on doing AGM to Lithium battery replacement

Hi all,


I've read a number of posts on the topic of converting to Lithium batteries, but I am still slightly unclear on all the steps needed to replace an old AGM battery with a new Lithium one.


I have a 2014 SMB (from Fresno).


I have the following setup:


12V 200mAh AGM (UB4D)
Blue Sea 12V shut off ML-ACR (it's one of PN 7620/7621/7622/7623)

Zamp solar charger

Magnum MS2000 inverter/charger with RC-50 controller


I checked with the Magnum folks and I can create a custom profile for a lithium battery with these settings

set CC/CV
14.6V absorb
13.8V float
70% float
14.6 EQ volts


I am thinking of getting a Renology 12V 200mAh battery that is basically the identical size to the current AGM and inserting that into the tray under the van as a replacement. I will add a battery monitor from Renology as well.



I am not sure if the equipment that I currently have will all work or if I need to replace/add any other items. It would be nice to just update the MS 2000 with the new settings and be done but is it that simple?


I know that having the battery under the van may not be ideal but that's really the best location I have for it. There's one spot inside the van it could go, but it'll make access to the water fill/shut off valve super hard (as it is I have to lie on the floor and reach under the coach to reach the valve when filling the water tank - stupid bad design SMB).


I am grateful for any help or comments since I'm not sure what I might be missing.


Thanks


Jon

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Old 10-31-2023, 10:42 PM   #2
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Originally Posted by JonBertsch View Post
I know that having the battery under the van may not be ideal but that's really the best location I have for it. There's one spot inside the van it could go, but it'll make access to the water fill/shut off valve super hard (as it is I have to lie on the floor and reach under the coach to reach the valve when filling the water tank - stupid bad design SMB).
We replaced our two 4D agm batteries with one 200 ah Renogy a couple years ago and went from 220 lb to 60 lb and mounted where one of the AGM batteries was under the side doors. So far we're very happy with the setup. Time will tell how the heat/cold will affect the longevity of the LiFePo battery. I had to cut off one side of the battery tray to fit the Renogy battery... it's deeper than the AGM we had by maybe 3/4". Still fit up in there but took some wranglin.

We also upgraded to a 50 amp DC to DC charge controller but others more knowledgeable can chime in on what you might want to do to upgrade your charging electronics.
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Old 10-31-2023, 11:29 PM   #3
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@bigriver Thanks for the info on the battery compartment, I was hoping it might just fit straight in but a little cutting and trimming should be ok.


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Old 10-31-2023, 11:39 PM   #4
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Jon, under the van mounting of a Lithium -

IF your battery reaches sub-32F temps you will not be able to charge your battery unless it has heating capability. Over ~ 135F battery temp and the Lith battery will shutdown (think fridge). So, managing temps around Lith is important. Our Lith batteries are in an insulated box below the floor and incorporate thermostats to control heating pads to keep the batteries above 34F. The box also keeps them out of the heat of the cabin, although a very hot day in the desert could pose a problem with heat off the ground.

I find charging Lith to be the biggest challenge for us. Mostly due to heating water with electricity. The AGM batteries were connected to the alternator and were fed whatever output available from the alternator without much worry of frying the alternator. A drawn down Lith will fry an alternator with its demands unless regulated which is where the DC to DC charger comes into the system .

But the DC to DC limitations become very apparent when the Lith battery is drawn down. Daily usage for fridge, mwave, water pump, lights, etc. can easily approach 100 amps. A 50AH DC to DC charger will pretty much get you real world 40AH less whatever your static draws are, so figure about 30Ah going to recharge batteries. That means 3 plus hours of driving everyday with solar helping out some depending on your array. Use the mwave for 5 mins means ~ 15 mins of charging to replace the draw. With the AGM, we would start the engine and the alternator took care of all the draw in real time. A 50 Ah DC to DC will require running the engine for 15 mins to replace what was used in 5 mins.

Our DC to DC system is a bit more complex than most people do - to charge the 412 AH Lith bank in a reasonable amount of engine run time we have 2 Victron DC to DC 30AH units plus a Sterling 70AH. We also have a Victron 12/18 to provide a way to charge the starter batteries from the solar panel or inverter/charger. We have 220AH of nominal alternator, the total of the DC to DC units capabilities are about half of that and I can turn off any of those three DC to DC units to limit alternator stress. There is a 400w panel to help.

re isolation - the DC to DC charger does this. Currently you have bi-directional charging with the BlueSea ACR so your starter battery is also topped off. There are a few DC to DC units that will also charge the starter but it is not anywhere near the same as what you have now. Some consideration should be given to keeping the starter battery topped off. We use the Victron 12/18 DC to DC to do this. Utilizing the ignition feed sensing wires can make most of this self managing.

I like the Lith abilities but it is not a plug and play replacement for AGM.
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Old 11-01-2023, 09:31 AM   #5
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Hi 1der, thank you for the extra info on the DC to DC setup. It looks like I'll need to add in an new unit to manage the alternator charging for the battery. Plus I need to look at some features in the battery itself for heating...more to get my head around.


Thank you


Jon
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Old 11-01-2023, 02:11 PM   #6
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Stay away from the Renogy DC2DC chargers. I recommend Victron, Kisae or otherwise.
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Old 11-01-2023, 05:10 PM   #7
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Quote:
Originally Posted by JonBertsch View Post

Zamp solar charger

Magnum MS2000 inverter/charger with RC-50 controller

I checked with the Magnum folks and I can create a custom profile for a lithium battery with these settings

set CC/CV
14.6V absorb
13.8V float
70% float
14.6 EQ volts


Jon

1. Replace the Blue Sea ACR with a lithium compatible DC-DC converter.

The Blue Sea ACR is bi-directional (ie charges the starter battery under the hood) .....you will lose this functionality with a DC-DC converter.

2. Your Magnum settings above should work but you have to turn off EQ (Equalization), and 14.6V is at the upper limit for absorb (that's 3.65V/cell max for lithium). That may result in nuisance trips of the battery BMS.

Typical settings are usually around 14.4V absorb and 13.4V for Float for lithium.

You want the same settings on your solar controller.....not sure what settings you have on the zamp, but for both the zamp and the Magnum AGM settings are usually very close.

3. Relax and enjoy your new lithium battery......totally worth it....
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Old 11-01-2023, 06:44 PM   #8
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Hi 86Scotty thanks for the note on the DC-DC. It looks like a lot of folks recommend the Victron brand. I'll check it out.


Thanks


Jon
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Old 11-01-2023, 06:51 PM   #9
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Hi boywonder, thank you for the info on the settings, I'll make a note of those numbers and check the Zamp manual as well.


Plus another vote for the DC-DC converter to replace the Blue Sea one.


Thank you


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Old 11-01-2023, 07:35 PM   #10
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The Blue Sea ACRs are just battery separators....big switches. DC-DC converters have a multi stage charge profile, just like your zamp and Magnum.

I have the Victron 30A Orion smart and it's great.

Consider getting a Lithium battery with a bluetooth BMS.......very useful.
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